From f33b7b3418dc06d99e3c818e2b25d4eed2196b6d Mon Sep 17 00:00:00 2001
From: Scott Wallace <scott@wallace.sh>
Date: Fri, 27 Sep 2024 10:44:42 +0100
Subject: [PATCH] Add ability to connect to specific address

---
 cert_deets.py | 38 +++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/cert_deets.py b/cert_deets.py
index 0a96e95..3f5be7a 100644
--- a/cert_deets.py
+++ b/cert_deets.py
@@ -19,6 +19,28 @@ from tabulate import tabulate
 SAN_GROUPING = 4
 
 
+def get_cert_with_servername(addr: tuple[str, int], servername: str = "") -> bytes:
+    """
+    Get TLS certificate from an address with an explicit servername override
+
+    Args:
+        addr (tuple[str, int]): adress in tuple form (address, port)
+        servername (str): SNI servername
+
+    Returns:
+        bytes: PEM bytes
+    """
+    context = ssl.create_default_context()
+    context.check_hostname = False
+
+    with socket.create_connection((addr[0], addr[1]), timeout=10) as sock:
+        with context.wrap_socket(sock, server_hostname=servername) as sslsock:
+            if der_cert := sslsock.getpeercert(True):
+                return ssl.DER_cert_to_PEM_cert(der_cert).encode("utf=8")
+
+    return bytes()
+
+
 def format_fingerprint(fingerprint: bytes | str) -> str:
     """
     Print a fingerprint as a colon-separated hex string
@@ -58,6 +80,7 @@ if __name__ == "__main__":
         parser = argparse.ArgumentParser()
 
         parser.add_argument("site", help="site to lookup")
+        parser.add_argument("-a", "--address", help="explicit address to connect to")
 
         return parser.parse_args()
 
@@ -89,17 +112,22 @@ if __name__ == "__main__":
         endpoint = f"{parts.hostname}:{parts.port}"
 
         try:
-            pem_data = ssl.get_server_certificate(
-                (parts.hostname, parts.port),
-                timeout=10,
-            ).encode("utf-8")
+            if args.address:
+                pem_data = get_cert_with_servername(
+                    (args.address, parts.port),
+                    servername=parts.hostname,
+                )
+            else:
+                pem_data = ssl.get_server_certificate(
+                    (parts.hostname, parts.port),
+                    timeout=10,
+                ).encode("utf-8")
 
             cert_chain = CertificateChain()
             try:
                 cert_chain = resolve(pem_data)
             except urllib.error.URLError:
                 pass
-
         except (
             ConnectionRefusedError,
             ConnectionResetError,