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//! # AEAD helpers //! //! This module contains some wrappers over the AEAD functions in the `ring` //! library. You are advised to not use these low-level functions directly, and //! instead use the functions provided by the [`cryptors`] module //! //! ## Examples //! //! You can encrypt (seal) and decrypt (open) a secret value as follows: //! //! ``` //! use ring::aead; //! use tindercrypt::rand::fill_buf; //! use tindercrypt::aead::{seal_in_place, open_in_place, NONCE_SIZE}; //! //! let algo = &aead::AES_256_GCM; //! let mut nonce = [0u8; NONCE_SIZE]; //! let aad = "My encryption context".as_bytes(); //! let mut key = vec![0u8; algo.key_len()]; //! let data = "The cake is a lie".as_bytes(); //! //! // Create a unique nonce and key. //! fill_buf(&mut nonce); //! fill_buf(&mut key); //! //! // Create a buffer large enough to hold the ciphertext and its tag. //! let mut buf = vec![0; data.len() + algo.tag_len()]; //! buf[..data.len()].copy_from_slice(&data); //! //! // Encrypt (seal) the data buffer in place, thereby ovewriting the //! // plaintext data with the ciphertext, and appending a tag at the end. //! seal_in_place(algo, nonce.clone(), &aad, &key, &mut buf); //! //! // Decrypt (open) the data buffer in place, thereby ovewriting ciphertext //! // with the plaintext (the previous tag will not be removed). //! open_in_place(algo, nonce.clone(), &aad, &key, &mut buf); //! assert_eq!(data, &buf[..data.len()]); //! //! // Ensure that the nonce is never used again. //! drop(nonce); //! //! ``` //! //! [`cryptors`]: ../cryptors/index.html use crate::errors; use ring::aead; /// The size of the nonces that `ring` expects. pub const NONCE_SIZE: usize = 12; /// Check if the provided key has the expected size for the specified /// algorithm. fn _check_key( algo: &'static aead::Algorithm, key: &[u8], ) -> Result<(), errors::Error> { if key.len() != algo.key_len() { return Err(errors::Error::KeySizeMismatch); } Ok(()) } /// Check if the buffer where the output will be stored is large enough to /// contain the tag. fn _check_in_out( algo: &'static aead::Algorithm, in_out: &[u8], ) -> Result<(), errors::Error> { if in_out.len() < algo.tag_len() { return Err(errors::Error::BufferTooSmall); } Ok(()) } /// Seal the contents of a data buffer in place. /// /// This function is a wrapper around the `seal_in_place()` function of the /// `ring` library. Its purpose is to simplify what needs to be passed to the /// underlying function and perform some early checks. The produced ciphertext /// will be stored in the same buffer as the plaintext, effectively erasing it. /// /// This function accepts the following parameters: /// /// * A `ring` AEAD algorithm, e.g., AES-256-GCM, /// * A nonce buffer with a specific size. This nonce must **NEVER** be reused /// for the same key. /// * A reference to some data (additional authenticated data), which won't be /// stored with the ciphertext, but will be used for the encryption and will /// be required for the decryption as well. /// * A reference to a symmetric key, whose size must match the size required /// by the AEAD algorithm. /// * A data buffer that holds the plaintext. The ciphertext will be /// stored in this buffer, so it must be large enough to contain the /// encrypted data and the tag as well. In practice, the user must craft a /// buffer that starts with the plaintext and add an empty space at the end, /// as large as the tag size expected by the algorithm. /// /// This function returns an error if the key/buffer sizes are not the expected /// ones. If the encryption fails, which should never happen in practice, this /// function panics. If the encryption succeeds, it returns the length of the /// plaintext. pub fn seal_in_place( algo: &'static aead::Algorithm, nonce: [u8; NONCE_SIZE], aad: &[u8], key: &[u8], in_out: &mut [u8], ) -> Result<usize, errors::Error> { _check_key(algo, key)?; _check_in_out(algo, in_out)?; let tag_size = algo.tag_len(); let plaintext_size: usize = in_out.len() - tag_size; let plaintext = &mut in_out[..plaintext_size]; let unbound_key = aead::UnboundKey::new(algo, key).unwrap(); let key = aead::LessSafeKey::new(unbound_key); let nonce = aead::Nonce::assume_unique_for_key(nonce); let aad = aead::Aad::from(aad); let res = key.seal_in_place_separate_tag(nonce, aad, plaintext); match res { Ok(t) => { let tag = &mut in_out[plaintext_size..]; tag.copy_from_slice(t.as_ref()); Ok(plaintext_size) } Err(error) => panic!("Error during sealing: {:?}", error), } } /// Open the contents of a sealed data buffer in place. /// /// This function is a wrapper around the `open_in_place()` function of the /// `ring` library. Its purpose is to simplify what needs to be passed to the /// underlying function and perform some early checks. The produced plaintext /// will be stored in the same buffer as the ciphertext, effectively erasing it. /// /// This function accepts the following parameters: /// /// * A `ring` AEAD algorithm, e.g., AES-256-GCM, /// * A nonce buffer with a specific size. /// * A reference to some data (additional authenticated data), which must be /// the same as the ones provided during the sealing process. /// * A reference to a symmetric key, whose size must match the size required /// by the AEAD algorithm. /// * A data buffer that holds the ciphertext and its tag. /// /// This function returns an error if the key/buffer sizes are not the expected /// ones, or if the decryption process fails, e.g., due to a wrong key, nonce, /// etc. If the decryption succeeds, it returns the length of the plaintext. pub fn open_in_place( algo: &'static aead::Algorithm, nonce: [u8; NONCE_SIZE], aad: &[u8], key: &[u8], in_out: &mut [u8], ) -> Result<usize, errors::Error> { _check_key(algo, key)?; _check_in_out(algo, in_out)?; let unbound_key = aead::UnboundKey::new(algo, key).unwrap(); let key = aead::LessSafeKey::new(unbound_key); let nonce = aead::Nonce::assume_unique_for_key(nonce); let aad = aead::Aad::from(aad); let res = key.open_in_place(nonce, aad, in_out); match res { Ok(plaintext) => Ok(plaintext.len()), Err(_) => Err(errors::Error::DecryptionError), } } #[cfg(test)] mod tests { use super::*; const BUF_SIZE: usize = 36; // 36 bytes can contain the tag and data. #[test] fn test_key() { // Check that a key with incorrect size produces an error. // FIXME: Why can't I iterate over array pointers with different size? for algo in &[&aead::AES_256_GCM, &aead::CHACHA20_POLY1305] { for key in &[ vec![], vec![0; 1], vec![0; algo.key_len() - 1], vec![0; algo.key_len() + 1], ] { assert_eq!( _check_key(algo, key), Err(errors::Error::KeySizeMismatch) ); } } } #[test] fn test_in_out() { // Check that a key with incorrect size produces an error. // FIXME: Why can't I iterate over array pointers with different size? for algo in &[&aead::AES_256_GCM, &aead::CHACHA20_POLY1305] { for in_out in &[vec![], vec![0; 1], vec![0; algo.tag_len() - 1]] { assert_eq!( _check_in_out(algo, in_out), Err(errors::Error::BufferTooSmall) ); } } } fn _test_seal_open(algo: &'static aead::Algorithm) { let nonce = [1; 12]; let aad = [2; 9]; let key = vec![3; algo.key_len()]; let mut in_out: [u8; BUF_SIZE]; let mut res: Result<usize, errors::Error>; let plaintext_size = BUF_SIZE - algo.tag_len(); let exp_res = Ok(plaintext_size); let dec_err = Err(errors::Error::DecryptionError); let buf_err = Err(errors::Error::BufferTooSmall); let key_err = Err(errors::Error::KeySizeMismatch); // NOTE: We create a closure to avoid repetitions. let seal = || { let r; let mut _in_out = [4; BUF_SIZE]; r = seal_in_place(algo, nonce.clone(), &aad, &key, &mut _in_out); assert_eq!(r, exp_res); _in_out }; // Check that any type of data corruption makes decryption fail. // // Corrupted nonce. in_out = seal(); let mut bad_nonce = nonce.clone(); bad_nonce[0] = 9; res = open_in_place(algo, bad_nonce.clone(), &aad, &key, &mut in_out); assert_eq!(res, dec_err); // Corrupted additional authenticated data. in_out = seal(); let mut bad_aad = aad.clone(); bad_aad[0] = 9; res = open_in_place(algo, nonce.clone(), &bad_aad, &key, &mut in_out); assert_eq!(res, dec_err); // Corrupted key. in_out = seal(); let mut bad_key = key.clone(); bad_key[0] = 9; res = open_in_place(algo, nonce.clone(), &aad, &bad_key, &mut in_out); assert_eq!(res, dec_err); // Corrupted data. in_out = seal(); let mut bad_in_out = in_out.clone(); bad_in_out[0] = 9; res = open_in_place(algo, nonce.clone(), &aad, &key, &mut bad_in_out); assert_eq!(res, dec_err); // Corrupted tag. in_out = seal(); let mut bad_in_out = in_out.clone(); bad_in_out[in_out.len() - 1] = 9; res = open_in_place(algo, nonce.clone(), &aad, &key, &mut bad_in_out); assert_eq!(res, dec_err); // Incomplete data buffer. res = seal_in_place(algo, nonce.clone(), &aad, &key, &mut []); assert_eq!(res, buf_err); res = open_in_place(algo, nonce.clone(), &aad, &key, &mut []); assert_eq!(res, buf_err); // Incomplete key. res = seal_in_place(algo, nonce.clone(), &aad, &[], &mut in_out); assert_eq!(res, key_err); res = open_in_place(algo, nonce.clone(), &aad, &[], &mut in_out); assert_eq!(res, key_err); // Incorrect encryption algorithm. let algo2: &'static aead::Algorithm; if algo == &aead::AES_256_GCM { algo2 = &aead::CHACHA20_POLY1305; } else { algo2 = &aead::AES_256_GCM; } in_out = seal(); res = open_in_place(algo2, nonce.clone(), &aad, &key, &mut in_out); assert_eq!(res, dec_err); // Correct decryption. in_out = seal(); res = open_in_place(algo, nonce.clone(), &aad, &key, &mut in_out); assert_eq!(res, exp_res); assert_eq!(in_out[..res.unwrap()], vec![4u8; res.unwrap()][..]); } #[test] fn test_seal_open_aes() { _test_seal_open(&aead::AES_256_GCM); } #[test] fn test_seal_open_chacha20() { _test_seal_open(&aead::CHACHA20_POLY1305); } }