CIP-0036

CIP	Title	Authors	Comments-URI	Status	Type	Created	License
36	Catalyst/Voltaire Registration Transaction Metadata Format (Updated)	Giacomo Pasini <giacomo.pasini@iohk.io>, Kevin Hammond <kevin.hammond@iohk.io>, Mark Stopka <mark.stopka@perlur.cloud>	https://forum.cardano.org/t/cip-catalyst-registration-metadata-format/44038	Proposed	Standards	2021-12-06	CC-BY-4.0

Abstract

Cardano uses a sidechain for its treasury system. One needs to "register" to participate on this sidechain by submitting a registration transaction on the mainnet chain. This CIP details the registration transaction format. This is a revised version of the original CIP-15.

Motivation

Cardano uses a sidechain for its treasury system ("Catalyst") and for other voting purposes. One of the desirable properties of this sidechain is that even if its safety is compromised, it doesn't cause loss of funds on the main Cardano chain. To achieve this, instead of using your wallet's recovery phrase on the sidechain, we need to use a brand new "voting key".

However, since 1 ADA = 1 vote, a user needs to associate their mainnet ADA to their new voting key. This can be achieved through a registration transaction.

In addition, to encourage participation by a broader range of ADA holders, it should be possible to delegate one's rights to vote to (possibly multiple) representatives and/or expert voters. Such delegations will still be able to receive Catalyst rewards.

We therefore need a registration transaction that serves three purposes:

1. Registers a "voting key" to be included in the sidechain and/or delegates to existing "voting key"s
2. Associates mainnet ADA to this voting key(s)
3. Declares an address to receive Catalyst rewards

Note: This schema does not attempt to differentiate delegations from direct registrations, as the two options have exactly the same format. It also does not distinguish between delegations that are made as "private" arrangements (proxy votes) from those that are made by delegating to representatives who promote themselves publicly. Distinguishing these possibilities is left to upper layers or future revisions of this standard, if required. In this document, we will use the term 'delegations' to refer to all these possibilities.

Specification

Registration metadata format

A registration transaction is a regular Cardano transaction with a specific transaction metadata associated with it.

Notably, there should be five entries inside the metadata map:

• A non-empty array of delegations, as described below;
• A stake address for the network that this transaction is submitted to (to point to the Ada that is being delegated);
• A Shelley address discriminated for the same network this transaction is submitted to to receive rewards.
• A nonce that identifies that most recent delegation
• A non-negative integer that indicates the purpose of the vote. This is an optional field to allow for compatibility with CIP-15. For now, we define 0 as the value to use for Catalyst, and leave others for future use. A new registration should not invalidate a previous one with a different voting purpose value.

Delegation format

A delegation assigns (a portion of) the ADA controlled by one or more UTxOs on mainnet to the voting key in the sidechain as voting power. The UTxOs can be identified via the stake address at some designated point in time.

Each delegation therefore contains:

• a voting key: simply an ED25519 public key. This is the spending credential in the sidechain that will receive voting power from this delegation. For direct voting it's necessary to have the corresponding private key to cast votes in the sidechain. How this key is created is up to the wallet.
• the weight that is associated with this key: this is a 4-byte unsigned integer (CBOR major type 0, The weight may range from 0 to 2^32-1) that represents the relative weight of this delegation over the total weight of all delegations in the same registration transaction.

Voting key derivation path

To avoid linking voting keys directly with Cardano spending keys, the voting key derivation path must start with a specific segment:

m / 1694' / 1815' / account' / chain / address_index

Associating voting power with a voting key

This method has been used since Fund 2. For future fund iterations, a new method making use of time-lock scripts may be introduced as described below.

Recall: Cardano uses the UTXO model so to completely associate a wallet's balance with a voting key (i.e. including enterprise addresses), we would need to associate every payment key to a voting key individually. Although there are attempts at this (see CIP-0008), the resulting data structure is a little excessive for on-chain metadata (which we want to keep small)

Given the above, we choose to associate staking credentials with voting keys. At the moment, the only supported staking credential is a staking key. Since most Cardano wallets only use base addresses for Shelley wallet types, in most cases this should perfectly match the user's wallet.

The voting power that is associated with each delegated voting key is derived from the user's total voting power as follows.

1. The total weight is calculated as a sum of all the weights;
2. The user's total voting power is calculated as a whole number of ADA (rounded down);
3. The voting power associated with each voting key in the delegation array is calculated as the weighted fraction of the total voting power (rounded down);
4. Any remaining voting power is assigned to the last voting key in the delegation array.

This ensures that the voter's total voting power is never accidentally reduced through poor choices of weights, and that all voting powers are exact ADA.

Example - Registration

Voting registration example:

61284: {
  // delegations - CBOR byte array 
  1: [["0xa6a3c0447aeb9cc54cf6422ba32b294e5e1c3ef6d782f2acff4a70694c4d1663", 1], ["0x00588e8e1d18cba576a4d35758069fe94e53f638b6faf7c07b8abd2bc5c5cdee", 3]],
  // stake_pub - CBOR byte array
  2: "0xad4b948699193634a39dd56f779a2951a24779ad52aa7916f6912b8ec4702cee",
  // reward_address - CBOR byte array
  3: "0x00588e8e1d18cba576a4d35758069fe94e53f638b6faf7c07b8abd2bc5c5cdee47b60edc7772855324c85033c638364214cbfc6627889f81c4",
  // nonce
  4: 5479467
  // voting_purpose: 0 = Catalyst
  5: 0
}

The entries under keys 1, 2, 3, 4 and 5 represent the Catalyst delegation array, the staking credential on the Cardano network, the address to receive rewards, a nonce, and a voting purpose, respectively. A registration with these metadata will be considered valid if the following conditions hold:

• The nonce is an unsigned integer (of CBOR major type 0) that should be monotonically rising across all transactions with the same staking key. The advised way to construct a nonce is to use the current slot number. This is a simple way to keep the nonce increasing without having to access the previous transaction data.
• The reward address is a Shelley address discriminated for the same network this transaction is submitted to.
• The delegation array is not empty
• The weights in the delegation array are not all zero

Delegation to the voting key 0xa6a3c0447aeb9cc54cf6422ba32b294e5e1c3ef6d782f2acff4a70694c4d1663 will have relative weight 1 and delegation to the voting key 0x00588e8e1d18cba576a4d35758069fe94e53f638b6faf7c07b8abd2bc5c5cdee relative weight 3 (for a total weight of 4). Such a registration will assign 1/4 and 3/4 of the value in ADA to those keys respectively, with any remainder assigned to the second key.

The registration witness depends on the type of stake credential used. To produce the witness field in case of a staking public key, the CBOR representation of a map containing a single entry with key 61284 and the registration metadata map in the format above is formed, designated here as sign_data. This data is signed with the staking key as follows: first, the blake2b-256 hash of sign_data is obtained. This hash is then signed using the Ed25519 signature algorithm. The witness metadata entry is added to the transaction under key 61285 as a CBOR map with a single entry that consists of the integer key 1 and signature as obtained above as the byte array value.

Witness example:

61285: {
  // witness - ED25119 signature CBOR byte array
  1: "0x8b508822ac89bacb1f9c3a3ef0dc62fd72a0bd3849e2381b17272b68a8f52ea8240dcc855f2264db29a8512bfcd522ab69b982cb011e5f43d0154e72f505f007"
}

Deregistration metadata format (Catalyst)

This deregistration format is currently only specified for Catalyst (vote_purpose=0), other voting chain purposes may handle a deregistration in a different way. There was a discussion before if an empty delegation array could also be used to fulfil a deregistration. This idea was cancelled, because it would currently require additional resources in the Hardware-Wallets state machine to do additional checks about an empty array. So the decision was made to leave the registration part untouched and only add the deregistration via the unused key 61286. Wallets/Tools are not forced to support this deregistration method.

Definition:

• A deregistration removes all the voting power (associated stake amount) for the provided stake credential from the delegated vote-public-keys.
• A deregistration resets the state of the stake credential on the voting chain like they were never registered before.
• A deregistration transaction is a regular Cardano transaction with a specific transaction metadata associated with it.

Notably, there should be three entries inside the metadata map (key 61286):

• The public key of the stake signing key
• A nonce that identifies that most recent deregistration.
• A non-negative integer that indicates the purpose of the vote. For now, we define 0 as the value to use for Catalyst, and leave others for future use.

Be aware, the deregistration metadata key is 61286, and not 61284 like it is used for a registration! The registraton metadata format and specification is independent from the deregistration one, and may not be supported by all wallets/tools.

Example - Deregistration (Catalyst)

{
  61286: {
    // stake_pub - CBOR byte array
    1: "0x57758911253f6b31df2a87c10eb08a2c9b8450768cb8dd0d378d93f7c2e220f0",
    // nonce
    2: 74412400,
    // voting_purpose: 0 = Catalyst
    3: 0
  },
  61285: {
    // witness - ED25119 signature CBOR byte array
    1: "0xadb7c90955c348e432545276798478f02ee7c2be61fd44d22f9de22131d9bcf0b23eb413766b74b9e7ba740e71266467a5d35363411346972db9e7b710b00603"
  }
}

CBOR-Hex: A219EF66A301582057758911253F6B31DF2A87C10EB08A2C9B8450768CB8DD0D378D93F7C2E220F0021A046F7170030019EF65A1015840ADB7C90955C348E432545276798478F02EE7C2BE61FD44D22F9DE22131D9BCF0B23EB413766B74B9E7BA740E71266467A5D35363411346972DB9E7B710B00603

The entries under keys 1, 2 and 3 represent the staking credential on the Cardano network, a nonce, and a voting purpose, respectively. A deregistration with these metadata will be considered valid if the following conditions hold:

• The stake credentials is a stake public-key byte array (of CBOR major type 2)
• The nonce is an unsigned integer (of CBOR major type 0) that should be monotonically rising across all transactions with the same staking key. The advised way to construct a nonce is to use the current slot number. This is a simple way to keep the nonce increasing without having to access the previous transaction data.
• The voting_purpose is an unsigned integer (of CBOR major type 0)

To produce the witness field in case of a staking public key, the CBOR representation of a map containing a single entry with key 61286 and the deregistration metadata map in the format above is formed, designated here as sign_data. This data is signed with the staking key as follows: first, the blake2b-256 hash of sign_data is obtained. This hash is then signed using the Ed25519 signature algorithm. The witness metadata entry is added to the transaction under key 61285 as a CBOR map with a single entry that consists of the integer key 1 and signature as obtained above as the byte array value.

Metadata schema

See the schema file

Test vector

See test vector file

Future development

A future change of the Catalyst system may make use of a time-lock script to commit ADA on the mainnet for the duration of a voting period. The voter registration metadata in this method will not need an association with a staking credential. Therefore, the staking_credential map entry and the registration_witness payload with key 61285 will no longer be required.

Changelog

Fund 3 added the reward_address inside the key_registration field.

Fund 4:

• added the nonce field to prevent replay attacks;
• changed the signature algorithm from one that signed sign_data directly to signing the Blake2b hash of sign_data to accommodate memory-constrained hardware wallet devices.

It was planned that since Fund 4, registration_signature and the staking_pub_key entry inside the key_registration field will be deprecated. This has been deferred to a future revision of the protocol.

Fund 8:

• renamed the voting_key field to delegations and add support for splitting voting power across multiple vote keys.
• added the voting_purpose field to limit the scope of the delegations.
• rename the staking_pub_key field to stake_credential and registration_signature to registration_witness to allow for future credentials additions.

Fund 11:

• added the deregistration metadata format.

Copyright

This CIP is licensed under CC-BY-4.0