{"record":{"id":"e93bdcd58868db09","repo":"kubernetes/kops","slug":"error-encoding-rsa-private-key-w","errorCode":null,"errorMessage":"error encoding RSA private key: %w","messagePattern":"error encoding RSA private key: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"pkg/pki/privatekey.go","lineNumber":157,"sourceCode":"\t\treturn nil, fmt.Errorf(\"error writing SSL private key: %v\", err)\n\t}\n\treturn json.Marshal(data.String())\n}\n\nvar _ io.WriterTo = &PrivateKey{}\n\nfunc (k *PrivateKey) WriteTo(w io.Writer) (int64, error) {\n\tif k.Key == nil {\n\t\t// For the dry-run case\n\t\treturn 0, nil\n\t}\n\n\tvar data bytes.Buffer\n\n\tswitch pk := k.Key.(type) {\n\tcase *rsa.PrivateKey:\n\t\tif err := pem.Encode(&data, &pem.Block{Type: \"RSA PRIVATE KEY\", Bytes: x509.MarshalPKCS1PrivateKey(pk)}); err != nil {\n\t\t\treturn 0, fmt.Errorf(\"error encoding RSA private key: %w\", err)\n\t\t}\n\tcase *ecdsa.PrivateKey:\n\t\tb, err := x509.MarshalECPrivateKey(pk)\n\t\tif err != nil {\n\t\t\treturn 0, fmt.Errorf(\"error encoding ECDSA private key: %w\", err)\n\t\t}\n\t\tif err := pem.Encode(&data, &pem.Block{Type: \"EC PRIVATE KEY\", Bytes: b}); err != nil {\n\t\t\treturn 0, fmt.Errorf(\"error encoding ECDSA private key: %w\", err)\n\t\t}\n\tdefault:\n\t\treturn 0, fmt.Errorf(\"unknown private key type: %T\", k.Key)\n\t}\n\n\treturn data.WriteTo(w)\n}\n\nfunc (k *PrivateKey) WriteToFile(filename string, perm os.FileMode) error {\n\tf, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)","sourceCodeStart":139,"sourceCodeEnd":175,"githubUrl":"https://github.com/kubernetes/kops/blob/4c8573c808a73d578c5eadc86d410646ea0b0d73/pkg/pki/privatekey.go#L139-L175","documentation":"PrivateKey.WriteTo encodes RSA keys as PKCS#1 DER inside a 'RSA PRIVATE KEY' PEM block; pem.Encode virtually never fails for a well-formed block, so this error indicates an unexpected internal encoding problem while writing the RSA key PEM.","triggerScenarios":"Calling WriteTo (directly or via AsString/AsBytes/MarshalJSON/WriteToFile) on a PrivateKey holding an *rsa.PrivateKey when pem.Encode returns an error on the internal bytes.Buffer.","commonSituations":"Extremely rare in practice because pem.Encode to a bytes.Buffer with valid DER cannot fail; would only surface from memory/IO anomalies or modified library code.","solutions":["Treat as unexpected: retry the operation once, then reproduce with a minimal key to file a bug if persistent.","Verify no custom middleware wraps io.Writer passed to WriteTo in a way that corrupts the buffer.","Confirm the key is a standard *rsa.PrivateKey (not a wrapper type) via %T inspection."],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":"if _, ok := key.Key.(*rsa.PrivateKey); !ok {\n    return fmt.Errorf(\"not an RSA private key\")\n}","typeGuard":"func isRSAKey(k *pki.PrivateKey) bool { return k != nil && k.Key != nil }, // use: _, ok := k.Key.(*rsa.PrivateKey)","tryCatchPattern":"s, err := key.AsString()\nif err != nil {\n    if strings.Contains(err.Error(), \"error encoding RSA private key\") {\n        // unexpected; retry once, then escalate\n    }\n    return err\n}","preventionTips":["Generate RSA keys via pki.GeneratePrivateKey() so encoding is well-tested.","Avoid wrapping *rsa.PrivateKey in custom signer types before storing in Key."],"tags":["pki","rsa","pem-encoding"],"backgroundTag":"private-key-encoding-failed","analyzedSha":"4c8573c808a73d578c5eadc86d410646ea0b0d73","analyzedAt":"2026-09-05T04:13:19.212Z","contentChangedAt":"2026-09-05T04:13:19.212Z","schemaVersion":2},"datasetVersion":"2026-09-12T07:17:12.445Z"}