# `ssl` --- 套接字对象的 TLS/SSL 包装器

源代码: Lib/ssl.py

本模块保证了对传安全传输层协议（TLS）的访问 (SSL)加密，并且提供客户端和服务端层面的网络嵌套字层面的对等连接认证技术。本模块使用OpenSSL库。适用于所有现代Unix系统、Windows以及Mac OS X。只要Open SSL存在的系统，都有机会正常使用。

注解

某些行为可能具有平台依赖，因为调用是根据操作系统的嵌套字API。不同版本的Open SSL也会引起差异：例如Open SSL版本1.0.1 自带TLSv1.1 和 TLSv1.2

警告

在阅读 Security considerations 前不要使用此模块。 这样做可能会导致虚假的安全感，因为ssl模块的默认设置不一定适合你的应用程序。

本文档记录"ssl"模块的对象和函数；更多关于TLS,SSL,和证书的信息，请参阅下方的“详情”选项

本模块提供了一个类 `ssl.SSLSocket`，它派生自 `socket.socket` 类型，并提供类似套接字的包装器，也能够对通过带 SSL 套接字的数据进行加密和解密。 它支持一些额外方法例如 `getpeercert()`，该方法可从连接的另一端获取证书，还有 `cipher()`，该方法可获取安全连接所使用的密码。

对于更复杂的应用程序，`ssl.SSLContext` 类有助于管理设置项和证书，进而可以被使用 `SSLContext.wrap_socket()` 方法创建的 SSL 套接字继承。

在 3.5.3 版更改: 更新以支持和 OpenSSL 1.1.0 的链接

在 3.6 版更改: OpenSSL 0.9.8、1.0.0 和 1.0.1 已过时，将不再被支持。在 ssl 模块未来的版本中，最低需要 OpenSSL 1.0.2 或 1.1.0。

## 方法、常量和异常处理

### 套接字创建

从 Python 3.2 和 2.7.9 开始，建议使用 `SSLContext` 实例的 `SSLContext.wrap_socket()` 来将套接字包装为 `SSLSocket` 对象。 辅助函数 `create_default_context()` 会返回一个新的带有安全默认设置的上下文。 旧的 `wrap_socket()` 函数已被弃用，因为它效率较差并且不支持服务器名称提示（SNI）和主机匹配。

客户端套接字实例，采用默认上下文和IPv4/IPv6双栈:

    import socket
    import ssl

    hostname = 'www.python.org'
    context = ssl.create_default_context()

    with socket.create_connection((hostname, 443)) as sock:
        with context.wrap_socket(sock, server_hostname=hostname) as ssock:
            print(ssock.version())

客户端套接字示例，带有自定义上下文和IPv4:

    hostname = 'www.python.org'
    # PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
    context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
    context.load_verify_locations('path/to/cabundle.pem')

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
        with context.wrap_socket(sock, server_hostname=hostname) as ssock:
            print(ssock.version())

服务器套接字实例，在localhost上监听IPv4:

    context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
    context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
        sock.bind(('127.0.0.1', 8443))
        sock.listen(5)
        with context.wrap_socket(sock, server_side=True) as ssock:
            conn, addr = ssock.accept()
            ...

### 上下文创建

便捷函数，可以帮助创建 `SSLContext` 对象，用于常见的目的。

`ssl.``create_default_context`(purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None)

  返回一个新的 `SSLContext` 对象，使用给定 purpose 的默认设置。 该设置由 `ssl` 模块选择，并且通常是代表一个比直接调用 `SSLContext` 构造器时更高的安全等级。

  cafile, capath, cadata 代表用于进行证书核验的可选受信任 CA 证书，与 `SSLContext.load_verify_locations()` 的一致。 如果三个参数均为 `None`，此函数可以转而选择信任系统的默认 CA 证书。

  设置包括: `PROTOCOL_TLS`, `OP_NO_SSLv2` 以及 `OP_NO_SSLv3`，具有不带 RC4 和不带无身份验证密码套件的高度加密密码套件。 传入 `SERVER_AUTH` 作为 purpose 会把 `verify_mode` 设为 `CERT_REQUIRED` 并且加载指定 CA 证书（当给出 cafile, capath 和 cadata 中的至少一个）或者使用 `SSLContext.load_default_certs()` 来加载默认 CA 证书。

  当 `keylog_filename` 受支持并且设置了环境变量 `SSLKEYLOGFILE` 时，`create_default_context()` 会启用密钥日志记录。

  注解

  协议、选项、密码和其他设置可随时更改为更具约束性的值而无须事先弃用。 这些值代表了兼容性和安全性之间的合理平衡。

  如果你的应用需要特定的设置，你应当创建一个 `SSLContext` 并自行应用设置。

  注解

  如果你发现当某些较旧的客户端或服务器尝试与用此函数创建的 `SSLContext` 进行连接时收到了报错提示 "Protocol or cipher suite mismatch"，这可能是因为它们只支持 SSL3.0 而它被此函数用 `OP_NO_SSLv3` 排除掉了。 SSL3.0 被广泛认为 完全不可用。 如果你仍希望继续使用此函数但仍允许 SSL 3.0 连接，你可以使用以下代码重新启用它们:

      ctx = ssl.create_default_context(Purpose.CLIENT_AUTH)
      ctx.options &= ~ssl.OP_NO_SSLv3

  3.4 新版功能.

  在 3.4.4 版更改: RC4 被从默认密码字符串中丢弃。

  在 3.6 版更改: ChaCha20/Poly1305 被添加到默认密码字符串中。

  3DES 被从默认密码字符串中丢弃。

  在 3.8 版更改: 增加了对密钥日志记录至 `SSLKEYLOGFILE` 的支持。

### 异常

exception `ssl.``SSLError`

  引发此异常以提示来自下层 SSL 实现（目前由 OpenSSL 库提供）的错误。 它表示在下层网络连接之上叠加的高层级加密和验证层存在某种问题。 此错误是 `OSError` 的一个子类型。 `SSLError` 实例的错误和消息是由 OpenSSL 库提供的。

  在 3.3 版更改: `SSLError` 曾经是 `socket.error` 的一个子类型。

  `library`

    一个字符串形式的助记符，用来指明发生错误的 OpenSSL 子模块，例如 `SSL`, `PEM` 或 `X509`。 可能的取值范围依赖于 OpenSSL 的版本。

    3.3 新版功能.

  `reason`

    一个字符串形式的助记符，用来指明发生错误的原因，例如 `CERTIFICATE_VERIFY_FAILED`。 可能的取值范围依赖于 OpenSSL 的版本。

    3.3 新版功能.

exception `ssl.``SSLZeroReturnError`

  `SSLError` 的子类，当尝试读取或写入且 SSL 连接已被完全关闭时会被引发。 请注意这并不意味着下层的传输（读取 TCP）已被关闭。

  3.3 新版功能.

exception `ssl.``SSLWantReadError`

  `SSLError` 的子类，当尝试读取或写入数据，但在请求被满足之前还需要在下层的 TCP 传输上接收更多数据时会被 非阻塞型 SSL 套接字 引发。

  3.3 新版功能.

exception `ssl.``SSLWantWriteError`

  `SSLError` 的子类，当尝试读取或写入数据，但在请求被满足之前还需要在下层的 TCP 传输上发送更多数据时会被 非阻塞型 SSL 套接字 引发。

  3.3 新版功能.

exception `ssl.``SSLSyscallError`

  `SSLError` 的子类，当尝试在 SSL 套接字上执行操作时遇到系统错误时会被引发。 不幸的是，没有简单的方式能检查原始 errno 编号。

  3.3 新版功能.

exception `ssl.``SSLEOFError`

  `SSLError` 的子类，当 SSL 连接被突然终止时会被引发。 通常，当遇到此错误时你不应再尝试重用下层的传输。

  3.3 新版功能.

exception `ssl.``SSLCertVerificationError`

  `SSLError` 的子类，当证书验证失败时会被引发。

  3.7 新版功能.

  `verify_code`

    一个数字形式的错误编号，用于表示验证错误。

  `verify_message`

    用于表示验证错误的人类可读的字符串。

exception `ssl.``CertificateError`

  `SSLCertVerificationError` 的别名。

  在 3.7 版更改: 此异常现在是 `SSLCertVerificationError` 的别名。

### 随机生成

`ssl.``RAND_bytes`(num)

  返回 num 个高加密强度伪随机字节数据。 如果 PRNG 未使用足够的数据作为随机种子或者如果当前 RAND 方法不支持该操作则会引发 `SSLError`。 `RAND_status()` 可被用来检查 PRNG 的状态而 `RAND_add()` 可被用来为 PRNG 设置随机种子。

  对于几乎所有应用程序都更推荐使用 `os.urandom()`。

  请阅读维基百科文章 Cryptographically secure pseudorandom number generator (CSPRNG) 以了解对于高加密强度生成器的具体要求。

  3.3 新版功能.

`ssl.``RAND_pseudo_bytes`(num)

  返回 (bytes, is_cryptographic): bytes 是 num 个伪随机字节数据，如果所生成的字节数据为高加密强度则 is_cryptographic 为 `True`。 如果当前 RAND 方法不支持此操作则会引发 `SSLError`。

  所生成的伪随机字节序列如果具有足够的长度则将会具有唯一性，并是并非不可预测。 它们可被用于非加密目的以及加密协议中的特定目的，但通常不可被用于密钥生成等目的。

  对于几乎所有应用程序都更推荐使用 `os.urandom()`。

  3.3 新版功能.

  3.6 版后已移除: OpenSSL 已弃用了 `ssl.RAND_pseudo_bytes()`，请改用 `ssl.RAND_bytes()`。

`ssl.``RAND_status`()

  如果 SSL 伪随机数生成器已使用‘足够的’随机性作为种子则返回 `True`，否则返回 `False`。 你可以使用 `ssl.RAND_egd()` 和 `ssl.RAND_add()` 来增加伪随机数生成器的随机性。

`ssl.``RAND_egd`(path)

  如果你在某处运行了一个熵收集守护程序（EGD），且 path 是向其打开的套接字连接路径名，此函数将从该套接字读取 256 个字节的随机性数据，并将其添加到 SSL 伪随机数生成器以增加所生成密钥的安全性。 此操作通常只在没有更好随机性源的系统上才是必要的。

  请查看 http://egd.sourceforge.net/ 或 http://prngd.sourceforge.net/ 来了解有关熵收集守护程序源的信息。

  可用性: 对于 LibreSSL 和 OpenSSL > 1.1.0 不可用。

`ssl.``RAND_add`(bytes, entropy)

  将给定的 bytes 混合到 SSL 伪随机数生成器中。 形参 entropy (float 类型) 是数据所包含的熵的下界 (因此你可以总是使用 `0.0`)。 请查看 RFC 1750 了解有关熵源的更多信息。

  在 3.5 版更改: 现在接受可写的 字节类对象。

### 证书处理

`ssl.``match_hostname`(cert, hostname)

  验证 cert (使用 `SSLSocket.getpeercert()` 所返回的已解码格式) 是否匹配给定的 hostname。 所应用的规则是在 RFC 2818, RFC 5280 和 RFC 6125 中描述的检查 HTTPS 服务器身份的规则。 除了 HTTPS，此函数还应当适用于各种基于 SSL 协议的服务器身份检查操作，例如 FTPS, IMAPS, POPS 等等。

  失败时引发 `CertificateError`。 成功时此函数无返回值:

      >>> cert = {'subject': ((('commonName', 'example.com'),),)}
      >>> ssl.match_hostname(cert, "example.com")
      >>> ssl.match_hostname(cert, "example.org")
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
        File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
      ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'

  3.2 新版功能.

  在 3.3.3 版更改: 此函数现在遵循 RFC 6125, 6.4.3 小节，它不会匹配多个通配符 (例如 `*.*.com` 或 `*a*.example.org`) 也不匹配国际化域名 (IDN) 片段内部的通配符。 IDN A 标签例如 `www*.xn--pthon-kva.org` 仍然受支持，但 `x*.python.org` 不再能匹配 `xn--tda.python.org`。

  在 3.5 版更改: 现在支持匹配存在于证书的 subjectAltName 字段中的 IP 地址。

  在 3.7 版更改: 此函数不再被用于 TLS 连接。 主机匹配现在是由 OpenSSL 执行的。

  允许位于段的最左端且为唯一字符的通配符。 部分通配符例如 `www*.example.com` 已不再受支持。

  3.7 版后已移除.

`ssl.``cert_time_to_seconds`(cert_time)

  返回距离 Unix 纪元零时的秒数，给定的 `cert_time` 字符串代表来自证书的 "notBefore" 或 "notAfter" 日期值，采用 `"%b %d %H:%M:%S %Y %Z"` strptime 格式（C 区域）。

  以下为示例代码:

      >>> import ssl
      >>> timestamp = ssl.cert_time_to_seconds("Jan  5 09:34:43 2018 GMT")
      >>> timestamp
      1515144883
      >>> from datetime import datetime
      >>> print(datetime.utcfromtimestamp(timestamp))
      2018-01-05 09:34:43

  "notBefore" 或 "notAfter" 日期值必须使用 GMT (RFC 5280)。

  在 3.5 版更改: 将输入时间解读为 UTC 时间，基于输入字符串中指明的 'GMT' 时区。 在之前使用的是本地时区。 返回一个整数（不带输入格式中秒的分数部分）

`ssl.``get_server_certificate`(addr, ssl_version=PROTOCOL_TLS, ca_certs=None)

  带 SSL 保护的服务器的地址 `addr` 以 (hostname, port-number) 对的形式给出，获取服务器的证书，并将其以 PEM 编码字符串的形式返回。 如果指定了 `ssl_version`，则使用该版本的 SSL 协议尝试连接服务器。 如果指定了 `ca_certs`，它应当是一个包含根证书列表的文件，使用与 `SSLContext.wrap_socket()` 中同名形参一致的格式。 该调用将尝试根据指定的根证书集来验证服务器证书，如果验证失败则该调用也将失败。

  在 3.3 版更改: 此函数现在是 IPv6 兼容的。-compatible.

  在 3.5 版更改: 默认的 ssl_version 从 `PROTOCOL_SSLv3` 改为 `PROTOCOL_TLS` 以保证与现代服务器的最大兼容性。

`ssl.``DER_cert_to_PEM_cert`(DER_cert_bytes)

  根据给定的 DER 编码字节块形式的证书，返回同一证书的 PEM 编码字符串版本。

`ssl.``PEM_cert_to_DER_cert`(PEM_cert_string)

  根据给定的 ASCII PEM 字符串形式的证书，返回同一证书的 DER 编码字节序列。

`ssl.``get_default_verify_paths`()

  返回包含 OpenSSL 的默认 cafile 和 capath 的路径的命名元组。 此路径与 `SSLContext.set_default_verify_paths()` 所使用的相同。 返回值是一个 named tuple `DefaultVerifyPaths`:

  - `cafile` - 解析出的 cafile 路径或者如果文件不存在则为 `None`,

  - `capath` - 解析出的 capath 路径或者如果目录不存在则为 `None`,

  - `openssl_cafile_env` - 指向一个 cafile 的 OpenSSL 环境键,

  - `openssl_cafile` - 一个 cafile 的硬编码路径,

  - `openssl_capath_env` - 指向一个 capath 的 OpenSSL 环境键,

  - `openssl_capath` - 一个 capath 目录的硬编码路径

  可用性: LibreSSL 会忽略环境变量 `openssl_cafile_env` 和 `openssl_capath_env`。

  3.4 新版功能.

`ssl.``enum_certificates`(store_name)

  从 Windows 的系统证书库中检索证书。 store_name 可以是 `CA`, `ROOT` 或 `MY` 中的一个。 Windows 也可能会提供额外的证书库。

  此函数返回一个包含 (cert_bytes, encoding_type, trust) 元组的列表。 encoding_type 指明 cert_bytes 的编码格式。 它可以为 `x509_asn` 以表示 X.509 ASN.1 数据或是 `pkcs_7_asn` 以表示 PKCS#7 ASN.1 数据。 trust 以 OIDS 集合的形式指明证书的目的，或者如果证书对于所有目的都可以信任则为 `True`。

  示例:

      >>> ssl.enum_certificates("CA")
      [(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
       (b'data...', 'x509_asn', True)]

  可用性: Windows。

  3.4 新版功能.

`ssl.``enum_crls`(store_name)

  Windows 的系统证书库中检索 CRL。 store_name 可以是 `CA`, `ROOT` 或 `MY` 中的一个。 Windows 也可能会提供额外的证书库。

  此函数返回一个包含 (cert_bytes, encoding_type, trust) 元组的列表。 encoding_type 指明 cert_bytes 的编码格式。 它可以为 `x509_asn` 以表示 X.509 ASN.1 数据或是 `pkcs_7_asn` 以表示 PKCS#7 ASN.1 数据。

  可用性: Windows。

  3.4 新版功能.

`ssl.``wrap_socket`(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version=PROTOCOL_TLS, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None)

  接受一个 `socket.socket` 的实例 `sock`，并返回一个 `ssl.SSLSocket` 的实例，该类型是 `socket.socket` 的子类型，它将下层的套接字包装在一个 SSL 上下文中。 `sock` 必须是一个 `SOCK_STREAM` 套接字；其他套接字类型不被支持。

  在内部，该函数会创建一个 `SSLContext`，其协议版本为 ssl_version 且 `SSLContext.options` 设为 cert_reqs。 如果设置了 keyfile, certfile, ca_certs 或 ciphers 等形参，则参数值会被传给 `SSLContext.load_cert_chain()`, `SSLContext.load_verify_locations()` 以及 `SSLContext.set_ciphers()`。

  参数 server_side, do_handshake_on_connect 和 suppress_ragged_eofs 具有与 `SSLContext.wrap_socket()` 相同的含义。

  3.7 版后已移除: 从 Python 3.2 和 2.7.9 开始，建议使用 `SSLContext.wrap_socket()` 来代替 `wrap_socket()`。 模块级函数的功能受限并且将创建不安全的客户端套接字，不带服务器名称提示或主机名匹配。

### 常量

> 所有常量现在都是 `enum.IntEnum` 或 `enum.IntFlag` 多项集的成员。

> 3.6 新版功能.

`ssl.``CERT_NONE`

  `SSLContext.verify_mode` 或 `wrap_socket()` 的 `cert_reqs` 形参可能的取值。 `PROTOCOL_TLS_CLIENT` 除外，这是默认的模式。 对于客户端套接字，几乎任何证书都是可接受的。 验证错误例如不受信任或过期的证书错误会被忽略并且不会中止 TLS/SSL 握手。

  在服务器模式下，不会从客户端请求任何证书，因此客户端不会发送任何用于客户端证书身份验证的证书。

  参见下文对于 Security considerations 的讨论。

`ssl.``CERT_OPTIONAL`

  `SSLContext.verify_mode` 或 `wrap_socket()` 的 `cert_reqs` 形参可能的取值。 `CERT_OPTIONAL` 具有与 `CERT_REQUIRED` 相同的含义。 对于客户端套接字推荐改用 `CERT_REQUIRED`。

  在服务器模式下，客户端证书请求会被发送给客户端。 客户端可以忽略请求也可以发送一个证书以执行 TLS 客户端证书身份验证。 如果客户端选择发送证书，则将对其执行验证。 任何验证错误都将立即中止 TLS 握手。

  使用此设置要求将一组有效的 CA 证书传递给 `SSLContext.load_verify_locations()` 或是作为 `wrap_socket()` 的 `ca_certs` 形参值。

`ssl.``CERT_REQUIRED`

  `SSLContext.verify_mode` 或 `wrap_socket()` 的 `cert_reqs` 形参可能的取值。 在此模式下，需要从套接字连接的另一端获取证书；如果未提供证书或验证失败则将引发 `SSLError`。 此模式 不能 在客户端模式下对证书进行验证，因为它不会匹配主机名。 `check_hostname` 也必须被启用以验证证书的真实性。 `PROTOCOL_TLS_CLIENT` 会使用 `CERT_REQUIRED` 并默认启用 `check_hostname`。

  对于服务器套接字，此模式会提供强制性的 TLS 客户端证书验证。 客户端证书请求会被发送给客户端并且客户端必须提供有效且受信任的证书。

  使用此设置要求将一组有效的 CA 证书传递给 `SSLContext.load_verify_locations()` 或是作为 `wrap_socket()` 的 `ca_certs` 形参值。

class `ssl.``VerifyMode`

  CERT_* 常量的 `enum.IntEnum` 多项集。

  3.6 新版功能.

`ssl.``VERIFY_DEFAULT`

  `SSLContext.verify_flags` 可能的取值。 在此模式下，证书吊销列表（CRL）并不会被检查。 OpenSSL 默认不要求也不验证 CRL。

  3.4 新版功能.

`ssl.``VERIFY_CRL_CHECK_LEAF`

  `SSLContext.verify_flags` 可能的取值。 在此模式下， 只会检查对等证书而不检查任何中间 CA 证书。 此模式要求提供由对等证书颁发者（其直接上级 CA）签名的有效 CRL。 如果未使用 `SSLContext.load_verify_locations` 加载正确的 CRL，则验证将失败。

  3.4 新版功能.

`ssl.``VERIFY_CRL_CHECK_CHAIN`

  `SSLContext.verify_flags` 可能的取值。 在此模式下，会检查对等证书链中所有证书的 CRL。

  3.4 新版功能.

`ssl.``VERIFY_X509_STRICT`

  `SSLContext.verify_flags` 可能的取值，用于禁用已损坏 X.509 证书的绕过操作。

  3.4 新版功能.

`ssl.``VERIFY_X509_TRUSTED_FIRST`

  `SSLContext.verify_flags` 可能的取值。 它指示 OpenSSL 在构建用于验证某个证书的信任链时首选受信任的证书。 此旗标将默认被启用。

  3.4.4 新版功能.

class `ssl.``VerifyFlags`

  VERIFY_* 常量的 `enum.IntFlag` 多项集。

  3.6 新版功能.

`ssl.``PROTOCOL_TLS`

  选择客户端和服务器均支持的最高协议版本。 此选项名称并不准确，实际上 "SSL" 和 "TLS" 协议均可被选择。

  3.6 新版功能.

`ssl.``PROTOCOL_TLS_CLIENT`

  像 `PROTOCOL_TLS` 一样地自动协商最高协议版本，但是只支持客户端 `SSLSocket` 连接。 此协议默认会启用 `CERT_REQUIRED` 和 `check_hostname`。

  3.6 新版功能.

`ssl.``PROTOCOL_TLS_SERVER`

  像 `PROTOCOL_TLS` 一样地自动协商最高协议版本，但是只支持服务器 `SSLSocket` 连接。

  3.6 新版功能.

`ssl.``PROTOCOL_SSLv23`

  `PROTOCOL_TLS` 的别名。

  3.6 版后已移除: 请改用 `PROTOCOL_TLS`。

`ssl.``PROTOCOL_SSLv2`

  选择 SSL 版本 2 作为通道加密协议。

  如果 OpenSSL 编译时使用了 `OPENSSL_NO_SSL2` 旗标则此协议将不可用。

  警告

  SSL 版本 2 并不安全。 极不建议使用它。

  3.6 版后已移除: OpenSSL 已经移除了对 SSLv2 的支持。

`ssl.``PROTOCOL_SSLv3`

  选择 SSL 版本 3 作为通道加密协议。

  如果 OpenSSL 编译时使用了 `OPENSSL_NO_SSLv3` 旗标则此协议将不可用。

  警告

  SSL 版本 3 并不安全。 极不建议使用它。

  3.6 版后已移除: OpenSSL 已经弃用了所有带有特定版本号的协议。 请改用默认协议 `PROTOCOL_TLS` 并附带 `OP_NO_SSLv3` 等旗标。

`ssl.``PROTOCOL_TLSv1`

  选择 TLS 版本 1.0 作为通道加密协议。

  3.6 版后已移除: OpenSSL 已经弃用了所有带有特定版本号的协议。 请改用默认协议 `PROTOCOL_TLS` 并附带 `OP_NO_SSLv3` 等旗标。

`ssl.``PROTOCOL_TLSv1_1`

  选择 TLS 版本 1.1 作为通道加密协议。 仅适用于 openssl 版本 1.0.1+。

  3.4 新版功能.

  3.6 版后已移除: OpenSSL 已经弃用了所有带有特定版本号的协议。 请改用默认协议 `PROTOCOL_TLS` 并附带 `OP_NO_SSLv3` 等旗标。

`ssl.``PROTOCOL_TLSv1_2`

  选译 TLS 版本 1.2 作为通道加密协议。 这是最新的版本，也应是能提供最大保护的最佳选择，如果通信双方都支持它的话。 仅适用于 openssl 版本 1.0.1+。

  3.4 新版功能.

  3.6 版后已移除: OpenSSL 已经弃用了所有带有特定版本号的协议。 请改用默认协议 `PROTOCOL_TLS` 并附带 `OP_NO_SSLv3` 等旗标。

`ssl.``OP_ALL`

  对存在于其他 SSL 实现中的各种缺陷启用绕过操作。 默认会设置此选项。 没有必要设置与 OpenSSL 的 `SSL_OP_ALL` 常量同名的旗标。

  3.2 新版功能.

`ssl.``OP_NO_SSLv2`

  阻止 SSLv2 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 SSLv2 作为协议版本。

  3.2 新版功能.

  3.6 版后已移除: SSLv2 已被弃用

`ssl.``OP_NO_SSLv3`

  阻止 SSLv3 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 SSLv3 作为协议版本。

  3.2 新版功能.

  3.6 版后已移除: SSLv3 已被弃用

`ssl.``OP_NO_TLSv1`

  阻止 TLSv1 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 TLSv1 作为协议版本。

  3.2 新版功能.

  3.7 版后已移除: 此选项自 OpenSSL 1.1.0 起已被弃用，请改用新的 `SSLContext.minimum_version` 和 `SSLContext.maximum_version`。

`ssl.``OP_NO_TLSv1_1`

  阻止 TLSv1.1 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 TLSv1.1 作为协议版本。 仅适用于 openssl 版本 1.0.1+。

  3.4 新版功能.

  3.7 版后已移除: 此选项自 OpenSSL 1.1.0 起已被弃用。

`ssl.``OP_NO_TLSv1_2`

  阻止 TLSv1.2 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 TLSv1.2 作为协议版本。 仅适用于 openssl 版本 1.0.1+。

  3.4 新版功能.

  3.7 版后已移除: 此选项自 OpenSSL 1.1.0 起已被弃用。

`ssl.``OP_NO_TLSv1_3`

  阻止 TLSv1.3 连接。 此选项仅可与 `PROTOCOL_TLS` 结合使用。 它会阻止对等方选择 TLSv1.3 作为协议版本。 TLS 1.3 适用于 OpenSSL 1.1.1 或更新的版本。 当 Python 编译是基于较旧版本的 OpenSSL 时，该旗标默认为 0。

  3.7 新版功能.

  3.7 版后已移除: 此选项自 OpenSSL 1.1.0 起已被弃用。 它被添加到 2.7.15, 3.6.3 和 3.7.0 是为了向下兼容 OpenSSL 1.0.2。

`ssl.``OP_NO_RENEGOTIATION`

  禁用所有 TLSv1.2 和更早版本的重协商操作。 不发送 HelloRequest 消息，并忽略通过 ClientHello 发起的重协商请求。

  此选项仅适用于 OpenSSL 1.1.0h 及更新的版本。

  3.7 新版功能.

`ssl.``OP_CIPHER_SERVER_PREFERENCE`

  使用服务器的密码顺序首选项，而不是客户端的首选项。 此选项在客户端套接字和 SSLv2 服务器套接字上无效。

  3.3 新版功能.

`ssl.``OP_SINGLE_DH_USE`

  阻止对于单独的 SSL 会话重用相同的 DH 密钥。 这会提升前向保密性但需要更多的计算资源。 此选项仅适用于服务器套接字。

  3.3 新版功能.

`ssl.``OP_SINGLE_ECDH_USE`

  阻止对于单独的 SSL 会话重用相同的 ECDH 密钥。 这会提升前向保密性但需要更多的计算资源。 此选项仅适用于服务器套接字。

  3.3 新版功能.

`ssl.``OP_ENABLE_MIDDLEBOX_COMPAT`

  在 TLS 1.3 握手中发送虚拟更改密码规格（CCS）消息以使得 TLS 1.3 连接看起来更像是 TLS 1.2 连接。

  此选项仅适用于 OpenSSL 1.1.1 及更新的版本。

  3.8 新版功能.

`ssl.``OP_NO_COMPRESSION`

  在 SSL 通道上禁用压缩。 这适用于应用协议支持自己的压缩方案的情况。

  此选项仅适用于 OpenSSL 1.0.0 及更新的版本。

  3.3 新版功能.

class `ssl.``Options`

  OP_* 常量的 `enum.IntFlag` 多项集。

`ssl.``OP_NO_TICKET`

  阻止客户端请求会话凭据。

  3.6 新版功能.

`ssl.``HAS_ALPN`

  OpenSSL 库是否具有对 RFC 7301 中描述的 应用层协议协商 TLS 扩展的内置支持。

  3.5 新版功能.

`ssl.``HAS_NEVER_CHECK_COMMON_NAME`

  OpenSSL 库是否具有对不检测目标通用名称的内置支持且 `SSLContext.hostname_checks_common_name` 为可写状态。

  3.7 新版功能.

`ssl.``HAS_ECDH`

  OpenSSL 库是否具有对基于椭圆曲线的 Diffie-Hellman 密钥交换的内置支持。 此常量应当为真值，除非发布者明确地禁用了此功能。

  3.3 新版功能.

`ssl.``HAS_SNI`

  OpenSSL 库是否具有对 服务器名称提示 扩展（在 RFC 6066 中定义）的内置支持。

  3.2 新版功能.

`ssl.``HAS_NPN`

  OpenSSL 库是否具有对 应用层协议协商 中描述的 下一协议协商 的内置支持。 当此常量为真值时，你可以使用 `SSLContext.set_npn_protocols()` 方法来公告你想要支持的协议。

  3.3 新版功能.

`ssl.``HAS_SSLv2`

  OpenSSL 库是否具有对 SSL 2.0 协议的内置支持。

  3.7 新版功能.

`ssl.``HAS_SSLv3`

  OpenSSL 库是否具有对 SSL 3.0 协议的内置支持。

  3.7 新版功能.

`ssl.``HAS_TLSv1`

  OpenSSL 库是否具有对 TLS 1.0 协议的内置支持。

  3.7 新版功能.

`ssl.``HAS_TLSv1_1`

  OpenSSL 库是否具有对 TLS 1.1 协议的内置支持。

  3.7 新版功能.

`ssl.``HAS_TLSv1_2`

  OpenSSL 库是否具有对 TLS 1.2 协议的内置支持。

  3.7 新版功能.

`ssl.``HAS_TLSv1_3`

  OpenSSL 库是否具有对 TLS 1.3 协议的内置支持。

  3.7 新版功能.

`ssl.``CHANNEL_BINDING_TYPES`

  受支持的 TLS 通道绑定类型组成的列表。 此列表中的字符串可被用作传给 `SSLSocket.get_channel_binding()` 的参数。

  3.3 新版功能.

`ssl.``OPENSSL_VERSION`

  解释器所加载的 OpenSSL 库的版本字符串:

      >>> ssl.OPENSSL_VERSION
      'OpenSSL 1.0.2k  26 Jan 2017'

  3.2 新版功能.

`ssl.``OPENSSL_VERSION_INFO`

  代表 OpenSSL 库的版本信息的五个整数所组成的元组:

      >>> ssl.OPENSSL_VERSION_INFO
      (1, 0, 2, 11, 15)

  3.2 新版功能.

`ssl.``OPENSSL_VERSION_NUMBER`

  OpenSSL 库的原始版本号，以单个整数表示:

      >>> ssl.OPENSSL_VERSION_NUMBER
      268443839
      >>> hex(ssl.OPENSSL_VERSION_NUMBER)
      '0x100020bf'

  3.2 新版功能.

`ssl.``ALERT_DESCRIPTION_HANDSHAKE_FAILURE`
`ssl.``ALERT_DESCRIPTION_INTERNAL_ERROR`
`ALERT_DESCRIPTION_*`

  来自 RFC 5246 等文档的警报描述。 IANA TLS Alert Registry 中包含了这个列表及对定义其含义的 RFC 引用。

  被用作 `SSLContext.set_servername_callback()` 中的回调函数的返回值。

  3.4 新版功能.

class `ssl.``AlertDescription`

  ALERT_DESCRIPTION_* 常量的 `enum.IntEnum` 多项集。

  3.6 新版功能.

`Purpose.``SERVER_AUTH`

  `create_default_context()` 和 `SSLContext.load_default_certs()` 的选项值。 这个值表明此上下文可以被用来验证 Web 服务器（因此，它将被用来创建客户端套接字）。

  3.4 新版功能.

`Purpose.``CLIENT_AUTH`

  `create_default_context()` 和 `SSLContext.load_default_certs()` 的选项值。 这个值表明此上下文可以被用来验证 Web 客户端（因此，它将被用来创建服务器端套接字）。

  3.4 新版功能.

class `ssl.``SSLErrorNumber`

  SSL_ERROR_* 常量的 `enum.IntEnum` 多项集。

  3.6 新版功能.

class `ssl.``TLSVersion`

  `SSLContext.maximum_version` 和 `SSLContext.minimum_version` 中的 SSL 和 TLS 版本的 `enum.IntEnum` 多项集。

  3.7 新版功能.

`TLSVersion.``MINIMUM_SUPPORTED`

`TLSVersion.``MAXIMUM_SUPPORTED`

  受支持的最低和最高 SSL 或 TLS 版本。 这些常量被称为魔术常量。 它们的值并不反映可用的最低和最高 TLS/SSL 版本。

`TLSVersion.``SSLv3`

`TLSVersion.``TLSv1`

`TLSVersion.``TLSv1_1`

`TLSVersion.``TLSv1_2`

`TLSVersion.``TLSv1_3`

  SSL 3.0 至 TLS 1.3。

## SSL 套接字

class `ssl.``SSLSocket`(socket.socket)

  SSL 套接字提供了 套接字对象 的下列方法:

  - `accept()`

  - `bind()`

  - `close()`

  - `connect()`

  - `detach()`

  - `fileno()`

  - `getpeername()`, `getsockname()`

  - `getsockopt()`, `setsockopt()`

  - `gettimeout()`, `settimeout()`, `setblocking()`

  - `listen()`

  - `makefile()`

  - `recv()`, `recv_into()` (but passing a non-zero `flags` argument is not allowed)

  - `send()`, `sendall()` (with the same limitation)

  - `sendfile()` (but `os.sendfile` will be used for plain-text sockets only, else `send()` will be used)

  - `shutdown()`

  但是，由于 SSL（和 TLS）协议在 TCP 之上具有自己的框架，因此 SSL 套接字抽象在某些方面可能与常规的 OS 层级套接字存在差异。 特别是要查看 非阻塞型套接字说明。

  `SSLSocket` 的实例必须使用 `SSLContext.wrap_socket()` 方法来创建。

  在 3.5 版更改: 新增了 `sendfile()` 方法。

  在 3.5 版更改: `shutdown()` 不会在每次接收或发送字节数据后重置套接字超时。 现在套接字超时为关闭的最大总持续时间。

  3.6 版后已移除: 直接创建 `SSLSocket` 实例的做法已被弃用，请使用 `SSLContext.wrap_socket()` 来包装套接字。

  在 3.7 版更改: `SSLSocket` 的实例必须使用 `wrap_socket()` 来创建。 在较早的版本中，直接创建实例是可能的。 但这从未被记入文档或是被正式支持。

SSL 套接字还具有下列方法和属性:

`SSLSocket.``read`(len=1024, buffer=None)

  从 SSL 套接字读取至多 len 个字节的数据并将结果作为 `bytes` 实例返回。 如果指定了 buffer，则改为读取到缓冲区，并返回所读取的字节数。

  如果套接字为 非阻塞型 则会引发 `SSLWantReadError` 或 `SSLWantWriteError` 且读取将阻塞。

  由于在任何时候重新协商都是可能的，因此调用 `read()` 也可能导致写入操作。

  在 3.5 版更改: 套接字超时在每次接收或发送字节数据后不会再被重置。 现在套接字超时为读取至多 len 个字节数据的最大总持续时间。

  3.6 版后已移除: 请使用 `recv()` 来代替 `read()`。

`SSLSocket.``write`(buf)

  将 buf 写入到 SSL 套接字并返回所写入的字节数。 buf 参数必须为支持缓冲区接口的对象。

  如果套接字为 非阻塞型 则会引发 `SSLWantReadError` 或 `SSLWantWriteError` 且读取将阻塞。

  由于在任何时候重新协商都是可能的，因此调用 `write()` 也可能导致读取操作。

  在 3.5 版更改: 套接字超时在每次接收或发送字节数据后不会再被重置。 现在套接字超时为写入 buf 的最大总持续时间。

  3.6 版后已移除: 请使用 `send()` 来代替 `write()`。

注解

`read()` 和 `write()` 方法是读写未加密的应用级数据，并将其解密/加密为带加密的线路级数据的低层级方法。 这些方法需要有激活的 SSL 连接，即握手已完成而 `SSLSocket.unwrap()` 尚未被调用。

通常你应当使用套接字 API 方法例如 `recv()` 和 `send()` 来代替这些方法。

`SSLSocket.``do_handshake`()

  执行 SSL 设置握手。

  在 3.4 版更改: 当套接字的 `context` 的 `check_hostname` 属性为真值时此握手方法还会执行 `match_hostname()`。

  在 3.5 版更改: 套接字超时在每次接收或发送字节数据时不会再被重置。 现在套接字超时为握手的最大总持续时间。

  在 3.7 版更改: 主机名或 IP 地址会在握手期间由 OpenSSL 进行匹配。 函数 `match_hostname()` 将不再被使用。 在 OpenSSL 拒绝主机名和 IP 地址的情况下，握手将提前被中止并向对等方发送 TLS 警告消息。

`SSLSocket.``getpeercert`(binary_form=False)

  如果连接另一端的对等方没有证书，则返回 `None`。 如果 SSL 握手还未完成，则会引发 `ValueError`。

  如果 `binary_form` 形参为 `False`，并且从对等方接收到了证书，此方法将返回一个 `dict` 实例。 如果证书未通过验证，则字典将为空。 如果证书通过验证，它将返回由多个密钥组成的字典，其中包括 `subject` (证书颁发给的主体) 和 `issuer` (颁发证书的主体)。 如果证书包含一个 Subject Alternative Name 扩展的实例 (see RFC 3280)，则字典中还将有一个 `subjectAltName` 键。

  `subject` 和 `issuer` 字段都是包含在证书中相应字段的数据结构中给出的相对专有名称（RDN）序列的元组，每个 RDN 均为 name-value 对的序列。 这里是一个实际的示例:

      {'issuer': ((('countryName', 'IL'),),
                  (('organizationName', 'StartCom Ltd.'),),
                  (('organizationalUnitName',
                    'Secure Digital Certificate Signing'),),
                  (('commonName',
                    'StartCom Class 2 Primary Intermediate Server CA'),)),
       'notAfter': 'Nov 22 08:15:19 2013 GMT',
       'notBefore': 'Nov 21 03:09:52 2011 GMT',
       'serialNumber': '95F0',
       'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
                   (('countryName', 'US'),),
                   (('stateOrProvinceName', 'California'),),
                   (('localityName', 'San Francisco'),),
                   (('organizationName', 'Electronic Frontier Foundation, Inc.'),),
                   (('commonName', '*.eff.org'),),
                   (('emailAddress', 'hostmaster@eff.org'),)),
       'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
       'version': 3}

  注解

  要验证特定服务的证书，你可以使用 `match_hostname()` 函数。

  如果 `binary_form` 形参为 `True`，并且提供了证书，此方法会将整个证书的 DER 编码形式作为字节序列返回，或者如果对等方未提供证书则返回 `None`。 对等方是否提供证书取决于 SSL 套接字的角色:

  - 对于客户端 SSL 套接字，服务器将总是提供证书，无论是否需要进行验证;

  - 对于服务器 SSL 套接字，客户端将仅在服务器要求时才提供证书；因此如果你使用了 `CERT_NONE` (而不是 `CERT_OPTIONAL` 或 `CERT_REQUIRED`) 则 `getpeercert()` 将返回 `None`。

  在 3.2 版更改: 返回的字典包括额外的条目例如 `issuer` 和 `notBefore`。

  在 3.4 版更改: 如果握手未完成则会引发 `ValueError`。 返回的字典包括额外的 X509v3 扩展条目例如 `crlDistributionPoints`, `caIssuers` 和 `OCSP` URI。

  在 3.9 版更改: IPv6 地址字符串不再附带末尾换行符。

`SSLSocket.``cipher`()

  返回由三个值组成的元组，其中包含所使用的密码名称，定义其使用方式的 SSL 协议版本，以及所使用的加密比特位数。 如果尚未建立连接，则返回 `None`。

`SSLSocket.``shared_ciphers`()

  返回在握手期间由客户端共享的密码列表。 所返回列表的每个条目都是由三个值组成的元组，其中包括密码名称，定义其使用方式的 SSL 协议版本，以及密码所使用的加密比特位数。 如果尚未建立连接或套接字为客户端套接字则 `shared_ciphers()` 将返回 `None`。

  3.5 新版功能.

`SSLSocket.``compression`()

  以字符串形式返回所使用的压缩算法，或者如果连接没有使用压缩则返回 `None`。

  如果高层级的协议支持自己的压缩机制，你可以使用 `OP_NO_COMPRESSION` 来禁用 SSL 层级的压缩。

  3.3 新版功能.

`SSLSocket.``get_channel_binding`(cb_type="tls-unique")

  为当前连接获取字节串形式的通道绑定数据。 如果尚未连接或握手尚未完成则返回 `None`。

  cb_type 形参允许选择需要的通道绑定类型。 有效的通道绑定类型在 `CHANNEL_BINDING_TYPES` 列表中列出。 目前只支持由 RFC 5929 所定义的 'tls-unique' 通道绑定。 如果请求了一个不受支持的通道绑定类型则将引发 `ValueError`。

  3.3 新版功能.

`SSLSocket.``selected_alpn_protocol`()

  返回在 TLS 握手期间所选择的协议。 如果 `SSLContext.set_alpn_protocols()` 未被调用，如果另一方不支持 ALPN，如果此套接字不支持任何客户端所用的协议，或者如果握手尚未发生，则将返回 `None`。

  3.5 新版功能.

`SSLSocket.``selected_npn_protocol`()

  返回在Return the higher-level protocol that was selected during the TLS/SSL 握手期间所选择的高层级协议。 如果 `SSLContext.set_npn_protocols()` 未被调用，或者如果另一方不支持 NPN，或者如果握手尚未发生，则将返回 `None`。

  3.3 新版功能.

`SSLSocket.``unwrap`()

  执行 SSL 关闭握手，这会从下层的套接字中移除 TLS 层，并返回下层的套接字对象。 这可被用来通过一个连接将加密操作转为非加密。 返回的套接字应当总是被用于同连接另一方的进一步通信，而不是原始的套接字。

`SSLSocket.``verify_client_post_handshake`()

  向一个 TLS 1.3 客户端请求握手后身份验证（PHA）。 只有在初始 TLS 握手之后且双方都启用了 PHA 的情况下才能为服务器端套接字的 TLS 1.3 连接启用 PHA，参见 `SSLContext.post_handshake_auth`。

  此方法不会立即执行证书交换。 服务器端会在下一次写入事件期间发送 CertificateRequest 并期待客户端在下一次读取事件期间附带证书进行响应。

  如果有任何前置条件未被满足（例如非 TLS 1.3，PHA 未启用），则会引发 `SSLError`。

  注解

  仅在 OpenSSL 1.1.1 且 TLS 1.3 被启用时可用。 没有 TLS 1.3 支持，此方法将引发 `NotImplementedError`。

  3.8 新版功能.

`SSLSocket.``version`()

  以字符串形式返回由连接协商确定的实际 SSL 协议版本，或者如果未建立安全连接则返回 `None`。 在撰写本文档时，可能的返回值包括 `"SSLv2"`, `"SSLv3"`, `"TLSv1"`, `"TLSv1.1"` 和 `"TLSv1.2"`。 最新的 OpenSSL 版本可能会定义更多的返回值。

  3.5 新版功能.

`SSLSocket.``pending`()

  返回在连接上等待被读取的已解密字节数。

`SSLSocket.``context`

  此 SSL 套接字所联结的 `SSLContext` 对象。 如果 SSL 套接字是使用已弃用的 `wrap_socket()` 函数 (而非 `SSLContext.wrap_socket()`) 创建的，则这将是为此 SSL 套接字创建的自定义上下文对象。

  3.2 新版功能.

`SSLSocket.``server_side`

  一个布尔值，对于服务器端套接字为 `True` 而对于客户端套接字则为 `False`。

  3.2 新版功能.

`SSLSocket.``server_hostname`

  Hostname of the server: `str` type, or `None` for server-side socket or if the hostname was not specified in the constructor.

  3.2 新版功能.

  在 3.7 版更改: The attribute is now always ASCII text. When `server_hostname` is an internationalized domain name (IDN), this attribute now stores the A-label form (`"xn--pythn-mua.org"`), rather than the U-label form (`"pythön.org"`).

`SSLSocket.``session`

  The `SSLSession` for this SSL connection. The session is available for client and server side sockets after the TLS handshake has been performed. For client sockets the session can be set before `do_handshake()` has been called to reuse a session.

  3.6 新版功能.

`SSLSocket.``session_reused`

  3.6 新版功能.

## SSL Contexts

3.2 新版功能.

An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.

class `ssl.``SSLContext`(protocol=PROTOCOL_TLS)

  Create a new SSL context. You may pass protocol which must be one of the `PROTOCOL_*` constants defined in this module. The parameter specifies which version of the SSL protocol to use. Typically, the server chooses a particular protocol version, and the client must adapt to the server's choice. Most of the versions are not interoperable with the other versions. If not specified, the default is `PROTOCOL_TLS`; it provides the most compatibility with other versions.

  Here's a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):

  > 客户端 / 服务器 | SSLv2 | SSLv3 | TLS 3 | TLSv1 | TLSv1.1 | TLSv1.2
  > SSLv2 | 是 | 否 | 否 1 | 否 | 否 | 否
  > SSLv3 | 否 | 是 | 否 2 | 否 | 否 | 否
  > TLS (SSLv23) 3 | 否 1 | 否 2 | 是 | 是 | 是 | 是
  > TLSv1 | 否 | 否 | 是 | 是 | 否 | 否
  > TLSv1.1 | 否 | 否 | 是 | 否 | 是 | 否
  > TLSv1.2 | 否 | 否 | 是 | 否 | 否 | 是

  脚注

  1(1,2)

    `SSLContext` disables SSLv2 with `OP_NO_SSLv2` by default.

  2(1,2)

    `SSLContext` disables SSLv3 with `OP_NO_SSLv3` by default.

  3(1,2)

    TLS 1.3 protocol will be available with `PROTOCOL_TLS` in OpenSSL >= 1.1.1. There is no dedicated PROTOCOL constant for just TLS 1.3.

  参见

  `create_default_context()` lets the `ssl` module choose security settings for a given purpose.

  在 3.6 版更改: The context is created with secure default values. The options `OP_NO_COMPRESSION`, `OP_CIPHER_SERVER_PREFERENCE`, `OP_SINGLE_DH_USE`, `OP_SINGLE_ECDH_USE`, `OP_NO_SSLv2` (except for `PROTOCOL_SSLv2`), and `OP_NO_SSLv3` (except for `PROTOCOL_SSLv3`) are set by default. The initial cipher suite list contains only `HIGH` ciphers, no `NULL` ciphers and no `MD5` ciphers (except for `PROTOCOL_SSLv2`).

`SSLContext` objects have the following methods and attributes:

`SSLContext.``cert_store_stats`()

  Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.

  Example for a context with one CA cert and one other cert:

      >>> context.cert_store_stats()
      {'crl': 0, 'x509_ca': 1, 'x509': 2}

  3.4 新版功能.

`SSLContext.``load_cert_chain`(certfile, keyfile=None, password=None)

  Load a private key and the corresponding certificate. The certfile string must be the path to a single file in PEM format containing the certificate as well as any number of CA certificates needed to establish the certificate's authenticity. The keyfile string, if present, must point to a file containing the private key in. Otherwise the private key will be taken from certfile as well. See the discussion of Certificates for more information on how the certificate is stored in the certfile.

  The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.

  If the password argument is not specified and a password is required, OpenSSL's built-in password prompting mechanism will be used to interactively prompt the user for a password.

  An `SSLError` is raised if the private key doesn't match with the certificate.

  在 3.3 版更改: New optional argument password.

`SSLContext.``load_default_certs`(purpose=Purpose.SERVER_AUTH)

  Load a set of default "certification authority" (CA) certificates from default locations. On Windows it loads CA certs from the `CA` and `ROOT` system stores. On other systems it calls `SSLContext.set_default_verify_paths()`. In the future the method may load CA certificates from other locations, too.

  The purpose flag specifies what kind of CA certificates are loaded. The default settings `Purpose.SERVER_AUTH` loads certificates, that are flagged and trusted for TLS web server authentication (client side sockets). `Purpose.CLIENT_AUTH` loads CA certificates for client certificate verification on the server side.

  3.4 新版功能.

`SSLContext.``load_verify_locations`(cafile=None, capath=None, cadata=None)

  Load a set of "certification authority" (CA) certificates used to validate other peers' certificates when `verify_mode` is other than `CERT_NONE`. At least one of cafile or capath must be specified.

  This method can also load certification revocation lists (CRLs) in PEM or DER format. In order to make use of CRLs, `SSLContext.verify_flags` must be configured properly.

  The cafile string, if present, is the path to a file of concatenated CA certificates in PEM format. See the discussion of Certificates for more information about how to arrange the certificates in this file.

  The capath string, if present, is the path to a directory containing several CA certificates in PEM format, following an OpenSSL specific layout.

  The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object of DER-encoded certificates. Like with capath extra lines around PEM-encoded certificates are ignored but at least one certificate must be present.

  在 3.4 版更改: New optional argument cadata

`SSLContext.``get_ca_certs`(binary_form=False)

  Get a list of loaded "certification authority" (CA) certificates. If the `binary_form` parameter is `False` each list entry is a dict like the output of `SSLSocket.getpeercert()`. Otherwise the method returns a list of DER-encoded certificates. The returned list does not contain certificates from capath unless a certificate was requested and loaded by a SSL connection.

  注解

  Certificates in a capath directory aren't loaded unless they have been used at least once.

  3.4 新版功能.

`SSLContext.``get_ciphers`()

  Get a list of enabled ciphers. The list is in order of cipher priority. See `SSLContext.set_ciphers()`.

  示例:

      >>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
      >>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
      >>> ctx.get_ciphers()  # OpenSSL 1.0.x
      [{'alg_bits': 256,
        'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                       'Enc=AESGCM(256) Mac=AEAD',
        'id': 50380848,
        'name': 'ECDHE-RSA-AES256-GCM-SHA384',
        'protocol': 'TLSv1/SSLv3',
        'strength_bits': 256},
       {'alg_bits': 128,
        'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                       'Enc=AESGCM(128) Mac=AEAD',
        'id': 50380847,
        'name': 'ECDHE-RSA-AES128-GCM-SHA256',
        'protocol': 'TLSv1/SSLv3',
        'strength_bits': 128}]

  On OpenSSL 1.1 and newer the cipher dict contains additional fields:

      >>> ctx.get_ciphers()  # OpenSSL 1.1+
      [{'aead': True,
        'alg_bits': 256,
        'auth': 'auth-rsa',
        'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                       'Enc=AESGCM(256) Mac=AEAD',
        'digest': None,
        'id': 50380848,
        'kea': 'kx-ecdhe',
        'name': 'ECDHE-RSA-AES256-GCM-SHA384',
        'protocol': 'TLSv1.2',
        'strength_bits': 256,
        'symmetric': 'aes-256-gcm'},
       {'aead': True,
        'alg_bits': 128,
        'auth': 'auth-rsa',
        'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                       'Enc=AESGCM(128) Mac=AEAD',
        'digest': None,
        'id': 50380847,
        'kea': 'kx-ecdhe',
        'name': 'ECDHE-RSA-AES128-GCM-SHA256',
        'protocol': 'TLSv1.2',
        'strength_bits': 128,
        'symmetric': 'aes-128-gcm'}]

  Availability: OpenSSL 1.0.2+.

  3.6 新版功能.

`SSLContext.``set_default_verify_paths`()

  Load a set of default "certification authority" (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there's no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.

`SSLContext.``set_ciphers`(ciphers)

  Set the available ciphers for sockets created with this context. It should be a string in the OpenSSL cipher list format. If no cipher can be selected (because compile-time options or other configuration forbids use of all the specified ciphers), an `SSLError` will be raised.

  注解

  when connected, the `SSLSocket.cipher()` method of SSL sockets will give the currently selected cipher.

  OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default. The suites cannot be disabled with `set_ciphers()`.

`SSLContext.``set_alpn_protocols`(protocols)

  Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of ASCII strings, like `['http/1.1', 'spdy/2']`, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to RFC 7301. After a successful handshake, the `SSLSocket.selected_alpn_protocol()` method will return the agreed-upon protocol.

  This method will raise `NotImplementedError` if `HAS_ALPN` is `False`.

  OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise `SSLError` when both sides support ALPN but cannot agree on a protocol. 1.1.0f+ behaves like 1.0.2, `SSLSocket.selected_alpn_protocol()` returns None.

  3.5 新版功能.

`SSLContext.``set_npn_protocols`(protocols)

  Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of strings, like `['http/1.1', 'spdy/2']`, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to the Application Layer Protocol Negotiation. After a successful handshake, the `SSLSocket.selected_npn_protocol()` method will return the agreed-upon protocol.

  This method will raise `NotImplementedError` if `HAS_NPN` is `False`.

  3.3 新版功能.

`SSLContext.``sni_callback`

  Register a callback function that will be called after the TLS Client Hello handshake message has been received by the SSL/TLS server when the TLS client specifies a server name indication. The server name indication mechanism is specified in RFC 6066 section 3 - Server Name Indication.

  Only one callback can be set per `SSLContext`. If sni_callback is set to `None` then the callback is disabled. Calling this function a subsequent time will disable the previously registered callback.

  The callback function will be called with three arguments; the first being the `ssl.SSLSocket`, the second is a string that represents the server name that the client is intending to communicate (or `None` if the TLS Client Hello does not contain a server name) and the third argument is the original `SSLContext`. The server name argument is text. For internationalized domain name, the server name is an IDN A-label (`"xn--pythn-mua.org"`).

  A typical use of this callback is to change the `ssl.SSLSocket`'s `SSLSocket.context` attribute to a new object of type `SSLContext` representing a certificate chain that matches the server name.

  Due to the early negotiation phase of the TLS connection, only limited methods and attributes are usable like `SSLSocket.selected_alpn_protocol()` and `SSLSocket.context`. `SSLSocket.getpeercert()`, `SSLSocket.getpeercert()`, `SSLSocket.cipher()` and `SSLSocket.compress()` methods require that the TLS connection has progressed beyond the TLS Client Hello and therefore will not contain return meaningful values nor can they be called safely.

  The sni_callback function must return `None` to allow the TLS negotiation to continue. If a TLS failure is required, a constant `ALERT_DESCRIPTION_*` can be returned. Other return values will result in a TLS fatal error with `ALERT_DESCRIPTION_INTERNAL_ERROR`.

  If an exception is raised from the sni_callback function the TLS connection will terminate with a fatal TLS alert message `ALERT_DESCRIPTION_HANDSHAKE_FAILURE`.

  This method will raise `NotImplementedError` if the OpenSSL library had OPENSSL_NO_TLSEXT defined when it was built.

  3.7 新版功能.

`SSLContext.``set_servername_callback`(server_name_callback)

  This is a legacy API retained for backwards compatibility. When possible, you should use `sni_callback` instead. The given server_name_callback is similar to sni_callback, except that when the server hostname is an IDN-encoded internationalized domain name, the server_name_callback receives a decoded U-label (`"pythön.org"`).

  If there is an decoding error on the server name, the TLS connection will terminate with an `ALERT_DESCRIPTION_INTERNAL_ERROR` fatal TLS alert message to the client.

  3.4 新版功能.

`SSLContext.``load_dh_params`(dhfile)

  Load the key generation parameters for Diffie-Hellman (DH) key exchange. Using DH key exchange improves forward secrecy at the expense of computational resources (both on the server and on the client). The dhfile parameter should be the path to a file containing DH parameters in PEM format.

  This setting doesn't apply to client sockets. You can also use the `OP_SINGLE_DH_USE` option to further improve security.

  3.3 新版功能.

`SSLContext.``set_ecdh_curve`(curve_name)

  Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key exchange. ECDH is significantly faster than regular DH while arguably as secure. The curve_name parameter should be a string describing a well-known elliptic curve, for example `prime256v1` for a widely supported curve.

  This setting doesn't apply to client sockets. You can also use the `OP_SINGLE_ECDH_USE` option to further improve security.

  This method is not available if `HAS_ECDH` is `False`.

  3.3 新版功能.

  参见

  SSL/TLS & Perfect Forward Secrecy

    Vincent Bernat.

`SSLContext.``wrap_socket`(sock, server_side=False, do_handshake_on_connect=True, suppress_ragged_eofs=True, server_hostname=None, session=None)

  Wrap an existing Python socket sock and return an instance of `SSLContext.sslsocket_class` (default `SSLSocket`). The returned SSL socket is tied to the context, its settings and certificates. sock must be a `SOCK_STREAM` socket; other socket types are unsupported.

  The parameter `server_side` is a boolean which identifies whether server-side or client-side behavior is desired from this socket.

  For client-side sockets, the context construction is lazy; if the underlying socket isn't connected yet, the context construction will be performed after `connect()` is called on the socket. For server-side sockets, if the socket has no remote peer, it is assumed to be a listening socket, and the server-side SSL wrapping is automatically performed on client connections accepted via the `accept()` method. The method may raise `SSLError`.

  On client connections, the optional parameter server_hostname specifies the hostname of the service which we are connecting to. This allows a single server to host multiple SSL-based services with distinct certificates, quite similarly to HTTP virtual hosts. Specifying server_hostname will raise a `ValueError` if server_side is true.

  The parameter `do_handshake_on_connect` specifies whether to do the SSL handshake automatically after doing a `socket.connect()`, or whether the application program will call it explicitly, by invoking the `SSLSocket.do_handshake()` method. Calling `SSLSocket.do_handshake()` explicitly gives the program control over the blocking behavior of the socket I/O involved in the handshake.

  The parameter `suppress_ragged_eofs` specifies how the `SSLSocket.recv()` method should signal unexpected EOF from the other end of the connection. If specified as `True` (the default), it returns a normal EOF (an empty bytes object) in response to unexpected EOF errors raised from the underlying socket; if `False`, it will raise the exceptions back to the caller.

  session, see `session`.

  在 3.5 版更改: Always allow a server_hostname to be passed, even if OpenSSL does not have SNI.

  在 3.6 版更改: session argument was added.

  在 3.7 版更改: The method returns on instance of `SSLContext.sslsocket_class` instead of hard-coded `SSLSocket`.

`SSLContext.``sslsocket_class`

  The return type of `SSLContext.wrap_socket()`, defaults to `SSLSocket`. The attribute can be overridden on instance of class in order to return a custom subclass of `SSLSocket`.

  3.7 新版功能.

`SSLContext.``wrap_bio`(incoming, outgoing, server_side=False, server_hostname=None, session=None)

  Wrap the BIO objects incoming and outgoing and return an instance of `SSLContext.sslobject_class` (default `SSLObject`). The SSL routines will read input data from the incoming BIO and write data to the outgoing BIO.

  The server_side, server_hostname and session parameters have the same meaning as in `SSLContext.wrap_socket()`.

  在 3.6 版更改: session argument was added.

  在 3.7 版更改: The method returns on instance of `SSLContext.sslobject_class` instead of hard-coded `SSLObject`.

`SSLContext.``sslobject_class`

  The return type of `SSLContext.wrap_bio()`, defaults to `SSLObject`. The attribute can be overridden on instance of class in order to return a custom subclass of `SSLObject`.

  3.7 新版功能.

`SSLContext.``session_stats`()

  Get statistics about the SSL sessions created or managed by this context. A dictionary is returned which maps the names of each piece of information to their numeric values. For example, here is the total number of hits and misses in the session cache since the context was created:

      >>> stats = context.session_stats()
      >>> stats['hits'], stats['misses']
      (0, 0)

`SSLContext.``check_hostname`

  Whether to match the peer cert's hostname with `match_hostname()` in `SSLSocket.do_handshake()`. The context's `verify_mode` must be set to `CERT_OPTIONAL` or `CERT_REQUIRED`, and you must pass server_hostname to `wrap_socket()` in order to match the hostname. Enabling hostname checking automatically sets `verify_mode` from `CERT_NONE` to `CERT_REQUIRED`. It cannot be set back to `CERT_NONE` as long as hostname checking is enabled. The `PROTOCOL_TLS_CLIENT` protocol enables hostname checking by default. With other protocols, hostname checking must be enabled explicitly.

  示例:

      import socket, ssl

      context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
      context.verify_mode = ssl.CERT_REQUIRED
      context.check_hostname = True
      context.load_default_certs()

      s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
      ssl_sock.connect(('www.verisign.com', 443))

  3.4 新版功能.

  在 3.7 版更改: `verify_mode` is now automatically changed to `CERT_REQUIRED` when hostname checking is enabled and `verify_mode` is `CERT_NONE`. Previously the same operation would have failed with a `ValueError`.

  注解

  This features requires OpenSSL 0.9.8f or newer.

`SSLContext.``keylog_filename`

  Write TLS keys to a keylog file, whenever key material is generated or received. The keylog file is designed for debugging purposes only. The file format is specified by NSS and used by many traffic analyzers such as Wireshark. The log file is opened in append-only mode. Writes are synchronized between threads, but not between processes.

  3.8 新版功能.

  注解

  This features requires OpenSSL 1.1.1 or newer.

`SSLContext.``maximum_version`

  A `TLSVersion` enum member representing the highest supported TLS version. The value defaults to `TLSVersion.MAXIMUM_SUPPORTED`. The attribute is read-only for protocols other than `PROTOCOL_TLS`, `PROTOCOL_TLS_CLIENT`, and `PROTOCOL_TLS_SERVER`.

  The attributes `maximum_version`, `minimum_version` and `SSLContext.options` all affect the supported SSL and TLS versions of the context. The implementation does not prevent invalid combination. For example a context with `OP_NO_TLSv1_2` in `options` and `maximum_version` set to `TLSVersion.TLSv1_2` will not be able to establish a TLS 1.2 connection.

  注解

  This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.0g or newer.

  3.7 新版功能.

`SSLContext.``minimum_version`

  Like `SSLContext.maximum_version` except it is the lowest supported version or `TLSVersion.MINIMUM_SUPPORTED`.

  注解

  This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.0g or newer.

  3.7 新版功能.

`SSLContext.``num_tickets`

  Control the number of TLS 1.3 session tickets of a `TLS_PROTOCOL_SERVER` context. The setting has no impact on TLS 1.0 to 1.2 connections.

  注解

  This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.1 or newer.

  3.8 新版功能.

`SSLContext.``options`

  An integer representing the set of SSL options enabled on this context. The default value is `OP_ALL`, but you can specify other options such as `OP_NO_SSLv2` by ORing them together.

  注解

  With versions of OpenSSL older than 0.9.8m, it is only possible to set options, not to clear them. Attempting to clear an option (by resetting the corresponding bits) will raise a `ValueError`.

  在 3.6 版更改: `SSLContext.options` returns `Options` flags:

      >>> ssl.create_default_context().options
      <Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>

`SSLContext.``post_handshake_auth`

  Enable TLS 1.3 post-handshake client authentication. Post-handshake auth is disabled by default and a server can only request a TLS client certificate during the initial handshake. When enabled, a server may request a TLS client certificate at any time after the handshake.

  When enabled on client-side sockets, the client signals the server that it supports post-handshake authentication.

  When enabled on server-side sockets, `SSLContext.verify_mode` must be set to `CERT_OPTIONAL` or `CERT_REQUIRED`, too. The actual client cert exchange is delayed until `SSLSocket.verify_client_post_handshake()` is called and some I/O is performed.

  注解

  Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the property value is None and can't be modified

  3.8 新版功能.

`SSLContext.``protocol`

  The protocol version chosen when constructing the context. This attribute is read-only.

`SSLContext.``hostname_checks_common_name`

  Whether `check_hostname` falls back to verify the cert's subject common name in the absence of a subject alternative name extension (default: true).

  注解

  Only writeable with OpenSSL 1.1.0 or higher.

  3.7 新版功能.

`SSLContext.``verify_flags`

  The flags for certificate verification operations. You can set flags like `VERIFY_CRL_CHECK_LEAF` by ORing them together. By default OpenSSL does neither require nor verify certificate revocation lists (CRLs). Available only with openssl version 0.9.8+.

  3.4 新版功能.

  在 3.6 版更改: `SSLContext.verify_flags` returns `VerifyFlags` flags:

      >>> ssl.create_default_context().verify_flags
      <VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>

`SSLContext.``verify_mode`

  Whether to try to verify other peers' certificates and how to behave if verification fails. This attribute must be one of `CERT_NONE`, `CERT_OPTIONAL` or `CERT_REQUIRED`.

  在 3.6 版更改: `SSLContext.verify_mode` returns `VerifyMode` enum:

      >>> ssl.create_default_context().verify_mode
      <VerifyMode.CERT_REQUIRED: 2>

## Certificates

Certificates in general are part of a public-key / private-key system. In this system, each principal, (which may be a machine, or a person, or an organization) is assigned a unique two-part encryption key. One part of the key is public, and is called the public key; the other part is kept secret, and is called the private key. The two parts are related, in that if you encrypt a message with one of the parts, you can decrypt it with the other part, and only with the other part.

A certificate contains information about two principals. It contains the name of a subject, and the subject's public key. It also contains a statement by a second principal, the issuer, that the subject is who they claim to be, and that this is indeed the subject's public key. The issuer's statement is signed with the issuer's private key, which only the issuer knows. However, anyone can verify the issuer's statement by finding the issuer's public key, decrypting the statement with it, and comparing it to the other information in the certificate. The certificate also contains information about the time period over which it is valid. This is expressed as two fields, called "notBefore" and "notAfter".

In the Python use of certificates, a client or server can use a certificate to prove who they are. The other side of a network connection can also be required to produce a certificate, and that certificate can be validated to the satisfaction of the client or server that requires such validation. The connection attempt can be set to raise an exception if the validation fails. Validation is done automatically, by the underlying OpenSSL framework; the application need not concern itself with its mechanics. But the application does usually need to provide sets of certificates to allow this process to take place.

Python uses files to contain certificates. They should be formatted as "PEM" (see RFC 1422), which is a base-64 encoded form wrapped with a header line and a footer line:

    -----BEGIN CERTIFICATE-----
    ... (certificate in base64 PEM encoding) ...
    -----END CERTIFICATE-----

### Certificate chains

The Python files which contain certificates can contain a sequence of certificates, sometimes called a certificate chain. This chain should start with the specific certificate for the principal who "is" the client or server, and then the certificate for the issuer of that certificate, and then the certificate for the issuer of that certificate, and so on up the chain till you get to a certificate which is self-signed, that is, a certificate which has the same subject and issuer, sometimes called a root certificate. The certificates should just be concatenated together in the certificate file. For example, suppose we had a three certificate chain, from our server certificate to the certificate of the certification authority that signed our server certificate, to the root certificate of the agency which issued the certification authority's certificate:

    -----BEGIN CERTIFICATE-----
    ... (certificate for your server)...
    -----END CERTIFICATE-----
    -----BEGIN CERTIFICATE-----
    ... (the certificate for the CA)...
    -----END CERTIFICATE-----
    -----BEGIN CERTIFICATE-----
    ... (the root certificate for the CA's issuer)...
    -----END CERTIFICATE-----

### CA certificates

If you are going to require validation of the other side of the connection's certificate, you need to provide a "CA certs" file, filled with the certificate chains for each issuer you are willing to trust. Again, this file just contains these chains concatenated together. For validation, Python will use the first chain it finds in the file which matches. The platform's certificates file can be used by calling `SSLContext.load_default_certs()`, this is done automatically with `create_default_context()`.

### Combined key and certificate

Often the private key is stored in the same file as the certificate; in this case, only the `certfile` parameter to `SSLContext.load_cert_chain()` and `wrap_socket()` needs to be passed. If the private key is stored with the certificate, it should come before the first certificate in the certificate chain:

    -----BEGIN RSA PRIVATE KEY-----
    ... (private key in base64 encoding) ...
    -----END RSA PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    ... (certificate in base64 PEM encoding) ...
    -----END CERTIFICATE-----

### Self-signed certificates

If you are going to create a server that provides SSL-encrypted connection services, you will need to acquire a certificate for that service. There are many ways of acquiring appropriate certificates, such as buying one from a certification authority. Another common practice is to generate a self-signed certificate. The simplest way to do this is with the OpenSSL package, using something like the following:

    % openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
    Generating a 1024 bit RSA private key
    .......++++++
    .............................++++++
    writing new private key to 'cert.pem'
    -----
    You are about to be asked to enter information that will be incorporated
    into your certificate request.
    What you are about to enter is what is called a Distinguished Name or a DN.
    There are quite a few fields but you can leave some blank
    For some fields there will be a default value,
    If you enter '.', the field will be left blank.
    -----
    Country Name (2 letter code) [AU]:US
    State or Province Name (full name) [Some-State]:MyState
    Locality Name (eg, city) []:Some City
    Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
    Organizational Unit Name (eg, section) []:My Group
    Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
    Email Address []:ops@myserver.mygroup.myorganization.com
    %

The disadvantage of a self-signed certificate is that it is its own root certificate, and no one else will have it in their cache of known (and trusted) root certificates.

## 示例

### Testing for SSL support

To test for the presence of SSL support in a Python installation, user code should use the following idiom:

    try:
        import ssl
    except ImportError:
        pass
    else:
        ...  # do something that requires SSL support

### Client-side operation

This example creates a SSL context with the recommended security settings for client sockets, including automatic certificate verification:

    >>> context = ssl.create_default_context()

If you prefer to tune security settings yourself, you might create a context from scratch (but beware that you might not get the settings right):

    >>> context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
    >>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")

(this snippet assumes your operating system places a bundle of all CA certificates in `/etc/ssl/certs/ca-bundle.crt`; if not, you'll get an error and have to adjust the location)

The `PROTOCOL_TLS_CLIENT` protocol configures the context for cert validation and hostname verification. `verify_mode` is set to `CERT_REQUIRED` and `check_hostname` is set to `True`. All other protocols create SSL contexts with insecure defaults.

When you use the context to connect to a server, `CERT_REQUIRED` and `check_hostname` validate the server certificate: it ensures that the server certificate was signed with one of the CA certificates, checks the signature for correctness, and verifies other properties like validity and identity of the hostname:

    >>> conn = context.wrap_socket(socket.socket(socket.AF_INET),
    ...                            server_hostname="www.python.org")
    >>> conn.connect(("www.python.org", 443))

You may then fetch the certificate:

    >>> cert = conn.getpeercert()

Visual inspection shows that the certificate does identify the desired service (that is, the HTTPS host `www.python.org`):

    >>> pprint.pprint(cert)
    {'OCSP': ('http://ocsp.digicert.com',),
     'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),
     'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',
                               'http://crl4.digicert.com/sha2-ev-server-g1.crl'),
     'issuer': ((('countryName', 'US'),),
                (('organizationName', 'DigiCert Inc'),),
                (('organizationalUnitName', 'www.digicert.com'),),
                (('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),
     'notAfter': 'Sep  9 12:00:00 2016 GMT',
     'notBefore': 'Sep  5 00:00:00 2014 GMT',
     'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',
     'subject': ((('businessCategory', 'Private Organization'),),
                 (('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
                 (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
                 (('serialNumber', '3359300'),),
                 (('streetAddress', '16 Allen Rd'),),
                 (('postalCode', '03894-4801'),),
                 (('countryName', 'US'),),
                 (('stateOrProvinceName', 'NH'),),
                 (('localityName', 'Wolfeboro'),),
                 (('organizationName', 'Python Software Foundation'),),
                 (('commonName', 'www.python.org'),)),
     'subjectAltName': (('DNS', 'www.python.org'),
                        ('DNS', 'python.org'),
                        ('DNS', 'pypi.org'),
                        ('DNS', 'docs.python.org'),
                        ('DNS', 'testpypi.org'),
                        ('DNS', 'bugs.python.org'),
                        ('DNS', 'wiki.python.org'),
                        ('DNS', 'hg.python.org'),
                        ('DNS', 'mail.python.org'),
                        ('DNS', 'packaging.python.org'),
                        ('DNS', 'pythonhosted.org'),
                        ('DNS', 'www.pythonhosted.org'),
                        ('DNS', 'test.pythonhosted.org'),
                        ('DNS', 'us.pycon.org'),
                        ('DNS', 'id.python.org')),
     'version': 3}

Now the SSL channel is established and the certificate verified, you can proceed to talk with the server:

    >>> conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
    >>> pprint.pprint(conn.recv(1024).split(b"\r\n"))
    [b'HTTP/1.1 200 OK',
     b'Date: Sat, 18 Oct 2014 18:27:20 GMT',
     b'Server: nginx',
     b'Content-Type: text/html; charset=utf-8',
     b'X-Frame-Options: SAMEORIGIN',
     b'Content-Length: 45679',
     b'Accept-Ranges: bytes',
     b'Via: 1.1 varnish',
     b'Age: 2188',
     b'X-Served-By: cache-lcy1134-LCY',
     b'X-Cache: HIT',
     b'X-Cache-Hits: 11',
     b'Vary: Cookie',
     b'Strict-Transport-Security: max-age=63072000; includeSubDomains',
     b'Connection: close',
     b'',
     b'']

参见下文对于 Security considerations 的讨论。

### Server-side operation

For server operation, typically you'll need to have a server certificate, and private key, each in a file. You'll first create a context holding the key and the certificate, so that clients can check your authenticity. Then you'll open a socket, bind it to a port, call `listen()` on it, and start waiting for clients to connect:

    import socket, ssl

    context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
    context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")

    bindsocket = socket.socket()
    bindsocket.bind(('myaddr.mydomain.com', 10023))
    bindsocket.listen(5)

When a client connects, you'll call `accept()` on the socket to get the new socket from the other end, and use the context's `SSLContext.wrap_socket()` method to create a server-side SSL socket for the connection:

    while True:
        newsocket, fromaddr = bindsocket.accept()
        connstream = context.wrap_socket(newsocket, server_side=True)
        try:
            deal_with_client(connstream)
        finally:
            connstream.shutdown(socket.SHUT_RDWR)
            connstream.close()

Then you'll read data from the `connstream` and do something with it till you are finished with the client (or the client is finished with you):

    def deal_with_client(connstream):
        data = connstream.recv(1024)
        # empty data means the client is finished with us
        while data:
            if not do_something(connstream, data):
                # we'll assume do_something returns False
                # when we're finished with client
                break
            data = connstream.recv(1024)
        # finished with client

And go back to listening for new client connections (of course, a real server would probably handle each client connection in a separate thread, or put the sockets in non-blocking mode and use an event loop).

## Notes on non-blocking sockets

SSL sockets behave slightly different than regular sockets in non-blocking mode. When working with non-blocking sockets, there are thus several things you need to be aware of:

- Most `SSLSocket` methods will raise either `SSLWantWriteError` or `SSLWantReadError` instead of `BlockingIOError` if an I/O operation would block. `SSLWantReadError` will be raised if a read operation on the underlying socket is necessary, and `SSLWantWriteError` for a write operation on the underlying socket. Note that attempts to write to an SSL socket may require reading from the underlying socket first, and attempts to read from the SSL socket may require a prior write to the underlying socket.

  在 3.5 版更改: In earlier Python versions, the `SSLSocket.send()` method returned zero instead of raising `SSLWantWriteError` or `SSLWantReadError`.

- Calling `select()` tells you that the OS-level socket can be read from (or written to), but it does not imply that there is sufficient data at the upper SSL layer. For example, only part of an SSL frame might have arrived. Therefore, you must be ready to handle `SSLSocket.recv()` and `SSLSocket.send()` failures, and retry after another call to `select()`.

- Conversely, since the SSL layer has its own framing, a SSL socket may still have data available for reading without `select()` being aware of it. Therefore, you should first call `SSLSocket.recv()` to drain any potentially available data, and then only block on a `select()` call if still necessary.

  (of course, similar provisions apply when using other primitives such as `poll()`, or those in the `selectors` module)

- The SSL handshake itself will be non-blocking: the `SSLSocket.do_handshake()` method has to be retried until it returns successfully. Here is a synopsis using `select()` to wait for the socket's readiness:

      while True:
          try:
              sock.do_handshake()
              break
          except ssl.SSLWantReadError:
              select.select([sock], [], [])
          except ssl.SSLWantWriteError:
              select.select([], [sock], [])

参见

The `asyncio` module supports non-blocking SSL sockets and provides a higher level API. It polls for events using the `selectors` module and handles `SSLWantWriteError`, `SSLWantReadError` and `BlockingIOError` exceptions. It runs the SSL handshake asynchronously as well.

## Memory BIO Support

3.5 新版功能.

Ever since the SSL module was introduced in Python 2.6, the `SSLSocket` class has provided two related but distinct areas of functionality:

- SSL protocol handling

- Network IO

The network IO API is identical to that provided by `socket.socket`, from which `SSLSocket` also inherits. This allows an SSL socket to be used as a drop-in replacement for a regular socket, making it very easy to add SSL support to an existing application.

Combining SSL protocol handling and network IO usually works well, but there are some cases where it doesn't. An example is async IO frameworks that want to use a different IO multiplexing model than the "select/poll on a file descriptor" (readiness based) model that is assumed by `socket.socket` and by the internal OpenSSL socket IO routines. This is mostly relevant for platforms like Windows where this model is not efficient. For this purpose, a reduced scope variant of `SSLSocket` called `SSLObject` is provided.

class `ssl.``SSLObject`

  A reduced-scope variant of `SSLSocket` representing an SSL protocol instance that does not contain any network IO methods. This class is typically used by framework authors that want to implement asynchronous IO for SSL through memory buffers.

  This class implements an interface on top of a low-level SSL object as implemented by OpenSSL. This object captures the state of an SSL connection but does not provide any network IO itself. IO needs to be performed through separate "BIO" objects which are OpenSSL's IO abstraction layer.

  This class has no public constructor. An `SSLObject` instance must be created using the `wrap_bio()` method. This method will create the `SSLObject` instance and bind it to a pair of BIOs. The incoming BIO is used to pass data from Python to the SSL protocol instance, while the outgoing BIO is used to pass data the other way around.

  可以使用以下方法：

  - `context`

  - `server_side`

  - `server_hostname`

  - `session`

  - `session_reused`

  - `read()`

  - `write()`

  - `getpeercert()`

  - `selected_alpn_protocol()`

  - `selected_npn_protocol()`

  - `cipher()`

  - `shared_ciphers()`

  - `compression()`

  - `pending()`

  - `do_handshake()`

  - `verify_client_post_handshake()`

  - `unwrap()`

  - `get_channel_binding()`

  - `version()`

  When compared to `SSLSocket`, this object lacks the following features:

  - Any form of network IO; `recv()` and `send()` read and write only to the underlying `MemoryBIO` buffers.

  - There is no do_handshake_on_connect machinery. You must always manually call `do_handshake()` to start the handshake.

  - There is no handling of suppress_ragged_eofs. All end-of-file conditions that are in violation of the protocol are reported via the `SSLEOFError` exception.

  - The method `unwrap()` call does not return anything, unlike for an SSL socket where it returns the underlying socket.

  - The server_name_callback callback passed to `SSLContext.set_servername_callback()` will get an `SSLObject` instance instead of a `SSLSocket` instance as its first parameter.

  Some notes related to the use of `SSLObject`:

  - All IO on an `SSLObject` is non-blocking. This means that for example `read()` will raise an `SSLWantReadError` if it needs more data than the incoming BIO has available.

  - There is no module-level `wrap_bio()` call like there is for `wrap_socket()`. An `SSLObject` is always created via an `SSLContext`.

  在 3.7 版更改: `SSLObject` instances must to created with `wrap_bio()`. In earlier versions, it was possible to create instances directly. This was never documented or officially supported.

An SSLObject communicates with the outside world using memory buffers. The class `MemoryBIO` provides a memory buffer that can be used for this purpose. It wraps an OpenSSL memory BIO (Basic IO) object:

class `ssl.``MemoryBIO`

  A memory buffer that can be used to pass data between Python and an SSL protocol instance.

  `pending`

    Return the number of bytes currently in the memory buffer.

  `eof`

    A boolean indicating whether the memory BIO is current at the end-of-file position.

  `read`(n=-1)

    Read up to n bytes from the memory buffer. If n is not specified or negative, all bytes are returned.

  `write`(buf)

    Write the bytes from buf to the memory BIO. The buf argument must be an object supporting the buffer protocol.

    The return value is the number of bytes written, which is always equal to the length of buf.

  `write_eof`()

    Write an EOF marker to the memory BIO. After this method has been called, it is illegal to call `write()`. The attribute `eof` will become true after all data currently in the buffer has been read.

## SSL session

3.6 新版功能.

class `ssl.``SSLSession`

  Session object used by `session`.

  `id`
  `time`
  `timeout`
  `ticket_lifetime_hint`
  `has_ticket`

## Security considerations

### Best defaults

For client use, if you don't have any special requirements for your security policy, it is highly recommended that you use the `create_default_context()` function to create your SSL context. It will load the system's trusted CA certificates, enable certificate validation and hostname checking, and try to choose reasonably secure protocol and cipher settings.

For example, here is how you would use the `smtplib.SMTP` class to create a trusted, secure connection to a SMTP server:

    >>> import ssl, smtplib
    >>> smtp = smtplib.SMTP("mail.python.org", port=587)
    >>> context = ssl.create_default_context()
    >>> smtp.starttls(context=context)
    (220, b'2.0.0 Ready to start TLS')

If a client certificate is needed for the connection, it can be added with `SSLContext.load_cert_chain()`.

By contrast, if you create the SSL context by calling the `SSLContext` constructor yourself, it will not have certificate validation nor hostname checking enabled by default. If you do so, please read the paragraphs below to achieve a good security level.

### Manual settings

#### Verifying certificates

When calling the `SSLContext` constructor directly, `CERT_NONE` is the default. Since it does not authenticate the other peer, it can be insecure, especially in client mode where most of time you would like to ensure the authenticity of the server you're talking to. Therefore, when in client mode, it is highly recommended to use `CERT_REQUIRED`. However, it is in itself not sufficient; you also have to check that the server certificate, which can be obtained by calling `SSLSocket.getpeercert()`, matches the desired service. For many protocols and applications, the service can be identified by the hostname; in this case, the `match_hostname()` function can be used. This common check is automatically performed when `SSLContext.check_hostname` is enabled.

在 3.7 版更改: Hostname matchings is now performed by OpenSSL. Python no longer uses `match_hostname()`.

In server mode, if you want to authenticate your clients using the SSL layer (rather than using a higher-level authentication mechanism), you'll also have to specify `CERT_REQUIRED` and similarly check the client certificate.

#### Protocol versions

SSL versions 2 and 3 are considered insecure and are therefore dangerous to use. If you want maximum compatibility between clients and servers, it is recommended to use `PROTOCOL_TLS_CLIENT` or `PROTOCOL_TLS_SERVER` as the protocol version. SSLv2 and SSLv3 are disabled by default.

    >>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
    >>> client_context.options |= ssl.OP_NO_TLSv1
    >>> client_context.options |= ssl.OP_NO_TLSv1_1

The SSL context created above will only allow TLSv1.2 and later (if supported by your system) connections to a server. `PROTOCOL_TLS_CLIENT` implies certificate validation and hostname checks by default. You have to load certificates into the context.

#### Cipher selection

If you have advanced security requirements, fine-tuning of the ciphers enabled when negotiating a SSL session is possible through the `SSLContext.set_ciphers()` method. Starting from Python 3.2.3, the ssl module disables certain weak ciphers by default, but you may want to further restrict the cipher choice. Be sure to read OpenSSL's documentation about the cipher list format. If you want to check which ciphers are enabled by a given cipher list, use `SSLContext.get_ciphers()` or the `openssl ciphers` command on your system.

### Multi-processing

If using this module as part of a multi-processed application (using, for example the `multiprocessing` or `concurrent.futures` modules), be aware that OpenSSL's internal random number generator does not properly handle forked processes. Applications must change the PRNG state of the parent process if they use any SSL feature with `os.fork()`. Any successful call of `RAND_add()`, `RAND_bytes()` or `RAND_pseudo_bytes()` is sufficient.

## TLS 1.3

3.7 新版功能.

Python has provisional and experimental support for TLS 1.3 with OpenSSL 1.1.1. The new protocol behaves slightly differently than previous version of TLS/SSL. Some new TLS 1.3 features are not yet available.

- TLS 1.3 uses a disjunct set of cipher suites. All AES-GCM and ChaCha20 cipher suites are enabled by default. The method `SSLContext.set_ciphers()` cannot enable or disable any TLS 1.3 ciphers yet, but `SSLContext.get_ciphers()` returns them.

- Session tickets are no longer sent as part of the initial handshake and are handled differently. `SSLSocket.session` and `SSLSession` are not compatible with TLS 1.3.

- Client-side certificates are also no longer verified during the initial handshake. A server can request a certificate at any time. Clients process certificate requests while they send or receive application data from the server.

- TLS 1.3 features like early data, deferred TLS client cert request, signature algorithm configuration, and rekeying are not supported yet.

## LibreSSL support

LibreSSL is a fork of OpenSSL 1.0.1. The ssl module has limited support for LibreSSL. Some features are not available when the ssl module is compiled with LibreSSL.

- LibreSSL >= 2.6.1 no longer supports NPN. The methods `SSLContext.set_npn_protocols()` and `SSLSocket.selected_npn_protocol()` are not available.

- `SSLContext.set_default_verify_paths()` ignores the env vars `SSL_CERT_FILE` and `SSL_CERT_PATH` although `get_default_verify_paths()` still reports them.

参见

Class `socket.socket`

  Documentation of underlying `socket` class

SSL/TLS Strong Encryption: An Introduction

  Apache HTTP Server文档介绍

RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management

  Steve Kent

RFC 4086: Randomness Requirements for Security

  Donald E., Jeffrey I. Schiller

RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

  D. Cooper

RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2

  T. Dierks et. al.

RFC 6066: Transport Layer Security (TLS) Extensions

  D. Eastlake

IANA TLS: Transport Layer Security (TLS) Parameters

  IANA

RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)

  IETF

Mozilla's Server Side TLS recommendations

  Mozilla