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 1.4 2014/01/31 16:39:19 tedu 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 "misc.h" 26 #include "cipher-chachapoly.h" 27 28 void chachapoly_init(struct chachapoly_ctx *ctx, 29 const u_char *key, u_int keylen) 30 { 31 if (keylen != (32 + 32)) /* 2 x 256 bit keys */ 32 fatal("%s: invalid keylen %u", __func__, keylen); 33 chacha_keysetup(&ctx->main_ctx, key, 256); 34 chacha_keysetup(&ctx->header_ctx, key + 32, 256); 35 } 36 37 /* 38 * chachapoly_crypt() operates as following: 39 * En/decrypt with header key 'aadlen' bytes from 'src', storing result 40 * to 'dest'. The ciphertext here is treated as additional authenticated 41 * data for MAC calculation. 42 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use 43 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication 44 * tag. This tag is written on encryption and verified on decryption. 45 */ 46 int 47 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, 48 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) 49 { 50 u_char seqbuf[8]; 51 const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */ 52 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; 53 int r = -1; 54 55 /* 56 * Run ChaCha20 once to generate the Poly1305 key. The IV is the 57 * packet sequence number. 58 */ 59 memset(poly_key, 0, sizeof(poly_key)); 60 put_u64(seqbuf, seqnr); 61 chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL); 62 chacha_encrypt_bytes(&ctx->main_ctx, 63 poly_key, poly_key, sizeof(poly_key)); 64 /* Set Chacha's block counter to 1 */ 65 chacha_ivsetup(&ctx->main_ctx, seqbuf, one); 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 goto out; 74 } 75 /* Crypt additional data */ 76 if (aadlen) { 77 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 78 chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen); 79 } 80 chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen, 81 dest + aadlen, len); 82 83 /* If encrypting, calculate and append tag */ 84 if (do_encrypt) { 85 poly1305_auth(dest + aadlen + len, dest, aadlen + len, 86 poly_key); 87 } 88 r = 0; 89 90 out: 91 explicit_bzero(expected_tag, sizeof(expected_tag)); 92 explicit_bzero(seqbuf, sizeof(seqbuf)); 93 explicit_bzero(poly_key, sizeof(poly_key)); 94 return r; 95 } 96 97 /* Decrypt and extract the encrypted packet length */ 98 int 99 chachapoly_get_length(struct chachapoly_ctx *ctx, 100 u_int *plenp, u_int seqnr, const u_char *cp, u_int len) 101 { 102 u_char buf[4], seqbuf[8]; 103 104 if (len < 4) 105 return -1; /* Insufficient length */ 106 put_u64(seqbuf, seqnr); 107 chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); 108 chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4); 109 *plenp = get_u32(buf); 110 return 0; 111 } 112 113