Forging policy keys for HD Wallets
Abstract
This document describes how to derive forging policy keys used for minting/burning tokens.
Motivation: why is this CIP necessary?
Forging tokens is derived from a script policy. The script policy includes hashes of keys needed to forge new tokens and must be witnessed by these keys in such a way as the script stipulates. This CIP defines the derivation path at wich parties are expected to derive such keys.
Specification
| Term | Definition |
|---|---|
| HD | Hierarchical Deterministic, refers to wallets as described in BIP-0032. |
HD Derivation
We consider the following HD derivation paths similarly to CIP-1852:
m / purpose' / coin_type' / policy_ix'To associate policy keys to a wallet, we reserve however purpose=1855' for policy keys for forging tokens. The coin type remains coin_type=1815' to identify Ada as registered in SLIP-0044. We use a hardened index for each policy key as derivation is not needed.
We can summarize the various paths and their respective domain in the following table:
purpose |
coin_type |
policy_ix |
|---|---|---|
1855' |
1815' |
[2^31 .. 2^32-1] |
CIP-0005 prefixes
To distinguish such keys & derived material in the human readable prefix of the bech32 representation, we introduce the following prefixes for insertion into CIP-0005:
Keys
| Prefix | Meaning | Contents |
|---|---|---|
policy_sk |
CIP-1855's policy private key | Ed25519 private key |
policy_vk |
CIP-1855's policy public key | Ed25519 public key |
Hashes
| Prefix | Meaning | Contents |
|---|---|---|
policy_vkh |
CIP-1855's Policy verification key hash | blake2b_224 digest of a policy verification key |
Examples
m/1855’/1815’/0’m/1855’/1815’/1’m/1855’/1815’/2’
Rationale: how does this CIP achieve its goals?
-
ERC20 Converter IOHK is developing needs to keep track of policy keys. Rather than having randomly generated policy keys, a policy key can be associated with a mnemonic which is easier to backup.
-
A 3rd party may want to have multiple tokens tied to same mnemonic, so we allow an index to specify the token.
-
Contrary to CIP 1852, we don't use the
roleandindexlevels of the derivation path, since index is expressed at the 3rd level and no roles for policy signing keys are currently anticipated. -
No prefixes are defined for extended keys, since currently this CIP does not define further derivations.
-
We use a different purpose for mainly two reasons:
-
It prevents mixing up standard wallets with policy keys used for forging.
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Using a different purpose also fits well the use-case on hardware wallets who can still rely on a single root seed to manage many types of wallets.
-
Related Work
| Description | Link |
|---|---|
| BIP-0032 - HD Wallets | https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki |
| CIP-5 - Common Bech32 Prefixes | https://github.com/cardano-foundation/CIPs/tree/master/CIP-0005 |
| CIP-1852 - Cardano HD Wallets | https://github.com/cardano-foundation/CIPs/tree/master/CIP-1852 |
| A Formal Specification of the Cardano Ledger | https://github.com/input-output-hk/cardano-ledger/releases/latest/download/shelley-ledger.pdf |
Path to Active
Acceptance Criteria
- Standardisation of this derivation path among three wallets as of the Shelley ledger era.
Implementation Plan
- Common agreement on the above Motivation, Rationale and Specification during the planning of Cardano's Shelley release.
Copyright
This CIP is licensed under CC-BY-4.0.