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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-libcrypto.c,v 1.1 2020/04/03 04:32:21 djm Exp $ */
#include "includes.h"
#include <sys/types.h>
#include <stdarg.h> /* needed for log.h */
#include <string.h>
#include <stdio.h> /* needed for misc.h */
#include <openssl/evp.h>
#include "log.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "cipher-chachapoly.h"
struct chachapoly_ctx {
EVP_CIPHER_CTX *main_evp, *header_evp;
};
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;
if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL ||
(ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL)
goto fail;
if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1))
goto fail;
if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1))
goto fail;
if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16)
goto fail;
return ctx;
fail:
chachapoly_free(ctx);
return NULL;
}
void
chachapoly_free(struct chachapoly_ctx *cpctx)
{
if (cpctx == NULL)
return;
EVP_CIPHER_CTX_free(cpctx->main_evp);
EVP_CIPHER_CTX_free(cpctx->header_evp);
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[16]; /* layout: u64 counter || u64 seqno */
int r = SSH_ERR_INTERNAL_ERROR;
u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
/*
* Run ChaCha20 once to generate the Poly1305 key. The IV is the
* packet sequence number.
*/
memset(seqbuf, 0, sizeof(seqbuf));
POKE_U64(seqbuf + 8, seqnr);
memset(poly_key, 0, sizeof(poly_key));
if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
EVP_Cipher(ctx->main_evp, poly_key,
poly_key, sizeof(poly_key)) < 0) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
/* 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) {
if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) ||
EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
}
/* Set Chacha's block counter to 1 */
seqbuf[0] = 1;
if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
/* 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[16];
if (len < 4)
return SSH_ERR_MESSAGE_INCOMPLETE;
memset(seqbuf, 0, sizeof(seqbuf));
POKE_U64(seqbuf + 8, seqnr);
if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0))
return SSH_ERR_LIBCRYPTO_ERROR;
if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0)
return SSH_ERR_LIBCRYPTO_ERROR;
*plenp = PEEK_U32(buf);
return 0;
}
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