crypto: ecdsa - Add support for ECDSA signature verification

Add support for parsing the parameters of a NIST P256 or NIST P192 key.
Enable signature verification using these keys. The new module is
enabled with CONFIG_ECDSA:
  Elliptic Curve Digital Signature Algorithm (NIST P192, P256 etc.)
  is A NIST cryptographic standard algorithm. Only signature verification
  is implemented.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -242,6 +242,16 @@ config CRYPTO_ECDH
 	help
 	  Generic implementation of the ECDH algorithm
 
+config CRYPTO_ECDSA
+	tristate "ECDSA (NIST P192, P256 etc.) algorithm"
+	select CRYPTO_ECC
+	select CRYPTO_AKCIPHER
+	select ASN1
+	help
+	  Elliptic Curve Digital Signature Algorithm (NIST P192, P256 etc.)
+	  is A NIST cryptographic standard algorithm. Only signature verification
+	  is implemented.
+
 config CRYPTO_ECRDSA
 	tristate "EC-RDSA (GOST 34.10) algorithm"
 	select CRYPTO_ECC

crypto/Makefile

@@ -50,6 +50,12 @@ sm2_generic-y += sm2.o
 
 obj-$(CONFIG_CRYPTO_SM2) += sm2_generic.o
 
+$(obj)/ecdsasignature.asn1.o: $(obj)/ecdsasignature.asn1.c $(obj)/ecdsasignature.asn1.h
+$(obj)/ecdsa.o: $(obj)/ecdsasignature.asn1.h
+ecdsa_generic-y += ecdsa.o
+ecdsa_generic-y += ecdsasignature.asn1.o
+obj-$(CONFIG_CRYPTO_ECDSA) += ecdsa_generic.o
+
 crypto_acompress-y := acompress.o
 crypto_acompress-y += scompress.o
 obj-$(CONFIG_CRYPTO_ACOMP2) += crypto_acompress.o

crypto/ecc.c

@@ -42,7 +42,7 @@ typedef struct {
 	u64 m_high;
 } uint128_t;
 
-static inline const struct ecc_curve *ecc_get_curve(unsigned int curve_id)
+const struct ecc_curve *ecc_get_curve(unsigned int curve_id)
 {
 	switch (curve_id) {
 	/* In FIPS mode only allow P256 and higher */
@@ -54,6 +54,7 @@ static inline const struct ecc_curve *ecc_get_curve(unsigned int curve_id)
 		return NULL;
 	}
 }
+EXPORT_SYMBOL(ecc_get_curve);
 
 static u64 *ecc_alloc_digits_space(unsigned int ndigits)
 {
@@ -1281,16 +1282,6 @@ void ecc_point_mult_shamir(const struct ecc_point *result,
 }
 EXPORT_SYMBOL(ecc_point_mult_shamir);
 
-static inline void ecc_swap_digits(const u64 *in, u64 *out,
-				   unsigned int ndigits)
-{
-	const __be64 *src = (__force __be64 *)in;
-	int i;
-
-	for (i = 0; i < ndigits; i++)
-		out[i] = be64_to_cpu(src[ndigits - 1 - i]);
-}
-
 static int __ecc_is_key_valid(const struct ecc_curve *curve,
 			      const u64 *private_key, unsigned int ndigits)
 {

crypto/ecc.h

@@ -33,6 +33,8 @@
 
 #define ECC_DIGITS_TO_BYTES_SHIFT 3
 
+#define ECC_MAX_BYTES (ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT)
+
 /**
  * struct ecc_point - elliptic curve point in affine coordinates
  *
@@ -70,6 +72,29 @@ struct ecc_curve {
 	u64 *b;
 };
 
+/**
+ * ecc_swap_digits() - Copy ndigits from big endian array to native array
+ * @in:       Input array
+ * @out:      Output array
+ * @ndigits:  Number of digits to copy
+ */
+static inline void ecc_swap_digits(const u64 *in, u64 *out, unsigned int ndigits)
+{
+	const __be64 *src = (__force __be64 *)in;
+	int i;
+
+	for (i = 0; i < ndigits; i++)
+		out[i] = be64_to_cpu(src[ndigits - 1 - i]);
+}
+
+/**
+ * ecc_get_curve()  - Get a curve given its curve_id
+ * @curve_id:  Id of the curve
+ *
+ * Returns pointer to the curve data, NULL if curve is not available
+ */
+const struct ecc_curve *ecc_get_curve(unsigned int curve_id);
+
 /**
  * ecc_is_key_valid() - Validate a given ECDH private key
  *

crypto/ecdsa.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2021 IBM Corporation
+ */
+
+#include <linux/module.h>
+#include <crypto/internal/akcipher.h>
+#include <crypto/akcipher.h>
+#include <crypto/ecdh.h>
+#include <linux/asn1_decoder.h>
+#include <linux/scatterlist.h>
+
+#include "ecc.h"
+#include "ecdsasignature.asn1.h"
+
+struct ecc_ctx {
+	unsigned int curve_id;
+	const struct ecc_curve *curve;
+
+	bool pub_key_set;
+	u64 x[ECC_MAX_DIGITS]; /* pub key x and y coordinates */
+	u64 y[ECC_MAX_DIGITS];
+	struct ecc_point pub_key;
+};
+
+struct ecdsa_signature_ctx {
+	const struct ecc_curve *curve;
+	u64 r[ECC_MAX_DIGITS];
+	u64 s[ECC_MAX_DIGITS];
+};
+
+/*
+ * Get the r and s components of a signature from the X509 certificate.
+ */
+static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag,
+				  const void *value, size_t vlen, unsigned int ndigits)
+{
+	size_t keylen = ndigits * sizeof(u64);
+	ssize_t diff = vlen - keylen;
+	const char *d = value;
+	u8 rs[ECC_MAX_BYTES];
+
+	if (!value || !vlen)
+		return -EINVAL;
+
+	/* diff = 0: 'value' has exacly the right size
+	 * diff > 0: 'value' has too many bytes; one leading zero is allowed that
+	 *           makes the value a positive integer; error on more
+	 * diff < 0: 'value' is missing leading zeros, which we add
+	 */
+	if (diff > 0) {
+		/* skip over leading zeros that make 'value' a positive int */
+		if (*d == 0) {
+			vlen -= 1;
+			diff--;
+			d++;
+		}
+		if (diff)
+			return -EINVAL;
+	}
+	if (-diff >= keylen)
+		return -EINVAL;
+
+	if (diff) {
+		/* leading zeros not given in 'value' */
+		memset(rs, 0, -diff);
+	}
+
+	memcpy(&rs[-diff], d, vlen);
+
+	ecc_swap_digits((u64 *)rs, dest, ndigits);
+
+	return 0;
+}
+
+int ecdsa_get_signature_r(void *context, size_t hdrlen, unsigned char tag,
+			  const void *value, size_t vlen)
+{
+	struct ecdsa_signature_ctx *sig = context;
+
+	return ecdsa_get_signature_rs(sig->r, hdrlen, tag, value, vlen,
+				      sig->curve->g.ndigits);
+}
+
+int ecdsa_get_signature_s(void *context, size_t hdrlen, unsigned char tag,
+			  const void *value, size_t vlen)
+{
+	struct ecdsa_signature_ctx *sig = context;
+
+	return ecdsa_get_signature_rs(sig->s, hdrlen, tag, value, vlen,
+				      sig->curve->g.ndigits);
+}
+
+static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, const u64 *s)
+{
+	const struct ecc_curve *curve = ctx->curve;
+	unsigned int ndigits = curve->g.ndigits;
+	u64 s1[ECC_MAX_DIGITS];
+	u64 u1[ECC_MAX_DIGITS];
+	u64 u2[ECC_MAX_DIGITS];
+	u64 x1[ECC_MAX_DIGITS];
+	u64 y1[ECC_MAX_DIGITS];
+	struct ecc_point res = ECC_POINT_INIT(x1, y1, ndigits);
+
+	/* 0 < r < n  and 0 < s < n */
+	if (vli_is_zero(r, ndigits) || vli_cmp(r, curve->n, ndigits) >= 0 ||
+	    vli_is_zero(s, ndigits) || vli_cmp(s, curve->n, ndigits) >= 0)
+		return -EBADMSG;
+
+	/* hash is given */
+	pr_devel("hash : %016llx %016llx ... %016llx\n",
+		 hash[ndigits - 1], hash[ndigits - 2], hash[0]);
+
+	/* s1 = (s^-1) mod n */
+	vli_mod_inv(s1, s, curve->n, ndigits);
+	/* u1 = (hash * s1) mod n */
+	vli_mod_mult_slow(u1, hash, s1, curve->n, ndigits);
+	/* u2 = (r * s1) mod n */
+	vli_mod_mult_slow(u2, r, s1, curve->n, ndigits);
+	/* res = u1*G + u2 * pub_key */
+	ecc_point_mult_shamir(&res, u1, &curve->g, u2, &ctx->pub_key, curve);
+
+	/* res.x = res.x mod n (if res.x > order) */
+	if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1))
+		/* faster alternative for NIST p256 & p192 */
+		vli_sub(res.x, res.x, curve->n, ndigits);
+
+	if (!vli_cmp(res.x, r, ndigits))
+		return 0;
+
+	return -EKEYREJECTED;
+}
+
+/*
+ * Verify an ECDSA signature.
+ */
+static int ecdsa_verify(struct akcipher_request *req)
+{
+	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+	size_t keylen = ctx->curve->g.ndigits * sizeof(u64);
+	struct ecdsa_signature_ctx sig_ctx = {
+		.curve = ctx->curve,
+	};
+	u8 rawhash[ECC_MAX_BYTES];
+	u64 hash[ECC_MAX_DIGITS];
+	unsigned char *buffer;
+	ssize_t diff;
+	int ret;
+
+	if (unlikely(!ctx->pub_key_set))
+		return -EINVAL;
+
+	buffer = kmalloc(req->src_len + req->dst_len, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	sg_pcopy_to_buffer(req->src,
+		sg_nents_for_len(req->src, req->src_len + req->dst_len),
+		buffer, req->src_len + req->dst_len, 0);
+
+	ret = asn1_ber_decoder(&ecdsasignature_decoder, &sig_ctx,
+			       buffer, req->src_len);
+	if (ret < 0)
+		goto error;
+
+	/* if the hash is shorter then we will add leading zeros to fit to ndigits */
+	diff = keylen - req->dst_len;
+	if (diff >= 0) {
+		if (diff)
+			memset(rawhash, 0, diff);
+		memcpy(&rawhash[diff], buffer + req->src_len, req->dst_len);
+	} else if (diff < 0) {
+		/* given hash is longer, we take the left-most bytes */
+		memcpy(&rawhash, buffer + req->src_len, keylen);
+	}
+
+	ecc_swap_digits((u64 *)rawhash, hash, ctx->curve->g.ndigits);
+
+	ret = _ecdsa_verify(ctx, hash, sig_ctx.r, sig_ctx.s);
+
+error:
+	kfree(buffer);
+
+	return ret;
+}
+
+static int ecdsa_ecc_ctx_init(struct ecc_ctx *ctx, unsigned int curve_id)
+{
+	ctx->curve_id = curve_id;
+	ctx->curve = ecc_get_curve(curve_id);
+	if (!ctx->curve)
+		return -EINVAL;
+
+	return 0;
+}
+
+
+static void ecdsa_ecc_ctx_deinit(struct ecc_ctx *ctx)
+{
+	ctx->pub_key_set = false;
+}
+
+static int ecdsa_ecc_ctx_reset(struct ecc_ctx *ctx)
+{
+	unsigned int curve_id = ctx->curve_id;
+	int ret;
+
+	ecdsa_ecc_ctx_deinit(ctx);
+	ret = ecdsa_ecc_ctx_init(ctx, curve_id);
+	if (ret == 0)
+		ctx->pub_key = ECC_POINT_INIT(ctx->x, ctx->y,
+					      ctx->curve->g.ndigits);
+	return ret;
+}
+
+/*
+ * Set the public key given the raw uncompressed key data from an X509
+ * certificate. The key data contain the concatenated X and Y coordinates of
+ * the public key.
+ */
+static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+	const unsigned char *d = key;
+	const u64 *digits = (const u64 *)&d[1];
+	unsigned int ndigits;
+	int ret;
+
+	ret = ecdsa_ecc_ctx_reset(ctx);
+	if (ret < 0)
+		return ret;
+
+	if (keylen < 1 || (((keylen - 1) >> 1) % sizeof(u64)) != 0)
+		return -EINVAL;
+	/* we only accept uncompressed format indicated by '4' */
+	if (d[0] != 4)
+		return -EINVAL;
+
+	keylen--;
+	ndigits = (keylen >> 1) / sizeof(u64);
+	if (ndigits != ctx->curve->g.ndigits)
+		return -EINVAL;
+
+	ecc_swap_digits(digits, ctx->pub_key.x, ndigits);
+	ecc_swap_digits(&digits[ndigits], ctx->pub_key.y, ndigits);
+	ret = ecc_is_pubkey_valid_full(ctx->curve, &ctx->pub_key);
+
+	ctx->pub_key_set = ret == 0;
+
+	return ret;
+}
+
+static void ecdsa_exit_tfm(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	ecdsa_ecc_ctx_deinit(ctx);
+}
+
+static unsigned int ecdsa_max_size(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	return ctx->pub_key.ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+}
+
+static int ecdsa_nist_p256_init_tfm(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	return ecdsa_ecc_ctx_init(ctx, ECC_CURVE_NIST_P256);
+}
+
+static struct akcipher_alg ecdsa_nist_p256 = {
+	.verify = ecdsa_verify,
+	.set_pub_key = ecdsa_set_pub_key,
+	.max_size = ecdsa_max_size,
+	.init = ecdsa_nist_p256_init_tfm,
+	.exit = ecdsa_exit_tfm,
+	.base = {
+		.cra_name = "ecdsa-nist-p256",
+		.cra_driver_name = "ecdsa-nist-p256-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecc_ctx),
+	},
+};
+
+static int ecdsa_nist_p192_init_tfm(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	return ecdsa_ecc_ctx_init(ctx, ECC_CURVE_NIST_P192);
+}
+
+static struct akcipher_alg ecdsa_nist_p192 = {
+	.verify = ecdsa_verify,
+	.set_pub_key = ecdsa_set_pub_key,
+	.max_size = ecdsa_max_size,
+	.init = ecdsa_nist_p192_init_tfm,
+	.exit = ecdsa_exit_tfm,
+	.base = {
+		.cra_name = "ecdsa-nist-p192",
+		.cra_driver_name = "ecdsa-nist-p192-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecc_ctx),
+	},
+};
+static bool ecdsa_nist_p192_registered;
+
+static int ecdsa_init(void)
+{
+	int ret;
+
+	/* NIST p192 may not be available in FIPS mode */
+	ret = crypto_register_akcipher(&ecdsa_nist_p192);
+	ecdsa_nist_p192_registered = ret == 0;
+
+	ret = crypto_register_akcipher(&ecdsa_nist_p256);
+	if (ret)
+		goto nist_p256_error;
+	return 0;
+
+nist_p256_error:
+	if (ecdsa_nist_p192_registered)
+		crypto_unregister_akcipher(&ecdsa_nist_p192);
+	return ret;
+}
+
+static void ecdsa_exit(void)
+{
+	if (ecdsa_nist_p192_registered)
+		crypto_unregister_akcipher(&ecdsa_nist_p192);
+	crypto_unregister_akcipher(&ecdsa_nist_p256);
+}
+
+subsys_initcall(ecdsa_init);
+module_exit(ecdsa_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Stefan Berger <stefanb@linux.ibm.com>");
+MODULE_DESCRIPTION("ECDSA generic algorithm");
+MODULE_ALIAS_CRYPTO("ecdsa-generic");

crypto/ecdsasignature.asn1

+ECDSASignature ::= SEQUENCE {
+	r	INTEGER ({ ecdsa_get_signature_r }),
+	s	INTEGER ({ ecdsa_get_signature_s })
+}

crypto/testmgr.c

@@ -4910,6 +4910,18 @@ static const struct alg_test_desc alg_test_descs[] = {
 		.suite = {
 			.kpp = __VECS(ecdh_tv_template)
 		}
+	}, {
+		.alg = "ecdsa-nist-p192",
+		.test = alg_test_akcipher,
+		.suite = {
+			.akcipher = __VECS(ecdsa_nist_p192_tv_template)
+		}
+	}, {
+		.alg = "ecdsa-nist-p256",
+		.test = alg_test_akcipher,
+		.suite = {
+			.akcipher = __VECS(ecdsa_nist_p256_tv_template)
+		}
 	}, {
 		.alg = "ecrdsa",
 		.test = alg_test_akcipher,