[PATCH v4 06/12] crypto: ecc - Add special case for NIST P521 in ecc_point_mult

Stefan Berger
2024-03-01T02:20:22Z

In ecc_point_mult use the number of bits of the NIST P521 curve + 2. The
change is required specifically for NIST P521 to pass mathematical tests
on the public key.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
crypto/ecc.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index ea7b28b5e00e..3430c2c4e62c 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1326,7 +1326,10 @@ static void ecc_point_mult(struct ecc_point *result,
carry = vli_add(sk[0], scalar, curve->n, ndigits);
vli_add(sk[1], sk[0], curve->n, ndigits);
scalar = sk[!carry];
- num_bits = sizeof(u64) * ndigits * 8 + 1;
+ if (ndigits == 9 && !strcmp(curve->name, "nist_521"))
+ num_bits = curve->nbits + 2;
+ else
+ num_bits = sizeof(u64) * ndigits * 8 + 1;

vli_set(rx[1], point->x, ndigits);
vli_set(ry[1], point->y, ndigits);
--
2.43.0