用c语言实现salsa算法

Salsa20是一种流密码，它可以用C语言实现。以下是Salsa20的C语言实现：

#include <stdio.h>
#include <stdint.h>

#define ROTL32(v, n) (((v) << (n)) | ((v) >> (32 - (n))))

void salsa20_quarter_round(uint32_t *a, uint32_t *b, uint32_t *c, uint32_t *d)
{
    *b ^= ROTL32((*a + *d), 7);
    *c ^= ROTL32((*b + *a), 9);
    *d ^= ROTL32((*c + *b), 13);
    *a ^= ROTL32((*d + *c), 18);
}

void salsa20_row_round(uint32_t x[16])
{
    salsa20_quarter_round(&x[0], &x[4], &x[8], &x[12]);
    salsa20_quarter_round(&x[5], &x[9], &x[13], &x[1]);
    salsa20_quarter_round(&x[10], &x[14], &x[2], &x[6]);
    salsa20_quarter_round(&x[15], &x[3], &x[7], &x[11]);
}

void salsa20_column_round(uint32_t x[16])
{
    salsa20_quarter_round(&x[0], &x[1], &x[2], &x[3]);
    salsa20_quarter_round(&x[5], &x[6], &x[7], &x[4]);
    salsa20_quarter_round(&x[10], &x[11], &x[8], &x[9]);
    salsa20_quarter_round(&x[15], &x[12], &x[13], &x[14]);
}

void salsa20_double_round(uint32_t x[16])
{
    salsa20_row_round(x);
    salsa20_column_round(x);
}

void salsa20_hash(uint32_t out[16], uint32_t in[16])
{
    uint32_t x[16];
    int i;

    for (i = 0; i < 16; ++i)
        x[i] = in[i];

    for (i = 0; i < 10; ++i)
        salsa20_double_round(x);

    for (i = 0; i < 16; ++i)
        out[i] = x[i] + in[i];
}

void salsa20_key_block(uint32_t block[16], uint32_t key[8], uint32_t nonce[2], uint32_t counter)
{
    int i;

    block[0] = 0x61707865;
    block[1] = key[0];
    block[2] = key[1];
    block[3] = key[2];
    block[4] = key[3];
    block[5] = 0x3320646e;
    block[6] = nonce[0];
    block[7] = nonce[1];
    block[8] = counter;
    block[9] = key[4];
    block[10] = key[5];
    block[11] = key[6];
    block[12] = key[7];
    block[13] = 0x79622d32;
    block[14] = 0x6b206574;
    block[15] = 0x03000000;

    salsa20_hash(block, block);
}

void salsa20_encrypt(uint8_t *out, uint8_t *in, uint32_t inlen, uint32_t key[8], uint32_t nonce[2], uint32_t counter)
{
    uint32_t block[16];
    uint8_t keystream[64];
    uint32_t i, j;

    while (inlen > 0)
    {
        salsa20_key_block(block, key, nonce, counter);

        for (i = 0; i < 16; ++i)
            block[i] = htonl(block[i]);

        for (i = 0; i < 64; ++i)
            keystream[i] = ((uint8_t *)block)[i];

        for (i = 0; i < 64 && i < inlen; ++i)
            out[i] = in[i] ^ keystream[i];

        inlen -= i;
        in += i;
        out += i;
        ++counter;
    }
}

int main()
{
    uint8_t in[1024] = "Hello, Salsa20!";
    uint8_t out[1024];
    uint32_t key[8] = {0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000};
    uint32_t nonce[2] = {0x00000000, 0x00000000};
    uint32_t counter = 0;

    salsa20_encrypt(out, in, sizeof(in), key, nonce, counter);

    printf("Input: %s\n", in);
    printf("Output: %s\n", out);

    return 0;
}

在此示例中，我们使用Salsa20加密算法对字符串“Hello, Salsa20!”进行加密。我们使用了一个8字节的密钥（所有位为0），一个8字节的nonce（所有位为0），和一个32位的计数器（初始值为0）。输出结果是加密后的字符串。注意，在实际使用中，您应该使用不同的密钥、nonce和计数器来保证安全性。