[PATCH v3 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order

[Stefan Berger]

The private key in ctx->private_key is currently initialized in reverse
byte order in ecdh_set_secret and whenever the key is needed in proper
byte order the variable priv is introduced and the bytes from
ctx->private_key are copied into priv while being byte-swapped
(ecc_swap_digits). To get rid of the unnecessary byte swapping initialize
ctx->private_key in proper byte order and clean up all functions that were
previously using priv or were called with ctx->private_key:

- ecc_gen_privkey: Directly initialize the passed ctx->private_key with
  random bytes filling all the digits of the private key. Get rid of the
  priv variable. This function only has ecdh_set_secret as a caller to
  create NIST P192/256/384 private keys.

- crypto_ecdh_shared_secret: Called only from ecdh_compute_value with
  ctx->private_key. Get rid of the priv variable and work with the passed
  private_key directly.

- ecc_make_pub_key: Called only from ecdh_compute_value with
  ctx->private_key. Get rid of the priv variable and work with the passed
  private_key directly.

Cc: Salvatore Benedetto <salvatore.benedetto@xxxxxxxxx>
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Acked-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
 crypto/ecc.c                  | 29 ++++++++++-------------------
 crypto/ecdh.c                 |  8 +++-----
 include/crypto/internal/ecc.h |  3 ++-
 3 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 2e05387b9499..c1d2e884be1e 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1497,10 +1497,10 @@ EXPORT_SYMBOL(ecc_is_key_valid);
  * This method generates a private key uniformly distributed in the range
  * [2, n-3].
  */
-int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
+		    u64 *private_key)
 {
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
-	u64 priv[ECC_MAX_DIGITS];
 	unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 	unsigned int nbits = vli_num_bits(curve->n, ndigits);
 	int err;
@@ -1509,7 +1509,7 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
 	 * Step 1 & 2: check that N is included in Table 1 of FIPS 186-5,
 	 * section 6.1.1.
 	 */
-	if (nbits < 224 || ndigits > ARRAY_SIZE(priv))
+	if (nbits < 224)
 		return -EINVAL;
 
 	/*
@@ -1527,17 +1527,16 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
 		return -EFAULT;
 
 	/* Step 3: obtain N returned_bits from the DRBG. */
-	err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
+	err = crypto_rng_get_bytes(crypto_default_rng,
+				   (u8 *)private_key, nbytes);
 	crypto_put_default_rng();
 	if (err)
 		return err;
 
 	/* Step 4: make sure the private key is in the valid range. */
-	if (__ecc_is_key_valid(curve, priv, ndigits))
+	if (__ecc_is_key_valid(curve, private_key, ndigits))
 		return -EINVAL;
 
-	ecc_swap_digits(priv, privkey, ndigits);
-
 	return 0;
 }
 EXPORT_SYMBOL(ecc_gen_privkey);
@@ -1547,23 +1546,20 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
 {
 	int ret = 0;
 	struct ecc_point *pk;
-	u64 priv[ECC_MAX_DIGITS];
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
 
-	if (!private_key || ndigits > ARRAY_SIZE(priv)) {
+	if (!private_key) {
 		ret = -EINVAL;
 		goto out;
 	}
 
-	ecc_swap_digits(private_key, priv, ndigits);
-
 	pk = ecc_alloc_point(ndigits);
 	if (!pk) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
-	ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
+	ecc_point_mult(pk, &curve->g, private_key, NULL, curve, ndigits);
 
 	/* SP800-56A rev 3 5.6.2.1.3 key check */
 	if (ecc_is_pubkey_valid_full(curve, pk)) {
@@ -1647,13 +1643,11 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 {
 	int ret = 0;
 	struct ecc_point *product, *pk;
-	u64 priv[ECC_MAX_DIGITS];
 	u64 rand_z[ECC_MAX_DIGITS];
 	unsigned int nbytes;
 	const struct ecc_curve *curve = ecc_get_curve(curve_id);
 
-	if (!private_key || !public_key ||
-	    ndigits > ARRAY_SIZE(priv) || ndigits > ARRAY_SIZE(rand_z)) {
+	if (!private_key || !public_key || ndigits > ARRAY_SIZE(rand_z)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1674,15 +1668,13 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 	if (ret)
 		goto err_alloc_product;
 
-	ecc_swap_digits(private_key, priv, ndigits);
-
 	product = ecc_alloc_point(ndigits);
 	if (!product) {
 		ret = -ENOMEM;
 		goto err_alloc_product;
 	}
 
-	ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);
+	ecc_point_mult(product, pk, private_key, rand_z, curve, ndigits);
 
 	if (ecc_point_is_zero(product)) {
 		ret = -EFAULT;
@@ -1692,7 +1684,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 	ecc_swap_digits(product->x, secret, ndigits);
 
 err_validity:
-	memzero_explicit(priv, sizeof(priv));
 	memzero_explicit(rand_z, sizeof(rand_z));
 	ecc_free_point(product);
 err_alloc_product:
diff --git a/crypto/ecdh.c b/crypto/ecdh.c
index c02c9a2b9682..72cfd1590156 100644
--- a/crypto/ecdh.c
+++ b/crypto/ecdh.c
@@ -27,7 +27,6 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 			   unsigned int len)
 {
 	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
-	u64 priv[ECC_MAX_DIGITS];
 	struct ecdh params;
 	int ret = 0;
 
@@ -41,15 +40,14 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 				       ctx->private_key);
 
-	memcpy(ctx->private_key, params.key, params.key_size);
-	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
+	ecc_digits_from_bytes(params.key, params.key_size,
+			      ctx->private_key, ctx->ndigits);
 
 	if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
-			     priv, params.key_size) < 0) {
+			     ctx->private_key, params.key_size) < 0) {
 		memzero_explicit(ctx->private_key, params.key_size);
 		ret = -EINVAL;
 	}
-	memzero_explicit(priv, sizeof(priv));
 
 	return ret;
 }
diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 4e2f5f938e91..7ca1f463d1ec 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -103,7 +103,8 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
  * Returns 0 if the private key was generated successfully, a negative value
  * if an error occurred.
  */
-int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey);
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
+		    u64 *private_key);
 
 /**
  * ecc_make_pub_key() - Compute an ECC public key
-- 
2.43.0