# aes-ccm [![Latest version](https://img.shields.io/crates/v/aes-ccm)](https://crates.io/crates/aes-ccm) [![Documentation](https://docs.rs/aes-ccm/badge.svg)](https://docs.rs/aes-ccm) [![License](https://img.shields.io/crates/l/aes-ccm)](https://github.com/martindisch/aes-ccm#license) A pure-Rust, `#![no_std]`, zero-allocation AES-CCM implementation ported from [TinyCrypt] using [RustCrypto's AES] (with support for optionally swapping in hardware-backed implementations). It implements the [`aead::AeadInPlace`] trait, so it can be used effortlessly together with other implementations. ## Overview CCM (for "Counter with CBC-MAC") mode is a NIST approved mode of operation defined in [SP 800-38C]. This implementation accepts: 1. Both non-empty payload and associated data (it encrypts and authenticates the payload and also authenticates the associated data). 2. Non-empty payload and empty associated data (it encrypts and authenticates the payload). 3. Non-empty associated data and empty payload (it degenerates to an authentication mode on the associated data). The implementation accepts payloads of any length between 0 and 2^16 bytes and associated data of any length between 0 and (2^16 - 2^8) bytes. ## Usage ```rust use aes_ccm::{ aead::{consts::U8, Aead, NewAead, Payload}, Aes128Ccm, }; let key = [ 0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF, ]; // `U8` represents the tag size as a `typenum` unsigned (8-bytes here) let ccm = Aes128Ccm::::new(&key.into()); let nonce = [ 0x00, 0x00, 0x00, 0x03, 0x02, 0x01, 0x00, 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, ]; let msg = [ 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, ]; let associated_data = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07]; let ciphertext = ccm .encrypt( &nonce.into(), Payload { aad: &associated_data, msg: &msg, }, ) .unwrap(); let plaintext = ccm .decrypt( &nonce.into(), Payload { aad: &associated_data, msg: &ciphertext, }, ) .unwrap(); assert_eq!(&msg[..], plaintext.as_slice()); ``` ## 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: ```rust use aes_ccm::{ aead::{ consts::{U128, U8}, heapless::Vec, AeadInPlace, NewAead, }, Aes128Ccm, }; let key = [ 0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF, ]; // `U8` represents the tag size as a `typenum` unsigned (8-bytes here) let ccm = Aes128Ccm::::new(&key.into()); let nonce = [ 0x00, 0x00, 0x00, 0x03, 0x02, 0x01, 0x00, 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, ]; let associated_data = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07]; let plaintext = [ 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, ]; let mut buffer: Vec = Vec::new(); buffer.extend_from_slice(&plaintext).unwrap(); // Encrypt `buffer` in-place, replacing the plaintext contents with // ciphertext ccm.encrypt_in_place(&nonce.into(), &associated_data, &mut buffer) .unwrap(); // `buffer` now contains the message ciphertext assert_ne!(&buffer, &plaintext); // Decrypt `buffer` in-place, replacing its ciphertext contents with the // original plaintext ccm.decrypt_in_place(&nonce.into(), &associated_data, &mut buffer) .unwrap(); assert_eq!(&buffer, &plaintext); ``` ## Security I'm not a cryptographer and this hasn't been audited in any way. It is however a careful port of [TinyCrypt], so if it's sound, then this *should* be too. The MAC length parameter is an important parameter to estimate the security against collision attacks (that aim at finding different messages that produce the same authentication tag). The implementation accepts any even integer between 4 and 16, as suggested in [SP 800-38C]. [RFC 3610], which also specifies CCM, presents a few relevant security suggestions, such as: * It is recommended that most applications use a MAC length greater than 8. * The usage of the same nonce for two different messages which are encrypted with the same key destroys the security of CCM mode. [TinyCrypt]: https://github.com/intel/tinycrypt [RustCrypto's AES]: https://github.com/RustCrypto/block-ciphers [`aead::AeadInPlace`]: https://docs.rs/aead/latest/aead/trait.AeadInPlace.html [SP 800-38C]: https://csrc.nist.gov/publications/detail/sp/800-38c/final [RFC 3610]: https://tools.ietf.org/html/rfc3610 [`AeadInPlace::encrypt_in_place`]: https://docs.rs/aead/latest/aead/trait.AeadInPlace.html#method.encrypt_in_place [`AeadInPlace::decrypt_in_place`]: https://docs.rs/aead/latest/aead/trait.AeadInPlace.html#method.decrypt_in_place [`aead::Buffer`]: https://docs.rs/aead/latest/aead/trait.Buffer.html [`heapless::Vec`]: https://docs.rs/heapless/latest/heapless/struct.Vec.html [`aead`]: https://docs.rs/aead/latest/aead/index.html ## License Licensed under either of * [Apache License, Version 2.0](LICENSE-APACHE) * [MIT license](LICENSE-MIT) at your option. This is a port of TinyCrypt's CCM mode, its license file is in [LICENSE-3RD-PARTY](LICENSE-3RD-PARTY). ### Contribution Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.