sshconnect1.c

OpenSSL Source code for SFTP, SSH, and many others

/*
 * Author: Tatu Ylonen <[e-mail]>
 * Copyright (c) 1995 Tatu Ylonen <[e-mail]>, Espoo, Finland
 *                    All rights reserved
 * Code to connect to a remote host, and to perform the client side of the
 * login (authentication) dialog.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"
RCSID("$OpenBSD: sshconnect1.c,v 1.51 2002/05/23 19:24:30 markus Exp $");

#include <openssl/bn.h>
#include <openssl/md5.h>

#ifdef KRB4
#include <krb.h>
#endif
#ifdef KRB5
#include <krb5.h>
#ifndef HEIMDAL
#define krb5_get_err_text(context,code) error_message(code)
#endif /* !HEIMDAL */
#endif
#ifdef AFS
#include <kafs.h>
#include "radix.h"
#endif

#include "ssh.h"
#include "ssh1.h"
#include "xmalloc.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "mpaux.h"
#include "uidswap.h"
#include "log.h"
#include "readconf.h"
#include "key.h"
#include "authfd.h"
#include "sshconnect.h"
#include "authfile.h"
#include "readpass.h"
#include "cipher.h"
#include "canohost.h"
#include "auth.h"

/* Session id for the current session. */
u_char session_id[16];
u_int supported_authentications = 0;

extern Options options;
extern char *__progname;

/*
 * Checks if the user has an authentication agent, and if so, tries to
 * authenticate using the agent.
 */
static int
try_agent_authentication(void)
{
	int type;
	char *comment;
	AuthenticationConnection *auth;
	u_char response[16];
	u_int i;
	Key *key;
	BIGNUM *challenge;

	/* Get connection to the agent. */
	auth = ssh_get_authentication_connection();
	if (!auth)
		return 0;

	if ((challenge = BN_new()) == NULL)
		fatal("try_agent_authentication: BN_new failed");
	/* Loop through identities served by the agent. */
	for (key = ssh_get_first_identity(auth, &comment, 1);
	    key != NULL;
	    key = ssh_get_next_identity(auth, &comment, 1)) {

		/* Try this identity. */
		debug("Trying RSA authentication via agent with '%.100s'", comment);
		xfree(comment);

		/* Tell the server that we are willing to authenticate using this key. */
		packet_start(SSH_CMSG_AUTH_RSA);
		packet_put_bignum(key->rsa->n);
		packet_send();
		packet_write_wait();

		/* Wait for server's response. */
		type = packet_read();

		/* The server sends failure if it doesn\'t like our key or
		   does not support RSA authentication. */
		if (type == SSH_SMSG_FAILURE) {
			debug("Server refused our key.");
			key_free(key);
			continue;
		}
		/* Otherwise it should have sent a challenge. */
		if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
			packet_disconnect("Protocol error during RSA authentication: %d",
					  type);

		packet_get_bignum(challenge);
		packet_check_eom();

		debug("Received RSA challenge from server.");

		/* Ask the agent to decrypt the challenge. */
		if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
			/*
			 * The agent failed to authenticate this identifier
			 * although it advertised it supports this.  Just
			 * return a wrong value.
			 */
			log("Authentication agent failed to decrypt challenge.");
			memset(response, 0, sizeof(response));
		}
		key_free(key);
		debug("Sending response to RSA challenge.");

		/* Send the decrypted challenge back to the server. */
		packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
		for (i = 0; i < 16; i++)
			packet_put_char(response[i]);
		packet_send();
		packet_write_wait();

		/* Wait for response from the server. */
		type = packet_read();

		/* The server returns success if it accepted the authentication. */
		if (type == SSH_SMSG_SUCCESS) {
			ssh_close_authentication_connection(auth);
			BN_clear_free(challenge);
			debug("RSA authentication accepted by server.");
			return 1;
		}
		/* Otherwise it should return failure. */
		if (type != SSH_SMSG_FAILURE)
			packet_disconnect("Protocol error waiting RSA auth response: %d",
					  type);
	}
	ssh_close_authentication_connection(auth);
	BN_clear_free(challenge);
	debug("RSA authentication using agent refused.");
	return 0;
}

/*
 * Computes the proper response to a RSA challenge, and sends the response to
 * the server.
 */
static void
respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
{
	u_char buf[32], response[16];
	MD5_CTX md;
	int i, len;

	/* Decrypt the challenge using the private key. */
	/* XXX think about Bleichenbacher, too */
	if (rsa_private_decrypt(challenge, challenge, prv) <= 0)
		packet_disconnect(
		    "respond_to_rsa_challenge: rsa_private_decrypt failed");

	/* Compute the response. */
	/* The response is MD5 of decrypted challenge plus session id. */
	len = BN_num_bytes(challenge);
	if (len <= 0 || len > sizeof(buf))
		packet_disconnect(
		    "respond_to_rsa_challenge: bad challenge length %d", len);

	memset(buf, 0, sizeof(buf));
	BN_bn2bin(challenge, buf + sizeof(buf) - len);
	MD5_Init(&md);
	MD5_Update(&md, buf, 32);
	MD5_Update(&md, session_id, 16);
	MD5_Final(response, &md);

	debug("Sending response to host key RSA challenge.");

	/* Send the response back to the server. */
	packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
		packet_put_char(response[i]);
	packet_send();
	packet_write_wait();

	memset(buf, 0, sizeof(buf));
	memset(response, 0, sizeof(response));
	memset(&md, 0, sizeof(md));
}

/*
 * Checks if the user has authentication file, and if so, tries to authenticate
 * the user using it.
 */
static int
try_rsa_authentication(int idx)
{
	BIGNUM *challenge;
	Key *public, *private;
	char buf[300], *passphrase, *comment, *authfile;
	int i, type, quit;

	public = options.identity_keys[idx];
	authfile = options.identity_files[idx];
	comment = xstrdup(authfile);

	debug("Trying RSA authentication with key '%.100s'", comment);

	/* Tell the server that we are willing to authenticate using this key. */
	packet_start(SSH_CMSG_AUTH_RSA);
	packet_put_bignum(public->rsa->n);
	packet_send();
	packet_write_wait();

	/* Wait for server's response. */
	type = packet_read();

	/*
	 * The server responds with failure if it doesn\'t like our key or
	 * doesn\'t support RSA authentication.
	 */
	if (type == SSH_SMSG_FAILURE) {
		debug("Server refused our key.");
		xfree(comment);
		return 0;
	}
	/* Otherwise, the server should respond with a challenge. */
	if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
		packet_disconnect("Protocol error during RSA authentication: %d", type);

	/* Get the challenge from the packet. */
	if ((challenge = BN_new()) == NULL)
		fatal("try_rsa_authentication: BN_new failed");
	packet_get_bignum(challenge);
	packet_check_eom();

	debug("Received RSA challenge from server.");

	/*
	 * If the key is not stored in external hardware, we have to
	 * load the private key.  Try first with empty passphrase; if it
	 * fails, ask for a passphrase.
	 */
	if (public->flags && KEY_FLAG_EXT)
		private = public;
	else
		private = key_load_private_type(KEY_RSA1, authfile, "", NULL);
	if (private == NULL && !options.batch_mode) {
		snprintf(buf, sizeof(buf),
		    "Enter passphrase for RSA key '%.100s': ", comment);
		for (i = 0; i < options.number_of_password_prompts; i++) {
			passphrase = read_passphrase(buf, 0);
			if (strcmp(passphrase, "") != 0) {
				private = key_load_private_type(KEY_RSA1,
				    authfile, passphrase, NULL);
				quit = 0;
			} else {
				debug2("no passphrase given, try next key");
				quit = 1;
			}
			memset(passphrase, 0, strlen(passphrase));
			xfree(passphrase);
			if (private != NULL || quit)
				break;
			debug2("bad passphrase given, try again...");
		}
	}
	/* We no longer need the comment. */
	xfree(comment);

	if (private == NULL) {
		if (!options.batch_mode)
			error("Bad passphrase.");

		/* Send a dummy response packet to avoid protocol error. */
		packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
		for (i = 0; i < 16; i++)
			packet_put_char(0);
		packet_send();
		packet_write_wait();

		/* Expect the server to reject it... */
		packet_read_expect(SSH_SMSG_FAILURE);
		BN_clear_free(challenge);
		return 0;
	}

	/* Compute and send a response to the challenge. */
	respond_to_rsa_challenge(challenge, private->rsa);

	/* Destroy the private key unless it in external hardware. */
	if (!(private->flags & KEY_FLAG_EXT))
		key_free(private);

	/* We no longer need the challenge. */
	BN_clear_free(challenge);

	/* Wait for response from the server. */
	type = packet_read();
	if (type == SSH_SMSG_SUCCESS) {
		debug("RSA authentication accepted by server.");
		return 1;
	}
	if (type != SSH_SMSG_FAILURE)
		packet_disconnect("Protocol error waiting RSA auth response: %d", type);
	debug("RSA authentication refused.");
	return 0;
}

/*
 * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
 * authentication and RSA host authentication.
 */
static int
try_rhosts_rsa_authentication(const char *local_user, Key * host_key)
{
	int type;
	BIGNUM *challenge;

	debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");

	/* Tell the server that we are willing to authenticate using this key. */
	packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
	packet_put_cstring(local_user);
	packet_put_int(BN_num_bits(host_key->rsa->n));
	packet_put_bignum(host_key->rsa->e);
	packet_put_bignum(host_key->rsa->n);
	packet_send();
	packet_write_wait();

	/* Wait for server's response. */
	type = packet_read();

	/* The server responds with failure if it doesn't admit our
	   .rhosts authentication or doesn't know our host key. */
	if (type == SSH_SMSG_FAILURE) {
		debug("Server refused our rhosts authentication or host key.");
		return 0;
	}
	/* Otherwise, the server should respond with a challenge. */
	if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
		packet_disconnect("Protocol error during RSA authentication: %d", type);

	/* Get the challenge from the packet. */
	if ((challenge = BN_new()) == NULL)
		fatal("try_rhosts_rsa_authentication: BN_new failed");
	packet_get_bignum(challenge);
	packet_check_eom();

	debug("Received RSA challenge for host key from server.");

	/* Compute a response to the challenge. */
	respond_to_rsa_challenge(challenge, host_key->rsa);

	/* We no longer need the challenge. */
	BN_clear_free(challenge);

	/* Wait for response from the server. */
	type = packet_read();
	if (type == SSH_SMSG_SUCCESS) {
		debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
		return 1;
	}
	if (type != SSH_SMSG_FAILURE)
		packet_disconnect("Protocol error waiting RSA auth response: %d", type);
	debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
	return 0;
}

#ifdef KRB4
static int
try_krb4_authentication(void)
{
	KTEXT_ST auth;		/* Kerberos data */
	char *reply;
	char inst[INST_SZ];
	char *realm;
	CREDENTIALS cred;
	int r, type;
	socklen_t slen;
	Key_schedule schedule;
	u_long checksum, cksum;
	MSG_DAT msg_data;
	struct sockaddr_in local, foreign;
	struct stat st;

	/* Don't do anything if we don't have any tickets. */
	if (stat(tkt_string(), &st) < 0)
		return 0;

	strlcpy(inst, (char *)krb_get_phost(get_canonical_hostname(1)),
	    INST_SZ);

	realm = (char *)krb_realmofhost(get_canonical_hostname(1));
	if (!realm) {
		debug("Kerberos v4: no realm for %s", get_canonical_hostname(1));
		return 0;
	}
	/* This can really be anything. */
	checksum = (u_long)getpid();

	r = krb_mk_req(&auth, KRB4_SERVICE_NAME, inst, realm, checksum);
	if (r != KSUCCESS) {
		debug("Kerberos v4 krb_mk_req failed: %s", krb_err_txt[r]);
		return 0;
	}
	/* Get session key to decrypt the server's reply with. */
	r = krb_get_cred(KRB4_SERVICE_NAME, inst, realm, &cred);
	if (r != KSUCCESS) {
		debug("get_cred failed: %s", krb_err_txt[r]);
		return 0;
	}
	des_key_sched((des_cblock *) cred.session, schedule);

	/* Send authentication info to server. */
	packet_start(SSH_CMSG_AUTH_KERBEROS);
	packet_put_string((char *) auth.dat, auth.length);
	packet_send();
	packet_write_wait();

	/* Zero the buffer. */
	(void) memset(auth.dat, 0, MAX_KTXT_LEN);