This gem implements the CMAC keyed hash function as described in RFC 4493. The CMAC function is written as a low-level C extension on top of OpenSSL, for speed and compatibility.

AES-CMAC provides stronger assurance of data integrity than a checksum or an error-detecting code. The verification of a checksum or an error-detecting code detects only accidental modifications of the data, while CMAC is designed to detect intentional, unauthorized modifications of the data, as well as accidental modifications.

AES-CMAC achieves a security goal similar to that of HMAC. Since AES-CMAC is based on a symmetric key block cipher, AES, and HMAC is based on a hash function, such as SHA-1, AES-CMAC is appropriate for information systems in which AES is more readily available than a hash function.

Warning: this package should not be considered cryptographically secure.

gem install cmac-rb

require 'cmac-rb'

digest = CMAC::Digest.new(key)
tag = digest.update(plaintext)

• RFC 4493 - The AES-CMAC algorithm
• NIST SP 800-38B - The CMAC Mode for Authentication

This program is released under the GNU Affero General Public License.