ec_25519.c
/*
* Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <string.h>
#include <openssl/err.h>
#include <openssl/rand.h>
#include "ec_lcl.h"
/* Length of Curve 25519 keys */
#define EC_X25519_KEYLEN 32
/* Group degree and order bits */
#define EC_X25519_BITS 253
/* Copy Curve25519 public key buffer, allocating is necessary */
static int x25519_init_public(EC_POINT *pub, const void *src)
{
if (pub->custom_data == NULL) {
pub->custom_data = OPENSSL_malloc(EC_X25519_KEYLEN);
if (pub->custom_data == NULL)
return 0;
}
if (src != NULL)
memcpy(pub->custom_data, src, EC_X25519_KEYLEN);
return 1;
}
/* Copy Curve25519 private key buffer, allocating is necessary */
static int x25519_init_private(EC_KEY *dst, const void *src)
{
if (dst->custom_data == NULL) {
dst->custom_data = OPENSSL_secure_malloc(EC_X25519_KEYLEN);
if (dst->custom_data == NULL)
return 0;
}
if (src != NULL)
memcpy(dst->custom_data, src, EC_X25519_KEYLEN);
return 1;
}
static int x25519_group_init(EC_GROUP *grp)
{
return 1;
}
static int x25519_group_copy(EC_GROUP *dst, const EC_GROUP *src)
{
return 1;
}
static int x25519_group_get_degree(const EC_GROUP *src)
{
return EC_X25519_BITS;
}
static int x25519_group_order_bits(const EC_GROUP *src)
{
return EC_X25519_BITS;
}
static int x25519_set_private(EC_KEY *eckey, const BIGNUM *priv_key)
{
if (BN_num_bytes(priv_key) > EC_X25519_KEYLEN)
return 0;
if (x25519_init_private(eckey, NULL))
return 0;
/* Convert BIGNUM form private key to internal format */
if (BN_bn2lebinpad(priv_key, eckey->custom_data, EC_X25519_KEYLEN)
!= EC_X25519_KEYLEN)
return 0;
return 1;
}
static int x25519_keycheck(const EC_KEY *eckey)
{
const char *pubkey;
if (eckey->pub_key == NULL)
return 0;
pubkey = eckey->pub_key->custom_data;
if (pubkey == NULL)
return 0;
if (eckey->custom_data != NULL) {
uint8_t tmp[EC_X25519_KEYLEN];
/* Check eckey->priv_key exists and matches eckey->custom_data */
if (eckey->priv_key == NULL)
return 0;
if (BN_bn2lebinpad(eckey->priv_key, tmp, EC_X25519_KEYLEN)
!= EC_X25519_KEYLEN
|| CRYPTO_memcmp(tmp, eckey->custom_data,
EC_X25519_KEYLEN) != 0) {
OPENSSL_cleanse(tmp, EC_X25519_KEYLEN);
return 0;
}
X25519_public_from_private(tmp, eckey->custom_data);
if (CRYPTO_memcmp(pubkey, tmp, EC_X25519_KEYLEN) == 0)
return 1;
return 0;
} else {
return 1;
}
}
static int x25519_keygenpub(EC_KEY *eckey)
{
X25519_public_from_private(eckey->pub_key->custom_data,
eckey->custom_data);
return 1;
}
static int x25519_keygen(EC_KEY *eckey)
{
unsigned char *key;
if (x25519_init_private(eckey, NULL) == 0)
return 0;
key = eckey->custom_data;
if (RAND_bytes(key, EC_X25519_KEYLEN) <= 0)
return 0;
key[0] &= 248;
key[31] &= 127;
key[31] |= 64;
/*
* Although the private key is kept as an array in eckey->custom_data
* Set eckey->priv_key too so existing code which uses
* EC_KEY_get0_private_key() still works.
*/
if (eckey->priv_key == NULL)
eckey->priv_key = BN_secure_new();
if (eckey->priv_key == NULL)
return 0;
if (BN_lebin2bn(eckey->custom_data, EC_X25519_KEYLEN, eckey->priv_key) ==
NULL)
return 0;
if (eckey->pub_key == NULL)
eckey->pub_key = EC_POINT_new(eckey->group);
if (eckey->pub_key == NULL)
return 0;
return x25519_keygenpub(eckey);
}
static void x25519_keyfinish(EC_KEY *eckey)
{
OPENSSL_secure_free(eckey->custom_data);
eckey->custom_data = NULL;
}
static int x25519_keycopy(EC_KEY *dest, const EC_KEY *src)
{
if (src->custom_data == NULL)
return 0;
return x25519_init_private(dest, src->custom_data);
}
static int x25519_oct2priv(EC_KEY *eckey, const unsigned char *buf, size_t len)
{
if (len != EC_X25519_KEYLEN)
return 0;
if (x25519_init_private(eckey, buf) == 0)
return 0;
/*
* Although the private key is kept as an array in eckey->custom_data
* Set eckey->priv_key too so existing code which uses
* EC_KEY_get0_private_key() still works.
*/
if (eckey->priv_key == NULL)
eckey->priv_key = BN_secure_new();
if (eckey->priv_key == NULL)
return 0;
if (BN_lebin2bn(buf, EC_X25519_KEYLEN, eckey->priv_key) == NULL)
return 0;
return 1;
}
static size_t x25519_priv2oct(const EC_KEY *eckey,
unsigned char *buf, size_t len)
{
size_t keylen = EC_X25519_KEYLEN;
if (eckey->custom_data == NULL)
return 0;
if (buf != NULL) {
if (len < keylen)
return 0;
memcpy(buf, eckey->custom_data, keylen);
}
return keylen;
}
static int x25519_point_init(EC_POINT *pt)
{
return x25519_init_public(pt, NULL);
}
static void x25519_point_finish(EC_POINT *pt)
{
OPENSSL_free(pt->custom_data);
pt->custom_data = NULL;
}
static void x25519_point_clear_finish(EC_POINT *pt)
{
OPENSSL_clear_free(pt->custom_data, EC_X25519_KEYLEN);
pt->custom_data = NULL;
}
static int x25519_point_copy(EC_POINT *dst, const EC_POINT *src)
{
memcpy(dst->custom_data, src->custom_data, EC_X25519_KEYLEN);
return 1;
}
static size_t x25519_point2oct(const EC_GROUP *grp, const EC_POINT *pt,
point_conversion_form_t form,
unsigned char *buf, size_t len, BN_CTX *ctx)
{
if (buf != NULL) {
if (len < EC_X25519_KEYLEN)
return 0;
memcpy(buf, pt->custom_data, EC_X25519_KEYLEN);
}
return EC_X25519_KEYLEN;
}
static int x25519_oct2point(const EC_GROUP *grp, EC_POINT *pt,
const unsigned char *buf, size_t len, BN_CTX *ctx)
{
unsigned char *pubkey = pt->custom_data;
if (len != EC_X25519_KEYLEN)
return 0;
memcpy(pubkey, buf, EC_X25519_KEYLEN);
/* Mask off MSB */
pubkey[EC_X25519_KEYLEN - 1] &= 0x7F;
return 1;
}
static int x25519_point_cmp(const EC_GROUP *group, const EC_POINT *a,
const EC_POINT *b, BN_CTX *ctx)
{
/* Shouldn't happen as initialised to non-zero */
if (a->custom_data == NULL || b->custom_data == NULL)
return -1;
if (CRYPTO_memcmp(a->custom_data, b->custom_data, EC_X25519_KEYLEN) == 0)
return 0;
return 1;
}
static int x25519_compute_key(unsigned char **psec, size_t *pseclen,
const EC_POINT *pub_key, const EC_KEY *ecdh)
{
unsigned char *key;
int ret = 0;
if (ecdh->custom_data == NULL)
return 0;
key = OPENSSL_malloc(EC_X25519_KEYLEN);
if (key == NULL)
return 0;
if (X25519(key, ecdh->custom_data, pub_key->custom_data) == 0)
goto err;
*psec = key;
*pseclen = EC_X25519_KEYLEN;
return 1;
err:
OPENSSL_clear_free(key, EC_X25519_KEYLEN);
return ret;
}
const EC_METHOD *ec_x25519_meth(void)
{
static const EC_METHOD ret = {
EC_FLAGS_CUSTOM_CURVE | EC_FLAGS_NO_SIGN,
NID_undef,
x25519_group_init, /* group_init */
0, /* group_finish */
0, /* group_clear_finish */
x25519_group_copy, /* group_copy */
0, /* group_set_curve */
0, /* group_get_curve */
x25519_group_get_degree,
x25519_group_order_bits,
0, /* group_check_discriminant */
x25519_point_init,
x25519_point_finish,
x25519_point_clear_finish,
x25519_point_copy,
0, /* point_set_to_infinity */
0, /* set_Jprojective_coordinates_GFp */
0, /* get_Jprojective_coordinates_GFp */
0, /* point_set_affine_coordinates */
0, /* point_get_affine_coordinates */
0, /* point_set_compressed_coordinates */
x25519_point2oct,
x25519_oct2point,
0, /* simple_add */
0, /* simple_dbl */
0, /* simple_invert */
0, /* simple_is_at_infinity */
0, /* simple_is_on_curve */
x25519_point_cmp,
0, /* simple_make_affine */
0, /* simple_points_make_affine */
0, /* points_mul */
0, /* precompute_mult */
0, /* have_precompute_mult */
0, /* field_mul */
0, /* field_sqr */
0, /* field_div */
0, /* field_encode */
0, /* field_decode */
0, /* field_set_to_one */
x25519_priv2oct,
x25519_oct2priv,
x25519_set_private,
x25519_keygen,
x25519_keycheck,
x25519_keygenpub,
x25519_keycopy,
x25519_keyfinish,
x25519_compute_key
};
return &ret;
}
