1 files changed, 343 insertions, 0 deletions
diff --git a/crypto/openssh/auth-rsa.c b/crypto/openssh/auth-rsa.c
new file mode 100644
index 0000000..69f9a58
--- /dev/null
+++ b/crypto/openssh/auth-rsa.c
@@ -0,0 +1,343 @@
+/* $OpenBSD: auth-rsa.c,v 1.72 2006/11/06 21:25:27 markus Exp $ */
+/*
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ *                    All rights reserved
+ * 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.
+ *
+ * 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/stat.h>
+
+#include <openssl/rsa.h>
+#include <openssl/md5.h>
+
+#include <pwd.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+
+#include "xmalloc.h"
+#include "rsa.h"
+#include "packet.h"
+#include "ssh1.h"
+#include "uidswap.h"
+#include "match.h"
+#include "buffer.h"
+#include "auth-options.h"
+#include "pathnames.h"
+#include "log.h"
+#include "servconf.h"
+#include "key.h"
+#include "hostfile.h"
+#include "auth.h"
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+#include "monitor_wrap.h"
+#include "ssh.h"
+#include "misc.h"
+
+/* import */
+extern ServerOptions options;
+
+/*
+ * Session identifier that is used to bind key exchange and authentication
+ * responses to a particular session.
+ */
+extern u_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 SSH_MAX_PUBKEY_BYTES characters.  See sshd(8) for a
+ * description of the options.
+ */
+
+BIGNUM *
+auth_rsa_generate_challenge(Key *key)
+{
+	BIGNUM *challenge;
+	BN_CTX *ctx;
+
+	if ((challenge = BN_new()) == NULL)
+		fatal("auth_rsa_generate_challenge: BN_new() failed");
+	/* Generate a random challenge. */
+	if (BN_rand(challenge, 256, 0, 0) == 0)
+		fatal("auth_rsa_generate_challenge: BN_rand failed");
+	if ((ctx = BN_CTX_new()) == NULL)
+		fatal("auth_rsa_generate_challenge: BN_CTX_new failed");
+	if (BN_mod(challenge, challenge, key->rsa->n, ctx) == 0)
+		fatal("auth_rsa_generate_challenge: BN_mod failed");
+	BN_CTX_free(ctx);
+
+	return challenge;
+}
+
+int
+auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16])
+{
+	u_char buf[32], mdbuf[16];
+	MD5_CTX md;
+	int len;
+
+	/* don't allow short keys */
+	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
+		error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",
+		    BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
+		return (0);
+	}
+
+	/* The response is MD5 of decrypted challenge plus session id. */
+	len = BN_num_bytes(challenge);
+	if (len <= 0 || len > 32)
+		fatal("auth_rsa_verify_response: bad challenge length %d", len);
+	memset(buf, 0, 32);
+	BN_bn2bin(challenge, buf + 32 - len);
+	MD5_Init(&md);
+	MD5_Update(&md, buf, 32);
+	MD5_Update(&md, session_id, 16);
+	MD5_Final(mdbuf, &md);
+
+	/* 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 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(Key *key)
+{
+	BIGNUM *challenge, *encrypted_challenge;
+	u_char response[16];
+	int i, success;
+
+	if ((encrypted_challenge = BN_new()) == NULL)
+		fatal("auth_rsa_challenge_dialog: BN_new() failed");
+
+	challenge = PRIVSEP(auth_rsa_generate_challenge(key));
+
+	/* Encrypt the challenge with the public key. */
+	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
+
+	/* Send the encrypted challenge to the client. */
+	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
+	packet_put_bignum(encrypted_challenge);
+	packet_send();
+	BN_clear_free(encrypted_challenge);
+	packet_write_wait();
+
+	/* Wait for a response. */
+	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
+	for (i = 0; i < 16; i++)
+		response[i] = (u_char)packet_get_char();
+	packet_check_eom();
+
+	success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
+	BN_clear_free(challenge);
+	return (success);
+}
+
+/*
+ * check if there's user key matching client_n,
+ * return key if login is allowed, NULL otherwise
+ */
+
+int
+auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
+{
+	char line[SSH_MAX_PUBKEY_BYTES], *file;
+	int allowed = 0;
+	u_int bits;
+	FILE *f;
+	u_long linenum = 0;
+	struct stat st;
+	Key *key;
+
+	/* Temporarily use the user's uid. */
+	temporarily_use_uid(pw);
+
+	/* The authorized keys. */
+	file = authorized_keys_file(pw);
+	debug("trying public RSA key file %s", file);
+
+	/* Fail quietly if file does not exist */
+	if (stat(file, &st) < 0) {
+		/* Restore the privileged uid. */
+		restore_uid();
+		xfree(file);
+		return (0);
+	}
+	/* Open the file containing the authorized keys. */
+	f = fopen(file, "r");
+	if (!f) {
+		/* Restore the privileged uid. */
+		restore_uid();
+		xfree(file);
+		return (0);
+	}
+	if (options.strict_modes &&
+	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
+		xfree(file);
+		fclose(f);
+		logit("Authentication refused: %s", line);
+		restore_uid();
+		return (0);
+	}
+
+	/* Flag indicating whether the key is allowed. */
+	allowed = 0;
+
+	key = key_new(KEY_RSA1);
+
+	/*
+	 * 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 (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
+		char *cp;
+		char *key_options;
+		int keybits;
+
+		/* Skip leading whitespace, empty and comment lines. */
+		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
+			;
+		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;
+			key_options = cp;
+			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
+				if (*cp == '\\' && cp[1] == '"')
+					cp++;	/* Skip both */
+				else if (*cp == '"')
+					quoted = !quoted;
+			}
+		} else
+			key_options = NULL;
+
+		/* Parse the key from the line. */
+		if (hostfile_read_key(&cp, &bits, key) == 0) {
+			debug("%.100s, line %lu: non ssh1 key syntax",
+			    file, 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(key->rsa->n, client_n) != 0)
+			continue;
+
+		/* check the real bits  */
+		keybits = BN_num_bits(key->rsa->n);
+		if (keybits < 0 || bits != (u_int)keybits)
+			logit("Warning: %s, line %lu: keysize mismatch: "
+			    "actual %d vs. announced %d.",
+			    file, linenum, BN_num_bits(key->rsa->n), bits);
+
+		/* We have found the desired key. */
+		/*
+		 * If our options do not allow this key to be used,
+		 * do not send challenge.
+		 */
+		if (!auth_parse_options(pw, key_options, file, linenum))
+			continue;
+
+		/* break out, this key is allowed */
+		allowed = 1;
+		break;
+	}
+
+	/* Restore the privileged uid. */
+	restore_uid();
+
+	/* Close the file. */
+	xfree(file);
+	fclose(f);
+
+	/* return key if allowed */
+	if (allowed && rkey != NULL)
+		*rkey = key;
+	else
+		key_free(key);
+	return (allowed);
+}
+
+/*
+ * 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(Authctxt *authctxt, BIGNUM *client_n)
+{
+	Key *key;
+	char *fp;
+	struct passwd *pw = authctxt->pw;
+
+	/* no user given */
+	if (!authctxt->valid)
+		return 0;
+
+	if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
+		auth_clear_options();
+		return (0);
+	}
+
+	/* Perform the challenge-response dialog for this key. */
+	if (!auth_rsa_challenge_dialog(key)) {
+		/* Wrong response. */
+		verbose("Wrong response to RSA authentication challenge.");
+		packet_send_debug("Wrong response to RSA authentication challenge.");
+		/*
+		 * Break out of the loop. Otherwise we might send
+		 * another challenge and break the protocol.
+		 */
+		key_free(key);
+		return (0);
+	}
+	/*
+	 * 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.
+	 */
+	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
+	verbose("Found matching %s key: %s",
+	    key_type(key), fp);
+	xfree(fp);
+	key_free(key);
+
+	packet_send_debug("RSA authentication accepted.");
+	return (1);
+}