CCC BTC Lock

CCC (Common Chains Connector) is a framework that enables interoperability between wallets from different blockchain ecosystems and Nervos CKB. It leverages CKB’s flexibility in cryptographic verification to validate signatures from external chains like BTC and ETH.

CCC BTC Lock is a specific implementation of the CCC framework that allows CKB transactions to be unlocked using signatures from Bitcoin wallets. It follows common CCC lock design principles and adapts them for Bitcoin’s secp256k1 key system and address formats. This Lock Script supports Bitcoin-style public key hashes and addresses, allowing seamless interaction between CKB and BTC wallet infrastructures.

How It Works

Detailed Overview

Detailed documentation

Lock Script Structure

A CCC BTC lock script has the following properties:

• code_hash: The hash of the deployed CCC BTC lock script code
• hash_type: Usually "type"
• args: A 20-byte secp256k1 public key hash, calculated as RIPEMD-160(SHA-256(compressed_pubkey))

Supported Bitcoin address types:

• P2PKH (decoded from base58)
• P2WPKH (decoded from bech32 or bech32m)

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Unlocking Process

To unlock a cell with a CCC BTC lock, the following process is performed:

1. Message Construction

A signing message is created using double SHA-256 over the following structure:

0x18                           # Length of the string "Bitcoin Signed Message:\n"
"Bitcoin Signed Message:\n"
<length_of_message_string>     # 1 byte
"Signing a CKB transaction: 0x{sighash_all}\n\nIMPORTANT: Please verify the integrity and authenticity of connected BTC wallet before signing this message"

• {sighash_all} is a 32-byte digest calculated via the ckbhash function, which uses blake2b.
• The resulting hash is the message to be signed.

2. Witness and Signature Format

The witness must be a valid WitnessArgs structure. In its lock field, it must contain a 65-byte secp256k1 signature formatted as:

<recId (1 byte)> <r (32 bytes)> <s (32 bytes)>

• recId is derived from the header byte in BIP 137 and can be:

  • 0~3
  • 27~30 (for P2PKH)
  • 39~42 (for P2WPKH)

• These values are normalized to 0~3 for public key recovery.

3. Verification

• The signature and recId are used to recover the compressed secp256k1 public key.
• This public key is hashed with SHA-256 and then RIPEMD-160.
• If the resulting 20-byte hash matches the args in the lock script, the script passes and the transaction is validated.

Deployment

• Testnet

parameter	value
code_hash	0x8f026d6113b24800e04bfb33703f98dfaa6db6719097ab5d3050db9cf4fec45e
hash_type	type
tx_hash	0xba5a1a77019be0e8942119ad549f01ca3c61fd9f911aa46e27d508a802236614
index	0x0
dep_type	code