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//! AES-GCM: [Authenticated Encryption and Associated Data (AEAD)][1] cipher //! based on AES in [Galois/Counter Mode][2]. //! //! ## 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: //! //! ```text //! RUSTFLAGS="-Ctarget-cpu=sandybridge -Ctarget-feature=+aes,+sse2,+sse4.1,+ssse3" //! ``` //! //! ## Security Notes //! //! This crate has received one [security audit by NCC Group][3], with no significant //! findings. We would like to thank [MobileCoin][4] 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 aes_gcm::Aes256Gcm; // Or `Aes128Gcm` //! use aead::{Aead, NewAead, generic_array::GenericArray}; //! //! let key = GenericArray::clone_from_slice(b"an example very very secret key."); //! let aead = Aes256Gcm::new(key); //! //! let nonce = GenericArray::from_slice(b"unique nonce"); // 96-bits; unique per message //! let ciphertext = aead.encrypt(nonce, b"plaintext message".as_ref()).expect("encryption failure!"); //! let plaintext = aead.decrypt(nonce, ciphertext.as_ref()).expect("decryption failure!"); //! 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 [`Aead::encrypt_in_place`][5] and [`Aead::decrypt_in_place`][6] //! methods accept any type that impls the [`aead::Buffer`][7] 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`][8] //! (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 aes_gcm::Aes256Gcm; // Or `Aes128Gcm` //! use aead::{Aead, NewAead}; //! use aead::generic_array::{GenericArray, typenum::U128}; //! use aead::heapless::Vec; //! //! let key = GenericArray::clone_from_slice(b"an example very very secret key."); //! let aead = Aes256Gcm::new(key); //! //! let nonce = GenericArray::from_slice(b"unique nonce"); // 96-bits; unique per message //! //! let mut buffer: Vec<u8, U128> = Vec::new(); //! buffer.extend_from_slice(b"plaintext message"); //! //! // Encrypt `buffer` in-place, replacing the plaintext contents with ciphertext //! aead.encrypt_in_place(nonce, b"", &mut buffer).expect("encryption failure!"); //! //! // `buffer` now contains the message ciphertext //! assert_ne!(&buffer, b"plaintext message"); //! //! // Decrypt `buffer` in-place, replacing its ciphertext context with the original plaintext //! aead.decrypt_in_place(nonce, b"", &mut buffer).expect("decryption failure!"); //! assert_eq!(&buffer, b"plaintext message"); //! ``` //! //! [1]: https://en.wikipedia.org/wiki/Authenticated_encryption //! [2]: https://en.wikipedia.org/wiki/Galois/Counter_Mode //! [3]: https://research.nccgroup.com/2020/02/26/public-report-rustcrypto-aes-gcm-and-chacha20poly1305-implementation-review/ //! [4]: https://www.mobilecoin.com/ //! [5]: https://docs.rs/aead/latest/aead/trait.Aead.html#method.encrypt_in_place //! [6]: https://docs.rs/aead/latest/aead/trait.Aead.html#method.decrypt_in_place //! [7]: https://docs.rs/aead/latest/aead/trait.Buffer.html //! [8]: https://docs.rs/heapless/latest/heapless/struct.Vec.html #![no_std] #![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")] #![warn(missing_docs, rust_2018_idioms)] mod ctr32; pub use aead; use self::ctr32::Ctr32; use aead::generic_array::{ typenum::{U0, U12, U16, U8}, GenericArray, }; use aead::{Aead, Error, NewAead}; use aes::{block_cipher_trait::BlockCipher, Aes128, Aes256}; use ghash::{universal_hash::UniversalHash, GHash}; use zeroize::Zeroize; /// Maximum length of associated data pub const A_MAX: u64 = 1 << 36; /// Maximum length of plaintext pub const P_MAX: u64 = 1 << 36; /// Maximum length of ciphertext pub const C_MAX: u64 = (1 << 36) + 16; /// AES-GCM tags pub type Tag = GenericArray<u8, U16>; /// AES-GCM with a 128-bit key pub type Aes128Gcm = AesGcm<Aes128>; /// AES-GCM with a 256-bit key pub type Aes256Gcm = AesGcm<Aes256>; /// AES-GCM #[derive(Clone)] pub struct AesGcm<C: BlockCipher<BlockSize = U16, ParBlocks = U8>> { /// Encryption cipher cipher: C, /// GHASH authenticator ghash: GHash, } impl<C> NewAead for AesGcm<C> where C: BlockCipher<BlockSize = U16, ParBlocks = U8>, { type KeySize = C::KeySize; fn new(mut key: GenericArray<u8, C::KeySize>) -> Self { let cipher = C::new(&key); key.as_mut_slice().zeroize(); let mut ghash_key = GenericArray::default(); cipher.encrypt_block(&mut ghash_key); let ghash = GHash::new(&ghash_key); ghash_key.zeroize(); Self { cipher, ghash } } } impl<C> Aead for AesGcm<C> where C: BlockCipher<BlockSize = U16, ParBlocks = U8>, { type NonceSize = U12; type TagSize = U16; type CiphertextOverhead = U0; fn encrypt_in_place_detached( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut [u8], ) -> Result<Tag, Error> { if buffer.len() as u64 > P_MAX || associated_data.len() as u64 > A_MAX { return Err(Error); } // TODO(tarcieri): interleave encryption with GHASH // See: <https://github.com/RustCrypto/AEADs/issues/74> let mut ctr = Ctr32::new(&self.cipher, nonce); ctr.seek(1); ctr.apply_keystream(buffer); let mut tag = compute_tag(&mut self.ghash.clone(), associated_data, buffer); ctr.seek(0); ctr.apply_keystream(tag.as_mut_slice()); Ok(tag) } fn decrypt_in_place_detached( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut [u8], tag: &Tag, ) -> Result<(), Error> { if buffer.len() as u64 > C_MAX || associated_data.len() as u64 > A_MAX { return Err(Error); } // TODO(tarcieri): interleave encryption with GHASH // See: <https://github.com/RustCrypto/AEADs/issues/74> let mut expected_tag = compute_tag(&mut self.ghash.clone(), associated_data, buffer); let mut ctr = Ctr32::new(&self.cipher, nonce); ctr.apply_keystream(expected_tag.as_mut_slice()); use subtle::ConstantTimeEq; if expected_tag.ct_eq(&tag).unwrap_u8() == 1 { ctr.apply_keystream(buffer); Ok(()) } else { Err(Error) } } } /// Authenticate the given plaintext and associated data using GHASH fn compute_tag(ghash: &mut GHash, associated_data: &[u8], buffer: &[u8]) -> Tag { ghash.update_padded(associated_data); ghash.update_padded(buffer); let associated_data_bits = (associated_data.len() as u64) * 8; let buffer_bits = (buffer.len() as u64) * 8; let mut block = GenericArray::default(); block[..8].copy_from_slice(&associated_data_bits.to_be_bytes()); block[8..].copy_from_slice(&buffer_bits.to_be_bytes()); ghash.update_block(&block); ghash.result_reset().into_bytes() }