Implement the obfuscated MTProto transport

Details at: https://core.telegram.org/mtproto/mtproto-transports#transport-obfuscation
Lonami · Dec 21, 2024 · ae3702e · ae3702e
1 parent bb46ef0
commit ae3702e
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Showing 10 changed files with 213 additions and 26 deletions.
diff --git a/lib/grammers-crypto/Cargo.toml b/lib/grammers-crypto/Cargo.toml
@@ -23,6 +23,7 @@ pbkdf2 = "0.12.2"
 sha1 = "0.10.6"
 sha2 = "0.10.8"
 num-traits = "0.2.19"
+ctr = "0.9.2"
 
 [dev-dependencies]
 bencher = "0.1.5"

diff --git a/lib/grammers-crypto/DEPS.md b/lib/grammers-crypto/DEPS.md
@@ -48,3 +48,7 @@ Used for methods relied on by the 2-factor offered by Telegram.
 ## toml
 
 Used to test that this file lists all dependencies from `Cargo.toml`.
+
+## ctr
+
+Used for the AES-CTR mode needed for the obfuscated MTProto transport.
diff --git a/lib/grammers-crypto/src/lib.rs b/lib/grammers-crypto/src/lib.rs
@@ -13,6 +13,7 @@ mod auth_key;
 pub mod deque_buffer;
 pub mod factorize;
 pub mod hex;
+pub mod obfuscated;
 pub mod rsa;
 pub mod sha;
 pub mod two_factor_auth;

diff --git a/lib/grammers-crypto/src/obfuscated.rs b/lib/grammers-crypto/src/obfuscated.rs
@@ -0,0 +1,43 @@
+// Copyright 2020 - developers of the `grammers` project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use aes::cipher::{generic_array::GenericArray, KeyIvInit, StreamCipher};
+
+/// This implements the AES-256-CTR cipher used by Telegram to encrypt data
+/// when using the obfuscated transport.
+///
+/// You're not supposed to use this directly, You're probably looking for the
+/// actual implementation in `grammers-mtproto`.
+pub struct ObfuscatedCipher {
+    rx: ctr::Ctr128BE<aes::Aes256>,
+    tx: ctr::Ctr128BE<aes::Aes256>,
+}
+
+impl ObfuscatedCipher {
+    pub fn new(init: &[u8; 64]) -> Self {
+        let init_rev = init.iter().copied().rev().collect::<Vec<_>>();
+        Self {
+            rx: ctr::Ctr128BE::<aes::Aes256>::new(
+                GenericArray::from_slice(&init_rev[8..40]),
+                GenericArray::from_slice(&init_rev[40..56]),
+            ),
+            tx: ctr::Ctr128BE::<aes::Aes256>::new(
+                GenericArray::from_slice(&init[8..40]),
+                GenericArray::from_slice(&init[40..56]),
+            ),
+        }
+    }
+
+    pub fn encrypt(&mut self, buffer: &mut [u8]) {
+        self.tx.apply_keystream(buffer);
+    }
+
+    pub fn decrypt(&mut self, buffer: &mut [u8]) {
+        self.rx.apply_keystream(buffer);
+    }
+}
diff --git a/lib/grammers-mtproto/src/transport/abridged.rs b/lib/grammers-mtproto/src/transport/abridged.rs
@@ -5,7 +5,7 @@
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-use super::{Error, Transport, UnpackedOffset};
+use super::{Error, Tagged, Transport, UnpackedOffset};
 use grammers_crypto::DequeBuffer;
 
 /// The lightest MTProto transport protocol available. This is an
@@ -63,7 +63,7 @@ impl Transport for Abridged {
         }
     }
 
-    fn unpack(&mut self, buffer: &[u8]) -> Result<UnpackedOffset, Error> {
+    fn unpack(&mut self, buffer: &mut [u8]) -> Result<UnpackedOffset, Error> {
         if buffer.is_empty() {
             return Err(Error::MissingBytes);
         }
@@ -112,6 +112,13 @@ impl Transport for Abridged {
     }
 }
 
+impl Tagged for Abridged {
+    fn init_tag(&mut self) -> [u8; 4] {
+        self.init = true;
+        [0xef, 0xef, 0xef, 0xef]
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -160,7 +167,7 @@ mod tests {
         let mut transport = Abridged::new();
         let mut buffer = DequeBuffer::with_capacity(1, 0);
         buffer.extend([1]);
-        assert_eq!(transport.unpack(&buffer[..]), Err(Error::MissingBytes));
+        assert_eq!(transport.unpack(&mut buffer[..]), Err(Error::MissingBytes));
     }
 
     #[test]
@@ -169,7 +176,7 @@ mod tests {
         let orig = buffer.clone();
         transport.pack(&mut buffer);
         let n = 1; // init byte
-        let offset = transport.unpack(&buffer[n..][..]).unwrap();
+        let offset = transport.unpack(&mut buffer[n..][..]).unwrap();
         assert_eq!(&buffer[n..][offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -187,12 +194,12 @@ mod tests {
         transport.pack(&mut buffer);
         two_buffer.extend(&buffer[..]);
 
-        let offset = transport.unpack(&two_buffer[..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
         assert_eq!(offset.next_offset, single_size);
 
         let n = offset.next_offset;
-        let offset = transport.unpack(&two_buffer[n..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[n..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -202,7 +209,7 @@ mod tests {
         let orig = buffer.clone();
         transport.pack(&mut buffer);
         let n = 1; // init byte
-        let offset = transport.unpack(&buffer[n..]).unwrap();
+        let offset = transport.unpack(&mut buffer[n..]).unwrap();
         assert_eq!(&buffer[n..][offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -214,7 +221,7 @@ mod tests {
         buffer.extend(&(-404_i32).to_le_bytes());
 
         assert_eq!(
-            transport.unpack(&buffer[..]),
+            transport.unpack(&mut buffer[..]),
             Err(Error::BadStatus { status: 404 })
         );
     }

diff --git a/lib/grammers-mtproto/src/transport/full.rs b/lib/grammers-mtproto/src/transport/full.rs
@@ -62,7 +62,7 @@ impl Transport for Full {
         self.send_seq += 1;
     }
 
-    fn unpack(&mut self, buffer: &[u8]) -> Result<UnpackedOffset, Error> {
+    fn unpack(&mut self, buffer: &mut [u8]) -> Result<UnpackedOffset, Error> {
         // Need 4 bytes for the initial length
         if buffer.len() < 4 {
             return Err(Error::MissingBytes);
@@ -188,15 +188,15 @@ mod tests {
         let mut transport = Full::new();
         let mut buffer = DequeBuffer::with_capacity(3, 0);
         buffer.extend([0, 1, 3]);
-        assert_eq!(transport.unpack(&buffer[..]), Err(Error::MissingBytes));
+        assert_eq!(transport.unpack(&mut buffer[..]), Err(Error::MissingBytes));
     }
 
     #[test]
     fn unpack_normal() {
         let (mut transport, mut buffer) = setup_pack(128);
         let orig = buffer.clone();
         transport.pack(&mut buffer);
-        let offset = transport.unpack(&buffer[..]).unwrap();
+        let offset = transport.unpack(&mut buffer[..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -214,12 +214,12 @@ mod tests {
         transport.pack(&mut buffer);
         two_buffer.extend(&buffer[..]);
 
-        let offset = transport.unpack(&two_buffer[..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
         assert_eq!(offset.next_offset, single_size);
 
         let n = offset.next_offset;
-        let offset = transport.unpack(&two_buffer[n..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[n..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -230,7 +230,7 @@ mod tests {
         buffer[4] = 1;
 
         assert_eq!(
-            transport.unpack(&buffer[..]),
+            transport.unpack(&mut buffer[..]),
             Err(Error::BadSeq {
                 expected: 0,
                 got: 1,
@@ -246,7 +246,7 @@ mod tests {
         buffer[len - 1] ^= 0xff;
 
         assert_eq!(
-            transport.unpack(&buffer[..]),
+            transport.unpack(&mut buffer[..]),
             Err(Error::BadCrc {
                 expected: 932541318,
                 got: 3365237638,
@@ -261,7 +261,7 @@ mod tests {
         buffer.extend(&(-404_i32).to_le_bytes());
 
         assert_eq!(
-            transport.unpack(&buffer[..]),
+            transport.unpack(&mut buffer[..]),
             Err(Error::BadStatus { status: 404 })
         );
     }

diff --git a/lib/grammers-mtproto/src/transport/intermediate.rs b/lib/grammers-mtproto/src/transport/intermediate.rs
@@ -5,7 +5,7 @@
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-use super::{Error, Transport, UnpackedOffset};
+use super::{Error, Tagged, Transport, UnpackedOffset};
 use grammers_crypto::DequeBuffer;
 
 /// A light MTProto transport protocol available that guarantees data padded
@@ -31,6 +31,8 @@ pub struct Intermediate {
 
 #[allow(clippy::new_without_default)]
 impl Intermediate {
+    const TAG: [u8; 4] = 0xee_ee_ee_ee_u32.to_le_bytes();
+
     pub fn new() -> Self {
         Self { init: false }
     }
@@ -44,12 +46,12 @@ impl Transport for Intermediate {
         buffer.extend_front(&(len as i32).to_le_bytes());
 
         if !self.init {
-            buffer.extend_front(&0xee_ee_ee_ee_u32.to_le_bytes());
+            buffer.extend_front(&Self::TAG);
             self.init = true;
         }
     }
 
-    fn unpack(&mut self, buffer: &[u8]) -> Result<UnpackedOffset, Error> {
+    fn unpack(&mut self, buffer: &mut [u8]) -> Result<UnpackedOffset, Error> {
         if buffer.len() < 4 {
             return Err(Error::MissingBytes);
         }
@@ -84,6 +86,13 @@ impl Transport for Intermediate {
     }
 }
 
+impl Tagged for Intermediate {
+    fn init_tag(&mut self) -> [u8; 4] {
+        self.init = true;
+        Self::TAG
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -123,7 +132,7 @@ mod tests {
         let mut transport = Intermediate::new();
         let mut buffer = DequeBuffer::with_capacity(1, 0);
         buffer.extend([1]);
-        assert_eq!(transport.unpack(&buffer[..],), Err(Error::MissingBytes));
+        assert_eq!(transport.unpack(&mut buffer[..],), Err(Error::MissingBytes));
     }
 
     #[test]
@@ -132,7 +141,7 @@ mod tests {
         let orig = buffer.clone();
         transport.pack(&mut buffer);
         let n = 4; // init bytes
-        let offset = transport.unpack(&buffer[n..]).unwrap();
+        let offset = transport.unpack(&mut buffer[n..]).unwrap();
         assert_eq!(&buffer[n..][offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -150,12 +159,12 @@ mod tests {
         transport.pack(&mut buffer);
         two_buffer.extend(&buffer[..]);
 
-        let offset = transport.unpack(&two_buffer[..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
         assert_eq!(offset.next_offset, single_size);
 
         let n = offset.next_offset;
-        let offset = transport.unpack(&two_buffer[n..]).unwrap();
+        let offset = transport.unpack(&mut two_buffer[n..]).unwrap();
         assert_eq!(&buffer[offset.data_start..offset.data_end], &orig[..]);
     }
 
@@ -167,7 +176,7 @@ mod tests {
         buffer.extend(&(-404_i32).to_le_bytes());
 
         assert_eq!(
-            transport.unpack(&buffer[..]),
+            transport.unpack(&mut buffer[..]),
             Err(Error::BadStatus { status: 404 })
         );
     }

diff --git a/lib/grammers-mtproto/src/transport/mod.rs b/lib/grammers-mtproto/src/transport/mod.rs
@@ -14,11 +14,13 @@
 mod abridged;
 mod full;
 mod intermediate;
+mod obfuscated;
 
 pub use abridged::Abridged;
 pub use full::Full;
 use grammers_crypto::DequeBuffer;
 pub use intermediate::Intermediate;
+pub use obfuscated::Obfuscated;
 use std::fmt;
 
 /// The error type reported by the different transports when something is wrong.
@@ -91,8 +93,17 @@ pub trait Transport {
     fn pack(&mut self, buffer: &mut DequeBuffer<u8>);
 
     /// Unpacks the input buffer in-place.
-    fn unpack(&mut self, buffer: &[u8]) -> Result<UnpackedOffset, Error>;
+    /// Subsequent calls to `unpack` should be made with the same buffer only
+    /// with the old data removed and new data appended.
+    fn unpack(&mut self, buffer: &mut [u8]) -> Result<UnpackedOffset, Error>;
 
     /// Reset the state, as if a new instance was just created.
     fn reset(&mut self);
 }
+
+/// The trait used by the obfuscated transport to get the transport tags.
+pub trait Tagged {
+    /// Gets the transport tag for use in the obfuscated transport and
+    /// changes the internal state to avoid sending the tag again.
+    fn init_tag(&mut self) -> [u8; 4];
+}
-Original file line number
+Diff line change
@@ Expand Up @@
     ## toml
     Used to test that this file lists all dependencies from `Cargo.toml`.
+    ## ctr
+    Used for the AES-CTR mode needed for the obfuscated MTProto transport.