Crate aes

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Pure Rust implementation of the Advanced Encryption Standard (AES, a.k.a. Rijndael).

§⚠️ Security Warning: Hazmat!

This crate implements only the low-level block cipher function, and is intended for use for implementing higher-level constructions only. It is NOT intended for direct use in applications.

USE AT YOUR OWN RISK!

§Supported backends

This crate provides multiple backends including a portable pure Rust backend as well as ones based on CPU intrinsics.

By default, it performs runtime detection of CPU intrinsics and uses them if they are available.

§“soft” portable backend

As a baseline implementation, this crate provides a constant-time pure Rust implementation based on fixslicing, a more advanced form of bitslicing implemented entirely in terms of bitwise arithmetic with no use of any lookup tables or data-dependent branches.

Enabling the aes_compact configuration flag will reduce the code size of this backend at the cost of decreased performance (using a modified form of the fixslicing technique called “semi-fixslicing”).

§ARMv8 intrinsics (Rust 1.61+)

On aarch64 targets including aarch64-apple-darwin (Apple M1) and Linux targets such as aarch64-unknown-linux-gnu and aarch64-unknown-linux-musl, support for using AES intrinsics provided by the ARMv8 Cryptography Extensions is available when using Rust 1.61 or above, and can be enabled using the aes_armv8 configuration flag.

On Linux and macOS, when the aes_armv8 flag is enabled support for AES intrinsics is autodetected at runtime. On other platforms the aes target feature must be enabled via RUSTFLAGS.

§x86/x86_64 intrinsics (AES-NI)

By default this crate uses runtime detection on i686/x86_64 targets in order to determine if AES-NI is available, and if it is not, it will fallback to using a constant-time software implementation.

Passing RUSTFLAGS=-C target-feature=+aes,+ssse3 explicitly at compile-time will override runtime detection and ensure that AES-NI is always used. Programs built in this manner will crash with an illegal instruction on CPUs which do not have AES-NI enabled.

Note: runtime detection is not possible on SGX targets. Please use the afforementioned RUSTFLAGS to leverage AES-NI on these targets.

§Examples

use aes::Aes128;
use aes::cipher::{
    BlockCipher, BlockEncrypt, BlockDecrypt, KeyInit,
    generic_array::GenericArray,
};

let key = GenericArray::from([0u8; 16]);
let mut block = GenericArray::from([42u8; 16]);

// Initialize cipher
let cipher = Aes128::new(&key);

let block_copy = block.clone();

// Encrypt block in-place
cipher.encrypt_block(&mut block);

// And decrypt it back
cipher.decrypt_block(&mut block);
assert_eq!(block, block_copy);

// Implementation supports parallel block processing. Number of blocks
// processed in parallel depends in general on hardware capabilities.
// This is achieved by instruction-level parallelism (ILP) on a single
// CPU core, which is differen from multi-threaded parallelism.
let mut blocks = [block; 100];
cipher.encrypt_blocks(&mut blocks);

for block in blocks.iter_mut() {
    cipher.decrypt_block(block);
    assert_eq!(block, &block_copy);
}

// `decrypt_blocks` also supports parallel block processing.
cipher.decrypt_blocks(&mut blocks);

for block in blocks.iter_mut() {
    cipher.encrypt_block(block);
    assert_eq!(block, &block_copy);
}

For implementation of block cipher modes of operation see block-modes repository.

§Configuration Flags

You can modify crate using the following configuration flags:

  • aes_armv8: enable ARMv8 AES intrinsics (Rust 1.61+).
  • aes_force_soft: force software implementation.
  • aes_compact: reduce code size at the cost of slower performance (affects only software backend).

It can be enabled using RUSTFLAGS environmental variable (e.g. RUSTFLAGS="--cfg aes_compact") or by modifying .cargo/config.

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