split key exchange (kex) and user authentication (user-auth), ok: provos@

2 files changed, 106 insertions, 81 deletions

diff --git a/usr.bin/ssh/sshconnect.c b/usr.bin/ssh/sshconnect.c
index 15db438c705..f16e2b32dab 100644
--- a/usr.bin/ssh/sshconnect.c
+++ b/usr.bin/ssh/sshconnect.c
@@ -8,7 +8,7 @@
  */
 
 #include "includes.h"
-RCSID("$Id: sshconnect.c,v 1.50 2000/01/05 08:32:42 markus Exp $");
+RCSID("$OpenBSD: sshconnect.c,v 1.51 2000/01/16 23:03:10 markus Exp $");
 
 #include <ssl/bn.h>
 #include "xmalloc.h"
@@ -28,6 +28,9 @@ RCSID("$Id: sshconnect.c,v 1.50 2000/01/05 08:32:42 markus Exp $");
 /* Session id for the current session. */
 unsigned char session_id[16];
 
+/* authentications supported by server */
+unsigned int supported_authentications;
+
 extern Options options;
 extern char *__progname;
 
@@ -1264,63 +1267,31 @@ check_host_key(char *host, struct sockaddr *hostaddr, RSA *host_key)
 }
 
 /*
- * Starts a dialog with the server, and authenticates the current user on the
- * server.  This does not need any extra privileges.  The basic connection
- * to the server must already have been established before this is called.
- * User is the remote user; if it is NULL, the current local user name will
- * be used.  Anonymous indicates that no rhosts authentication will be used.
- * If login fails, this function prints an error and never returns.
- * This function does not require super-user privileges.
+ * SSH1 key exchange
  */
 void
-ssh_login(int host_key_valid,
-	  RSA *own_host_key,
-	  const char *orighost,
-	  struct sockaddr *hostaddr,
-	  uid_t original_real_uid)
+ssh_kex(char *host, struct sockaddr *hostaddr)
 {
-	int i, type;
-	struct passwd *pw;
+	int i;
 	BIGNUM *key;
 	RSA *host_key;
 	RSA *public_key;
 	int bits, rbits;
 	unsigned char session_key[SSH_SESSION_KEY_LENGTH];
-	const char *server_user, *local_user;
-	char *host, *cp;
-	unsigned char check_bytes[8];
-	unsigned int supported_ciphers, supported_authentications;
+	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;
 
-	/* Convert the user-supplied hostname into all lowercase. */
-	host = xstrdup(orighost);
-	for (cp = host; *cp; cp++)
-		if (isupper(*cp))
-			*cp = tolower(*cp);
-
-	/* Exchange protocol version identification strings with the server. */
-	ssh_exchange_identification();
-
-	/* Put the connection into non-blocking mode. */
-	packet_set_nonblocking();
-
-	/* Get local user name.  Use it as server user if no user name was given. */
-	pw = getpwuid(original_real_uid);
-	if (!pw)
-		fatal("User id %d not found from user database.", original_real_uid);
-	local_user = xstrdup(pw->pw_name);
-	server_user = options.user ? options.user : local_user;
-
 	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 check bytes from the packet. */
+	/* Get cookie from the packet. */
 	for (i = 0; i < 8; i++)
-		check_bytes[i] = packet_get_char();
+		cookie[i] = packet_get_char();
 
 	/* Get the public key. */
 	public_key = RSA_new();
@@ -1373,7 +1344,7 @@ ssh_login(int host_key_valid,
 
 	client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
 
-	compute_session_id(session_id, check_bytes, host_key->n, public_key->n);
+	compute_session_id(session_id, cookie, host_key->n, public_key->n);
 
 	/* Generate a session key. */
 	arc4random_stir();
@@ -1456,9 +1427,9 @@ ssh_login(int host_key_valid,
 	packet_start(SSH_CMSG_SESSION_KEY);
 	packet_put_char(options.cipher);
 
-	/* Send the check bytes back to the server. */
+	/* Send the cookie back to the server. */
 	for (i = 0; i < 8; i++)
-		packet_put_char(check_bytes[i]);
+		packet_put_char(cookie[i]);
 
 	/* Send the encrypted encryption key. */
 	packet_put_bignum(key);
@@ -1490,6 +1461,26 @@ ssh_login(int host_key_valid,
 	packet_read_expect(&payload_len, SSH_SMSG_SUCCESS);
 
 	debug("Received encrypted confirmation.");
+}
+
+/*
+ * Authenticate user
+ */
+void
+ssh_userauth(int host_key_valid, RSA *own_host_key,
+    uid_t original_real_uid, char *host)
+{
+	int i, type;
+	int payload_len;
+	struct passwd *pw;
+	const char *server_user, *local_user;
+
+	/* Get local user name.  Use it as server user if no user name was given. */
+	pw = getpwuid(original_real_uid);
+	if (!pw)
+		fatal("User id %d not found from user database.", original_real_uid);
+	local_user = xstrdup(pw->pw_name);
+	server_user = options.user ? options.user : local_user;
 
 	/* Send the name of the user to log in as on the server. */
 	packet_start(SSH_CMSG_USER);
@@ -1608,3 +1599,37 @@ ssh_login(int host_key_valid,
 	fatal("Permission denied.");
 	/* NOTREACHED */
 }
+
+/*
+ * Starts a dialog with the server, and authenticates the current user on the
+ * server.  This does not need any extra privileges.  The basic connection
+ * to the server must already have been established before this is called.
+ * If login fails, this function prints an error and never returns.
+ * This function does not require super-user privileges.
+ */
+void
+ssh_login(int host_key_valid, RSA *own_host_key, const char *orighost,
+    struct sockaddr *hostaddr, uid_t original_real_uid)
+{
+	char *host, *cp;
+
+	/* Convert the user-supplied hostname into all lowercase. */
+	host = xstrdup(orighost);
+	for (cp = host; *cp; cp++)
+		if (isupper(*cp))
+			*cp = tolower(*cp);
+
+	/* Exchange protocol version identification strings with the server. */
+	ssh_exchange_identification();
+
+	/* Put the connection into non-blocking mode. */
+	packet_set_nonblocking();
+
+	supported_authentications = 0;
+	/* key exchange */
+	ssh_kex(host, hostaddr);
+	if (supported_authentications == 0)
+		fatal("supported_authentications == 0.");
+	/* authenticate user */
+	ssh_userauth(host_key_valid, own_host_key, original_real_uid, host);
+}
diff --git a/usr.bin/ssh/sshd.c b/usr.bin/ssh/sshd.c
index e25ace295bf..1c8b3aee5f1 100644
--- a/usr.bin/ssh/sshd.c
+++ b/usr.bin/ssh/sshd.c
@@ -11,7 +11,7 @@
  */
 
 #include "includes.h"
-RCSID("$Id: sshd.c,v 1.76 2000/01/04 16:54:58 markus Exp $");
+RCSID("$OpenBSD: sshd.c,v 1.77 2000/01/16 23:03:10 markus Exp $");
 
 #include <poll.h>
 
@@ -129,8 +129,8 @@ int received_sighup = 0;
 RSA *public_key;
 
 /* Prototypes for various functions defined later in this file. */
-void do_connection();
-void do_authentication(char *user);
+void do_ssh_kex();
+void do_authentication();
 void do_authloop(struct passwd * pw);
 void do_fake_authloop(char *user);
 void do_authenticated(struct passwd * pw);
@@ -858,8 +858,11 @@ main(int ac, char **av)
 
 	packet_set_nonblocking();
 
-	/* Handle the connection. */
-	do_connection();
+	/* perform the key exchange */
+	do_ssh_kex();
+
+	/* authenticate user and start session */
+	do_authentication();
 
 #ifdef KRB4
 	/* Cleanup user's ticket cache file. */
@@ -878,20 +881,17 @@ main(int ac, char **av)
 }
 
 /*
- * Process an incoming connection.  Protocol version identifiers have already
- * been exchanged.  This sends server key and performs the key exchange.
- * Server and host keys will no longer be needed after this functions.
+ * SSH1 key exchange
  */
 void
-do_connection()
+do_ssh_kex()
 {
 	int i, len;
+	int plen, slen;
 	BIGNUM *session_key_int;
 	unsigned char session_key[SSH_SESSION_KEY_LENGTH];
-	unsigned char check_bytes[8];
-	char *user;
+	unsigned char cookie[8];
 	unsigned int cipher_type, auth_mask, protocol_flags;
-	int plen, slen, ulen;
 	u_int32_t rand = 0;
 
 	/*
@@ -906,7 +906,7 @@ do_connection()
 	for (i = 0; i < 8; i++) {
 		if (i % 4 == 0)
 			rand = arc4random();
-		check_bytes[i] = rand & 0xff;
+		cookie[i] = rand & 0xff;
 		rand >>= 8;
 	}
 
@@ -917,7 +917,7 @@ do_connection()
 	 */
 	packet_start(SSH_SMSG_PUBLIC_KEY);
 	for (i = 0; i < 8; i++)
-		packet_put_char(check_bytes[i]);
+		packet_put_char(cookie[i]);
 
 	/* Store our public server RSA key. */
 	packet_put_int(BN_num_bits(public_key->n));
@@ -980,7 +980,7 @@ do_connection()
 	/* Get check bytes from the packet.  These must match those we
 	   sent earlier with the public key packet. */
 	for (i = 0; i < 8; i++)
-		if (check_bytes[i] != packet_get_char())
+		if (cookie[i] != packet_get_char())
 			packet_disconnect("IP Spoofing check bytes do not match.");
 
 	debug("Encryption type: %.200s", cipher_name(cipher_type));
@@ -1028,10 +1028,15 @@ do_connection()
 				    sensitive_data.private_key);
 	}
 
-	compute_session_id(session_id, check_bytes,
+	compute_session_id(session_id, cookie,
 			   sensitive_data.host_key->n,
 			   sensitive_data.private_key->n);
 
+	/* Destroy the private and public keys.  They will no longer be needed. */
+	RSA_free(public_key);
+	RSA_free(sensitive_data.private_key);
+	RSA_free(sensitive_data.host_key);
+
 	/*
 	 * Extract session key from the decrypted integer.  The key is in the
 	 * least significant 256 bits of the integer; the first byte of the
@@ -1046,13 +1051,13 @@ do_connection()
 	memset(session_key, 0, sizeof(session_key));
 	BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
 
+	/* Destroy the decrypted integer.  It is no longer needed. */
+	BN_clear_free(session_key_int);
+
 	/* Xor the first 16 bytes of the session key with the session id. */
 	for (i = 0; i < 16; i++)
 		session_key[i] ^= session_id[i];
 
-	/* Destroy the decrypted integer.  It is no longer needed. */
-	BN_clear_free(session_key_int);
-
 	/* Set the session key.  From this on all communications will be encrypted. */
 	packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);
 
@@ -1065,24 +1070,9 @@ do_connection()
 	packet_start(SSH_SMSG_SUCCESS);
 	packet_send();
 	packet_write_wait();
-
-	/* Get the name of the user that we wish to log in as. */
-	packet_read_expect(&plen, SSH_CMSG_USER);
-
-	/* Get the user name. */
-	user = packet_get_string(&ulen);
-	packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
-
-	/* Destroy the private and public keys.  They will no longer be needed. */
-	RSA_free(public_key);
-	RSA_free(sensitive_data.private_key);
-	RSA_free(sensitive_data.host_key);
-
-	setproctitle("%s", user);
-	/* Do the authentication. */
-	do_authentication(user);
 }
 
+
 /*
  * Check if the user is allowed to log in via ssh. If user is listed in
  * DenyUsers or user's primary group is listed in DenyGroups, false will
@@ -1158,13 +1148,23 @@ allowed_user(struct passwd * pw)
 
 /*
  * Performs authentication of an incoming connection.  Session key has already
- * been exchanged and encryption is enabled.  User is the user name to log
- * in as (received from the client).
+ * been exchanged and encryption is enabled.
  */
 void
-do_authentication(char *user)
+do_authentication()
 {
 	struct passwd *pw, pwcopy;
+	int plen, ulen;
+	char *user;
+
+	/* Get the name of the user that we wish to log in as. */
+	packet_read_expect(&plen, SSH_CMSG_USER);
+
+	/* Get the user name. */
+	user = packet_get_string(&ulen);
+	packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
+
+	setproctitle("%s", user);
 
 #ifdef AFS
 	/* If machine has AFS, set process authentication group. */