diff --git a/src/algorithm.rs b/src/algorithm.rs
index 4e9996b..ecf2595 100644
--- a/src/algorithm.rs
+++ b/src/algorithm.rs
@@ -215,9 +215,10 @@ impl FromStr for MacAlgorithm {
         use self::MacAlgorithm::*;
         match s
         {
-            "hmac-sha1" => Ok(MacAlgorithm::HMAC_SHA1),
-            "hmac-sha2-256" => Ok(MacAlgorithm::HMAC_SHA2_256),
-            "hmac-sha2-512" => Ok(MacAlgorithm::HMAC_SHA2_512),
+            "hmac-sha1" => Ok(HMAC_SHA1),
+            "hmac-sha2-256" => Ok(HMAC_SHA2_256),
+            "hmac-sha2-512" => Ok(HMAC_SHA2_512),
+            "none" => Ok(MacAlgorithm::None),
             _ => {
                 debug!("Unknown mac algorithm: {}", s);
                 Err(())
diff --git a/src/bin/ssh-keygen.rs b/src/bin/ssh-keygen.rs
index 2974297..d301d48 100644
--- a/src/bin/ssh-keygen.rs
+++ b/src/bin/ssh-keygen.rs
@@ -1,6 +1,5 @@
 extern crate ssh;
 use std::fs::File;
-use std::io::prelude::*;
 
 use ssh::public_key;
 
diff --git a/src/connection.rs b/src/connection.rs
index a92906a..31a9847 100644
--- a/src/connection.rs
+++ b/src/connection.rs
@@ -1,4 +1,3 @@
-use std::borrow::BorrowMut;
 use std::io::{self, BufRead, BufReader, Read, Write};
 use std::sync::Arc;
 
@@ -20,7 +19,6 @@ enum ConnectionState {
 #[derive(Clone)]
 pub enum ConnectionType {
     Server(Arc<ServerConfig>),
-    Client,
 }
 
 #[derive(Default, Debug)]
@@ -88,7 +86,7 @@ impl<'a> Connection {
             trace!("Packet {} received: {:?}", self.seq.0, packet);
             self.process(packet)?;
 
-            self.seq.0 += 1;
+            self.seq.0.wrapping_add(1);
         }
     }
 
@@ -109,7 +107,7 @@ impl<'a> Connection {
             packet.write_to(&mut self.stream)?;
         }
 
-        self.seq.1 += 1;
+        self.seq.1.wrapping_add(1);
 
         if let Some((_, ref mut mac)) = self.mac {
             let mut sig = vec![0; mac.size()];
@@ -322,7 +320,7 @@ impl<'a> Connection {
 
                 if want_reply {
                     let mut res = Packet::new(MessageType::ChannelSuccess);
-                    res.with_writer(&|w| w.write_uint32(0));
+                    res.with_writer(&|w| w.write_uint32(0))?;
                     self.send(res)?;
                 }
 
@@ -340,7 +338,7 @@ impl<'a> Connection {
                     Ok(())
                 })?;
 
-                self.send(res);
+                self.send(res)?;
 
                 debug!(
                     "Channel {} Data ({} bytes): {:?}",
diff --git a/src/key_exchange/curve25519.rs b/src/key_exchange/curve25519.rs
index 8e3457b..f4c7481 100644
--- a/src/key_exchange/curve25519.rs
+++ b/src/key_exchange/curve25519.rs
@@ -86,7 +86,7 @@ impl KeyExchange for Curve25519 {
                     buf.write_mpint(BigInt::from_bytes_be(
                         Sign::Plus,
                         &curve25519::curve25519(&server_secret, &client_public),
-                    ));
+                    )).ok();
                     buf
                 };
 
@@ -106,10 +106,10 @@ impl KeyExchange for Curve25519 {
                         ];
 
                     for item in items.iter() {
-                        buf.write_bytes(item);
+                        buf.write_bytes(item).ok();
                     }
 
-                    buf.write_raw_bytes(&shared_secret);
+                    buf.write_raw_bytes(&shared_secret).ok();
 
                     buf
                 };
diff --git a/src/key_exchange/mod.rs b/src/key_exchange/mod.rs
index f6c27e2..7300223 100644
--- a/src/key_exchange/mod.rs
+++ b/src/key_exchange/mod.rs
@@ -1,8 +1,8 @@
 mod curve25519;
-mod dh_group_sha1;
+// mod dh_group_sha1;
 
 pub use self::curve25519::Curve25519;
-pub use self::dh_group_sha1::DhGroupSha1;
+// pub use self::dh_group_sha1::DhGroupSha1;
 
 use connection::Connection;
 use packet::Packet;
diff --git a/src/public_key/ed25519.rs b/src/public_key/ed25519.rs
index 8430ed0..4bacb08 100644
--- a/src/public_key/ed25519.rs
+++ b/src/public_key/ed25519.rs
@@ -103,8 +103,8 @@ impl KeyPair for Ed25519KeyPair {
         if let Some(private_key) = self.private {
             let mut result = Vec::new();
             let sig = ed25519::signature(data, &private_key);
-            result.write_string("ssh-ed25519").or(Err(()));
-            result.write_bytes(&sig).or(Err(()));
+            result.write_string("ssh-ed25519").or(Err(()))?;
+            result.write_bytes(&sig).or(Err(()))?;
             Ok(result)
         }
         else {