Message Digest no. 5 (MD5) is an algorithm used in authentication protocols that is based on one-way transmission using a hash function and a key. Therefore, no conclusions about the key can be drawn from the result.
According to the procedure, a 128-bithash value; the message digest( MD), is formed from a message of any length and appended to the unencrypted message. The receiver compares the message digest with the value it determined from the information.
The MD5 algorithm is derived from MD4. It is optimized for 32-bit computers, but is not as fast as MD4. The MD5 algorithm is an extension of the MD4 algorithm and provides higher data security. However, it should not be used for cryptographic authentication. MD5 is described in RFC 1321, HMAC-MD5 in RFC 2104. Other message digest algorithms are MD2 for authentication and MD4 for digitalsignature encryption.