upstream: U2F/FIDO middleware interface

Supports enrolling (generating) keys and signatures.

feedback & ok markus@

OpenBSD-Commit-ID: 73d1dd5939454f9c7bd840f48236cba41e8ad592

1 files changed, 377 insertions, 0 deletions

diff --git a/ssh-sk.c b/ssh-sk.c
new file mode 100644
index 000000000..7d313f57b
--- /dev/null
+++ b/ssh-sk.c
@@ -0,0 +1,377 @@
+/* $OpenBSD: ssh-sk.c,v 1.1 2019/10/31 21:16:20 djm Exp $ */
+/*
+ * Copyright (c) 2019 Google LLC
+ *
+ * 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.
+ */
+
+/* #define DEBUG_SK 1 */
+
+#include "includes.h"
+
+#include <dlfcn.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdio.h>
+
+#include <openssl/objects.h>
+#include <openssl/ec.h>
+
+#include "log.h"
+#include "misc.h"
+#include "sshbuf.h"
+#include "sshkey.h"
+#include "ssherr.h"
+#include "digest.h"
+
+#include "ssh-sk.h"
+#include "sk-api.h"
+
+struct sshsk_provider {
+        char *path;
+        void *dlhandle;
+
+        /* Return the version of the middleware API */
+        uint32_t (*sk_api_version)(void);
+
+        /* Enroll a U2F key (private key generation) */
+        int (*sk_enroll)(const uint8_t *challenge, size_t challenge_len,
+            const char *application, uint8_t flags,
+            struct sk_enroll_response **enroll_response);
+
+        /* Sign a challenge */
+        int (*sk_sign)(const uint8_t *message, size_t message_len,
+            const char *application,
+            const uint8_t *key_handle, size_t key_handle_len,
+            uint8_t flags, struct sk_sign_response **sign_response);
+};
+
+static void
+sshsk_free(struct sshsk_provider *p)
+{
+        if (p == NULL)
+                return;
+        free(p->path);
+        if (p->dlhandle != NULL)
+                dlclose(p->dlhandle);
+        free(p);
+}
+
+static struct sshsk_provider *
+sshsk_open(const char *path)
+{
+        struct sshsk_provider *ret = NULL;
+        uint32_t version;
+
+        if ((ret = calloc(1, sizeof(*ret))) == NULL) {
+                error("%s: calloc failed", __func__);
+                return NULL;
+        }
+        if ((ret->path = strdup(path)) == NULL) {
+                error("%s: strdup failed", __func__);
+                goto fail;
+        }
+        if ((ret->dlhandle = dlopen(path, RTLD_NOW)) == NULL) {
+                error("Security key provider %s dlopen failed: %s",
+                    path, dlerror());
+                goto fail;
+        }
+        if ((ret->sk_api_version = dlsym(ret->dlhandle,
+            "sk_api_version")) == NULL) {
+                error("Security key provider %s dlsym(sk_api_version) "
+                    "failed: %s", path, dlerror());
+                goto fail;
+        }
+        version = ret->sk_api_version();
+        debug("%s: provider %s implements version 0x%08lx", __func__,
+            ret->path, (u_long)version);
+        if ((version & SSH_SK_VERSION_MAJOR_MASK) != SSH_SK_VERSION_MAJOR) {
+                error("Security key provider %s implements unsupported version "
+                    "0x%08lx (supported: 0x%08lx)", path, (u_long)version,
+                    (u_long)SSH_SK_VERSION_MAJOR);
+                goto fail;
+        }
+        if ((ret->sk_enroll = dlsym(ret->dlhandle, "sk_enroll")) == NULL) {
+                error("Security key  provider %s dlsym(sk_enroll) "
+                    "failed: %s", path, dlerror());
+                goto fail;
+        }
+        if ((ret->sk_sign = dlsym(ret->dlhandle, "sk_sign")) == NULL) {
+                error("Security key provider %s dlsym(sk_sign) failed: %s",
+                    path, dlerror());
+                goto fail;
+        }
+        /* success */
+        return ret;
+fail:
+        sshsk_free(ret);
+        return NULL;
+}
+
+static void
+sshsk_free_enroll_response(struct sk_enroll_response *r)
+{
+        if (r == NULL)
+                return;
+        freezero(r->key_handle, r->key_handle_len);
+        freezero(r->public_key, r->public_key_len);
+        freezero(r->signature, r->signature_len);
+        freezero(r->attestation_cert, r->attestation_cert_len);
+        freezero(r, sizeof(*r));
+};
+
+static void
+sshsk_free_sign_response(struct sk_sign_response *r)
+{
+        if (r == NULL)
+                return;
+        freezero(r->sig_r, r->sig_r_len);
+        freezero(r->sig_s, r->sig_s_len);
+        freezero(r, sizeof(*r));
+};
+
+int
+sshsk_enroll(const char *provider_path, const char *application,
+    uint8_t flags, struct sshbuf *challenge_buf, struct sshkey **keyp,
+    struct sshbuf *attest)
+{
+        struct sshsk_provider *skp = NULL;
+        struct sshkey *key = NULL;
+        u_char randchall[32];
+        const u_char *challenge;
+        size_t challenge_len;
+        struct sk_enroll_response *resp = NULL;
+        int r = SSH_ERR_INTERNAL_ERROR;
+        struct sshbuf *b = NULL;
+        EC_POINT *q = NULL;
+
+        *keyp = NULL;
+        if (attest)
+                sshbuf_reset(attest);
+        if (provider_path == NULL) {
+                error("%s: missing provider", __func__);
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        }
+        if (application == NULL || *application == '\0') {
+                error("%s: missing application", __func__);
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        }
+        if (challenge_buf == NULL) {
+                debug("%s: using random challenge", __func__);
+                arc4random_buf(randchall, sizeof(randchall));
+                challenge = randchall;
+                challenge_len = sizeof(randchall);
+        } else if (sshbuf_len(challenge_buf) == 0) {
+                error("Missing enrollment challenge");
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        } else {
+                challenge = sshbuf_ptr(challenge_buf);
+                challenge_len = sshbuf_len(challenge_buf);
+                debug3("%s: using explicit challenge len=%zd",
+                    __func__, challenge_len);
+        }
+        if ((skp = sshsk_open(provider_path)) == NULL) {
+                r = SSH_ERR_INVALID_FORMAT; /* XXX sshsk_open return code? */
+                goto out;
+        }
+        /* XXX validate flags? */
+        /* enroll key */
+        if ((r = skp->sk_enroll(challenge, challenge_len, application,
+            flags, &resp)) != 0) {
+                error("Security key provider %s returned failure %d",
+                    provider_path, r);
+                r = SSH_ERR_INVALID_FORMAT; /* XXX error codes in API? */
+                goto out;
+        }
+        /* Check response validity */
+        if (resp->public_key == NULL || resp->key_handle == NULL ||
+            resp->signature == NULL || resp->attestation_cert == NULL) {
+                error("%s: sk_enroll response invalid", __func__);
+                r = SSH_ERR_INVALID_FORMAT;
+                goto out;
+        }
+        /* Assemble key from response */
+        if ((key = sshkey_new(KEY_ECDSA_SK)) == NULL) {
+                error("%s: sshkey_new failed", __func__);
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        key->ecdsa_nid = NID_X9_62_prime256v1;
+        key->sk_flags = flags;
+        if ((key->ecdsa = EC_KEY_new_by_curve_name(key->ecdsa_nid)) == NULL ||
+            (q = EC_POINT_new(EC_KEY_get0_group(key->ecdsa))) == NULL ||
+            (key->sk_key_handle = sshbuf_new()) == NULL ||
+            (key->sk_reserved = sshbuf_new()) == NULL ||
+            (b = sshbuf_new()) == NULL) {
+                error("%s: allocation failed", __func__);
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = sshbuf_put_string(b,
+            resp->public_key, resp->public_key_len)) != 0) {
+                error("%s: buffer error: %s", __func__, ssh_err(r));
+                goto out;
+        }
+        if ((key->sk_application = strdup(application)) == NULL) {
+                error("%s: strdup application failed", __func__);
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = sshbuf_get_ec(b, q, EC_KEY_get0_group(key->ecdsa))) != 0) {
+                error("%s: parse key: %s", __func__, ssh_err(r));
+                r = SSH_ERR_INVALID_FORMAT;
+                goto out;
+        }
+        if (sshkey_ec_validate_public(EC_KEY_get0_group(key->ecdsa), q) != 0) {
+                error("Security key returned invalid ECDSA key");
+                r = SSH_ERR_KEY_INVALID_EC_VALUE;
+                goto out;
+        }
+        if (EC_KEY_set_public_key(key->ecdsa, q) != 1) {
+                /* XXX assume it is a allocation error */
+                error("%s: allocation failed", __func__);
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = sshbuf_put(key->sk_key_handle, resp->key_handle,
+            resp->key_handle_len)) != 0) {
+                error("%s: buffer error: %s", __func__, ssh_err(r));
+                goto out;
+        }
+        /* Optionally fill in the attestation information */
+        if (attest != NULL) {
+                if ((r = sshbuf_put_cstring(attest, "sk-attest-v00")) != 0 ||
+                    (r = sshbuf_put_u32(attest, 1)) != 0 || /* XXX U2F ver */
+                    (r = sshbuf_put_string(attest,
+                    resp->attestation_cert, resp->attestation_cert_len)) != 0 ||
+                    (r = sshbuf_put_string(attest,
+                    resp->signature, resp->signature_len)) != 0 ||
+                    (r = sshbuf_put_u32(attest, flags)) != 0 || /* XXX right? */
+                    (r = sshbuf_put_string(attest, NULL, 0)) != 0) {
+                        error("%s: buffer error: %s", __func__, ssh_err(r));
+                        goto out;
+                }
+        }
+        /* success */
+        *keyp = key;
+        key = NULL; /* transferred */
+        r = 0;
+ out:
+        EC_POINT_free(q);
+        sshsk_free(skp);
+        sshbuf_free(b);
+        sshkey_free(key);
+        sshsk_free_enroll_response(resp);
+        explicit_bzero(randchall, sizeof(randchall));
+        return r;
+}
+
+int
+sshsk_ecdsa_sign(const char *provider_path, const struct sshkey *key,
+    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
+    u_int compat)
+{
+        struct sshsk_provider *skp = NULL;
+        int r = SSH_ERR_INTERNAL_ERROR;
+        struct sk_sign_response *resp = NULL;
+        struct sshbuf *inner_sig = NULL, *sig = NULL;
+        uint8_t message[32];
+
+        if (sigp != NULL)
+                *sigp = NULL;
+        if (lenp != NULL)
+                *lenp = 0;
+        if (provider_path == NULL ||
+            sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
+            key->sk_key_handle == NULL ||
+            key->sk_application == NULL || *key->sk_application == '\0') {
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        }
+        if ((skp = sshsk_open(provider_path)) == NULL) {
+                r = SSH_ERR_INVALID_FORMAT; /* XXX sshsk_open return code? */
+                goto out;
+        }
+
+        /* hash data to be signed before it goes to the security key */
+        if ((r = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen,
+            message, sizeof(message))) != 0) {
+                error("%s: hash application failed: %s", __func__, ssh_err(r));
+                r = SSH_ERR_INTERNAL_ERROR;
+                goto out;
+        }
+        if ((r = skp->sk_sign(message, sizeof(message),
+            key->sk_application,
+            sshbuf_ptr(key->sk_key_handle), sshbuf_len(key->sk_key_handle),
+            key->sk_flags, &resp)) != 0) {
+                debug("%s: sk_sign failed with code %d", __func__, r);
+                goto out;
+        }
+        if ((sig = sshbuf_new()) == NULL ||
+            (inner_sig = sshbuf_new()) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        /* Prepare inner signature object */
+        if ((r = sshbuf_put_bignum2_bytes(inner_sig,
+            resp->sig_r, resp->sig_r_len)) != 0 ||
+            (r = sshbuf_put_bignum2_bytes(inner_sig,
+            resp->sig_s, resp->sig_s_len)) != 0 ||
+            (r = sshbuf_put_u8(inner_sig, resp->flags)) != 0 ||
+            (r = sshbuf_put_u32(inner_sig, resp->counter)) != 0) {
+                debug("%s: buffer error (inner): %s", __func__, ssh_err(r));
+                goto out;
+        }
+        /* Assemble outer signature */
+        if ((r = sshbuf_put_cstring(sig, sshkey_ssh_name_plain(key))) != 0 ||
+            (r = sshbuf_put_stringb(sig, inner_sig)) != 0) {
+                debug("%s: buffer error (outer): %s", __func__, ssh_err(r));
+                goto out;
+        }
+#ifdef DEBUG_SK
+        fprintf(stderr, "%s: sig_r:\n", __func__);
+        sshbuf_dump_data(resp->sig_r, resp->sig_r_len, stderr);
+        fprintf(stderr, "%s: sig_s:\n", __func__);
+        sshbuf_dump_data(resp->sig_s, resp->sig_s_len, stderr);
+        fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
+            __func__, resp->flags, resp->counter);
+        fprintf(stderr, "%s: hashed message:\n", __func__);
+        sshbuf_dump_data(message, sizeof(message), stderr);
+        fprintf(stderr, "%s: inner:\n", __func__);
+        sshbuf_dump(inner_sig, stderr);
+        fprintf(stderr, "%s: sigbuf:\n", __func__);
+        sshbuf_dump(sig, stderr);
+#endif
+        if (sigp != NULL) {
+                if ((*sigp = malloc(sshbuf_len(sig))) == NULL) {
+                        r = SSH_ERR_ALLOC_FAIL;
+                        goto out;
+                }
+                memcpy(*sigp, sshbuf_ptr(sig), sshbuf_len(sig));
+        }
+        if (lenp != NULL)
+                *lenp = sshbuf_len(sig);
+        /* success */
+        r = 0;
+ out:
+        explicit_bzero(message, sizeof(message));
+        sshsk_free(skp);
+        sshsk_free_sign_response(resp);
+        sshbuf_free(sig);
+        sshbuf_free(inner_sig);
+        return r;
+}