Struct Gcm 

pub struct Gcm<C> { /* private fields */ }

Galois/Counter Mode (GCM) with a full 128-bit authentication tag.

Per NIST SP 800-38D, this implementation enforces a per-call payload limit of (2^32 - 2) counter blocks (68_719_476_704 bytes) so the 32-bit counter field cannot wrap.

Callers must still ensure nonce uniqueness per key; this API is stateless and cannot enforce global (key, nonce) uniqueness.

Examples

use cryptography::{Aes256, Gcm};

let key = [0x11u8; 32];
let nonce = [0x22u8; 12];
let aad = b"hdr";
let mut ciphertext = *b"payload";

let aead = Gcm::new(Aes256::new(&key));
let tag = aead.encrypt(&nonce, aad, &mut ciphertext);

let mut recovered = ciphertext;
assert!(aead.decrypt(&nonce, aad, &mut recovered, &tag));
assert_eq!(recovered, *b"payload");

Implementations

impl<C> Gcm<C>

pub fn new(cipher: C) -> Self

Wrap a 128-bit block cipher in SP 800-38D GCM mode.

pub fn cipher(&self) -> &C

Borrow the wrapped block cipher.

impl<C: BlockCipher> Gcm<C>

pub fn compute_tag( &self, nonce: &[u8], aad: &[u8], ciphertext: &[u8], ) -> [u8; 16]

Compute the GCM authentication tag over aad and ciphertext.

Panics if ciphertext.len() exceeds the SP 800-38D per-call bound of 68_719_476_704 bytes.

pub fn encrypt(&self, nonce: &[u8], aad: &[u8], data: &mut [u8]) -> [u8; 16]

Encrypt in place and return the 128-bit authentication tag.

Panics if data.len() exceeds the SP 800-38D per-call bound of 68_719_476_704 bytes.

pub fn decrypt( &self, nonce: &[u8], aad: &[u8], data: &mut [u8], tag: &[u8], ) -> bool

Verify the tag and, if valid, decrypt in place.

Returns false and leaves data unchanged if tag verification fails.

Panics if data.len() exceeds the SP 800-38D per-call bound of 68_719_476_704 bytes.

Trait Implementations

impl<C: BlockCipher> Aead for Gcm<C>

type Tag = [u8; 16]

Detached authentication tag type.

fn encrypt_in_place( &self, nonce: &[u8], aad: &[u8], data: &mut [u8], ) -> Self::Tag

Encrypt data in place and return its authentication tag.

fn decrypt_in_place( &self, nonce: &[u8], aad: &[u8], data: &mut [u8], tag: &Self::Tag, ) -> bool

Decrypt data in place after authenticating tag.

fn encrypt( &self, nonce: &[u8], aad: &[u8], plaintext: &[u8], ) -> (Vec<u8>, Self::Tag)

Encrypt plaintext and return (ciphertext, tag).

fn decrypt( &self, nonce: &[u8], aad: &[u8], ciphertext: &[u8], tag: &Self::Tag, ) -> Option<Vec<u8>>

Decrypt ciphertext and return plaintext on successful authentication.