crypto: ed25519 cert verification

This patch adds the support of eddsa(currently ed25519) which is described
in RFC8032 section 5.1.7 [1].

[1]: https://tools.ietf.org/html/rfc8032#section-5.1.7

Signed-off-by: Hongbo Li <herberthbli@tencent.com>

crypto/Kconfig

@@ -268,6 +268,17 @@ config CRYPTO_ECRDSA
 config CRYPTO_EC_MPI
 	tristate
 
+config CRYPTO_EDDSA
+	tristate "EDDSA (ed25519) algorithm"
+	select CRYPTO_ECC
+	select CRYPTO_EC_MPI
+	select CRYPTO_AKCIPHER
+	select ASN1
+	help
+	  Edwards-curve Digital Signature Algorithm (ed25519) is a variant
+	  of Schnorr's signature system with (possibly twisted) Edwards curves.
+	  Only signature verification is implemented.
+
 config CRYPTO_SM2
 	tristate "SM2 algorithm"
 	select CRYPTO_SM3

crypto/Makefile

@@ -56,6 +56,9 @@ ecdsa_generic-y += ecdsa.o
 ecdsa_generic-y += ecdsasignature.asn1.o
 obj-$(CONFIG_CRYPTO_ECDSA) += ecdsa_generic.o
 
+eddsa_generic-y += eddsa.o
+obj-$(CONFIG_CRYPTO_EDDSA) += eddsa_generic.o
+
 crypto_acompress-y := acompress.o
 crypto_acompress-y += scompress.o
 obj-$(CONFIG_CRYPTO_ACOMP2) += crypto_acompress.o

crypto/eddsa.c

@@ -0,0 +1,326 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * EDDSA generic algorithm.
+ *
+ * Copyright (c) 2021 Hongbo Li <herberthbli@tencent.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/mpi.h>
+#include <linux/module.h>
+#include <linux/oid_registry.h>
+#include <crypto/hash.h>
+#include <crypto/sha2.h>
+#include <crypto/ecdh.h>
+#include <crypto/curve25519.h>
+#include <crypto/internal/akcipher.h>
+#include "ec_mpi.h"
+
+struct eddsa_ctx {
+	enum OID algo_oid;
+	struct mpi_ec_ctx ec_ctx;
+};
+
+static MPI p58;
+static MPI seven;
+static MPI m1;
+
+static const struct ecc_domain_parms ed25519_domain_params = {
+	.desc = "ed25519",
+	.nbits = 256,
+	.fips = 0,
+	.model = MPI_EC_EDWARDS,
+	.dialect = ECC_DIALECT_ED25519,
+	.p = "0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFED",
+	.a = "-0x01",
+	.b = "-0x2DFC9311D490018C7338BF8688861767FF8FF5B2BEBE27548A14B235ECA6874A",
+	.n = "0x1000000000000000000000000000000014DEF9DEA2F79CD65812631A5CF5D3ED",
+	.g_x = "0x216936D3CD6E53FEC0A4E231FDD6DC5C692CC7609525A7B2C9562D608F25D51A",
+	.g_y = "0x6666666666666666666666666666666666666666666666666666666666666658",
+	.h = 8,
+};
+
+static void reverse_buffer(u8 *buffer, u32 length)
+{
+	u32 tmp, i;
+
+	for (i = 0; i < length / 2; i++) {
+		tmp = buffer[i];
+		buffer[i] = buffer[length - 1 - i];
+		buffer[length - 1 - i] = tmp;
+	}
+}
+
+static int eddsa_encode_x_y(MPI x, MPI y, u8 *buf, u32 key_size)
+{
+	memcpy(buf, y->d, key_size);
+	if (mpi_test_bit(x, 0))
+		buf[key_size - 1] |= 0x80;
+
+	return 0;
+}
+
+int ecc_eddsa_encodepoint(MPI_POINT point, struct mpi_ec_ctx *ec,
+			  MPI x, MPI y, u8 *buf, u32 key_size)
+{
+	if (mpi_ec_get_affine(x, y, point, ec))
+		return -EINVAL;
+
+	return eddsa_encode_x_y(x, y, buf, key_size);
+}
+
+/* Recover X from Y and SIGN (which actually is a parity bit).  */
+static int eddsa_recover_x(MPI x, MPI y, int sign, struct mpi_ec_ctx *ec)
+{
+	MPI u, v, v3, t;
+	int ret = 0;
+
+	if (ec->dialect != ECC_DIALECT_ED25519)
+		return -ENOPKG;
+
+	u = mpi_new(0);
+	v = mpi_new(0);
+	v3 = mpi_new(0);
+	t = mpi_new(0);
+
+	/* Compute u and v */
+	/* u = y^2 */
+	mpi_mulm(u, y, y, ec->p);
+	/* v = b*y^2 */
+	mpi_mulm(v, ec->b, u, ec->p);
+	/* u = y^2-1 */
+	mpi_sub_ui(u, u, 1);
+	/* v = b*y^2+1 */
+	mpi_add_ui(v, v, 1);
+
+	/* Compute sqrt(u/v) */
+	/* v3 = v^3 */
+	mpi_powm(v3, v, mpi_const(MPI_C_THREE), ec->p);
+	/* t = v3 * v3 * u * v = u * v^7 */
+	mpi_powm(t, v, seven, ec->p);
+	mpi_mulm(t, t, u, ec->p);
+	/* t = t^((p-5)/8) = (u * v^7)^((p-5)/8)  */
+	mpi_powm(t, t, p58, ec->p);
+	/* x = t * u * v^3 = (u * v^3) * (u * v^7)^((p-5)/8) */
+	mpi_mulm(t, t, u, ec->p);
+	mpi_mulm(x, t, v3, ec->p);
+
+	/* Adjust if needed. */
+	/* t = v * x^2 */
+	mpi_mulm(t, x, x, ec->p);
+	mpi_mulm(t, t, v, ec->p);
+	/* -t == u ? x = x * sqrt(-1) */
+	mpi_sub(t, ec->p, t);
+	if (!mpi_cmp(t, u)) {
+		mpi_mulm(x, x, m1, ec->p);
+		/* t = v * x^2 */
+		mpi_mulm(t, x, x, ec->p);
+		mpi_mulm(t, t, v, ec->p);
+		/* -t == u ? x = x * sqrt(-1) */
+		mpi_sub(t, ec->p, t);
+		if (!mpi_cmp(t, u))
+			ret = -EINVAL;
+	}
+
+	/* Choose the desired square root according to parity */
+	if (mpi_test_bit(x, 0) != !!sign)
+		mpi_sub(x, ec->p, x);
+
+	mpi_free(t);
+	mpi_free(v3);
+	mpi_free(v);
+	mpi_free(u);
+
+	return ret;
+}
+
+static int ecc_eddsa_decodepoint(const u8 *pk, int key_size,
+				 struct mpi_ec_ctx *ec, MPI_POINT result)
+{
+	MPI y;
+	u8 *rawmpi;
+	int sign, ret = 0;
+
+	rawmpi = kmalloc(key_size, GFP_KERNEL);
+	if (!rawmpi)
+		return -ENOMEM;
+	memcpy(rawmpi, pk, key_size);
+	reverse_buffer(rawmpi, key_size);
+
+	sign = !!(rawmpi[0] & 0x80);
+	rawmpi[0] &= 0x7f;
+
+	y = mpi_read_raw_data(rawmpi, key_size);
+	if (!y) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	mpi_normalize(y);
+	mpi_set(result->y, y);
+	mpi_free(y);
+
+	ret = eddsa_recover_x(result->x, result->y, sign, ec);
+	mpi_set_ui(result->z, 1);
+out:
+	kfree(rawmpi);
+	return ret;
+}
+
+int eddsa_verify(struct akcipher_request *req)
+{
+	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+	struct eddsa_ctx *ctx = akcipher_tfm_ctx(tfm);
+	struct mpi_ec_ctx *ec = &ctx->ec_ctx;
+	struct gcry_mpi_point sb, ka;
+	MPI s = NULL;
+	MPI k = NULL;
+	u8 sig[CURVE25519_KEY_SIZE * 2], digest[SHA512_DIGEST_SIZE];
+	u8 *buf;
+	u32 key_size;
+	int ret = 0;
+
+	if (ctx->algo_oid != OID_ed25519)
+		return -ENOPKG;
+
+	key_size = CURVE25519_KEY_SIZE;
+
+	if (!ec->Q || req->src_len != key_size * 2)
+		return -EINVAL;
+
+	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);
+
+	reverse_buffer(digest, SHA512_DIGEST_SIZE);
+	k = mpi_read_raw_data(digest, SHA512_DIGEST_SIZE);
+
+	reverse_buffer(sig + key_size, key_size);
+	s = mpi_read_raw_data(sig + key_size, key_size);
+
+	mpi_point_init(&sb);
+	mpi_point_init(&ka);
+
+	mpi_ec_mul_point(&sb, s, ec->G, ec);
+	mpi_ec_mul_point(&ka, k, ec->Q, ec);
+	mpi_sub(ka.x, ec->p, ka.x);
+	mpi_ec_add_points(&sb, &sb, &ka, ec);
+
+	buf = kmalloc(key_size, GFP_KERNEL);
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = ecc_eddsa_encodepoint(&sb, ec, s, k, buf, key_size);
+	if (ret)
+		goto out;
+
+	if (memcmp(buf, sig, key_size))
+		ret = -EKEYREJECTED;
+
+out:
+	mpi_point_free_parts(&sb);
+	mpi_point_free_parts(&ka);
+	mpi_free(k);
+	mpi_free(s);
+	kfree(buf);
+	return ret;
+}
+
+static int eddsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
+			     unsigned int keylen)
+{
+	struct eddsa_ctx *ctx = akcipher_tfm_ctx(tfm);
+	struct mpi_ec_ctx *ec = &ctx->ec_ctx;
+	const u8 *pk = key;
+
+	if (ctx->algo_oid != OID_ed25519)
+		return -ENOPKG;
+
+	if (keylen != CURVE25519_KEY_SIZE)
+		return -EINVAL;
+
+	return ecc_eddsa_decodepoint(pk, keylen, ec, ec->Q);
+}
+
+u32 eddsa_max_size(struct crypto_akcipher *tfm)
+{
+	struct eddsa_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	if (ctx->algo_oid == OID_ed25519)
+		return CURVE25519_KEY_SIZE;
+
+	return 0;
+}
+
+static int eddsa_25519_init_tfm(struct crypto_akcipher *tfm)
+{
+	struct eddsa_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	ctx->algo_oid = OID_ed25519;
+	p58 = mpi_scanval("0FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFD");
+	if (!p58)
+		return -ENOMEM;
+
+	m1 = mpi_scanval("2B8324804FC1DF0B2B4D00993DFBD7A72F431806AD2FE478C4EE1B274A0EA0B0");
+	if (!m1)
+		return -ENOMEM;
+
+	seven = mpi_set_ui(NULL, 7);
+
+	return ec_mpi_ctx_init(&ctx->ec_ctx, &ed25519_domain_params);
+}
+
+static void eddsa_exit_tfm(struct crypto_akcipher *tfm)
+{
+	struct eddsa_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	ec_mpi_ctx_deinit(&ctx->ec_ctx);
+	mpi_free(p58);
+	mpi_free(seven);
+	mpi_free(m1);
+}
+
+
+static struct akcipher_alg eddsa_25519 = {
+	.verify = eddsa_verify,
+	.set_pub_key = eddsa_set_pub_key,
+	.max_size = eddsa_max_size,
+	.init = eddsa_25519_init_tfm,
+	.exit = eddsa_exit_tfm,
+	.base = {
+		.cra_name = "eddsa-25519",
+		.cra_driver_name = "eddsa-25519-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct eddsa_ctx),
+	},
+};
+
+static int eddsa_mod_init(void)
+{
+	return crypto_register_akcipher(&eddsa_25519);
+}
+
+static void eddsa_mod_exit(void)
+{
+	crypto_unregister_akcipher(&eddsa_25519);
+}
+
+module_init(eddsa_mod_init);
+module_exit(eddsa_mod_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Hongbo Li <herberthbli@tencent.com>");
+MODULE_ALIAS_CRYPTO("eddsa");
+MODULE_ALIAS_CRYPTO("eddsa-generic");
+MODULE_DESCRIPTION("EDDSA generic algorithm");