ssh-agent.c - third_party/openssh-portable - Git at Google

 /*	$OpenBSD: ssh-agent.c,v 1.31 2000/04/29 18:11:52 markus Exp $	*/

 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
  * Created: Wed Mar 29 03:46:59 1995 ylo
  * The authentication agent program.
  */

 #include "includes.h"
 RCSID("$OpenBSD: ssh-agent.c,v 1.31 2000/04/29 18:11:52 markus Exp $");

 #include "ssh.h"
 #include "rsa.h"
 #include "authfd.h"
 #include "buffer.h"
 #include "bufaux.h"
 #include "xmalloc.h"
 #include "packet.h"
 #include "getput.h"
 #include "mpaux.h"

 #include <openssl/md5.h>

 typedef struct {
 	int fd;
 	enum {
 		AUTH_UNUSED, AUTH_SOCKET, AUTH_CONNECTION
 	} type;
 	Buffer input;
 	Buffer output;
 } SocketEntry;

 unsigned int sockets_alloc = 0;
 SocketEntry *sockets = NULL;

 typedef struct {
 	RSA *key;
 	char *comment;
 } Identity;

 unsigned int num_identities = 0;
 Identity *identities = NULL;

 int max_fd = 0;

 /* pid of shell == parent of agent */
 pid_t parent_pid = -1;

 /* pathname and directory for AUTH_SOCKET */
 char socket_name[1024];
 char socket_dir[1024];

 #ifdef HAVE___PROGNAME
 extern char *__progname;
 #else /* HAVE___PROGNAME */
 static const char *__progname = "ssh-agent";
 #endif /* HAVE___PROGNAME */

 void
 process_request_identity(SocketEntry *e)
 {
 	Buffer msg;
 	int i;

 	buffer_init(&msg);
 	buffer_put_char(&msg, SSH_AGENT_RSA_IDENTITIES_ANSWER);
 	buffer_put_int(&msg, num_identities);
 	for (i = 0; i < num_identities; i++) {
 		buffer_put_int(&msg, BN_num_bits(identities[i].key->n));
 		buffer_put_bignum(&msg, identities[i].key->e);
 		buffer_put_bignum(&msg, identities[i].key->n);
 		buffer_put_string(&msg, identities[i].comment,
 				  strlen(identities[i].comment));
 	}
 	buffer_put_int(&e->output, buffer_len(&msg));
 	buffer_append(&e->output, buffer_ptr(&msg), buffer_len(&msg));
 	buffer_free(&msg);
 }

 void
 process_authentication_challenge(SocketEntry *e)
 {
 	int i, pub_bits, len;
 	BIGNUM *pub_e, *pub_n, *challenge;
 	Buffer msg;
 	MD5_CTX md;
 	unsigned char buf[32], mdbuf[16], session_id[16];
 	unsigned int response_type;

 	buffer_init(&msg);
 	pub_e = BN_new();
 	pub_n = BN_new();
 	challenge = BN_new();
 	pub_bits = buffer_get_int(&e->input);
 	buffer_get_bignum(&e->input, pub_e);
 	buffer_get_bignum(&e->input, pub_n);
 	buffer_get_bignum(&e->input, challenge);
 	if (buffer_len(&e->input) == 0) {
 		/* Compatibility code for old servers. */
 		memset(session_id, 0, 16);
 		response_type = 0;
 	} else {
 		/* New code. */
 		buffer_get(&e->input, (char *) session_id, 16);
 		response_type = buffer_get_int(&e->input);
 	}
 	for (i = 0; i < num_identities; i++)
 		if (pub_bits == BN_num_bits(identities[i].key->n) &&
 		    BN_cmp(pub_e, identities[i].key->e) == 0 &&
 		    BN_cmp(pub_n, identities[i].key->n) == 0) {
 			/* Decrypt the challenge using the private key. */
 			rsa_private_decrypt(challenge, challenge, identities[i].key);

 			/* Compute the desired response. */
 			switch (response_type) {
 			case 0:/* As of protocol 1.0 */
 				/* This response type is no longer supported. */
 				log("Compatibility with ssh protocol 1.0 no longer supported.");
 				buffer_put_char(&msg, SSH_AGENT_FAILURE);
 				goto send;

 			case 1:/* As of protocol 1.1 */
 				/* The response is MD5 of decrypted challenge plus session id. */
 				len = BN_num_bytes(challenge);

 				if (len <= 0 || len > 32) {
 					fatal("process_authentication_challenge: "
 					 "bad challenge length %d", len);
 				}
 				memset(buf, 0, 32);
 				BN_bn2bin(challenge, buf + 32 - len);
 				MD5_Init(&md);
 				MD5_Update(&md, buf, 32);
 				MD5_Update(&md, session_id, 16);
 				MD5_Final(mdbuf, &md);
 				break;

 			default:
 				fatal("process_authentication_challenge: bad response_type %d",
 				      response_type);
 				break;
 			}

 			/* Send the response. */
 			buffer_put_char(&msg, SSH_AGENT_RSA_RESPONSE);
 			for (i = 0; i < 16; i++)
 				buffer_put_char(&msg, mdbuf[i]);

 			goto send;
 		}
 	/* Unknown identity.  Send failure. */
 	buffer_put_char(&msg, SSH_AGENT_FAILURE);
 send:
 	buffer_put_int(&e->output, buffer_len(&msg));
 	buffer_append(&e->output, buffer_ptr(&msg),
 		      buffer_len(&msg));
 	buffer_free(&msg);
 	BN_clear_free(pub_e);
 	BN_clear_free(pub_n);
 	BN_clear_free(challenge);
 }

 void
 process_remove_identity(SocketEntry *e)
 {
 	unsigned int bits;
 	unsigned int i;
 	BIGNUM *dummy, *n;

 	dummy = BN_new();
 	n = BN_new();

 	/* Get the key from the packet. */
 	bits = buffer_get_int(&e->input);
 	buffer_get_bignum(&e->input, dummy);
 	buffer_get_bignum(&e->input, n);

 	if (bits != BN_num_bits(n))
 		log("Warning: identity keysize mismatch: actual %d, announced %d",
 		      BN_num_bits(n), bits);

 	/* Check if we have the key. */
 	for (i = 0; i < num_identities; i++)
 		if (BN_cmp(identities[i].key->n, n) == 0) {
 			/*
 			 * We have this key.  Free the old key.  Since we
 			 * don\'t want to leave empty slots in the middle of
 			 * the array, we actually free the key there and copy
 			 * data from the last entry.
 			 */
 			RSA_free(identities[i].key);
 			xfree(identities[i].comment);
 			if (i < num_identities - 1)
 				identities[i] = identities[num_identities - 1];
 			num_identities--;
 			BN_clear_free(dummy);
 			BN_clear_free(n);

 			/* Send success. */
 			buffer_put_int(&e->output, 1);
 			buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 			return;
 		}
 	/* We did not have the key. */
 	BN_clear(dummy);
 	BN_clear(n);

 	/* Send failure. */
 	buffer_put_int(&e->output, 1);
 	buffer_put_char(&e->output, SSH_AGENT_FAILURE);
 }

 /*
  * Removes all identities from the agent.
  */
 void
 process_remove_all_identities(SocketEntry *e)
 {
 	unsigned int i;

 	/* Loop over all identities and clear the keys. */
 	for (i = 0; i < num_identities; i++) {
 		RSA_free(identities[i].key);
 		xfree(identities[i].comment);
 	}

 	/* Mark that there are no identities. */
 	num_identities = 0;

 	/* Send success. */
 	buffer_put_int(&e->output, 1);
 	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 	return;
 }

 /*
  * Adds an identity to the agent.
  */
 void
 process_add_identity(SocketEntry *e)
 {
 	RSA *k;
 	int i;
 	BIGNUM *aux;
 	BN_CTX *ctx;

 	if (num_identities == 0)
 		identities = xmalloc(sizeof(Identity));
 	else
 		identities = xrealloc(identities, (num_identities + 1) * sizeof(Identity));

 	identities[num_identities].key = RSA_new();
 	k = identities[num_identities].key;
 	buffer_get_int(&e->input);	/* bits */
 	k->n = BN_new();
 	buffer_get_bignum(&e->input, k->n);
 	k->e = BN_new();
 	buffer_get_bignum(&e->input, k->e);
 	k->d = BN_new();
 	buffer_get_bignum(&e->input, k->d);
 	k->iqmp = BN_new();
 	buffer_get_bignum(&e->input, k->iqmp);
 	/* SSH and SSL have p and q swapped */
 	k->q = BN_new();
 	buffer_get_bignum(&e->input, k->q);	/* p */
 	k->p = BN_new();
 	buffer_get_bignum(&e->input, k->p);	/* q */

 	/* Generate additional parameters */
 	aux = BN_new();
 	ctx = BN_CTX_new();

 	BN_sub(aux, k->q, BN_value_one());
 	k->dmq1 = BN_new();
 	BN_mod(k->dmq1, k->d, aux, ctx);

 	BN_sub(aux, k->p, BN_value_one());
 	k->dmp1 = BN_new();
 	BN_mod(k->dmp1, k->d, aux, ctx);

 	BN_clear_free(aux);
 	BN_CTX_free(ctx);

 	identities[num_identities].comment = buffer_get_string(&e->input, NULL);

 	/* Check if we already have the key. */
 	for (i = 0; i < num_identities; i++)
 		if (BN_cmp(identities[i].key->n, k->n) == 0) {
 			/*
 			 * We already have this key.  Clear and free the new
 			 * data and return success.
 			 */
 			RSA_free(k);
 			xfree(identities[num_identities].comment);

 			/* Send success. */
 			buffer_put_int(&e->output, 1);
 			buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 			return;
 		}
 	/* Increment the number of identities. */
 	num_identities++;

 	/* Send a success message. */
 	buffer_put_int(&e->output, 1);
 	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
 }

 void
 process_message(SocketEntry *e)
 {
 	unsigned int msg_len;
 	unsigned int type;
 	unsigned char *cp;
 	if (buffer_len(&e->input) < 5)
 		return;		/* Incomplete message. */
 	cp = (unsigned char *) buffer_ptr(&e->input);
 	msg_len = GET_32BIT(cp);
 	if (msg_len > 256 * 1024) {
 		shutdown(e->fd, SHUT_RDWR);
 		close(e->fd);
 		e->type = AUTH_UNUSED;
 		return;
 	}
 	if (buffer_len(&e->input) < msg_len + 4)
 		return;
 	buffer_consume(&e->input, 4);
 	type = buffer_get_char(&e->input);

 	switch (type) {
 	case SSH_AGENTC_REQUEST_RSA_IDENTITIES:
 		process_request_identity(e);
 		break;
 	case SSH_AGENTC_RSA_CHALLENGE:
 		process_authentication_challenge(e);
 		break;
 	case SSH_AGENTC_ADD_RSA_IDENTITY:
 		process_add_identity(e);
 		break;
 	case SSH_AGENTC_REMOVE_RSA_IDENTITY:
 		process_remove_identity(e);
 		break;
 	case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
 		process_remove_all_identities(e);
 		break;
 	default:
 		/* Unknown message.  Respond with failure. */
 		error("Unknown message %d", type);
 		buffer_clear(&e->input);
 		buffer_put_int(&e->output, 1);
 		buffer_put_char(&e->output, SSH_AGENT_FAILURE);
 		break;
 	}
 }

 void
 new_socket(int type, int fd)
 {
 	unsigned int i, old_alloc;
 	if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0)
 		error("fcntl O_NONBLOCK: %s", strerror(errno));

 	if (fd > max_fd)
 		max_fd = fd;

 	for (i = 0; i < sockets_alloc; i++)
 		if (sockets[i].type == AUTH_UNUSED) {
 			sockets[i].fd = fd;
 			sockets[i].type = type;
 			buffer_init(&sockets[i].input);
 			buffer_init(&sockets[i].output);
 			return;
 		}
 	old_alloc = sockets_alloc;
 	sockets_alloc += 10;
 	if (sockets)
 		sockets = xrealloc(sockets, sockets_alloc * sizeof(sockets[0]));
 	else
 		sockets = xmalloc(sockets_alloc * sizeof(sockets[0]));
 	for (i = old_alloc; i < sockets_alloc; i++)
 		sockets[i].type = AUTH_UNUSED;
 	sockets[old_alloc].type = type;
 	sockets[old_alloc].fd = fd;
 	buffer_init(&sockets[old_alloc].input);
 	buffer_init(&sockets[old_alloc].output);
 }

 void
 prepare_select(fd_set *readset, fd_set *writeset)
 {
 	unsigned int i;
 	for (i = 0; i < sockets_alloc; i++)
 		switch (sockets[i].type) {
 		case AUTH_SOCKET:
 		case AUTH_CONNECTION:
 			FD_SET(sockets[i].fd, readset);
 			if (buffer_len(&sockets[i].output) > 0)
 				FD_SET(sockets[i].fd, writeset);
 			break;
 		case AUTH_UNUSED:
 			break;
 		default:
 			fatal("Unknown socket type %d", sockets[i].type);
 			break;
 		}
 }

 void
 after_select(fd_set *readset, fd_set *writeset)
 {
 	unsigned int i;
 	int len, sock;
 	socklen_t slen;
 	char buf[1024];
 	struct sockaddr_un sunaddr;

 	for (i = 0; i < sockets_alloc; i++)
 		switch (sockets[i].type) {
 		case AUTH_UNUSED:
 			break;
 		case AUTH_SOCKET:
 			if (FD_ISSET(sockets[i].fd, readset)) {
 				slen = sizeof(sunaddr);
 				sock = accept(sockets[i].fd, (struct sockaddr *) & sunaddr, &slen);
 				if (sock < 0) {
 					perror("accept from AUTH_SOCKET");
 					break;
 				}
 				new_socket(AUTH_CONNECTION, sock);
 			}
 			break;
 		case AUTH_CONNECTION:
 			if (buffer_len(&sockets[i].output) > 0 &&
 			    FD_ISSET(sockets[i].fd, writeset)) {
 				len = write(sockets[i].fd, buffer_ptr(&sockets[i].output),
 					 buffer_len(&sockets[i].output));
 				if (len <= 0) {
 					shutdown(sockets[i].fd, SHUT_RDWR);
 					close(sockets[i].fd);
 					sockets[i].type = AUTH_UNUSED;
 					buffer_free(&sockets[i].input);
 					buffer_free(&sockets[i].output);
 					break;
 				}
 				buffer_consume(&sockets[i].output, len);
 			}
 			if (FD_ISSET(sockets[i].fd, readset)) {
 				len = read(sockets[i].fd, buf, sizeof(buf));
 				if (len <= 0) {
 					shutdown(sockets[i].fd, SHUT_RDWR);
 					close(sockets[i].fd);
 					sockets[i].type = AUTH_UNUSED;
 					buffer_free(&sockets[i].input);
 					buffer_free(&sockets[i].output);
 					break;
 				}
 				buffer_append(&sockets[i].input, buf, len);
 				process_message(&sockets[i]);
 			}
 			break;
 		default:
 			fatal("Unknown type %d", sockets[i].type);
 		}
 }

 void
 check_parent_exists(int sig)
 {
 	if (parent_pid != -1 && kill(parent_pid, 0) < 0) {
 		/* printf("Parent has died - Authentication agent exiting.\n"); */
 		exit(1);
 	}
 	signal(SIGALRM, check_parent_exists);
 	alarm(10);
 }

 void
 cleanup_socket(void)
 {
 	remove(socket_name);
 	rmdir(socket_dir);
 }

 void
 cleanup_exit(int i)
 {
 	cleanup_socket();
 	exit(i);
 }

 void
 usage()
 {
 	fprintf(stderr, "ssh-agent version %s\n", SSH_VERSION);
 	fprintf(stderr, "Usage: %s [-c | -s] [-k] [command {args...]]\n",
 		__progname);
 	exit(1);
 }

 int
 main(int ac, char **av)
 {
 	fd_set readset, writeset;
 	int sock, c_flag = 0, k_flag = 0, s_flag = 0, ch;
 	struct sockaddr_un sunaddr;
 	pid_t pid;
 	char *shell, *format, *pidstr, pidstrbuf[1 + 3 * sizeof pid];
 	extern int optind;

 	/* check if RSA support exists */
 	if (rsa_alive() == 0) {
 		fprintf(stderr,
 			"%s: no RSA support in libssl and libcrypto.  See ssl(8).\n",
 			__progname);
 		exit(1);
 	}
 #ifdef __GNU_LIBRARY__
 	while ((ch = getopt(ac, av, "+cks")) != -1) {
 #else /* __GNU_LIBRARY__ */
 	while ((ch = getopt(ac, av, "cks")) != -1) {
 #endif /* __GNU_LIBRARY__ */
 		switch (ch) {
 		case 'c':
 			if (s_flag)
 				usage();
 			c_flag++;
 			break;
 		case 'k':
 			k_flag++;
 			break;
 		case 's':
 			if (c_flag)
 				usage();
 			s_flag++;
 			break;
 		default:
 			usage();
 		}
 	}
 	ac -= optind;
 	av += optind;

 	if (ac > 0 && (c_flag || k_flag || s_flag))
 		usage();

 	if (ac == 0 && !c_flag && !k_flag && !s_flag) {
 		shell = getenv("SHELL");
 		if (shell != NULL && strncmp(shell + strlen(shell) - 3, "csh", 3) == 0)
 			c_flag = 1;
 	}
 	if (k_flag) {
 		pidstr = getenv(SSH_AGENTPID_ENV_NAME);
 		if (pidstr == NULL) {
 			fprintf(stderr, "%s not set, cannot kill agent\n",
 				SSH_AGENTPID_ENV_NAME);
 			exit(1);
 		}
 		pid = atoi(pidstr);
 		if (pid < 1) {	/* XXX PID_MAX check too */
 		/* Yes, PID_MAX check please */
 			fprintf(stderr, "%s=\"%s\", which is not a good PID\n",
 				SSH_AGENTPID_ENV_NAME, pidstr);
 			exit(1);
 		}
 		if (kill(pid, SIGTERM) == -1) {
 			perror("kill");
 			exit(1);
 		}
 		format = c_flag ? "unsetenv %s;\n" : "unset %s;\n";
 		printf(format, SSH_AUTHSOCKET_ENV_NAME);
 		printf(format, SSH_AGENTPID_ENV_NAME);
 		printf("echo Agent pid %d killed;\n", pid);
 		exit(0);
 	}
 	parent_pid = getpid();

 	/* Create private directory for agent socket */
 	strlcpy(socket_dir, "/tmp/ssh-XXXXXXXX", sizeof socket_dir);
 	if (mkdtemp(socket_dir) == NULL) {
 		perror("mkdtemp: private socket dir");
 		exit(1);
 	}
 	snprintf(socket_name, sizeof socket_name, "%s/agent.%d", socket_dir,
 		 parent_pid);

 	/*
 	 * Create socket early so it will exist before command gets run from
 	 * the parent.
 	 */
 	sock = socket(AF_UNIX, SOCK_STREAM, 0);
 	if (sock < 0) {
 		perror("socket");
 		cleanup_exit(1);
 	}
 	memset(&sunaddr, 0, sizeof(sunaddr));
 	sunaddr.sun_family = AF_UNIX;
 	strlcpy(sunaddr.sun_path, socket_name, sizeof(sunaddr.sun_path));
 	if (bind(sock, (struct sockaddr *) & sunaddr, sizeof(sunaddr)) < 0) {
 		perror("bind");
 		cleanup_exit(1);
 	}
 	if (listen(sock, 5) < 0) {
 		perror("listen");
 		cleanup_exit(1);
 	}
 	/*
 	 * Fork, and have the parent execute the command, if any, or present
 	 * the socket data.  The child continues as the authentication agent.
 	 */
 	pid = fork();
 	if (pid == -1) {
 		perror("fork");
 		exit(1);
 	}
 	if (pid != 0) {		/* Parent - execute the given command. */
 		close(sock);
 		snprintf(pidstrbuf, sizeof pidstrbuf, "%d", pid);
 		if (ac == 0) {
 			format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
 			printf(format, SSH_AUTHSOCKET_ENV_NAME, socket_name,
 			       SSH_AUTHSOCKET_ENV_NAME);
 			printf(format, SSH_AGENTPID_ENV_NAME, pidstrbuf,
 			       SSH_AGENTPID_ENV_NAME);
 			printf("echo Agent pid %d;\n", pid);
 			exit(0);
 		}
 		setenv(SSH_AUTHSOCKET_ENV_NAME, socket_name, 1);
 		setenv(SSH_AGENTPID_ENV_NAME, pidstrbuf, 1);
 		execvp(av[0], av);
 		perror(av[0]);
 		exit(1);
 	}
 	close(0);
 	close(1);
 	close(2);

 	if (setsid() == -1) {
 		perror("setsid");
 		cleanup_exit(1);
 	}
 	if (atexit(cleanup_socket) < 0) {
 		perror("atexit");
 		cleanup_exit(1);
 	}
 	new_socket(AUTH_SOCKET, sock);
 	if (ac > 0) {
 		signal(SIGALRM, check_parent_exists);
 		alarm(10);
 	}
 	signal(SIGINT, SIG_IGN);
 	signal(SIGPIPE, SIG_IGN);
 	signal(SIGHUP, cleanup_exit);
 	signal(SIGTERM, cleanup_exit);
 	while (1) {
 		FD_ZERO(&readset);
 		FD_ZERO(&writeset);
 		prepare_select(&readset, &writeset);
 		if (select(max_fd + 1, &readset, &writeset, NULL, NULL) < 0) {
 			if (errno == EINTR)
 				continue;
 			exit(1);
 		}
 		after_select(&readset, &writeset);
 	}
 	/* NOTREACHED */
 }
	/* $OpenBSD: ssh-agent.c,v 1.31 2000/04/29 18:11:52 markus Exp $ */

	/*
	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	* Created: Wed Mar 29 03:46:59 1995 ylo
	* The authentication agent program.
	*/

	#include "includes.h"
	RCSID("$OpenBSD: ssh-agent.c,v 1.31 2000/04/29 18:11:52 markus Exp $");

	#include "ssh.h"
	#include "rsa.h"
	#include "authfd.h"
	#include "buffer.h"
	#include "bufaux.h"
	#include "xmalloc.h"
	#include "packet.h"
	#include "getput.h"
	#include "mpaux.h"

	#include <openssl/md5.h>

	typedef struct {
	int fd;
	enum {
	AUTH_UNUSED, AUTH_SOCKET, AUTH_CONNECTION
	} type;
	Buffer input;
	Buffer output;
	} SocketEntry;

	unsigned int sockets_alloc = 0;
	SocketEntry *sockets = NULL;

	typedef struct {
	RSA *key;
	char *comment;
	} Identity;

	unsigned int num_identities = 0;
	Identity *identities = NULL;

	int max_fd = 0;

	/* pid of shell == parent of agent */
	pid_t parent_pid = -1;

	/* pathname and directory for AUTH_SOCKET */
	char socket_name[1024];
	char socket_dir[1024];

	#ifdef HAVE___PROGNAME
	extern char *__progname;
	#else /* HAVE___PROGNAME */
	static const char *__progname = "ssh-agent";
	#endif /* HAVE___PROGNAME */

	void
	process_request_identity(SocketEntry *e)
	{
	Buffer msg;
	int i;

	buffer_init(&msg);
	buffer_put_char(&msg, SSH_AGENT_RSA_IDENTITIES_ANSWER);
	buffer_put_int(&msg, num_identities);
	for (i = 0; i < num_identities; i++) {
	buffer_put_int(&msg, BN_num_bits(identities[i].key->n));
	buffer_put_bignum(&msg, identities[i].key->e);
	buffer_put_bignum(&msg, identities[i].key->n);
	buffer_put_string(&msg, identities[i].comment,
	strlen(identities[i].comment));
	}
	buffer_put_int(&e->output, buffer_len(&msg));
	buffer_append(&e->output, buffer_ptr(&msg), buffer_len(&msg));
	buffer_free(&msg);
	}

	void
	process_authentication_challenge(SocketEntry *e)
	{
	int i, pub_bits, len;
	BIGNUM pub_e, pub_n, *challenge;
	Buffer msg;
	MD5_CTX md;
	unsigned char buf[32], mdbuf[16], session_id[16];
	unsigned int response_type;

	buffer_init(&msg);
	pub_e = BN_new();
	pub_n = BN_new();
	challenge = BN_new();
	pub_bits = buffer_get_int(&e->input);
	buffer_get_bignum(&e->input, pub_e);
	buffer_get_bignum(&e->input, pub_n);
	buffer_get_bignum(&e->input, challenge);
	if (buffer_len(&e->input) == 0) {
	/* Compatibility code for old servers. */
	memset(session_id, 0, 16);
	response_type = 0;
	} else {
	/* New code. */
	buffer_get(&e->input, (char *) session_id, 16);
	response_type = buffer_get_int(&e->input);
	}
	for (i = 0; i < num_identities; i++)
	if (pub_bits == BN_num_bits(identities[i].key->n) &&
	BN_cmp(pub_e, identities[i].key->e) == 0 &&
	BN_cmp(pub_n, identities[i].key->n) == 0) {
	/* Decrypt the challenge using the private key. */
	rsa_private_decrypt(challenge, challenge, identities[i].key);

	/* Compute the desired response. */
	switch (response_type) {
	case 0:/* As of protocol 1.0 */
	/* This response type is no longer supported. */
	log("Compatibility with ssh protocol 1.0 no longer supported.");
	buffer_put_char(&msg, SSH_AGENT_FAILURE);
	goto send;

	case 1:/* As of protocol 1.1 */
	/* The response is MD5 of decrypted challenge plus session id. */
	len = BN_num_bytes(challenge);

	if (len <= 0 \|\| len > 32) {
	fatal("process_authentication_challenge: "
	"bad challenge length %d", len);
	}
	memset(buf, 0, 32);
	BN_bn2bin(challenge, buf + 32 - len);
	MD5_Init(&md);
	MD5_Update(&md, buf, 32);
	MD5_Update(&md, session_id, 16);
	MD5_Final(mdbuf, &md);
	break;

	default:
	fatal("process_authentication_challenge: bad response_type %d",
	response_type);
	break;
	}

	/* Send the response. */
	buffer_put_char(&msg, SSH_AGENT_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
	buffer_put_char(&msg, mdbuf[i]);

	goto send;
	}
	/* Unknown identity. Send failure. */
	buffer_put_char(&msg, SSH_AGENT_FAILURE);
	send:
	buffer_put_int(&e->output, buffer_len(&msg));
	buffer_append(&e->output, buffer_ptr(&msg),
	buffer_len(&msg));
	buffer_free(&msg);
	BN_clear_free(pub_e);
	BN_clear_free(pub_n);
	BN_clear_free(challenge);
	}

	void
	process_remove_identity(SocketEntry *e)
	{
	unsigned int bits;
	unsigned int i;
	BIGNUM dummy, n;

	dummy = BN_new();
	n = BN_new();

	/* Get the key from the packet. */
	bits = buffer_get_int(&e->input);
	buffer_get_bignum(&e->input, dummy);
	buffer_get_bignum(&e->input, n);

	if (bits != BN_num_bits(n))
	log("Warning: identity keysize mismatch: actual %d, announced %d",
	BN_num_bits(n), bits);

	/* Check if we have the key. */
	for (i = 0; i < num_identities; i++)
	if (BN_cmp(identities[i].key->n, n) == 0) {
	/*
	* We have this key. Free the old key. Since we
	* don\'t want to leave empty slots in the middle of
	* the array, we actually free the key there and copy
	* data from the last entry.
	*/
	RSA_free(identities[i].key);
	xfree(identities[i].comment);
	if (i < num_identities - 1)
	identities[i] = identities[num_identities - 1];
	num_identities--;
	BN_clear_free(dummy);
	BN_clear_free(n);

	/* Send success. */
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
	return;
	}
	/* We did not have the key. */
	BN_clear(dummy);
	BN_clear(n);

	/* Send failure. */
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_FAILURE);
	}

	/*
	* Removes all identities from the agent.
	*/
	void
	process_remove_all_identities(SocketEntry *e)
	{
	unsigned int i;

	/* Loop over all identities and clear the keys. */
	for (i = 0; i < num_identities; i++) {
	RSA_free(identities[i].key);
	xfree(identities[i].comment);
	}

	/* Mark that there are no identities. */
	num_identities = 0;

	/* Send success. */
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
	return;
	}

	/*
	* Adds an identity to the agent.
	*/
	void
	process_add_identity(SocketEntry *e)
	{
	RSA *k;
	int i;
	BIGNUM *aux;
	BN_CTX *ctx;

	if (num_identities == 0)
	identities = xmalloc(sizeof(Identity));
	else
	identities = xrealloc(identities, (num_identities + 1) * sizeof(Identity));

	identities[num_identities].key = RSA_new();
	k = identities[num_identities].key;
	buffer_get_int(&e->input); /* bits */
	k->n = BN_new();
	buffer_get_bignum(&e->input, k->n);
	k->e = BN_new();
	buffer_get_bignum(&e->input, k->e);
	k->d = BN_new();
	buffer_get_bignum(&e->input, k->d);
	k->iqmp = BN_new();
	buffer_get_bignum(&e->input, k->iqmp);
	/* SSH and SSL have p and q swapped */
	k->q = BN_new();
	buffer_get_bignum(&e->input, k->q); /* p */
	k->p = BN_new();
	buffer_get_bignum(&e->input, k->p); /* q */

	/* Generate additional parameters */
	aux = BN_new();
	ctx = BN_CTX_new();

	BN_sub(aux, k->q, BN_value_one());
	k->dmq1 = BN_new();
	BN_mod(k->dmq1, k->d, aux, ctx);

	BN_sub(aux, k->p, BN_value_one());
	k->dmp1 = BN_new();
	BN_mod(k->dmp1, k->d, aux, ctx);

	BN_clear_free(aux);
	BN_CTX_free(ctx);

	identities[num_identities].comment = buffer_get_string(&e->input, NULL);

	/* Check if we already have the key. */
	for (i = 0; i < num_identities; i++)
	if (BN_cmp(identities[i].key->n, k->n) == 0) {
	/*
	* We already have this key. Clear and free the new
	* data and return success.
	*/
	RSA_free(k);
	xfree(identities[num_identities].comment);

	/* Send success. */
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
	return;
	}
	/* Increment the number of identities. */
	num_identities++;

	/* Send a success message. */
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_SUCCESS);
	}

	void
	process_message(SocketEntry *e)
	{
	unsigned int msg_len;
	unsigned int type;
	unsigned char *cp;
	if (buffer_len(&e->input) < 5)
	return; /* Incomplete message. */
	cp = (unsigned char *) buffer_ptr(&e->input);
	msg_len = GET_32BIT(cp);
	if (msg_len > 256 * 1024) {
	shutdown(e->fd, SHUT_RDWR);
	close(e->fd);
	e->type = AUTH_UNUSED;
	return;
	}
	if (buffer_len(&e->input) < msg_len + 4)
	return;
	buffer_consume(&e->input, 4);
	type = buffer_get_char(&e->input);

	switch (type) {
	case SSH_AGENTC_REQUEST_RSA_IDENTITIES:
	process_request_identity(e);
	break;
	case SSH_AGENTC_RSA_CHALLENGE:
	process_authentication_challenge(e);
	break;
	case SSH_AGENTC_ADD_RSA_IDENTITY:
	process_add_identity(e);
	break;
	case SSH_AGENTC_REMOVE_RSA_IDENTITY:
	process_remove_identity(e);
	break;
	case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
	process_remove_all_identities(e);
	break;
	default:
	/* Unknown message. Respond with failure. */
	error("Unknown message %d", type);
	buffer_clear(&e->input);
	buffer_put_int(&e->output, 1);
	buffer_put_char(&e->output, SSH_AGENT_FAILURE);
	break;
	}
	}

	void
	new_socket(int type, int fd)
	{
	unsigned int i, old_alloc;
	if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0)
	error("fcntl O_NONBLOCK: %s", strerror(errno));

	if (fd > max_fd)
	max_fd = fd;

	for (i = 0; i < sockets_alloc; i++)
	if (sockets[i].type == AUTH_UNUSED) {
	sockets[i].fd = fd;
	sockets[i].type = type;
	buffer_init(&sockets[i].input);
	buffer_init(&sockets[i].output);
	return;
	}
	old_alloc = sockets_alloc;
	sockets_alloc += 10;
	if (sockets)
	sockets = xrealloc(sockets, sockets_alloc * sizeof(sockets[0]));
	else
	sockets = xmalloc(sockets_alloc * sizeof(sockets[0]));
	for (i = old_alloc; i < sockets_alloc; i++)
	sockets[i].type = AUTH_UNUSED;
	sockets[old_alloc].type = type;
	sockets[old_alloc].fd = fd;
	buffer_init(&sockets[old_alloc].input);
	buffer_init(&sockets[old_alloc].output);
	}

	void
	prepare_select(fd_set readset, fd_set writeset)
	{
	unsigned int i;
	for (i = 0; i < sockets_alloc; i++)
	switch (sockets[i].type) {
	case AUTH_SOCKET:
	case AUTH_CONNECTION:
	FD_SET(sockets[i].fd, readset);
	if (buffer_len(&sockets[i].output) > 0)
	FD_SET(sockets[i].fd, writeset);
	break;
	case AUTH_UNUSED:
	break;
	default:
	fatal("Unknown socket type %d", sockets[i].type);
	break;
	}
	}

	void
	after_select(fd_set readset, fd_set writeset)
	{
	unsigned int i;
	int len, sock;
	socklen_t slen;
	char buf[1024];
	struct sockaddr_un sunaddr;

	for (i = 0; i < sockets_alloc; i++)
	switch (sockets[i].type) {
	case AUTH_UNUSED:
	break;
	case AUTH_SOCKET:
	if (FD_ISSET(sockets[i].fd, readset)) {
	slen = sizeof(sunaddr);
	sock = accept(sockets[i].fd, (struct sockaddr *) & sunaddr, &slen);
	if (sock < 0) {
	perror("accept from AUTH_SOCKET");
	break;
	}
	new_socket(AUTH_CONNECTION, sock);
	}
	break;
	case AUTH_CONNECTION:
	if (buffer_len(&sockets[i].output) > 0 &&
	FD_ISSET(sockets[i].fd, writeset)) {
	len = write(sockets[i].fd, buffer_ptr(&sockets[i].output),
	buffer_len(&sockets[i].output));
	if (len <= 0) {
	shutdown(sockets[i].fd, SHUT_RDWR);
	close(sockets[i].fd);
	sockets[i].type = AUTH_UNUSED;
	buffer_free(&sockets[i].input);
	buffer_free(&sockets[i].output);
	break;
	}
	buffer_consume(&sockets[i].output, len);
	}
	if (FD_ISSET(sockets[i].fd, readset)) {
	len = read(sockets[i].fd, buf, sizeof(buf));
	if (len <= 0) {
	shutdown(sockets[i].fd, SHUT_RDWR);
	close(sockets[i].fd);
	sockets[i].type = AUTH_UNUSED;
	buffer_free(&sockets[i].input);
	buffer_free(&sockets[i].output);
	break;
	}
	buffer_append(&sockets[i].input, buf, len);
	process_message(&sockets[i]);
	}
	break;
	default:
	fatal("Unknown type %d", sockets[i].type);
	}
	}

	void
	check_parent_exists(int sig)
	{
	if (parent_pid != -1 && kill(parent_pid, 0) < 0) {
	/* printf("Parent has died - Authentication agent exiting.\n"); */
	exit(1);
	}
	signal(SIGALRM, check_parent_exists);
	alarm(10);
	}

	void
	cleanup_socket(void)
	{
	remove(socket_name);
	rmdir(socket_dir);
	}

	void
	cleanup_exit(int i)
	{
	cleanup_socket();
	exit(i);
	}

	void
	usage()
	{
	fprintf(stderr, "ssh-agent version %s\n", SSH_VERSION);
	fprintf(stderr, "Usage: %s [-c \| -s] [-k] [command {args...]]\n",
	__progname);
	exit(1);
	}

	int
	main(int ac, char **av)
	{
	fd_set readset, writeset;
	int sock, c_flag = 0, k_flag = 0, s_flag = 0, ch;
	struct sockaddr_un sunaddr;
	pid_t pid;
	char shell, format, pidstr, pidstrbuf[1 + 3 sizeof pid];
	extern int optind;

	/* check if RSA support exists */
	if (rsa_alive() == 0) {
	fprintf(stderr,
	"%s: no RSA support in libssl and libcrypto. See ssl(8).\n",
	__progname);
	exit(1);
	}
	#ifdef __GNU_LIBRARY__
	while ((ch = getopt(ac, av, "+cks")) != -1) {
	#else /* __GNU_LIBRARY__ */
	while ((ch = getopt(ac, av, "cks")) != -1) {
	#endif /* __GNU_LIBRARY__ */
	switch (ch) {
	case 'c':
	if (s_flag)
	usage();
	c_flag++;
	break;
	case 'k':
	k_flag++;
	break;
	case 's':
	if (c_flag)
	usage();
	s_flag++;
	break;
	default:
	usage();
	}
	}
	ac -= optind;
	av += optind;

	if (ac > 0 && (c_flag \|\| k_flag \|\| s_flag))
	usage();

	if (ac == 0 && !c_flag && !k_flag && !s_flag) {
	shell = getenv("SHELL");
	if (shell != NULL && strncmp(shell + strlen(shell) - 3, "csh", 3) == 0)
	c_flag = 1;
	}
	if (k_flag) {
	pidstr = getenv(SSH_AGENTPID_ENV_NAME);
	if (pidstr == NULL) {
	fprintf(stderr, "%s not set, cannot kill agent\n",
	SSH_AGENTPID_ENV_NAME);
	exit(1);
	}
	pid = atoi(pidstr);
	if (pid < 1) { /* XXX PID_MAX check too */
	/* Yes, PID_MAX check please */
	fprintf(stderr, "%s=\"%s\", which is not a good PID\n",
	SSH_AGENTPID_ENV_NAME, pidstr);
	exit(1);
	}
	if (kill(pid, SIGTERM) == -1) {
	perror("kill");
	exit(1);
	}
	format = c_flag ? "unsetenv %s;\n" : "unset %s;\n";
	printf(format, SSH_AUTHSOCKET_ENV_NAME);
	printf(format, SSH_AGENTPID_ENV_NAME);
	printf("echo Agent pid %d killed;\n", pid);
	exit(0);
	}
	parent_pid = getpid();

	/* Create private directory for agent socket */
	strlcpy(socket_dir, "/tmp/ssh-XXXXXXXX", sizeof socket_dir);
	if (mkdtemp(socket_dir) == NULL) {
	perror("mkdtemp: private socket dir");
	exit(1);
	}
	snprintf(socket_name, sizeof socket_name, "%s/agent.%d", socket_dir,
	parent_pid);

	/*
	* Create socket early so it will exist before command gets run from
	* the parent.
	*/
	sock = socket(AF_UNIX, SOCK_STREAM, 0);
	if (sock < 0) {
	perror("socket");
	cleanup_exit(1);
	}
	memset(&sunaddr, 0, sizeof(sunaddr));
	sunaddr.sun_family = AF_UNIX;
	strlcpy(sunaddr.sun_path, socket_name, sizeof(sunaddr.sun_path));
	if (bind(sock, (struct sockaddr *) & sunaddr, sizeof(sunaddr)) < 0) {
	perror("bind");
	cleanup_exit(1);
	}
	if (listen(sock, 5) < 0) {
	perror("listen");
	cleanup_exit(1);
	}
	/*
	* Fork, and have the parent execute the command, if any, or present
	* the socket data. The child continues as the authentication agent.
	*/
	pid = fork();
	if (pid == -1) {
	perror("fork");
	exit(1);
	}
	if (pid != 0) { /* Parent - execute the given command. */
	close(sock);
	snprintf(pidstrbuf, sizeof pidstrbuf, "%d", pid);
	if (ac == 0) {
	format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
	printf(format, SSH_AUTHSOCKET_ENV_NAME, socket_name,
	SSH_AUTHSOCKET_ENV_NAME);
	printf(format, SSH_AGENTPID_ENV_NAME, pidstrbuf,
	SSH_AGENTPID_ENV_NAME);
	printf("echo Agent pid %d;\n", pid);
	exit(0);
	}
	setenv(SSH_AUTHSOCKET_ENV_NAME, socket_name, 1);
	setenv(SSH_AGENTPID_ENV_NAME, pidstrbuf, 1);
	execvp(av[0], av);
	perror(av[0]);
	exit(1);
	}
	close(0);
	close(1);
	close(2);

	if (setsid() == -1) {
	perror("setsid");
	cleanup_exit(1);
	}
	if (atexit(cleanup_socket) < 0) {
	perror("atexit");
	cleanup_exit(1);
	}
	new_socket(AUTH_SOCKET, sock);
	if (ac > 0) {
	signal(SIGALRM, check_parent_exists);
	alarm(10);
	}
	signal(SIGINT, SIG_IGN);
	signal(SIGPIPE, SIG_IGN);
	signal(SIGHUP, cleanup_exit);
	signal(SIGTERM, cleanup_exit);
	while (1) {
	FD_ZERO(&readset);
	FD_ZERO(&writeset);
	prepare_select(&readset, &writeset);
	if (select(max_fd + 1, &readset, &writeset, NULL, NULL) < 0) {
	if (errno == EINTR)
	continue;
	exit(1);
	}
	after_select(&readset, &writeset);
	}
	/* NOTREACHED */
	}