improve rsa encryption (#61)

* clrify encryption schemes

* increase SMP ping delay

* include authTag and msg size in encrypted message header, pad messages to fixed size

* use newtype for Key and IV bytestrings

* rename CryptoError constructors

* refactor Word to Int conversion

* refactor padding, replace padding character

* rfc corrections, comment

* rename aesTagSize -> authTagSize

* failing test

src/Simplex/Messaging/Client.hs

@@ -69,7 +69,9 @@ data SMPClientConfig = SMPClientConfig
   { qSize :: Natural,
     defaultPort :: ServiceName,
     tcpTimeout :: Int,
-    smpPing :: Int
+    smpPing :: Int,
+    blockSize :: Int,
+    smpCommandSize :: Int
   }
 
 smpDefaultConfig :: SMPClientConfig
@@ -78,7 +80,9 @@ smpDefaultConfig =
     { qSize = 16,
       defaultPort = "5223",
       tcpTimeout = 2_000_000,
-      smpPing = 30_000_000
+      smpPing = 30_000_000,
+      blockSize = 8_192, -- 16_384,
+      smpCommandSize = 256
     }
 
 data Request = Request