| /* $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" |
| |
| #ifdef ENABLE_SK |
| |
| #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; |
| } |
| #endif /* ENABLE_SK */ |