ssh-pkcs11-client.c - platform/external/openssh - Gitiles

 /* $OpenBSD: ssh-pkcs11-client.c,v 1.14 2019/01/20 22:57:45 djm Exp $ */
 /*
  * Copyright (c) 2010 Markus Friedl.  All rights reserved.
  * Copyright (c) 2014 Pedro Martelletto. All rights reserved.
  *
  * 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.
  */

 #include "includes.h"

 #ifdef ENABLE_PKCS11

 #include <sys/types.h>
 #ifdef HAVE_SYS_TIME_H
 # include <sys/time.h>
 #endif
 #include <sys/socket.h>

 #include <stdarg.h>
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>

 #include <openssl/ecdsa.h>
 #include <openssl/rsa.h>

 #include "openbsd-compat/openssl-compat.h"

 #include "pathnames.h"
 #include "xmalloc.h"
 #include "sshbuf.h"
 #include "log.h"
 #include "misc.h"
 #include "sshkey.h"
 #include "authfd.h"
 #include "atomicio.h"
 #include "ssh-pkcs11.h"
 #include "ssherr.h"

 /* borrows code from sftp-server and ssh-agent */

 int fd = -1;
 pid_t pid = -1;

 static void
 send_msg(struct sshbuf *m)
 {
 	u_char buf[4];
 	size_t mlen = sshbuf_len(m);
 	int r;

 	POKE_U32(buf, mlen);
 	if (atomicio(vwrite, fd, buf, 4) != 4 ||
 	    atomicio(vwrite, fd, sshbuf_mutable_ptr(m),
 	    sshbuf_len(m)) != sshbuf_len(m))
 		error("write to helper failed");
 	if ((r = sshbuf_consume(m, mlen)) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 }

 static int
 recv_msg(struct sshbuf *m)
 {
 	u_int l, len;
 	u_char c, buf[1024];
 	int r;

 	if ((len = atomicio(read, fd, buf, 4)) != 4) {
 		error("read from helper failed: %u", len);
 		return (0); /* XXX */
 	}
 	len = PEEK_U32(buf);
 	if (len > 256 * 1024)
 		fatal("response too long: %u", len);
 	/* read len bytes into m */
 	sshbuf_reset(m);
 	while (len > 0) {
 		l = len;
 		if (l > sizeof(buf))
 			l = sizeof(buf);
 		if (atomicio(read, fd, buf, l) != l) {
 			error("response from helper failed.");
 			return (0); /* XXX */
 		}
 		if ((r = sshbuf_put(m, buf, l)) != 0)
 			fatal("%s: buffer error: %s", __func__, ssh_err(r));
 		len -= l;
 	}
 	if ((r = sshbuf_get_u8(m, &c)) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 	return c;
 }

 int
 pkcs11_init(int interactive)
 {
 	return (0);
 }

 void
 pkcs11_terminate(void)
 {
 	if (fd >= 0)
 		close(fd);
 }

 static int
 rsa_encrypt(int flen, const u_char *from, u_char *to, RSA *rsa, int padding)
 {
 	struct sshkey *key = NULL;
 	struct sshbuf *msg = NULL;
 	u_char *blob = NULL, *signature = NULL;
 	size_t blen, slen = 0;
 	int r, ret = -1;

 	if (padding != RSA_PKCS1_PADDING)
 		goto fail;
 	key = sshkey_new(KEY_UNSPEC);
 	if (key == NULL) {
 		error("%s: sshkey_new failed", __func__);
 		goto fail;
 	}
 	key->type = KEY_RSA;
 	RSA_up_ref(rsa);
 	key->rsa = rsa;
 	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
 		error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
 		goto fail;
 	}
 	if ((msg = sshbuf_new()) == NULL)
 		fatal("%s: sshbuf_new failed", __func__);
 	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
 	    (r = sshbuf_put_string(msg, blob, blen)) != 0 ||
 	    (r = sshbuf_put_string(msg, from, flen)) != 0 ||
 	    (r = sshbuf_put_u32(msg, 0)) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 	send_msg(msg);
 	sshbuf_reset(msg);

 	if (recv_msg(msg) == SSH2_AGENT_SIGN_RESPONSE) {
 		if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
 			fatal("%s: buffer error: %s", __func__, ssh_err(r));
 		if (slen <= (size_t)RSA_size(rsa)) {
 			memcpy(to, signature, slen);
 			ret = slen;
 		}
 		free(signature);
 	}
  fail:
 	free(blob);
 	sshkey_free(key);
 	sshbuf_free(msg);
 	return (ret);
 }

 #ifdef HAVE_EC_KEY_METHOD_NEW
 static ECDSA_SIG *
 ecdsa_do_sign(const unsigned char *dgst, int dgst_len, const BIGNUM *inv,
     const BIGNUM *rp, EC_KEY *ec)
 {
 	struct sshkey *key = NULL;
 	struct sshbuf *msg = NULL;
 	ECDSA_SIG *ret = NULL;
 	const u_char *cp;
 	u_char *blob = NULL, *signature = NULL;
 	size_t blen, slen = 0;
 	int r, nid;

 	nid = sshkey_ecdsa_key_to_nid(ec);
 	if (nid < 0) {
 		error("%s: couldn't get curve nid", __func__);
 		goto fail;
 	}

 	key = sshkey_new(KEY_UNSPEC);
 	if (key == NULL) {
 		error("%s: sshkey_new failed", __func__);
 		goto fail;
 	}
 	key->ecdsa = ec;
 	key->ecdsa_nid = nid;
 	key->type = KEY_ECDSA;
 	EC_KEY_up_ref(ec);

 	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
 		error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
 		goto fail;
 	}
 	if ((msg = sshbuf_new()) == NULL)
 		fatal("%s: sshbuf_new failed", __func__);
 	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
 	    (r = sshbuf_put_string(msg, blob, blen)) != 0 ||
 	    (r = sshbuf_put_string(msg, dgst, dgst_len)) != 0 ||
 	    (r = sshbuf_put_u32(msg, 0)) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 	send_msg(msg);
 	sshbuf_reset(msg);

 	if (recv_msg(msg) == SSH2_AGENT_SIGN_RESPONSE) {
 		if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
 			fatal("%s: buffer error: %s", __func__, ssh_err(r));
 		cp = signature;
 		ret = d2i_ECDSA_SIG(NULL, &cp, slen);
 		free(signature);
 	}

  fail:
 	free(blob);
 	sshkey_free(key);
 	sshbuf_free(msg);
 	return (ret);
 }
 #endif /* HAVE_EC_KEY_METHOD_NEW */

 static RSA_METHOD	*helper_rsa;
 #ifdef HAVE_EC_KEY_METHOD_NEW
 static EC_KEY_METHOD	*helper_ecdsa;
 #endif /* HAVE_EC_KEY_METHOD_NEW */

 /* redirect private key crypto operations to the ssh-pkcs11-helper */
 static void
 wrap_key(struct sshkey *k)
 {
 	if (k->type == KEY_RSA)
 		RSA_set_method(k->rsa, helper_rsa);
 #ifdef HAVE_EC_KEY_METHOD_NEW
 	else if (k->type == KEY_ECDSA)
 		EC_KEY_set_method(k->ecdsa, helper_ecdsa);
 #endif /* HAVE_EC_KEY_METHOD_NEW */
 	else
 		fatal("%s: unknown key type", __func__);
 }

 static int
 pkcs11_start_helper_methods(void)
 {
 	if (helper_rsa != NULL)
 		return (0);

 #ifdef HAVE_EC_KEY_METHOD_NEW
 	int (*orig_sign)(int, const unsigned char *, int, unsigned char *,
 	    unsigned int *, const BIGNUM *, const BIGNUM *, EC_KEY *) = NULL;
 	if (helper_ecdsa != NULL)
 		return (0);
 	helper_ecdsa = EC_KEY_METHOD_new(EC_KEY_OpenSSL());
 	if (helper_ecdsa == NULL)
 		return (-1);
 	EC_KEY_METHOD_get_sign(helper_ecdsa, &orig_sign, NULL, NULL);
 	EC_KEY_METHOD_set_sign(helper_ecdsa, orig_sign, NULL, ecdsa_do_sign);
 #endif /* HAVE_EC_KEY_METHOD_NEW */

 	if ((helper_rsa = RSA_meth_dup(RSA_get_default_method())) == NULL)
 		fatal("%s: RSA_meth_dup failed", __func__);
 	if (!RSA_meth_set1_name(helper_rsa, "ssh-pkcs11-helper") ||
 	    !RSA_meth_set_priv_enc(helper_rsa, rsa_encrypt))
 		fatal("%s: failed to prepare method", __func__);

 	return (0);
 }

 static int
 pkcs11_start_helper(void)
 {
 	int pair[2];
 	char *helper;

 	if (pkcs11_start_helper_methods() == -1) {
 		error("pkcs11_start_helper_methods failed");
 		return (-1);
 	}

 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
 		error("socketpair: %s", strerror(errno));
 		return (-1);
 	}
 	if ((pid = fork()) == -1) {
 		error("fork: %s", strerror(errno));
 		return (-1);
 	} else if (pid == 0) {
 		if ((dup2(pair[1], STDIN_FILENO) == -1) ||
 		    (dup2(pair[1], STDOUT_FILENO) == -1)) {
 			fprintf(stderr, "dup2: %s\n", strerror(errno));
 			_exit(1);
 		}
 		close(pair[0]);
 		close(pair[1]);
 		helper = getenv("SSH_PKCS11_HELPER");
 		if (helper == NULL || strlen(helper) == 0)
 			helper = _PATH_SSH_PKCS11_HELPER;
 		execlp(helper, helper, (char *)NULL);
 		fprintf(stderr, "exec: %s: %s\n", helper, strerror(errno));
 		_exit(1);
 	}
 	close(pair[1]);
 	fd = pair[0];
 	return (0);
 }

 int
 pkcs11_add_provider(char *name, char *pin, struct sshkey ***keysp)
 {
 	struct sshkey *k;
 	int r, type;
 	u_char *blob;
 	size_t blen;
 	u_int nkeys, i;
 	struct sshbuf *msg;

 	if (fd < 0 && pkcs11_start_helper() < 0)
 		return (-1);

 	if ((msg = sshbuf_new()) == NULL)
 		fatal("%s: sshbuf_new failed", __func__);
 	if ((r = sshbuf_put_u8(msg, SSH_AGENTC_ADD_SMARTCARD_KEY)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, name)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, pin)) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 	send_msg(msg);
 	sshbuf_reset(msg);

 	type = recv_msg(msg);
 	if (type == SSH2_AGENT_IDENTITIES_ANSWER) {
 		if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
 			fatal("%s: buffer error: %s", __func__, ssh_err(r));
 		*keysp = xcalloc(nkeys, sizeof(struct sshkey *));
 		for (i = 0; i < nkeys; i++) {
 			/* XXX clean up properly instead of fatal() */
 			if ((r = sshbuf_get_string(msg, &blob, &blen)) != 0 ||
 			    (r = sshbuf_skip_string(msg)) != 0)
 				fatal("%s: buffer error: %s",
 				    __func__, ssh_err(r));
 			if ((r = sshkey_from_blob(blob, blen, &k)) != 0)
 				fatal("%s: bad key: %s", __func__, ssh_err(r));
 			wrap_key(k);
 			(*keysp)[i] = k;
 			free(blob);
 		}
 	} else if (type == SSH2_AGENT_FAILURE) {
 		if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
 			nkeys = -1;
 	} else {
 		nkeys = -1;
 	}
 	sshbuf_free(msg);
 	return (nkeys);
 }

 int
 pkcs11_del_provider(char *name)
 {
 	int r, ret = -1;
 	struct sshbuf *msg;

 	if ((msg = sshbuf_new()) == NULL)
 		fatal("%s: sshbuf_new failed", __func__);
 	if ((r = sshbuf_put_u8(msg, SSH_AGENTC_REMOVE_SMARTCARD_KEY)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, name)) != 0 ||
 	    (r = sshbuf_put_cstring(msg, "")) != 0)
 		fatal("%s: buffer error: %s", __func__, ssh_err(r));
 	send_msg(msg);
 	sshbuf_reset(msg);

 	if (recv_msg(msg) == SSH_AGENT_SUCCESS)
 		ret = 0;
 	sshbuf_free(msg);
 	return (ret);
 }

 #endif /* ENABLE_PKCS11 */
	/* $OpenBSD: ssh-pkcs11-client.c,v 1.14 2019/01/20 22:57:45 djm Exp $ */
	/*
	* Copyright (c) 2010 Markus Friedl. All rights reserved.
	* Copyright (c) 2014 Pedro Martelletto. All rights reserved.
	*
	* 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.
	*/

	#include "includes.h"

	#ifdef ENABLE_PKCS11

	#include <sys/types.h>
	#ifdef HAVE_SYS_TIME_H
	# include <sys/time.h>
	#endif
	#include <sys/socket.h>

	#include <stdarg.h>
	#include <string.h>
	#include <unistd.h>
	#include <errno.h>

	#include <openssl/ecdsa.h>
	#include <openssl/rsa.h>

	#include "openbsd-compat/openssl-compat.h"

	#include "pathnames.h"
	#include "xmalloc.h"
	#include "sshbuf.h"
	#include "log.h"
	#include "misc.h"
	#include "sshkey.h"
	#include "authfd.h"
	#include "atomicio.h"
	#include "ssh-pkcs11.h"
	#include "ssherr.h"

	/* borrows code from sftp-server and ssh-agent */

	int fd = -1;
	pid_t pid = -1;

	static void
	send_msg(struct sshbuf *m)
	{
	u_char buf[4];
	size_t mlen = sshbuf_len(m);
	int r;

	POKE_U32(buf, mlen);
	if (atomicio(vwrite, fd, buf, 4) != 4 \|\|
	atomicio(vwrite, fd, sshbuf_mutable_ptr(m),
	sshbuf_len(m)) != sshbuf_len(m))
	error("write to helper failed");
	if ((r = sshbuf_consume(m, mlen)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	}

	static int
	recv_msg(struct sshbuf *m)
	{
	u_int l, len;
	u_char c, buf[1024];
	int r;

	if ((len = atomicio(read, fd, buf, 4)) != 4) {
	error("read from helper failed: %u", len);
	return (0); /* XXX */
	}
	len = PEEK_U32(buf);
	if (len > 256 * 1024)
	fatal("response too long: %u", len);
	/* read len bytes into m */
	sshbuf_reset(m);
	while (len > 0) {
	l = len;
	if (l > sizeof(buf))
	l = sizeof(buf);
	if (atomicio(read, fd, buf, l) != l) {
	error("response from helper failed.");
	return (0); /* XXX */
	}
	if ((r = sshbuf_put(m, buf, l)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	len -= l;
	}
	if ((r = sshbuf_get_u8(m, &c)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	return c;
	}

	int
	pkcs11_init(int interactive)
	{
	return (0);
	}

	void
	pkcs11_terminate(void)
	{
	if (fd >= 0)
	close(fd);
	}

	static int
	rsa_encrypt(int flen, const u_char from, u_char to, RSA *rsa, int padding)
	{
	struct sshkey *key = NULL;
	struct sshbuf *msg = NULL;
	u_char blob = NULL, signature = NULL;
	size_t blen, slen = 0;
	int r, ret = -1;

	if (padding != RSA_PKCS1_PADDING)
	goto fail;
	key = sshkey_new(KEY_UNSPEC);
	if (key == NULL) {
	error("%s: sshkey_new failed", __func__);
	goto fail;
	}
	key->type = KEY_RSA;
	RSA_up_ref(rsa);
	key->rsa = rsa;
	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
	error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
	goto fail;
	}
	if ((msg = sshbuf_new()) == NULL)
	fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 \|\|
	(r = sshbuf_put_string(msg, blob, blen)) != 0 \|\|
	(r = sshbuf_put_string(msg, from, flen)) != 0 \|\|
	(r = sshbuf_put_u32(msg, 0)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	send_msg(msg);
	sshbuf_reset(msg);

	if (recv_msg(msg) == SSH2_AGENT_SIGN_RESPONSE) {
	if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	if (slen <= (size_t)RSA_size(rsa)) {
	memcpy(to, signature, slen);
	ret = slen;
	}
	free(signature);
	}
	fail:
	free(blob);
	sshkey_free(key);
	sshbuf_free(msg);
	return (ret);
	}

	#ifdef HAVE_EC_KEY_METHOD_NEW
	static ECDSA_SIG *
	ecdsa_do_sign(const unsigned char dgst, int dgst_len, const BIGNUM inv,
	const BIGNUM rp, EC_KEY ec)
	{
	struct sshkey *key = NULL;
	struct sshbuf *msg = NULL;
	ECDSA_SIG *ret = NULL;
	const u_char *cp;
	u_char blob = NULL, signature = NULL;
	size_t blen, slen = 0;
	int r, nid;

	nid = sshkey_ecdsa_key_to_nid(ec);
	if (nid < 0) {
	error("%s: couldn't get curve nid", __func__);
	goto fail;
	}

	key = sshkey_new(KEY_UNSPEC);
	if (key == NULL) {
	error("%s: sshkey_new failed", __func__);
	goto fail;
	}
	key->ecdsa = ec;
	key->ecdsa_nid = nid;
	key->type = KEY_ECDSA;
	EC_KEY_up_ref(ec);

	if ((r = sshkey_to_blob(key, &blob, &blen)) != 0) {
	error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
	goto fail;
	}
	if ((msg = sshbuf_new()) == NULL)
	fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 \|\|
	(r = sshbuf_put_string(msg, blob, blen)) != 0 \|\|
	(r = sshbuf_put_string(msg, dgst, dgst_len)) != 0 \|\|
	(r = sshbuf_put_u32(msg, 0)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	send_msg(msg);
	sshbuf_reset(msg);

	if (recv_msg(msg) == SSH2_AGENT_SIGN_RESPONSE) {
	if ((r = sshbuf_get_string(msg, &signature, &slen)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	cp = signature;
	ret = d2i_ECDSA_SIG(NULL, &cp, slen);
	free(signature);
	}

	fail:
	free(blob);
	sshkey_free(key);
	sshbuf_free(msg);
	return (ret);
	}
	#endif /* HAVE_EC_KEY_METHOD_NEW */

	static RSA_METHOD *helper_rsa;
	#ifdef HAVE_EC_KEY_METHOD_NEW
	static EC_KEY_METHOD *helper_ecdsa;
	#endif /* HAVE_EC_KEY_METHOD_NEW */

	/* redirect private key crypto operations to the ssh-pkcs11-helper */
	static void
	wrap_key(struct sshkey *k)
	{
	if (k->type == KEY_RSA)
	RSA_set_method(k->rsa, helper_rsa);
	#ifdef HAVE_EC_KEY_METHOD_NEW
	else if (k->type == KEY_ECDSA)
	EC_KEY_set_method(k->ecdsa, helper_ecdsa);
	#endif /* HAVE_EC_KEY_METHOD_NEW */
	else
	fatal("%s: unknown key type", __func__);
	}

	static int
	pkcs11_start_helper_methods(void)
	{
	if (helper_rsa != NULL)
	return (0);

	#ifdef HAVE_EC_KEY_METHOD_NEW
	int (orig_sign)(int, const unsigned char , int, unsigned char *,
	unsigned int , const BIGNUM , const BIGNUM , EC_KEY ) = NULL;
	if (helper_ecdsa != NULL)
	return (0);
	helper_ecdsa = EC_KEY_METHOD_new(EC_KEY_OpenSSL());
	if (helper_ecdsa == NULL)
	return (-1);
	EC_KEY_METHOD_get_sign(helper_ecdsa, &orig_sign, NULL, NULL);
	EC_KEY_METHOD_set_sign(helper_ecdsa, orig_sign, NULL, ecdsa_do_sign);
	#endif /* HAVE_EC_KEY_METHOD_NEW */

	if ((helper_rsa = RSA_meth_dup(RSA_get_default_method())) == NULL)
	fatal("%s: RSA_meth_dup failed", __func__);
	if (!RSA_meth_set1_name(helper_rsa, "ssh-pkcs11-helper") \|\|
	!RSA_meth_set_priv_enc(helper_rsa, rsa_encrypt))
	fatal("%s: failed to prepare method", __func__);

	return (0);
	}

	static int
	pkcs11_start_helper(void)
	{
	int pair[2];
	char *helper;

	if (pkcs11_start_helper_methods() == -1) {
	error("pkcs11_start_helper_methods failed");
	return (-1);
	}

	if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
	error("socketpair: %s", strerror(errno));
	return (-1);
	}
	if ((pid = fork()) == -1) {
	error("fork: %s", strerror(errno));
	return (-1);
	} else if (pid == 0) {
	if ((dup2(pair[1], STDIN_FILENO) == -1) \|\|
	(dup2(pair[1], STDOUT_FILENO) == -1)) {
	fprintf(stderr, "dup2: %s\n", strerror(errno));
	_exit(1);
	}
	close(pair[0]);
	close(pair[1]);
	helper = getenv("SSH_PKCS11_HELPER");
	if (helper == NULL \|\| strlen(helper) == 0)
	helper = _PATH_SSH_PKCS11_HELPER;
	execlp(helper, helper, (char *)NULL);
	fprintf(stderr, "exec: %s: %s\n", helper, strerror(errno));
	_exit(1);
	}
	close(pair[1]);
	fd = pair[0];
	return (0);
	}

	int
	pkcs11_add_provider(char name, char pin, struct sshkey ***keysp)
	{
	struct sshkey *k;
	int r, type;
	u_char *blob;
	size_t blen;
	u_int nkeys, i;
	struct sshbuf *msg;

	if (fd < 0 && pkcs11_start_helper() < 0)
	return (-1);

	if ((msg = sshbuf_new()) == NULL)
	fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_u8(msg, SSH_AGENTC_ADD_SMARTCARD_KEY)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, name)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, pin)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	send_msg(msg);
	sshbuf_reset(msg);

	type = recv_msg(msg);
	if (type == SSH2_AGENT_IDENTITIES_ANSWER) {
	if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	keysp = xcalloc(nkeys, sizeof(struct sshkey ));
	for (i = 0; i < nkeys; i++) {
	/* XXX clean up properly instead of fatal() */
	if ((r = sshbuf_get_string(msg, &blob, &blen)) != 0 \|\|
	(r = sshbuf_skip_string(msg)) != 0)
	fatal("%s: buffer error: %s",
	__func__, ssh_err(r));
	if ((r = sshkey_from_blob(blob, blen, &k)) != 0)
	fatal("%s: bad key: %s", __func__, ssh_err(r));
	wrap_key(k);
	(*keysp)[i] = k;
	free(blob);
	}
	} else if (type == SSH2_AGENT_FAILURE) {
	if ((r = sshbuf_get_u32(msg, &nkeys)) != 0)
	nkeys = -1;
	} else {
	nkeys = -1;
	}
	sshbuf_free(msg);
	return (nkeys);
	}

	int
	pkcs11_del_provider(char *name)
	{
	int r, ret = -1;
	struct sshbuf *msg;

	if ((msg = sshbuf_new()) == NULL)
	fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_u8(msg, SSH_AGENTC_REMOVE_SMARTCARD_KEY)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, name)) != 0 \|\|
	(r = sshbuf_put_cstring(msg, "")) != 0)
	fatal("%s: buffer error: %s", __func__, ssh_err(r));
	send_msg(msg);
	sshbuf_reset(msg);

	if (recv_msg(msg) == SSH_AGENT_SUCCESS)
	ret = 0;
	sshbuf_free(msg);
	return (ret);
	}

	#endif /* ENABLE_PKCS11 */