Rewrited Error type

- Added ErrorKind
- Added Error::new() for creating error message
- Implemented std::error::Error for Error

src/lib.rs

@@ -1,4 +1,5 @@
-use crate::Error::Decrypt;
+use std::{error::Error as StdError, fmt};
+
 use byteorder::{ByteOrder, NetworkEndian, WriteBytesExt};
 use pqc_kyber::{
     Keypair, KyberError, PublicKey, SecretKey, KYBER_CIPHERTEXTBYTES, KYBER_SECRETKEYBYTES,
@@ -52,19 +53,19 @@ pub fn encrypt_into<T: AsRef<[u8]>, R: AsRef<[u8]>, V: AsRef<[u8]>, O: AsMut<[u8
     let plaintext = plaintext.as_ref();
     let plaintext_length = plaintext.len();
     let ret = ret.as_mut();
+    //,
 
     if nonce.len() != 32 {
-        return Err(Error::Encrypt(format!(
-            "Nonce must be 32 bytes, got {}",
-            nonce.len()
-        )));
+        return Err(Error::new(
+            format!("Nonce must be 32 bytes, got {}", nonce.len()),
+            ErrorKind::Encrypt,
+        ));
     }
-
     if ret.len() < ct_len(plaintext.len()) {
-        return Err(Error::Encrypt(format!(
-            "Bad output buffer len {}",
-            ret.len()
-        )));
+        return Err(Error::new(
+            format!("Bad output buffer len {}", ret.len()),
+            ErrorKind::Encrypt,
+        ));
     }
 
     if plaintext_length != 0 {
@@ -106,11 +107,18 @@ pub fn decrypt<T: AsRef<[u8]>, R: AsRef<[u8]>>(
     const CIPHERTEXT_BLOCK_LEN: usize = pqc_kyber::KYBER_CIPHERTEXTBYTES;
 
     if ciphertext.len() < CIPHERTEXT_BLOCK_LEN {
-        return Err(Decrypt("The input ciphertext is too short".to_string()));
+        return Err(Error::new(
+            "The input ciphertext is too short".to_string(),
+            ErrorKind::Decrypt,
+        ));
     }
 
-    let plaintext_length = plaintext_len(ciphertext)
-        .ok_or_else(|| Error::Decrypt("Invalid ciphertext input length".to_string()))?;
+    let plaintext_length = plaintext_len(ciphertext).ok_or_else(|| {
+        Error::new(
+            "Invalid ciphertext input length".to_string(),
+            ErrorKind::Decrypt,
+        )
+    })?;
     let split_pt = ciphertext.len().saturating_sub(8);
     let (concatenated_ciphertexts, _) = ciphertext.split_at(split_pt);
     // pt len < 32: size must be 32
@@ -147,9 +155,33 @@ pub fn kem_keypair() -> Result<Keypair, KyberError> {
 }
 
 #[derive(Debug, Clone)]
-pub enum Error {
-    Encrypt(String),
-    Decrypt(String),
+pub enum ErrorKind {
+    Encrypt,
+    Decrypt,
+}
+
+#[derive(Debug, Clone)]
+pub struct Error {
+    msg: String,
+    err_kind: ErrorKind,
+}
+
+impl Error {
+    pub fn new(msg: String, err_kind: ErrorKind) -> Self {
+        Self { msg, err_kind }
+    }
+}
+
+impl StdError for Error {
+    fn description(&self) -> &str {
+        &self.msg
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}, ErrorKind: {:?}", self.msg, self.err_kind)
+    }
 }
 
 fn div_ceil(a: f32, b: f32) -> usize {