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#![warn(clippy::pedantic)] #![warn(clippy::nursery)] #![allow(clippy::doc_markdown)] //! //! This library features implementations of the ARX-KW family of novel [Key Wrap](https://wikipedia.org/wiki/Key_Wrap) constructions. //! //! --- //! //! # Background //! //! ARX-KW was first presented in [this paper](https://ia.cr/2020/059) written by Satō Shinichi and submitted to the IACR Cryptology ePrint Archive in January 2020. As the name //! suggests, these constructions make extensive use of add-rotate-xor algorithms: each of the four //! variants specified involves both the [SipHash-2-4](https://wikipedia.org/wiki/SipHash) pseudorandom function with 128-bit output and //! a stream cipher from the [`ChaCha`](https://en.wikipedia.org/wiki/Salsa20) family of stream ciphers. //! //! ARX-KW is a cipher for deteministic, authenticated encryption which aims to provide strong //! authenticity and confidentiality while minimizing the storage overhead and simplicity of use //! when compared to existing constructions using the ChaCha cipher either which require keeping state for a nonce and //! a block counter or have a substantial storage overhead in order to manage the nonce //! statelessly. //! //! ARX-KW has a static overhead of 128 bits for each of its four variants without the need to keep //! state for the nonce used by ChaCha, making the storage overhead only 50% for a 256-bit key //! //! --- //! //! # Use //! //! ## When //! //! As noted above, the ARX-KW constructions are **Key Wrap** algorithms, designed and intended to //! protect other cryptographic keys using [symmetric encryption](https://wikipedia.org/wiki/Symmetric_encryption). It is important to note that as ARX-KW, like all Key Wrap constructions, //! was designed with the expectation that its input data is highly [entropic](https://wikipedia.org/wiki/Entropic_security), as is the case with secret keys. This is because it is //! a [deterministic encryption](https://wikipedia.org/wiki/Deterministic_encryption) scheme and //! will always yield the same ciphertext output for a given input; if used to encrypt low-entropy //! data (as with general-purpose encryption schemes), it is vulnerable to "leakage", described here: //! //! > Deterministic encryption can leak information to an eavesdropper, who may recognize known ciphertexts. For example, when an adversary learns that a given ciphertext corresponds to some interesting message, they can learn something every time that ciphertext is transmitted. To gain information about the meaning of various ciphertexts, an adversary might perform a statistical analysis of messages transmitted over an encrypted channel, or attempt to correlate ciphertexts with observed actions (e.g., noting that a given ciphertext is always received immediately before a submarine dive). //! //! If used to store secret key material (by nature high entropy), this is not an issue as an attacker gains no information about the key encapsulated within. //! //! ## How //! //! Each public module of this crate contains a struct corresponding to one of the four specified //! ARX-KW-8-2-4 variants: ARX-8-2-4-`E`, ARX-8-2-4-`G`, ARX-8-2-4-`EX`, and ARX-8-2-4-`GX`. If you're not //! sure which to use, `gx::GX` is recommended. The functionality is provided by the `ArxKW` trait, //! so that will need to be in scope to use the `encrypt` and `decrypt` methods. //! //! --- //! //! ### Encrypt a key //! //! ``` //! # extern crate anyhow; //! # use anyhow::Result; //! extern crate hex; //! use hex::FromHex; //! //! use arx_kw::{ //! ArxKW, //! gx::GX //! }; //! //! # fn main() -> Result<(), Box<dyn std::error::Error>> { //!// Encrypt a key using ARX-KW-8-2-4-GX //! //!// The values used here are from the test vectors in the original ARX-KW paper. //! // Inputs //! let k = <[u8; 32]>::from_hex("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f")?; // The key we are using to wrap the plaintext secret key //! let p = <[u8; 32]>::from_hex("deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef")?; // The plaintext secret key we want to store/transport securely //! // Expected outputs //! let c_expected = <[u8; 32]>::from_hex("2f83f391c97f3606ccd5709c6ee15d66cd7e65a2aeb7dc3066636e8f6b0d39c3")?; // The ciphertext which contains the wrapped key. //! let t_expected = <[u8; 16]>::from_hex("016325cf6a3c4b2e3b039675e1ccbc65")?; // The authentication tag //! //! let (ciphertext, authentication_tag) = GX::encrypt(&k, &p)?; //! assert_eq!(ciphertext, c_expected); //! assert_eq!(authentication_tag, t_expected); //! //! // Decrypt the wrapped key //! //! let plaintext = GX::decrypt(&k, &ciphertext, &authentication_tag)?; //! assert_eq!(plaintext, p); //! # Ok(()) //! # } //! ``` //! //! //! //! extern crate chacha; extern crate siphasher; extern crate byteorder; #[macro_use] extern crate arrayref; extern crate thiserror; use thiserror::Error; mod lqb; mod util; mod generate; pub mod e; pub mod g; pub mod ex; pub mod gx; #[derive(Error,Debug)] pub enum InvalidLengthError { #[error("Invalid key length: {0} (expected {1})")] _Fixed(usize,usize), #[error("Invalid authentication tag length: {0} (Maximum: {1}")] UpTo(usize,usize) } #[derive(Error,Debug)] pub enum ArxKwError { #[error("Invalid length: {0}")] InvalidLength(#[from] InvalidLengthError), #[error("Reached end of {0}ChaCha8 stream.")] ChaChaError(String), // Use "X" if it occurs while using an extended stream or "" otherwise #[error("Authentication tag does not match {0:x?} (Expected {1:x?})")] BadTags(AuthTag,AuthTag) } /// The type used as the authentication tag (unencrypted data to be stored alongside encrypted keys) /// This is the same for all variants at time of writing (a single, static 128 bits), making /// for a 50% storage overhead for a 256-bit key like those used for `ChaCha` pub type AuthTag = [u8; 16]; /// Provides encryption and decryption capabilites /// /// The ArxKW trait requires a fixed-length array reference for keys and authentication tags, /// but the ciphertext and plaintext inputs can be slices (their lengths are verified to be valid /// if used with the E and G variants) pub trait ArxKW { /// The type of data which is used as a key for the type that `impl`s this trait. /// Note that this is not the same for all variants of ARX-KW. all of the currently-defined variants use the same-sized keys type Key; /// Encrypts the plaintext using ARX-KW and returns the encrypted ciphertext and an `AuthTag` /// /// The authentication tag can be stored/transported alongside it and is needed (along with the /// key used to encrypt the plaintext) in order to decrypt the wrapped key. /// /// # Errors /// Returns an error if the key or plaintext is /// of invalid length or if the end of the ChaCha cipher is reached unexpectedly. fn encrypt(key: &Self::Key, plaintext: &[u8]) -> Result<(Vec<u8>, AuthTag), ArxKwError>; /// Attempts to decrypt the ciphertext using ARX-KW and returns the decrypted plaintext if /// successful. As ARX-KW is a form of authenticated encryption, the authenticity of the /// decrypted text is verified if the function returns an `Ok` value. /// which can be stored/transported alongside it. /// ///# Errors /// Returns an error if the key or ciphertext is of invalid length or if the end of the ChaCha cipher is reached unexpectedly. fn decrypt(key: &Self::Key, ciphertext: &[u8], authentication_tag: &AuthTag) -> Result<Vec<u8>, ArxKwError>; }