/* $OpenBSD: ssh-sk.c,v 1.19 2019/12/30 09:20:36 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 #include #include #include #include #ifdef WITH_OPENSSL #include #include #endif /* WITH_OPENSSL */ #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" #include "crypto_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)(int alg, 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)(int alg, 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); }; /* Built-in version */ int ssh_sk_enroll(int alg, const uint8_t *challenge, size_t challenge_len, const char *application, uint8_t flags, struct sk_enroll_response **enroll_response); int ssh_sk_sign(int alg, 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; } /* Skip the rest if we're using the linked in middleware */ if (strcasecmp(ret->path, "internal") == 0) { #ifdef ENABLE_SK_INTERNAL ret->sk_enroll = ssh_sk_enroll; ret->sk_sign = ssh_sk_sign; #else error("internal security key support not enabled"); #endif return ret; } 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)); } #ifdef WITH_OPENSSL /* Assemble key from response */ static int sshsk_ecdsa_assemble(struct sk_enroll_response *resp, struct sshkey **keyp) { struct sshkey *key = NULL; struct sshbuf *b = NULL; EC_POINT *q = NULL; int r; *keyp = NULL; 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; if ((key->ecdsa = EC_KEY_new_by_curve_name(key->ecdsa_nid)) == NULL || (q = EC_POINT_new(EC_KEY_get0_group(key->ecdsa))) == 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 ((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; } /* success */ *keyp = key; key = NULL; /* transferred */ r = 0; out: EC_POINT_free(q); sshkey_free(key); sshbuf_free(b); return r; } #endif /* WITH_OPENSSL */ static int sshsk_ed25519_assemble(struct sk_enroll_response *resp, struct sshkey **keyp) { struct sshkey *key = NULL; int r; *keyp = NULL; if (resp->public_key_len != ED25519_PK_SZ) { error("%s: invalid size: %zu", __func__, resp->public_key_len); r = SSH_ERR_INVALID_FORMAT; goto out; } if ((key = sshkey_new(KEY_ED25519_SK)) == NULL) { error("%s: sshkey_new failed", __func__); r = SSH_ERR_ALLOC_FAIL; goto out; } if ((key->ed25519_pk = malloc(ED25519_PK_SZ)) == NULL) { error("%s: malloc failed", __func__); r = SSH_ERR_ALLOC_FAIL; goto out; } memcpy(key->ed25519_pk, resp->public_key, ED25519_PK_SZ); /* success */ *keyp = key; key = NULL; /* transferred */ r = 0; out: sshkey_free(key); return r; } static int sshsk_key_from_response(int alg, const char *application, uint8_t flags, struct sk_enroll_response *resp, struct sshkey **keyp) { struct sshkey *key = NULL; int r = SSH_ERR_INTERNAL_ERROR; *keyp = NULL; /* Check response validity */ if (resp->public_key == NULL || resp->key_handle == NULL || resp->signature == NULL || (resp->attestation_cert == NULL && resp->attestation_cert_len != 0)) { error("%s: sk_enroll response invalid", __func__); r = SSH_ERR_INVALID_FORMAT; goto out; } switch (alg) { #ifdef WITH_OPENSSL case SSH_SK_ECDSA: if ((r = sshsk_ecdsa_assemble(resp, &key)) != 0) goto out; break; #endif /* WITH_OPENSSL */ case SSH_SK_ED25519: if ((r = sshsk_ed25519_assemble(resp, &key)) != 0) goto out; break; default: error("%s: unsupported algorithm %d", __func__, alg); r = SSH_ERR_INVALID_ARGUMENT; goto out; } key->sk_flags = flags; if ((key->sk_key_handle = sshbuf_new()) == NULL || (key->sk_reserved = sshbuf_new()) == NULL) { error("%s: allocation failed", __func__); r = SSH_ERR_ALLOC_FAIL; 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_put(key->sk_key_handle, resp->key_handle, resp->key_handle_len)) != 0) { error("%s: buffer error: %s", __func__, ssh_err(r)); goto out; } /* success */ r = 0; *keyp = key; key = NULL; out: sshkey_free(key); return r; } int sshsk_enroll(int type, 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; int alg; debug("%s: provider \"%s\", application \"%s\", flags 0x%02x, " "challenge len %zu", __func__, provider_path, application, flags, challenge_buf == NULL ? 0 : sshbuf_len(challenge_buf)); *keyp = NULL; if (attest) sshbuf_reset(attest); switch (type) { #ifdef WITH_OPENSSL case KEY_ECDSA_SK: alg = SSH_SK_ECDSA; break; #endif /* WITH_OPENSSL */ case KEY_ED25519_SK: alg = SSH_SK_ED25519; break; default: error("%s: unsupported key type", __func__); r = SSH_ERR_INVALID_ARGUMENT; goto out; } 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(alg, 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; } if ((r = sshsk_key_from_response(alg, application, flags, resp, &key)) != 0) 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: sshsk_free(skp); sshkey_free(key); sshsk_free_enroll_response(resp); explicit_bzero(randchall, sizeof(randchall)); return r; } #ifdef WITH_OPENSSL static int sshsk_ecdsa_sig(struct sk_sign_response *resp, struct sshbuf *sig) { struct sshbuf *inner_sig = NULL; int r = SSH_ERR_INTERNAL_ERROR; /* Check response validity */ if (resp->sig_r == NULL || resp->sig_s == NULL) { error("%s: sk_sign response invalid", __func__); r = SSH_ERR_INVALID_FORMAT; goto out; } if ((inner_sig = sshbuf_new()) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } /* Prepare and append 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) { debug("%s: buffer error: %s", __func__, ssh_err(r)); goto out; } if ((r = sshbuf_put_stringb(sig, inner_sig)) != 0 || (r = sshbuf_put_u8(sig, resp->flags)) != 0 || (r = sshbuf_put_u32(sig, resp->counter)) != 0) { debug("%s: buffer error: %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: inner:\n", __func__); sshbuf_dump(inner_sig, stderr); #endif r = 0; out: sshbuf_free(inner_sig); return r; } #endif /* WITH_OPENSSL */ static int sshsk_ed25519_sig(struct sk_sign_response *resp, struct sshbuf *sig) { int r = SSH_ERR_INTERNAL_ERROR; /* Check response validity */ if (resp->sig_r == NULL) { error("%s: sk_sign response invalid", __func__); r = SSH_ERR_INVALID_FORMAT; goto out; } if ((r = sshbuf_put_string(sig, resp->sig_r, resp->sig_r_len)) != 0 || (r = sshbuf_put_u8(sig, resp->flags)) != 0 || (r = sshbuf_put_u32(sig, resp->counter)) != 0) { debug("%s: buffer error: %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); #endif r = 0; out: return 0; } int sshsk_sign(const char *provider_path, 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; int type, alg; struct sk_sign_response *resp = NULL; struct sshbuf *inner_sig = NULL, *sig = NULL; uint8_t message[32]; debug("%s: provider \"%s\", key %s, flags 0x%02x", __func__, provider_path, sshkey_type(key), key->sk_flags); if (sigp != NULL) *sigp = NULL; if (lenp != NULL) *lenp = 0; type = sshkey_type_plain(key->type); switch (type) { #ifdef WITH_OPENSSL case KEY_ECDSA_SK: alg = SSH_SK_ECDSA; break; #endif /* WITH_OPENSSL */ case KEY_ED25519_SK: alg = SSH_SK_ED25519; break; default: return SSH_ERR_INVALID_ARGUMENT; } if (provider_path == NULL || 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(alg, 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; } /* Assemble signature */ if ((sig = sshbuf_new()) == NULL) { r = SSH_ERR_ALLOC_FAIL; goto out; } if ((r = sshbuf_put_cstring(sig, sshkey_ssh_name_plain(key))) != 0) { debug("%s: buffer error (outer): %s", __func__, ssh_err(r)); goto out; } switch (type) { #ifdef WITH_OPENSSL case KEY_ECDSA_SK: if ((r = sshsk_ecdsa_sig(resp, sig)) != 0) goto out; break; #endif /* WITH_OPENSSL */ case KEY_ED25519_SK: if ((r = sshsk_ed25519_sig(resp, sig)) != 0) goto out; break; } #ifdef DEBUG_SK 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: 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 */