more

Cargo.lock

@@ -249,6 +249,7 @@ name = "fakessh"
 version = "0.1.0"
 dependencies = [
  "eyre",
+ "hex-literal",
  "ssh-transport",
  "tokio",
  "tracing",
@@ -700,6 +701,7 @@ dependencies = [
  "rand",
  "rand_core",
  "sha2",
+ "subtle",
  "tracing",
  "tracing-subscriber",
  "x25519-dalek",

Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 
 [dependencies]
 eyre = "0.6.12"
+hex-literal = "0.4.1"
 ssh-transport = { path = "./ssh-transport" }
 
 tokio = { version = "1.39.2", features = ["full"] }

ssh-transport/Cargo.toml

@@ -12,6 +12,7 @@ poly1305 = "0.8.0"
 rand = "0.8.5"
 rand_core = "0.6.4"
 sha2 = "0.10.8"
+subtle = "2.6.1"
 tracing = "0.1.40"
 tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
 x25519-dalek = "2.0.1"

ssh-transport/src/keys.rs

@@ -1,6 +1,6 @@
 use chacha20::cipher::{KeyInit, KeyIvInit, StreamCipher, StreamCipherSeek};
-use poly1305::universal_hash::UniversalHash;
 use sha2::Digest;
+use subtle::ConstantTimeEq;
 
 use crate::{
     packet::{Packet, RawPacket},
@@ -73,17 +73,18 @@ impl Decryptor for Session {
 
 /// Derive a key from the shared secret K and exchange hash H.
 /// <https://datatracker.ietf.org/doc/html/rfc4253#section-7.2>
-fn derive_key<const KEY_LEN: usize>(
+fn derive_key(k: [u8; 32], h: [u8; 32], letter: &str, session_id: [u8; 32]) -> [u8; 64] {
-    k: [u8; 32],
-    h: [u8; 32],
-    letter: &str,
-    session_id: [u8; 32],
-) -> [u8; KEY_LEN] {
     let sha2len = sha2::Sha256::output_size();
+    let mut output = [0; 64];
 
-    let mut output = [0; KEY_LEN];
+    //let mut hash = sha2::Sha256::new();
+    //encode_mpint_for_hash(&k, |data| hash.update(data));
+    //hash.update(h);
+    //hash.update(letter.as_bytes());
+    //hash.update(session_id);
+    //output[..sha2len].copy_from_slice(&hash.finalize());
 
-    for i in 0..(KEY_LEN / sha2len) {
+    for i in 0..(64 / sha2len) {
         let mut hash = sha2::Sha256::new();
         encode_mpint_for_hash(&k, |data| hash.update(data));
         hash.update(h);
@@ -91,8 +92,9 @@ fn derive_key<const KEY_LEN: usize>(
         if i == 0 {
             hash.update(letter.as_bytes());
             hash.update(session_id);
+        } else {
+            hash.update(&output[..(i * sha2len)]);
         }
-        hash.update(&output[..(i * sha2len)]);
 
         output[(i * sha2len)..][..sha2len].copy_from_slice(&hash.finalize())
     }
@@ -135,6 +137,7 @@ impl SshChaCha20Poly1305 {
     }
 
     fn decrypt_len(&self, bytes: &mut [u8], packet_number: u64) {
+        eprintln!("encrypted len: {:x?}", &bytes);
         // <https://github.com/openssh/openssh-portable/blob/1ec0a64c5dc57b8a2053a93b5ef0d02ff8598e5c/PROTOCOL.chacha20poly1305>
         let mut cipher = SshChaCha20::new(&self.header_key, &packet_number.to_be_bytes().into());
         cipher.apply_keystream(bytes);
@@ -156,23 +159,36 @@ impl SshChaCha20Poly1305 {
         //)
         //.map_err(|err| crate::client_error!("failed to decrypt invalid poly1305 MAC: {err}"))?;
 
-        let mut cipher = SshChaCha20::new(&self.main_key2, &packet_number.to_be_bytes().into());
+        let mut cipher = <chacha20::ChaCha20Legacy as chacha20::cipher::KeyIvInit>::new(
-
+            &self.main_key2,
-        let mut mac = {
+            &packet_number.to_be_bytes().into(),
-            let mut poly1305_key = [0; poly1305::KEY_SIZE];
+        );
-            cipher.apply_keystream(&mut poly1305_key);
-            poly1305::Poly1305::new(&poly1305_key.into())
-        };
 
         let tag_offset = bytes.full_packet().len() - 16;
-        let aead_payload = &bytes.full_packet()[..tag_offset];
+        let data_to_mac = &bytes.full_packet()[..tag_offset];
-        mac.update_padded(aead_payload);
+        eprintln!("data_to_mac: {:x?}", &data_to_mac);
+
+        let mac = {
+            let mut poly1305_key = [0; poly1305::KEY_SIZE];
+            cipher.apply_keystream(&mut poly1305_key);
+            poly1305::Poly1305::new(&poly1305_key.into()).compute_unpadded(data_to_mac)
+        };
+
         let read_tag = poly1305::Tag::from_slice(&bytes.full_packet()[tag_offset..]);
 
-        mac.verify(read_tag)
+        eprintln!("expected MAC: {mac:x?}");
-            .map_err(|err| crate::client_error!("failed to decrypt invalid poly1305 MAC: {err}"))?;
+        eprintln!("found    MAC: {read_tag:x?}");
 
-        cipher.seek(1);
+        if !bool::from(mac.ct_eq(read_tag)) {
+            return Err(crate::client_error!(
+                "failed to decrypt: invalid poly1305 MAC"
+            ));
+        }
+
+        //mac.verify(read_tag)
+        //    .map_err(|err| crate::client_error!("failed to decrypt invalid poly1305 MAC: {err}"))?;
+
+        cipher.seek(64);
 
         todo!()
     }

ssh-transport/src/packet.rs

@@ -325,6 +325,8 @@ impl PacketParser {
                 let packet_length = u32::from_be_bytes(len_to_decrypt);
                 let packet_length = packet_length.try_into().unwrap();
 
+                dbg!(packet_length);
+
                 self.packet_length = Some(packet_length);
 
                 // We have the data.