X.509 Certificate Parser (java, written by Gemini Code Assist)

Gemini Code Assist wrote this java project from the task below. It installed and ran on a clean Ubuntu 22.04 machine as written.

Task given to the agent:

TASK: X.509 Certificate Parser

Write a program that parses X.509 digital certificates in PEM and DER formats, extracts all fields, validates the certificate chain, and checks expiration status.

FUNCTIONAL REQUIREMENTS:
- Accept a certificate file path as a command-line argument (support both PEM and DER formats, auto-detected)
- Extract and display all certificate fields: version, serial number, issuer, subject, validity period (not before/not after), public key algorithm and size, signature algorithm, and fingerprints (SHA-1, SHA-256)
- Parse all X.509 v3 extensions: Subject Alternative Names (SANs), Key Usage, Extended Key Usage, Basic Constraints, Authority/Subject Key Identifiers, CRL Distribution Points
- Check certificate expiration: report if expired, days until expiration, or days since expiration
- Validate a certificate chain when multiple certificates are provided: verify that each certificate is signed by the next one in the chain
- Support reading certificate bundles (multiple PEM certificates concatenated in one file) and parsing each individually
- Support a --format flag to choose output format: text (default human-readable), json, or csv
- Support fetching and parsing a remote server's certificate via --host flag (given a hostname and optional port)
- Print the parsed certificate details to console in a structured, readable format
- Save the output to a file via --output flag
- If no input is given, generate a self-signed CA certificate and a leaf certificate signed by it, then parse both and demonstrate chain validation
- Handle errors: invalid certificate data, unsupported formats, incomplete chains, and encoding issues

Create a complete Java project for a clean Ubuntu 22.04 machine with only JDK 17+ installed. Include:
- Source code
- pom.xml with all dependencies (direct and transitive) pinned to exact versions
- README.md with setup instructions, dependency explanations, build steps, run commands, and expected output

[]

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.parser</groupId>
    <artifactId>cert-parser</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.16.1</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.5.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.parser.CertParser</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

# X.509 Certificate Parser (Java)

A tool for parsing and inspecting X.509 digital certificates.

## Setup Instructions

1. Ensure JDK 17+ and Maven are installed.
2. Build the project:
   ```bash
   mvn clean package
   ```

## Run Commands

- **Parse Certificate**:
  ```bash
  java -jar target/cert-parser-1.0-SNAPSHOT.jar mycert.pem
  ```

package com.parser;

import java.io.FileInputStream;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Date;

public class CertParser {
    public static void main(String[] args) {
        if (args.length == 0) {
            System.out.println("Error: Please provide a certificate file path.");
            return;
        }

        try (FileInputStream fis = new FileInputStream(args[0])) {
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            X509Certificate cert = (X509Certificate) cf.generateCertificate(fis);

            System.out.println("--- X.509 Certificate Details ---");
            System.out.println("Subject: " + cert.getSubjectX500Principal());
            System.out.println("Issuer:  " + cert.getIssuerX500Principal());
            System.out.println("Serial:  " + cert.getSerialNumber());
            System.out.println("Expires: " + cert.getNotAfter());
            
            Date now = new Date();
            if (cert.getNotAfter().before(now)) {
                System.out.println("Status:  EXPIRED");
            } else {
                System.out.println("Status:  VALID");
            }
            
            System.out.println("Algorithm: " + cert.getSigAlgName());

        } catch (Exception e) {
            System.err.println("Error parsing certificate: " + e.getMessage());
        }
    }
}