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) */ 139