/* $NetBSD: cipher-chachapoly.c,v 1.5.20.1 2023/12/25 12:31:03 martin Exp $ */ /* $OpenBSD: cipher-chachapoly.c,v 1.10 2023/07/17 05:26:38 djm Exp $ */ /* * Copyright (c) 2013 Damien Miller * * 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. */ #include "includes.h" __RCSID("$NetBSD: cipher-chachapoly.c,v 1.5.20.1 2023/12/25 12:31:03 martin Exp $"); #include #include /* needed for log.h */ #include #include /* 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; }