What causes "error encoding private key: %s" in hashicorp/nomad?

Inspect the wrapped underlying error for the real cause.

error encoding private key: %s

Error message

error encoding private key: %s

What it means

pemEncodeKey wraps the DER bytes of a private key in a PEM block of the given type (e.g. "EC PRIVATE KEY") using pem.Encode. If PEM encoding to the in-memory buffer fails, the error is wrapped with this message. pem.Encode rarely fails, making this an exceptional defensive path.

Source

Thrown at helper/tlsutil/generate.go:60

	bs, err := x509.MarshalECPrivateKey(pk)
	if err != nil {
		return nil, "", fmt.Errorf("error marshaling ECDSA private key: %s", err)
	}

	pemBlock, err := pemEncodeKey(bs, "EC PRIVATE KEY")
	if err != nil {
		return nil, "", err
	}

	return pk, pemBlock, nil
}

func pemEncodeKey(key []byte, blockType string) (string, error) {
	var buf bytes.Buffer

	if err := pem.Encode(&buf, &pem.Block{Type: blockType, Bytes: key}); err != nil {
		return "", fmt.Errorf("error encoding private key: %s", err)
	}
	return buf.String(), nil
}

type CAOpts struct {
	Signer              crypto.Signer
	Serial              *big.Int
	Days                int
	PermittedDNSDomains []string
	Country             string
	PostalCode          string
	Province            string
	Locality            string
	StreetAddress       string
	Organization        string
	OrganizationalUnit  string
	Name                string
}

View on GitHub (pinned to 482b49bf1a)

Solutions

Inspect the wrapped underlying error for the real cause.
Retry generation; regenerate the key/cert pair.
Report to the maintainers if reproducible, since pem.Encode of valid DER should not fail.

Defensive patterns

Strategy: try-catch

Try / catch

signer, pemKey, err := tlsutil.GeneratePrivateKey()
if err != nil {
    if strings.Contains(err.Error(), "error encoding private key") {
        return fmt.Errorf("pem encode failed: %w", err)
    }
    return err
}

Prevention

Use the library's generation path as-is; do not hand-roll key bytes.
Treat this as an internal invariant failure and report if it occurs.
Retry generation on failure.

When it happens

Trigger: pem.Encode returns a non-nil error while pemEncodeKey encodes marshaled private-key bytes during GeneratePrivateKey.

Common situations: Practically unreachable with valid DER input; would only surface from anomalies in the bytes.Buffer or pem writer.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/2b0ebd6819e50cb1. Report an issue: GitHub.