荨麻双鱼 CBC

Question

我在标准 ecb 模式下使用 nettle 的 twofish 没有问题，但是我不确定这个 cbc 模式有什么问题？解密的消息将与原始消息不匹配。（仅出于测试目的使用一些硬编码值，如 iv）。

https://www.lysator.liu.se/~nisse/nettle/nettle.html

    const uint8_t key[TWOFISH_KEY_SIZE] = {
        0xea, 0xad, 0xdd, 0x6c, 0x32, 0x5a, 0xdc, 0x4f, 0x01, 0x5b, 0x4c,
        0xde, 0xbb, 0x45, 0xc9, 0xe5, 0x5a, 0xb7, 0x5f, 0x3b, 0x01, 0x9a,
        0xf8, 0x39, 0xd0, 0x74, 0x05, 0xeb, 0xf1, 0xaa, 0xa7, 0x67};
    const uint8_t src[TWOFISH_BLOCK_SIZE] = {
        0x3a, 0x53, 0xec, 0xae, 0xc0, 0xcf, 0xd3, 0xd8,
        0xae, 0x05, 0x5d, 0xc0, 0x07, 0x3c, 0x04, 0x0d};
    const uint8_t iv[TWOFISH_BLOCK_SIZE] = {
        0xa0, 0xfb, 0x59, 0x3d, 0x70, 0x98, 0xdf, 0x8f,
        0xff, 0xa0, 0x3b, 0xd5, 0xc5, 0x8b, 0x2c, 0x45};
    uint8_t encrypted[TWOFISH_BLOCK_SIZE];
    uint8_t decrypted[TWOFISH_BLOCK_SIZE];

    struct CBC_CTX(struct twofish_ctx, TWOFISH_BLOCK_SIZE) ctx;
    twofish256_set_key(&ctx.ctx, key);
    CBC_SET_IV(&ctx, iv);

    CBC_ENCRYPT(&ctx, twofish_encrypt, TWOFISH_BLOCK_SIZE, encrypted, src);
    CBC_DECRYPT(&ctx, twofish_decrypt, TWOFISH_BLOCK_SIZE, decrypted,
                encrypted);

    for(int i = 0; i < TWOFISH_BLOCK_SIZE; i++) {
        printf("\n%hhX\n", src[i]);
        printf("%hhX\n", encrypted[i]);
        printf("%hhX\n-------------------", decrypted[i]);
    }

Answer 1

James说的对：解密前需要重新设置IV。来自 Nettle 文档：

The final ciphertext block processed is copied into iv before returning, so that large message be processed be a sequence of calls to cbc_encrypt.

即加密上下文中的 IV 丢失并被最后一个密文块替换。因此，您需要重新将其设置为正确的值。

Nettle 是一个低级库，所以这个结构很有意义；更高级别的库可能会使用流式传输或假设您始终在调用中提供完整的 plaintext/ciphertext。

荨麻双鱼 CBC

nettle twofish CBC

c

encryption

cryptography

cbc-mode

nettle