slackhq/nebula · error

invalid curve for PKCS#11: %s

Error message

invalid curve for PKCS#11: %s

What it means

nebula-cert's `keytext`/key generation path rejected the -curve value because PKCS#11 mode only supports P256. When -pkcs11 is set, any curve other than "P256" returns this error before any key material is generated.

Source

Thrown at cmd/nebula-cert/keygen.go:61

	if !isP11 {
		if err = mustFlagString("out-key", cf.outKeyPath); err != nil {
			return err
		}
	} else if *cf.outKeyPath != "" {
		return newHelpErrorf("cannot set -out-key with -pkcs11")
	}
	if err = mustFlagString("out-pub", cf.outPubPath); err != nil {
		return err
	}

	var pub, rawPriv []byte
	var curve cert.Curve
	if isP11 {
		switch *cf.curve {
		case "P256":
			curve = cert.Curve_P256
		default:
			return fmt.Errorf("invalid curve for PKCS#11: %s", *cf.curve)
		}
	} else {
		switch *cf.curve {
		case "25519", "X25519", "Curve25519", "CURVE25519":
			if fips140.Enforced() {
				return errors.New("use of Curve25519 is not allowed in FIPS 140-only mode")
			}
			pub, rawPriv = x25519Keypair()
			curve = cert.Curve_CURVE25519
		case "P256":
			pub, rawPriv = p256Keypair()
			curve = cert.Curve_P256
		default:
			return fmt.Errorf("invalid curve: %s", *cf.curve)
		}
	}

	var claims ioClaims

View on GitHub (pinned to dd8f660c0a)

Solutions

1. Add `-curve P256` to the keygen command when using -pkcs11.
2. Remove -pkcs11 if local (software) key generation was intended.
3. Verify the HSM supports P256 before choosing PKCS#11 mode.
4. Note Curve25519 is additionally blocked under FIPS 140 enforcement, so P256 is the only valid PKCS#11 curve.

Example fix

// before
nebula-cert keygen -pkcs11 -curve 25519 -out-key host.key -out-pub host.pub
// after
nebula-cert keygen -pkcs11 -curve P256 -out-key host.key -out-pub host.pub

#!/bin/sh
if [ -n "$P11" ] && [ "$CURVE" != "P256" ]; then
  echo "PKCS#11 requires -curve P256" >&2
  exit 1
fi

func validP11Curve(curve string) bool {
    return curve == "P256"
}

When it happens

Trigger: Running `nebula-cert keygen -pkcs11 ...` with -curve set to 25519/X25519/Curve25519/CURVE25519 (or any value other than P256).

Common situations: Reusing a non-PKCS#11 keygen command line (which defaults to Curve25519) after adding the -pkcs11 flag; HSM hardware that only supports 25519; copying an older script that omitted -curve P256.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• invalid curve for PKCS#11: %s
• invalid curve: %s
• invalid curve: %s
• invalid curve: %s
• error while creating PKCS#11 client: %w

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/74ba9b51640f1ae7. Report an issue: GitHub.