feat: update introduction bundle encoding

closes: #27

Cargo.lock

@@ -97,7 +97,7 @@ dependencies = [
 [[package]]
 name = "chat-proto"
 version = "0.1.0"
-source = "git+https://github.com/logos-messaging/chat_proto#21cd52b0649c959f43eec19e1edad12451ccc382"
+source = "git+https://github.com/logos-messaging/chat_proto#44d5360c41d721a011d20ee69a75a85357b33b0e"
 dependencies = [
  "prost",
 ]
@@ -503,6 +503,7 @@ checksum = "df1d3c3b53da64cf5760482273a98e575c651a67eec7f77df96b5b642de8f039"
 name = "logos-chat"
 version = "0.1.0"
 dependencies = [
+ "base64ct",
  "blake2",
  "chat-proto",
  "crypto",

conversations/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2024"
 crate-type = ["staticlib","dylib"]
 
 [dependencies]
+base64ct = { version = "1.6", features = ["alloc"] }
 blake2.workspace = true
 chat-proto = { git = "https://github.com/logos-messaging/chat_proto" }
 crypto = { path = "../crypto" }

conversations/src/inbox/inbox.rs

@@ -17,6 +17,8 @@ use crate::inbox::handshake::InboxHandshake;
 use crate::proto;
 use crate::types::{AddressedEncryptedPayload, ContentData};
 
+use super::introduction::{sign_intro_binding, verify_intro_binding};
+
 /// Compute the deterministic Delivery_address for an installation
 fn delivery_address_for_installation(_: PublicKey) -> String {
     // TODO: Implement Delivery Address
@@ -59,10 +61,12 @@ impl Inbox {
         self.ephemeral_keys
             .insert(hex::encode(signed_prekey.as_bytes()), ephemeral);
 
+        let signature = sign_intro_binding(self.ident.secret(), &signed_prekey, OsRng);
+
         PrekeyBundle {
             identity_key: self.ident.public_key(),
-            signed_prekey: signed_prekey,
+            signed_prekey,
-            signature: [0u8; 64],
+            signature,
             onetime_prekey: None,
         }
     }
@@ -74,11 +78,17 @@ impl Inbox {
     ) -> Result<(PrivateV1Convo, Vec<AddressedEncryptedPayload>), ChatError> {
         let mut rng = OsRng;
 
-        // TODO: Include signature in introduction bundle. Manaully fill for now
+        verify_intro_binding(
+            &remote_bundle.installation_key,
+            &remote_bundle.ephemeral_key,
+            &remote_bundle.signature,
+        )
+        .map_err(|_| ChatError::BadBundleValue("invalid signature".into()))?;
+
         let pkb = PrekeyBundle {
             identity_key: remote_bundle.installation_key,
             signed_prekey: remote_bundle.ephemeral_key,
-            signature: [0u8; 64],
+            signature: remote_bundle.signature,
             onetime_prekey: None,
         };
 

conversations/src/inbox/introduction.rs

@@ -1,12 +1,48 @@
+use base64ct::{Base64UrlUnpadded, Encoding};
+use chat_proto::logoschat::intro::IntroBundle;
 use crypto::PrekeyBundle;
-use x25519_dalek::PublicKey;
+use prost::Message;
+use rand_core::{CryptoRng, RngCore};
+use x25519_dalek::{PublicKey, StaticSecret};
 
 use crate::errors::ChatError;
 
+const BUNDLE_PREFIX: &str = "logos_chatintro_1_";
+
+const INTRO_DOMAIN_SEPARATOR: &[u8] = b"logos_chatintro_v1_bind";
+
+fn intro_binding_message(identity: &PublicKey, ephemeral: &PublicKey) -> Vec<u8> {
+    let mut message = Vec::with_capacity(INTRO_DOMAIN_SEPARATOR.len() + 64);
+    message.extend_from_slice(INTRO_DOMAIN_SEPARATOR);
+    message.extend_from_slice(identity.as_bytes());
+    message.extend_from_slice(ephemeral.as_bytes());
+    message
+}
+
+pub(crate) fn sign_intro_binding<R: RngCore + CryptoRng>(
+    secret: &StaticSecret,
+    ephemeral: &PublicKey,
+    rng: R,
+) -> [u8; 64] {
+    let identity = PublicKey::from(secret);
+    let message = intro_binding_message(&identity, ephemeral);
+    crypto::xeddsa_sign(secret, &message, rng)
+}
+
+pub(crate) fn verify_intro_binding(
+    pubkey: &PublicKey,
+    ephemeral: &PublicKey,
+    signature: &[u8; 64],
+) -> Result<(), crypto::SignatureError> {
+    let message = intro_binding_message(pubkey, ephemeral);
+    crypto::xeddsa_verify(pubkey, &message, signature)
+}
+
 /// Supplies remote participants with the required keys to use Inbox protocol
 pub struct Introduction {
     pub installation_key: PublicKey,
     pub ephemeral_key: PublicKey,
+    pub signature: [u8; 64],
 }
 
 impl From<PrekeyBundle> for Introduction {
@@ -14,20 +50,28 @@ impl From<PrekeyBundle> for Introduction {
         Introduction {
             installation_key: value.identity_key,
             ephemeral_key: value.signed_prekey,
+            signature: value.signature,
         }
     }
 }
 
-impl Into<Vec<u8>> for Introduction {
+impl From<Introduction> for Vec<u8> {
-    fn into(self) -> Vec<u8> {
+    fn from(intro: Introduction) -> Vec<u8> {
-        // TODO: avoid copies, via writing directly to slice
+        use prost::bytes::Bytes;
-        let link = format!(
-            "Bundle:{}:{}",
-            hex::encode(self.installation_key.as_bytes()),
-            hex::encode(self.ephemeral_key.as_bytes()),
-        );
 
-        link.into_bytes()
+        let bundle = IntroBundle {
+            installation_pubkey: Bytes::copy_from_slice(intro.installation_key.as_bytes()),
+            ephemeral_pubkey: Bytes::copy_from_slice(intro.ephemeral_key.as_bytes()),
+            signature: Bytes::copy_from_slice(&intro.signature),
+        };
+
+        let base64_encoded = Base64UrlUnpadded::encode_string(&bundle.encode_to_vec());
+
+        let mut result = String::with_capacity(BUNDLE_PREFIX.len() + base64_encoded.len());
+        result.push_str(BUNDLE_PREFIX);
+        result.push_str(&base64_encoded);
+
+        result.into_bytes()
     }
 }
 
@@ -35,30 +79,102 @@ impl TryFrom<&[u8]> for Introduction {
     type Error = ChatError;
 
     fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
-        let str_value = String::from_utf8_lossy(value);
+        let str_value = std::str::from_utf8(value)
-        let parts: Vec<&str> = str_value.splitn(3, ':').collect();
+            .map_err(|_| ChatError::BadBundleValue("invalid UTF-8".into()))?;
 
-        if parts[0] != "Bundle" {
+        let base64_part = str_value.strip_prefix(BUNDLE_PREFIX).ok_or_else(|| {
-            return Err(ChatError::BadBundleValue(
+            ChatError::BadBundleValue("not recognized as an introduction bundle".into())
-                "not recognized as an introduction bundle".into(),
+        })?;
-            ));
-        }
 
-        let installation_bytes: [u8; 32] = hex::decode(parts[1])
+        let proto_bytes = Base64UrlUnpadded::decode_vec(base64_part)
-            .map_err(|_| ChatError::BadParsing("installation_key"))?
+            .map_err(|_| ChatError::BadBundleValue("invalid base64".into()))?;
+
+        let bundle = IntroBundle::decode(proto_bytes.as_slice())
+            .map_err(|_| ChatError::BadBundleValue("invalid protobuf".into()))?;
+
+        let installation_bytes: [u8; 32] = bundle
+            .installation_pubkey
+            .as_ref()
             .try_into()
             .map_err(|_| ChatError::InvalidKeyLength)?;
-        let installation_key = PublicKey::from(installation_bytes);
 
-        let ephemeral_bytes: [u8; 32] = hex::decode(parts[2])
+        let ephemeral_bytes: [u8; 32] = bundle
-            .map_err(|_| ChatError::BadParsing("ephemeral_key"))?
+            .ephemeral_pubkey
+            .as_ref()
             .try_into()
             .map_err(|_| ChatError::InvalidKeyLength)?;
-        let ephemeral_key = PublicKey::from(ephemeral_bytes);
+
+        let signature: [u8; 64] = bundle
+            .signature
+            .as_ref()
+            .try_into()
+            .map_err(|_| ChatError::BadBundleValue("invalid signature length".into()))?;
 
         Ok(Introduction {
-            installation_key,
+            installation_key: PublicKey::from(installation_bytes),
-            ephemeral_key,
+            ephemeral_key: PublicKey::from(ephemeral_bytes),
+            signature,
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rand_core::OsRng;
+
+    fn create_test_introduction() -> Introduction {
+        let install_secret = StaticSecret::random_from_rng(OsRng);
+        let install_pub = PublicKey::from(&install_secret);
+
+        let ephemeral_secret = StaticSecret::random_from_rng(OsRng);
+        let ephemeral_pub = PublicKey::from(&ephemeral_secret);
+
+        let signature = sign_intro_binding(&install_secret, &ephemeral_pub, OsRng);
+
+        Introduction {
+            installation_key: install_pub,
+            ephemeral_key: ephemeral_pub,
+            signature,
+        }
+    }
+
+    #[test]
+    fn test_serialization_roundtrip() {
+        let intro = create_test_introduction();
+        let original_install = intro.installation_key;
+        let original_ephemeral = intro.ephemeral_key;
+        let original_signature = intro.signature;
+
+        let encoded: Vec<u8> = intro.into();
+        let decoded = Introduction::try_from(encoded.as_slice()).unwrap();
+
+        assert_eq!(decoded.installation_key, original_install);
+        assert_eq!(decoded.ephemeral_key, original_ephemeral);
+        assert_eq!(decoded.signature, original_signature);
+    }
+
+    #[test]
+    fn test_invalid_prefix_rejected() {
+        assert!(Introduction::try_from(b"wrong_prefix_AAAA".as_slice()).is_err());
+    }
+
+    #[test]
+    fn test_invalid_base64_rejected() {
+        assert!(Introduction::try_from(b"logos_chatintro_1_!!!invalid!!!".as_slice()).is_err());
+    }
+
+    #[test]
+    fn test_truncated_payload_rejected() {
+        let intro = create_test_introduction();
+        let encoded: Vec<u8> = intro.into();
+        let encoded_str = String::from_utf8(encoded).unwrap();
+
+        let truncated = format!(
+            "logos_chatintro_1_{}",
+            &encoded_str[BUNDLE_PREFIX.len()..][..10]
+        );
+
+        assert!(Introduction::try_from(truncated.as_bytes()).is_err());
+    }
+}

crypto/src/lib.rs

@@ -1,5 +1,7 @@
 mod keys;
 mod x3dh;
+mod xeddsa_sign;
 
 pub use keys::{GenericArray, SecretKey};
 pub use x3dh::{DomainSeparator, PrekeyBundle, X3Handshake};
+pub use xeddsa_sign::{xeddsa_sign, xeddsa_verify, SignatureError};

crypto/src/xeddsa_sign.rs

@@ -0,0 +1,118 @@
+//! XEdDSA signing using X25519 keys.
+//!
+//! This module provides generic XEdDSA sign and verify functions
+//! that allow signing arbitrary messages with X25519 keys.
+
+use rand_core::{CryptoRng, RngCore};
+use x25519_dalek::{PublicKey, StaticSecret};
+use xeddsa::{xed25519, Sign, Verify};
+
+/// Error type for signature verification failures.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SignatureError;
+
+impl std::fmt::Display for SignatureError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "signature verification failed")
+    }
+}
+
+impl std::error::Error for SignatureError {}
+
+/// Sign a message using XEdDSA with an X25519 secret key.
+///
+/// # Arguments
+/// * `secret` - The X25519 secret key to sign with
+/// * `message` - The message to sign
+/// * `rng` - A cryptographically secure random number generator
+///
+/// # Returns
+/// A 64-byte XEdDSA signature
+pub fn xeddsa_sign<R: RngCore + CryptoRng>(
+    secret: &StaticSecret,
+    message: &[u8],
+    mut rng: R,
+) -> [u8; 64] {
+    let signing_key = xed25519::PrivateKey::from(secret);
+    signing_key.sign(message, &mut rng)
+}
+
+/// Verify an XEdDSA signature using an X25519 public key.
+///
+/// # Arguments
+/// * `pubkey` - The X25519 public key to verify with
+/// * `message` - The message that was signed
+/// * `signature` - The 64-byte XEdDSA signature to verify
+///
+/// # Returns
+/// `Ok(())` if the signature is valid, `Err(SignatureError)` otherwise
+pub fn xeddsa_verify(
+    pubkey: &PublicKey,
+    message: &[u8],
+    signature: &[u8; 64],
+) -> Result<(), SignatureError> {
+    let verify_key = xed25519::PublicKey::from(pubkey);
+    verify_key.verify(message, signature).map_err(|_| SignatureError)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rand_core::OsRng;
+
+    #[test]
+    fn test_sign_and_verify_roundtrip() {
+        let secret = StaticSecret::random_from_rng(OsRng);
+        let public = PublicKey::from(&secret);
+        let message = b"test message";
+
+        let signature = xeddsa_sign(&secret, message, OsRng);
+
+        assert!(xeddsa_verify(&public, message, &signature).is_ok());
+    }
+
+    #[test]
+    fn test_wrong_key_fails() {
+        let secret = StaticSecret::random_from_rng(OsRng);
+        let message = b"test message";
+
+        let signature = xeddsa_sign(&secret, message, OsRng);
+
+        let wrong_secret = StaticSecret::random_from_rng(OsRng);
+        let wrong_public = PublicKey::from(&wrong_secret);
+
+        assert_eq!(
+            xeddsa_verify(&wrong_public, message, &signature),
+            Err(SignatureError)
+        );
+    }
+
+    #[test]
+    fn test_wrong_message_fails() {
+        let secret = StaticSecret::random_from_rng(OsRng);
+        let public = PublicKey::from(&secret);
+        let message = b"test message";
+
+        let signature = xeddsa_sign(&secret, message, OsRng);
+
+        assert_eq!(
+            xeddsa_verify(&public, b"wrong message", &signature),
+            Err(SignatureError)
+        );
+    }
+
+    #[test]
+    fn test_corrupted_signature_fails() {
+        let secret = StaticSecret::random_from_rng(OsRng);
+        let public = PublicKey::from(&secret);
+        let message = b"test message";
+
+        let mut signature = xeddsa_sign(&secret, message, OsRng);
+        signature[0] ^= 0xFF;
+
+        assert_eq!(
+            xeddsa_verify(&public, message, &signature),
+            Err(SignatureError)
+        );
+    }
+}