split auth/sshconnect in one file per protocol version

1 files changed, 1020 insertions, 0 deletions

diff --git a/usr.bin/ssh/sshconnect1.c b/usr.bin/ssh/sshconnect1.c
new file mode 100644
index 00000000000..c5a76654bc6
--- /dev/null
+++ b/usr.bin/ssh/sshconnect1.c
@@ -0,0 +1,1020 @@
+/*
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ *                    All rights reserved
+ * Created: Sat Mar 18 22:15:47 1995 ylo
+ * Code to connect to a remote host, and to perform the client side of the
+ * login (authentication) dialog.
+ *
+ */
+
+#include "includes.h"
+RCSID("$OpenBSD: sshconnect1.c,v 1.1 2000/04/26 21:28:33 markus Exp $");
+
+#include <openssl/bn.h>
+#include <openssl/dsa.h>
+#include <openssl/rsa.h>
+#include <openssl/evp.h>
+
+#include "xmalloc.h"
+#include "rsa.h"
+#include "ssh.h"
+#include "buffer.h"
+#include "packet.h"
+#include "authfd.h"
+#include "cipher.h"
+#include "mpaux.h"
+#include "uidswap.h"
+#include "readconf.h"
+#include "key.h"
+#include "sshconnect.h"
+#include "authfile.h"
+
+/* Session id for the current session. */
+unsigned char session_id[16];
+unsigned 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.
+ */
+int
+try_agent_authentication()
+{
+	int status, type;
+	char *comment;
+	AuthenticationConnection *auth;
+	unsigned char response[16];
+	unsigned int i;
+	BIGNUM *e, *n, *challenge;
+
+	/* Get connection to the agent. */
+	auth = ssh_get_authentication_connection();
+	if (!auth)
+		return 0;
+
+	e = BN_new();
+	n = BN_new();
+	challenge = BN_new();
+
+	/* Loop through identities served by the agent. */
+	for (status = ssh_get_first_identity(auth, e, n, &comment);
+	     status;
+	     status = ssh_get_next_identity(auth, e, n, &comment)) {
+		int plen, clen;
+
+		/* 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(n);
+		packet_send();
+		packet_write_wait();
+
+		/* Wait for server's response. */
+		type = packet_read(&plen);
+
+		/* 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.");
+			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, &clen);
+
+		packet_integrity_check(plen, clen, type);
+
+		debug("Received RSA challenge from server.");
+
+		/* Ask the agent to decrypt the challenge. */
+		if (!ssh_decrypt_challenge(auth, e, n, 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));
+		}
+		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(&plen);
+
+		/* The server returns success if it accepted the authentication. */
+		if (type == SSH_SMSG_SUCCESS) {
+			debug("RSA authentication accepted by server.");
+			BN_clear_free(e);
+			BN_clear_free(n);
+			BN_clear_free(challenge);
+			return 1;
+		}
+		/* Otherwise it should return failure. */
+		if (type != SSH_SMSG_FAILURE)
+			packet_disconnect("Protocol error waiting RSA auth response: %d",
+					  type);
+	}
+
+	BN_clear_free(e);
+	BN_clear_free(n);
+	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.
+ */
+void
+respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
+{
+	unsigned char buf[32], response[16];
+	MD5_CTX md;
+	int i, len;
+
+	/* Decrypt the challenge using the private key. */
+	rsa_private_decrypt(challenge, challenge, prv);
+
+	/* 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.
+ */
+int
+try_rsa_authentication(const char *authfile)
+{
+	BIGNUM *challenge;
+	Key *public;
+	Key *private;
+	char *passphrase, *comment;
+	int type, i;
+	int plen, clen;
+
+	/* Try to load identification for the authentication key. */
+	public = key_new(KEY_RSA);
+	if (!load_public_key(authfile, public, &comment)) {
+		key_free(public);
+		/* Could not load it.  Fail. */
+		return 0;
+	}
+	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();
+
+	/* We no longer need the public key. */
+	key_free(public);
+
+	/* Wait for server's response. */
+	type = packet_read(&plen);
+
+	/*
+	 * 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. */
+	challenge = BN_new();
+	packet_get_bignum(challenge, &clen);
+
+	packet_integrity_check(plen, clen, type);
+
+	debug("Received RSA challenge from server.");
+
+	private = key_new(KEY_RSA);
+	/*
+	 * Load the private key.  Try first with empty passphrase; if it
+	 * fails, ask for a passphrase.
+	 */
+	if (!load_private_key(authfile, "", private, NULL)) {
+		char buf[300];
+		snprintf(buf, sizeof buf, "Enter passphrase for RSA key '%.100s': ",
+		    comment);
+		if (!options.batch_mode)
+			passphrase = read_passphrase(buf, 0);
+		else {
+			debug("Will not query passphrase for %.100s in batch mode.",
+			      comment);
+			passphrase = xstrdup("");
+		}
+
+		/* Load the authentication file using the pasphrase. */
+		if (!load_private_key(authfile, passphrase, private, NULL)) {
+			memset(passphrase, 0, strlen(passphrase));
+			xfree(passphrase);
+			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(&plen, SSH_SMSG_FAILURE);
+			xfree(comment);
+			return 0;
+		}
+		/* Destroy the passphrase. */
+		memset(passphrase, 0, strlen(passphrase));
+		xfree(passphrase);
+	}
+	/* We no longer need the comment. */
+	xfree(comment);
+
+	/* Compute and send a response to the challenge. */
+	respond_to_rsa_challenge(challenge, private->rsa);
+
+	/* Destroy the private key. */
+	key_free(private);
+
+	/* We no longer need the challenge. */
+	BN_clear_free(challenge);
+
+	/* Wait for response from the server. */
+	type = packet_read(&plen);
+	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.
+ */
+int
+try_rhosts_rsa_authentication(const char *local_user, RSA * host_key)
+{
+	int type;
+	BIGNUM *challenge;
+	int plen, clen;
+
+	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_string(local_user, strlen(local_user));
+	packet_put_int(BN_num_bits(host_key->n));
+	packet_put_bignum(host_key->e);
+	packet_put_bignum(host_key->n);
+	packet_send();
+	packet_write_wait();
+
+	/* Wait for server's response. */
+	type = packet_read(&plen);
+
+	/* 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. */
+	challenge = BN_new();
+	packet_get_bignum(challenge, &clen);
+
+	packet_integrity_check(plen, clen, type);
+
+	debug("Received RSA challenge for host key from server.");
+
+	/* Compute a response to the challenge. */
+	respond_to_rsa_challenge(challenge, host_key);
+
+	/* We no longer need the challenge. */
+	BN_clear_free(challenge);
+
+	/* Wait for response from the server. */
+	type = packet_read(&plen);
+	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
+int
+try_kerberos_authentication()
+{
+	KTEXT_ST auth;		/* Kerberos data */
+	char *reply;
+	char inst[INST_SZ];
+	char *realm;
+	CREDENTIALS cred;
+	int r, type, plen;
+	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;
+
+	strncpy(inst, (char *) krb_get_phost(get_canonical_hostname()), INST_SZ);
+
+	realm = (char *) krb_realmofhost(get_canonical_hostname());
+	if (!realm) {
+		debug("Kerberos V4: no realm for %s", get_canonical_hostname());
+		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);
+
+	slen = sizeof(local);
+	memset(&local, 0, sizeof(local));
+	if (getsockname(packet_get_connection_in(),
+			(struct sockaddr *) & local, &slen) < 0)
+		debug("getsockname failed: %s", strerror(errno));
+
+	slen = sizeof(foreign);
+	memset(&foreign, 0, sizeof(foreign));
+	if (getpeername(packet_get_connection_in(),
+			(struct sockaddr *) & foreign, &slen) < 0) {
+		debug("getpeername failed: %s", strerror(errno));
+		fatal_cleanup();
+	}
+	/* Get server reply. */
+	type = packet_read(&plen);
+	switch (type) {
+	case SSH_SMSG_FAILURE:
+		/* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
+		debug("Kerberos V4 authentication failed.");
+		return 0;
+		break;
+
+	case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
+		/* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
+		debug("Kerberos V4 authentication accepted.");
+
+		/* Get server's response. */
+		reply = packet_get_string((unsigned int *) &auth.length);
+		memcpy(auth.dat, reply, auth.length);
+		xfree(reply);
+
+		packet_integrity_check(plen, 4 + auth.length, type);
+
+		/*
+		 * If his response isn't properly encrypted with the session
+		 * key, and the decrypted checksum fails to match, he's
+		 * bogus. Bail out.
+		 */
+		r = krb_rd_priv(auth.dat, auth.length, schedule, &cred.session,
+				&foreign, &local, &msg_data);
+		if (r != KSUCCESS) {
+			debug("Kerberos V4 krb_rd_priv failed: %s", krb_err_txt[r]);
+			packet_disconnect("Kerberos V4 challenge failed!");
+		}
+		/* Fetch the (incremented) checksum that we supplied in the request. */
+		(void) memcpy((char *) &cksum, (char *) msg_data.app_data, sizeof(cksum));
+		cksum = ntohl(cksum);
+
+		/* If it matches, we're golden. */
+		if (cksum == checksum + 1) {
+			debug("Kerberos V4 challenge successful.");
+			return 1;
+		} else
+			packet_disconnect("Kerberos V4 challenge failed!");
+		break;
+
+	default:
+		packet_disconnect("Protocol error on Kerberos V4 response: %d", type);
+	}
+	return 0;
+}
+
+#endif /* KRB4 */
+
+#ifdef AFS
+int
+send_kerberos_tgt()
+{
+	CREDENTIALS *creds;
+	char pname[ANAME_SZ], pinst[INST_SZ], prealm[REALM_SZ];
+	int r, type, plen;
+	char buffer[8192];
+	struct stat st;
+
+	/* Don't do anything if we don't have any tickets. */
+	if (stat(tkt_string(), &st) < 0)
+		return 0;
+
+	creds = xmalloc(sizeof(*creds));
+
+	if ((r = krb_get_tf_fullname(TKT_FILE, pname, pinst, prealm)) != KSUCCESS) {
+		debug("Kerberos V4 tf_fullname failed: %s", krb_err_txt[r]);
+		return 0;
+	}
+	if ((r = krb_get_cred("krbtgt", prealm, prealm, creds)) != GC_OK) {
+		debug("Kerberos V4 get_cred failed: %s", krb_err_txt[r]);
+		return 0;
+	}
+	if (time(0) > krb_life_to_time(creds->issue_date, creds->lifetime)) {
+		debug("Kerberos V4 ticket expired: %s", TKT_FILE);
+		return 0;
+	}
+	creds_to_radix(creds, (unsigned char *)buffer);
+	xfree(creds);
+
+	packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
+	packet_put_string(buffer, strlen(buffer));
+	packet_send();
+	packet_write_wait();
+
+	type = packet_read(&plen);
+
+	if (type == SSH_SMSG_FAILURE)
+		debug("Kerberos TGT for realm %s rejected.", prealm);
+	else if (type != SSH_SMSG_SUCCESS)
+		packet_disconnect("Protocol error on Kerberos TGT response: %d", type);
+
+	return 1;
+}
+
+void
+send_afs_tokens(void)
+{
+	CREDENTIALS creds;
+	struct ViceIoctl parms;
+	struct ClearToken ct;
+	int i, type, len, plen;
+	char buf[2048], *p, *server_cell;
+	char buffer[8192];
+
+	/* Move over ktc_GetToken, here's something leaner. */
+	for (i = 0; i < 100; i++) {	/* just in case */
+		parms.in = (char *) &i;
+		parms.in_size = sizeof(i);
+		parms.out = buf;
+		parms.out_size = sizeof(buf);
+		if (k_pioctl(0, VIOCGETTOK, &parms, 0) != 0)
+			break;
+		p = buf;
+
+		/* Get secret token. */
+		memcpy(&creds.ticket_st.length, p, sizeof(unsigned int));
+		if (creds.ticket_st.length > MAX_KTXT_LEN)
+			break;
+		p += sizeof(unsigned int);
+		memcpy(creds.ticket_st.dat, p, creds.ticket_st.length);
+		p += creds.ticket_st.length;
+
+		/* Get clear token. */
+		memcpy(&len, p, sizeof(len));
+		if (len != sizeof(struct ClearToken))
+			break;
+		p += sizeof(len);
+		memcpy(&ct, p, len);
+		p += len;
+		p += sizeof(len);	/* primary flag */
+		server_cell = p;
+
+		/* Flesh out our credentials. */
+		strlcpy(creds.service, "afs", sizeof creds.service);
+		creds.instance[0] = '\0';
+		strlcpy(creds.realm, server_cell, REALM_SZ);
+		memcpy(creds.session, ct.HandShakeKey, DES_KEY_SZ);
+		creds.issue_date = ct.BeginTimestamp;
+		creds.lifetime = krb_time_to_life(creds.issue_date, ct.EndTimestamp);
+		creds.kvno = ct.AuthHandle;
+		snprintf(creds.pname, sizeof(creds.pname), "AFS ID %d", ct.ViceId);
+		creds.pinst[0] = '\0';
+
+		/* Encode token, ship it off. */
+		if (!creds_to_radix(&creds, (unsigned char*) buffer))
+			break;
+		packet_start(SSH_CMSG_HAVE_AFS_TOKEN);
+		packet_put_string(buffer, strlen(buffer));
+		packet_send();
+		packet_write_wait();
+
+		/* Roger, Roger. Clearance, Clarence. What's your vector,
+		   Victor? */
+		type = packet_read(&plen);
+
+		if (type == SSH_SMSG_FAILURE)
+			debug("AFS token for cell %s rejected.", server_cell);
+		else if (type != SSH_SMSG_SUCCESS)
+			packet_disconnect("Protocol error on AFS token response: %d", type);
+	}
+}
+
+#endif /* AFS */
+
+/*
+ * Tries to authenticate with any string-based challenge/response system.
+ * Note that the client code is not tied to s/key or TIS.
+ */
+int
+try_skey_authentication()
+{
+	int type, i;
+	int payload_len;
+	unsigned int clen;
+	char *challenge, *response;
+
+	debug("Doing skey authentication.");
+
+	/* request a challenge */
+	packet_start(SSH_CMSG_AUTH_TIS);
+	packet_send();
+	packet_write_wait();
+
+	type = packet_read(&payload_len);
+	if (type != SSH_SMSG_FAILURE &&
+	    type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
+		packet_disconnect("Protocol error: got %d in response "
+				  "to skey-auth", type);
+	}
+	if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
+		debug("No challenge for skey authentication.");
+		return 0;
+	}
+	challenge = packet_get_string(&clen);
+	packet_integrity_check(payload_len, (4 + clen), type);
+	if (options.cipher == SSH_CIPHER_NONE)
+		log("WARNING: Encryption is disabled! "
+		    "Reponse will be transmitted in clear text.");
+	fprintf(stderr, "%s\n", challenge);
+	xfree(challenge);
+	fflush(stderr);
+	for (i = 0; i < options.number_of_password_prompts; i++) {
+		if (i != 0)
+			error("Permission denied, please try again.");
+		response = read_passphrase("Response: ", 0);
+		packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
+		packet_put_string(response, strlen(response));
+		memset(response, 0, strlen(response));
+		xfree(response);
+		packet_send();
+		packet_write_wait();
+		type = packet_read(&payload_len);
+		if (type == SSH_SMSG_SUCCESS)
+			return 1;
+		if (type != SSH_SMSG_FAILURE)
+			packet_disconnect("Protocol error: got %d in response "
+					  "to skey-auth-reponse", type);
+	}
+	/* failure */
+	return 0;
+}
+
+/*
+ * Tries to authenticate with plain passwd authentication.
+ */
+int
+try_password_authentication(char *prompt)
+{
+	int type, i, payload_len;
+	char *password;
+
+	debug("Doing password authentication.");
+	if (options.cipher == SSH_CIPHER_NONE)
+		log("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
+	for (i = 0; i < options.number_of_password_prompts; i++) {
+		if (i != 0)
+			error("Permission denied, please try again.");
+		password = read_passphrase(prompt, 0);
+		packet_start(SSH_CMSG_AUTH_PASSWORD);
+		packet_put_string(password, strlen(password));
+		memset(password, 0, strlen(password));
+		xfree(password);
+		packet_send();
+		packet_write_wait();
+
+		type = packet_read(&payload_len);
+		if (type == SSH_SMSG_SUCCESS)
+			return 1;
+		if (type != SSH_SMSG_FAILURE)
+			packet_disconnect("Protocol error: got %d in response to passwd auth", type);
+	}
+	/* failure */
+	return 0;
+}
+
+/*
+ * SSH1 key exchange
+ */
+void
+ssh_kex(char *host, struct sockaddr *hostaddr)
+{
+	int i;
+	BIGNUM *key;
+	RSA *host_key;
+	RSA *public_key;
+	Key k;
+	int bits, rbits;
+	int ssh_cipher_default = SSH_CIPHER_3DES;
+	unsigned char session_key[SSH_SESSION_KEY_LENGTH];
+	unsigned char cookie[8];
+	unsigned int supported_ciphers;
+	unsigned int server_flags, client_flags;
+	int payload_len, clen, sum_len = 0;
+	u_int32_t rand = 0;
+
+	debug("Waiting for server public key.");
+
+	/* Wait for a public key packet from the server. */
+	packet_read_expect(&payload_len, SSH_SMSG_PUBLIC_KEY);
+
+	/* Get cookie from the packet. */
+	for (i = 0; i < 8; i++)
+		cookie[i] = packet_get_char();
+
+	/* Get the public key. */
+	public_key = RSA_new();
+	bits = packet_get_int();/* bits */
+	public_key->e = BN_new();
+	packet_get_bignum(public_key->e, &clen);
+	sum_len += clen;
+	public_key->n = BN_new();
+	packet_get_bignum(public_key->n, &clen);
+	sum_len += clen;
+
+	rbits = BN_num_bits(public_key->n);
+	if (bits != rbits) {
+		log("Warning: Server lies about size of server public key: "
+		    "actual size is %d bits vs. announced %d.", rbits, bits);
+		log("Warning: This may be due to an old implementation of ssh.");
+	}
+	/* Get the host key. */
+	host_key = RSA_new();
+	bits = packet_get_int();/* bits */
+	host_key->e = BN_new();
+	packet_get_bignum(host_key->e, &clen);
+	sum_len += clen;
+	host_key->n = BN_new();
+	packet_get_bignum(host_key->n, &clen);
+	sum_len += clen;
+
+	rbits = BN_num_bits(host_key->n);
+	if (bits != rbits) {
+		log("Warning: Server lies about size of server host key: "
+		    "actual size is %d bits vs. announced %d.", rbits, bits);
+		log("Warning: This may be due to an old implementation of ssh.");
+	}
+
+	/* Get protocol flags. */
+	server_flags = packet_get_int();
+	packet_set_protocol_flags(server_flags);
+
+	supported_ciphers = packet_get_int();
+	supported_authentications = packet_get_int();
+
+	debug("Received server public key (%d bits) and host key (%d bits).",
+	      BN_num_bits(public_key->n), BN_num_bits(host_key->n));
+
+	packet_integrity_check(payload_len,
+			       8 + 4 + sum_len + 0 + 4 + 0 + 0 + 4 + 4 + 4,
+			       SSH_SMSG_PUBLIC_KEY);
+	k.type = KEY_RSA;
+	k.rsa = host_key;
+	check_host_key(host, hostaddr, &k,
+	    options.user_hostfile, options.system_hostfile);
+
+	client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
+
+	compute_session_id(session_id, cookie, host_key->n, public_key->n);
+
+	/* Generate a session key. */
+	arc4random_stir();
+
+	/*
+	 * Generate an encryption key for the session.   The key is a 256 bit
+	 * random number, interpreted as a 32-byte key, with the least
+	 * significant 8 bits being the first byte of the key.
+	 */
+	for (i = 0; i < 32; i++) {
+		if (i % 4 == 0)
+			rand = arc4random();
+		session_key[i] = rand & 0xff;
+		rand >>= 8;
+	}
+
+	/*
+	 * According to the protocol spec, the first byte of the session key
+	 * is the highest byte of the integer.  The session key is xored with
+	 * the first 16 bytes of the session id.
+	 */
+	key = BN_new();
+	BN_set_word(key, 0);
+	for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
+		BN_lshift(key, key, 8);
+		if (i < 16)
+			BN_add_word(key, session_key[i] ^ session_id[i]);
+		else
+			BN_add_word(key, session_key[i]);
+	}
+
+	/*
+	 * Encrypt the integer using the public key and host key of the
+	 * server (key with smaller modulus first).
+	 */
+	if (BN_cmp(public_key->n, host_key->n) < 0) {
+		/* Public key has smaller modulus. */
+		if (BN_num_bits(host_key->n) <
+		    BN_num_bits(public_key->n) + SSH_KEY_BITS_RESERVED) {
+			fatal("respond_to_rsa_challenge: host_key %d < public_key %d + "
+			      "SSH_KEY_BITS_RESERVED %d",
+			      BN_num_bits(host_key->n),
+			      BN_num_bits(public_key->n),
+			      SSH_KEY_BITS_RESERVED);
+		}
+		rsa_public_encrypt(key, key, public_key);
+		rsa_public_encrypt(key, key, host_key);
+	} else {
+		/* Host key has smaller modulus (or they are equal). */
+		if (BN_num_bits(public_key->n) <
+		    BN_num_bits(host_key->n) + SSH_KEY_BITS_RESERVED) {
+			fatal("respond_to_rsa_challenge: public_key %d < host_key %d + "
+			      "SSH_KEY_BITS_RESERVED %d",
+			      BN_num_bits(public_key->n),
+			      BN_num_bits(host_key->n),
+			      SSH_KEY_BITS_RESERVED);
+		}
+		rsa_public_encrypt(key, key, host_key);
+		rsa_public_encrypt(key, key, public_key);
+	}
+
+	/* Destroy the public keys since we no longer need them. */
+	RSA_free(public_key);
+	RSA_free(host_key);
+
+	if (options.cipher == SSH_CIPHER_NOT_SET) {
+		if (cipher_mask1() & supported_ciphers & (1 << ssh_cipher_default))
+			options.cipher = ssh_cipher_default;
+		else {
+			debug("Cipher %s not supported, using %.100s instead.",
+			      cipher_name(ssh_cipher_default),
+			      cipher_name(SSH_FALLBACK_CIPHER));
+			options.cipher = SSH_FALLBACK_CIPHER;
+		}
+	}
+	/* Check that the selected cipher is supported. */
+	if (!(supported_ciphers & (1 << options.cipher)))
+		fatal("Selected cipher type %.100s not supported by server.",
+		      cipher_name(options.cipher));
+
+	debug("Encryption type: %.100s", cipher_name(options.cipher));
+
+	/* Send the encrypted session key to the server. */
+	packet_start(SSH_CMSG_SESSION_KEY);
+	packet_put_char(options.cipher);
+
+	/* Send the cookie back to the server. */
+	for (i = 0; i < 8; i++)
+		packet_put_char(cookie[i]);
+
+	/* Send and destroy the encrypted encryption key integer. */
+	packet_put_bignum(key);
+	BN_clear_free(key);
+
+	/* Send protocol flags. */
+	packet_put_int(client_flags);
+
+	/* Send the packet now. */
+	packet_send();
+	packet_write_wait();
+
+	debug("Sent encrypted session key.");
+
+	/* Set the encryption key. */
+	packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options.cipher);
+
+	/* We will no longer need the session key here.  Destroy any extra copies. */
+	memset(session_key, 0, sizeof(session_key));
+
+	/*
+	 * Expect a success message from the server.  Note that this message
+	 * will be received in encrypted form.
+	 */
+	packet_read_expect(&payload_len, SSH_SMSG_SUCCESS);
+
+	debug("Received encrypted confirmation.");
+}
+
+/*
+ * Authenticate user
+ */
+void
+ssh_userauth(
+    const char* local_user,
+    const char* server_user,
+    char *host,
+    int host_key_valid, RSA *own_host_key)
+{
+	int i, type;
+	int payload_len;
+
+	if (supported_authentications == 0)
+		fatal("ssh_userauth: server supports no auth methods");
+
+	/* Send the name of the user to log in as on the server. */
+	packet_start(SSH_CMSG_USER);
+	packet_put_string(server_user, strlen(server_user));
+	packet_send();
+	packet_write_wait();
+
+	/*
+	 * The server should respond with success if no authentication is
+	 * needed (the user has no password).  Otherwise the server responds
+	 * with failure.
+	 */
+	type = packet_read(&payload_len);
+
+	/* check whether the connection was accepted without authentication. */
+	if (type == SSH_SMSG_SUCCESS)
+		return;
+	if (type != SSH_SMSG_FAILURE)
+		packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER",
+				  type);
+
+#ifdef AFS
+	/* Try Kerberos tgt passing if the server supports it. */
+	if ((supported_authentications & (1 << SSH_PASS_KERBEROS_TGT)) &&
+	    options.kerberos_tgt_passing) {
+		if (options.cipher == SSH_CIPHER_NONE)
+			log("WARNING: Encryption is disabled! Ticket will be transmitted in the clear!");
+		(void) send_kerberos_tgt();
+	}
+	/* Try AFS token passing if the server supports it. */
+	if ((supported_authentications & (1 << SSH_PASS_AFS_TOKEN)) &&
+	    options.afs_token_passing && k_hasafs()) {
+		if (options.cipher == SSH_CIPHER_NONE)
+			log("WARNING: Encryption is disabled! Token will be transmitted in the clear!");
+		send_afs_tokens();
+	}
+#endif /* AFS */
+
+#ifdef KRB4
+	if ((supported_authentications & (1 << SSH_AUTH_KERBEROS)) &&
+	    options.kerberos_authentication) {
+		debug("Trying Kerberos authentication.");
+		if (try_kerberos_authentication()) {
+			/* The server should respond with success or failure. */
+			type = packet_read(&payload_len);
+			if (type == SSH_SMSG_SUCCESS)
+				return;
+			if (type != SSH_SMSG_FAILURE)
+				packet_disconnect("Protocol error: got %d in response to Kerberos auth", type);
+		}
+	}
+#endif /* KRB4 */
+
+	/*
+	 * Use rhosts authentication if running in privileged socket and we
+	 * do not wish to remain anonymous.
+	 */
+	if ((supported_authentications & (1 << SSH_AUTH_RHOSTS)) &&
+	    options.rhosts_authentication) {
+		debug("Trying rhosts authentication.");
+		packet_start(SSH_CMSG_AUTH_RHOSTS);
+		packet_put_string(local_user, strlen(local_user));
+		packet_send();
+		packet_write_wait();
+
+		/* The server should respond with success or failure. */
+		type = packet_read(&payload_len);
+		if (type == SSH_SMSG_SUCCESS)
+			return;
+		if (type != SSH_SMSG_FAILURE)
+			packet_disconnect("Protocol error: got %d in response to rhosts auth",
+					  type);
+	}
+	/*
+	 * Try .rhosts or /etc/hosts.equiv authentication with RSA host
+	 * authentication.
+	 */
+	if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
+	    options.rhosts_rsa_authentication && host_key_valid) {
+		if (try_rhosts_rsa_authentication(local_user, own_host_key))
+			return;
+	}
+	/* Try RSA authentication if the server supports it. */
+	if ((supported_authentications & (1 << SSH_AUTH_RSA)) &&
+	    options.rsa_authentication) {
+		/*
+		 * Try RSA authentication using the authentication agent. The
+		 * agent is tried first because no passphrase is needed for
+		 * it, whereas identity files may require passphrases.
+		 */
+		if (try_agent_authentication())
+			return;
+
+		/* Try RSA authentication for each identity. */
+		for (i = 0; i < options.num_identity_files; i++)
+			if (try_rsa_authentication(options.identity_files[i]))
+				return;
+	}
+	/* Try skey authentication if the server supports it. */
+	if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
+	    options.skey_authentication && !options.batch_mode) {
+		if (try_skey_authentication())
+			return;
+	}
+	/* Try password authentication if the server supports it. */
+	if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
+	    options.password_authentication && !options.batch_mode) {
+		char prompt[80];
+
+		snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
+		    server_user, host);
+		if (try_password_authentication(prompt))
+			return;
+	}
+	/* All authentication methods have failed.  Exit with an error message. */
+	fatal("Permission denied.");
+	/* NOTREACHED */
+}