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- markus@cvs.openbsd.org 2001/02/23 18:15:13

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[sshd.c]
     the random session key depends now on the session_key_int
     sent by the 'attacker'
             dig1 = md5(cookie|session_key_int);
             dig2 = md5(dig1|cookie|session_key_int);
             fake_session_key = dig1|dig2;
     this change is caused by a mail from anakin@pobox.com
     patch based on discussions with my german advisor niels@openbsd.org
This commit is contained in:
Ben Lindstrom 2001-03-05 06:00:29 +00:00
parent f4c73112d0
commit eb648a749b
2 changed files with 53 additions and 21 deletions
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11
ChangeLog
View File

@ -37,6 +37,15 @@
- markus@cvs.openbsd.org 2001/02/23 15:34:53
[serverloop.c]
debug2->3
- markus@cvs.openbsd.org 2001/02/23 18:15:13
[sshd.c]
the random session key depends now on the session_key_int
sent by the 'attacker'
dig1 = md5(cookie|session_key_int);
dig2 = md5(dig1|cookie|session_key_int);
fake_session_key = dig1|dig2;
this change is caused by a mail from anakin@pobox.com
patch based on discussions with my german advisor niels@openbsd.org
20010304
- (bal) Remove make-ssh-known-hosts.1 since it's no longer valid.
@ -4229,4 +4238,4 @@
- Wrote replacements for strlcpy and mkdtemp
- Released 1.0pre1
$Id: ChangeLog,v 1.863 2001/03/05 05:58:23 mouring Exp $
$Id: ChangeLog,v 1.864 2001/03/05 06:00:29 mouring Exp $

63
sshd.c
View File

@ -40,7 +40,7 @@
*/
#include "includes.h"
RCSID("$OpenBSD: sshd.c,v 1.168 2001/02/19 23:09:05 deraadt Exp $");
RCSID("$OpenBSD: sshd.c,v 1.169 2001/02/23 18:15:13 markus Exp $");
#include <openssl/dh.h>
#include <openssl/bn.h>
@ -154,6 +154,7 @@ struct {
Key **host_keys; /* all private host keys */
int have_ssh1_key;
int have_ssh2_key;
u_char ssh1_cookie[SSH_SESSION_KEY_LENGTH];
} sensitive_data;
/*
@ -274,13 +275,23 @@ grace_alarm_handler(int sig)
void
generate_empheral_server_key(void)
{
u_int32_t rand = 0;
int i;
log("Generating %s%d bit RSA key.", sensitive_data.server_key ? "new " : "",
options.server_key_bits);
if (sensitive_data.server_key != NULL)
key_free(sensitive_data.server_key);
sensitive_data.server_key = key_generate(KEY_RSA1, options.server_key_bits);
arc4random_stir();
log("RSA key generation complete.");
for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
if (i % 4 == 0)
rand = arc4random();
sensitive_data.ssh1_cookie[i] = rand & 0xff;
rand >>= 8;
}
arc4random_stir();
}
void
@ -438,6 +449,7 @@ destroy_sensitive_data(void)
}
}
sensitive_data.ssh1_host_key = NULL;
memset(sensitive_data.ssh1_cookie, 0, SSH_SESSION_KEY_LENGTH);
}
Key *
load_private_key_autodetect(const char *filename)
@ -1338,14 +1350,6 @@ do_ssh1_kex(void)
sensitive_data.server_key->rsa) < 0)
rsafail++;
}
compute_session_id(session_id, cookie,
sensitive_data.ssh1_host_key->rsa->n,
sensitive_data.server_key->rsa->n);
/* Destroy the private and public keys. They will no longer be needed. */
destroy_sensitive_data();
/*
* Extract session key from the decrypted integer. The key is in the
* least significant 256 bits of the integer; the first byte of the
@ -1363,24 +1367,43 @@ do_ssh1_kex(void)
memset(session_key, 0, sizeof(session_key));
BN_bn2bin(session_key_int,
session_key + sizeof(session_key) - len);
compute_session_id(session_id, cookie,
sensitive_data.ssh1_host_key->rsa->n,
sensitive_data.server_key->rsa->n);
/*
* 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];
}
}
if (rsafail) {
int bytes = BN_num_bytes(session_key_int);
char *buf = xmalloc(bytes);
MD5_CTX md;
log("do_connection: generating a fake encryption key");
for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
if (i % 4 == 0)
rand = arc4random();
session_key[i] = rand & 0xff;
rand >>= 8;
}
BN_bn2bin(session_key_int, buf);
MD5_Init(&md);
MD5_Update(&md, buf, bytes);
MD5_Update(&md, sensitive_data.ssh1_cookie, SSH_SESSION_KEY_LENGTH);
MD5_Final(session_key, &md);
MD5_Init(&md);
MD5_Update(&md, session_key, 16);
MD5_Update(&md, buf, bytes);
MD5_Update(&md, sensitive_data.ssh1_cookie, SSH_SESSION_KEY_LENGTH);
MD5_Final(session_key + 16, &md);
memset(buf, 0, bytes);
xfree(buf);
}
/* Destroy the private and public keys. They will no longer be needed. */
destroy_sensitive_data();
/* 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];
/* Set the session key. From this on all communications will be encrypted. */
packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);