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RIOT/sys/crypto/chacha20poly1305.c
2020-10-20 17:16:09 +02:00

170 lines
5.7 KiB
C

/*
* Copyright (C) 2008 D. J. Bernstein (dedicated to the public domain)
* Copyright (C) 2015 René Kijewski <rene.kijewski@fu-berlin.de>
* Copyright (C) 2018 Koen Zandberg
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup sys_crypto_chacha20poly1305
* @{
* @file
* @brief Implementation of the chacha20poly1305 aead cipher
*
* @author Koen Zandberg <koen@bergzand.net>
* @see https://tools.ietf.org/html/rfc8439
* @}
*/
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include "crypto/helper.h"
#include "crypto/chacha20poly1305.h"
#include "crypto/poly1305.h"
#include "unaligned.h"
/* Missing operations to convert numbers to little endian prevents this from
* working on big endian systems */
#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
# error "This code is implementented in a way that it will only work for little-endian systems!"
#endif
/* Nothing to hide here, Literally "expand 32-byte k" */
static const uint32_t constant[] = {0x61707865,
0x3320646e,
0x79622d32,
0x6b206574};
/* Padding to add to the poly1305 authentication tag */
static const uint8_t padding[15] = {0};
/* Single round */
static void _r(uint32_t *a, uint32_t *b, uint32_t *d, unsigned c)
{
*a += *b;
uint32_t tmp = *a ^ *d;
*d = (tmp << c) | (tmp >> (32 - c));
}
static void _add_initial(chacha20poly1305_ctx_t *ctx, const uint8_t *key,
const uint8_t *nonce, uint32_t blk)
{
for (unsigned i = 0; i < 4; i++) {
ctx->state[i] += constant[i];
}
for (unsigned i = 0; i < 8; i++) {
ctx->state[i+4] += unaligned_get_u32(key + 4*i);
}
ctx->state[12] += unaligned_get_u32((uint8_t*)&blk);
ctx->state[13] += unaligned_get_u32(nonce);
ctx->state[14] += unaligned_get_u32(nonce+4);
ctx->state[15] += unaligned_get_u32(nonce+8);
}
static void _keystream(chacha20poly1305_ctx_t *ctx, const uint8_t *key,
const uint8_t *nonce, uint32_t blk)
{
/* Initialize block state */
memset(ctx->state, 0, sizeof(ctx->state));
_add_initial(ctx, key, nonce, blk);
/* perform rounds */
for (unsigned i = 0; i < 80; ++i) {
uint32_t *a = &ctx->state[((i ) & 3) ];
uint32_t *b = &ctx->state[((i + ((i & 4) ? 1 : 0)) & 3) + (4 * 1)];
uint32_t *c = &ctx->state[((i + ((i & 4) ? 2 : 0)) & 3) + (4 * 2)];
uint32_t *d = &ctx->state[((i + ((i & 4) ? 3 : 0)) & 3) + (4 * 3)];
_r(a, b, d, 16);
_r(c, d, b, 12);
_r(a, b, d, 8);
_r(c, d, b, 7);
}
/* add initial state */
_add_initial(ctx, key, nonce, blk);
}
static void _xcrypt(chacha20poly1305_ctx_t *ctx, const uint8_t *key,
const uint8_t *nonce, const uint8_t *in, uint8_t *out, size_t len)
{
/* Number of full 64 byte blocks */
const size_t num_blocks = len >> 6;
size_t pos = 0;
/* xcrypt full blocks */
for (size_t i = 0; i < num_blocks; i++, pos += 64) {
_keystream(ctx, key, nonce, i+1);
for (size_t j = 0; j < 64; j++) {
out[pos+j] = in[pos+j] ^ ((uint8_t*)ctx->state)[j];
}
}
/* xcrypt remaining bytes */
if (len - pos) {
_keystream(ctx, key, nonce, num_blocks+1);
for (size_t j = 0; j < len - pos; j++) {
out[pos+j] = in[pos+j] ^ ((uint8_t*)ctx->state)[j];
}
}
}
static void _poly1305_padded(poly1305_ctx_t *pctx, const uint8_t *data, size_t len)
{
poly1305_update(pctx, data, len);
const size_t padlen = (16 - len) & 0xF;
poly1305_update(pctx, padding, padlen);
}
/* Generate a poly1305 tag */
static void _poly1305_gentag(uint8_t *mac, const uint8_t *key, const uint8_t *nonce,
const uint8_t *cipher, size_t cipherlen,
const uint8_t *aad, size_t aadlen)
{
chacha20poly1305_ctx_t ctx;
/* generate one time key */
_keystream(&ctx, key, nonce, 0);
poly1305_init(&ctx.poly, (uint8_t*)ctx.state);
/* Add aad */
_poly1305_padded(&ctx.poly, aad, aadlen);
/* Add ciphertext */
_poly1305_padded(&ctx.poly, cipher, cipherlen);
/* Add aad length */
const uint64_t lengths[2] = {aadlen, cipherlen};
poly1305_update(&ctx.poly, (uint8_t*)lengths, sizeof(lengths));
poly1305_finish(&ctx.poly, mac);
crypto_secure_wipe(&ctx, sizeof(ctx));
}
void chacha20poly1305_encrypt(uint8_t *cipher, const uint8_t *msg,
size_t msglen, const uint8_t *aad, size_t aadlen,
const uint8_t *key, const uint8_t *nonce)
{
chacha20poly1305_ctx_t ctx;
_xcrypt(&ctx, key, nonce, msg, cipher, msglen);
crypto_secure_wipe(&ctx, sizeof(ctx));
/* Generate tag */
_poly1305_gentag(&cipher[msglen], key, nonce,
cipher, msglen, aad, aadlen);
/* Wipe structures */
}
int chacha20poly1305_decrypt(const uint8_t *cipher, size_t cipherlen,
uint8_t *msg, size_t *msglen,
const uint8_t *aad, size_t aadlen,
const uint8_t *key, const uint8_t *nonce)
{
*msglen = cipherlen - CHACHA20POLY1305_TAG_BYTES;
uint8_t mac[16];
_poly1305_gentag(mac, key, nonce, cipher,
cipherlen - CHACHA20POLY1305_TAG_BYTES, aad, aadlen);
if (crypto_equals(cipher+*msglen, mac, CHACHA20POLY1305_TAG_BYTES) == 0) {
return 0;
}
chacha20poly1305_ctx_t ctx;
/* Number of full blocks */
_xcrypt(&ctx, key, nonce, cipher, msg, *msglen);
return 1;
}