This README is the one indexed from the repository at its latest ref, not from the tag for this version.

Crystal Lang CMAC

Crystal implementation of the Cipher-based Message Authentication Code (CMAC) as defined in RFC4493, RFC4494, and RFC4615. Message authentication codes provide integrity protection of data given that two parties share a secret key.

key = Random.new.random_bytes(16)
message = "attack at dawn"
cmac = CMAC.new(key)
cmac.sign(message)
 => Bytes[246, 184, 193, 76, 93, 115, 191, 26, 135, 60, 164, 161, 90, 224, 102, 170]

Once you've obtained the signature (also called a tag) of a message you can use CMAC to verify it as well.

tag = Bytes[246, 184, 193, 76, 93, 115, 191, 26, 135, 60, 164, 161, 90, 224, 102, 170]
cmac.valid_message?(tag, message)
 => true
cmac.valid_message?(tag, "attack at dusk")
 => false

CMAC can also be used with a variable length input key as described in RFC4615.

key = "setec astronomy"
message = "attack at dawn"
cmac = CMAC.new(key)
cmac.sign(message)
 => Bytes[92, 17, 144, 230, 145, 178, 196, 130, 96, 144, 166, 236, 58, 14, 28, 243]