PMAC (cryptography)

PMAC, or Parallel Message Authentication Code, is a block cipher-based message authentication code (MAC) algorithm. It provides message integrity and authenticity assurances, meaning it allows one to verify that a message has not been altered in transit and that it originated from the claimed sender.

PMAC leverages the parallelizability of the underlying block cipher, allowing for faster computation compared to sequential MAC algorithms, especially when dealing with large messages. This parallel structure is a key advantage in environments where performance is crucial.

The PMAC algorithm operates by dividing the message into blocks and processing these blocks in parallel using a block cipher, typically AES. It incorporates a sophisticated padding scheme to handle messages that are not an exact multiple of the block size. The final MAC value is derived from the output of these parallel computations, ensuring a strong cryptographic hash value.

Unlike some other MAC algorithms like CBC-MAC, PMAC is provably secure even for variable-length messages. Its security is based on the pseudorandomness of the underlying block cipher. Proper implementation is essential for maintaining this security, as vulnerabilities can arise from incorrect parameter choices or implementation flaws.

PMAC's parallel nature makes it particularly well-suited for hardware implementations and multi-core processors. Its efficiency and security have contributed to its adoption in various cryptographic protocols and applications.