Begin work on MAC field processing

src/handshake/types.rs

@@ -0,0 +1,81 @@
+use std::error::Error;
+use std::fmt;
+
+use crate::types::KeyPair;
+
+/* Internal types for the noise IKpsk2 implementation */
+
+// config error
+
+#[derive(Debug)]
+pub struct ConfigError(String);
+
+impl ConfigError {
+    pub fn new(s: &str) -> Self {
+        ConfigError(s.to_string())
+    }
+}
+
+impl fmt::Display for ConfigError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "ConfigError({})", self.0)
+    }
+}
+
+impl Error for ConfigError {
+    fn description(&self) -> &str {
+        &self.0
+    }
+
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        None
+    }
+}
+
+// handshake error
+
+#[derive(Debug)]
+pub enum HandshakeError {
+    DecryptionFailure,
+    UnknownPublicKey,
+    UnknownReceiverId,
+    InvalidMessageFormat,
+    OldTimestamp,
+    InvalidState,
+}
+
+impl fmt::Display for HandshakeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            HandshakeError::DecryptionFailure => write!(f, "Failed to AEAD:OPEN"),
+            HandshakeError::UnknownPublicKey => write!(f, "Unknown public key"),
+            HandshakeError::UnknownReceiverId => {
+                write!(f, "Receiver id not allocated to any handshake")
+            }
+            HandshakeError::InvalidMessageFormat => write!(f, "Invalid handshake message format"),
+            HandshakeError::OldTimestamp => write!(f, "Timestamp is less/equal to the newest"),
+            HandshakeError::InvalidState => write!(f, "Message does not apply to handshake state"),
+        }
+    }
+}
+
+impl Error for HandshakeError {
+    fn description(&self) -> &str {
+        "Generic Handshake Error"
+    }
+
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        None
+    }
+}
+
+pub type Output<T> = (
+    T, // external identifier associated with peer
+    // (e.g. a reference or vector index)
+    Option<Vec<u8>>, // message to send
+    Option<KeyPair>, // resulting key-pair of successful handshake
+);
+
+// preshared key
+
+pub type Psk = [u8; 32];