LibTomCrypt is a well documented, public domain open source cryptographic
 toolkit written in C. It supports lots of block ciphers (Blowfish, Twofish,
 AES, XTEA, ...), chaining modes (ECB, CBC, OFB, CFB, CTR, ...), hash functions
 (MD5, SHA-1, SHA-256, RIPE-MD, ...), HMAC mechanisms, pseudo-random number
 generators and public key algorithms. It has several optimizations for the
 i386, x86_64 and ppc32 architectures.