1 /* $OpenBSD: cipher-chachapoly-libcrypto.c,v 1.2 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 <openssl/evp.h> 31 32 #include "log.h" 33 #include "sshbuf.h" 34 #include "ssherr.h" 35 #include "cipher-chachapoly.h" 36 37 struct chachapoly_ctx { 38 EVP_CIPHER_CTX *main_evp, *header_evp; 39 }; 40 41 struct chachapoly_ctx * 42 chachapoly_new(const u_char *key, u_int keylen) 43 { 44 struct chachapoly_ctx *ctx; 45 46 if (keylen != (32 + 32)) /* 2 x 256 bit keys */ 47 return NULL; 48 if ((ctx = calloc(1, sizeof(*ctx))) == NULL) 49 return NULL; 50 if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL || 51 (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL) 52 goto fail; 53 if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1)) 54 goto fail; 55 if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1)) 56 goto fail; 57 if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16) 58 goto fail; 59 return ctx; 60 fail: 61 chachapoly_free(ctx); 62 return NULL; 63 } 64 65 void 66 chachapoly_free(struct chachapoly_ctx *cpctx) 67 { 68 if (cpctx == NULL) 69 return; 70 EVP_CIPHER_CTX_free(cpctx->main_evp); 71 EVP_CIPHER_CTX_free(cpctx->header_evp); 72 freezero(cpctx, sizeof(*cpctx)); 73 } 74 75 /* 76 * chachapoly_crypt() operates as following: 77 * En/decrypt with header key 'aadlen' bytes from 'src', storing result 78 * to 'dest'. The ciphertext here is treated as additional authenticated 79 * data for MAC calculation. 80 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use 81 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication 82 * tag. This tag is written on encryption and verified on decryption. 83 */ 84 int 85 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, 86 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) 87 { 88 u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */ 89 int r = SSH_ERR_INTERNAL_ERROR; 90 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; 91 92 /* 93 * Run ChaCha20 once to generate the Poly1305 key. The IV is the 94 * packet sequence number. 95 */ 96 memset(seqbuf, 0, sizeof(seqbuf)); 97 POKE_U64(seqbuf + 8, seqnr); 98 memset(poly_key, 0, sizeof(poly_key)); 99 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) || 100 EVP_Cipher(ctx->main_evp, poly_key, 101 poly_key, sizeof(poly_key)) < 0) { 102 r = SSH_ERR_LIBCRYPTO_ERROR; 103 goto out; 104 } 105 106 /* If decrypting, check tag before anything else */ 107 if (!do_encrypt) { 108 const u_char *tag = src + aadlen + len; 109 110 poly1305_auth(expected_tag, src, aadlen + len, poly_key); 111 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) { 112 r = SSH_ERR_MAC_INVALID; 113 goto out; 114 } 115 } 116 117 /* Crypt additional data */ 118 if (aadlen) { 119 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) || 120 EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) { 121 r = SSH_ERR_LIBCRYPTO_ERROR; 122 goto out; 123 } 124 } 125 126 /* Set Chacha's block counter to 1 */ 127 seqbuf[0] = 1; 128 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) || 129 EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) { 130 r = SSH_ERR_LIBCRYPTO_ERROR; 131 goto out; 132 } 133 134 /* If encrypting, calculate and append tag */ 135 if (do_encrypt) { 136 poly1305_auth(dest + aadlen + len, dest, aadlen + len, 137 poly_key); 138 } 139 r = 0; 140 out: 141 explicit_bzero(expected_tag, sizeof(expected_tag)); 142 explicit_bzero(seqbuf, sizeof(seqbuf)); 143 explicit_bzero(poly_key, sizeof(poly_key)); 144 return r; 145 } 146 147 /* Decrypt and extract the encrypted packet length */ 148 int 149 chachapoly_get_length(struct chachapoly_ctx *ctx, 150 u_int *plenp, u_int seqnr, const u_char *cp, u_int len) 151 { 152 u_char buf[4], seqbuf[16]; 153 154 if (len < 4) 155 return SSH_ERR_MESSAGE_INCOMPLETE; 156 memset(seqbuf, 0, sizeof(seqbuf)); 157 POKE_U64(seqbuf + 8, seqnr); 158 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0)) 159 return SSH_ERR_LIBCRYPTO_ERROR; 160 if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0) 161 return SSH_ERR_LIBCRYPTO_ERROR; 162 *plenp = PEEK_U32(buf); 163 return 0; 164 } 165 #endif /* defined(HAVE_EVP_CHACHA20) && !defined(HAVE_BROKEN_CHACHA20) */ 166