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 <sys/types.h> 19 #include <stdarg.h> /* needed for log.h */ 20 #include <string.h> 21 #include <stdio.h> /* needed for misc.h */ 22 23 #include <openssl/evp.h> 24 25 #include "log.h" 26 #include "sshbuf.h" 27 #include "ssherr.h" 28 #include "cipher-chachapoly.h" 29 30 struct chachapoly_ctx { 31 EVP_CIPHER_CTX *main_evp, *header_evp; 32 }; 33 34 struct chachapoly_ctx * 35 chachapoly_new(const u_char *key, u_int keylen) 36 { 37 struct chachapoly_ctx *ctx; 38 39 if (keylen != (32 + 32)) /* 2 x 256 bit keys */ 40 return NULL; 41 if ((ctx = calloc(1, sizeof(*ctx))) == NULL) 42 return NULL; 43 if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL || 44 (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL) 45 goto fail; 46 if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1)) 47 goto fail; 48 if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1)) 49 goto fail; 50 if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16) 51 goto fail; 52 return ctx; 53 fail: 54 chachapoly_free(ctx); 55 return NULL; 56 } 57 58 void 59 chachapoly_free(struct chachapoly_ctx *cpctx) 60 { 61 if (cpctx == NULL) 62 return; 63 EVP_CIPHER_CTX_free(cpctx->main_evp); 64 EVP_CIPHER_CTX_free(cpctx->header_evp); 65 freezero(cpctx, sizeof(*cpctx)); 66 } 67 68 /* 69 * chachapoly_crypt() operates as following: 70 * En/decrypt with header key 'aadlen' bytes from 'src', storing result 71 * to 'dest'. The ciphertext here is treated as additional authenticated 72 * data for MAC calculation. 73 * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use 74 * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication 75 * tag. This tag is written on encryption and verified on decryption. 76 */ 77 int 78 chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, 79 const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) 80 { 81 u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */ 82 int r = SSH_ERR_INTERNAL_ERROR; 83 u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; 84 85 /* 86 * Run ChaCha20 once to generate the Poly1305 key. The IV is the 87 * packet sequence number. 88 */ 89 memset(seqbuf, 0, sizeof(seqbuf)); 90 POKE_U64(seqbuf + 8, seqnr); 91 memset(poly_key, 0, sizeof(poly_key)); 92 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) || 93 EVP_Cipher(ctx->main_evp, poly_key, 94 poly_key, sizeof(poly_key)) < 0) { 95 r = SSH_ERR_LIBCRYPTO_ERROR; 96 goto out; 97 } 98 99 /* If decrypting, check tag before anything else */ 100 if (!do_encrypt) { 101 const u_char *tag = src + aadlen + len; 102 103 poly1305_auth(expected_tag, src, aadlen + len, poly_key); 104 if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) { 105 r = SSH_ERR_MAC_INVALID; 106 goto out; 107 } 108 } 109 110 /* Crypt additional data */ 111 if (aadlen) { 112 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) || 113 EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) { 114 r = SSH_ERR_LIBCRYPTO_ERROR; 115 goto out; 116 } 117 } 118 119 /* Set Chacha's block counter to 1 */ 120 seqbuf[0] = 1; 121 if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) || 122 EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) { 123 r = SSH_ERR_LIBCRYPTO_ERROR; 124 goto out; 125 } 126 127 /* If encrypting, calculate and append tag */ 128 if (do_encrypt) { 129 poly1305_auth(dest + aadlen + len, dest, aadlen + len, 130 poly_key); 131 } 132 r = 0; 133 out: 134 explicit_bzero(expected_tag, sizeof(expected_tag)); 135 explicit_bzero(seqbuf, sizeof(seqbuf)); 136 explicit_bzero(poly_key, sizeof(poly_key)); 137 return r; 138 } 139 140 /* Decrypt and extract the encrypted packet length */ 141 int 142 chachapoly_get_length(struct chachapoly_ctx *ctx, 143 u_int *plenp, u_int seqnr, const u_char *cp, u_int len) 144 { 145 u_char buf[4], seqbuf[16]; 146 147 if (len < 4) 148 return SSH_ERR_MESSAGE_INCOMPLETE; 149 memset(seqbuf, 0, sizeof(seqbuf)); 150 POKE_U64(seqbuf + 8, seqnr); 151 if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0)) 152 return SSH_ERR_LIBCRYPTO_ERROR; 153 if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0) 154 return SSH_ERR_LIBCRYPTO_ERROR; 155 *plenp = PEEK_U32(buf); 156 return 0; 157 } 158