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NetBSD/crypto/dist/ssh/sshconnect1.c

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/*
* 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"
RCSID("$OpenBSD: sshconnect1.c,v 1.27 2001/02/15 23:19:59 markus Exp $");
#include <openssl/bn.h>
#include <openssl/evp.h>
#ifdef KRB4
#include <krb.h>
#endif
#ifdef AFS
#include <kafs.h>
#include "radix.h"
#endif
#ifdef KRB5
#include <krb5.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;
int plen, clen;
Key *key;
BIGNUM *challenge;
/* Get connection to the agent. */
auth = ssh_get_authentication_connection();
if (!auth)
return 0;
challenge = BN_new();
/* 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(&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.");
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, &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, 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(&plen);
/* 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(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_RSA1);
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_RSA1);
/*
* 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);
key_free(private);
BN_clear_free(challenge);
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.
*/
static 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
static int
try_krb4_authentication(void)
{
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(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);
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((u_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 KRB5
int
try_krb5_authentication(krb5_context *context, krb5_auth_context *auth_context)
{
krb5_error_code problem;
const char *tkfile;
struct stat buf;
krb5_ccache ccache = NULL;
const char *remotehost;
krb5_data ap;
int type, payload_len;
krb5_ap_rep_enc_part *reply = NULL;
int ret;
memset(&ap, 0, sizeof(ap));
problem = krb5_init_context(context);
if (problem) {
ret = 0;
goto out;
}
tkfile = krb5_cc_default_name(*context);
if (strncmp(tkfile, "FILE:", 5) == 0)
tkfile += 5;
if (stat(tkfile, &buf) == 0 && getuid() != buf.st_uid) {
debug("Kerberos V5: could not get default ccache (permission denied).");
ret = 0;
goto out;
}
problem = krb5_cc_default(*context, &ccache);
if (problem) {
ret = 0;
goto out;
}
remotehost = get_canonical_hostname(1);
problem = krb5_mk_req(*context, auth_context, AP_OPTS_MUTUAL_REQUIRED,
"host", remotehost, NULL, ccache, &ap);
if (problem) {
ret = 0;
goto out;
}
packet_start(SSH_CMSG_AUTH_KERBEROS);
packet_put_string((char *) ap.data, ap.length);
packet_send();
packet_write_wait();
xfree(ap.data);
ap.length = 0;
type = packet_read(&payload_len);
switch (type) {
case SSH_SMSG_FAILURE:
/* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
debug("Kerberos V5 authentication failed.");
ret = 0;
break;
case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
/* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
debug("Kerberos V5 authentication accepted.");
/* Get server's response. */
ap.data = packet_get_string((unsigned int *) &ap.length);
packet_integrity_check(payload_len, 4 + ap.length, type);
/* XXX je to dobre? */
problem = krb5_rd_rep(*context, *auth_context, &ap, &reply);
if (problem) {
ret = 0;
}
ret = 1;
break;
default:
packet_disconnect("Protocol error on Kerberos V5 response: %d", type);
ret = 0;
break;
}
out:
if (ccache != NULL)
krb5_cc_close(*context, ccache);
if (reply != NULL)
krb5_free_ap_rep_enc_part(*context, reply);
if (ap.length > 0)
krb5_data_free(&ap);
return ret;
}
void
send_krb5_tgt(krb5_context context, krb5_auth_context auth_context)
{
int fd;
int type, payload_len;
krb5_error_code problem;
krb5_data outbuf;
krb5_ccache ccache = NULL;
krb5_creds creds;
krb5_kdc_flags flags;
const char* remotehost = get_canonical_hostname(1);
memset(&creds, 0, sizeof(creds));
memset(&outbuf, 0, sizeof(outbuf));
fd = packet_get_connection_in();
problem = krb5_auth_con_setaddrs_from_fd(context, auth_context, &fd);
if (problem) {
goto out;
}
#if 0
tkfile = krb5_cc_default_name(context);
if (strncmp(tkfile, "FILE:", 5) == 0)
tkfile += 5;
if (stat(tkfile, &buf) == 0 && getuid() != buf.st_uid) {
debug("Kerberos V5: could not get default ccache (permission denied).");
goto out;
}
#endif
problem = krb5_cc_default(context, &ccache);
if (problem) {
goto out;
}
problem = krb5_cc_get_principal(context, ccache, &creds.client);
if (problem) {
goto out;
}
problem = krb5_build_principal(context, &creds.server,
strlen(creds.client->realm),
creds.client->realm,
"krbtgt",
creds.client->realm,
NULL);
if (problem) {
goto out;
}
creds.times.endtime = 0;
flags.i = 0;
flags.b.forwarded = 1;
flags.b.forwardable = krb5_config_get_bool(context, NULL,
"libdefaults", "forwardable", NULL);
problem = krb5_get_forwarded_creds (context,
auth_context,
ccache,
flags.i,
remotehost,
&creds,
&outbuf);
if (problem) {
goto out;
}
packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
packet_put_string((char *)outbuf.data, outbuf.length);
packet_send();
packet_write_wait();
type = packet_read(&payload_len);
switch (type) {
case SSH_SMSG_SUCCESS:
break;
case SSH_SMSG_FAILURE:
break;
default:
break;
}
out:
if (creds.client)
krb5_free_principal(context, creds.client);
if (creds.server)
krb5_free_principal(context, creds.server);
if (ccache)
krb5_cc_close(context, ccache);
if (outbuf.data)
xfree(outbuf.data);
return;
}
#endif /* KRB5 */
#ifdef AFS
int
send_krb4_tgt(void)
{
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, (u_char *)buffer, sizeof 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(u_int));
if (creds.ticket_st.length > MAX_KTXT_LEN)
break;
p += sizeof(u_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, (u_char *) buffer, sizeof buffer) <= 0)
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.
*/
static int
try_challenge_reponse_authentication(void)
{
int type, i;
int payload_len;
u_int clen;
char prompt[1024];
char *challenge, *response;
debug("Doing challenge reponse 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(&payload_len);
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_integrity_check(payload_len, (4 + clen), type);
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)
log("WARNING: Encryption is disabled! "
"Reponse 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(&payload_len);
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, 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);
ssh_put_password(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;
u_char session_key[SSH_SESSION_KEY_LENGTH];
u_char cookie[8];
u_int supported_ciphers;
u_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_RSA1;
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_mask_ssh1(1) & supported_ciphers & (1 << ssh_cipher_default))
options.cipher = ssh_cipher_default;
} else if (options.cipher == SSH_CIPHER_ILLEGAL ||
!(cipher_mask_ssh1(1) & (1 << options.cipher))) {
log("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(&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 KRB5
if ((supported_authentications & (1 << SSH_AUTH_KERBEROS)) &&
options.kerberos_authentication){
krb5_context ssh_context = NULL;
krb5_auth_context auth_context = NULL;
debug("Trying Kerberos V5 authentication.");
if (try_krb5_authentication(&ssh_context, &auth_context)) {
type = packet_read(&payload_len);
if (type == SSH_SMSG_SUCCESS) {
if ((supported_authentications & (1 << SSH_PASS_KERBEROS_TGT)) &&
options.krb5_tgt_passing) {
if (options.cipher == SSH_CIPHER_NONE)
log("WARNING: Encryption is disabled! Ticket will be transmitted in the clear!");
send_krb5_tgt(ssh_context, auth_context);
}
krb5_auth_con_free(ssh_context, auth_context);
krb5_free_context(ssh_context);
return;
}
if (type != SSH_SMSG_FAILURE)
packet_disconnect("Protocol error: got %d in response to Kerberos5 auth", type);
}
}
#endif /* KRB5 */
#ifdef AFS
/* Try Kerberos tgt passing if the server supports it. */
if ((supported_authentications & (1 << SSH_PASS_KERBEROS_TGT)) &&
options.krb4_tgt_passing) {
if (options.cipher == SSH_CIPHER_NONE)
log("WARNING: Encryption is disabled! Ticket will be transmitted in the clear!");
(void) send_krb4_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_krb4_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 (options.identity_files_type[i] == KEY_RSA1 &&
try_rsa_authentication(options.identity_files[i]))
return;
}
/* Try challenge response authentication if the server supports it. */
if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
options.challenge_reponse_authentication && !options.batch_mode) {
if (try_challenge_reponse_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@%.128s'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 */
}
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