Make script

Author: PythonCoderAS

main.py

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+import argparse
+
+from OpenSSL import crypto
+import re
+from requests import Session
+import sys
+
+ca_url_pattern = re.compile(r'CA Issuers \- URI:(\S+)\n')
+
+class CertChainBuilder:
+    def get_next_cert_url(self, cert_data: bytes):
+        is_pem = False
+        try:
+            cert_data.decode("utf-8")
+            is_pem = True
+        except UnicodeDecodeError:
+            pass
+        if is_pem:
+            cert = crypto.load_certificate(crypto.FILETYPE_PEM, cert_data)
+        else:
+            cert = crypto.load_certificate(crypto.FILETYPE_ASN1, cert_data)
+        self.certs.append(cert)
+        for i in range(cert.get_extension_count()):
+            ext = cert.get_extension(i)
+            if ext.get_short_name() == b"authorityInfoAccess":
+                if match := ca_url_pattern.search(str(ext)):
+                    return match.group(1)
+                return None
+        return None
+
+    def __init__(self, verbose: bool):
+        self.certs = []
+        self.session = Session()
+        self.verbose = verbose
+
+    def get_cert_from_url(self, url: str) -> bytes:
+        with self.session.get(url) as response:
+            return response.content
+
+    @staticmethod
+    def get_cert_common_name(cert: crypto.X509) -> str:
+        return cert.get_subject().CN
+
+
+    def feed(self, inital_cert: bytes):
+        next_url = self.get_next_cert_url(inital_cert)
+        while next_url:
+            if self.verbose:
+                print(f"Fetching next certificate from {next_url}", file=sys.stderr)
+            next_cert = self.get_cert_from_url(next_url)
+            next_url = self.get_next_cert_url(next_cert)
+
+    @staticmethod
+    def get_cert_pem(cert: crypto.X509) -> str:
+        return crypto.dump_certificate(crypto.FILETYPE_PEM, cert).decode("utf-8").rstrip("\n")
+
+    def build_chain(self) -> str:
+        # Order: Initial, Intermediate Certs, Root
+        # Intermediate Certs: Highest -> Lowest (in the context of self.certs, this means from higher indices to lower)
+        # Initial: self.certs[0]
+        # Root: self.certs[-1]
+        chain = [self.get_cert_pem(self.certs[0])]
+        for cert in self.certs[-2:0:-1]: # Starts from the second highest index and goes to the second lowest index
+            chain.append(self.get_cert_pem(cert))
+        chain.append(self.get_cert_pem(self.certs[-1]))
+        return "\n".join(chain)
+
+def main(args=None):
+    parser = argparse.ArgumentParser(description="Build a certificate chain from a certificate")
+    parser.add_argument("cert", help="The certificate to build the chain from")
+    parser.add_argument("--out", help="The file to write the chain to (otherwise writes to stdout)")
+    parser.add_argument("--verbose", help="Logs intermediate certificate URLs", action="store_true")
+    parser.add_argument("--save-intermediate-certificates", help="Saves intermediate certificates", action="store_true")
+    args = parser.parse_args(args)
+    with open(args.cert, "rb") as f:
+        cert_data = f.read()
+    builder = CertChainBuilder(verbose=args.verbose)
+    builder.feed(cert_data)
+    chain = builder.build_chain()
+    if args.out:
+        with open(args.out, "w") as f:
+            f.write(chain)
+    else:
+        print(chain)
+    return
+
+if __name__ == "__main__":
+    main()

requirements.txt

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+pyopenssl==24.2.1
+requests==2.32.3