Hashing module

The Message Digest (MD) or Hashing module provides one-way hashing functions. Such functions can be used for creating a hash message authentication code (HMAC) when sending a message. Such a HMAC can be used in combination with a private key for authentication, which is a message integrity control.

All hash algorithms can be accessed via the generic MD layer (see `mbedtls_md_setup()`)

The following hashing-algorithms are provided:

- MD2, MD4, MD5 128-bit one-way hash functions by Ron Rivest.
- SHA-1, SHA-256, SHA-384/512 160-bit or more one-way hash functions by NIST and NSA.

This module provides one-way hashing which can be used for authentication.