broadcast¶

Echo Broadcast Protocol Implementation

Implements Bracha’s reliable broadcast protocol for Byzantine fault tolerance. Ensures all honest parties receive the same message from each sender.

Based on: Bracha’s Reliable Broadcast (1987)
Reference: “Asynchronous Byzantine Agreement Protocols” - Gabriel Bracha

Used in: DKLS23 Threshold ECDSA DKG for broadcast consistency verification

Authors:: Elton de Souza
Date:: 01/2026

class broadcast.EchoBroadcast(num_parties: int, fault_threshold: int | None = None)[source]¶

Bases: object

Echo broadcast protocol for Byzantine fault tolerant message delivery.

Ensures that if any honest party accepts a message from a sender, all honest parties accept the same message (consistency).

This implements echo broadcast verification as used in distributed key generation (DKG) protocols to prevent equivocation attacks where a malicious sender sends different messages to different recipients.

Attributes:

n: Number of parties in the protocol f: Byzantine fault threshold (default: (n-1)//3)

Example:

>>> broadcast = EchoBroadcast(num_parties=5)
>>> msg = broadcast.create_broadcast_message(1, {'value': 42})
>>> 'sender_id' in msg and 'hash' in msg
True

compute_message_hash(message: Any) → bytes[source]¶

Compute hash of a message for echo comparison.

Parameters¶

messageAny: The message to hash. Can be bytes, dict, or any serializable type.

Returns¶

bytes: SHA-256 hash of the message

create_broadcast_message(party_id: int, message: Any) → Dict[str, Any][source]¶

Create a broadcast message with its hash for echo verification.

Parameters¶

party_idint: The sender’s party identifier
messageAny: The message content to broadcast

Returns¶

dict: Broadcast message containing: - sender_id: The sender’s party ID - message: The original message content - hash: SHA-256 hash of the message

process_echo(verifier_id: int, sender_id: int, msg_hash: bytes, echo_state: Dict[int, Dict[int, bytes]] | None = None) → Dict[int, Dict[int, bytes]][source]¶

Process an echo from another party.

Records what message hash a verifier claims to have received from a sender.

Parameters¶

verifier_idint: ID of the party reporting what they received
sender_idint: ID of the original sender
msg_hashbytes: Hash of the message the verifier claims to have received
echo_statedict, optional: Current echo state to update. If None, creates new state.

Returns¶

dict: Updated echo state: {verifier_id: {sender_id: msg_hash}}

verify_consistency(echo_msgs: Dict[int, Dict[int, bytes]]) → bool[source]¶

Verify all parties received consistent messages from each sender.

Checks that for each sender, all verifiers report the same message hash. If any sender sent different messages to different recipients (equivocation), raises ValueError with details about the inconsistency.

Parameters¶

echo_msgsdict: Echo state mapping {verifier_id: {sender_id: msg_hash}}

Returns¶

bool: True if all messages are consistent

Raises¶

ValueError

If broadcast inconsistency is detected, with details about which sender sent different messages to different recipients

Example:

>>> broadcast = EchoBroadcast(num_parties=3)
>>> # All parties received same hash from sender 1
>>> echo_msgs = {1: {1: b'hash1'}, 2: {1: b'hash1'}, 3: {1: b'hash1'}}
>>> broadcast.verify_consistency(echo_msgs)
True