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, 9 insertions, 5 deletions

diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
index 3f9ec273a121..e819d0983bd3 100644
--- a/crypto/ecdsa.c
+++ b/crypto/ecdsa.c
@@ -222,9 +222,8 @@ static int ecdsa_ecc_ctx_reset(struct ecc_ctx *ctx)
 static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)
 {
 	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+	unsigned int digitlen, ndigits;
 	const unsigned char *d = key;
-	const u64 *digits = (const u64 *)&d[1];
-	unsigned int ndigits;
 	int ret;
 
 	ret = ecdsa_ecc_ctx_reset(ctx);
@@ -238,12 +237,17 @@ static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsig
 		return -EINVAL;
 
 	keylen--;
-	ndigits = (keylen >> 1) / sizeof(u64);
+	digitlen = keylen >> 1;
+
+	ndigits = DIV_ROUND_UP(digitlen, 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);
+	d++;
+
+	ecc_digits_from_bytes(d, digitlen, ctx->pub_key.x, ndigits);
+	ecc_digits_from_bytes(&d[digitlen], digitlen, ctx->pub_key.y, ndigits);
+
 	ret = ecc_is_pubkey_valid_full(ctx->curve, &ctx->pub_key);
 
 	ctx->pub_key_set = ret == 0;