// SPDX-License-Identifier: GPL-2.0+
/*
* Elliptic Curve (Russian) Digital Signature Algorithm for Cryptographic API
*
* Copyright (c) 2019 Vitaly Chikunov <vt@altlinux.org>
*
* References:
* GOST 34.10-2018, GOST R 34.10-2012, RFC 7091, ISO/IEC 14888-3:2018.
*
* Historical references:
* GOST R 34.10-2001, RFC 4357, ISO/IEC 14888-3:2006/Amd 1:2010.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*/
#include <linux/module.h>
#include <linux/crypto.h>
#include <crypto/streebog.h>
#include <crypto/internal/akcipher.h>
#include <crypto/akcipher.h>
#include <linux/oid_registry.h>
#include "ecrdsa_params.asn1.h"
#include "ecrdsa_pub_key.asn1.h"
#include "ecc.h"
#include "ecrdsa_defs.h"
#define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8)
#define ECRDSA_MAX_DIGITS (512 / 64)
struct ecrdsa_ctx {
enum OID algo_oid; /* overall public key oid */
enum OID curve_oid; /* parameter */
enum OID digest_oid; /* parameter */
const struct ecc_curve *curve; /* curve from oid */
unsigned int digest_len; /* parameter (bytes) */
const char *digest; /* digest name from oid */
unsigned int key_len; /* @key length (bytes) */
const char *key; /* raw public key */
struct ecc_point pub_key;
u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */
};
static const struct ecc_curve *get_curve_by_oid(enum OID oid)
{
switch (oid) {
case OID_gostCPSignA:
case OID_gostTC26Sign256B:
return &gost_cp256a;
case OID_gostCPSignB:
case OID_gostTC26Sign256C:
return &gost_cp256b;
case OID_gostCPSignC:
case OID_gostTC26Sign256D:
return &gost_cp256c;
case OID_gostTC26Sign512A:
return &gost_tc512a;
case OID_gostTC26Sign512B:
return &gost_tc512b;
/* The following two aren't implemented: */
case OID_gostTC26Sign256A:
case OID_gostTC26Sign512C:
default:
return NULL;
}
}
static int ecrdsa_verify(struct akcipher_request *req)
{
struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
unsigned char sig[ECRDSA_MAX_SIG_SIZE];
unsigned char digest[STREEBOG512_DIGEST_SIZE];
unsigned int ndigits = req->dst_len / sizeof(u64);
u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */
u64 _r[ECRDSA_MAX_DIGITS]; /* -r */
u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */
u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */
u64 *v = e; /* e^{-1} \mod q */
u64 z1[ECRDSA_MAX_DIGITS];
u64 *z2 = _r;
struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */
/*
* Digest value, digest algorithm, and curve (modulus) should have the
* same length (256 or 512 bits), public key and signature should be
* twice bigger.
*/
if (!ctx->curve ||
!ctx->digest ||
!req->src ||
!ctx->pub_key.x ||
req->dst_len != ctx->digest_len ||
req->dst_len != ctx->curve->g.ndigits * sizeof(u64) ||
ctx->pub_key.ndigits != ctx->curve->g.ndigits ||
req->dst_len * 2 != req->src_len ||
WARN_ON(req->src_len > sizeof(sig)) ||
WARN_ON(req->dst_len > sizeof(digest)))
return -EBADMSG;
sg_copy_to_buffer(req->src, sg_nents_for_len(req->src, req->src_len),
sig, req->src_len);
sg_pcopy_to_buffer(req->src,
sg_nents_for_len(req->src,
req->src_len + req->dst_len),
digest, req->dst_len, req->src_len);
vli_from_be64(s, sig, ndigits);
vli_from_be64(r, sig + ndigits * sizeof(u64), ndigits);
/* Step 1: verify that 0 < r < q, 0 < s < q */
if (vli_is_zero(r, ndigits) ||
vli_cmp(r, ctx->curve->n, ndigits) == 1 ||
vli_is_zero(s, ndigits) ||
vli_cmp(s, ctx->curve->n, ndigits) == 1)
return -EKEYREJECTED;
/* Step 2: calculate hash (h) of the message (passed as input) */
/* Step 3: calculate e = h \mod q */
vli_from_le64(e, digest, ndigits);
if (vli_cmp(e, ctx->curve->n, ndigits) == 1)
vli_sub(e, e, ctx->curve->n, ndigits);
if (vli_is_zero(e, ndigits))
e[0] = 1;
/* Step 4: calculate v = e^{-1} \mod q */
vli_mod_inv(v, e, ctx->curve->n, ndigits);
/* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */
vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits);
vli_sub(_r, ctx->curve->n, r, ndigits);
vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits);
/* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */
ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key,
ctx->curve);
if (vli_cmp(cc.x, ctx->curve->n, ndigits) == 1)
vli_sub(cc.x, cc.x, ctx->curve->n, ndigits);
/* Step 7: if R == r signature is valid */
if (!vli_cmp(cc.x, r, ndigits))
return 0;
else
return -EKEYREJECTED;
}
int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag,
const void *value, size_t vlen)
{
struct ecrdsa_ctx *ctx = context;
ctx->curve_oid = look_up_OID(value, vlen);
if (!ctx->curve_oid)
return -EINVAL;
ctx->curve = get_curve_by_oid(ctx->curve_oid);
return 0;
}
/* Optional. If present should match expected digest algo OID. */
int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag,
const void *value, size_t vlen)
{
struct ecrdsa_ctx *ctx = context;
int digest_oid = look_up_OID(value, vlen);
if (digest_oid != ctx->digest_oid)
return -EINVAL;
return 0;
}
int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag,
const void *value, size_t vlen)
{
struct ecrdsa_ctx *ctx = context;
ctx->key = value;
ctx->key_len = vlen;
return 0;
}
static u8 *ecrdsa_unpack_u32(u32 *dst, void *src)
{
memcpy(dst, src, sizeof(u32));
return src + sizeof(u32);
}
/* Parse BER encoded subjectPublicKey. */
static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen)
{
struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
unsigned int ndigits;
u32 algo, paramlen;
u8 *params;
int err;
err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen);
if (err < 0)
return err;
/* Key parameters is in the key after keylen. */
params = ecrdsa_unpack_u32(¶mlen,
ecrdsa_unpack_u32(&algo, (u8 *)key + keylen));
if (algo == OID_gost2012PKey256) {
ctx->digest = "streebog256";
ctx->digest_oid = OID_gost2012Digest256;
ctx->digest_len = 256 / 8;
} else if (algo == OID_gost2012PKey512) {
ctx->digest = "streebog512";
ctx->digest_oid = OID_gost2012Digest512;
ctx->digest_len = 512 / 8;
} else
return -ENOPKG;
ctx->algo_oid = algo;
/* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */
err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen);
if (err < 0)
return err;
/*
* Sizes of algo (set in digest_len) and curve should match
* each other.
*/
if (!ctx->curve ||
ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len)
return -ENOPKG;
/*
* Key is two 256- or 512-bit coordinates which should match
* curve size.
*/
if ((ctx->key_len != (2 * 256 / 8) &&
ctx->key_len != (2 * 512 / 8)) ||
ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2)
return -ENOPKG;
ndigits = ctx->key_len / sizeof(u64) / 2;
ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits);
vli_from_le64(ctx->pub_key.x, ctx->key, ndigits);
vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64),
ndigits);
if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key))
return -EKEYREJECTED;
return 0;
}
static unsigned int ecrdsa_max_size(struct crypto_akcipher *tfm)
{
struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
/*
* Verify doesn't need any output, so it's just informational
* for keyctl to determine the key bit size.
*/
return ctx->pub_key.ndigits * sizeof(u64);
}
static void ecrdsa_exit_tfm(struct crypto_akcipher *tfm)
{
}
static struct akcipher_alg ecrdsa_alg = {
.verify = ecrdsa_verify,
.set_pub_key = ecrdsa_set_pub_key,
.max_size = ecrdsa_max_size,
.exit = ecrdsa_exit_tfm,
.base = {
.cra_name = "ecrdsa",
.cra_driver_name = "ecrdsa-generic",
.cra_priority = 100,
.cra_module = THIS_MODULE,
.cra_ctxsize = sizeof(struct ecrdsa_ctx),
},
};
static int __init ecrdsa_mod_init(void)
{
return crypto_register_akcipher(&ecrdsa_alg);
}
static void __exit ecrdsa_mod_fini(void)
{
crypto_unregister_akcipher(&ecrdsa_alg);
}
module_init(ecrdsa_mod_init);
module_exit(ecrdsa_mod_fini);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>");
MODULE_DESCRIPTION("EC-RDSA generic algorithm");
MODULE_ALIAS_CRYPTO("ecrdsa-generic");
