diff --git a/Cargo.toml b/Cargo.toml
index ec96c0a..af65514 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,3 +8,5 @@ authors = ["klutzytheklutzy@gmail.com"]
 
 log = "*"
 rand = "*"
+num = "*"
+enum_primitive = "*"
diff --git a/examples/google.rs b/examples/google.rs
index 8dcef56..7ead7c1 100644
--- a/examples/google.rs
+++ b/examples/google.rs
@@ -1,5 +1,3 @@
-#![feature(net)]
-
 extern crate suruga;
 
 use std::io::prelude::*;
diff --git a/src/cipher/chacha20_poly1305.rs b/src/cipher/chacha20_poly1305.rs
index 6b539ff..ae6dd07 100644
--- a/src/cipher/chacha20_poly1305.rs
+++ b/src/cipher/chacha20_poly1305.rs
@@ -118,18 +118,18 @@ impl Aead for ChaCha20Poly1305 {
     }
 
     #[inline(always)]
-    fn new_encryptor(&self, key: Vec<u8>) -> Box<Encryptor + 'static> {
+    fn new_encryptor(&self, key: Vec<u8>) -> Box<Encryptor + Send + 'static> {
         let encryptor = ChaCha20Poly1305Encryptor {
             key: key,
         };
-        Box::new(encryptor) as Box<Encryptor>
+        Box::new(encryptor) as Box<Encryptor + Send>
     }
 
     #[inline(always)]
-    fn new_decryptor(&self, key: Vec<u8>) -> Box<Decryptor + 'static> {
+    fn new_decryptor(&self, key: Vec<u8>) -> Box<Decryptor + Send + 'static> {
         let decryptor = ChaCha20Poly1305Decryptor {
             key: key,
         };
-        Box::new(decryptor) as Box<Decryptor>
+        Box::new(decryptor) as Box<Decryptor + Send>
     }
 }
diff --git a/src/cipher/mod.rs b/src/cipher/mod.rs
index 2f09ca1..b27930f 100644
--- a/src/cipher/mod.rs
+++ b/src/cipher/mod.rs
@@ -15,8 +15,8 @@ pub trait Aead {
     fn key_size(&self) -> usize;
     fn fixed_iv_len(&self) -> usize;
     fn mac_len(&self) -> usize;
-    fn new_encryptor(&self, key: Vec<u8>) -> Box<Encryptor + 'static>;
-    fn new_decryptor(&self, key: Vec<u8>) -> Box<Decryptor + 'static>;
+    fn new_encryptor(&self, key: Vec<u8>) -> Box<Encryptor + Send + 'static>;
+    fn new_decryptor(&self, key: Vec<u8>) -> Box<Decryptor + Send + 'static>;
 }
 
 pub trait Encryptor {
@@ -41,7 +41,7 @@ macro_rules! cipher_suite {
         $id:ident = $kex:ident, $cipher:ident, $mac:ident, $v1:expr, $v2:expr;
     )+) => (
         #[allow(non_camel_case_types)]
-        #[derive(Copy, PartialEq, Debug)]
+        #[derive(Copy, Clone, PartialEq, Debug)]
         pub enum CipherSuite {
             $(
                 $id,
diff --git a/src/client.rs b/src/client.rs
index 279e094..d4693f2 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -7,7 +7,7 @@ use rand::{Rng, OsRng};
 
 use tls_result::TlsResult;
 use tls_result::TlsErrorKind::{UnexpectedMessage, InternalError, DecryptError, IllegalParameter};
-use util::crypto_compare;
+use util::{SurugaError, crypto_compare};
 use cipher::{self, Aead};
 use cipher::prf::Prf;
 use crypto::sha2::sha256;
@@ -255,7 +255,10 @@ impl<R: Read, W: Write> Write for TlsClient<R, W> {
             Err(err) => {
                 let err = self.tls.send_tls_alert(err);
                 // FIXME more verbose io error
-                Err(io::Error::new(io::ErrorKind::Other, "TLS write error", Some(err.desc)))
+                Err(io::Error::new(io::ErrorKind::Other, SurugaError {
+                    desc: "TLS write error",
+                    cause: Some(Box::new(err)),
+                }))
             }
         }
     }
@@ -280,7 +283,7 @@ impl<R: Read, W: Write> Read for TlsClient<R, W> {
 
             let selflen = self.buf.len();
             let necessary = cmp::min(remaining, selflen);
-            copy_memory(&mut buf[pos .. pos + necessary], &self.buf[.. necessary]);
+            copy_memory(&self.buf[.. necessary], &mut buf[pos .. pos + necessary]);
             pos += necessary;
 
             self.buf = self.buf[necessary..].to_vec();
diff --git a/src/crypto/wrapping.rs b/src/crypto/wrapping.rs
index 388e69d..0d7276c 100644
--- a/src/crypto/wrapping.rs
+++ b/src/crypto/wrapping.rs
@@ -3,7 +3,7 @@
 // NOTE: since there is no const fn (yet), you can't use `w32(100)` function
 // for consts and statics. (workaround: use `Wrapping(100)`.)
 
-pub use std::num::wrapping::{Wrapping, WrappingOps};
+pub use std::num::Wrapping;
 
 pub trait ToWrapping {
     fn to_w64(self) -> w64;
diff --git a/src/lib.rs b/src/lib.rs
index b0bbeab..e4a8896 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,11 +3,15 @@
 
 #![allow(missing_copy_implementations)]
 
-#![feature(io, core, collections, net)]
+#![feature(core, collections)]
 
 #[macro_use]
 extern crate log;
 extern crate rand;
+extern crate num;
+
+#[macro_use]
+extern crate enum_primitive;
 
 pub use tls::Tls;
 pub use client::TlsClient;
diff --git a/src/record.rs b/src/record.rs
index 8ed5137..9bba1e4 100644
--- a/src/record.rs
+++ b/src/record.rs
@@ -1,5 +1,5 @@
 use std::io::prelude::*;
-use std::num::FromPrimitive;
+use num::traits::FromPrimitive;
 
 use tls_result::TlsResult;
 use tls_result::TlsErrorKind::{UnexpectedMessage, RecordOverflow, BadRecordMac, AlertReceived};
@@ -15,14 +15,16 @@ use self::ContentType::{ChangeCipherSpecTy, AlertTy, HandshakeTy, ApplicationDat
 use self::Message::{HandshakeMessage, ChangeCipherSpecMessage, AlertMessage,
                     ApplicationDataMessage};
 
-#[repr(u8)]
-#[derive(Copy, PartialEq, FromPrimitive, Debug)]
-pub enum ContentType {
-    ChangeCipherSpecTy = 20,
-    AlertTy = 21,
-    HandshakeTy = 22,
-    ApplicationDataTy = 23,
-    // HeartBeat = 24, RFC 6520 extension :-)
+enum_from_primitive! {
+    #[repr(u8)]
+    #[derive(Copy, Clone, PartialEq, Debug)]
+    pub enum ContentType {
+        ChangeCipherSpecTy = 20,
+        AlertTy = 21,
+        HandshakeTy = 22,
+        ApplicationDataTy = 23,
+        // HeartBeat = 24, RFC 6520 extension :-)
+    }
 }
 
 /// maximum length of Record (excluding content_type, version, length fields)
@@ -84,7 +86,7 @@ impl EncryptedRecord {
 pub struct RecordWriter<W: Write> {
     writer: W,
     // if encryptor is None, handshake is not done yet.
-    encryptor: Option<Box<Encryptor + 'static>>,
+    encryptor: Option<Box<Encryptor + Send + 'static>>,
     write_count: u64,
 }
 
@@ -97,7 +99,7 @@ impl<W: Write> RecordWriter<W> {
         }
     }
 
-    pub fn set_encryptor(&mut self, encryptor: Box<Encryptor + 'static>) {
+    pub fn set_encryptor(&mut self, encryptor: Box<Encryptor + Send + 'static>) {
         self.encryptor = Some(encryptor);
         self.write_count = 0;
     }
@@ -191,7 +193,7 @@ pub enum Message {
 pub struct RecordReader<R: ReadExt> {
     reader: R,
     // if decryptor is none, handshake is not done yet.
-    decryptor: Option<Box<Decryptor + 'static>>,
+    decryptor: Option<Box<Decryptor + Send + 'static>>,
     read_count: u64,
     handshake_buffer: HandshakeBuffer,
 }
@@ -206,7 +208,7 @@ impl<R: ReadExt> RecordReader<R> {
         }
     }
 
-    pub fn set_decryptor(&mut self, decryptor: Box<Decryptor + 'static>) {
+    pub fn set_decryptor(&mut self, decryptor: Box<Decryptor + Send + 'static>) {
         self.decryptor = Some(decryptor);
         self.read_count = 0;
     }
diff --git a/src/test.rs b/src/test.rs
index e42fcfa..5e6462f 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -30,9 +30,9 @@ impl Decryptor for NullDecryptor {
 fn null_tls<R: Read, W: Write>(reader: R, writer: W) -> Tls<R, W> {
     let mut tls = Tls::new(reader, writer, OsRng::new().unwrap());
 
-    let null_encryptor = Box::new(NullEncryptor) as Box<Encryptor>;
+    let null_encryptor = Box::new(NullEncryptor) as Box<Encryptor + Send>;
     tls.writer.set_encryptor(null_encryptor);
-    let null_decryptor = Box::new(NullDecryptor) as Box<Decryptor>;
+    let null_decryptor = Box::new(NullDecryptor) as Box<Decryptor + Send>;
     tls.reader.set_decryptor(null_decryptor);
 
     tls
diff --git a/src/tls_item.rs b/src/tls_item.rs
index 7ac3ecc..841e7ca 100644
--- a/src/tls_item.rs
+++ b/src/tls_item.rs
@@ -89,13 +89,15 @@ macro_rules! tls_enum {
             ),+
         }
     ) => (
-        #[allow(non_camel_case_types)]
-        #[derive(Copy, PartialEq, FromPrimitive)]
-        $(#[$a])*
-        pub enum $name {
-            $(
-                $item = $n,
-            )+
+        enum_from_primitive! {
+            #[allow(non_camel_case_types)]
+            #[derive(Copy, Clone, PartialEq)]
+            $(#[$a])*
+            pub enum $name {
+                $(
+                    $item = $n,
+                )+
+            }
         }
 
         impl TlsItem for $name {
@@ -106,7 +108,7 @@ macro_rules! tls_enum {
 
             fn tls_read<R: ReadExt>(reader: &mut R) -> ::tls_result::TlsResult<$name> {
                 let num = stry_read_num!($repr_ty, reader) as u64;
-                let n: Option<$name> = ::std::num::FromPrimitive::from_u64(num);
+                let n: Option<$name> = ::num::traits::FromPrimitive::from_u64(num);
                 match n {
                     Some(n) => Ok(n),
                     None => tls_err!(::tls_result::TlsErrorKind::DecodeError,
diff --git a/src/tls_result.rs b/src/tls_result.rs
index cae0f31..1b53292 100644
--- a/src/tls_result.rs
+++ b/src/tls_result.rs
@@ -1,8 +1,8 @@
-use std::error::{Error, FromError};
+use std::error::Error;
 use std::io;
 use std::fmt;
 
-#[derive(Copy, PartialEq, Debug)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub enum TlsErrorKind {
     // corresponds to alert messages
 
@@ -54,8 +54,8 @@ impl Error for TlsError {
     }
 }
 
-impl FromError<io::Error> for TlsError {
-    fn from_error(err: io::Error) -> TlsError {
+impl From<io::Error> for TlsError {
+    fn from(err: io::Error) -> TlsError {
         TlsError {
             kind: TlsErrorKind::IoFailure,
             desc: format!("io error: {}", err),
diff --git a/src/util.rs b/src/util.rs
index 24a87f8..3a6eeb0 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,7 +1,28 @@
-use std::mem;
-use std::num::Int;
+use std::{mem, fmt};
+use std::error::Error;
 use std::io::{self, Read, Write};
 
+#[derive(Debug)]
+pub struct SurugaError {
+    pub desc: &'static str,
+    pub cause: Option<Box<Error + Send + Sync + 'static>>,
+}
+
+impl fmt::Display for SurugaError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        <Self as fmt::Debug>::fmt(self, fmt)
+    }
+}
+
+impl Error for SurugaError {
+    fn description(&self) -> &str {
+        self.desc
+    }
+
+    // FIXME: implement fn cause(&self) -> Option<&Error>
+    // This runs into difficulties with differing trait bounds.
+}
+
 /// constant-time compare function.
 /// `a` and `b` may be SECRET, but the length is known.
 /// precondition: `a.len() == b.len()`
@@ -62,7 +83,10 @@ pub trait ReadExt: Read {
         while pos < len {
             let num_bytes = try!(self.read(&mut buf[pos..]));
             if num_bytes == 0 {
-                return Err(io::Error::new(io::ErrorKind::Other, "EOF during `fill_exact`", None));
+                return Err(io::Error::new(io::ErrorKind::Other, SurugaError {
+                    desc: "EOF during `fill_exact`",
+                    cause: None
+                }));
             }
             pos += num_bytes;
         }