Cmac

Mojo struct 🡭

Cmac

@memory_only
struct Cmac[Cipher: BlockCipherEncryptable & Copyable & Deinitable]

CMAC (OMAC1): a cipher-based message authentication code.

CMAC turns any block cipher into a MAC by chaining input blocks through the cipher like CBC-MAC, then masking the final block with one of two subkeys derived from the cipher itself. The subkey mask is what closes CBC-MAC’s classic forgery on variable-length messages.

NIST SP 800-38B: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38b.pdf RFC 4493 (AES-CMAC): https://www.rfc-editor.org/rfc/rfc4493

Aliases

• BLOCK_SIZE = Cipher.BLOCK_SIZE
• TAG_SIZE = Cmac[Cipher].BLOCK_SIZE

Parameters

• Cipher (BlockCipherEncryptable & Copyable & Deinitable)

Implemented traits

AnyType, Copyable, Deinitable, Mac, Movable

Methods

__init__

fn def __init__(out self, var cipher: Cipher)

Initialize CMAC from an already-keyed block cipher.

Args:

• cipher (Cipher)
• self (Self)

Returns:

Self

update

fn def update[o: Origin[mut=o.mut]](mut self, data: Span[UInt8, o])

Absorb more input.

Parameters:

• o (Origin[mut=mut])

Args:

• self (Self)
• data (Span[UInt8, o])

Raises:

finalize

fn def finalize(var self) -> Array[UInt8, Cipher.BLOCK_SIZE]

Consume self and return the TAG_SIZE-byte authentication tag.

Derives K1 (and K2, if the buffered final block turned out to be partial) per NIST SP 800-38B’s subkey generation algorithm, masks the buffered final block with it, and runs one more cipher block to produce the tag.

Args:

• self (Self)

Returns:

Array[UInt8, Cipher.BLOCK_SIZE]

Raises:

reset

fn def reset(mut self)

Reset the accumulator to its initial state while keeping the key.

Args:

• self (Self)