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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 1.9 2020/04/03 04:27:03 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 "sshbuf.h"
#include "ssherr.h"
#include "cipher-chachapoly.h"
struct chachapoly_ctx {
struct chacha_ctx main_ctx, header_ctx;
};
struct chachapoly_ctx *
chachapoly_new(const u_char *key, u_int keylen)
{
struct chachapoly_ctx *ctx;
if (keylen != (32 + 32)) /* 2 x 256 bit keys */
return NULL;
if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
return NULL;
chacha_keysetup(&ctx->main_ctx, key, 256);
chacha_keysetup(&ctx->header_ctx, key + 32, 256);
return ctx;
}
void
chachapoly_free(struct chachapoly_ctx *cpctx)
{
freezero(cpctx, sizeof(*cpctx));
}
/*
* chachapoly_crypt() operates as following:
* En/decrypt with header key 'aadlen' bytes from 'src', storing result
* to 'dest'. The ciphertext here is treated as additional authenticated
* data for MAC calculation.
* 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.
*/
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];
const 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 = SSH_ERR_INTERNAL_ERROR;
/*
* Run ChaCha20 once to generate the Poly1305 key. The IV is the
* packet sequence number.
*/
memset(poly_key, 0, sizeof(poly_key));
POKE_U64(seqbuf, seqnr);
chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
chacha_encrypt_bytes(&ctx->main_ctx,
poly_key, poly_key, sizeof(poly_key));
/* 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) {
r = SSH_ERR_MAC_INVALID;
goto out;
}
}
/* Crypt additional data */
if (aadlen) {
chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
}
/* Set Chacha's block counter to 1 */
chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
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:
explicit_bzero(expected_tag, sizeof(expected_tag));
explicit_bzero(seqbuf, sizeof(seqbuf));
explicit_bzero(poly_key, sizeof(poly_key));
return r;
}
/* Decrypt and extract the encrypted packet length */
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 SSH_ERR_MESSAGE_INCOMPLETE;
POKE_U64(seqbuf, seqnr);
chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
*plenp = PEEK_U32(buf);
return 0;
}
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