Various evidence-related fixes

examples/src/simple.rs

@@ -1,4 +1,8 @@
-use alloc::collections::{BTreeMap, BTreeSet};
+use alloc::{
+    collections::{BTreeMap, BTreeSet},
+    format,
+    string::String,
+};
 use core::fmt::Debug;
 
 use manul::protocol::*;
@@ -15,6 +19,10 @@ pub enum SimpleProtocolError {
 }
 
 impl ProtocolError for SimpleProtocolError {
+    fn description(&self) -> String {
+        format!("{:?}", self)
+    }
+
     fn required_direct_messages(&self) -> BTreeSet<RoundId> {
         match self {
             Self::Round1InvalidPosition => BTreeSet::new(),

examples/src/simple_malicious.rs

@@ -188,8 +188,8 @@ fn serialized_garbage() {
     let report1 = reports.remove(&v1).unwrap();
     let report2 = reports.remove(&v2).unwrap();
 
-    assert!(report1.provable_errors[&v0].verify(&v0).is_ok());
-    assert!(report2.provable_errors[&v0].verify(&v0).is_ok());
+    assert!(report1.provable_errors[&v0].verify().is_ok());
+    assert!(report2.provable_errors[&v0].verify().is_ok());
 }
 
 #[test]
@@ -234,8 +234,8 @@ fn attributable_failure() {
     let report1 = reports.remove(&v1).unwrap();
     let report2 = reports.remove(&v2).unwrap();
 
-    assert!(report1.provable_errors[&v0].verify(&v0).is_ok());
-    assert!(report2.provable_errors[&v0].verify(&v0).is_ok());
+    assert!(report1.provable_errors[&v0].verify().is_ok());
+    assert!(report2.provable_errors[&v0].verify().is_ok());
 }
 
 #[test]
@@ -280,6 +280,6 @@ fn attributable_failure_round2() {
     let report1 = reports.remove(&v1).unwrap();
     let report2 = reports.remove(&v2).unwrap();
 
-    assert!(report1.provable_errors[&v0].verify(&v0).is_ok());
-    assert!(report2.provable_errors[&v0].verify(&v0).is_ok());
+    assert!(report1.provable_errors[&v0].verify().is_ok());
+    assert!(report2.provable_errors[&v0].verify().is_ok());
 }

manul/benches/empty_rounds.rs

@@ -1,6 +1,9 @@
 extern crate alloc;
 
-use alloc::collections::{BTreeMap, BTreeSet};
+use alloc::{
+    collections::{BTreeMap, BTreeSet},
+    string::String,
+};
 use core::fmt::Debug;
 
 use criterion::{criterion_group, criterion_main, Criterion};
@@ -23,6 +26,9 @@ pub struct EmptyProtocol;
 pub struct EmptyProtocolError;
 
 impl ProtocolError for EmptyProtocolError {
+    fn description(&self) -> String {
+        unimplemented!()
+    }
     fn verify_messages_constitute_error(
         &self,
         _deserializer: &Deserializer,

manul/src/protocol/round.rs

@@ -2,6 +2,7 @@ use alloc::{
     boxed::Box,
     collections::{BTreeMap, BTreeSet},
     format,
+    string::String,
     vec::Vec,
 };
 use core::{any::Any, fmt::Debug};
@@ -84,6 +85,11 @@ impl RoundId {
         }
     }
 
+    /// Returns `true` if this is an ID of an echo broadcast round.
+    pub(crate) fn is_echo(&self) -> bool {
+        self.is_echo
+    }
+
     /// Returns the identifier of the echo round corresponding to the given non-echo round.
     ///
     /// Panics if `self` is already an echo round identifier.
@@ -116,7 +122,7 @@ impl RoundId {
 }
 
 /// A distributed protocol.
-pub trait Protocol: 'static + Sized {
+pub trait Protocol: 'static {
     /// The successful result of an execution of this protocol.
     type Result: Debug;
 
@@ -161,6 +167,7 @@ pub trait Protocol: 'static + Sized {
     ///
     /// Normally one would use [`EchoBroadcast::verify_is_not`] when implementing this.
     fn verify_normal_broadcast_is_invalid(
+        #[allow(unused_variables)] deserializer: &Deserializer,
         round_id: RoundId,
         #[allow(unused_variables)] message: &NormalBroadcast,
     ) -> Result<(), MessageValidationError> {
@@ -175,6 +182,11 @@ pub trait Protocol: 'static + Sized {
 /// Provable here means that we can create an evidence object entirely of messages signed by some party,
 /// which, in combination, prove the party's malicious actions.
 pub trait ProtocolError: Debug + Clone + Send {
+    /// A description of the error that will be included in the generated evidence.
+    ///
+    /// Make it short and informative.
+    fn description(&self) -> String;
+
     /// The rounds direct messages from which are required to prove malicious behavior for this error.
     ///
     /// **Note:** Should not include the round where the error happened.

manul/src/session.rs

@@ -16,6 +16,7 @@ mod transcript;
 mod wire_format;
 
 pub use crate::protocol::{LocalError, RemoteError};
+pub use evidence::{Evidence, EvidenceError};
 pub use message::MessageBundle;
 pub use session::{CanFinalize, RoundAccumulator, RoundOutcome, Session, SessionId, SessionParameters};
 pub use transcript::{SessionOutcome, SessionReport};

manul/src/session/echo.rs

@@ -2,6 +2,7 @@ use alloc::{
     boxed::Box,
     collections::{BTreeMap, BTreeSet},
     format,
+    string::String,
     vec::Vec,
 };
 use core::fmt::Debug;
@@ -17,8 +18,9 @@ use super::{
 };
 use crate::{
     protocol::{
-        Artifact, Deserializer, DirectMessage, EchoBroadcast, FinalizeError, FinalizeOutcome, NormalBroadcast,
-        ObjectSafeRound, Payload, Protocol, ProtocolMessagePart, ReceiveError, Round, RoundId, Serializer,
+        Artifact, Deserializer, DirectMessage, EchoBroadcast, FinalizeError, FinalizeOutcome, MessageValidationError,
+        NormalBroadcast, ObjectSafeRound, Payload, Protocol, ProtocolMessagePart, ReceiveError, Round, RoundId,
+        Serializer,
     },
     utils::SerializableMap,
 };
@@ -45,6 +47,17 @@ pub(crate) enum EchoRoundError<Id> {
     },
 }
 
+impl<Id> EchoRoundError<Id> {
+    pub(crate) fn description(&self) -> String {
+        match self {
+            Self::InvalidEcho(_) => "Invalid message received among the ones echoed".into(),
+            Self::MismatchedBroadcasts { .. } => {
+                "The echoed message is different from the originally received one".into()
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, Serialize, Deserialize)]
 pub(crate) enum MismatchedBroadcastsError {
     /// The originally received message and the echoed one had different payloads.
@@ -55,7 +68,7 @@ pub(crate) enum MismatchedBroadcastsError {
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub(crate) struct EchoRoundMessage<SP: SessionParameters> {
-    pub(crate) echo_broadcasts: SerializableMap<SP::Verifier, SignedMessage<EchoBroadcast>>,
+    pub(super) echo_broadcasts: SerializableMap<SP::Verifier, SignedMessage<EchoBroadcast>>,
 }
 
 /// Each protocol round can contain one `EchoRound` with "echo messages" that are sent to all
@@ -105,6 +118,25 @@ where
             artifacts,
         }
     }
+
+    // Since the echo round doesn't have its own `Protocol`, these methods live here.
+
+    pub fn verify_direct_message_is_invalid(message: &DirectMessage) -> Result<(), MessageValidationError> {
+        // We don't send any direct messages in the echo round
+        message.verify_is_some()
+    }
+
+    pub fn verify_echo_broadcast_is_invalid(message: &EchoBroadcast) -> Result<(), MessageValidationError> {
+        // We don't send any echo broadcasts in the echo round
+        message.verify_is_some()
+    }
+
+    pub fn verify_normal_broadcast_is_invalid(
+        deserializer: &Deserializer,
+        message: &NormalBroadcast,
+    ) -> Result<(), MessageValidationError> {
+        message.verify_is_not::<EchoRoundMessage<SP>>(deserializer)
+    }
 }
 
 impl<P, SP> Round<SP::Verifier> for EchoRound<P, SP>