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crypto/elliptic: tolerate zero-padded scalars in generic P-256

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Fixes #52075

Change-Id: I595a7514c9a0aa1b9c76aedfc2307e1124271f27
Reviewed-on: https://go-review.googlesource.com/c/go/+/397135
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
This commit is contained in:
Filippo Valsorda 2022-03-31 12:31:58 -04:00
parent 5138401209
commit 37065847d8
2 changed files with 15 additions and 1 deletions
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2
src/crypto/elliptic/p256.go
View file

@ -51,7 +51,7 @@ func p256GetScalar(out *[32]byte, in []byte) {
n := new(big.Int).SetBytes(in)
var scalarBytes []byte
if n.Cmp(p256Params.N) >= 0 {
if n.Cmp(p256Params.N) >= 0 || len(in) > len(out) {
n.Mod(n, p256Params.N)
scalarBytes = n.Bytes()
} else {

14
src/crypto/elliptic/p256_test.go
View file

@ -136,3 +136,17 @@ func TestP256CombinedMult(t *testing.T) {
t.Errorf("1×G + (-1)×G = (%d, %d), should be ∞", x, y)
}
}
func TestIssue52075(t *testing.T) {
Gx, Gy := P256().Params().Gx, P256().Params().Gy
scalar := make([]byte, 33)
scalar[32] = 1
x, y := P256().ScalarBaseMult(scalar)
if x.Cmp(Gx) != 0 || y.Cmp(Gy) != 0 {
t.Errorf("unexpected output (%v,%v)", x, y)
}
x, y = P256().ScalarMult(Gx, Gy, scalar)
if x.Cmp(Gx) != 0 || y.Cmp(Gy) != 0 {
t.Errorf("unexpected output (%v,%v)", x, y)
}
}