发布 v0.2.0：新增 BLS 签名与 FPE 格式保留加密
新增功能： - BLS 签名：基于 BN256 配对的最小签名尺寸变体 - BLS 门限签名：Shamir 秘密分享 + Lagrange 插值聚合 - Hash-to-Curve：RFC 9380 兼容，SM3 消息扩展 - FPE 格式保留加密：基于 SM4 的 Feistel 密码 - SM9 Fp 平方根：Tonelli-Shanks 算法 文档更新： - README 添加 BLS/FPE 算法描述 - CHANGELOG 添加 v0.2.0 变更记录 - SECURITY 更新版本支持表
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//! FPE（Format-Preserving Encryption）保留格式加密
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//!
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//! 基于 FNR（Flexible Naor-Reingold）算法，使用 SM4 作为底层密码：
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//! - 支持 1~128 位任意长度的明密文域
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//! - 明密文在同一域内（位数相同）
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//! - 支持 tweak（调整值）参数化加密
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//!
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//! # 使用示例
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//!
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//! ```rust
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//! # #[cfg(feature = "alloc")]
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//! # {
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//! use libsmx::fpe::FpeKey;
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//!
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//! let key = [0u8; 16];
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//! let fpe = FpeKey::new(&key, 32).unwrap(); // 32 位域（如 IPv4 地址）
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//! let tweak = fpe.expand_tweak(b"my-tweak");
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//!
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//! let plaintext: u32 = 192_168_1_100; // 某 IPv4 地址
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//! let mut data = plaintext.to_be_bytes();
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//! let mut block = [0u8; 16];
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//! block[..4].copy_from_slice(&data);
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//!
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//! fpe.encrypt(&tweak, &mut block);
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//! fpe.decrypt(&tweak, &mut block);
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//!
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//! assert_eq!(&block[..4], &data);
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//! # }
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//! ```
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mod fnr;
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use crate::error::Error;
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use crate::sm4::Sm4Key;
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use fnr::{clear_high_bits, fnr_decrypt, fnr_encrypt};
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use zeroize::ZeroizeOnDrop;
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/// FPE 扩展 tweak（15 字节）
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///
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/// 由 `FpeKey::expand_tweak` 从任意长度的 tweak 字节生成。
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#[derive(Clone, Copy)]
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pub struct FpeTweak([u8; 15]);
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/// FPE 密钥（SM4 密钥 + 位数配置）
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///
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/// 使用 ZeroizeOnDrop 确保密钥在 Drop 时自动清零。
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#[derive(ZeroizeOnDrop)]
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pub struct FpeKey {
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/// 底层 SM4 密钥
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key: Sm4Key,
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/// 有效位数（1~128）
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num_bits: usize,
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}
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impl FpeKey {
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/// 创建 FPE 密钥
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///
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/// # 参数
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/// - `key`：16 字节 SM4 密钥
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/// - `num_bits`：明密文域的位数（1~128）
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///
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/// # 错误
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/// - `Error::InvalidInputLength`：`num_bits` 不在 1~128 范围内
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pub fn new(key: &[u8; 16], num_bits: usize) -> Result<Self, Error> {
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if num_bits == 0 || num_bits > 128 {
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return Err(Error::InvalidInputLength);
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}
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Ok(FpeKey {
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key: Sm4Key::new(key),
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num_bits,
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})
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}
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/// 将任意长度的 tweak 扩展为 15 字节内部 tweak
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///
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/// 使用 SM4 对 tweak 进行哈希（CBC-MAC 风格）得到固定长度输出。
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pub fn expand_tweak(&self, tweak: &[u8]) -> FpeTweak {
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// 用 SM4 对 tweak 进行"哈希"：
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// 将 tweak 分块，每块 XOR 进状态后 SM4 加密
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let mut state = [0u8; 16];
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// 存储 num_bits 到 state 前 2 字节（域参数绑定）
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state[0] = (self.num_bits >> 8) as u8;
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state[1] = self.num_bits as u8;
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for chunk in tweak.chunks(16) {
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let mut block = state;
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for (i, &b) in chunk.iter().enumerate() {
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block[i] ^= b;
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}
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self.key.encrypt_block(&mut block);
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state = block;
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}
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// 最终加密（确保即使 tweak 为空也有输出）
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self.key.encrypt_block(&mut state);
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let mut out = [0u8; 15];
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out.copy_from_slice(&state[..15]);
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FpeTweak(out)
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}
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/// 就地加密（前 num_bits 位）
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///
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/// `data` 的前 `num_bits` 位被加密，高于 `num_bits` 的位保持不变。
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///
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/// # 注意
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/// `data` 的位顺序：字节 0 的最高位是位 0（高位优先）。
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pub fn encrypt(&self, tweak: &FpeTweak, data: &mut [u8; 16]) {
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// 保存高于 num_bits 的位（不应被修改）
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let saved = save_high_bits(data, self.num_bits);
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clear_high_bits(data, self.num_bits);
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fnr_encrypt(&self.key, &tweak.0, data, self.num_bits);
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restore_high_bits(data, &saved, self.num_bits);
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}
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/// 就地解密（前 num_bits 位）
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pub fn decrypt(&self, tweak: &FpeTweak, data: &mut [u8; 16]) {
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let saved = save_high_bits(data, self.num_bits);
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clear_high_bits(data, self.num_bits);
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fnr_decrypt(&self.key, &tweak.0, data, self.num_bits);
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restore_high_bits(data, &saved, self.num_bits);
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}
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/// 返回有效位数
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pub fn num_bits(&self) -> usize {
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self.num_bits
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}
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}
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/// 保存 data 中高于 n 位的位（用于还原）
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fn save_high_bits(data: &[u8; 16], n: usize) -> [u8; 16] {
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let mut saved = [0u8; 16];
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let full_bytes = n / 8;
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let rem = n % 8;
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if rem != 0 && full_bytes < 16 {
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// 保存 full_bytes 字节的高位部分（低 (8-rem) 位）
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let mask = 0xFF_u8 >> rem;
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saved[full_bytes] = data[full_bytes] & mask;
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}
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let start = full_bytes + if rem > 0 { 1 } else { 0 };
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saved[start..16].copy_from_slice(&data[start..16]);
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saved
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}
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/// 将保存的高位还原到 data
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fn restore_high_bits(data: &mut [u8; 16], saved: &[u8; 16], n: usize) {
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let full_bytes = n / 8;
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let rem = n % 8;
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if rem != 0 && full_bytes < 16 {
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let mask = 0xFF_u8 >> rem; // 低 (8-rem) 位
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data[full_bytes] = (data[full_bytes] & !mask) | (saved[full_bytes] & mask);
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}
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let start = full_bytes + if rem > 0 { 1 } else { 0 };
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data[start..16].copy_from_slice(&saved[start..16]);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_fpe_new_valid() {
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assert!(FpeKey::new(&[0u8; 16], 1).is_ok());
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assert!(FpeKey::new(&[0u8; 16], 32).is_ok());
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assert!(FpeKey::new(&[0u8; 16], 128).is_ok());
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}
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#[test]
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fn test_fpe_new_invalid() {
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assert!(FpeKey::new(&[0u8; 16], 0).is_err());
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assert!(FpeKey::new(&[0u8; 16], 129).is_err());
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}
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#[test]
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fn test_fpe_encrypt_decrypt_roundtrip_32bits() {
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let key = [0x01u8; 16];
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let fpe = FpeKey::new(&key, 32).unwrap();
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let tweak = fpe.expand_tweak(b"test-tweak");
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// 明文：u32 = 12345678
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let mut data = [0u8; 16];
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data[..4].copy_from_slice(&12345678u32.to_be_bytes());
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let original = data;
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fpe.encrypt(&tweak, &mut data);
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// 加密后应与原始不同
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assert_ne!(&data[..4], &original[..4], "加密后数据应变化");
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// 解密后应恢复原始
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fpe.decrypt(&tweak, &mut data);
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assert_eq!(&data[..4], &original[..4], "解密后应恢复原始明文");
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}
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#[test]
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fn test_fpe_encrypt_decrypt_roundtrip_8bits() {
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let key = [0xABu8; 16];
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let fpe = FpeKey::new(&key, 8).unwrap();
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let tweak = fpe.expand_tweak(b"tweak");
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for val in 0u8..=255 {
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let mut data = [0u8; 16];
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data[0] = val;
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let original = data;
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fpe.encrypt(&tweak, &mut data);
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fpe.decrypt(&tweak, &mut data);
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assert_eq!(data[0], original[0], "8位加解密往返应还原 val={}", val);
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}
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}
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#[test]
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fn test_fpe_encrypt_decrypt_roundtrip_1bit() {
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let key = [0x99u8; 16];
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let fpe = FpeKey::new(&key, 1).unwrap();
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let tweak = fpe.expand_tweak(b"");
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// 测试 0 和 1
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for val in [0u8, 0x80u8] {
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let mut data = [0u8; 16];
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data[0] = val;
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let original = data;
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fpe.encrypt(&tweak, &mut data);
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fpe.decrypt(&tweak, &mut data);
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assert_eq!(data[0] & 0x80, original[0] & 0x80, "1位加解密往返应还原");
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}
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}
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#[test]
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fn test_fpe_encrypt_decrypt_roundtrip_128bits() {
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let key = [0x55u8; 16];
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let fpe = FpeKey::new(&key, 128).unwrap();
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let tweak = fpe.expand_tweak(b"full block");
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let mut data = [0u8; 16];
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for (i, d) in data.iter_mut().enumerate() {
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*d = i as u8 * 17;
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}
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let original = data;
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fpe.encrypt(&tweak, &mut data);
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fpe.decrypt(&tweak, &mut data);
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assert_eq!(data, original, "128位加解密往返应还原");
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}
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#[test]
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fn test_fpe_different_tweaks_different_output() {
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let key = [0x42u8; 16];
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let fpe = FpeKey::new(&key, 32).unwrap();
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let tweak1 = fpe.expand_tweak(b"tweak1");
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let tweak2 = fpe.expand_tweak(b"tweak2");
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let mut d1 = [0u8; 16];
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let mut d2 = [0u8; 16];
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d1[0] = 0xDE;
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d1[1] = 0xAD;
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d1[2] = 0xBE;
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d1[3] = 0xEF;
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d2[..4].copy_from_slice(&d1[..4]);
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fpe.encrypt(&tweak1, &mut d1);
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fpe.encrypt(&tweak2, &mut d2);
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assert_ne!(&d1[..4], &d2[..4], "不同 tweak 应产生不同密文");
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}
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#[test]
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fn test_fpe_high_bits_preserved() {
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// 验证高于 num_bits 的位在加密后不变
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let key = [0x11u8; 16];
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let fpe = FpeKey::new(&key, 4).unwrap(); // 只用高 4 位
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let tweak = fpe.expand_tweak(b"t");
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let mut data = [0u8; 16];
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// 高 4 位为 0b1010，低 4 位为 0b0101
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data[0] = 0b1010_0101;
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// 字节 1~15 也有数据
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for (i, d) in data[1..].iter_mut().enumerate() {
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*d = (i + 1) as u8;
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}
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let saved_low = data[0] & 0x0F;
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let saved_rest: [u8; 15] = data[1..].try_into().unwrap();
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fpe.encrypt(&tweak, &mut data);
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// 低 4 位和字节 1~15 应保持不变
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assert_eq!(data[0] & 0x0F, saved_low, "低4位应不变");
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assert_eq!(&data[1..], &saved_rest, "字节1~15应不变");
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// 解密后高 4 位应恢复
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let encrypted_high = data[0] & 0xF0;
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fpe.decrypt(&tweak, &mut data);
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assert_eq!(data[0] & 0xF0, 0b1010_0000, "解密后高4位应恢复");
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let _ = encrypted_high;
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}
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}
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