diff options
Diffstat (limited to 'dss.c')
| -rw-r--r-- | dss.c | 421 |
1 files changed, 421 insertions, 0 deletions
@@ -0,0 +1,421 @@ +/* + * 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); + if (ret == DROPBEAR_FAILURE) { + m_free(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); + if (mp_mod(&dss_protok, key->q, &dss_k) != MP_OKAY) { + dropbear_exit("dss error"); + } + 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 */ |