int
mac_compute(Mac *mac, u_int32_t seqno, u_char *data, int datalen,
u_char *digest, size_t dlen)
{
static u_char m[MAC_DIGEST_LEN_MAX];
u_char b[4], nonce[8];
if (mac->mac_len > sizeof(m))
return SSH_ERR_INTERNAL_ERROR;
switch (mac->type) {
case SSH_EVP:
POKE_U32(b, seqno);
/* reset HMAC context */
if (HMAC_Init(&mac->evp_ctx, NULL, 0, NULL) != 1 ||
HMAC_Update(&mac->evp_ctx, b, sizeof(b)) != 1 ||
HMAC_Update(&mac->evp_ctx, data, datalen) != 1 ||
HMAC_Final(&mac->evp_ctx, m, NULL) != 1)
return SSH_ERR_LIBCRYPTO_ERROR;
break;
case SSH_UMAC:
POKE_U64(nonce, seqno);
umac_update(mac->umac_ctx, data, datalen);
umac_final(mac->umac_ctx, m, nonce);
break;
default:
return SSH_ERR_INVALID_ARGUMENT;
}
if (digest != NULL) {
if (dlen > mac->mac_len)
dlen = mac->mac_len;
memcpy(digest, m, dlen);
}
return 0;
}
int
sshbuf_put_u64(struct sshbuf *buf, u_int64_t val)
{
u_char *p;
int r;
if ((r = sshbuf_reserve(buf, 8, &p)) < 0)
return r;
POKE_U64(p, val);
return 0;
}
/*
* 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;
}
