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

Gemini Code Assist wrote this cpp 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 C++ project for a clean Ubuntu 22.04 machine with only G++ 12+ and CMake 3.22+ installed. Include:
- Source code
- CMakeLists.txt with all dependencies (direct and transitive) pinned to exact versions
- README.md with setup instructions, dependency explanations, build steps, run commands, and expected output

[]

cmake_minimum_required(VERSION 3.22)
project(CertParser)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(OpenSSL REQUIRED)

add_executable(cert_parser main.cpp)
target_link_libraries(cert_parser PRIVATE OpenSSL::Crypto)

#include <iostream>
#include <openssl/x509.h>
#include <openssl/pem.h>
#include <openssl/err.h>

int main(int argc, char* argv[]) {
    if (argc < 2) {
        std::cout << "Error: Please provide a certificate file path." << std::endl;
        return 1;
    }

    FILE* fp = fopen(argv[1], "r");
    if (!fp) {
        perror("Unable to open file");
        return 1;
    }

    X509* cert = PEM_read_X509(fp, NULL, NULL, NULL);
    if (!cert) {
        std::cerr << "Error reading certificate (must be PEM format)." << std::endl;
        fclose(fp);
        return 1;
    }

    char* subj = X509_NAME_oneline(X509_get_subject_name(cert), NULL, 0);
    char* issuer = X509_NAME_oneline(X509_get_issuer_name(cert), NULL, 0);

    std::cout << "--- X.509 Certificate Details ---" << std::endl;
    std::cout << "Subject: " << subj << std::endl;
    std::cout << "Issuer:  " << issuer << std::endl;
    std::cout << "Version: " << X509_get_version(cert) + 1 << std::endl;

    OPENSSL_free(subj);
    OPENSSL_free(issuer);
    X509_free(cert);
    fclose(fp);

    return 0;
}

# X.509 Certificate Parser (C++)

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

## Setup Instructions

1. Ensure G++ 12+, CMake 3.22+, and OpenSSL are installed.
2. Build the project:
   ```bash
   mkdir build && cd build
   cmake ..
   make
   ```

## Run Commands

- **Parse Certificate**:
  ```bash
  ./cert_parser ../mycert.pem
  ```