21 - LLMQ DKG Data Sharing#
DIP: 0021 Title: LLMQ DKG Data Sharing Author(s): dustinface Special-Thanks: Comments-Summary: No comments yet. Status: Proposed Type: Standard Created: 2021-03-08 License: MIT License
Table of Contents#
Abstract#
This document introduces two new P2P messages called QGETDATA
and QDATA
. The QGETDATA
message
allows masternodes to request QDATA
messages containing various data payloads, such as quorum
verification vectors or distributed key generation (DKG) contributions, from members of a Long
Living Masternode Quorum (LLMQ).
Motivation#
There are the following two problems which can be solved with the proposed P2P messages:
In Tenderdash a validator-set is represented by an LLMQ. In order to change the validator-set from LLMQx to LLMQy, LLMQx must include all required data (including public key shares) of LLMQy in the Tenderdash block which proposes/executes the validator-set rotation. This means that for validator-set rotation in Tenderdash to work, all members of LLMQx must have the quorum verification vector of LLMQy (which currently isn’t the case) so they can calculate the public key shares for all LLMQy members.
If a member of LLMQx needs to reindex or wipe the data directory (e.g. due to unexpected issues during an upgrade or unexpected file corruption), it currently loses all the information it requires to participate in LLMQx signing sessions. This information includes the quorum verification vector and its own DKG secret key share. Currently there is no mechanism for masternodes to recover this data from other members.
Prior work#
Specification#
Two new messages are defined: QGETDATA
and QDATA
. The two new P2P messages will only be
available for masternodes, must be ignored by non-masternode connections and must be rate limited to
prevent potential DoS attacks. Masternodes will only be allowed to request DKG data with QGETDATA
from each member once every 5 minutes.
Any incorrect usage of these messages should result in a connection ban score increase of:
10 - For duplicate/invalid/malformed messages
25 - For exceeding the rate limit threshold
These messages will be available upon activation of protocol version 70219.
P2P - QGETDATA#
The QGETDATA
message is used to request a QDATA
message from another masternode. The following
table defines its available parameters:
Payload description#
Field |
Type |
Size |
Description |
---|---|---|---|
quorumType |
uint8 |
1 byte |
Type of the quorum to request data from. |
quorumHash |
uint256 |
32 bytes |
Hash of the quorum to request data from. |
dataMask |
uint16 |
2 bytes |
Defines which data to request, see Available data flags. |
protxHash |
uint256 |
32 bytes |
(Optional) Protx hash. See 0x0002 in Available data flags. |
Where quorumHash
and quorumType
define from which quorum the data defined by dataMask
gets
requested.
P2P - QDATA#
The QDATA
message is the response to QGETDATA
messages. It should be ignored and result in a
small ban-score increase if it has not been requested. The following table describes its possible
payload:
Payload description#
Field |
Type |
Size |
Description |
---|---|---|---|
quorumType |
uint8 |
1 byte |
Type of the quorum the data is about. |
quorumHash |
uint256 |
32 bytes |
Hash of the quorum the data is about. |
dataMask |
uint16 |
2 bytes |
See Available data flags. This value should be equal to the |
protxHash |
uint256 |
32 bytes |
This is the protx hash of the member which can decrypt the data in |
error |
uint8 |
1 byte |
|
data_0001 |
BLSVerificationVector |
Variable |
Included if 0x0001 is set in |
data_0002 |
std::vector<CBLSIESEncryptedObject<CBLSSecretKey>> |
Variable |
Included if 0x0002 is set in |
Available data flags#
Flag |
Description |
Response |
---|---|---|
0x0001 |
Request the quorum verification vector of the LLMQ. |
The quorum verification vector of the LLMQ. Type: std::vector<CBLSPublicKey> Size: <quorum_threshold> * 48 bytes Max. size: ~16,320 bytes |
0x0002 |
Request all encrypted DKG contributions directed to the member with the protx hash provided in the protxHash field. |
Set of secret keys encrypted with the operator key of the requesting masternode. Type: std::vector<CBLSIESEncryptedObject<CBLSSecretKey>> Size: <valid_member_count> * 112 bytes Max. Size: 44,800 bytes |
Possible error codes#
Value |
Name |
Description |
---|---|---|
0x00 |
NONE |
No error, this value indicates the |
0x01 |
QUORUM_TYPE_INVALID |
The quorum type provided in the |
0x02 |
QUORUM_BLOCK_NOT_FOUND |
The hash provided in the |
0x03 |
QUORUM_NOT_FOUND |
The quorum (combination of |
0x04 |
MASTERNODE_IS_NO_MEMBER |
The masternode with the protx-hash provided in the |
0x05 |
QUORUM_VERIFICATION_VECTOR_MISSING |
The quorum verification vector for the requested quorum is missing on the node servicing the request. |
0x06 |
ENCRYPTED_CONTRIBUTIONS_MISSING |
The encrypted DKG contributions for the requested member are missing on the node servicing the request. |
Processing and usage#
For each QDATA
message received, the receiving masternode must validate and store the related
data. The following table shows the steps required depending on the dataType received:
dataType |
Validate and process the data |
Usage |
---|---|---|
0x0001 |
Calculate the hash of the received quorum verification vector. The calculated hash must match |
Mainly used to make the quorum verification vector of other LLMQs available on platform validators. Another use case is described in “Usage” of the flag 0x0002 below. |
0x0002 |
Decrypt all the contributions with the operator key, aggregate them to the secret key share and make sure its public key matches the public key share calculated with the quorum verification vector for the masternode’s |
This can be wrapped into a workflow where a masternode which is a member of one or more quorums has lost its LLMQ DKG data. By requesting 0x0002 it can recover its secret key share. When combined with 0x0001, it can recover itself as a valid member of the LLMQ by just asking other LLMQ-Members for the required data after a re-sync/re-index. |
Reference implementation#
Copyright#
Copyright (c) 2021 Dash Core Group, Inc. Licensed under the MIT License