[RFC PATCH v2 1/4] crypto: ecc - add privkey generation support

[Tudor Ambarus <tudor.ambarus@microchip.com>]

Add support for generating ecc private keys.

Generation of ecc private keys is helpful in a user-space to kernel
ecdh offload because the keys are not revealed to user-space. Private
key generation is also helpful to implement forward secrecy.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
---
 crypto/ecc.c | 20 ++++++++++++++++++++
 crypto/ecc.h | 14 ++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 414c78a..a591907 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -927,6 +927,26 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
 	return 0;
 }
 
+int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
+{
+	const struct ecc_curve *curve = ecc_get_curve(curve_id);
+	u64 priv[ndigits];
+	unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+
+	get_random_bytes(priv, nbytes);
+
+	if (vli_is_zero(priv, ndigits))
+		return -EINVAL;
+
+	/* Make sure the private key is in the range [1, n-1]. */
+	if (vli_cmp(curve->n, priv, ndigits) != 1)
+		return -EINVAL;
+
+	ecc_swap_digits(priv, privkey, ndigits);
+
+	return 0;
+}
+
 int ecdh_make_pub_key(unsigned int curve_id, unsigned int ndigits,
 		      const u8 *private_key, unsigned int private_key_len,
 		      u8 *public_key, unsigned int public_key_len)
diff --git a/crypto/ecc.h b/crypto/ecc.h
index 663d598..b94b7ce 100644
--- a/crypto/ecc.h
+++ b/crypto/ecc.h
@@ -44,6 +44,20 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
 		     const u8 *private_key, unsigned int private_key_len);
 
 /**
+ * ecc_gen_privkey() -  Generates an ECC private key.
+ * The private key is a random integer in the range 0 < random < n, where n is a
+ * prime that is the order of the cyclic subgroup generated by the distinguished
+ * point G.
+ * @curve_id:		id representing the curve to use
+ * @ndigits:		curve number of digits
+ * @private_key:	buffer for storing the generated private key
+ *
+ * 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);
+
+/**
  * ecdh_make_pub_key() - Compute an ECC public key
  *
  * @curve_id:		id representing the curve to use
-- 
2.7.4