diff options
Diffstat (limited to 'crypto/openssh/sshconnect1.c')
| -rw-r--r-- | crypto/openssh/sshconnect1.c | 750 |
1 files changed, 750 insertions, 0 deletions
diff --git a/crypto/openssh/sshconnect1.c b/crypto/openssh/sshconnect1.c new file mode 100644 index 0000000..7bd6cb0 --- /dev/null +++ b/crypto/openssh/sshconnect1.c @@ -0,0 +1,750 @@ +/* $OpenBSD: sshconnect1.c,v 1.72 2013/09/02 22:00:34 deraadt 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); + free(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."); + free(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)); + free(passphrase); + if (private != NULL || quit) + break; + debug2("bad passphrase given, try again..."); + } + } + /* We no longer need the comment. */ + free(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: "); + free(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) { + free(response); + break; + } + packet_start(SSH_CMSG_AUTH_TIS_RESPONSE); + ssh_put_password(response); + memset(response, 0, strlen(response)); + free(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)); + free(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 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 */ +} |
