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/* Diffie-Hellman Key Agreement Method [RFC2631]
*
* Copyright (c) 2016, Intel Corporation
* Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
*
* 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 <crypto/internal/kpp.h>
#include <crypto/kpp.h>
#include <crypto/dh.h>
#include <linux/mpi.h>
struct dh_ctx {
MPI p; /* Value is guaranteed to be set. */
MPI q; /* Value is optional. */
MPI g; /* Value is guaranteed to be set. */
MPI xa; /* Value is guaranteed to be set. */
};
static void dh_clear_ctx(struct dh_ctx *ctx)
{
mpi_free(ctx->p);
mpi_free(ctx->q);
mpi_free(ctx->g);
mpi_free(ctx->xa);
memset(ctx, 0, sizeof(*ctx));
}
/*
* If base is g we compute the public key
* ya = g^xa mod p; [RFC2631 sec 2.1.1]
* else if base if the counterpart public key we compute the shared secret
* ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
*/
static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
{
/* val = base^xa mod p */
return mpi_powm(val, base, ctx->xa, ctx->p);
}
static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
{
return kpp_tfm_ctx(tfm);
}
static int dh_check_params_length(unsigned int p_len)
{
return (p_len < 1536) ? -EINVAL : 0;
}
static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
{
if (dh_check_params_length(params->p_size << 3))
return -EINVAL;
ctx->p = mpi_read_raw_data(params->p, params->p_size);
if (!ctx->p)
return -EINVAL;
if (params->q && params->q_size) {
ctx->q = mpi_read_raw_data(params->q, params->q_size);
if (!ctx->q)
return -EINVAL;
}
ctx->g = mpi_read_raw_data(params->g, params->g_size);
if (!ctx->g)
return -EINVAL;
return 0;
}
static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
unsigned int len)
{
struct dh_ctx *ctx = dh_get_ctx(tfm);
struct dh params;
/* Free the old MPI key if any */
dh_clear_ctx(ctx);
if (crypto_dh_decode_key(buf, len, ¶ms) < 0)
goto err_clear_ctx;
if (dh_set_params(ctx, ¶ms) < 0)
goto err_clear_ctx;
ctx->xa = mpi_read_raw_data(params.key, params.key_size);
if (!ctx->xa)
goto err_clear_ctx;
return 0;
err_clear_ctx:
dh_clear_ctx(ctx);
return -EINVAL;
}
/*
* SP800-56A public key verification:
*
* * If Q is provided as part of the domain paramenters, a full validation
* according to SP800-56A section 5.6.2.3.1 is performed.
*
* * If Q is not provided, a partial validation according to SP800-56A section
* 5.6.2.3.2 is performed.
*/
static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
{
if (unlikely(!ctx->p))
return -EINVAL;
/*
* Step 1: Verify that 2 <= y <= p - 2.
*
* The upper limit check is actually y < p instead of y < p - 1
* as the mpi_sub_ui function is yet missing.
*/
if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
return -EINVAL;
/* Step 2: Verify that 1 = y^q mod p */
if (ctx->q) {
MPI val = mpi_alloc(0);
int ret;
if (!val)
return -ENOMEM;
ret = mpi_powm(val, y, ctx->q, ctx->p);
if (ret) {
mpi_free(val);
return ret;
}
ret = mpi_cmp_ui(val, 1);
mpi_free(val);
if (ret != 0)
return -EINVAL;
}
return 0;
}
static int dh_compute_value(struct kpp_request *req)
{
struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
struct dh_ctx *ctx = dh_get_ctx(tfm);
MPI base, val = mpi_alloc(0);
int ret = 0;
int sign;
if (!val)
return -ENOMEM;
if (unlikely(!ctx->xa)) {
ret = -EINVAL;
goto err_free_val;
}
if (req->src) {
base = mpi_read_raw_from_sgl(req->src, req->src_len);
if (!base) {
ret = -EINVAL;
goto err_free_val;
}
ret = dh_is_pubkey_valid(ctx, base);
if (ret)
goto err_free_val;
} else {
base = ctx->g;
}
ret = _compute_val(ctx, base, val);
if (ret)
goto err_free_base;
ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
if (ret)
goto err_free_base;
if (sign < 0)
ret = -EBADMSG;
err_free_base:
if (req->src)
mpi_free(base);
err_free_val:
mpi_free(val);
return ret;
}
static unsigned int dh_max_size(struct crypto_kpp *tfm)
{
struct dh_ctx *ctx = dh_get_ctx(tfm);
return mpi_get_size(ctx->p);
}
static void dh_exit_tfm(struct crypto_kpp *tfm)
{
struct dh_ctx *ctx = dh_get_ctx(tfm);
dh_clear_ctx(ctx);
}
static struct kpp_alg dh = {
.set_secret = dh_set_secret,
.generate_public_key = dh_compute_value,
.compute_shared_secret = dh_compute_value,
.max_size = dh_max_size,
.exit = dh_exit_tfm,
.base = {
.cra_name = "dh",
.cra_driver_name = "dh-generic",
.cra_priority = 100,
.cra_module = THIS_MODULE,
.cra_ctxsize = sizeof(struct dh_ctx),
},
};
static int dh_init(void)
{
return crypto_register_kpp(&dh);
}
static void dh_exit(void)
{
crypto_unregister_kpp(&dh);
}
module_init(dh_init);
module_exit(dh_exit);
MODULE_ALIAS_CRYPTO("dh");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("DH generic algorithm");
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