Crate mc_oblivious_aes_gcm

WARNING

You should use the aes-gcm crate, not this one. This crate is a patch/fork of the execellent RustCrypto crate to support a very, very niche use-case for MobileCoin, and as such it’s maintenance and security are necessarily going to lag behind that of RustCrypto’s crate.

Original README

AES-GCM: Authenticated Encryption and Associated Data (AEAD) cipher based on AES in Galois/Counter Mode.

Performance Notes

By default this crate will use software implementations of both AES and the POLYVAL universal hash function.

When targeting modern x86/x86_64 CPUs, use the following RUSTFLAGS to take advantage of high performance AES-NI and CLMUL CPU intrinsics:

RUSTFLAGS="-Ctarget-cpu=sandybridge -Ctarget-feature=+aes,+sse2,+sse4.1,+ssse3"

Security Notes

This crate has received one security audit by NCC Group, with no significant findings. We would like to thank MobileCoin for funding the audit.

All implementations contained in the crate are designed to execute in constant time, either by relying on hardware intrinsics (i.e. AES-NI and CLMUL on x86/x86_64), or using a portable implementation which is only constant time on processors which implement constant-time multiplication.

It is not suitable for use on processors with a variable-time multiplication operation (e.g. short circuit on multiply-by-zero / multiply-by-one, such as certain 32-bit PowerPC CPUs and some non-ARM microcontrollers).

Usage

Simple usage (allocating, no associated data):

use mc_oblivious_aes_gcm::{
    aead::{Aead, KeyInit, OsRng},
    Aes256Gcm, Nonce // Or `Aes128Gcm`
};

let key = Aes256Gcm::generate_key(&mut OsRng);
let cipher = Aes256Gcm::new(&key);
let nonce = Nonce::from_slice(b"unique nonce"); // 96-bits; unique per message
let ciphertext = cipher.encrypt(nonce, b"plaintext message".as_ref())?;
let plaintext = cipher.decrypt(nonce, ciphertext.as_ref())?;
assert_eq!(&plaintext, b"plaintext message");

In-place Usage (eliminates alloc requirement)

This crate has an optional alloc feature which can be disabled in e.g. microcontroller environments that don’t have a heap.

The AeadInPlace::encrypt_in_place and AeadInPlace::decrypt_in_place methods accept any type that impls the aead::Buffer trait which contains the plaintext for encryption or ciphertext for decryption.

Note that if you enable the heapless feature of this crate, you will receive an impl of aead::Buffer for heapless::Vec (re-exported from the aead crate as aead::heapless::Vec), which can then be passed as the buffer parameter to the in-place encrypt and decrypt methods:

use mc_oblivious_aes_gcm::{
    aead::{AeadInPlace, KeyInit, OsRng, heapless::Vec},
    Aes256Gcm, Nonce, // Or `Aes128Gcm`
};

let key = Aes256Gcm::generate_key(&mut OsRng);
let cipher = Aes256Gcm::new(&key);
let nonce = Nonce::from_slice(b"unique nonce"); // 96-bits; unique per message

let mut buffer: Vec<u8, 128> = Vec::new(); // Note: buffer needs 16-bytes overhead for auth tag tag
buffer.extend_from_slice(b"plaintext message");

// Encrypt `buffer` in-place, replacing the plaintext contents with ciphertext
cipher.encrypt_in_place(nonce, b"", &mut buffer)?;

// `buffer` now contains the message ciphertext
assert_ne!(&buffer, b"plaintext message");

// Decrypt `buffer` in-place, replacing its ciphertext context with the original plaintext
cipher.decrypt_in_place(nonce, b"", &mut buffer)?;
assert_eq!(&buffer, b"plaintext message");

Re-exports

pub use aead;

pub use aes;

Structs

AesGcm

AES-GCM: generic over an underlying AES implementation and nonce size.

CtDecryptResult

A new-type wrapper around choice with the #[must_use] annotation that Result has. This wraps the value Choice::from(true) when decryption succeeded, and Choice::from(false) otherwise.

Error

Error type.

Constants

A_MAX

Maximum length of associated data.

C_MAX

Maximum length of ciphertext.

P_MAX

Maximum length of plaintext.

Traits

AeadCore

Authenticated Encryption with Associated Data (AEAD) algorithm core trait.

AeadInPlace

In-place stateless AEAD trait.

CtAeadDecrypt

API for Aead in-place decryption which is constant-time with respect to the mac check failing

KeyInit

Types which can be initialized from key.

KeySizeUser

Types which use key for initialization.

Type Aliases

Aes128Gcmaes

AES-GCM with a 128-bit key and 96-bit nonce.

Aes256Gcmaes

AES-GCM with a 256-bit key and 96-bit nonce.

Key

Key used by KeySizeUser implementors.

Nonce

AES-GCM nonces.

Tag

AES-GCM tags.