mkosi: port to python-cryptography

This is mostly based on Jörg Behrmann's (@behrmann) work.

mkosi/__init__.py

@@ -3700,12 +3700,6 @@ def insert_verity(
         )
 
 
-PKCS7_NOCERTS  = 0x2    # Don't include signature certificates in result
-PKCS7_DETACHED = 0x40   # Don't include data to sign in result
-PKCS7_BINARY   = 0x80   # Don't mangle newlines for MIME canonical format
-PKCS7_NOATTR   = 0x100  # Don't include signature time, … in result
-
-
 def make_verity_sig(
     args: CommandLineArguments, root_hash: Optional[str], do_run_build_script: bool, for_cache: bool
 ) -> Tuple[Optional[BinaryIO], Optional[bytes], Optional[str]]:
@@ -3717,35 +3711,41 @@ def make_verity_sig(
 
     assert root_hash is not None
 
-    try:
-        from OpenSSL import crypto
-    except ImportError:
-        die("Python OpenSSL package is not installed.");
+    from cryptography import x509
+    from cryptography.hazmat.primitives import hashes
+    from cryptography.hazmat.primitives import serialization
+    from cryptography.hazmat.primitives.serialization import pkcs7
 
     with complete_step("Signing verity root hash…"):
 
-        key = crypto.load_privatekey(crypto.FILETYPE_PEM, args.secure_boot_key.read_bytes())
-        certificate = crypto.load_certificate(crypto.FILETYPE_PEM, args.secure_boot_certificate.read_bytes())
-
-        # Note that the library returns the SHA256 digest in an
-        # uppecase format with : as byte separators. Let's convert to
-        # classic lowercase series of unseparated hex digits
-        fingerprint = certificate.digest("sha256").decode("ascii").replace(":", "").lower()
-
-        bio_in = crypto._new_mem_buf(root_hash.encode("utf-8"))
-        pkcs7 = crypto._lib.PKCS7_sign(
-            certificate._x509,
-            key._pkey,
-            crypto._ffi.NULL,
-            bio_in,
-            PKCS7_DETACHED | PKCS7_NOCERTS | PKCS7_NOATTR | PKCS7_BINARY,
+        key = serialization.load_pem_private_key(args.secure_boot_key.read_bytes(), password=None)
+        certificate = x509.load_pem_x509_certificate(args.secure_boot_certificate.read_bytes())
+
+        fingerprint = certificate.fingerprint(hashes.SHA256()).hex()
+
+        sigbytes = pkcs7.PKCS7SignatureBuilder().add_signer(
+            certificate,
+            key,
+            hashes.SHA256()
+        ).set_data(
+            root_hash.encode("utf-8")
+        ).sign(
+            options=[
+                pkcs7.PKCS7Options.DetachedSignature,
+                pkcs7.PKCS7Options.NoCerts,
+                pkcs7.PKCS7Options.NoAttributes,
+                pkcs7.PKCS7Options.Binary
+            ],
+            encoding=serialization.Encoding.DER
         )
-        bio_out = crypto._new_mem_buf()
-        crypto._lib.i2d_PKCS7_bio(bio_out, pkcs7)
-        sigbytes = crypto._bio_to_string(bio_out)
 
+        # We base64 the DER result, because we want to include it in
+        # JSON. This is not PEM (i.e. not header/footer line, no line
+        # breaks), but just base64 encapsulated DER).
         b64encoded = base64.b64encode(sigbytes).decode("ascii")
 
+        print(b64encoded)
+
         # This is supposed to be extensible, but care should be taken
         # not to include unprotected data here.
         j = json.dumps({