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/*
* 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. */
/* Perform RSA operations on data, including reading keys, signing and
* verification.
*
* The format is specified in rfc2437, Applied Cryptography or The Handbook of
* Applied Cryptography detail the general algorithm. */
#include "includes.h"
#include "dbutil.h"
#include "bignum.h"
#include "rsa.h"
#include "buffer.h"
#include "ssh.h"
#include "random.h"
#ifdef DROPBEAR_RSA
static void rsa_pad_em(rsa_key * key,
const unsigned char * data, unsigned int len,
mp_int * rsa_em);
/* Load a public rsa key from a buffer, initialising the values.
* The key will have the same format as buf_put_rsa_key.
* These should be freed with rsa_key_free.
* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
int buf_get_rsa_pub_key(buffer* buf, rsa_key *key) {
TRACE(("enter buf_get_rsa_pub_key"))
dropbear_assert(key != NULL);
key->e = m_malloc(sizeof(mp_int));
key->n = m_malloc(sizeof(mp_int));
m_mp_init_multi(key->e, key->n, NULL);
key->d = NULL;
key->p = NULL;
key->q = NULL;
buf_incrpos(buf, 4+SSH_SIGNKEY_RSA_LEN); /* int + "ssh-rsa" */
if (buf_getmpint(buf, key->e) == DROPBEAR_FAILURE
|| buf_getmpint(buf, key->n) == DROPBEAR_FAILURE) {
TRACE(("leave buf_get_rsa_pub_key: failure"))
return DROPBEAR_FAILURE;
}
if (mp_count_bits(key->n) < MIN_RSA_KEYLEN) {
dropbear_log(LOG_WARNING, "rsa key too short");
return DROPBEAR_FAILURE;
}
TRACE(("leave buf_get_rsa_pub_key: success"))
return DROPBEAR_SUCCESS;
}
/* Same as buf_get_rsa_pub_key, but reads a private "x" key at the end.
* Loads a private rsa key from a buffer
* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
int buf_get_rsa_priv_key(buffer* buf, rsa_key *key) {
dropbear_assert(key != NULL);
TRACE(("enter buf_get_rsa_priv_key"))
if (buf_get_rsa_pub_key(buf, key) == DROPBEAR_FAILURE) {
TRACE(("leave buf_get_rsa_priv_key: pub: ret == DROPBEAR_FAILURE"))
return DROPBEAR_FAILURE;
}
key->d = m_malloc(sizeof(mp_int));
m_mp_init(key->d);
if (buf_getmpint(buf, key->d) == DROPBEAR_FAILURE) {
TRACE(("leave buf_get_rsa_priv_key: d: ret == DROPBEAR_FAILURE"))
return DROPBEAR_FAILURE;
}
/* old Dropbear private keys didn't keep p and q, so we will ignore them*/
if (buf->pos == buf->len) {
key->p = NULL;
key->q = NULL;
} else {
key->p = m_malloc(sizeof(mp_int));
key->q = m_malloc(sizeof(mp_int));
m_mp_init_multi(key->p, key->q, NULL);
if (buf_getmpint(buf, key->p) == DROPBEAR_FAILURE) {
TRACE(("leave buf_get_rsa_priv_key: p: ret == DROPBEAR_FAILURE"))
return DROPBEAR_FAILURE;
}
if (buf_getmpint(buf, key->q) == DROPBEAR_FAILURE) {
TRACE(("leave buf_get_rsa_priv_key: q: ret == DROPBEAR_FAILURE"))
return DROPBEAR_FAILURE;
}
}
TRACE(("leave buf_get_rsa_priv_key"))
return DROPBEAR_SUCCESS;
}
/* Clear and free the memory used by a public or private key */
void rsa_key_free(rsa_key *key) {
TRACE(("enter rsa_key_free"))
if (key == NULL) {
TRACE(("leave rsa_key_free: key == NULL"))
return;
}
if (key->d) {
mp_clear(key->d);
m_free(key->d);
}
if (key->e) {
mp_clear(key->e);
m_free(key->e);
}
if (key->n) {
mp_clear(key->n);
m_free(key->n);
}
if (key->p) {
mp_clear(key->p);
m_free(key->p);
}
if (key->q) {
mp_clear(key->q);
m_free(key->q);
}
m_free(key);
TRACE(("leave rsa_key_free"))
}
/* Put the public rsa key into the buffer in the required format:
*
* string "ssh-rsa"
* mp_int e
* mp_int n
*/
void buf_put_rsa_pub_key(buffer* buf, rsa_key *key) {
TRACE(("enter buf_put_rsa_pub_key"))
dropbear_assert(key != NULL);
buf_putstring(buf, SSH_SIGNKEY_RSA, SSH_SIGNKEY_RSA_LEN);
buf_putmpint(buf, key->e);
buf_putmpint(buf, key->n);
TRACE(("leave buf_put_rsa_pub_key"))
}
/* Same as buf_put_rsa_pub_key, but with the private "x" key appended */
void buf_put_rsa_priv_key(buffer* buf, rsa_key *key) {
TRACE(("enter buf_put_rsa_priv_key"))
dropbear_assert(key != NULL);
buf_put_rsa_pub_key(buf, key);
buf_putmpint(buf, key->d);
/* new versions have p and q, old versions don't */
if (key->p) {
buf_putmpint(buf, key->p);
}
if (key->q) {
buf_putmpint(buf, key->q);
}
TRACE(("leave buf_put_rsa_priv_key"))
}
#ifdef DROPBEAR_SIGNKEY_VERIFY
/* Verify a signature in buf, made on data by the key given.
* Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
int buf_rsa_verify(buffer * buf, rsa_key *key, const unsigned char* data,
unsigned int len) {
unsigned int slen;
DEF_MP_INT(rsa_s);
DEF_MP_INT(rsa_mdash);
DEF_MP_INT(rsa_em);
int ret = DROPBEAR_FAILURE;
TRACE(("enter buf_rsa_verify"))
dropbear_assert(key != NULL);
m_mp_init_multi(&rsa_mdash, &rsa_s, &rsa_em, NULL);
slen = buf_getint(buf);
if (slen != (unsigned int)mp_unsigned_bin_size(key->n)) {
TRACE(("bad size"))
goto out;
}
if (mp_read_unsigned_bin(&rsa_s, buf_getptr(buf, buf->len - buf->pos),
buf->len - buf->pos) != MP_OKAY) {
TRACE(("failed reading rsa_s"))
goto out;
}
/* check that s <= n-1 */
if (mp_cmp(&rsa_s, key->n) != MP_LT) {
TRACE(("s > n-1"))
goto out;
}
/* create the magic PKCS padded value */
rsa_pad_em(key, data, len, &rsa_em);
if (mp_exptmod(&rsa_s, key->e, key->n, &rsa_mdash) != MP_OKAY) {
TRACE(("failed exptmod rsa_s"))
goto out;
}
if (mp_cmp(&rsa_em, &rsa_mdash) == MP_EQ) {
/* signature is valid */
TRACE(("success!"))
ret = DROPBEAR_SUCCESS;
}
out:
mp_clear_multi(&rsa_mdash, &rsa_s, &rsa_em, NULL);
TRACE(("leave buf_rsa_verify: ret %d", ret))
return ret;
}
#endif /* DROPBEAR_SIGNKEY_VERIFY */
/* Sign the data presented with key, writing the signature contents
* to the buffer */
void buf_put_rsa_sign(buffer* buf, rsa_key *key, const unsigned char* data,
unsigned int len) {
unsigned int nsize, ssize;
unsigned int i;
DEF_MP_INT(rsa_s);
DEF_MP_INT(rsa_tmp1);
DEF_MP_INT(rsa_tmp2);
DEF_MP_INT(rsa_tmp3);
unsigned char *tmpbuf;
TRACE(("enter buf_put_rsa_sign"))
dropbear_assert(key != NULL);
m_mp_init_multi(&rsa_s, &rsa_tmp1, &rsa_tmp2, &rsa_tmp3, NULL);
rsa_pad_em(key, data, len, &rsa_tmp1);
/* the actual signing of the padded data */
#ifdef RSA_BLINDING
/* With blinding, s = (r^(-1))((em)*r^e)^d mod n */
/* generate the r blinding value */
/* rsa_tmp2 is r */
gen_random_mpint(key->n, &rsa_tmp2);
/* rsa_tmp1 is em */
/* em' = em * r^e mod n */
mp_exptmod(&rsa_tmp2, key->e, key->n, &rsa_s); /* rsa_s used as a temp var*/
mp_invmod(&rsa_tmp2, key->n, &rsa_tmp3);
mp_mulmod(&rsa_tmp1, &rsa_s, key->n, &rsa_tmp2);
/* rsa_tmp2 is em' */
/* s' = (em')^d mod n */
mp_exptmod(&rsa_tmp2, key->d, key->n, &rsa_tmp1);
/* rsa_tmp1 is s' */
/* rsa_tmp3 is r^(-1) mod n */
/* s = (s')r^(-1) mod n */
mp_mulmod(&rsa_tmp1, &rsa_tmp3, key->n, &rsa_s);
#else
/* s = em^d mod n */
/* rsa_tmp1 is em */
if (mp_exptmod(&rsa_tmp1, key->d, key->n, &rsa_s) != MP_OKAY) {
dropbear_exit("rsa error");
}
#endif /* RSA_BLINDING */
mp_clear_multi(&rsa_tmp1, &rsa_tmp2, &rsa_tmp3, NULL);
/* create the signature to return */
buf_putstring(buf, SSH_SIGNKEY_RSA, SSH_SIGNKEY_RSA_LEN);
nsize = mp_unsigned_bin_size(key->n);
/* string rsa_signature_blob length */
buf_putint(buf, nsize);
/* pad out s to same length as n */
ssize = mp_unsigned_bin_size(&rsa_s);
dropbear_assert(ssize <= nsize);
for (i = 0; i < nsize-ssize; i++) {
buf_putbyte(buf, 0x00);
}
if (mp_to_unsigned_bin(&rsa_s, buf_getwriteptr(buf, ssize)) != MP_OKAY) {
dropbear_exit("rsa error");
}
buf_incrwritepos(buf, ssize);
mp_clear(&rsa_s);
#if defined(DEBUG_RSA) && defined(DEBUG_TRACE)
printhex("RSA sig", buf->data, buf->len);
#endif
TRACE(("leave buf_put_rsa_sign"))
}
/* Creates the message value as expected by PKCS, see rfc2437 etc */
/* format to be padded to is:
* EM = 01 | FF* | 00 | prefix | hash
*
* where FF is repeated enough times to make EM one byte
* shorter than the size of key->n
*
* prefix is the ASN1 designator prefix,
* hex 30 21 30 09 06 05 2B 0E 03 02 1A 05 00 04 14
*
* rsa_em must be a pointer to an initialised mp_int.
*/
static void rsa_pad_em(rsa_key * key,
const unsigned char * data, unsigned int len,
mp_int * rsa_em) {
/* ASN1 designator (including the 0x00 preceding) */
const unsigned char rsa_asn1_magic[] =
{0x00, 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b,
0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14};
const unsigned int RSA_ASN1_MAGIC_LEN = 16;
buffer * rsa_EM = NULL;
hash_state hs;
unsigned int nsize;
dropbear_assert(key != NULL);
dropbear_assert(data != NULL);
nsize = mp_unsigned_bin_size(key->n);
rsa_EM = buf_new(nsize-1);
/* type byte */
buf_putbyte(rsa_EM, 0x01);
/* Padding with 0xFF bytes */
while(rsa_EM->pos != rsa_EM->size - RSA_ASN1_MAGIC_LEN - SHA1_HASH_SIZE) {
buf_putbyte(rsa_EM, 0xff);
}
/* Magic ASN1 stuff */
memcpy(buf_getwriteptr(rsa_EM, RSA_ASN1_MAGIC_LEN),
rsa_asn1_magic, RSA_ASN1_MAGIC_LEN);
buf_incrwritepos(rsa_EM, RSA_ASN1_MAGIC_LEN);
/* The hash of the data */
sha1_init(&hs);
sha1_process(&hs, data, len);
sha1_done(&hs, buf_getwriteptr(rsa_EM, SHA1_HASH_SIZE));
buf_incrwritepos(rsa_EM, SHA1_HASH_SIZE);
dropbear_assert(rsa_EM->pos == rsa_EM->size);
/* Create the mp_int from the encoded bytes */
buf_setpos(rsa_EM, 0);
bytes_to_mp(rsa_em, buf_getptr(rsa_EM, rsa_EM->size),
rsa_EM->size);
buf_free(rsa_EM);
}
#endif /* DROPBEAR_RSA */