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PIP-53: Supporting secp256k1 Curve

Add secp256k1 (ECDSA) support, including encoding, addresses, and HD derivation

Authors Pactus Development Team [[email protected]]
Discussion View Discussion PIP-53
Category Core
Created 2026-05-12

Table of Contents

Abstract #

This PIP proposes adding support for the secp256k1 elliptic curve and the associated ECDSA signature scheme. It defines address and key encodings for secp256k1 key pairs, a fixed-size signature format, and a hierarchical deterministic (HD) derivation path.

Motivation #

secp256k1 is the most widely used elliptic curve in blockchain ecosystems. Adding native secp256k1 support to Pactus enables broader wallet interoperability, reduces conversion costs for existing key material, and supports applications already built on the curve.

Using deterministic ECDSA nonces according to RFC 6979 also improves resilience against poor randomness in key generation and signing implementations.

Specification #

This proposal follows the secp256k1 curve parameters defined in SEC 2 and uses ECDSA signatures for signing and verification.

It also defines address and key encoding rules for secp256k1 key pairs, as well as an HD derivation path suitable for secp256k1 key generation.

Encoding #

Address Format #

This proposal introduces address type 4 as a new account address subtype for secp256k1 public keys. This is distinct from existing address types used in Pactus.

The address payload is derived from the compressed secp256k1 public key:

address_data = ripemd160(blake2b_256(public_key))

Addresses are encoded using Bech32m.

address_string = bech32m(HRP="pc", TYPE="4", DATA="<address_data>")

secp256k1 addresses start with pc1y....

Public Key #

secp256k1 public keys are compressed to 33 bytes using the standard 0x02/0x03 prefix notation.

Public keys are serialized with Bech32m using a dedicated HRP.

public_key_string = bech32m(HRP="public", TYPE="4", DATA="<compressed_public_key>")

Private Key #

secp256k1 private keys are 32-byte values in the range [1, n-1], where n is the curve order.

Private keys are serialized with Bech32m using a dedicated HRP.

private_key_string = bech32m(HRP="SECRET", TYPE="4", DATA="<private_key_data>")

Signature Format #

ECDSA signatures use the secp256k1 curve and follow these rules:

  • Message digests use BLAKE2b (blake2b_256).
  • Signature values are generated using deterministic nonce generation per RFC 6979.
  • The signature is encoded as a fixed 64-byte sequence: r || s.
  • The value s MUST be in the lower half of the curve order to ensure a unique canonical representation.

Verification follows the standard ECDSA verification algorithm over secp256k1.

HD Wallet #

Derivation Path #

For hierarchical deterministic key generation, this proposal follows SLIP-10 with a fully hardened derivation path.

m / purpose' / coin_type' / address_type' / address_index'

All components in the derivation path MUST be hardened.

Purpose #

The purpose is set to 44, following BIP-44.

Hardened derivation is used at this level.

Coin Type #

The coin type is set to 21888, which matches the PAC coin type registered in SLIP-0044.

Hardened derivation is used at this level.

Address Type #

The address type is set to 4 for secp256k1 account addresses.

Hardened derivation is used at this level.

Address Index #

Addresses start at index 0 and increase sequentially.

Hardened derivation is used at this level.

Example Paths # 
m/44'/21888'/4'/0'   # first secp256k1 account/address
m/44'/21888'/4'/1'   # second secp256k1 account/address

Test Cases #

Encoding Test Cases #

The following test vectors demonstrate the encoding and decoding of secp256k1 keys and addresses:

  • Private Key Data (hex): 000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
  • Public Key Data (compressed hex): 036d6caac248af96f6afa7f904f550253a0f3ef3f5aa2fe6838a95b216691468e2
  • Address Data (hex): 042bc1db7e0797c45b918dc401093c9257c6012b4c
  • Encoded Private Key: SECRET1YQQQSYQCYQ5RQWZQFPG9SCRGWPUGPZYSNZS23V9CCRYDPK8QARC0SPVXU8Z
  • Encoded Public Key: public1yqdkke2kzfzheda405lusfa2sy5aq70hn7k4zle5r322my9nfz35wyfamrfs
  • Encoded Address: pc1y90qakls8jlz9hyvdcsqsj0yj2lrqz26vqu7l0z
  • Message (bytes): pactus
  • Message Digest (hex): ea020ace5c968f755dfc1b5921e574191cd9ff438639badae8a69f667e0d5970
  • Signature (hex): c86779676d217b04979434e5bd37eddd02b671e9a54b48d3a812c7862dcb539631bb5e8459fec007608f50ea5661e0a5215aac976705404cb4f36ee623e63199

HD Wallet Test Cases #

For hierarchical deterministic wallet test vectors, refer to SLIP-0010.

Implementations #


Copyright

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