diff options
Diffstat (limited to 'rsa.c')
| -rw-r--r-- | rsa.c | 424 |
1 files changed, 424 insertions, 0 deletions
@@ -0,0 +1,424 @@ +/* + * 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) { + + int ret = DROPBEAR_FAILURE; + 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")) + goto out; + } + + if (mp_count_bits(key->n) < MIN_RSA_KEYLEN) { + dropbear_log(LOG_WARNING, "rsa key too short"); + goto out; + } + + TRACE(("leave buf_get_rsa_pub_key: success")) + ret = DROPBEAR_SUCCESS; +out: + if (ret == DROPBEAR_FAILURE) { + m_free(key->e); + m_free(key->n); + } + return ret; +} + +/* Same as buf_get_rsa_pub_key, but reads private bits 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) { + int ret = DROPBEAR_FAILURE; + + TRACE(("enter buf_get_rsa_priv_key")) + dropbear_assert(key != NULL); + + 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 = NULL; + key->p = NULL; + key->q = NULL; + + 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")) + goto out; + } + + if (buf->pos == buf->len) { + /* old Dropbear private keys didn't keep p and q, so we will ignore them*/ + } 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")) + goto out; + } + + if (buf_getmpint(buf, key->q) == DROPBEAR_FAILURE) { + TRACE(("leave buf_get_rsa_priv_key: q: ret == DROPBEAR_FAILURE")) + goto out; + } + } + + ret = DROPBEAR_SUCCESS; +out: + if (ret == DROPBEAR_FAILURE) { + m_free(key->d); + m_free(key->p); + m_free(key->q); + } + TRACE(("leave buf_get_rsa_priv_key")) + return ret; +} + + +/* 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); + + 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 */ + + /* rsa_s used as a temp var*/ + if (mp_exptmod(&rsa_tmp2, key->e, key->n, &rsa_s) != MP_OKAY) { + dropbear_exit("rsa error"); + } + if (mp_invmod(&rsa_tmp2, key->n, &rsa_tmp3) != MP_OKAY) { + dropbear_exit("rsa error"); + } + if (mp_mulmod(&rsa_tmp1, &rsa_s, key->n, &rsa_tmp2) != MP_OKAY) { + dropbear_exit("rsa error"); + } + + /* rsa_tmp2 is em' */ + /* s' = (em')^d mod n */ + if (mp_exptmod(&rsa_tmp2, key->d, key->n, &rsa_tmp1) != MP_OKAY) { + dropbear_exit("rsa error"); + } + + /* rsa_tmp1 is s' */ + /* rsa_tmp3 is r^(-1) mod n */ + /* s = (s')r^(-1) mod n */ + if (mp_mulmod(&rsa_tmp1, &rsa_tmp3, key->n, &rsa_s) != MP_OKAY) { + dropbear_exit("rsa error"); + } + +#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 */ |