crypto: ecdsa - Convert byte arrays with key coordinates to digits

For NIST P192/256/384 the public key's x and y parameters could be copied
directly from a given array since both parameters filled 'ndigits' of
digits (a 'digit' is a u64). For support of NIST P521 the key parameters
need to have leading zeros prepended to the most significant digit since
only 2 bytes of the most significant digit are provided.

Therefore, implement ecc_digits_from_bytes to convert a byte array into an
array of digits and use this function in ecdsa_set_pub_key where an input
byte array needs to be converted into digits.

Suggested-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 4f6c1a68882f..ab722a8986b7 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -57,6 +57,27 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
 }
 
 /**
+ * ecc_digits_from_bytes() - Create ndigits-sized digits array from byte array
+ * @in:       Input byte array
+ * @nbytes    Size of input byte array
+ * @out       Output digits array
+ * @ndigits:  Number of digits to create from byte array
+ */
+static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
+					 u64 *out, unsigned int ndigits)
+{
+	unsigned int o = nbytes & 7;
+	__be64 msd = 0;
+
+	if (o) {
+		memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
+		out[--ndigits] = be64_to_cpu(msd);
+		in += o;
+	}
+	ecc_swap_digits(in, out, ndigits);
+}
+
+/**
  * ecc_is_key_valid() - Validate a given ECDH private key
  *
  * @curve_id:		id representing the curve to use