encryption/encryptor/
chacha20poly1305_ietf.rs

1// Copyright (c) 2026 erik <erik@erik.xyz> — https://erik.xyz
2
3//! IETF ChaCha20-Poly1305（RFC 8439，96-bit nonce）；载荷：`v1 | Nonce(12) | Tag(16) | 密文`。
4//!
5//! 与 `sodium-xchacha20` 是同一族原语：密钥、tag、底层 crate 都相同，区别只在
6//! nonce 宽度（12 字节 vs 24 字节）。nonce 每次随机生成，12 字节在单密钥下
7//! 可安全处理海量消息（RFC 8439 §4 的生日界远大于本库的密钥生命周期）。
8
9use chacha20poly1305::aead::AeadInPlace;
10use chacha20poly1305::{ChaCha20Poly1305, KeyInit, Nonce, Tag};
11use rand_core::{OsRng, RngCore};
12
13use crate::contract::{Identified, SymmetricCipher};
14use crate::error::{Error, Result};
15use crate::key::Key;
16
17const LABEL: &str = "ChaCha20-Poly1305-IETF";
18const PREFIX: &[u8] = b"v1";
19const NONCE_LEN: usize = 12;
20const TAG_LEN: usize = 16;
21
22/// IETF ChaCha20-Poly1305 加密器。
23#[derive(Debug)]
24pub struct ChaCha20Poly1305IetfEncryptor {
25    key: Key<32>,
26}
27
28impl ChaCha20Poly1305IetfEncryptor {
29    pub const IDENTIFIER: &'static str = "chacha20-poly1305-ietf";
30
31    pub fn new(key: [u8; 32]) -> Self {
32        Self { key: Key::new(key) }
33    }
34
35    pub fn from_slice(key: &[u8]) -> Result<Self> {
36        Ok(Self {
37            key: Key::from_slice(key, LABEL)?,
38        })
39    }
40
41    /// 显式 nonce 的加密，返回完整载荷（`v1 | Nonce | Tag | 密文`）。
42    ///
43    /// 生产路径只经由 [`SymmetricCipher::encrypt`] 调用（`aad` 恒为 `b""`）；
44    /// `aad` 参数是为了让测试能对 RFC 8439 §2.8.2 的官方向量（带 12 字节 AAD）
45    /// 做逐字节比对，而不必自造期望值。
46    pub(crate) fn encrypt_with_nonce(
47        &self,
48        nonce: &[u8; NONCE_LEN],
49        aad: &[u8],
50        plaintext: &[u8],
51    ) -> Result<Vec<u8>> {
52        // Key<32> 保证长度，new_from_slice 不会失败。
53        let cipher = ChaCha20Poly1305::new_from_slice(self.key.as_bytes())
54            .expect("key length is fixed at 32");
55
56        let mut buffer = plaintext.to_vec();
57        let tag = cipher
58            .encrypt_in_place_detached(Nonce::from_slice(nonce), aad, &mut buffer)
59            .map_err(|_| Error::EncryptionFailed { label: LABEL })?;
60
61        let mut blob = Vec::with_capacity(PREFIX.len() + NONCE_LEN + TAG_LEN + buffer.len());
62        blob.extend_from_slice(PREFIX);
63        blob.extend_from_slice(nonce);
64        blob.extend_from_slice(&tag);
65        blob.extend_from_slice(&buffer);
66        Ok(blob)
67    }
68
69    /// 显式 AAD 的解密（`aad` 的用途同上，生产路径恒为 `b""`）。
70    pub(crate) fn decrypt_with_aad(&self, ciphertext: &[u8], aad: &[u8]) -> Result<Vec<u8>> {
71        let body = ciphertext
72            .strip_prefix(PREFIX)
73            .ok_or(Error::InvalidPrefix { label: LABEL })?;
74        if body.len() < NONCE_LEN + TAG_LEN {
75            return Err(Error::TooShort { label: LABEL });
76        }
77
78        let (nonce, rest) = body.split_at(NONCE_LEN);
79        let (tag, ct) = rest.split_at(TAG_LEN);
80
81        let cipher = ChaCha20Poly1305::new_from_slice(self.key.as_bytes())
82            .expect("key length is fixed at 32");
83        let mut buffer = ct.to_vec();
84        cipher
85            .decrypt_in_place_detached(
86                Nonce::from_slice(nonce),
87                aad,
88                &mut buffer,
89                Tag::from_slice(tag),
90            )
91            .map_err(|_| Error::DecryptionFailed { label: LABEL })?;
92        Ok(buffer)
93    }
94}
95
96impl Identified for ChaCha20Poly1305IetfEncryptor {
97    fn identifier(&self) -> &str {
98        Self::IDENTIFIER
99    }
100}
101
102impl SymmetricCipher for ChaCha20Poly1305IetfEncryptor {
103    fn encrypt(&self, plaintext: &[u8]) -> Result<Vec<u8>> {
104        let mut nonce = [0u8; NONCE_LEN];
105        OsRng.fill_bytes(&mut nonce);
106        self.encrypt_with_nonce(&nonce, b"", plaintext)
107    }
108
109    fn decrypt(&self, ciphertext: &[u8]) -> Result<Vec<u8>> {
110        self.decrypt_with_aad(ciphertext, b"")
111    }
112}
113
114#[cfg(test)]
115mod tests {
116    use super::*;
117    use crate::internal::hex_decode;
118
119    // 官方向量：RFC 8439 §2.8.2（Example and Test Vector for
120    // AEAD_CHACHA20_POLY1305），逐字节誊自 RFC 文本
121    // www.rfc-editor.org/rfc/rfc8439.txt（2026-10 取用）。
122    //
123    // nonce 注意：RFC 把 12 字节 nonce 拆成「IV（8 字节）4041424344454647」与
124    // 「32-bit fixed-common part（sender id=7）07000000」两段分别列出，但实际
125    // nonce 是 fixed-common part 在前 —— RFC 自己的 ChaCha 状态字给出
126    // 00000007 43424140 47464544（§2.8.2 "Setup for generating Poly1305
127    // one-time key"），RustCrypto 的 crate 测试与独立实现复算也一致。
128    // 明文 114 字节、无填充（Poly1305 的 16 字节对齐只在 MAC 输入侧，不进密文）。
129    const KEY: &str = "808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9f";
130    const NONCE: &str = "070000004041424344454647";
131    const AAD: &str = "50515253c0c1c2c3c4c5c6c7";
132    const PLAINTEXT: &str = "Ladies and Gentlemen of the class of '99: If I could offer you only one tip for the future, sunscreen would be it.";
133    const CIPHERTEXT: &str = "d31a8d34648e60db7b86afbc53ef7ec2a4aded51296e08fea9e2b5a736ee62d6\
134                              3dbea45e8ca9671282fafb69da92728b1a71de0a9e060b2905d6a5b67ecd3b\
135                              3692ddbd7f2d778b8c9803aee328091b58fab324e4fad675945585808b4831d7\
136                              bc3ff4def08e4b7a9de576d26586cec64b6116";
137    const TAG: &str = "1ae10b594f09e26a7e902ecbd0600691";
138
139    #[test]
140    fn kat_rfc_8439_2_8_2_is_byte_for_byte() {
141        let nonce: [u8; NONCE_LEN] = hex_decode(NONCE).unwrap().try_into().unwrap();
142        let aad = hex_decode(AAD).unwrap();
143        let ct = hex_decode(CIPHERTEXT).unwrap();
144        let tag = hex_decode(TAG).unwrap();
145        // 先验证「无填充」：官方密文长度 == 官方明文长度。
146        assert_eq!(ct.len(), PLAINTEXT.len());
147
148        let encryptor =
149            ChaCha20Poly1305IetfEncryptor::new(hex_decode(KEY).unwrap().try_into().unwrap());
150
151        let mut expected = PREFIX.to_vec();
152        expected.extend_from_slice(&nonce);
153        expected.extend_from_slice(&tag);
154        expected.extend_from_slice(&ct);
155        assert_eq!(
156            encryptor.encrypt_with_nonce(&nonce, &aad, PLAINTEXT.as_bytes()),
157            Ok(expected)
158        );
159
160        // 反方向：官方密文帧解出官方明文。
161        let blob = encryptor
162            .encrypt_with_nonce(&nonce, &aad, PLAINTEXT.as_bytes())
163            .unwrap();
164        assert_eq!(
165            encryptor.decrypt_with_aad(&blob, &aad).unwrap(),
166            PLAINTEXT.as_bytes()
167        );
168    }
169
170    #[test]
171    fn roundtrip_and_tamper_detection() {
172        let encryptor = ChaCha20Poly1305IetfEncryptor::new([7u8; 32]);
173        let blob = encryptor.encrypt(b"data").unwrap();
174        assert_eq!(blob.len(), 2 + NONCE_LEN + TAG_LEN + 4);
175        assert_eq!(encryptor.decrypt(&blob).unwrap(), b"data");
176
177        let mut tampered = blob.clone();
178        let last = tampered.len() - 1;
179        tampered[last] ^= 0x01;
180        assert_eq!(
181            encryptor.decrypt(&tampered).unwrap_err(),
182            Error::DecryptionFailed { label: LABEL }
183        );
184    }
185
186    #[test]
187    fn every_encrypt_uses_a_fresh_nonce() {
188        let encryptor = ChaCha20Poly1305IetfEncryptor::new([7u8; 32]);
189        let first = encryptor.encrypt(b"same").unwrap();
190        let second = encryptor.encrypt(b"same").unwrap();
191        assert_ne!(first, second);
192        assert_ne!(first[2..2 + NONCE_LEN], second[2..2 + NONCE_LEN]);
193    }
194
195    #[test]
196    fn wrong_key_and_bad_prefix_fail() {
197        let blob = ChaCha20Poly1305IetfEncryptor::new([7u8; 32])
198            .encrypt(b"x")
199            .unwrap();
200        let other = ChaCha20Poly1305IetfEncryptor::new([8u8; 32]);
201        assert_eq!(
202            other.decrypt(&blob).unwrap_err(),
203            Error::DecryptionFailed { label: LABEL }
204        );
205        assert_eq!(
206            other.decrypt(b"v9....").unwrap_err(),
207            Error::InvalidPrefix { label: LABEL }
208        );
209        assert_eq!(
210            other.decrypt(b"v1short").unwrap_err(),
211            Error::TooShort { label: LABEL }
212        );
213    }
214
215    #[test]
216    fn key_length_is_checked() {
217        assert_eq!(
218            ChaCha20Poly1305IetfEncryptor::from_slice(&[0u8; 16]).unwrap_err(),
219            Error::InvalidKeyLength {
220                label: LABEL,
221                expected: 32,
222                got: 16
223            }
224        );
225    }
226}
encryption/encryptor/chacha20poly1305_ietf.rs

encryption/encryptor/
chacha20poly1305_ietf.rs
