From d4209dd5bdf4406505827525f6cd2ce56eca6258 Mon Sep 17 00:00:00 2001
From: Victor Lyuboslavsky <2685025+getvictor@users.noreply.github.com>
Date: Sun, 13 Jul 2025 12:09:01 +0200
Subject: [PATCH 1/2] Fix P-521 coordinate length calculation

The P-521 curve has 521 bits (65.125 bytes), but JWK EC coordinates must be zero-padded to 66 bytes. Using `crv.Params().BitSize/8` truncates to 65 bytes. Updating the calculation to round up
---
 keyutil/jwk.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/keyutil/jwk.go b/keyutil/jwk.go
index 6a25191..4b28055 100644
--- a/keyutil/jwk.go
+++ b/keyutil/jwk.go
@@ -198,7 +198,7 @@ func (ec *jwkEC) params() (crv elliptic.Curve, byteLen int, e error) {
 	default:
 		return nil, 0, fmt.Errorf("Unsupported ECC curve '%s'", ec.Curve)
 	}
-	return crv, crv.Params().BitSize / 8, nil
+	return crv, (crv.Params().BitSize + 7) / 8, nil
 }
 
 func (ec *jwkEC) PublicKey() (*ecdsa.PublicKey, error) {

From 7fdf9e7888ec2cdfe5097e7bed021909c76dfb03 Mon Sep 17 00:00:00 2001
From: Victor Lyuboslavsky <2685025+getvictor@users.noreply.github.com>
Date: Fri, 25 Jul 2025 08:34:12 +0200
Subject: [PATCH 2/2] Update jwk.go

---
 keyutil/jwk.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/keyutil/jwk.go b/keyutil/jwk.go
index 4b28055..e77e256 100644
--- a/keyutil/jwk.go
+++ b/keyutil/jwk.go
@@ -198,6 +198,7 @@ func (ec *jwkEC) params() (crv elliptic.Curve, byteLen int, e error) {
 	default:
 		return nil, 0, fmt.Errorf("Unsupported ECC curve '%s'", ec.Curve)
 	}
+	// The P-521 curve has 521 bits (65.125 bytes), so we must round up to get the bytes. We need 66 bytes to store 521 bits.
 	return crv, (crv.Params().BitSize + 7) / 8, nil
 }