/* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 djm Exp $ */ /* * Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2010 Damien Miller. All rights reserved. * Copyright (c) 2019 Google Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ /* #define DEBUG_SK 1 */ #include "includes.h" #include #ifdef WITH_OPENSSL #include #include #include #include #endif #include #include /* needed for DEBUG_SK only */ #include "openbsd-compat/openssl-compat.h" #include "sshbuf.h" #include "ssherr.h" #include "digest.h" #define SSHKEY_INTERNAL #include "sshkey.h" /* ARGSUSED */ int ssh_ecdsa_sk_verify(const struct sshkey *key, const u_char *signature, size_t signaturelen, const u_char *data, size_t datalen, u_int compat, struct sshkey_sig_details **detailsp) { #ifdef OPENSSL_HAS_ECC ECDSA_SIG *sig = NULL; BIGNUM *sig_r = NULL, *sig_s = NULL; u_char sig_flags; u_char msghash[32], apphash[32], sighash[32]; u_int sig_counter; int ret = SSH_ERR_INTERNAL_ERROR; struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL; char *ktype = NULL; struct sshkey_sig_details *details = NULL; #ifdef DEBUG_SK char *tmp = NULL; #endif if (detailsp != NULL) *detailsp = NULL; if (key == NULL || key->ecdsa == NULL || sshkey_type_plain(key->type) != KEY_ECDSA_SK || signature == NULL || signaturelen == 0) return SSH_ERR_INVALID_ARGUMENT; if (key->ecdsa_nid != NID_X9_62_prime256v1) return SSH_ERR_INTERNAL_ERROR; /* fetch signature */ if ((b = sshbuf_from(signature, signaturelen)) == NULL) return SSH_ERR_ALLOC_FAIL; if (sshbuf_get_cstring(b, &ktype, NULL) != 0 || sshbuf_froms(b, &sigbuf) != 0 || sshbuf_get_u8(b, &sig_flags) != 0 || sshbuf_get_u32(b, &sig_counter) != 0) { ret = SSH_ERR_INVALID_FORMAT; goto out; } if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) { ret = SSH_ERR_KEY_TYPE_MISMATCH; goto out; } if (sshbuf_len(b) != 0) { ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; goto out; } /* parse signature */ if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 || sshbuf_get_bignum2(sigbuf, &sig_s) != 0) { ret = SSH_ERR_INVALID_FORMAT; goto out; } if ((sig = ECDSA_SIG_new()) == NULL) { ret = SSH_ERR_ALLOC_FAIL; goto out; } if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) { ret = SSH_ERR_LIBCRYPTO_ERROR; goto out; } #ifdef DEBUG_SK fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen); /* sshbuf_dump_data(data, datalen, stderr); */ fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r))); free(tmp); fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s))); free(tmp); fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n", __func__, sig_flags, sig_counter); #endif sig_r = sig_s = NULL; /* transferred */ if (sshbuf_len(sigbuf) != 0) { ret = SSH_ERR_UNEXPECTED_TRAILING_DATA; goto out; } /* Reconstruct data that was supposedly signed */ if ((original_signed = sshbuf_new()) == NULL) { ret = SSH_ERR_ALLOC_FAIL; goto out; } if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen, msghash, sizeof(msghash))) != 0) goto out; /* Application value is hashed before signature */ if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application, strlen(key->sk_application), apphash, sizeof(apphash))) != 0) goto out; #ifdef DEBUG_SK fprintf(stderr, "%s: hashed application:\n", __func__); sshbuf_dump_data(apphash, sizeof(apphash), stderr); fprintf(stderr, "%s: hashed message:\n", __func__); sshbuf_dump_data(msghash, sizeof(msghash), stderr); #endif if ((ret = sshbuf_put(original_signed, apphash, sizeof(apphash))) != 0 || (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 || (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 || (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0) goto out; /* Signature is over H(original_signed) */ if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed, sighash, sizeof(sighash))) != 0) goto out; if ((details = calloc(1, sizeof(*details))) == NULL) { ret = SSH_ERR_ALLOC_FAIL; goto out; } details->sk_counter = sig_counter; details->sk_flags = sig_flags; #ifdef DEBUG_SK fprintf(stderr, "%s: signed buf:\n", __func__); sshbuf_dump(original_signed, stderr); fprintf(stderr, "%s: signed hash:\n", __func__); sshbuf_dump_data(sighash, sizeof(sighash), stderr); #endif /* Verify it */ switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) { case 1: ret = 0; break; case 0: ret = SSH_ERR_SIGNATURE_INVALID; goto out; default: ret = SSH_ERR_LIBCRYPTO_ERROR; goto out; } /* success */ if (detailsp != NULL) { *detailsp = details; details = NULL; } out: explicit_bzero(&sig_flags, sizeof(sig_flags)); explicit_bzero(&sig_counter, sizeof(sig_counter)); explicit_bzero(msghash, sizeof(msghash)); explicit_bzero(sighash, sizeof(msghash)); explicit_bzero(apphash, sizeof(apphash)); sshkey_sig_details_free(details); sshbuf_free(original_signed); sshbuf_free(sigbuf); sshbuf_free(b); ECDSA_SIG_free(sig); BN_clear_free(sig_r); BN_clear_free(sig_s); free(ktype); return ret; #else return SSH_ERR_INTERNAL_ERROR; #endif }