Add basic functions to sign and validate a signature.

This is blessedly simple and I'm assuming working with the very basic tests I've done.

gongor/aegis.py

@@ -1,5 +1,12 @@
+import argparse
+from pathlib import Path
 import subprocess
 
+from cryptography import x509
+from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.serialization import pkcs12
+from cryptography.hazmat.primitives.asymmetric import ec, ed25519, padding
+
 MAX_HUMAN_AGE = 365 * 200
 def generate():
 	print("Please name this aegis. You can call it anything. Frequently people use their legal name.")
@@ -17,3 +24,52 @@ def generate():
 		"-keyout", "key.pem", # Generate an encrypted private key file with a .pem extension
 		],
 		check=True,)
+
+def sign():
+	"Sign some arbitrary data."
+	parser = argparse.ArgumentParser()
+	parser.add_argument("aegis_key_pem", type=Path, help="The file for the PEM-encoded aegis private key.")
+	parser.add_argument("message", type=Path, help="The file containing the message to sign.")
+	parser.add_argument("-p", "--password", help="The password to use to open the key file.")
+	args = parser.parse_args()
+
+	with open(args.aegis_key_pem, "rb") as f:
+		private_key = serialization.load_pem_private_key(
+			data=f.read(),
+			password=args.password.encode("UTF-8"),
+		)
+	with open(args.message, "rb") as f:
+		data = f.read()
+		signature = private_key.sign(
+			data,
+			ec.ECDSA(hashes.SHA256()),
+		)
+	with open("signature.bin", "wb") as f:
+		f.write(signature)
+	print("Wrote signature to signature.bin")
+
+def validate():
+	"Validate the signature of some arbitrary data."
+	parser = argparse.ArgumentParser()
+	parser.add_argument("aegis_cert_pem", type=Path, help="The file for the PEM-encoded aegis public certificate.")
+	parser.add_argument("message", type=Path, help="The file containing the message to validate.")
+	parser.add_argument("signature", type=Path, help="The file containing the signature to validate.")
+	args = parser.parse_args()
+
+	with open(args.aegis_cert_pem, "rb") as f:
+		certificate = x509.load_pem_x509_certificate(
+			data=f.read(),
+		)
+	with open(args.message, "rb") as f:
+		data = f.read()
+	with open(args.signature, "rb") as f:
+		signature = f.read()
+
+	key = certificate.public_key()
+	key.verify(
+		signature=signature,
+		data=data,
+		signature_algorithm=ec.ECDSA(hashes.SHA256()),
+	)
+	print("Signature is valid")
+

pyproject.toml

@@ -8,6 +8,10 @@ license = {file = "LICENSE.txt"}
 
 [project.scripts]
 aegis-generate = "gongor.aegis:generate"
+aegis-sign = "gongor.aegis:sign"
+aegis-validate-signature = "gongor.aegis:validate"
+aegis-box = "gongor.aegis:box"
+aegis-unbox = "gongor.cipher:unbox"
 
 [build-system]
 requires = ["setuptools >= 61.0.0"]