Add symm_encrypt/decrypt methods in KeyRing w/ tests

nkms/crypto/keyring.py

@@ -1,5 +1,6 @@
 import sha3
 from nacl.utils import random
+from nacl.secret import SecretBox
 from nkms.crypto.keypairs import SigningKeypair, EncryptingKeypair
 from npre import umbral
 
@@ -137,6 +138,32 @@ class KeyRing(object):
         # TODO: What to do if not enough shares, or invalid?
         return self.enc_keypair.combine(shares)
 
+    def symm_encrypt(self, key, plaintext):
+        """
+        Encrypts the plaintext using SecretBox symmetric encryption.
+
+        :param bytes key: Key to encrypt with
+        :param bytes plaintext: Plaintext to encrypt
+
+        :rtype: bytes
+        :return: Ciphertext from SecretBox symmetric encryption
+        """
+        cipher = SecretBox(key)
+        return cipher.encrypt(plaintext)
+
+    def symm_decrypt(self, key, ciphertext):
+        """
+        Decrypts the ciphertext using SecretBox symmetric decryption.
+
+        :param bytes key: Key to decrypt with
+        :param bytes ciphertext: Ciphertext from SecretBox encryption
+
+        :rtype: bytes
+        :return: Plaintext from SecretBox decryption
+        """
+        cipher = SecretBox(key)
+        return cipher.decrypt(ciphertext)
+
     def secure_random(self, length):
         """
         Generates a bytestring from a secure random source for keys, etc.

tests/crypto/test_keyring.py

@@ -79,6 +79,23 @@ class TestKeyRing(unittest.TestCase):
         self.assertEqual(32, len(dec_key))
         self.assertTrue(dec_key == raw_key)
 
+    def test_symm_encryption(self):
+        key = self.keyring_a.secure_random(32)
+        self.assertEqual(32, len(key))
+
+        ciphertext = self.keyring_a.symm_encrypt(key, self.msg)
+        self.assertTrue(self.msg not in ciphertext)
+
+    def test_symm_decryption(self):
+        key = self.keyring_a.secure_random(32)
+        self.assertEqual(32, len(key))
+
+        ciphertext = self.keyring_a.symm_encrypt(key, self.msg)
+        self.assertTrue(self.msg not in ciphertext)
+
+        plaintext = self.keyring_a.symm_decrypt(key, ciphertext)
+        self.assertTrue(self.msg == plaintext)
+
     def test_secure_random(self):
         length = random.randrange(1, 100)
         rand_bytes = self.keyring_a.secure_random(length)