skion · June 21, 2016 10:17 · Jun 21, 2016
diff --git a/pem_to_jwk.py b/pem_to_jwk.py
@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+Convert a PEM encoded X509 certificate into a JWK RSA public key.
+"""
+import base64
+import json
+
+from cryptography import x509
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.backends import default_backend
+
+file_name = "instance/cert.pem"
+
+pem_data = open(file_name, "rb").read()
+cert = x509.load_pem_x509_certificate(pem_data, default_backend())
+
+public_key = cert.public_key()
+public_numbers = public_key.public_numbers()
+
+e = public_numbers.e.to_bytes(3, byteorder="big")
+n = public_numbers.n.to_bytes(256, byteorder="big")
+x5c = cert.public_bytes(serialization.Encoding.DER)
+
+e = base64.urlsafe_b64encode(e).rstrip(b"=").decode("ascii")
+n = base64.urlsafe_b64encode(n).rstrip(b"=").decode("ascii")
+x5c = base64.b64encode(x5c).decode("ascii")
+
+jwk = {
+    "kty": "RSA",
+    "use": "sig",
+    "alg": "RS256",
+    "e": e,
+    "n": n,
+    "x5c": x5c,
+}
+
+print(json.dumps(jwk, indent=4))