diff options
Diffstat (limited to 'cipher-chachapoly.c')
| -rw-r--r-- | cipher-chachapoly.c | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/cipher-chachapoly.c b/cipher-chachapoly.c new file mode 100644 index 0000000..716f8d4 --- /dev/null +++ b/cipher-chachapoly.c @@ -0,0 +1,139 @@ +/* + * Copyright (c) 2013 Damien Miller <djm@mindrot.org> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +/* $OpenBSD: cipher-chachapoly.c,v 1.9 2020/04/03 04:27:03 djm Exp $ */ + +#include "includes.h" +#ifdef WITH_OPENSSL +#include "openbsd-compat/openssl-compat.h" +#endif + +#if !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20) + +#include <sys/types.h> +#include <stdarg.h> /* needed for log.h */ +#include <string.h> +#include <stdio.h> /* needed for misc.h */ + +#include "log.h" +#include "sshbuf.h" +#include "ssherr.h" +#include "cipher-chachapoly.h" + +struct chachapoly_ctx { + struct chacha_ctx main_ctx, header_ctx; +}; + +struct chachapoly_ctx * +chachapoly_new(const u_char *key, u_int keylen) +{ + struct chachapoly_ctx *ctx; + + if (keylen != (32 + 32)) /* 2 x 256 bit keys */ + return NULL; + if ((ctx = calloc(1, sizeof(*ctx))) == NULL) + return NULL; + chacha_keysetup(&ctx->main_ctx, key, 256); + chacha_keysetup(&ctx->header_ctx, key + 32, 256); + return ctx; +} + +void +chachapoly_free(struct chachapoly_ctx *cpctx) +{ + freezero(cpctx, sizeof(*cpctx)); +} + +/* + * chachapoly_crypt() operates as following: + * En/decrypt with header key 'aadlen' bytes from 'src', storing result + * to 'dest'. The ciphertext here is treated as additional authenticated + * data for MAC calculation. + * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use + * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication + * tag. This tag is written on encryption and verified on decryption. + */ +int +chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest, + const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt) +{ + u_char seqbuf[8]; + const u_char one[8] = { 1, 0, 0, 0, 0, 0, 0, 0 }; /* NB little-endian */ + u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN]; + int r = SSH_ERR_INTERNAL_ERROR; + + /* + * Run ChaCha20 once to generate the Poly1305 key. The IV is the + * packet sequence number. + */ + memset(poly_key, 0, sizeof(poly_key)); + POKE_U64(seqbuf, seqnr); + chacha_ivsetup(&ctx->main_ctx, seqbuf, NULL); + chacha_encrypt_bytes(&ctx->main_ctx, + poly_key, poly_key, sizeof(poly_key)); + + /* If decrypting, check tag before anything else */ + if (!do_encrypt) { + const u_char *tag = src + aadlen + len; + + poly1305_auth(expected_tag, src, aadlen + len, poly_key); + if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) { + r = SSH_ERR_MAC_INVALID; + goto out; + } + } + + /* Crypt additional data */ + if (aadlen) { + chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); + chacha_encrypt_bytes(&ctx->header_ctx, src, dest, aadlen); + } + + /* Set Chacha's block counter to 1 */ + chacha_ivsetup(&ctx->main_ctx, seqbuf, one); + chacha_encrypt_bytes(&ctx->main_ctx, src + aadlen, + dest + aadlen, len); + + /* If encrypting, calculate and append tag */ + if (do_encrypt) { + poly1305_auth(dest + aadlen + len, dest, aadlen + len, + poly_key); + } + r = 0; + out: + explicit_bzero(expected_tag, sizeof(expected_tag)); + explicit_bzero(seqbuf, sizeof(seqbuf)); + explicit_bzero(poly_key, sizeof(poly_key)); + return r; +} + +/* Decrypt and extract the encrypted packet length */ +int +chachapoly_get_length(struct chachapoly_ctx *ctx, + u_int *plenp, u_int seqnr, const u_char *cp, u_int len) +{ + u_char buf[4], seqbuf[8]; + + if (len < 4) + return SSH_ERR_MESSAGE_INCOMPLETE; + POKE_U64(seqbuf, seqnr); + chacha_ivsetup(&ctx->header_ctx, seqbuf, NULL); + chacha_encrypt_bytes(&ctx->header_ctx, cp, buf, 4); + *plenp = PEEK_U32(buf); + return 0; +} + +#endif /* !defined(HAVE_EVP_CHACHA20) || defined(HAVE_BROKEN_CHACHA20) */ |