"hashlib" --- Secure hashes and message digests
***********************************************

**Código-fonte:** Lib/hashlib.py

======================================================================

This module implements a common interface to many different secure
hash and message digest algorithms.  Included are the FIPS secure hash
algorithms SHA1, SHA224, SHA256, SHA384, SHA512, (defined in the FIPS
180-4 standard), the SHA-3 series (defined in the FIPS 202 standard)
as well as RSA's MD5 algorithm (defined in internet **RFC 1321**).
The terms "secure hash" and "message digest" are interchangeable.
Older algorithms were called message digests.  The modern term is
secure hash.

Nota:

  Se você quiser as funções de hash adler32 ou crc32, elas estão
  disponíveis no módulo "zlib".


Algoritmos de hash
==================

Há um método construtor nomeado para cada tipo de *hash*. Todos
retornam um objeto hash com a mesma interface simples. Por exemplo:
use "sha256()" para criar um objeto hash SHA-256. Agora você pode
alimentar este objeto com *objetos bytes ou similares* (normalmente
"bytes") usando o método "update". A qualquer momento, você pode
solicitar o *digest* da concatenação dos dados alimentados até o
momento usando os métodos "digest()" ou "hexdigest()".

Para permitir multithreading, a *GIL* do Python é liberada ao calcular
um hash fornecido com mais de 2047 bytes de dados de uma só vez em seu
construtor ou método ".update".

Os construtores para algoritmos de hash sempre presentes neste módulo
são "sha1()", "sha224()", "sha256()", "sha384()", "sha512()",
"sha3_224()", "sha3_256()", "sha3_384()", "sha3_512()", "shake_128()",
"shake_256()", "blake2b()" e "blake2s()". "md5()" normalmente também
está disponível, embora possa estar ausente ou bloqueado se você
estiver usando uma construção rara do Python "compatível com FIPS".
Eles correspondem a "algorithms_guaranteed".

Algoritmos adicionais também podem estar disponíveis se o "hashlib" da
sua distribuição Python tiver sido vinculado a uma construção do
OpenSSL que forneça outros algoritmos. Outros *não têm garantia de
disponibilidade* em todas as instalações e só serão acessíveis pelo
nome via "new()". Consulte "algorithms_available".

Aviso:

  Alguns algoritmos apresentam vulnerabilidades conhecidas em colisões
  de hash (incluindo MD5 e SHA1). Consulte Ataques a algoritmos de
  hash criptográficos e a seção hashlib-seealso no final deste
  documento.

Novo na versão 3.6: Os construtores SHA3 (Keccak) e SHAKE
"sha3_224()", "sha3_256()", "sha3_384()", "sha3_512()", "shake_128()",
"shake_256()" foram adicionados. "blake2b()" e "blake2s()" foram
adicionados.

Alterado na versão 3.9: Todos os construtores de hashlib aceitam um
argumento somente-nomeado *usedforsecurity* com o valor padrão "True".
Um valor falso permite o uso de algoritmos de hash inseguros e
bloqueados em ambientes restritos. "False" indica que o algoritmo de
hash não é usado em um contexto de segurança, por exemplo, como uma
função de compressão unidirecional não criptográfica.

Alterado na versão 3.9: O hashlib agora usa SHA3 e SHAKE do OpenSSL,
se ele os fornecer.


Uso
===

Para obter o resumo da string de bytes "b"Nobody inspects the spammish
repetition"":

   >>> import hashlib
   >>> m = hashlib.sha256()
   >>> m.update(b"Nobody inspects")
   >>> m.update(b" the spammish repetition")
   >>> m.digest()
   b'\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\\x00o\xa5u+7\xfd\xdf\xf7\xbcN\x84:\xa6\xaf\x0c\x95\x0fK\x94\x06'
   >>> m.hexdigest()
   '031edd7d41651593c5fe5c006fa5752b37fddff7bc4e843aa6af0c950f4b9406'

Mais condensado:

>>> hashlib.sha256(b"Nobody inspects the spammish repetition").hexdigest()
'031edd7d41651593c5fe5c006fa5752b37fddff7bc4e843aa6af0c950f4b9406'


Construtores
============

hashlib.new(name, [data, ]*, usedforsecurity=True)

   É um construtor genérico que recebe a string *name* do algoritmo
   desejado como seu primeiro parâmetro. Ele também existe para
   permitir acesso aos hashes listados acima, bem como a quaisquer
   outros algoritmos que sua biblioteca OpenSSL possa oferecer.

Usando "new()" com um nome de algoritmo:

>>> h = hashlib.new('sha256')
>>> h.update(b"Nobody inspects the spammish repetition")
>>> h.hexdigest()
'031edd7d41651593c5fe5c006fa5752b37fddff7bc4e843aa6af0c950f4b9406'

hashlib.md5([data, ]*, usedforsecurity=True)

hashlib.sha1([data, ]*, usedforsecurity=True)

hashlib.sha224([data, ]*, usedforsecurity=True)

hashlib.sha256([data, ]*, usedforsecurity=True)

hashlib.sha384([data, ]*, usedforsecurity=True)

hashlib.sha512([data, ]*, usedforsecurity=True)

hashlib.sha3_224([data, ]*, usedforsecurity=True)

hashlib.sha3_256([data, ]*, usedforsecurity=True)

hashlib.sha3_384([data, ]*, usedforsecurity=True)

hashlib.sha3_512([data, ]*, usedforsecurity=True)

Construtores nomeados como esses são mais rápidos do que passar um
nome de algoritmo para "new()".


Atributos
=========

O hashlib fornece os seguintes atributos de módulo constantes:

hashlib.algorithms_guaranteed

   Um conjunto contendo os nomes dos algoritmos de hash com suporte
   garantido por este módulo em todas as plataformas. Observe que
   "md5" está nesta lista, apesar de alguns fornecedores originais
   oferecerem uma estranha construção Python "compatível com FIPS" que
   o exclui.

   Novo na versão 3.2.

hashlib.algorithms_available

   Um conjunto contendo os nomes dos algoritmos de hash disponíveis no
   interpretador Python em execução. Esses nomes serão reconhecidos
   quando passados para "new()". "algorithms_guaranteed" sempre será
   um subconjunto. O mesmo algoritmo pode aparecer várias vezes neste
   conjunto com nomes diferentes (graças ao OpenSSL).

   Novo na versão 3.2.


Objetos hash
============

Os seguintes valores são fornecidos como atributos constantes dos
objetos hash retornados pelos construtores:

hash.digest_size

   O tamanho do hash resultante em bytes.

hash.block_size

   O tamanho do bloco interna do algoritmo de hash em bytes.

Um objeto hash tem os seguintes atributos:

hash.name

   O nome canônico deste hash, sempre em minúsculas e sempre adequado
   como parâmetro para "new()" para criar outro hash deste tipo.

   Alterado na versão 3.4: O atributo name está presente no CPython
   desde o seu início, mas até o Python 3.4 não era especificado
   formalmente, então pode não existir em algumas plataformas.

Um objeto hash tem os seguintes métodos:

hash.update(data)

   Atualiza o objeto hash com o *objeto bytes ou similar*. Chamadas
   repetidas são equivalentes a uma única chamada com a concatenação
   de todos os argumentos: "m.update(a); m.update(b)" é equivalente a
   "m.update(a+b)".

   Alterado na versão 3.1: The Python GIL is released to allow other
   threads to run while hash updates on data larger than 2047 bytes is
   taking place when using hash algorithms supplied by OpenSSL.

hash.digest()

   Retorna o resumo dos dados passados ao método "update()" até o
   momento. Este é um objeto bytes de tamanho "digest_size" que pode
   conter bytes em todo o intervalo de 0 a 255.

hash.hexdigest()

   Similar a "digest()", exceto que o resumo é retornado como um
   objeto string de comprimento duplo, contendo apenas dígitos
   hexadecimais. Isso pode ser usado para trocar o valor com segurança
   em e-mails ou outros ambientes não binários.

hash.copy()

   Retorna uma cópia ("clone") do objeto hash. Isso pode ser usado
   para calcular com eficiência os resumos de dados que compartilham
   uma substring inicial comum.


Resumos de comprimento variável de SHAKE
========================================

hashlib.shake_128([data, ]*, usedforsecurity=True)

hashlib.shake_256([data, ]*, usedforsecurity=True)

Os algoritmos "shake_128()" e "shake_256()" fornecem resumos de
comprimento variável com length_in_bits//2 de até 128 ou 256 bits de
segurança. Portanto, seus métodos de resumo exigem um comprimento. O
comprimento máximo não é limitado pelo algoritmo SHAKE.

shake.digest(length)

   Retorna o resumo dos dados passados ao método "update()" até o
   momento. Este é um objeto bytes de tamanho *length* que pode conter
   bytes em todo o intervalo de 0 a 255.

shake.hexdigest(length)

   Similar a "digest()", exceto que o resumo é retornado como um
   objeto string de comprimento duplo, contendo apenas dígitos
   hexadecimais. Isso pode ser usado para trocar o valor em e-mails ou
   outros ambientes não binários.

Exemplo de uso:

>>> h = hashlib.shake_256(b'Nobody inspects the spammish repetition')
>>> h.hexdigest(20)
'44709d6fcb83d92a76dcb0b668c98e1b1d3dafe7'


Hash de arquivo
===============

O módulo hashlib fornece uma função auxiliar para hash eficiente de um
objeto arquivo ou similar.

hashlib.file_digest(fileobj, digest, /)

   Retorna um objeto resumo que foi atualizado com o conteúdo do
   objeto arquivo.

   *fileobj* must be a file-like object opened for reading in binary
   mode. It accepts file objects from  builtin "open()", "BytesIO"
   instances, SocketIO objects from "socket.socket.makefile()", and
   similar. The function may bypass Python's I/O and use the file
   descriptor from "fileno()" directly. *fileobj* must be assumed to
   be in an unknown state after this function returns or raises. It is
   up to the caller to close *fileobj*.

   *digest* deve ser um nome de algoritmo de hash como *str*, um
   construtor de hash ou um chamável que retorna um objeto de hash.

   Exemplo:

   >>> import io, hashlib, hmac
   >>> with open(hashlib.__file__, "rb") as f:
   ...     digest = hashlib.file_digest(f, "sha256")
   ...
   >>> digest.hexdigest()  
   '...'

   >>> buf = io.BytesIO(b"somedata")
   >>> mac1 = hmac.HMAC(b"key", digestmod=hashlib.sha512)
   >>> digest = hashlib.file_digest(buf, lambda: mac1)

   >>> digest is mac1
   True
   >>> mac2 = hmac.HMAC(b"key", b"somedata", digestmod=hashlib.sha512)
   >>> mac1.digest() == mac2.digest()
   True

   Novo na versão 3.11.


Derivação de chave
==================

Algoritmos de alongamento de chave e derivação de chave são projetados
para criar hashes de senhas seguros. Algoritmos ingênuos como
"sha1(password)" não são resistentes a ataques de força bruta. Uma boa
função de hashing de senhas deve ser ajustável, lenta e incluir um
salt.

hashlib.pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None)

   A função fornece a função 2 de derivação de chave baseada em senha
   PKCS#5. Ela usa HMAC como função pseudoaleatória.

   A string *hash_name* é o nome desejado do algoritmo de resumo de
   hash para HMAC, por exemplo, 'sha1' ou 'sha256'. *password* e
   *salt* são interpretados como buffers de bytes. Aplicações e
   bibliotecas devem limitar *password* a um comprimento razoável (por
   exemplo, 1024). *salt* deve ter cerca de 16 bytes ou mais de uma
   fonte adequada, por exemplo, "os.urandom()".

   O número de *iterations* deve ser escolhido com base no algoritmo
   de hash e no poder computacional. A partir de 2022, centenas de
   milhares de iterações do SHA-256 são sugeridas. Para entender por
   que e como escolher o que é melhor para sua aplicação, leia o
   *Appendix A.2.2* do NIST-SP-800-132. As respostas à pergunta sobre
   iterações de pbkdf2 no StackExchange explicam em detalhes.

   *dklen* is the length of the derived key. If *dklen* is "None" then
   the digest size of the hash algorithm *hash_name* is used, e.g. 64
   for SHA-512.

   >>> from hashlib import pbkdf2_hmac
   >>> our_app_iters = 500_000  # Application specific, read above.
   >>> dk = pbkdf2_hmac('sha256', b'password', b'bad salt'*2, our_app_iters)
   >>> dk.hex()
   '15530bba69924174860db778f2c6f8104d3aaf9d26241840c8c4a641c8d000a9'

   Novo na versão 3.4.

   Nota:

     A fast implementation of *pbkdf2_hmac* is available with OpenSSL.
     The Python implementation uses an inline version of "hmac". It is
     about three times slower and doesn't release the GIL.

   Obsoleto desde a versão 3.10: Slow Python implementation of
   *pbkdf2_hmac* is deprecated. In the future the function will only
   be available when Python is compiled with OpenSSL.

hashlib.scrypt(password, *, salt, n, r, p, maxmem=0, dklen=64)

   A função fornece a função de derivação de chave baseada em senha
   scrypt, conforme definido em **RFC 7914**.

   *password* e *salt* devem ser *objetos bytes ou similares*.
   Aplicações e bibliotecas devem limitar *password* a um tamanho
   razoável (por exemplo, 1024). *salt* deve ter cerca de 16 bytes ou
   mais de uma fonte adequada, por exemplo, "os.urandom()".

   *n* is the CPU/Memory cost factor, *r* the block size, *p*
   parallelization factor and *maxmem* limits memory (OpenSSL 1.1.0
   defaults to 32 MiB). *dklen* is the length of the derived key.

   Novo na versão 3.6.


BLAKE2
======

BLAKE2 é uma função hash criptográfica definida em **RFC 7693** que
vem em dois sabores:

* **BLAKE2b**, otimizado para plataformas de 64 bits e produz resumos
  de qualquer tamanho entre 1 e 64 bytes,

* **BLAKE2s**, otimizado para plataformas de 8 a 32 bits e produz
  resumos de qualquer tamanho entre 1 e 32 bytes.

BLAKE2 supports **keyed mode** (a faster and simpler replacement for
HMAC), **salted hashing**, **personalization**, and **tree hashing**.

Hash objects from this module follow the API of standard library's
"hashlib" objects.


Creating hash objects
---------------------

New hash objects are created by calling constructor functions:

hashlib.blake2b(data=b'', *, digest_size=64, key=b'', salt=b'', person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, node_depth=0, inner_size=0, last_node=False, usedforsecurity=True)

hashlib.blake2s(data=b'', *, digest_size=32, key=b'', salt=b'', person=b'', fanout=1, depth=1, leaf_size=0, node_offset=0, node_depth=0, inner_size=0, last_node=False, usedforsecurity=True)

These functions return the corresponding hash objects for calculating
BLAKE2b or BLAKE2s. They optionally take these general parameters:

* *data*: initial chunk of data to hash, which must be *bytes-like
  object*.  It can be passed only as positional argument.

* *digest_size*: size of output digest in bytes.

* *key*: key for keyed hashing (up to 64 bytes for BLAKE2b, up to 32
  bytes for BLAKE2s).

* *salt*: salt for randomized hashing (up to 16 bytes for BLAKE2b, up
  to 8 bytes for BLAKE2s).

* *person*: personalization string (up to 16 bytes for BLAKE2b, up to
  8 bytes for BLAKE2s).

The following table shows limits for general parameters (in bytes):

+---------+-------------+----------+-----------+-------------+
| Hash    | digest_size | len(key) | len(salt) | len(person) |
|=========|=============|==========|===========|=============|
| BLAKE2b | 64          | 64       | 16        | 16          |
+---------+-------------+----------+-----------+-------------+
| BLAKE2s | 32          | 32       | 8         | 8           |
+---------+-------------+----------+-----------+-------------+

Nota:

  BLAKE2 specification defines constant lengths for salt and
  personalization parameters, however, for convenience, this
  implementation accepts byte strings of any size up to the specified
  length. If the length of the parameter is less than specified, it is
  padded with zeros, thus, for example, "b'salt'" and "b'salt\x00'" is
  the same value. (This is not the case for *key*.)

These sizes are available as module constants described below.

Constructor functions also accept the following tree hashing
parameters:

* *fanout*: fanout (0 to 255, 0 if unlimited, 1 in sequential mode).

* *depth*: maximal depth of tree (1 to 255, 255 if unlimited, 1 in
  sequential mode).

* *leaf_size*: maximal byte length of leaf (0 to "2**32-1", 0 if
  unlimited or in sequential mode).

* *node_offset*: node offset (0 to "2**64-1" for BLAKE2b, 0 to
  "2**48-1" for BLAKE2s, 0 for the first, leftmost, leaf, or in
  sequential mode).

* *node_depth*: node depth (0 to 255, 0 for leaves, or in sequential
  mode).

* *inner_size*: inner digest size (0 to 64 for BLAKE2b, 0 to 32 for
  BLAKE2s, 0 in sequential mode).

* *last_node*: boolean indicating whether the processed node is the
  last one ("False" for sequential mode).

   [imagem: Explanation of tree mode parameters.][imagem]

See section 2.10 in BLAKE2 specification for comprehensive review of
tree hashing.


Constantes
----------

blake2b.SALT_SIZE

blake2s.SALT_SIZE

Salt length (maximum length accepted by constructors).

blake2b.PERSON_SIZE

blake2s.PERSON_SIZE

Personalization string length (maximum length accepted by
constructors).

blake2b.MAX_KEY_SIZE

blake2s.MAX_KEY_SIZE

Maximum key size.

blake2b.MAX_DIGEST_SIZE

blake2s.MAX_DIGEST_SIZE

Maximum digest size that the hash function can output.


Exemplos
--------


Simple hashing
~~~~~~~~~~~~~~

To calculate hash of some data, you should first construct a hash
object by calling the appropriate constructor function ("blake2b()" or
"blake2s()"), then update it with the data by calling "update()" on
the object, and, finally, get the digest out of the object by calling
"digest()" (or "hexdigest()" for hex-encoded string).

>>> from hashlib import blake2b
>>> h = blake2b()
>>> h.update(b'Hello world')
>>> h.hexdigest()
'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'

As a shortcut, you can pass the first chunk of data to update directly
to the constructor as the positional argument:

>>> from hashlib import blake2b
>>> blake2b(b'Hello world').hexdigest()
'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'

You can call "hash.update()" as many times as you need to iteratively
update the hash:

>>> from hashlib import blake2b
>>> items = [b'Hello', b' ', b'world']
>>> h = blake2b()
>>> for item in items:
...     h.update(item)
>>> h.hexdigest()
'6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'


Using different digest sizes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

BLAKE2 has configurable size of digests up to 64 bytes for BLAKE2b and
up to 32 bytes for BLAKE2s. For example, to replace SHA-1 with BLAKE2b
without changing the size of output, we can tell BLAKE2b to produce
20-byte digests:

>>> from hashlib import blake2b
>>> h = blake2b(digest_size=20)
>>> h.update(b'Replacing SHA1 with the more secure function')
>>> h.hexdigest()
'd24f26cf8de66472d58d4e1b1774b4c9158b1f4c'
>>> h.digest_size
20
>>> len(h.digest())
20

Hash objects with different digest sizes have completely different
outputs (shorter hashes are *not* prefixes of longer hashes); BLAKE2b
and BLAKE2s produce different outputs even if the output length is the
same:

>>> from hashlib import blake2b, blake2s
>>> blake2b(digest_size=10).hexdigest()
'6fa1d8fcfd719046d762'
>>> blake2b(digest_size=11).hexdigest()
'eb6ec15daf9546254f0809'
>>> blake2s(digest_size=10).hexdigest()
'1bf21a98c78a1c376ae9'
>>> blake2s(digest_size=11).hexdigest()
'567004bf96e4a25773ebf4'


Keyed hashing
~~~~~~~~~~~~~

Keyed hashing can be used for authentication as a faster and simpler
replacement for Hash-based message authentication code (HMAC). BLAKE2
can be securely used in prefix-MAC mode thanks to the
indifferentiability property inherited from BLAKE.

This example shows how to get a (hex-encoded) 128-bit authentication
code for message "b'message data'" with key "b'pseudorandom key'":

   >>> from hashlib import blake2b
   >>> h = blake2b(key=b'pseudorandom key', digest_size=16)
   >>> h.update(b'message data')
   >>> h.hexdigest()
   '3d363ff7401e02026f4a4687d4863ced'

As a practical example, a web application can symmetrically sign
cookies sent to users and later verify them to make sure they weren't
tampered with:

   >>> from hashlib import blake2b
   >>> from hmac import compare_digest
   >>>
   >>> SECRET_KEY = b'pseudorandomly generated server secret key'
   >>> AUTH_SIZE = 16
   >>>
   >>> def sign(cookie):
   ...     h = blake2b(digest_size=AUTH_SIZE, key=SECRET_KEY)
   ...     h.update(cookie)
   ...     return h.hexdigest().encode('utf-8')
   >>>
   >>> def verify(cookie, sig):
   ...     good_sig = sign(cookie)
   ...     return compare_digest(good_sig, sig)
   >>>
   >>> cookie = b'user-alice'
   >>> sig = sign(cookie)
   >>> print("{0},{1}".format(cookie.decode('utf-8'), sig))
   user-alice,b'43b3c982cf697e0c5ab22172d1ca7421'
   >>> verify(cookie, sig)
   True
   >>> verify(b'user-bob', sig)
   False
   >>> verify(cookie, b'0102030405060708090a0b0c0d0e0f00')
   False

Even though there's a native keyed hashing mode, BLAKE2 can, of
course, be used in HMAC construction with "hmac" module:

   >>> import hmac, hashlib
   >>> m = hmac.new(b'secret key', digestmod=hashlib.blake2s)
   >>> m.update(b'message')
   >>> m.hexdigest()
   'e3c8102868d28b5ff85fc35dda07329970d1a01e273c37481326fe0c861c8142'


Randomized hashing
~~~~~~~~~~~~~~~~~~

By setting *salt* parameter users can introduce randomization to the
hash function. Randomized hashing is useful for protecting against
collision attacks on the hash function used in digital signatures.

   Randomized hashing is designed for situations where one party, the
   message preparer, generates all or part of a message to be signed
   by a second party, the message signer. If the message preparer is
   able to find cryptographic hash function collisions (i.e., two
   messages producing the same hash value), then they might prepare
   meaningful versions of the message that would produce the same hash
   value and digital signature, but with different results (e.g.,
   transferring $1,000,000 to an account, rather than $10).
   Cryptographic hash functions have been designed with collision
   resistance as a major goal, but the current concentration on
   attacking cryptographic hash functions may result in a given
   cryptographic hash function providing less collision resistance
   than expected. Randomized hashing offers the signer additional
   protection by reducing the likelihood that a preparer can generate
   two or more messages that ultimately yield the same hash value
   during the digital signature generation process --- even if it is
   practical to find collisions for the hash function. However, the
   use of randomized hashing may reduce the amount of security
   provided by a digital signature when all portions of the message
   are prepared by the signer.

   (NIST SP-800-106 "Randomized Hashing for Digital Signatures")

In BLAKE2 the salt is processed as a one-time input to the hash
function during initialization, rather than as an input to each
compression function.

Aviso:

  *Salted hashing* (or just hashing) with BLAKE2 or any other general-
  purpose cryptographic hash function, such as SHA-256, is not
  suitable for hashing passwords.  See BLAKE2 FAQ for more
  information.

>>> import os
>>> from hashlib import blake2b
>>> msg = b'some message'
>>> # Calculate the first hash with a random salt.
>>> salt1 = os.urandom(blake2b.SALT_SIZE)
>>> h1 = blake2b(salt=salt1)
>>> h1.update(msg)
>>> # Calculate the second hash with a different random salt.
>>> salt2 = os.urandom(blake2b.SALT_SIZE)
>>> h2 = blake2b(salt=salt2)
>>> h2.update(msg)
>>> # The digests are different.
>>> h1.digest() != h2.digest()
True


Personalization
~~~~~~~~~~~~~~~

Sometimes it is useful to force hash function to produce different
digests for the same input for different purposes. Quoting the authors
of the Skein hash function:

   We recommend that all application designers seriously consider
   doing this; we have seen many protocols where a hash that is
   computed in one part of the protocol can be used in an entirely
   different part because two hash computations were done on similar
   or related data, and the attacker can force the application to make
   the hash inputs the same. Personalizing each hash function used in
   the protocol summarily stops this type of attack.

   (The Skein Hash Function Family, p. 21)

BLAKE2 can be personalized by passing bytes to the *person* argument:

   >>> from hashlib import blake2b
   >>> FILES_HASH_PERSON = b'MyApp Files Hash'
   >>> BLOCK_HASH_PERSON = b'MyApp Block Hash'
   >>> h = blake2b(digest_size=32, person=FILES_HASH_PERSON)
   >>> h.update(b'the same content')
   >>> h.hexdigest()
   '20d9cd024d4fb086aae819a1432dd2466de12947831b75c5a30cf2676095d3b4'
   >>> h = blake2b(digest_size=32, person=BLOCK_HASH_PERSON)
   >>> h.update(b'the same content')
   >>> h.hexdigest()
   'cf68fb5761b9c44e7878bfb2c4c9aea52264a80b75005e65619778de59f383a3'

Personalization together with the keyed mode can also be used to
derive different keys from a single one.

>>> from hashlib import blake2s
>>> from base64 import b64decode, b64encode
>>> orig_key = b64decode(b'Rm5EPJai72qcK3RGBpW3vPNfZy5OZothY+kHY6h21KM=')
>>> enc_key = blake2s(key=orig_key, person=b'kEncrypt').digest()
>>> mac_key = blake2s(key=orig_key, person=b'kMAC').digest()
>>> print(b64encode(enc_key).decode('utf-8'))
rbPb15S/Z9t+agffno5wuhB77VbRi6F9Iv2qIxU7WHw=
>>> print(b64encode(mac_key).decode('utf-8'))
G9GtHFE1YluXY1zWPlYk1e/nWfu0WSEb0KRcjhDeP/o=


Modo árvore
~~~~~~~~~~~

Here's an example of hashing a minimal tree with two leaf nodes:

     10
    /  \
   00  01

This example uses 64-byte internal digests, and returns the 32-byte
final digest:

   >>> from hashlib import blake2b
   >>>
   >>> FANOUT = 2
   >>> DEPTH = 2
   >>> LEAF_SIZE = 4096
   >>> INNER_SIZE = 64
   >>>
   >>> buf = bytearray(6000)
   >>>
   >>> # Left leaf
   ... h00 = blake2b(buf[0:LEAF_SIZE], fanout=FANOUT, depth=DEPTH,
   ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
   ...               node_offset=0, node_depth=0, last_node=False)
   >>> # Right leaf
   ... h01 = blake2b(buf[LEAF_SIZE:], fanout=FANOUT, depth=DEPTH,
   ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
   ...               node_offset=1, node_depth=0, last_node=True)
   >>> # Root node
   ... h10 = blake2b(digest_size=32, fanout=FANOUT, depth=DEPTH,
   ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
   ...               node_offset=0, node_depth=1, last_node=True)
   >>> h10.update(h00.digest())
   >>> h10.update(h01.digest())
   >>> h10.hexdigest()
   '3ad2a9b37c6070e374c7a8c508fe20ca86b6ed54e286e93a0318e95e881db5aa'


Credits
-------

BLAKE2 was designed by *Jean-Philippe Aumasson*, *Samuel Neves*,
*Zooko Wilcox-O'Hearn*, and *Christian Winnerlein* based on SHA-3
finalist BLAKE created by *Jean-Philippe Aumasson*, *Luca Henzen*,
*Willi Meier*, and *Raphael C.-W. Phan*.

It uses core algorithm from ChaCha cipher designed by *Daniel J.
Bernstein*.

The stdlib implementation is based on pyblake2 module. It was written
by *Dmitry Chestnykh* based on C implementation written by *Samuel
Neves*. The documentation was copied from pyblake2 and written by
*Dmitry Chestnykh*.

The C code was partly rewritten for Python by *Christian Heimes*.

The following public domain dedication applies for both C hash
function implementation, extension code, and this documentation:

   To the extent possible under law, the author(s) have dedicated all
   copyright and related and neighboring rights to this software to
   the public domain worldwide. This software is distributed without
   any warranty.

   You should have received a copy of the CC0 Public Domain Dedication
   along with this software. If not, see
   https://creativecommons.org/publicdomain/zero/1.0/.

The following people have helped with development or contributed their
changes to the project and the public domain according to the Creative
Commons Public Domain Dedication 1.0 Universal:

* *Alexandr Sokolovskiy*

Ver também:

  Module "hmac"
     A module to generate message authentication codes using hashes.

  Módulo "base64"
     Another way to encode binary hashes for non-binary environments.

  https://nvlpubs.nist.gov/nistpubs/fips/nist.fips.180-4.pdf
     The FIPS 180-4 publication on Secure Hash Algorithms.

  https://csrc.nist.gov/publications/detail/fips/202/final
     The FIPS 202 publication on the SHA-3 Standard.

  https://www.blake2.net/
     Official BLAKE2 website.

  https://en.wikipedia.org/wiki/Cryptographic_hash_function
     Wikipedia article with information on which algorithms have known
     issues and what that means regarding their use.

  https://www.ietf.org/rfc/rfc8018.txt
     PKCS #5: Password-Based Cryptography Specification Version 2.1

  https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication8
  00-132.pdf
     NIST Recommendation for Password-Based Key Derivation.
