from flask import Flask, request, render_template_string, redirect, url_for
from cryptography import x509
from cryptography.hazmat.backends import default_backend
app = Flask(__name__)
# Simple HTML Form
HTML_TEMPLATE = """
SSL Certificate Decoder - View CN, SAN, Issuer & More
Decode SSL Certificate
{% if cert_info %}
Certificate Information:
{{ cert_info }}
{% endif %}
"""
def parse_certificate(pem_data):
try:
cert = x509.load_pem_x509_certificate(pem_data.encode(), default_backend())
except Exception as e:
return f"Invalid certificate: {e}"
issuer = cert.issuer.get_attributes_for_oid(x509.OID_COMMON_NAME)
subject = cert.subject.get_attributes_for_oid(x509.OID_COMMON_NAME)
not_before = cert.not_valid_before
not_after = cert.not_valid_after
serial_number = cert.serial_number
sig_algo = cert.signature_hash_algorithm.name
# Get SANs
try:
ext = cert.extensions.get_extension_for_class(x509.SubjectAlternativeName)
sans = ext.value.get_values_for_type(x509.DNSName)
except x509.ExtensionNotFound:
sans = []
output = f"""
Subject CN: {subject[0].value if subject else 'N/A'}
Issuer CN: {issuer[0].value if issuer else 'N/A'}
Valid From: {not_before}
Valid Until: {not_after}
Serial Number: {serial_number}
Signature Alg: {sig_algo}
SANs: {', '.join(sans) if sans else 'None'}
"""
return output.strip()
@app.route("/", methods=["GET", "POST"])
def index():
if request.method == "POST":
pem_cert = request.form.get("certificate", "").strip()
cert_info = parse_certificate(pem_cert)
# Store result temporarily in session or pass via GET param
return redirect(url_for('index', cert_info=cert_info))
# GET Request — show result if available
cert_info = request.args.get('cert_info')
return render_template_string(HTML_TEMPLATE, cert_info=cert_info)
if __name__ == "__main__":
app.run(debug=True, port=5000)