CBOR tag definition - ED25519-BIP32 Keys

Abstract

CIP-0003 defines ED25519-BIP32 Keys, Key derivation and a signature scheme. This CIP defines CBOR Tags and formalizes the Canonical encoding of data structures for CIP-0003. The intention is to have these tags registered in the IANA CBOR Tag Registry.

Motivation: why is this CIP necessary?

Project Catalyst is in the process of defining new CBOR data structures. We needed a way to reliably disambiguate different 32 byte strings. Rather than making a non-standard encoding scheme specific to our structures we would like to use standard CBOR Tags.

This CIP is informed by CPS-0014 and CIP-0114.

Without this Tag definition, a metadata CIP which uses ED25519-BIP32 public keys:

• Is likely to just encode public keys as a byte string of 32 bytes; and
• Needs to redundantly define how the keys are encoded in the byte string.
• May encode these keys differently to another CIP, which can lead to confusion and potential error.

BIP32 also defines secp256k1 keys which are also 32 bytes long. This CIP would help disambiguate between these keys and inform the decoder which key is being utilized.

Specification

NOTE: These tags are preliminary and subject to change until IANA registration is complete. They MUST not be used outside of testing purposes. They MUST not be used in any data intended to be posted to main-net.

ED25519-BIP32 Private Key

This key is defined in ED25519-BIP32.

This is encoded as a byte string of size 32 bytes.

CDDL

ed25519_private_key = #6.32771(bstr .size 32)

Data for the key inside the byte string is encoded in network byte order.

ED25519-BIP32 Extended Private Key

This key is defined in ED25519-BIP32.

This is encoded as a byte string of size 64 bytes.

CDDL

ed25519_extended_private_key = #6.32772(bstr .size 64)

Data for the key inside the byte string is encoded in network byte order.

ED25519-BIP32 Public Key

This key is defined in ED25519-BIP32.

This is encoded as a byte string of size 32 bytes.

CDDL

ed25519_public_key = #6.32773(bstr .size 32)

Data for the key inside the byte string is encoded in network byte order.

ED25519-BIP32 Signature

ED25519-BIP32 defines how signatures can be generated on data from private keys. These signatures are defined to be 64 bytes long.

Signatures are encoded as a byte string of size 64 bytes.

CDDL

ed25519_bip32_signature = #6.32774(bstr .size 64)

Data for the signature inside the byte string is encoded in network byte order.

Rationale: how does this CIP achieve its goals?

By defining concrete CBOR tags, it is possible for metadata to unambiguously mark the kind of data encoded. This is conformant with the intent of Tags in CBOR, and aligns with [CIP-CBOR-TAGS].

An official published spec is required to register these Tags with IANA. This document also serves that purpose.

Path to Active

Acceptance Criteria

• These tags to be included in [CIP-CBOR-TAGS].
• One downstream CIP uses at least one of the tags defined in this CIP.
• IANA register all the tags as defined herein.

Implementation Plan

• Tags are to be used by Project Catalyst for CBOR data structure definitions.
• Project Catalyst will also make the application to IANA to register the Tags.

References

• CPS-0014 - Register of CBOR Tags for Cardano Data structures
• CIP-0003 - Wallet Key Generation
• CIP-0114 - CBOR Tags Registry
• RFC8949 - Concise Binary Object Representation (CBOR)
• RFC8610 - Concise Data Definition Language (CDDL)
• RFC1700 Data Notations (Network Byte Order)
• BIP32 - Hierarchical Deterministic Wallets
• ED25519-BIP32 - Hierarchical Deterministic Keys over a Non-linear Keyspace
• IANA CBOR Tag Registry

Copyright

This CIP is licensed under CC-BY-4.0

Code samples and reference material are licensed under Apache 2.0