--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dss.c	Wed Mar 08 13:23:58 2006 +0000
@@ -0,0 +1,416 @@
+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+#include "includes.h"
+#include "dbutil.h"
+#include "bignum.h"
+#include "dss.h"
+#include "buffer.h"
+#include "ssh.h"
+#include "random.h"
+
+/* Handle DSS (Digital Signature Standard), aka DSA (D.S. Algorithm),
+ * operations, such as key reading, signing, verification. Key generation
+ * is in gendss.c, since it isn't required in the server itself.
+ *
+ * See FIPS186 or the Handbook of Applied Cryptography for details of the
+ * algorithm */
+
+#ifdef DROPBEAR_DSS 
+
+/* Load a dss key from a buffer, initialising the values.
+ * The key will have the same format as buf_put_dss_key.
+ * These should be freed with dss_key_free.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_get_dss_pub_key(buffer* buf, dss_key *key) {
+
+	TRACE(("enter buf_get_dss_pub_key"))
+	dropbear_assert(key != NULL);
+	key->p = m_malloc(sizeof(mp_int));
+	key->q = m_malloc(sizeof(mp_int));
+	key->g = m_malloc(sizeof(mp_int));
+	key->y = m_malloc(sizeof(mp_int));
+	m_mp_init_multi(key->p, key->q, key->g, key->y, NULL);
+	key->x = NULL;
+
+	buf_incrpos(buf, 4+SSH_SIGNKEY_DSS_LEN); /* int + "ssh-dss" */
+	if (buf_getmpint(buf, key->p) == DROPBEAR_FAILURE
+	 || buf_getmpint(buf, key->q) == DROPBEAR_FAILURE
+	 || buf_getmpint(buf, key->g) == DROPBEAR_FAILURE
+	 || buf_getmpint(buf, key->y) == DROPBEAR_FAILURE) {
+		TRACE(("leave buf_get_dss_pub_key: failed reading mpints"))
+		return DROPBEAR_FAILURE;
+	}
+
+	if (mp_count_bits(key->p) < MIN_DSS_KEYLEN) {
+		dropbear_log(LOG_WARNING, "DSS key too short");
+		TRACE(("leave buf_get_dss_pub_key: short key"))
+		return DROPBEAR_FAILURE;
+	}
+
+	TRACE(("leave buf_get_dss_pub_key: success"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Same as buf_get_dss_pub_key, but reads a private "x" key at the end.
+ * Loads a private dss key from a buffer
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_get_dss_priv_key(buffer* buf, dss_key *key) {
+
+	int ret = DROPBEAR_FAILURE;
+
+	dropbear_assert(key != NULL);
+
+	ret = buf_get_dss_pub_key(buf, key);
+	if (ret == DROPBEAR_FAILURE) {
+		return DROPBEAR_FAILURE;
+	}
+
+	key->x = m_malloc(sizeof(mp_int));
+	m_mp_init(key->x);
+	ret = buf_getmpint(buf, key->x);
+
+	return ret;
+}
+	
+
+/* Clear and free the memory used by a public or private key */
+void dss_key_free(dss_key *key) {
+
+	TRACE(("enter dsa_key_free"))
+	if (key == NULL) {
+		TRACE(("enter dsa_key_free: key == NULL"))
+		return;
+	}
+	if (key->p) {
+		mp_clear(key->p);
+		m_free(key->p);
+	}
+	if (key->q) {
+		mp_clear(key->q);
+		m_free(key->q);
+	}
+	if (key->g) {
+		mp_clear(key->g);
+		m_free(key->g);
+	}
+	if (key->y) {
+		mp_clear(key->y);
+		m_free(key->y);
+	}
+	if (key->x) {
+		mp_clear(key->x);
+		m_free(key->x);
+	}
+	m_free(key);
+	TRACE(("leave dsa_key_free"))
+}
+
+/* put the dss public key into the buffer in the required format:
+ *
+ * string	"ssh-dss"
+ * mpint	p
+ * mpint	q
+ * mpint	g
+ * mpint	y
+ */
+void buf_put_dss_pub_key(buffer* buf, dss_key *key) {
+
+	dropbear_assert(key != NULL);
+	buf_putstring(buf, SSH_SIGNKEY_DSS, SSH_SIGNKEY_DSS_LEN);
+	buf_putmpint(buf, key->p);
+	buf_putmpint(buf, key->q);
+	buf_putmpint(buf, key->g);
+	buf_putmpint(buf, key->y);
+
+}
+
+/* Same as buf_put_dss_pub_key, but with the private "x" key appended */
+void buf_put_dss_priv_key(buffer* buf, dss_key *key) {
+
+	dropbear_assert(key != NULL);
+	buf_put_dss_pub_key(buf, key);
+	buf_putmpint(buf, key->x);
+
+}
+
+#ifdef DROPBEAR_SIGNKEY_VERIFY
+/* Verify a DSS signature (in buf) made on data by the key given. 
+ * returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_dss_verify(buffer* buf, dss_key *key, const unsigned char* data,
+		unsigned int len) {
+
+	unsigned char msghash[SHA1_HASH_SIZE];
+	hash_state hs;
+	int ret = DROPBEAR_FAILURE;
+	DEF_MP_INT(val1);
+	DEF_MP_INT(val2);
+	DEF_MP_INT(val3);
+	DEF_MP_INT(val4);
+	char * string = NULL;
+	int stringlen;
+
+	TRACE(("enter buf_dss_verify"))
+	dropbear_assert(key != NULL);
+
+	m_mp_init_multi(&val1, &val2, &val3, &val4, NULL);
+
+	/* get blob, check length */
+	string = buf_getstring(buf, &stringlen);
+	if (stringlen != 2*SHA1_HASH_SIZE) {
+		goto out;
+	}
+
+	/* hash the data */
+	sha1_init(&hs);
+	sha1_process(&hs, data, len);
+	sha1_done(&hs, msghash);
+
+	/* create the signature - s' and r' are the received signatures in buf */
+	/* w = (s')-1 mod q */
+	/* let val1 = s' */
+	bytes_to_mp(&val1, &string[SHA1_HASH_SIZE], SHA1_HASH_SIZE);
+
+	if (mp_cmp(&val1, key->q) != MP_LT) {
+		TRACE(("verify failed, s' >= q"))
+		goto out;
+	}
+	/* let val2 = w = (s')^-1 mod q*/
+	if (mp_invmod(&val1, key->q, &val2) != MP_OKAY) {
+		goto out;
+	}
+
+	/* u1 = ((SHA(M')w) mod q */
+	/* let val1 = SHA(M') = msghash */
+	bytes_to_mp(&val1, msghash, SHA1_HASH_SIZE);
+
+	/* let val3 = u1 = ((SHA(M')w) mod q */
+	if (mp_mulmod(&val1, &val2, key->q, &val3) != MP_OKAY) {
+		goto out;
+	}
+
+	/* u2 = ((r')w) mod q */
+	/* let val1 = r' */
+	bytes_to_mp(&val1, &string[0], SHA1_HASH_SIZE);
+	if (mp_cmp(&val1, key->q) != MP_LT) {
+		TRACE(("verify failed, r' >= q"))
+		goto out;
+	}
+	/* let val4 = u2 = ((r')w) mod q */
+	if (mp_mulmod(&val1, &val2, key->q, &val4) != MP_OKAY) {
+		goto out;
+	}
+
+	/* v = (((g)^u1 (y)^u2) mod p) mod q */
+	/* val2 = g^u1 mod p */
+	if (mp_exptmod(key->g, &val3, key->p, &val2) != MP_OKAY) {
+		goto out;
+	}
+	/* val3 = y^u2 mod p */
+	if (mp_exptmod(key->y, &val4, key->p, &val3) != MP_OKAY) {
+		goto out;
+	}
+	/* val4 = ((g)^u1 (y)^u2) mod p */
+	if (mp_mulmod(&val2, &val3, key->p, &val4) != MP_OKAY) {
+		goto out;
+	}
+	/* val2 = v = (((g)^u1 (y)^u2) mod p) mod q */
+	if (mp_mod(&val4, key->q, &val2) != MP_OKAY) {
+		goto out;
+	}
+	
+	/* check whether signatures verify */
+	if (mp_cmp(&val2, &val1) == MP_EQ) {
+		/* good sig */
+		ret = DROPBEAR_SUCCESS;
+	}
+
+out:
+	mp_clear_multi(&val1, &val2, &val3, &val4, NULL);
+	m_free(string);
+
+	return ret;
+
+}
+#endif /* DROPBEAR_SIGNKEY_VERIFY */
+
+#ifdef DSS_PROTOK	
+/* convert an unsigned mp into an array of bytes, malloced.
+ * This array must be freed after use, len contains the length of the array,
+ * if len != NULL */
+static unsigned char* mptobytes(mp_int *mp, int *len) {
+	
+	unsigned char* ret;
+	int size;
+
+	size = mp_unsigned_bin_size(mp);
+	ret = m_malloc(size);
+	if (mp_to_unsigned_bin(mp, ret) != MP_OKAY) {
+		dropbear_exit("mem alloc error");
+	}
+	if (len != NULL) {
+		*len = size;
+	}
+	return ret;
+}
+#endif
+
+/* Sign the data presented with key, writing the signature contents
+ * to the buffer
+ *
+ * When DSS_PROTOK is #defined:
+ * The alternate k generation method is based on the method used in PuTTY. 
+ * In particular to avoid being vulnerable to attacks using flaws in random
+ * generation of k, we use the following:
+ *
+ * proto_k = SHA512 ( SHA512(x) || SHA160(message) )
+ * k = proto_k mod q
+ *
+ * Now we aren't relying on the random number generation to protect the private
+ * key x, which is a long term secret */
+void buf_put_dss_sign(buffer* buf, dss_key *key, const unsigned char* data,
+		unsigned int len) {
+
+	unsigned char msghash[SHA1_HASH_SIZE];
+	unsigned int writelen;
+	unsigned int i;
+#ifdef DSS_PROTOK
+	unsigned char privkeyhash[SHA512_HASH_SIZE];
+	unsigned char *privkeytmp;
+	unsigned char proto_k[SHA512_HASH_SIZE];
+	DEF_MP_INT(dss_protok);
+#endif
+	DEF_MP_INT(dss_k);
+	DEF_MP_INT(dss_m);
+	DEF_MP_INT(dss_temp1);
+	DEF_MP_INT(dss_temp2);
+	DEF_MP_INT(dss_r);
+	DEF_MP_INT(dss_s);
+	hash_state hs;
+	
+	TRACE(("enter buf_put_dss_sign"))
+	dropbear_assert(key != NULL);
+	
+	/* hash the data */
+	sha1_init(&hs);
+	sha1_process(&hs, data, len);
+	sha1_done(&hs, msghash);
+
+	m_mp_init_multi(&dss_k, &dss_temp1, &dss_temp2, &dss_r, &dss_s,
+			&dss_m, NULL);
+#ifdef DSS_PROTOK	
+	/* hash the privkey */
+	privkeytmp = mptobytes(key->x, &i);
+	sha512_init(&hs);
+	sha512_process(&hs, "the quick brown fox jumped over the lazy dog", 44);
+	sha512_process(&hs, privkeytmp, i);
+	sha512_done(&hs, privkeyhash);
+	m_burn(privkeytmp, i);
+	m_free(privkeytmp);
+
+	/* calculate proto_k */
+	sha512_init(&hs);
+	sha512_process(&hs, privkeyhash, SHA512_HASH_SIZE);
+	sha512_process(&hs, msghash, SHA1_HASH_SIZE);
+	sha512_done(&hs, proto_k);
+
+	/* generate k */
+	m_mp_init(&dss_protok);
+	bytes_to_mp(&dss_protok, proto_k, SHA512_HASH_SIZE);
+	mp_mod(&dss_protok, key->q, &dss_k);
+	mp_clear(&dss_protok);
+	m_burn(proto_k, SHA512_HASH_SIZE);
+#else /* DSS_PROTOK not defined*/
+	gen_random_mpint(key->q, &dss_k);
+#endif
+
+	/* now generate the actual signature */
+	bytes_to_mp(&dss_m, msghash, SHA1_HASH_SIZE);
+
+	/* g^k mod p */
+	if (mp_exptmod(key->g, &dss_k, key->p, &dss_temp1) !=  MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+	/* r = (g^k mod p) mod q */
+	if (mp_mod(&dss_temp1, key->q, &dss_r) != MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+
+	/* x*r mod q */
+	if (mp_mulmod(&dss_r, key->x, key->q, &dss_temp1) != MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+	/* (SHA1(M) + xr) mod q) */
+	if (mp_addmod(&dss_m, &dss_temp1, key->q, &dss_temp2) != MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+	
+	/* (k^-1) mod q */
+	if (mp_invmod(&dss_k, key->q, &dss_temp1) != MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+
+	/* s = (k^-1(SHA1(M) + xr)) mod q */
+	if (mp_mulmod(&dss_temp1, &dss_temp2, key->q, &dss_s) != MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+
+	buf_putstring(buf, SSH_SIGNKEY_DSS, SSH_SIGNKEY_DSS_LEN);
+	buf_putint(buf, 2*SHA1_HASH_SIZE);
+
+	writelen = mp_unsigned_bin_size(&dss_r);
+	dropbear_assert(writelen <= SHA1_HASH_SIZE);
+	/* need to pad to 160 bits with leading zeros */
+	for (i = 0; i < SHA1_HASH_SIZE - writelen; i++) {
+		buf_putbyte(buf, 0);
+	}
+	if (mp_to_unsigned_bin(&dss_r, buf_getwriteptr(buf, writelen)) 
+			!= MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+	mp_clear(&dss_r);
+	buf_incrwritepos(buf, writelen);
+
+	writelen = mp_unsigned_bin_size(&dss_s);
+	dropbear_assert(writelen <= SHA1_HASH_SIZE);
+	/* need to pad to 160 bits with leading zeros */
+	for (i = 0; i < SHA1_HASH_SIZE - writelen; i++) {
+		buf_putbyte(buf, 0);
+	}
+	if (mp_to_unsigned_bin(&dss_s, buf_getwriteptr(buf, writelen)) 
+			!= MP_OKAY) {
+		dropbear_exit("dss error");
+	}
+	mp_clear(&dss_s);
+	buf_incrwritepos(buf, writelen);
+
+	mp_clear_multi(&dss_k, &dss_temp1, &dss_temp2, &dss_r, &dss_s,
+			&dss_m, NULL);
+	
+	/* create the signature to return */
+
+	TRACE(("leave buf_put_dss_sign"))
+}
+
+#endif /* DROPBEAR_DSS */