crypto/openssh/cipher-chachapoly.c

   1 /* $OpenBSD: cipher-chachapoly.c,v 1.10 2023/07/17 05:26:38 djm Exp $ */
   2 /*
   3  * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 #include "includes.h"
  19 #ifdef WITH_OPENSSL
  20 #include "openbsd-compat/openssl-compat.h"
  21 #endif
  22
  23 #if !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20)
  24
  25 #include <sys/types.h>
  26 #include <stdarg.h> /* needed for log.h */
  27 #include <string.h>
  28 #include <stdio.h>  /* needed for misc.h */
  29
  30 #include "log.h"
  31 #include "sshbuf.h"
  32 #include "ssherr.h"
  33 #include "cipher-chachapoly.h"
  34
  35 struct chachapoly_ctx {
  36         struct chacha_ctx main_ctx, header_ctx;
  37 };
  38
  39 struct chachapoly_ctx *
  40 chachapoly_new(const u_char *key, u_int keylen)
  41 {
  42         struct chachapoly_ctx *ctx;
  43
  44         if (keylen != (32 + 32)) /* 2 x 256 bit keys */
  45                 return NULL;
  46         if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
  47                 return NULL;
  48         chacha_keysetup(&ctx->main_ctx, key, 256);
  49         chacha_keysetup(&ctx->header_ctx, key + 32, 256);
  50         return ctx;
  51 }
  52
  53 void
  54 chachapoly_free(struct chachapoly_ctx *cpctx)
  55 {
  56         freezero(cpctx, sizeof(*cpctx));
  57 }
  58
  59 /*
  60  * chachapoly_crypt() operates as following:
  61  * En/decrypt with header key 'aadlen' bytes from 'src', storing result
  62  * to 'dest'. The ciphertext here is treated as additional authenticated
  63  * data for MAC calculation.
  64  * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
  65  * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
  66  * tag. This tag is written on encryption and verified on decryption.
  67  */
  68 int
  69 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
  70     const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
  71 {
  72         u_char seqbuf[8];
  73         const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */
  74         u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
  75         int r = SSH_ERR_INTERNAL_ERROR;
  76
  77         /*
  78          * Run ChaCha20 once to generate the Poly1305 key. The IV is the
  79          * packet sequence number.
  80          */
  81         memset(poly_key, 0, sizeof(poly_key));
  82         POKE_U64(seqbuf, seqnr);
  83         chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL);
  84         chacha_encrypt_bytes(&ctx->main_ctx,
  85             poly_key, poly_key, sizeof(poly_key));
  86
  87         /* If decrypting, check tag before anything else */
  88         if (!do_encrypt) {
  89                 const u_char *tag = src + aadlen + len;
  90
  91                 poly1305_auth(expected_tag, src, aadlen + len, poly_key);
  92                 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
  93                         r = SSH_ERR_MAC_INVALID;
  94                         goto out;
  95                 }
  96         }
  97
  98         /* Crypt additional data */
  99         if (aadlen) {
 100                 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
 101                 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen);
 102         }
 103
 104         /* Set Chacha's block counter to 1 */
 105         chacha_ivsetup(&ctx->main_ctx, seqbuf, one);
 106         chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen,
 107             dest + aadlen, len);
 108
 109         /* If encrypting, calculate and append tag */
 110         if (do_encrypt) {
 111                 poly1305_auth(dest + aadlen + len, dest, aadlen + len,
 112                     poly_key);
 113         }
 114         r = 0;
 115  out:
 116         explicit_bzero(expected_tag, sizeof(expected_tag));
 117         explicit_bzero(seqbuf, sizeof(seqbuf));
 118         explicit_bzero(poly_key, sizeof(poly_key));
 119         return r;
 120 }
 121
 122 /* Decrypt and extract the encrypted packet length */
 123 int
 124 chachapoly_get_length(struct chachapoly_ctx *ctx,
 125     u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
 126 {
 127         u_char buf[4], seqbuf[8];
 128
 129         if (len < 4)
 130                 return SSH_ERR_MESSAGE_INCOMPLETE;
 131         POKE_U64(seqbuf, seqnr);
 132         chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL);
 133         chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4);
 134         *plenp = PEEK_U32(buf);
 135         return 0;
 136 }
 137
 138 #endif /* !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20) */