103 lines
2.8 KiB
C
103 lines
2.8 KiB
C
#include "chacha.h"
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#define ROTL32(v, n) (((v) << (n)) | ((v) >> (32 - (n))))
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#define ROTATE(v, c) ROTL32((v), (c))
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#define XOR(v, w) ((v) ^ (w))
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#define PLUS(x, y) ((x) + (y))
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#define U32TO8_LITTLE(p, v) \
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{ (p)[0] = ((v) ) & 0xff; (p)[1] = ((v) >> 8) & 0xff; \
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(p)[2] = ((v) >> 16) & 0xff; (p)[3] = ((v) >> 24) & 0xff; }
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#define U8TO32_LITTLE(p) \
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(((u32)((p)[0]) ) | ((u32)((p)[1]) << 8) | \
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((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24) )
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#define QUARTERROUND(a,b,c,d) \
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x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]),16); \
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x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]),12); \
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x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]), 8); \
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x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]), 7);
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// sigma contains the ChaCha constants, which happen to be an ASCII string.
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static const uint8_t sigma[16] = { 'e', 'x', 'p', 'a', 'n', 'd', ' ', '3',
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'2', '-', 'b', 'y', 't', 'e', ' ', 'k' };
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void chacha20_encrypt(const u32 input[16],
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unsigned char output[64],
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int num_rounds)
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{
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u32 x[16];
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int i;
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memcpy(x, input, sizeof(u32) * 16);
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for (i = num_rounds; i > 0; i -= 2) {
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QUARTERROUND( 0, 4, 8,12)
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QUARTERROUND( 1, 5, 9,13)
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QUARTERROUND( 2, 6,10,14)
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QUARTERROUND( 3, 7,11,15)
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QUARTERROUND( 0, 5,10,15)
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QUARTERROUND( 1, 6,11,12)
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QUARTERROUND( 2, 7, 8,13)
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QUARTERROUND( 3, 4, 9,14)
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}
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for (i = 0; i < 16; ++i) {
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x[i] = PLUS(x[i], input[i]);
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}
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for (i = 0; i < 16; ++i) {
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U32TO8_LITTLE(output + 4 * i, x[i]);
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}
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}
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void chacha20_encrypt_ctr(const uint8_t *in, uint8_t *out, size_t in_len,
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const uint8_t key[CHACHA_KEY_SIZE],
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const uint8_t nonce[CHACHA_NONCE_SIZE],
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uint32_t counter)
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{
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uint32_t input[16];
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uint8_t buf[64];
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size_t todo, i;
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input[0] = U8TO32_LITTLE(sigma + 0);
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input[1] = U8TO32_LITTLE(sigma + 4);
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input[2] = U8TO32_LITTLE(sigma + 8);
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input[3] = U8TO32_LITTLE(sigma + 12);
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input[4] = U8TO32_LITTLE(key + 0);
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input[5] = U8TO32_LITTLE(key + 4);
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input[6] = U8TO32_LITTLE(key + 8);
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input[7] = U8TO32_LITTLE(key + 12);
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input[8] = U8TO32_LITTLE(key + 16);
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input[9] = U8TO32_LITTLE(key + 20);
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input[10] = U8TO32_LITTLE(key + 24);
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input[11] = U8TO32_LITTLE(key + 28);
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input[12] = counter;
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input[13] = U8TO32_LITTLE(nonce + 0);
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input[14] = U8TO32_LITTLE(nonce + 4);
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input[15] = U8TO32_LITTLE(nonce + 8);
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while (in_len > 0) {
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todo = sizeof(buf);
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if (in_len < todo) {
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todo = in_len;
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}
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chacha20_encrypt(input, buf, 20);
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for (i = 0; i < todo; i++) {
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out[i] = in[i] ^ buf[i];
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}
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out += todo;
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in += todo;
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in_len -= todo;
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input[12]++;
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}
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}
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