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#include "includes.h"
#include "options.h"
#include "ecc.h"
#include "dbutil.h"
#include "bignum.h"
#ifdef DROPBEAR_ECC
/* .dp members are filled out by dropbear_ecc_fill_dp() at startup */
#ifdef DROPBEAR_ECC_256
struct dropbear_ecc_curve ecc_curve_nistp256 = {
.ltc_size = 32,
.hash_desc = &sha256_desc,
.name = "nistp256"
};
#endif
#ifdef DROPBEAR_ECC_384
struct dropbear_ecc_curve ecc_curve_nistp384 = {
.ltc_size = 48,
.hash_desc = &sha384_desc,
.name = "nistp384"
};
#endif
#ifdef DROPBEAR_ECC_521
struct dropbear_ecc_curve ecc_curve_nistp521 = {
.ltc_size = 66,
.hash_desc = &sha512_desc,
.name = "nistp521"
};
#endif
struct dropbear_ecc_curve *dropbear_ecc_curves[] = {
#ifdef DROPBEAR_ECC_256
&ecc_curve_nistp256,
#endif
#ifdef DROPBEAR_ECC_384
&ecc_curve_nistp384,
#endif
#ifdef DROPBEAR_ECC_521
&ecc_curve_nistp521,
#endif
NULL
};
void dropbear_ecc_fill_dp() {
struct dropbear_ecc_curve **curve;
/* libtomcrypt guarantees they're ordered by size */
const ltc_ecc_set_type *dp = ltc_ecc_sets;
for (curve = dropbear_ecc_curves; *curve; curve++) {
for (;dp->size > 0; dp++) {
if (dp->size == (*curve)->ltc_size) {
(*curve)->dp = dp;
break;
}
}
if (!(*curve)->dp) {
dropbear_exit("Missing ECC params %s", (*curve)->name);
}
}
}
struct dropbear_ecc_curve* curve_for_dp(const ltc_ecc_set_type *dp) {
struct dropbear_ecc_curve **curve = NULL;
for (curve = dropbear_ecc_curves; *curve; curve++) {
if ((*curve)->dp == dp) {
break;
}
}
assert(*curve);
return *curve;
}
ecc_key * new_ecc_key(void) {
ecc_key *key = m_malloc(sizeof(*key));
m_mp_alloc_init_multi(&key->pubkey.x, &key->pubkey.y,
&key->pubkey.z, &key->k, NULL);
return key;
}
// Copied from libtomcrypt ecc_import.c (version there is static), modified
// for different mp_int pointer without LTC_SOURCE
static int ecc_is_point(ecc_key *key)
{
mp_int *prime, *b, *t1, *t2;
int err;
prime = m_malloc(sizeof(mp_int));
b = m_malloc(sizeof(mp_int));
t1 = m_malloc(sizeof(mp_int));
t2 = m_malloc(sizeof(mp_int));
m_mp_alloc_init_multi(&prime, &b, &t1, &t2, NULL);
/* load prime and b */
if ((err = mp_read_radix(prime, key->dp->prime, 16)) != CRYPT_OK) { goto error; }
if ((err = mp_read_radix(b, key->dp->B, 16)) != CRYPT_OK) { goto error; }
/* compute y^2 */
if ((err = mp_sqr(key->pubkey.y, t1)) != CRYPT_OK) { goto error; }
/* compute x^3 */
if ((err = mp_sqr(key->pubkey.x, t2)) != CRYPT_OK) { goto error; }
if ((err = mp_mod(t2, prime, t2)) != CRYPT_OK) { goto error; }
if ((err = mp_mul(key->pubkey.x, t2, t2)) != CRYPT_OK) { goto error; }
/* compute y^2 - x^3 */
if ((err = mp_sub(t1, t2, t1)) != CRYPT_OK) { goto error; }
/* compute y^2 - x^3 + 3x */
if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK) { goto error; }
if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK) { goto error; }
if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK) { goto error; }
if ((err = mp_mod(t1, prime, t1)) != CRYPT_OK) { goto error; }
while (mp_cmp_d(t1, 0) == LTC_MP_LT) {
if ((err = mp_add(t1, prime, t1)) != CRYPT_OK) { goto error; }
}
while (mp_cmp(t1, prime) != LTC_MP_LT) {
if ((err = mp_sub(t1, prime, t1)) != CRYPT_OK) { goto error; }
}
/* compare to b */
if (mp_cmp(t1, b) != LTC_MP_EQ) {
err = CRYPT_INVALID_PACKET;
} else {
err = CRYPT_OK;
}
error:
mp_clear_multi(prime, b, t1, t2, NULL);
m_free(prime);
m_free(b);
m_free(t1);
m_free(t2);
return err;
}
/* For the "ephemeral public key octet string" in ECDH (rfc5656 section 4) */
void buf_put_ecc_raw_pubkey_string(buffer *buf, ecc_key *key) {
unsigned long len = key->dp->size*2 + 1;
buf_putint(buf, len);
int err = ecc_ansi_x963_export(key, buf_getwriteptr(buf, len), &len);
if (err != CRYPT_OK) {
dropbear_exit("ECC error");
}
buf_incrwritepos(buf, len);
}
/* For the "ephemeral public key octet string" in ECDH (rfc5656 section 4) */
ecc_key * buf_get_ecc_raw_pubkey(buffer *buf, const struct dropbear_ecc_curve *curve) {
ecc_key *key = NULL;
int ret = DROPBEAR_FAILURE;
const unsigned int size = curve->dp->size;
unsigned char first;
TRACE(("enter buf_get_ecc_raw_pubkey"))
buf_setpos(buf, 0);
first = buf_getbyte(buf);
if (first == 2 || first == 3) {
dropbear_log(LOG_WARNING, "Dropbear doesn't support ECC point compression");
return NULL;
}
if (first != 4 || buf->len != 1+2*size) {
TRACE(("leave, wrong size"))
return NULL;
}
key = new_ecc_key();
key->dp = curve->dp;
if (mp_read_unsigned_bin(key->pubkey.x, buf_getptr(buf, size), size) != MP_OKAY) {
TRACE(("failed to read x"))
goto out;
}
buf_incrpos(buf, size);
if (mp_read_unsigned_bin(key->pubkey.y, buf_getptr(buf, size), size) != MP_OKAY) {
TRACE(("failed to read y"))
goto out;
}
buf_incrpos(buf, size);
mp_set(key->pubkey.z, 1);
if (ecc_is_point(key) != CRYPT_OK) {
TRACE(("failed, not a point"))
goto out;
}
// SEC1 3.2.3.1 Check that Q != 0
if (mp_cmp_d(key->pubkey.x, 0) == LTC_MP_EQ) {
TRACE(("failed, x == 0"))
goto out;
}
if (mp_cmp_d(key->pubkey.y, 0) == LTC_MP_EQ) {
TRACE(("failed, y == 0"))
goto out;
}
ret = DROPBEAR_SUCCESS;
out:
if (ret == DROPBEAR_FAILURE) {
if (key) {
ecc_free(key);
m_free(key);
key = NULL;
}
}
return key;
}
// a modified version of libtomcrypt's "ecc_shared_secret" to output
// a mp_int instead.
mp_int * dropbear_ecc_shared_secret(ecc_key *public_key, ecc_key *private_key)
{
ecc_point *result = NULL;
mp_int *prime = NULL, *shared_secret = NULL;
int err = DROPBEAR_FAILURE;
/* type valid? */
if (private_key->type != PK_PRIVATE) {
goto done;
}
if (private_key->dp != public_key->dp) {
goto done;
}
/* make new point */
result = ltc_ecc_new_point();
if (result == NULL) {
goto done;
}
prime = m_malloc(sizeof(*prime));
m_mp_init(prime);
if (mp_read_radix(prime, (char *)private_key->dp->prime, 16) != CRYPT_OK) {
goto done;
}
if (ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, prime, 1) != CRYPT_OK) {
goto done;
}
err = DROPBEAR_SUCCESS;
done:
if (err == DROPBEAR_SUCCESS) {
shared_secret = m_malloc(sizeof(*shared_secret));
m_mp_init(shared_secret);
mp_copy(result->x, shared_secret);
}
if (prime) {
mp_clear(prime);
m_free(prime);
}
if (result)
{
ltc_ecc_del_point(result);
}
if (err == DROPBEAR_FAILURE) {
dropbear_exit("ECC error");
}
return shared_secret;
}
#endif
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