Keep the shared secret around

src/dnscrypt.rs

@@ -4,17 +4,26 @@ use crate::dnscrypt_certs::*;
 use crate::errors::*;
 
 use libsodium_sys::*;
+use rand::prelude::*;
 use std::ffi::CStr;
 use std::ptr;
 
 pub const DNSCRYPT_CLIENT_MAGIC_SIZE: usize = 8;
 pub const DNSCRYPT_CLIENT_PK_SIZE: usize = 32;
-pub const DNSCRYPT_CLIENT_NONCE_SIZE: usize = 12;
+pub const DNSCRYPT_CLIENT_NONCE_SIZE: usize =
+    crypto_box_curve25519xchacha20poly1305_HALFNONCEBYTES as usize;
 
 pub fn decrypt(
     wrapped_packet: &[u8],
     dnscrypt_encryption_params_set: &[DNSCryptEncryptionParams],
-) -> Result<Vec<u8>, Error> {
+) -> Result<
+    (
+        SharedKey,
+        [u8; crypto_box_curve25519xchacha20poly1305_NONCEBYTES as usize],
+        Vec<u8>,
+    ),
+    Error,
+> {
     ensure!(
         wrapped_packet.len()
             >= DNSCRYPT_CLIENT_MAGIC_SIZE
@@ -37,11 +46,20 @@ pub fn decrypt(
         .find(|p| p.client_magic() == client_magic)
         .ok_or_else(|| format_err!("Client magic not found"))?;
 
-    let mut nonce = vec![0u8; crypto_box_curve25519xchacha20poly1305_NONCEBYTES as usize];
-    &mut nonce[..crypto_box_curve25519xchacha20poly1305_HALFNONCEBYTES]
-        .copy_from_slice(client_nonce);
+    let mut nonce = [0u8; crypto_box_curve25519xchacha20poly1305_NONCEBYTES as usize];
+    &mut nonce[..DNSCRYPT_CLIENT_NONCE_SIZE].copy_from_slice(client_nonce);
     let resolver_kp = dnscrypt_encryption_params.resolver_kp();
-    let shared_secret = resolver_kp.compute_shared_key(client_pk)?;
-    let packet = shared_secret.decrypt(&nonce, encrypted_packet)?;
-    Ok(packet)
+    let shared_key = resolver_kp.compute_shared_key(client_pk)?;
+    let packet = shared_key.decrypt(&nonce, encrypted_packet)?;
+    rand::thread_rng().fill_bytes(&mut nonce[DNSCRYPT_CLIENT_NONCE_SIZE..]);
+
+    Ok((shared_key, nonce, packet))
+}
+
+pub fn encrypt(
+    packet: &[u8],
+    shared_key: &SharedKey,
+    nonce: &[u8; crypto_box_curve25519xchacha20poly1305_NONCEBYTES as usize],
+) {
+    //
 }

src/main.rs

@@ -72,7 +72,11 @@ enum ClientCtx {
     Tcp(TcpClientCtx),
 }
 
-async fn respond_to_query(client_ctx: ClientCtx, packet: Vec<u8>) -> Result<(), Error> {
+async fn respond_to_query(
+    client_ctx: ClientCtx,
+    packet: Vec<u8>,
+    shared_key: Option<SharedKey>,
+) -> Result<(), Error> {
     ensure!(dns::is_response(&packet), "Packet is not a response");
     match client_ctx {
         ClientCtx::Udp(client_ctx) => {
@@ -98,21 +102,21 @@ async fn handle_client_query(
     client_ctx: ClientCtx,
     encrypted_packet: Vec<u8>,
 ) -> Result<(), Error> {
-    let packet = dnscrypt::decrypt(&encrypted_packet, &globals.dnscrypt_encryption_params_set);
-    let mut packet = match packet {
-        Ok(packet) => packet,
-        Err(_) => {
-            let packet = encrypted_packet;
-            if let Some(synth_packet) = serve_certificates(
-                &packet,
-                &globals.provider_name,
-                &globals.dnscrypt_encryption_params_set,
-            )? {
-                return respond_to_query(client_ctx, synth_packet).await;
+    let (shared_key, nonce, mut packet) =
+        match dnscrypt::decrypt(&encrypted_packet, &globals.dnscrypt_encryption_params_set) {
+            Ok(x) => x,
+            Err(_) => {
+                let packet = encrypted_packet;
+                if let Some(synth_packet) = serve_certificates(
+                    &packet,
+                    &globals.provider_name,
+                    &globals.dnscrypt_encryption_params_set,
+                )? {
+                    return respond_to_query(client_ctx, synth_packet, None).await;
+                }
+                bail!("Unencrypted query");
             }
-            bail!("Unencrypted query");
-        }
-    };
+        };
     ensure!(packet.len() >= DNS_HEADER_SIZE, "Short packet");
     ensure!(qdcount(&packet) == 1, "No question");
     ensure!(
@@ -171,7 +175,7 @@ async fn handle_client_query(
         );
     }
     dns::set_tid(&mut response, original_tid);
-    respond_to_query(client_ctx, response).await
+    respond_to_query(client_ctx, response, Some(shared_key)).await
 }
 
 async fn tcp_acceptor(globals: Arc<Globals>, tcp_listener: TcpListener) -> Result<(), Error> {