upstream: Initial infrastructure for U2F/FIDO support

Key library support: including allocation, marshalling public/private
keys and certificates, signature validation.

feedback & ok markus@

OpenBSD-Commit-ID: a17615ba15e0f7932ac4360cb18fc9a9544e68c7

1 files changed, 180 insertions, 0 deletions

diff --git a/ssh-ecdsa-sk.c b/ssh-ecdsa-sk.c
new file mode 100644
index 000000000..6441cd7fa
--- /dev/null
+++ b/ssh-ecdsa-sk.c
@@ -0,0 +1,180 @@
+/* $OpenBSD: ssh-ecdsa-sk.c,v 1.1 2019/10/31 21:15:14 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 <sys/types.h>
+
+#include <openssl/bn.h>
+#include <openssl/ec.h>
+#include <openssl/ecdsa.h>
+#include <openssl/evp.h>
+
+#include <string.h>
+#include <stdio.h> /* needed for DEBUG_SK only */
+
+#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)
+{
+        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;
+#ifdef DEBUG_SK
+        char *tmp = NULL;
+#endif
+
+        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) {
+                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 ||
+            sshbuf_get_u8(sigbuf, &sig_flags) != 0 ||
+            sshbuf_get_u32(sigbuf, &sig_counter) != 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: 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)
+                return SSH_ERR_ALLOC_FAIL;
+        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 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;
+#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;
+        }
+
+ 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));
+        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;
+}