--- /dev/null
+/* $OpenBSD: ssh-verify-attestation.c,v 1.1 2024/12/04 16:42:49 djm Exp $ */
+/*
+ * Copyright (c) 2022-2024 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.
+ */
+
+/*
+ * This is a small program to verify FIDO attestation objects that
+ * ssh-keygen(1) can record when enrolling a FIDO key. It requires that
+ * the attestation object and challenge used when creating the key be
+ * recorded.
+ *
+ * Example usage:
+ *
+ * $ # Generate a random challenge.
+ * $ dd if=/dev/urandom of=key_ecdsa_sk.challenge bs=32 count=1
+ * $ # Generate a key, record the attestation blob.
+ * $ ssh-keygen -f key_ecdsa_sk -t ecdsa-sk \
+ * -Ochallenge=key_ecdsa_sk.challenge \
+ * -Owrite-attestation=key_ecdsa_sk.attest -N ''
+ * $ # Validate the challenge (-A = print attestation CA cert)
+ * $ ./obj/ssh-verify-attestation -A key_ecdsa_sk key_ecdsa_sk.challenge \
+ * key_ecdsa_sk.attest
+ *
+ * Limitations/TODO:
+ *
+ * 1) It doesn't automatically detect the attestation statement format. It
+ * assumes the "packed" format used by FIDO2 keys. If that doesn't work,
+ * then try using the -U option to select the "fido-u2f" format.
+ * 2) Only ECDSA keys are currently supported. Ed25519 support is not yet
+ * implemented.
+ * 3) Probably bugs.
+ *
+ */
+
+#include <stdint.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdarg.h>
+
+#include "xmalloc.h"
+#include "log.h"
+#include "sshbuf.h"
+#include "sshkey.h"
+#include "authfile.h"
+#include "ssherr.h"
+#include "misc.h"
+#include "digest.h"
+
+#include <fido.h>
+#include <openssl/x509.h>
+#include <openssl/x509v3.h>
+#include <openssl/bio.h>
+#include <openssl/err.h>
+#include <openssl/pem.h>
+
+extern char *__progname;
+
+#define ATTEST_MAGIC "ssh-sk-attest-v01"
+
+static int
+prepare_fido_cred(fido_cred_t *cred, int credtype, const char *attfmt,
+ const char *rp_id, struct sshbuf *b, const struct sshbuf *challenge,
+ struct sshbuf **attestation_certp)
+{
+ struct sshbuf *attestation_cert = NULL, *sig = NULL, *authdata = NULL;
+ char *magic = NULL;
+ int r = SSH_ERR_INTERNAL_ERROR;
+
+ *attestation_certp = NULL;
+
+ /* Make sure it's the format we're expecting */
+ if ((r = sshbuf_get_cstring(b, &magic, NULL)) != 0) {
+ error_fr(r, "parse header");
+ goto out;
+ }
+ if (strcmp(magic, ATTEST_MAGIC) != 0) {
+ error_f("unsupported format");
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ /* Parse the remaining fields */
+ if ((r = sshbuf_froms(b, &attestation_cert)) != 0 ||
+ (r = sshbuf_froms(b, &sig)) != 0 ||
+ (r = sshbuf_froms(b, &authdata)) != 0 ||
+ (r = sshbuf_get_u32(b, NULL)) != 0 || /* reserved flags */
+ (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) { /* reserved */
+ error_fr(r, "parse body");
+ goto out;
+ }
+ debug3_f("blob len=%zu, attestation cert len=%zu, sig len=%zu, "
+ "authdata len=%zu challenge len=%zu", sshbuf_len(attestation_cert),
+ sshbuf_len(b), sshbuf_len(sig), sshbuf_len(authdata),
+ sshbuf_len(challenge));
+
+ fido_cred_set_type(cred, COSE_ES256);
+ fido_cred_set_fmt(cred, attfmt);
+ fido_cred_set_clientdata(cred, sshbuf_ptr(challenge),
+ sshbuf_len(challenge));
+ fido_cred_set_rp(cred, rp_id, NULL);
+ fido_cred_set_authdata(cred, sshbuf_ptr(authdata),
+ sshbuf_len(authdata));
+ /* XXX set_extensions, set_rk, set_uv */
+ fido_cred_set_x509(cred, sshbuf_ptr(attestation_cert),
+ sshbuf_len(attestation_cert));
+ fido_cred_set_sig(cred, sshbuf_ptr(sig), sshbuf_len(sig));
+
+ /* success */
+ *attestation_certp = attestation_cert;
+ attestation_cert = NULL;
+ r = 0;
+ out:
+ free(magic);
+ sshbuf_free(attestation_cert);
+ sshbuf_free(sig);
+ sshbuf_free(authdata);
+ return r;
+}
+
+static uint8_t *
+get_pubkey_from_cred_ecdsa(const fido_cred_t *cred, size_t *pubkey_len)
+{
+ const uint8_t *ptr;
+ uint8_t *pubkey = NULL, *ret = NULL;
+ BIGNUM *x = NULL, *y = NULL;
+ EC_POINT *q = NULL;
+ EC_GROUP *g = NULL;
+
+ if ((x = BN_new()) == NULL ||
+ (y = BN_new()) == NULL ||
+ (g = EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1)) == NULL ||
+ (q = EC_POINT_new(g)) == NULL) {
+ error_f("libcrypto setup failed");
+ goto out;
+ }
+ if ((ptr = fido_cred_pubkey_ptr(cred)) == NULL) {
+ error_f("fido_cred_pubkey_ptr failed");
+ goto out;
+ }
+ if (fido_cred_pubkey_len(cred) != 64) {
+ error_f("bad fido_cred_pubkey_len %zu",
+ fido_cred_pubkey_len(cred));
+ goto out;
+ }
+
+ if (BN_bin2bn(ptr, 32, x) == NULL ||
+ BN_bin2bn(ptr + 32, 32, y) == NULL) {
+ error_f("BN_bin2bn failed");
+ goto out;
+ }
+ if (EC_POINT_set_affine_coordinates_GFp(g, q, x, y, NULL) != 1) {
+ error_f("EC_POINT_set_affine_coordinates_GFp failed");
+ goto out;
+ }
+ *pubkey_len = EC_POINT_point2oct(g, q,
+ POINT_CONVERSION_UNCOMPRESSED, NULL, 0, NULL);
+ if (*pubkey_len == 0 || *pubkey_len > 2048) {
+ error_f("bad pubkey length %zu", *pubkey_len);
+ goto out;
+ }
+ if ((pubkey = malloc(*pubkey_len)) == NULL) {
+ error_f("malloc pubkey failed");
+ goto out;
+ }
+ if (EC_POINT_point2oct(g, q, POINT_CONVERSION_UNCOMPRESSED,
+ pubkey, *pubkey_len, NULL) == 0) {
+ error_f("EC_POINT_point2oct failed");
+ goto out;
+ }
+ /* success */
+ ret = pubkey;
+ pubkey = NULL;
+ out:
+ free(pubkey);
+ EC_POINT_free(q);
+ EC_GROUP_free(g);
+ BN_clear_free(x);
+ BN_clear_free(y);
+ return ret;
+}
+
+/* copied from sshsk_ecdsa_assemble() */
+static int
+cred_matches_key_ecdsa(const fido_cred_t *cred, const struct sshkey *k)
+{
+ struct sshkey *key = NULL;
+ struct sshbuf *b = NULL;
+ EC_KEY *ec = NULL;
+ uint8_t *pubkey = NULL;
+ size_t pubkey_len;
+ int r;
+
+ if ((key = sshkey_new(KEY_ECDSA_SK)) == NULL) {
+ error_f("sshkey_new failed");
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ key->ecdsa_nid = NID_X9_62_prime256v1;
+ if ((key->pkey = EVP_PKEY_new()) == NULL ||
+ (ec = EC_KEY_new_by_curve_name(key->ecdsa_nid)) == NULL ||
+ (b = sshbuf_new()) == NULL) {
+ error_f("allocation failed");
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((pubkey = get_pubkey_from_cred_ecdsa(cred, &pubkey_len)) == NULL) {
+ error_f("get_pubkey_from_cred_ecdsa failed");
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if ((r = sshbuf_put_string(b, pubkey, pubkey_len)) != 0) {
+ error_fr(r, "sshbuf_put_string");
+ goto out;
+ }
+ if ((r = sshbuf_get_eckey(b, ec)) != 0) {
+ error_fr(r, "parse");
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (sshkey_ec_validate_public(EC_KEY_get0_group(ec),
+ EC_KEY_get0_public_key(ec)) != 0) {
+ error("Authenticator returned invalid ECDSA key");
+ r = SSH_ERR_KEY_INVALID_EC_VALUE;
+ goto out;
+ }
+ if (EVP_PKEY_set1_EC_KEY(key->pkey, ec) != 1) {
+ /* XXX assume it is a allocation error */
+ error_f("allocation failed");
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ key->sk_application = xstrdup(k->sk_application); /* XXX */
+ if (!sshkey_equal_public(key, k)) {
+ error("sshkey_equal_public failed");
+ r = SSH_ERR_INVALID_ARGUMENT;
+ goto out;
+ }
+ r = 0; /* success */
+ out:
+ EC_KEY_free(ec);
+ free(pubkey);
+ sshkey_free(key);
+ sshbuf_free(b);
+ return r;
+}
+
+static int
+cred_matches_key(const fido_cred_t *cred, const struct sshkey *k)
+{
+ switch (sshkey_type_plain(k->type)) {
+ case KEY_ECDSA_SK:
+ return cred_matches_key_ecdsa(cred, k);
+ default:
+ error_f("key type %s not supported", sshkey_type(k));
+ return -1;
+ }
+}
+
+int
+main(int argc, char **argv)
+{
+ LogLevel log_level = SYSLOG_LEVEL_INFO;
+ int r, ch, credtype = -1;
+ struct sshkey *k = NULL;
+ struct sshbuf *attestation = NULL, *challenge = NULL;
+ struct sshbuf *attestation_cert = NULL;
+ char *fp;
+ const char *attfmt = "packed";
+ fido_cred_t *cred = NULL;
+ int write_attestation_cert = 0;
+ extern int optind;
+ /* extern char *optarg; */
+
+ ERR_load_crypto_strings();
+
+ sanitise_stdfd();
+ log_init(__progname, log_level, SYSLOG_FACILITY_AUTH, 1);
+
+ while ((ch = getopt(argc, argv, "UAv")) != -1) {
+ switch (ch) {
+ case 'U':
+ attfmt = "fido-u2f";
+ break;
+ case 'A':
+ write_attestation_cert = 1;
+ break;
+ case 'v':
+ if (log_level == SYSLOG_LEVEL_ERROR)
+ log_level = SYSLOG_LEVEL_DEBUG1;
+ else if (log_level < SYSLOG_LEVEL_DEBUG3)
+ log_level++;
+ break;
+ default:
+ goto usage;
+ }
+ }
+ log_init(__progname, log_level, SYSLOG_FACILITY_AUTH, 1);
+ argv += optind;
+ argc -= optind;
+
+ if (argc < 3) {
+ usage:
+ fprintf(stderr, "usage: %s [-vAU] "
+ "pubkey challenge attestation-blob\n", __progname);
+ exit(1);
+ }
+ if ((r = sshkey_load_public(argv[0], &k, NULL)) != 0)
+ fatal_r(r, "load key %s", argv[0]);
+ if ((fp = sshkey_fingerprint(k, SSH_FP_HASH_DEFAULT,
+ SSH_FP_DEFAULT)) == NULL)
+ fatal("sshkey_fingerprint failed");
+ debug2("key %s: %s %s", argv[2], sshkey_type(k), fp);
+ free(fp);
+ if ((r = sshbuf_load_file(argv[1], &challenge)) != 0)
+ fatal_r(r, "load challenge %s", argv[1]);
+ if ((r = sshbuf_load_file(argv[2], &attestation)) != 0)
+ fatal_r(r, "load attestation %s", argv[2]);
+ if ((cred = fido_cred_new()) == NULL)
+ fatal("fido_cred_new failed");
+
+ switch (sshkey_type_plain(k->type)) {
+ case KEY_ECDSA_SK:
+ credtype = COSE_ES256;
+ break;
+ default:
+ fatal("unsupported key type %s", sshkey_type(k));
+ }
+
+ if ((r = prepare_fido_cred(cred, credtype, attfmt, k->sk_application,
+ attestation, challenge, &attestation_cert)) != 0)
+ fatal_r(r, "prepare_fido_cred %s", argv[2]);
+ if (fido_cred_x5c_ptr(cred) != NULL) {
+ debug("basic attestation");
+ r = fido_cred_verify(cred);
+ } else {
+ debug("self attestation");
+ r = fido_cred_verify_self(cred);
+ }
+ if (r != FIDO_OK)
+ fatal("verification of attestation data failed");
+ if (cred_matches_key(cred, k) != 0)
+ fatal("cred authdata does not match key");
+
+ fido_cred_free(&cred);
+
+ if (write_attestation_cert) {
+ PEM_write(stdout, "CERTIFICATE", NULL,
+ sshbuf_ptr(attestation_cert), sshbuf_len(attestation_cert));
+ }
+ sshbuf_free(attestation_cert);
+
+ logit("%s: GOOD", argv[2]);
+
+ return (0);
+}
projects / thirdparty / openssh-portable.git / commitdiff
