1 /* 2 * Copyright (c) 2013 Damien Miller <djm (at) 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 } 119
