rsa.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* RSA asymmetric public-key algorithm [RFC3447]
 *
 * Copyright (c) 2015, Intel Corporation
 * Authors: Tadeusz Struk <tadeusz.struk@intel.com>
 */

#include <linux/fips.h>
#include <linux/module.h>
#include <linux/mpi.h>
#include <crypto/internal/rsa.h>
#include <crypto/internal/akcipher.h>
#include <crypto/akcipher.h>
#include <crypto/algapi.h>

struct rsa_mpi_key {
	MPI n;
	MPI e;
	MPI d;
	MPI p;
	MPI q;
	MPI dp;
	MPI dq;
	MPI qinv;
};

/*
 * RSAEP function [RFC3447 sec 5.1.1]
 * c = m^e mod n;
 */
static int _rsa_enc(const struct rsa_mpi_key *key, MPI c, MPI m)
{
	/* (1) Validate 0 <= m < n */
	if (mpi_cmp_ui(m, 0) < 0 || mpi_cmp(m, key->n) >= 0)
		return -EINVAL;

	/* (2) c = m^e mod n */
	return mpi_powm(c, m, key->e, key->n);
}

/*
 * RSADP function [RFC3447 sec 5.1.2]
 * m_1 = c^dP mod p;
 * m_2 = c^dQ mod q;
 * h = (m_1 - m_2) * qInv mod p;
 * m = m_2 + q * h;
 */
static int _rsa_dec_crt(const struct rsa_mpi_key *key, MPI m_or_m1_or_h, MPI c)
{
	MPI m2, m12_or_qh;
	int ret = -ENOMEM;

	/* (1) Validate 0 <= c < n */
	if (mpi_cmp_ui(c, 0) < 0 || mpi_cmp(c, key->n) >= 0)
		return -EINVAL;

	m2 = mpi_alloc(0);
	m12_or_qh = mpi_alloc(0);
	if (!m2 || !m12_or_qh)
		goto err_free_mpi;

	/* (2i) m_1 = c^dP mod p */
	ret = mpi_powm(m_or_m1_or_h, c, key->dp, key->p);
	if (ret)
		goto err_free_mpi;

	/* (2i) m_2 = c^dQ mod q */
	ret = mpi_powm(m2, c, key->dq, key->q);
	if (ret)
		goto err_free_mpi;

	/* (2iii) h = (m_1 - m_2) * qInv mod p */
	mpi_sub(m12_or_qh, m_or_m1_or_h, m2);
	mpi_mulm(m_or_m1_or_h, m12_or_qh, key->qinv, key->p);

	/* (2iv) m = m_2 + q * h */
	mpi_mul(m12_or_qh, key->q, m_or_m1_or_h);
	mpi_addm(m_or_m1_or_h, m2, m12_or_qh, key->n);

	ret = 0;

err_free_mpi:
	mpi_free(m12_or_qh);
	mpi_free(m2);
	return ret;
}

static inline struct rsa_mpi_key *rsa_get_key(struct crypto_akcipher *tfm)
{
	return akcipher_tfm_ctx(tfm);
}

static int rsa_enc(struct akcipher_request *req)
{
	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
	const struct rsa_mpi_key *pkey = rsa_get_key(tfm);
	MPI m, c = mpi_alloc(0);
	int ret = 0;
	int sign;

	if (!c)
		return -ENOMEM;

	if (unlikely(!pkey->n || !pkey->e)) {
		ret = -EINVAL;
		goto err_free_c;
	}

	ret = -ENOMEM;
	m = mpi_read_raw_from_sgl(req->src, req->src_len);
	if (!m)
		goto err_free_c;

	ret = _rsa_enc(pkey, c, m);
	if (ret)
		goto err_free_m;

	ret = mpi_write_to_sgl(c, req->dst, req->dst_len, &sign);
	if (ret)
		goto err_free_m;

	if (sign < 0)
		ret = -EBADMSG;

err_free_m:
	mpi_free(m);
err_free_c:
	mpi_free(c);
	return ret;
}

static int rsa_dec(struct akcipher_request *req)
{
	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
	const struct rsa_mpi_key *pkey = rsa_get_key(tfm);
	MPI c, m = mpi_alloc(0);
	int ret = 0;
	int sign;

	if (!m)
		return -ENOMEM;

	if (unlikely(!pkey->n || !pkey->d)) {
		ret = -EINVAL;
		goto err_free_m;
	}

	ret = -ENOMEM;
	c = mpi_read_raw_from_sgl(req->src, req->src_len);
	if (!c)
		goto err_free_m;

	ret = _rsa_dec_crt(pkey, m, c);
	if (ret)
		goto err_free_c;

	ret = mpi_write_to_sgl(m, req->dst, req->dst_len, &sign);
	if (ret)
		goto err_free_c;

	if (sign < 0)
		ret = -EBADMSG;
err_free_c:
	mpi_free(c);
err_free_m:
	mpi_free(m);
	return ret;
}

static void rsa_free_mpi_key(struct rsa_mpi_key *key)
{
	mpi_free(key->d);
	mpi_free(key->e);
	mpi_free(key->n);
	mpi_free(key->p);
	mpi_free(key->q);
	mpi_free(key->dp);
	mpi_free(key->dq);
	mpi_free(key->qinv);
	key->d = NULL;
	key->e = NULL;
	key->n = NULL;
	key->p = NULL;
	key->q = NULL;
	key->dp = NULL;
	key->dq = NULL;
	key->qinv = NULL;
}

static int rsa_check_key_length(unsigned int len)
{
	switch (len) {
	case 512:
	case 1024:
	case 1536:
		if (fips_enabled)
			return -EINVAL;
		fallthrough;
	case 2048:
	case 3072:
	case 4096:
		return 0;
	}

	return -EINVAL;
}

static int rsa_check_exponent_fips(MPI e)
{
	MPI e_max = NULL;

	/* check if odd */
	if (!mpi_test_bit(e, 0)) {
		return -EINVAL;
	}

	/* check if 2^16 < e < 2^256. */
	if (mpi_cmp_ui(e, 65536) <= 0) {
		return -EINVAL;
	}

	e_max = mpi_alloc(0);
	mpi_set_bit(e_max, 256);

	if (mpi_cmp(e, e_max) >= 0) {
		mpi_free(e_max);
		return -EINVAL;
	}

	mpi_free(e_max);
	return 0;
}

static int rsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
			   unsigned int keylen)
{
	struct rsa_mpi_key *mpi_key = akcipher_tfm_ctx(tfm);
	struct rsa_key raw_key = {0};
	int ret;

	/* Free the old MPI key if any */
	rsa_free_mpi_key(mpi_key);

	ret = rsa_parse_pub_key(&raw_key, key, keylen);
	if (ret)
		return ret;

	mpi_key->e = mpi_read_raw_data(raw_key.e, raw_key.e_sz);
	if (!mpi_key->e)
		goto err;

	mpi_key->n = mpi_read_raw_data(raw_key.n, raw_key.n_sz);
	if (!mpi_key->n)
		goto err;

	if (rsa_check_key_length(mpi_get_size(mpi_key->n) << 3)) {
		rsa_free_mpi_key(mpi_key);
		return -EINVAL;
	}

	if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
		rsa_free_mpi_key(mpi_key);
		return -EINVAL;
	}

	return 0;

err:
	rsa_free_mpi_key(mpi_key);
	return -ENOMEM;
}

static int rsa_set_priv_key(struct crypto_akcipher *tfm, const void *key,
			    unsigned int keylen)
{
	struct rsa_mpi_key *mpi_key = akcipher_tfm_ctx(tfm);
	struct rsa_key raw_key = {0};
	int ret;

	/* Free the old MPI key if any */
	rsa_free_mpi_key(mpi_key);

	ret = rsa_parse_priv_key(&raw_key, key, keylen);
	if (ret)
		return ret;

	mpi_key->d = mpi_read_raw_data(raw_key.d, raw_key.d_sz);
	if (!mpi_key->d)
		goto err;

	mpi_key->e = mpi_read_raw_data(raw_key.e, raw_key.e_sz);
	if (!mpi_key->e)
		goto err;

	mpi_key->n = mpi_read_raw_data(raw_key.n, raw_key.n_sz);
	if (!mpi_key->n)
		goto err;

	mpi_key->p = mpi_read_raw_data(raw_key.p, raw_key.p_sz);
	if (!mpi_key->p)
		goto err;

	mpi_key->q = mpi_read_raw_data(raw_key.q, raw_key.q_sz);
	if (!mpi_key->q)
		goto err;

	mpi_key->dp = mpi_read_raw_data(raw_key.dp, raw_key.dp_sz);
	if (!mpi_key->dp)
		goto err;

	mpi_key->dq = mpi_read_raw_data(raw_key.dq, raw_key.dq_sz);
	if (!mpi_key->dq)
		goto err;

	mpi_key->qinv = mpi_read_raw_data(raw_key.qinv, raw_key.qinv_sz);
	if (!mpi_key->qinv)
		goto err;

	if (rsa_check_key_length(mpi_get_size(mpi_key->n) << 3)) {
		rsa_free_mpi_key(mpi_key);
		return -EINVAL;
	}

	if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
		rsa_free_mpi_key(mpi_key);
		return -EINVAL;
	}

	return 0;

err:
	rsa_free_mpi_key(mpi_key);
	return -ENOMEM;
}

static unsigned int rsa_max_size(struct crypto_akcipher *tfm)
{
	struct rsa_mpi_key *pkey = akcipher_tfm_ctx(tfm);

	return mpi_get_size(pkey->n);
}

static void rsa_exit_tfm(struct crypto_akcipher *tfm)
{
	struct rsa_mpi_key *pkey = akcipher_tfm_ctx(tfm);

	rsa_free_mpi_key(pkey);
}

static struct akcipher_alg rsa = {
	.encrypt = rsa_enc,
	.decrypt = rsa_dec,
	.set_priv_key = rsa_set_priv_key,
	.set_pub_key = rsa_set_pub_key,
	.max_size = rsa_max_size,
	.exit = rsa_exit_tfm,
	.base = {
		.cra_name = "rsa",
		.cra_driver_name = "rsa-generic",
		.cra_priority = 100,
		.cra_module = THIS_MODULE,
		.cra_ctxsize = sizeof(struct rsa_mpi_key),
	},
};

static int __init rsa_init(void)
{
	int err;

	err = crypto_register_akcipher(&rsa);
	if (err)
		return err;

	err = crypto_register_template(&rsa_pkcs1pad_tmpl);
	if (err) {
		crypto_unregister_akcipher(&rsa);
		return err;
	}

	return 0;
}

static void __exit rsa_exit(void)
{
	crypto_unregister_template(&rsa_pkcs1pad_tmpl);
	crypto_unregister_akcipher(&rsa);
}

subsys_initcall(rsa_init);
module_exit(rsa_exit);
MODULE_ALIAS_CRYPTO("rsa");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("RSA generic algorithm");