Struct Mac 

pub struct Mac { /* private fields */ }

Stateful MAC context.

See the module-level documentation for the cycle of life and the buffer ownership model.

Implementations

impl Mac

pub fn new(algo: Algorithm) -> Self

Create a new MAC context for the given algorithm. The actual key (and nonce / customization string for GMAC / KMAC) is loaded later by Self::init, Self::init_kmac or Self::init_with_nonce.

pub fn init(&mut self, key: &[u8]) -> Result<(), Error>

Initialize the MAC with a key. This is the right entry point for HMAC, CMAC and KMAC (with an empty customization string). For GMAC, use Self::init_with_nonce instead.

HMAC accepts arbitrary key lengths per RFC 2104 (the key is hashed if it exceeds the hash block size and zero-padded otherwise). CMAC requires the exact key length for the chosen cipher. KMAC accepts arbitrary key lengths.

Errors

• Error::InvalidKeyLen for CMAC if the length is wrong.
• Error::WrongInitVariant if called on GMAC.

pub fn init_kmac(&mut self, key: &[u8], custom: &[u8]) -> Result<(), Error>

Initialize KMAC with a key and a customization string.

Errors

Error::WrongInitVariant if called on a non-KMAC algorithm.

pub fn init_with_nonce(&mut self, key: &[u8], nonce: &[u8]) -> Result<(), Error>

Initialize GMAC with a key and a 12-byte nonce. The nonce must be unique per message under a given key (reusing it breaks GMAC catastrophically).

Errors

• Error::WrongInitVariant if called on a non-GMAC algorithm.
• Error::InvalidKeyLen if the key length does not match.
• Error::InvalidNonceLen if the nonce is not 12 bytes.

pub const fn tag_len(&self) -> usize

Tag length in bytes for this MAC algorithm.

pub fn update(&mut self, data: &[u8]) -> Result<(), Error>

Feed data into the MAC. May be called any number of times between init and sign / verify. Empty slices are allowed.

pub fn sign(&mut self, out: &mut [u8]) -> Result<usize, Error>

Finalize the MAC and write the tag into out. Returns the number of bytes written, which is always Self::tag_len. After this call the context is in the finalized state and must be re-initialized before further use.

Errors

• Error::NotInitialized / Error::AlreadyFinalized.
• Error::OutputBufferTooSmall if out.len() < tag_len().

pub fn verify(&mut self, expected_tag: &[u8]) -> Result<(), Error>

Finalize and verify the tag against expected_tag in constant time. Supports tag truncation: expected_tag.len() may be less than or equal to tag_len(). Comparison is XOR-accumulate-then-test, with no early exit.

Errors

• Error::NotInitialized / Error::AlreadyFinalized.
• Error::VerificationFailed if the tag does not match (or expected_tag.len() == 0 or > tag_len()).

pub fn sign_to_vec(&mut self) -> Result<Vec<u8>, Error>

Allocating helper around Self::sign.