{"record":{"id":"29efb8444f2a6dc2","repo":"eclipse-vertx/vert.x","slug":"invalid-der-length-field-too-big","errorCode":null,"errorMessage":"Invalid DER: length field too big (","messagePattern":"Invalid DER: length field too big \\(","errorType":"exception","errorClass":"VertxException","httpStatus":null,"severity":"error","filePath":"vertx-core/src/main/java/io/vertx/core/net/impl/pkcs1/PrivateKeyParser.java","lineNumber":372,"sourceCode":"     * </ul>\n     *\n     * @return The length as integer\n     * @throws VertxException\n     */\n    private int getLength() throws VertxException {\n\n      int i = readByte();\n\n      // A single byte short length\n      if ((i & ~0x7F) == 0) {\n        return i;\n      }\n\n      int num = i & 0x7F;\n\n      // We can't handle length longer than 4 bytes\n      if (i >= 0xFF || num > 4) {\n        throw new VertxException(\"Invalid DER: length field too big (\"\n          + i + \")\");\n      }\n\n      byte[] bytes = readBytes(num);\n      return new BigInteger(1, bytes).intValue();\n    }\n  }\n\n\n  /**\n   * An ASN.1 TLV. The object is not parsed. It can\n   * only handle integers and strings.\n   *\n   * @author zhang\n   */\n  static class Asn1Object {\n\n    protected final int type;","sourceCodeStart":354,"sourceCodeEnd":390,"githubUrl":"https://github.com/eclipse-vertx/vert.x/blob/fb308bd8c3f12c79f4ae89bef67fadf6c80d036e/vertx-core/src/main/java/io/vertx/core/net/impl/pkcs1/PrivateKeyParser.java#L354-L390","documentation":"Thrown by DerParser.getLength when a DER long-form length byte is 0xFF or the following length-of-length exceeds 4 bytes. DER lengths of more than 4 bytes are unsupported by this parser, so such input is rejected. Practically it means the data is not a plausible DER key structure.","triggerScenarios":"Reading a length byte 0xFF (reserved/indefinite long form) or a long-form length with num > 4 following length bytes in the parsed DER stream.","commonSituations":"Parsing BER (not DER) data using indefinite lengths (0x80) as produced by some crypto libraries; corrupted key material where a length byte reads 0xFF; non-key binary data passed by mistake.","solutions":["Convert the key to strict DER: openssl asn1parse -genconf / re-export with openssl (DER is definite-length).","Confirm the input is actual key material, not a keystore blob or encrypted container.","Re-derive the DER bytes from the PEM with a clean base64 decode and retry.","If the key is legitimately huge, parse it with a general ASN.1 library (Bouncy Castle) instead."],"exampleFix":"// before\n// BER with indefinite length (0x80) from a custom encoder\n// after\nopenssl asn1parse -in key.der -inform DER -i  # verify definite lengths\n// or: openssl rsa -in key.pem -outform DER -out key.der","handlingStrategy":"validation","validationCode":"// Reject BER-style indefinite lengths before parsing: scan length bytes for 0x80/0xFF long forms\nbyte[] der = Base64.getMimeDecoder().decode(pemBody);\n// Stronger: validate the whole structure with an external ASN.1 check first\n// openssl asn1parse -inform DER -in key.der  -> fails on indefinite/oversized lengths","typeGuard":null,"tryCatchPattern":"try {\n    return PrivateKeyParser.getECKeySpec(der);\n} catch (VertxException e) {\n    if (e.getMessage().contains(\"length field too big\")) {\n        throw new KeyFormatException(\"Input is likely BER, not DER: \" + e.getMessage());\n    }\n    throw e;\n}","preventionTips":["Convert BER-encoded keys to strict DER via OpenSSL","Reject encrypted keystore blobs passed as raw key material","Validate DER structure externally before parsing"],"tags":["der","asn1","length-field","ber","encoding"],"backgroundTag":"invalid-argument-format","analyzedSha":"fb308bd8c3f12c79f4ae89bef67fadf6c80d036e","analyzedAt":"2026-09-06T11:37:12.241Z","contentChangedAt":"2026-09-06T11:37:12.241Z","schemaVersion":2},"datasetVersion":"2026-09-14T00:17:10.932Z"}