From ccf406a0b344a9ed82518b400bf95d337aa18117 Mon Sep 17 00:00:00 2001
From: Kevin Froman <beardog@mailbox.org>
Date: Sun, 31 May 2020 17:48:58 -0500
Subject: [PATCH] finished session encrypt/decrypt implementation

---
 tests/session/testSessionEncrypt.cs           | 56 ++++++++++++++-----
 .../chestcrypto/session/crypto/encrypt.cs     | 15 +++++
 treasurechest/chestcrypto/session/session.cs  |  2 +
 3 files changed, 60 insertions(+), 13 deletions(-)

diff --git a/tests/session/testSessionEncrypt.cs b/tests/session/testSessionEncrypt.cs
index 761aa23..7afc5c6 100644
--- a/tests/session/testSessionEncrypt.cs
+++ b/tests/session/testSessionEncrypt.cs
@@ -20,21 +20,51 @@ namespace sessionTestEncrypt
         public long getFutureTime(int seconds){return DateTimeOffset.UtcNow.ToUnixTimeSeconds() + (long) seconds;}
 
         [Test]
-        public void TestEncrypt(){
-            var pair1 = PublicKeyBox.GenerateKeyPair();
-            byte[] publicK = pair1.PublicKey;
-            byte[] privateK = pair1.PrivateKey;
-            var pair = PublicKeyBox.GenerateKeyPair();
-            byte[] privKey = pair.PrivateKey;
-            byte[] pubKey = pair.PublicKey;
+        public void TestDecrypt(){
+            var us = PublicKeyBox.GenerateKeyPair();
+            var them = PublicKeyBox.GenerateKeyPair();
             byte[] message = UTF8Encoding.UTF8.GetBytes("Hello friend");
-            Session session = new Session(privateK, publicK, true, 5);
-            session.setMinimumKeyExpireSeconds(10);
-            session.setMessageDelay((long) 25);
-            session.addPublic(pubKey, getFutureTime(100));
+            Session session = new Session(us.PrivateKey, them.PublicKey, true, 5);
+            var ourNew = PublicKeyBox.GenerateKeyPair();
+            session.addPrivate(ourNew.PrivateKey, getFutureTime(1000));
+            byte[] encrypted = Curve25519.encrypt(them.PrivateKey, ourNew.PublicKey, message);
+            Assert.AreEqual(
+                SessionCrypto.decrypt(session, encrypted),
+                message
+            );
+        }
+
+        [Test]
+        public void TestDecryptOlderKey(){
+            var us = PublicKeyBox.GenerateKeyPair();
+            var them = PublicKeyBox.GenerateKeyPair();
+            byte[] message = UTF8Encoding.UTF8.GetBytes("Hello friend");
+            Session session = new Session(us.PrivateKey, them.PublicKey, true, 5);
+            var ourNew = PublicKeyBox.GenerateKeyPair();
+            var ourNew2 = PublicKeyBox.GenerateKeyPair();
+            session.addPrivate(ourNew.PrivateKey, getFutureTime(1000));
+            byte[] encrypted = Curve25519.encrypt(them.PrivateKey, ourNew.PublicKey, message);
+            session.addPrivate(ourNew2.PrivateKey, getFutureTime(1005));
+            Assert.AreEqual(
+                SessionCrypto.decrypt(session, encrypted),
+                message
+            );
+        }
+
+        [Test]
+        public void TestEncrypt(){
+            // Test ephemeral encrypt
+            var us = PublicKeyBox.GenerateKeyPair();
+            var them = PublicKeyBox.GenerateKeyPair();
+            var ephemeral = PublicKeyBox.GenerateKeyPair();
+            byte[] message = UTF8Encoding.UTF8.GetBytes("Hello friend");
+            Session session = new Session(us.PrivateKey, them.PublicKey, true, 5);
+            session.addPublic(ephemeral.PublicKey, getFutureTime(1000));
             byte[] encrypted = SessionCrypto.encrypt(session, message);
-            byte[] decrypted = Curve25519.decrypt(privKey, publicK, encrypted);
-            Assert.AreEqual(decrypted, message);
+            Assert.AreEqual(
+                Curve25519.decrypt(ephemeral.PrivateKey, us.PublicKey, encrypted),
+                message
+            );
         }
 
     }
diff --git a/treasurechest/chestcrypto/session/crypto/encrypt.cs b/treasurechest/chestcrypto/session/crypto/encrypt.cs
index 7dfdcf7..20e36d2 100644
--- a/treasurechest/chestcrypto/session/crypto/encrypt.cs
+++ b/treasurechest/chestcrypto/session/crypto/encrypt.cs
@@ -13,6 +13,21 @@ namespace chestcrypto.session.crypto{
             return Curve25519.encrypt(privateKey, publicKey, message);
         }
 
+        public static byte[] decrypt(Session activeSession, byte[] ciphertext){
+            byte[] publicKey = activeSession.getTheirMasterPublic();
+            byte[] decrypted;
+            byte[] privateKey;
+            foreach (var privKey in activeSession.getAllPrivateKeys()){
+                try{
+                    privateKey = privKey.Item2;
+                    decrypted = Curve25519.decrypt(privateKey, publicKey, ciphertext);
+                    return decrypted;
+                }
+                catch(System.Security.Cryptography.CryptographicException){}
+            }
+            throw new System.Security.Cryptography.CryptographicException();
+        }
+
     }
 
 }
\ No newline at end of file
diff --git a/treasurechest/chestcrypto/session/session.cs b/treasurechest/chestcrypto/session/session.cs
index 24d7e0a..068da4b 100644
--- a/treasurechest/chestcrypto/session/session.cs
+++ b/treasurechest/chestcrypto/session/session.cs
@@ -99,6 +99,8 @@ namespace chestcrypto{
                 return key.Item2;
             }
 
+            public (long, byte[])[] getAllPrivateKeys(){return ourPrivateKeys.ToArray();}
+
             public void addPrivate(byte[] privateKey, long timestamp){
                 validateKeyLength(privateKey);
                 validateTimestamp(timestamp);