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Diffstat (limited to 'usr.bin/ssh/auth-rsa.c')
-rw-r--r--usr.bin/ssh/auth-rsa.c437
1 files changed, 437 insertions, 0 deletions
diff --git a/usr.bin/ssh/auth-rsa.c b/usr.bin/ssh/auth-rsa.c
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+++ b/usr.bin/ssh/auth-rsa.c
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+/*
+
+auth-rsa.c
+
+Author: Tatu Ylonen <ylo@cs.hut.fi>
+
+Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ All rights reserved
+
+Created: Mon Mar 27 01:46:52 1995 ylo
+
+RSA-based authentication. This code determines whether to admit a login
+based on RSA authentication. This file also contains functions to check
+validity of the host key.
+
+*/
+
+#include "includes.h"
+RCSID("$Id: auth-rsa.c,v 1.1 1999/09/28 04:45:35 provos Exp $");
+
+#include "rsa.h"
+#include "packet.h"
+#include "xmalloc.h"
+#include "ssh.h"
+#include "ssh_md5.h"
+#include "mpaux.h"
+#include "uidswap.h"
+
+#include <ssl/rsa.h>
+
+/* Flags that may be set in authorized_keys options. */
+extern int no_port_forwarding_flag;
+extern int no_agent_forwarding_flag;
+extern int no_x11_forwarding_flag;
+extern int no_pty_flag;
+extern char *forced_command;
+extern struct envstring *custom_environment;
+
+/* Session identifier that is used to bind key exchange and authentication
+ responses to a particular session. */
+extern unsigned char session_id[16];
+
+/* The .ssh/authorized_keys file contains public keys, one per line, in the
+ following format:
+ options bits e n comment
+ where bits, e and n are decimal numbers,
+ and comment is any string of characters up to newline. The maximum
+ length of a line is 8000 characters. See the documentation for a
+ description of the options.
+*/
+
+/* Performs the RSA authentication challenge-response dialog with the client,
+ and returns true (non-zero) if the client gave the correct answer to
+ our challenge; returns zero if the client gives a wrong answer. */
+
+int
+auth_rsa_challenge_dialog(unsigned int bits, BIGNUM *e, BIGNUM *n)
+{
+ BIGNUM *challenge, *encrypted_challenge, *aux;
+ RSA *pk;
+ BN_CTX *ctx = BN_CTX_new();
+ unsigned char buf[32], mdbuf[16], response[16];
+ struct MD5Context md;
+ unsigned int i;
+ int plen, len;
+
+ encrypted_challenge = BN_new();
+ challenge = BN_new();
+ aux = BN_new();
+
+ /* Generate a random challenge. */
+ BN_rand(challenge, 256, 0, 0);
+ BN_mod(challenge, challenge, n, ctx);
+
+ /* Create the public key data structure. */
+ pk = RSA_new();
+ pk->e = BN_new();
+ BN_copy(pk->e, e);
+ pk->n = BN_new();
+ BN_copy(pk->n, n);
+
+ /* Encrypt the challenge with the public key. */
+ rsa_public_encrypt(encrypted_challenge, challenge, pk);
+ RSA_free(pk);
+
+ /* Send the encrypted challenge to the client. */
+ packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
+ packet_put_bignum(encrypted_challenge);
+ packet_send();
+ packet_write_wait();
+
+ /* The response is MD5 of decrypted challenge plus session id. */
+ len = (BN_num_bits(challenge) + 7) / 8;
+ assert(len <= 32 && len);
+ memset(buf, 0, 32);
+ BN_bn2bin(challenge, buf + 32 - len);
+ MD5Init(&md);
+ MD5Update(&md, buf, 32);
+ MD5Update(&md, session_id, 16);
+ MD5Final(mdbuf, &md);
+
+ /* We will no longer need these. */
+ BN_clear_free(encrypted_challenge);
+ BN_clear_free(challenge);
+ BN_clear_free(aux);
+ BN_CTX_free(ctx);
+
+ /* Wait for a response. */
+ packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
+ packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
+ for (i = 0; i < 16; i++)
+ response[i] = packet_get_char();
+
+ /* Verify that the response is the original challenge. */
+ if (memcmp(response, mdbuf, 16) != 0)
+ {
+ /* Wrong answer. */
+ return 0;
+ }
+
+ /* Correct answer. */
+ return 1;
+}
+
+/* Performs the RSA authentication dialog with the client. This returns
+ 0 if the client could not be authenticated, and 1 if authentication was
+ successful. This may exit if there is a serious protocol violation. */
+
+int
+auth_rsa(struct passwd *pw, BIGNUM *client_n)
+{
+ char line[8192];
+ int authenticated;
+ unsigned int bits;
+ FILE *f;
+ unsigned long linenum = 0;
+ struct stat st;
+ BIGNUM *e, *n;
+
+ /* Open the file containing the authorized keys. */
+ sprintf(line, "%.500s/%.100s", pw->pw_dir, SSH_USER_PERMITTED_KEYS);
+
+ /* Temporarily use the user's uid. */
+ temporarily_use_uid(pw->pw_uid);
+ if (stat(line, &st) < 0)
+ {
+ /* Restore the privileged uid. */
+ restore_uid();
+ return 0;
+ }
+ f = fopen(line, "r");
+ if (!f)
+ {
+ /* Restore the privileged uid. */
+ restore_uid();
+ packet_send_debug("Could not open %.900s for reading.", line);
+ packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
+ return 0;
+ }
+
+ /* Flag indicating whether authentication has succeeded. */
+ authenticated = 0;
+
+ /* Initialize mp-int variables. */
+ e = BN_new();
+ n = BN_new();
+
+ /* Go though the accepted keys, looking for the current key. If found,
+ perform a challenge-response dialog to verify that the user really has
+ the corresponding private key. */
+ while (fgets(line, sizeof(line), f))
+ {
+ char *cp;
+ char *options;
+
+ linenum++;
+
+ /* Skip leading whitespace. */
+ for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
+ ;
+
+ /* Skip empty and comment lines. */
+ if (!*cp || *cp == '\n' || *cp == '#')
+ continue;
+
+ /* Check if there are options for this key, and if so, save their
+ starting address and skip the option part for now. If there are no
+ options, set the starting address to NULL. */
+ if (*cp < '0' || *cp > '9')
+ {
+ int quoted = 0;
+ options = cp;
+ for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++)
+ {
+ if (*cp == '\\' && cp[1] == '"')
+ cp++; /* Skip both */
+ else
+ if (*cp == '"')
+ quoted = !quoted;
+ }
+ }
+ else
+ options = NULL;
+
+ /* Parse the key from the line. */
+ if (!auth_rsa_read_key(&cp, &bits, e, n))
+ {
+ debug("%.100s, line %lu: bad key syntax",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ packet_send_debug("%.100s, line %lu: bad key syntax",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ continue;
+ }
+ /* cp now points to the comment part. */
+
+ /* Check if the we have found the desired key (identified by its
+ modulus). */
+ if (BN_cmp(n, client_n) != 0)
+ continue; /* Wrong key. */
+
+ /* We have found the desired key. */
+
+ /* Perform the challenge-response dialog for this key. */
+ if (!auth_rsa_challenge_dialog(bits, e, n))
+ {
+ /* Wrong response. */
+ log("Wrong response to RSA authentication challenge.");
+ packet_send_debug("Wrong response to RSA authentication challenge.");
+ continue;
+ }
+
+ /* Correct response. The client has been successfully authenticated.
+ Note that we have not yet processed the options; this will be reset
+ if the options cause the authentication to be rejected. */
+ authenticated = 1;
+
+ /* RSA part of authentication was accepted. Now process the options. */
+ if (options)
+ {
+ while (*options && *options != ' ' && *options != '\t')
+ {
+ cp = "no-port-forwarding";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ packet_send_debug("Port forwarding disabled.");
+ no_port_forwarding_flag = 1;
+ options += strlen(cp);
+ goto next_option;
+ }
+ cp = "no-agent-forwarding";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ packet_send_debug("Agent forwarding disabled.");
+ no_agent_forwarding_flag = 1;
+ options += strlen(cp);
+ goto next_option;
+ }
+ cp = "no-X11-forwarding";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ packet_send_debug("X11 forwarding disabled.");
+ no_x11_forwarding_flag = 1;
+ options += strlen(cp);
+ goto next_option;
+ }
+ cp = "no-pty";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ packet_send_debug("Pty allocation disabled.");
+ no_pty_flag = 1;
+ options += strlen(cp);
+ goto next_option;
+ }
+ cp = "command=\"";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ int i;
+ options += strlen(cp);
+ forced_command = xmalloc(strlen(options) + 1);
+ i = 0;
+ while (*options)
+ {
+ if (*options == '"')
+ break;
+ if (*options == '\\' && options[1] == '"')
+ {
+ options += 2;
+ forced_command[i++] = '"';
+ continue;
+ }
+ forced_command[i++] = *options++;
+ }
+ if (!*options)
+ {
+ debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ packet_send_debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ continue;
+ }
+ forced_command[i] = 0;
+ packet_send_debug("Forced command: %.900s", forced_command);
+ options++;
+ goto next_option;
+ }
+ cp = "environment=\"";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ int i;
+ char *s;
+ struct envstring *new_envstring;
+ options += strlen(cp);
+ s = xmalloc(strlen(options) + 1);
+ i = 0;
+ while (*options)
+ {
+ if (*options == '"')
+ break;
+ if (*options == '\\' && options[1] == '"')
+ {
+ options += 2;
+ s[i++] = '"';
+ continue;
+ }
+ s[i++] = *options++;
+ }
+ if (!*options)
+ {
+ debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ packet_send_debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ continue;
+ }
+ s[i] = 0;
+ packet_send_debug("Adding to environment: %.900s", s);
+ debug("Adding to environment: %.900s", s);
+ options++;
+ new_envstring = xmalloc(sizeof(struct envstring));
+ new_envstring->s = s;
+ new_envstring->next = custom_environment;
+ custom_environment = new_envstring;
+ goto next_option;
+ }
+ cp = "from=\"";
+ if (strncmp(options, cp, strlen(cp)) == 0)
+ {
+ char *patterns = xmalloc(strlen(options) + 1);
+ int i;
+ options += strlen(cp);
+ i = 0;
+ while (*options)
+ {
+ if (*options == '"')
+ break;
+ if (*options == '\\' && options[1] == '"')
+ {
+ options += 2;
+ patterns[i++] = '"';
+ continue;
+ }
+ patterns[i++] = *options++;
+ }
+ if (!*options)
+ {
+ debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ packet_send_debug("%.100s, line %lu: missing end quote",
+ SSH_USER_PERMITTED_KEYS, linenum);
+ continue;
+ }
+ patterns[i] = 0;
+ options++;
+ if (!match_hostname(get_canonical_hostname(), patterns,
+ strlen(patterns)) &&
+ !match_hostname(get_remote_ipaddr(), patterns,
+ strlen(patterns)))
+ {
+ log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).",
+ pw->pw_name, get_canonical_hostname(),
+ get_remote_ipaddr());
+ packet_send_debug("Your host '%.200s' is not permitted to use this key for login.",
+ get_canonical_hostname());
+ xfree(patterns);
+ authenticated = 0;
+ break;
+ }
+ xfree(patterns);
+ /* Host name matches. */
+ goto next_option;
+ }
+ bad_option:
+ /* Unknown option. */
+ log("Bad options in %.100s file, line %lu: %.50s",
+ SSH_USER_PERMITTED_KEYS, linenum, options);
+ packet_send_debug("Bad options in %.100s file, line %lu: %.50s",
+ SSH_USER_PERMITTED_KEYS, linenum, options);
+ authenticated = 0;
+ break;
+
+ next_option:
+ /* Skip the comma, and move to the next option (or break out
+ if there are no more). */
+ if (!*options)
+ fatal("Bugs in auth-rsa.c option processing.");
+ if (*options == ' ' || *options == '\t')
+ break; /* End of options. */
+ if (*options != ',')
+ goto bad_option;
+ options++;
+ /* Process the next option. */
+ continue;
+ }
+ }
+
+ /* Break out of the loop if authentication was successful; otherwise
+ continue searching. */
+ if (authenticated)
+ break;
+ }
+
+ /* Restore the privileged uid. */
+ restore_uid();
+
+ /* Close the file. */
+ fclose(f);
+
+ /* Clear any mp-int variables. */
+ BN_clear_free(n);
+ BN_clear_free(e);
+
+ if (authenticated)
+ packet_send_debug("RSA authentication accepted.");
+
+ /* Return authentication result. */
+ return authenticated;
+}
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