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/* $OpenBSD: sshconnect1.c,v 1.70 2006/11/06 21:25:28 markus Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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"
#include <sys/types.h>
#include <sys/socket.h>
#include <openssl/bn.h>
#include <openssl/md5.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <pwd.h>
#include "xmalloc.h"
#include "ssh.h"
#include "ssh1.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "key.h"
#include "cipher.h"
#include "kex.h"
#include "uidswap.h"
#include "log.h"
#include "readconf.h"
#include "authfd.h"
#include "sshconnect.h"
#include "authfile.h"
#include "misc.h"
#include "canohost.h"
#include "hostfile.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.
*/
logit("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 || (u_int)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, perm_ok = 1, 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,
&perm_ok);
if (private == NULL && !options.batch_mode && perm_ok) {
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, 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 && perm_ok)
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;
}
/*
* Tries to authenticate with any string-based challenge/response system.
* Note that the client code is not tied to s/key or TIS.
*/
static int
try_challenge_response_authentication(void)
{
int type, i;
u_int clen;
char prompt[1024];
char *challenge, *response;
debug("Doing challenge response authentication.");
for (i = 0; i < options.number_of_password_prompts; i++) {
/* request a challenge */
packet_start(SSH_CMSG_AUTH_TIS);
packet_send();
packet_write_wait();
type = packet_read();
if (type != SSH_SMSG_FAILURE &&
type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
packet_disconnect("Protocol error: got %d in response "
"to SSH_CMSG_AUTH_TIS", type);
}
if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
debug("No challenge.");
return 0;
}
challenge = packet_get_string(&clen);
packet_check_eom();
snprintf(prompt, sizeof prompt, "%s%s", challenge,
strchr(challenge, '\n') ? "" : "\nResponse: ");
xfree(challenge);
if (i != 0)
error("Permission denied, please try again.");
if (options.cipher == SSH_CIPHER_NONE)
logit("WARNING: Encryption is disabled! "
"Response will be transmitted in clear text.");
response = read_passphrase(prompt, 0);
if (strcmp(response, "") == 0) {
xfree(response);
break;
}
packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
ssh_put_password(response);
memset(response, 0, strlen(response));
xfree(response);
packet_send();
packet_write_wait();
type = packet_read();
if (type == SSH_SMSG_SUCCESS)
return 1;
if (type != SSH_SMSG_FAILURE)
packet_disconnect("Protocol error: got %d in response "
"to SSH_CMSG_AUTH_TIS_RESPONSE", type);
}
/* failure */
return 0;
}
/*
* Tries to authenticate with plain passwd authentication.
*/
static int
try_password_authentication(char *prompt)
{
int type, i;
char *password;
debug("Doing password authentication.");
if (options.cipher == SSH_CIPHER_NONE)
logit("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);
ssh_put_password(password);
memset(password, 0, strlen(password));
xfree(password);
packet_send();
packet_write_wait();
type = packet_read();
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;
Key *host_key, *server_key;
int bits, rbits;
int ssh_cipher_default = SSH_CIPHER_3DES;
u_char session_key[SSH_SESSION_KEY_LENGTH];
u_char cookie[8];
u_int supported_ciphers;
u_int server_flags, client_flags;
u_int32_t rnd = 0;
debug("Waiting for server public key.");
/* Wait for a public key packet from the server. */
packet_read_expect(SSH_SMSG_PUBLIC_KEY);
/* Get cookie from the packet. */
for (i = 0; i < 8; i++)
cookie[i] = packet_get_char();
/* Get the public key. */
server_key = key_new(KEY_RSA1);
bits = packet_get_int();
packet_get_bignum(server_key->rsa->e);
packet_get_bignum(server_key->rsa->n);
rbits = BN_num_bits(server_key->rsa->n);
if (bits != rbits) {
logit("Warning: Server lies about size of server public key: "
"actual size is %d bits vs. announced %d.", rbits, bits);
logit("Warning: This may be due to an old implementation of ssh.");
}
/* Get the host key. */
host_key = key_new(KEY_RSA1);
bits = packet_get_int();
packet_get_bignum(host_key->rsa->e);
packet_get_bignum(host_key->rsa->n);
rbits = BN_num_bits(host_key->rsa->n);
if (bits != rbits) {
logit("Warning: Server lies about size of server host key: "
"actual size is %d bits vs. announced %d.", rbits, bits);
logit("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();
packet_check_eom();
debug("Received server public key (%d bits) and host key (%d bits).",
BN_num_bits(server_key->rsa->n), BN_num_bits(host_key->rsa->n));
if (verify_host_key(host, hostaddr, host_key) == -1)
fatal("Host key verification failed.");
client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
derive_ssh1_session_id(host_key->rsa->n, server_key->rsa->n, cookie, session_id);
/* 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)
rnd = arc4random();
session_key[i] = rnd & 0xff;
rnd >>= 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.
*/
if ((key = BN_new()) == NULL)
fatal("ssh_kex: BN_new failed");
if (BN_set_word(key, 0) == 0)
fatal("ssh_kex: BN_set_word failed");
for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
if (BN_lshift(key, key, 8) == 0)
fatal("ssh_kex: BN_lshift failed");
if (i < 16) {
if (BN_add_word(key, session_key[i] ^ session_id[i])
== 0)
fatal("ssh_kex: BN_add_word failed");
} else {
if (BN_add_word(key, session_key[i]) == 0)
fatal("ssh_kex: BN_add_word failed");
}
}
/*
* Encrypt the integer using the public key and host key of the
* server (key with smaller modulus first).
*/
if (BN_cmp(server_key->rsa->n, host_key->rsa->n) < 0) {
/* Public key has smaller modulus. */
if (BN_num_bits(host_key->rsa->n) <
BN_num_bits(server_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
fatal("respond_to_rsa_challenge: host_key %d < server_key %d + "
"SSH_KEY_BITS_RESERVED %d",
BN_num_bits(host_key->rsa->n),
BN_num_bits(server_key->rsa->n),
SSH_KEY_BITS_RESERVED);
}
rsa_public_encrypt(key, key, server_key->rsa);
rsa_public_encrypt(key, key, host_key->rsa);
} else {
/* Host key has smaller modulus (or they are equal). */
if (BN_num_bits(server_key->rsa->n) <
BN_num_bits(host_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
fatal("respond_to_rsa_challenge: server_key %d < host_key %d + "
"SSH_KEY_BITS_RESERVED %d",
BN_num_bits(server_key->rsa->n),
BN_num_bits(host_key->rsa->n),
SSH_KEY_BITS_RESERVED);
}
rsa_public_encrypt(key, key, host_key->rsa);
rsa_public_encrypt(key, key, server_key->rsa);
}
/* Destroy the public keys since we no longer need them. */
key_free(server_key);
key_free(host_key);
if (options.cipher == SSH_CIPHER_NOT_SET) {
if (cipher_mask_ssh1(1) & supported_ciphers & (1 << ssh_cipher_default))
options.cipher = ssh_cipher_default;
} else if (options.cipher == SSH_CIPHER_INVALID ||
!(cipher_mask_ssh1(1) & (1 << options.cipher))) {
logit("No valid SSH1 cipher, using %.100s instead.",
cipher_name(ssh_cipher_default));
options.cipher = ssh_cipher_default;
}
/* 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(SSH_SMSG_SUCCESS);
debug("Received encrypted confirmation.");
}
/*
* Authenticate user
*/
void
ssh_userauth1(const char *local_user, const char *server_user, char *host,
Sensitive *sensitive)
{
int i, type;
if (supported_authentications == 0)
fatal("ssh_userauth1: 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_cstring(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();
/* check whether the connection was accepted without authentication. */
if (type == SSH_SMSG_SUCCESS)
goto success;
if (type != SSH_SMSG_FAILURE)
packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER", type);
/*
* Try .rhosts or /etc/hosts.equiv authentication with RSA host
* authentication.
*/
if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
options.rhosts_rsa_authentication) {
for (i = 0; i < sensitive->nkeys; i++) {
if (sensitive->keys[i] != NULL &&
sensitive->keys[i]->type == KEY_RSA1 &&
try_rhosts_rsa_authentication(local_user,
sensitive->keys[i]))
goto success;
}
}
/* 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())
goto success;
/* Try RSA authentication for each identity. */
for (i = 0; i < options.num_identity_files; i++)
if (options.identity_keys[i] != NULL &&
options.identity_keys[i]->type == KEY_RSA1 &&
try_rsa_authentication(i))
goto success;
}
/* Try challenge response authentication if the server supports it. */
if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
options.challenge_response_authentication && !options.batch_mode) {
if (try_challenge_response_authentication())
goto success;
}
/* 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@%.128s's password: ",
server_user, host);
if (try_password_authentication(prompt))
goto success;
}
/* All authentication methods have failed. Exit with an error message. */
fatal("Permission denied.");
/* NOTREACHED */
success:
return; /* need statement after label */
}
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