15. Cryptographic Services
**************************

The modules described in this chapter implement various algorithms of
a cryptographic nature.  They are available at the discretion of the
installation. On Unix systems, the "crypt" module may also be
available. Here's an overview:

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

  * 15.1.1. Hash algorithms

  * 15.1.2. SHAKE variable length digests

  * 15.1.3. Key derivation

  * 15.1.4. BLAKE2

    * 15.1.4.1. Creating hash objects

    * 15.1.4.2. Constants

    * 15.1.4.3. 示例

      * 15.1.4.3.1. Simple hashing

      * 15.1.4.3.2. Using different digest sizes

      * 15.1.4.3.3. Keyed hashing

      * 15.1.4.3.4. Randomized hashing

      * 15.1.4.3.5. Personalization

      * 15.1.4.3.6. Tree mode

    * 15.1.4.4. Credits

* 15.2. "hmac" --- Keyed-Hashing for Message Authentication

* 15.3. "secrets" --- Generate secure random numbers for managing
  secrets

  * 15.3.1. Random numbers

  * 15.3.2. Generating tokens

    * 15.3.2.1. How many bytes should tokens use?

  * 15.3.3. Other functions

  * 15.3.4. Recipes and best practices
