What causes "error while encrypting out-key: %s" in slackhq/nebula?

Ensure a valid non-empty passphrase is provided when -encrypt is set

error while encrypting out-key: %s

Error message

error while encrypting out-key: %s

What it means

Wraps a failure from cert.EncryptAndMarshalSigningPrivateKey(curve, rawPriv, passphrase, kdfParams) when -encrypt is set in `nebula-cert ca`. The private key could not be encrypted and marshaled (e.g. KDF derivation or AEAD sealing failed), so the command aborts before writing the key file.

Source

Thrown at cmd/nebula-cert/ca.go:342

	var c cert.Certificate
	var b []byte

	if isP11 {
		c, err = t.SignWith(nil, curve, p11Client.SignASN1)
		if err != nil {
			return fmt.Errorf("error while signing with PKCS#11: %w", err)
		}
	} else {
		c, err = t.Sign(nil, curve, rawPriv)
		if err != nil {
			return fmt.Errorf("error while signing: %s", err)
		}

		if *cf.encryption {
			b, err = cert.EncryptAndMarshalSigningPrivateKey(curve, rawPriv, passphrase, kdfParams)
			if err != nil {
				return fmt.Errorf("error while encrypting out-key: %s", err)
			}
		} else {
			b = cert.MarshalSigningPrivateKeyToPEM(curve, rawPriv)
		}

		err = writeOutput(*cf.outKeyPath, b, 0600, out)
		if err != nil {
			return fmt.Errorf("error while writing out-key: %s", err)
		}
	}

	b, err = c.MarshalPEM()
	if err != nil {
		return fmt.Errorf("error while marshalling certificate: %s", err)
	}

	err = writeOutput(*cf.outCertPath, b, 0600, out)
	if err != nil {

View on GitHub (pinned to dd8f660c0a)

Solutions

Ensure a valid non-empty passphrase is provided when -encrypt is set
Check the wrapped error for KDF/AEAD specifics and adjust crypto settings (FIPS mode, kdf params)
Drop -encrypt to write the key in plaintext PEM if protection is handled elsewhere
Upgrade nebula if the wrapped error points to a known crypto-library incompatibility

Example fix

// before
nebula-cert ca -encrypt -name "my ca"           # empty passphrase reaches encryption
// after
nebula-cert ca -encrypt -name "my ca"           # ensure -passphrase/-nonce supplied
# or drop encryption:
nebula-cert ca -name "my ca"

Defensive patterns

Strategy: validation

Validate before calling

if encrypt && (passphrase == "") {
	return fmt.Errorf("-encrypt requires a non-empty passphrase")
}

Try / catch

out, err := exec.Command("nebula-cert", "ca", "-encrypt", ...).CombinedOutput()
if err != nil && strings.Contains(string(out), "error while encrypting out-key") {
	log.Printf("key encryption failed: %s", out)
	return fmt.Errorf("could not encrypt key: %s", out)
}

Prevention

Always supply a non-empty passphrase when using -encrypt
Keep flag combinations consistent (encrypt implies a passphrase source)
Check FIPS/KDF compatibility if using restricted crypto modes
Store passphrases in a secret manager, not inline in scripts

When it happens

Trigger: nebula-cert ca -encrypt ... where EncryptAndMarshalSigningPrivateKey fails: passphrase rejected by the crypto layer, unsupported curve for encryption, or internal KDF/AEAD failure (rare; usually indicates invalid inputs like an empty passphrase slipped past earlier checks).

Common situations: Scripting passes an empty or malformed passphrase via -nonce/-passphrase handling; FIPS-mode crypto rejecting the configured KDF parameters; inconsistent flag combinations (encryption enabled with stdio without passphrase).

Related errors

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/13fff599874c6bce. Report an issue: GitHub.