[ excerpt from developer's www site ]

The Cryptokit library for Objective Caml provides a variety of
cryptographic primitives that can be used to implement cryptographic
protocols in security-sensitive applications. The primitives provided
include:

Symmetric-key cryptography: AES, DES, Triple-DES, ARCfour, in ECB,
CBC, CFB and OFB modes. Public-key cryptography: RSA encryption and
signature; Diffie-Hellman key agreement. Hash functions and MACs:
SHA-1, MD5, and MACs based on AES and DES. Random number generation.
Encodings and compression: base 64, hexadecimal, Zlib compression.

Additional ciphers and hashes can easily be used in conjunction
with the library. In particular, basic mechanisms such as chaining
modes, output buffering, and padding are provided by generic classes
that can easily be composed with user-provided ciphers. More
generally, the library promotes a "Lego"-like style of constructing
and composing transformations over character streams.