crypto/openssh/cipher-chachapoly.c

   1 /*
   2  * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 /* $OpenBSD: cipher-chachapoly.c,v 1.7 2015/01/14 10:24:42 markus Exp $ */
  18
  19 #include "includes.h"
  20
  21 #include <sys/types.h>
  22 #include <stdarg.h> /* needed for log.h */
  23 #include <string.h>
  24 #include <stdio.h>  /* needed for misc.h */
  25
  26 #include "log.h"
  27 #include "sshbuf.h"
  28 #include "ssherr.h"
  29 #include "cipher-chachapoly.h"
  30
  31 int chachapoly_init(struct chachapoly_ctx *ctx,
  32     const u_char *key, u_int keylen)
  33 {
  34         if (keylen != (32 + 32)) /* 2 x 256 bit keys */
  35                 return SSH_ERR_INVALID_ARGUMENT;
  36         chacha_keysetup(&ctx->main_ctx, key, 256);
  37         chacha_keysetup(&ctx->header_ctx, key + 32, 256);
  38         return 0;
  39 }
  40
  41 /*
  42  * chachapoly_crypt() operates as following:
  43  * En/decrypt with header key 'aadlen' bytes from 'src', storing result
  44  * to 'dest'. The ciphertext here is treated as additional authenticated
  45  * data for MAC calculation.
  46  * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
  47  * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
  48  * tag. This tag is written on encryption and verified on decryption.
  49  */
  50 int
  51 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
  52     const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
  53 {
  54         u_char seqbuf[8];
  55         const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
  56         u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
  57         int r = SSH_ERR_INTERNAL_ERROR;
  58
  59         /*
  60          * Run ChaCha20 once to generate the Poly1305 key. The IV is the
  61          * packet sequence number.
  62          */
  63         memset(poly_key, 0, sizeof(poly_key));
  64         POKE_U64(seqbuf, seqnr);
  65         chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
  66         chacha_encrypt_bytes(&ctx->main_ctx,
  67             poly_key, poly_key, sizeof(poly_key));
  68
  69         /* If decrypting, check tag before anything else */
  70         if (!do_encrypt) {
  71                 const u_char *tag = src + aadlen + len;
  72
  73                 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
  74                 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
  75                         r = SSH_ERR_MAC_INVALID;
  76                         goto out;
  77                 }
  78         }
  79
  80         /* Crypt additional data */
  81         if (aadlen) {
  82                 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
  83                 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
  84         }
  85
  86         /* Set Chacha's block counter to 1 */
  87         chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
  88         chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
  89             dest + aadlen, len);
  90
  91         /* If encrypting, calculate and append tag */
  92         if (do_encrypt) {
  93                 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
  94                     poly_key);
  95         }
  96         r = 0;
  97  out:
  98         explicit_bzero(expected_tag, sizeof(expected_tag));
  99         explicit_bzero(seqbuf, sizeof(seqbuf));
 100         explicit_bzero(poly_key, sizeof(poly_key));
 101         return r;
 102 }
 103
 104 /* Decrypt and extract the encrypted packet length */
 105 int
 106 chachapoly_get_length(struct chachapoly_ctx *ctx,
 107     u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
 108 {
 109         u_char buf[4], seqbuf[8];
 110
 111         if (len < 4)
 112                 return SSH_ERR_MESSAGE_INCOMPLETE;
 113         POKE_U64(seqbuf, seqnr);
 114         chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
 115         chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
 116         *plenp = PEEK_U32(buf);
 117         return 0;
 118 }