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 <sys/types.h> 20 #include <stdarg.h> /* needed for log.h */ 21 #include <string.h> 22 #include <stdio.h> /* needed for misc.h */ 23 24 #include "log.h" 25 #include "sshbuf.h" 26 #include "ssherr.h" 27 #include "cipher-chachapoly.h" 28 29 int chachapoly_init(struct chachapoly_ctx *ctx, 30 const u_char *key, u_int keylen) 31 { 32 if (keylen != (32 + 32)) /* 2 x 256 bit keys */ 33 return SSH_ERR_INVALID_ARGUMENT; 34 chacha_keysetup(&ctx->main_ctx, key, 256); 35 chacha_keysetup(&ctx->header_ctx, key + 32, 256); 36 return 0; 37 } 38 39 /* 40 * chachapoly_crypt() operates as following: 41 * En/decrypt with header key 'aadlen' bytes from 'src', storing result 42 * to 'dest'. The ciphertext here is treated as additional authenticated 43 * data for MAC calculation. 44 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use 45 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication 46 * tag. This tag is written on encryption and verified on decryption. 47 */ 48 int 49 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, 50 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) 51 { 52 u_char seqbuf[8]; 53 const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */ 54 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; 55 int r = SSH_ERR_INTERNAL_ERROR; 56 57 /* 58 * Run ChaCha20 once to generate the Poly1305 key. The IV is the 59 * packet sequence number. 60 */ 61 memset(poly_key, 0, sizeof(poly_key)); 62 POKE_U64(seqbuf, seqnr); 63 chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL); 64 chacha_encrypt_bytes(&ctx->main_ctx, 65 poly_key, poly_key, sizeof(poly_key)); 66 67 /* If decrypting, check tag before anything else */ 68 if (!do_encrypt) { 69 const u_char *tag = src + aadlen + len; 70 71 poly1305_auth(expected_tag, src, aadlen + len, poly_key); 72 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) { 73 r = SSH_ERR_MAC_INVALID; 74 goto out; 75 } 76 } 77 78 /* Crypt additional data */ 79 if (aadlen) { 80 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 81 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen); 82 } 83 84 /* Set Chacha's block counter to 1 */ 85 chacha_ivsetup(&ctx->main_ctx, seqbuf, one); 86 chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen, 87 dest + aadlen, len); 88 89 /* If encrypting, calculate and append tag */ 90 if (do_encrypt) { 91 poly1305_auth(dest + aadlen + len, dest, aadlen + len, 92 poly_key); 93 } 94 r = 0; 95 out: 96 explicit_bzero(expected_tag, sizeof(expected_tag)); 97 explicit_bzero(seqbuf, sizeof(seqbuf)); 98 explicit_bzero(poly_key, sizeof(poly_key)); 99 return r; 100 } 101 102 /* Decrypt and extract the encrypted packet length */ 103 int 104 chachapoly_get_length(struct chachapoly_ctx *ctx, 105 u_int *plenp, u_int seqnr, const u_char *cp, u_int len) 106 { 107 u_char buf[4], seqbuf[8]; 108 109 if (len < 4) 110 return SSH_ERR_MESSAGE_INCOMPLETE; 111 POKE_U64(seqbuf, seqnr); 112 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 113 chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4); 114 *plenp = PEEK_U32(buf); 115 return 0; 116 } 117