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 1.8 2016/08/03 05:41:57 djm 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 32 chachapoly_init(struct chachapoly_ctx *ctx, 33 const u_char *key, u_int keylen) 34 { 35 if (keylen != (32 + 32)) /* 2 x 256 bit keys */ 36 return SSH_ERR_INVALID_ARGUMENT; 37 chacha_keysetup(&ctx->main_ctx, key, 256); 38 chacha_keysetup(&ctx->header_ctx, key + 32, 256); 39 return 0; 40 } 41 42 /* 43 * chachapoly_crypt() operates as following: 44 * En/decrypt with header key 'aadlen' bytes from 'src', storing result 45 * to 'dest'. The ciphertext here is treated as additional authenticated 46 * data for MAC calculation. 47 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use 48 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication 49 * tag. This tag is written on encryption and verified on decryption. 50 */ 51 int 52 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, 53 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) 54 { 55 u_char seqbuf[8]; 56 const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */ 57 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; 58 int r = SSH_ERR_INTERNAL_ERROR; 59 60 /* 61 * Run ChaCha20 once to generate the Poly1305 key. The IV is the 62 * packet sequence number. 63 */ 64 memset(poly_key, 0, sizeof(poly_key)); 65 POKE_U64(seqbuf, seqnr); 66 chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL); 67 chacha_encrypt_bytes(&ctx->main_ctx, 68 poly_key, poly_key, sizeof(poly_key)); 69 70 /* If decrypting, check tag before anything else */ 71 if (!do_encrypt) { 72 const u_char *tag = src + aadlen + len; 73 74 poly1305_auth(expected_tag, src, aadlen + len, poly_key); 75 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) { 76 r = SSH_ERR_MAC_INVALID; 77 goto out; 78 } 79 } 80 81 /* Crypt additional data */ 82 if (aadlen) { 83 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 84 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen); 85 } 86 87 /* Set Chacha's block counter to 1 */ 88 chacha_ivsetup(&ctx->main_ctx, seqbuf, one); 89 chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen, 90 dest + aadlen, len); 91 92 /* If encrypting, calculate and append tag */ 93 if (do_encrypt) { 94 poly1305_auth(dest + aadlen + len, dest, aadlen + len, 95 poly_key); 96 } 97 r = 0; 98 out: 99 explicit_bzero(expected_tag, sizeof(expected_tag)); 100 explicit_bzero(seqbuf, sizeof(seqbuf)); 101 explicit_bzero(poly_key, sizeof(poly_key)); 102 return r; 103 } 104 105 /* Decrypt and extract the encrypted packet length */ 106 int 107 chachapoly_get_length(struct chachapoly_ctx *ctx, 108 u_int *plenp, u_int seqnr, const u_char *cp, u_int len) 109 { 110 u_char buf[4], seqbuf[8]; 111 112 if (len < 4) 113 return SSH_ERR_MESSAGE_INCOMPLETE; 114 POKE_U64(seqbuf, seqnr); 115 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 116 chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4); 117 *plenp = PEEK_U32(buf); 118 return 0; 119 } 120
