A message digest is a piece of data that can be used to verify if the contents of the message are not altered during transit. When a message is sent over a network, the sender computes a message digest by performing a one-way hash function using a secret key known only to the sender and recipient. The recipient also computes the message digest by performing the same one-way hash function using the secret key. If the two message digests are identical, the recipient can be sure that the message has not been modified during transit.

• Hashed Message Authentication Code (HMAC)
• Message Digest algorithm 2 (MD2)
• Message Digest algorithm 5 (MD5)
• Message Digest Cipher 2 (MDC2)
• RACE Integrity Primitives Evaluation Message Digest (RIPEMD)
• Secure Hash Algorithm (SHA)
• Secure Hash Algorithm 1 (SHA1)