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December 11, 2013 18:57
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cipher-chachapoly.c
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/* | |
* Copyright (c) 2013 Damien Miller <djm@mindrot.org> | |
* | |
* Permission to use, copy, modify, and distribute this software for any | |
* purpose with or without fee is hereby granted, provided that the above | |
* copyright notice and this permission notice appear in all copies. | |
* | |
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | |
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | |
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR | |
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES | |
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN | |
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF | |
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. | |
*/ | |
/* $OpenBSD: cipher-chachapoly.c,v 1.2 2013/11/21 02:50:00 djm Exp $ */ | |
#include <sys/types.h> | |
#include <stdarg.h> /* needed for log.h */ | |
#include <string.h> | |
#include <stdio.h> /* needed for misc.h */ | |
#include "log.h" | |
#include "misc.h" | |
#include "cipher-chachapoly.h" | |
void chachapoly_init(struct chachapoly_ctx *ctx, | |
const u_char *key, u_int keylen) | |
{ | |
if (keylen != (32 + 32)) /* 2 x 256 bit keys */ | |
fatal("%s: invalid keylen %u", __func__, keylen); | |
chacha_keysetup(&ctx->main_ctx, key, 256); | |
chacha_keysetup(&ctx->header_ctx, key + 32, 256); | |
} | |
/* | |
* chachapoly_crypt() operates as following: | |
* Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'. | |
* Theses bytes are treated as additional authenticated data. | |
* En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. | |
* Use POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the | |
* authentication tag. | |
* This tag is written on encryption and verified on decryption. | |
* Both 'aadlen' and 'authlen' can be set to 0. | |
*/ | |
int | |
chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, | |
const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) | |
{ | |
u_char seqbuf[8]; | |
u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB. little-endian */ | |
u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; | |
int r = -1; | |
/* | |
* Run ChaCha20 once to generate the Poly1305 key. The IV is the | |
* packet sequence number. | |
*/ | |
bzero(poly_key, sizeof(poly_key)); | |
put_u64(seqbuf, seqnr); | |
chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL); | |
chacha_encrypt_bytes(&ctx->main_ctx, | |
poly_key, poly_key, sizeof(poly_key)); | |
/* Set Chacha's block counter to 1 */ | |
chacha_ivsetup(&ctx->main_ctx, seqbuf, one); | |
/* If decrypting, check tag before anything else */ | |
if (!do_encrypt) { | |
const u_char *tag = src + aadlen + len; | |
poly1305_auth(expected_tag, src, aadlen + len, poly_key); | |
if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) | |
goto out; | |
} | |
/* Crypt additional data */ | |
if (aadlen) { | |
chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); | |
chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen); | |
} | |
chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen, | |
dest + aadlen, len); | |
/* If encrypting, calculate and append tag */ | |
if (do_encrypt) { | |
poly1305_auth(dest + aadlen + len, dest, aadlen + len, | |
poly_key); | |
} | |
r = 0; | |
out: | |
bzero(expected_tag, sizeof(expected_tag)); | |
bzero(seqbuf, sizeof(seqbuf)); | |
bzero(poly_key, sizeof(poly_key)); | |
return r; | |
} | |
int | |
chachapoly_get_length(struct chachapoly_ctx *ctx, | |
u_int *plenp, u_int seqnr, const u_char *cp, u_int len) | |
{ | |
u_char buf[4], seqbuf[8]; | |
if (len < 4) | |
return -1; /* Insufficient length */ | |
put_u64(seqbuf, seqnr); | |
chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); | |
chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4); | |
*plenp = get_u32(buf); | |
return 0; | |
} |
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