pluggable encryption

ssh-transport/src/keys.rs

@@ -8,14 +8,23 @@ use crate::{
     Msg, Result, SshRng,
 };
 
+pub trait AlgorithmName {
+    fn name(&self) -> &'static str;
+}
+
 #[derive(Clone, Copy)]
 pub struct KexAlgorithm {
-    pub name: &'static str,
+    name: &'static str,
     pub exchange: fn(
         client_public_key: &[u8],
         random: &mut (dyn SshRng + Send + Sync),
     ) -> Result<KexAlgorithmOutput>,
 }
+impl AlgorithmName for KexAlgorithm {
+    fn name(&self) -> &'static str {
+        self.name
+    }
+}
 pub struct KexAlgorithmOutput {
     /// K
     pub shared_secret: Vec<u8>,
@@ -69,15 +78,47 @@ pub const KEX_ECDH_SHA2_NISTP256: KexAlgorithm = KexAlgorithm {
     },
 };
 
+#[derive(Clone, Copy)]
+pub struct EncryptionAlgorithm {
+    name: &'static str,
+    decrypt_len: fn(keys: &[u8], bytes: &mut [u8], packet_number: u64),
+    decrypt_packet: fn(keys: &[u8], bytes: RawPacket, packet_number: u64) -> Result<Packet>,
+    encrypt_packet: fn(keys: &[u8], packet: Packet, packet_number: u64) -> EncryptedPacket,
+}
+impl AlgorithmName for EncryptionAlgorithm {
+    fn name(&self) -> &'static str {
+        self.name
+    }
+}
+pub const ENC_CHACHA20POLY1305: EncryptionAlgorithm = EncryptionAlgorithm {
+    name: "chacha20-poly1305@openssh.com",
+    decrypt_len: |keys, bytes, packet_number| {
+        let alg = SshChaCha20Poly1305::from_keys(keys);
+        alg.decrypt_len(bytes, packet_number)
+    },
+    decrypt_packet: |keys, bytes, packet_number| {
+        let alg = SshChaCha20Poly1305::from_keys(keys);
+        alg.decrypt_packet(bytes, packet_number)
+    },
+    encrypt_packet: |keys, packet, packet_number| {
+        let alg = SshChaCha20Poly1305::from_keys(keys);
+        alg.encrypt_packet(packet, packet_number)
+    },
+};
+
 pub struct AlgorithmNegotiation<T> {
-    pub supported: Vec<(&'static str, T)>,
+    pub supported: Vec<T>,
 }
 
-impl<T: Copy> AlgorithmNegotiation<T> {
-    pub fn find<'a>(&self, client_supports: &str) -> Result<T> {
+impl<T: AlgorithmName> AlgorithmNegotiation<T> {
+    pub fn find<'a>(mut self, client_supports: &str) -> Result<T> {
         for client_alg in client_supports.split(',') {
-            if let Some(alg) = self.supported.iter().find(|alg| alg.0 == client_alg) {
-                return Ok(alg.1);
+            if let Some(alg) = self
+                .supported
+                .iter()
+                .position(|alg| alg.name() == client_alg)
+            {
+                return Ok(self.supported.remove(alg));
             }
         }
 
@@ -89,8 +130,10 @@ impl<T: Copy> AlgorithmNegotiation<T> {
 
 pub(crate) struct Session {
     session_id: [u8; 32],
-    encryption_key_client_to_server: SshChaCha20Poly1305,
-    encryption_key_server_to_client: SshChaCha20Poly1305,
+    encryption_key_client_to_server: [u8; 64],
+    encryption_client_to_server: EncryptionAlgorithm,
+    encryption_key_server_to_client: [u8; 64],
+    encryption_server_to_client: EncryptionAlgorithm,
 }
 
 pub(crate) trait Keys: Send + Sync + 'static {
@@ -100,7 +143,13 @@ pub(crate) trait Keys: Send + Sync + 'static {
     fn encrypt_packet_to_msg(&mut self, packet: Packet, packet_number: u64) -> Msg;
 
     fn additional_mac_len(&self) -> usize;
-    fn rekey(&mut self, h: [u8; 32], k: &[u8]) -> Result<(), ()>;
+    fn rekey(
+        &mut self,
+        h: [u8; 32],
+        k: &[u8],
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
+    ) -> Result<(), ()>;
 }
 
 pub(crate) struct Plaintext;
@@ -115,29 +164,52 @@ impl Keys for Plaintext {
     fn additional_mac_len(&self) -> usize {
         0
     }
-    fn rekey(&mut self, _: [u8; 32], _: &[u8]) -> Result<(), ()> {
+    fn rekey(
+        &mut self,
+        _: [u8; 32],
+        _: &[u8],
+        _: EncryptionAlgorithm,
+        _: EncryptionAlgorithm,
+    ) -> Result<(), ()> {
         Err(())
     }
 }
 
 impl Session {
-    pub(crate) fn new(h: [u8; 32], k: &[u8]) -> Self {
-        Self::from_keys(h, h, k)
+    pub(crate) fn new(
+        h: [u8; 32],
+        k: &[u8],
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
+    ) -> Self {
+        Self::from_keys(
+            h,
+            h,
+            k,
+            encryption_client_to_server,
+            encryption_server_to_client,
+        )
     }
 
     /// <https://datatracker.ietf.org/doc/html/rfc4253#section-7.2>
-    fn from_keys(session_id: [u8; 32], h: [u8; 32], k: &[u8]) -> Self {
-        let encryption_key_client_to_server =
-            SshChaCha20Poly1305::new(derive_key(k, h, "C", session_id));
-        let encryption_key_server_to_client =
-            SshChaCha20Poly1305::new(derive_key(k, h, "D", session_id));
+    fn from_keys(
+        session_id: [u8; 32],
+        h: [u8; 32],
+        k: &[u8],
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
+    ) -> Self {
+        let encryption_key_client_to_server = derive_key(k, h, "C", session_id);
+        let encryption_key_server_to_client = derive_key(k, h, "D", session_id);
 
         Self {
             session_id,
             // client_to_server_iv: derive("A").into(),
             // server_to_client_iv: derive("B").into(),
             encryption_key_client_to_server,
+            encryption_client_to_server,
             encryption_key_server_to_client,
+            encryption_server_to_client,
             // integrity_key_client_to_server: derive("E").into(),
             // integrity_key_server_to_client: derive("F").into(),
         }
@@ -146,19 +218,27 @@ impl Session {
 
 impl Keys for Session {
     fn decrypt_len(&mut self, bytes: &mut [u8; 4], packet_number: u64) {
-        self.encryption_key_client_to_server
-            .decrypt_len(bytes, packet_number);
+        (self.encryption_client_to_server.decrypt_len)(
+            &self.encryption_key_client_to_server,
+            bytes,
+            packet_number,
+        );
     }
 
     fn decrypt_packet(&mut self, bytes: RawPacket, packet_number: u64) -> Result<Packet> {
-        self.encryption_key_client_to_server
-            .decrypt_packet(bytes, packet_number)
+        (self.encryption_client_to_server.decrypt_packet)(
+            &self.encryption_key_client_to_server,
+            bytes,
+            packet_number,
+        )
     }
 
     fn encrypt_packet_to_msg(&mut self, packet: Packet, packet_number: u64) -> Msg {
-        let packet = self
-            .encryption_key_server_to_client
-            .encrypt_packet(packet, packet_number);
+        let packet = (self.encryption_server_to_client.encrypt_packet)(
+            &self.encryption_key_server_to_client,
+            packet,
+            packet_number,
+        );
         Msg(MsgKind::EncryptedPacket(packet))
     }
 
@@ -166,8 +246,20 @@ impl Keys for Session {
         poly1305::BLOCK_SIZE
     }
 
-    fn rekey(&mut self, h: [u8; 32], k: &[u8]) -> Result<(), ()> {
-        *self = Self::from_keys(self.session_id, h, k);
+    fn rekey(
+        &mut self,
+        h: [u8; 32],
+        k: &[u8],
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
+    ) -> Result<(), ()> {
+        *self = Self::from_keys(
+            self.session_id,
+            h,
+            k,
+            encryption_client_to_server,
+            encryption_server_to_client,
+        );
         Ok(())
     }
 }
@@ -225,10 +317,11 @@ struct SshChaCha20Poly1305 {
 }
 
 impl SshChaCha20Poly1305 {
-    fn new(key: [u8; 64]) -> Self {
+    fn from_keys(keys: &[u8]) -> Self {
+        assert_eq!(keys.len(), 64);
         Self {
-            main_key: <[u8; 32]>::try_from(&key[..32]).unwrap().into(),
-            header_key: <[u8; 32]>::try_from(&key[32..]).unwrap().into(),
+            main_key: <[u8; 32]>::try_from(&keys[..32]).unwrap().into(),
+            header_key: <[u8; 32]>::try_from(&keys[32..]).unwrap().into(),
         }
     }
 
@@ -241,7 +334,7 @@ impl SshChaCha20Poly1305 {
         cipher.apply_keystream(bytes);
     }
 
-    fn decrypt_packet(&mut self, mut bytes: RawPacket, packet_number: u64) -> Result<Packet> {
+    fn decrypt_packet(&self, mut bytes: RawPacket, packet_number: u64) -> Result<Packet> {
         // <https://github.com/openssh/openssh-portable/blob/1ec0a64c5dc57b8a2053a93b5ef0d02ff8598e5c/PROTOCOL.chacha20poly1305>
 
         let mut cipher = <SshChaCha20 as chacha20::cipher::KeyIvInit>::new(
@@ -276,7 +369,7 @@ impl SshChaCha20Poly1305 {
         Packet::from_full(encrypted_packet_content)
     }
 
-    fn encrypt_packet(&mut self, packet: Packet, packet_number: u64) -> EncryptedPacket {
+    fn encrypt_packet(&self, packet: Packet, packet_number: u64) -> EncryptedPacket {
         let mut bytes = packet.to_bytes(false);
 
         // Prepare the main cipher.

ssh-transport/src/lib.rs

@@ -6,7 +6,7 @@ use core::str;
 use std::{collections::VecDeque, mem::take};
 
 use ed25519_dalek::ed25519::signature::Signer;
-use keys::AlgorithmNegotiation;
+use keys::{AlgorithmName, AlgorithmNegotiation, EncryptionAlgorithm};
 use packet::{
     DhKeyExchangeInitReplyPacket, KeyExchangeEcDhInitPacket, KeyExchangeInitPacket, Packet,
     PacketTransport, SshPublicKey, SshSignature,
@@ -64,10 +64,14 @@ enum ServerState {
         client_kexinit: Vec<u8>,
         server_kexinit: Vec<u8>,
         kex_algorithm: keys::KexAlgorithm,
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
     },
     NewKeys {
         h: [u8; 32],
         k: Vec<u8>,
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
     },
     ServiceRequest,
     Open,
@@ -163,41 +167,37 @@ impl ServerConnection {
                 } => {
                     let kex = KeyExchangeInitPacket::parse(&packet.payload)?;
 
-                    let require_algorithm = |expected: &'static str,
-                                             list: NameList<'_>|
-                     -> Result<&'static str> {
-                        if list.iter().any(|alg| alg == expected) {
-                            Ok(expected)
-                        } else {
-                            Err(client_error!(
+                    let require_algorithm =
+                        |expected: &'static str, list: NameList<'_>| -> Result<&'static str> {
+                            if list.iter().any(|alg| alg == expected) {
+                                Ok(expected)
+                            } else {
+                                Err(client_error!(
                                 "client does not support algorithm {expected}. supported: {list:?}",
                             ))
-                        }
-                    };
+                            }
+                        };
 
                     let kex_algorithms = AlgorithmNegotiation {
-                        supported: vec![(
-                            keys::KEX_CURVE_25519_SHA256.name,
-                            keys::KEX_CURVE_25519_SHA256,
-                        ), (
-                            keys::KEX_ECDH_SHA2_NISTP256.name,
-                            keys::KEX_ECDH_SHA2_NISTP256,
-                        )],
+                        supported: vec![keys::KEX_CURVE_25519_SHA256, keys::KEX_ECDH_SHA2_NISTP256],
                     };
                     let kex_algorithm = kex_algorithms.find(kex.kex_algorithms.0)?;
 
                     let server_host_key_algorithm =
                         require_algorithm("ssh-ed25519", kex.server_host_key_algorithms)?;
 
+                    let encryption_algorithms_client_to_server = AlgorithmNegotiation {
+                        supported: vec![keys::ENC_CHACHA20POLY1305],
+                    };
+                    let encryption_algorithms_server_to_client = AlgorithmNegotiation {
+                        supported: vec![keys::ENC_CHACHA20POLY1305],
+                    };
+
                     // TODO: support aes256-gcm@openssh.com
-                    let encryption_algorithm_client_to_server = require_algorithm(
-                        "chacha20-poly1305@openssh.com",
-                        kex.encryption_algorithms_client_to_server,
-                    )?;
-                    let encryption_algorithm_server_to_client = require_algorithm(
-                        "chacha20-poly1305@openssh.com",
-                        kex.encryption_algorithms_server_to_client,
-                    )?;
+                    let encryption_client_to_server = encryption_algorithms_client_to_server
+                        .find(kex.encryption_algorithms_client_to_server.0)?;
+                    let encryption_server_to_client = encryption_algorithms_server_to_client
+                        .find(kex.encryption_algorithms_server_to_client.0)?;
                     let mac_algorithm_client_to_server =
                         require_algorithm("hmac-sha2-256", kex.mac_algorithms_client_to_server)?;
                     let mac_algorithm_server_to_client =
@@ -218,13 +218,13 @@ impl ServerConnection {
 
                     let server_kexinit = KeyExchangeInitPacket {
                         cookie: [0; 16],
-                        kex_algorithms: NameList::one(kex_algorithm.name),
+                        kex_algorithms: NameList::one(kex_algorithm.name()),
                         server_host_key_algorithms: NameList::one(server_host_key_algorithm),
                         encryption_algorithms_client_to_server: NameList::one(
-                            encryption_algorithm_client_to_server,
+                            encryption_client_to_server.name(),
                         ),
                         encryption_algorithms_server_to_client: NameList::one(
-                            encryption_algorithm_server_to_client,
+                            encryption_server_to_client.name(),
                         ),
                         mac_algorithms_client_to_server: NameList::one(
                             mac_algorithm_client_to_server,
@@ -253,6 +253,8 @@ impl ServerConnection {
                         client_kexinit: packet.payload,
                         server_kexinit: server_kexinit_payload,
                         kex_algorithm,
+                        encryption_client_to_server,
+                        encryption_server_to_client,
                     };
                 }
                 ServerState::DhKeyInit {
@@ -260,6 +262,8 @@ impl ServerConnection {
                     client_kexinit,
                     server_kexinit,
                     kex_algorithm,
+                    encryption_client_to_server,
+                    encryption_server_to_client,
                 } => {
                     // TODO: move to keys.rs
                     let dh = KeyExchangeEcDhInitPacket::parse(&packet.payload)?;
@@ -333,9 +337,16 @@ impl ServerConnection {
                     self.state = ServerState::NewKeys {
                         h: hash.into(),
                         k: shared_secret,
+                        encryption_client_to_server: *encryption_client_to_server,
+                        encryption_server_to_client: *encryption_server_to_client,
                     };
                 }
-                ServerState::NewKeys { h, k } => {
+                ServerState::NewKeys {
+                    h,
+                    k,
+                    encryption_client_to_server,
+                    encryption_server_to_client,
+                } => {
                     if packet.payload != [Packet::SSH_MSG_NEWKEYS] {
                         return Err(client_error!("did not send SSH_MSG_NEWKEYS"));
                     }
@@ -343,7 +354,12 @@ impl ServerConnection {
                     self.packet_transport.queue_packet(Packet {
                         payload: vec![Packet::SSH_MSG_NEWKEYS],
                     });
-                    self.packet_transport.set_key(*h, k);
+                    self.packet_transport.set_key(
+                        *h,
+                        k,
+                        *encryption_client_to_server,
+                        *encryption_server_to_client,
+                    );
                     self.state = ServerState::ServiceRequest {};
                 }
                 ServerState::ServiceRequest => {

ssh-transport/src/packet.rs

@@ -3,7 +3,7 @@ mod ctors;
 use std::collections::VecDeque;
 
 use crate::client_error;
-use crate::keys::{Keys, Plaintext, Session};
+use crate::keys::{EncryptionAlgorithm, Keys, Plaintext, Session};
 use crate::parse::{NameList, Parser, Writer};
 use crate::Result;
 
@@ -101,9 +101,25 @@ impl PacketTransport {
         self.send_packets.pop_front()
     }
 
-    pub(crate) fn set_key(&mut self, h: [u8; 32], k: &[u8]) {
-        if let Err(()) = self.keys.rekey(h, k) {
-            self.keys = Box::new(Session::new(h, k));
+    pub(crate) fn set_key(
+        &mut self,
+        h: [u8; 32],
+        k: &[u8],
+        encryption_client_to_server: EncryptionAlgorithm,
+        encryption_server_to_client: EncryptionAlgorithm,
+    ) {
+        if let Err(()) = self.keys.rekey(
+            h,
+            k,
+            encryption_client_to_server,
+            encryption_server_to_client,
+        ) {
+            self.keys = Box::new(Session::new(
+                h,
+                k,
+                encryption_client_to_server,
+                encryption_server_to_client,
+            ));
         }
     }
 }