Hashing routines
================

Libucw contains two cryptographic hash algorithms: MD5 (RFC 1321) and SHA1 (RFC
3174). A SHA1-HMAC (RFC 2104) message authentication is available.

There are non-cryptographic hashes as well.

<<crypto,Cryptographic ones>>:

- <<md5,MD5>>
- <<sha1,SHA1>>
- <<sha1:sha1_hmac(),SHA1_HMAC>>
- <<usage,Common usage>>

<<nocrypto,Non-cryptographic ones>>:

- <<strhash,String & block hashes>>
- <<inthash,Integer hashes>>

[[crypto]]
Cryptographic hashes
--------------------

[[md5]]
MD5
~~~
!!ucw/md5.h

[[sha1]]
SHA1
~~~~
!!ucw/sha1.h

[[usage]]
Common usage
~~~~~~~~~~~~

There are two ways you can use the hashing routines.

- Single-shot interface. If you have an in-memory buffer of the whole
  message you want to hash, you can use this.

  char *message = "Hello world";
  byte output[MD5_SIZE];
  md5_hash_buffer(output, message, strlen(message));

- Multi-shot interface. If you have the message scattered in many
  buffers or you get it by parts, you do not need to concatenate the
  parts together.

  byte buffer[MAX_BUFFER];
  uns buffer_len;
  md5_context c;
  md5_init(&c);
  while(buffer_len = get_chunk(buffer, MAX_BUFFER)) {
    md5_update(&c, buffer, buffer_len);
  }
  byte output[MD5_SIZE];
  memcpy(output, md5_final(&c), MD5_SIZE);

SHA1 has the same interface, so the same two ways apply.

See also <<string:mem_to_hex()>>.

[[nocrypto]]
Non-cryptographic hashes
------------------------

All these functions expect to be moduled by the size of a hash table.
The size should be a prime number (it gives better distribution).

!!ucw/hashfunc.h