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TRANSACTION.md

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Kaspa Transaction Serialization

Overview

The custom transaction serialization presented is for Kaspa.

Amount units

The base unit in Kaspa is the KAS and the smallest unit used in raw transaction is the sompi: 1 KAS = 100000000 sompi.

Address format

Kaspa addresses begin with kaspa: followed by 61 base32 characters for a total of 67 bytes for Schnorr-signed and P2SH addresses. P2SH addresses are supported only as a send address by this app.

For ECDSA-signed addresses (supported by this app only as a send address), it begins with kaspa: followed by 63 bytes for a total of 69 bytes.

Structure

Transaction

Field Size (bytes) Description
version 2 The version of the transaction being signed
n_inputs 1 The number of inputs. Max 255.
n_outputs 1 The number of outputs. Exactly 1 or 2.
change_address_type 1 0 if RECEIVE or 1 if CHANGE*
change_address_index 4 0x00000000 to 0xFFFFFFFF**
account 4 0x80000000 to 0xFFFFFFFF, normally should use 0x80000000 (the default account)***

* While this will be used for the change, the path may be either RECEIVE or CHANGE. This is necessary in case the user wants to send the change back to the same address. In this case, the change_address_type has to be set to RECEIVE.

** change_address_type and change_address_index are ignored if n_outputs == 1. If n_outputs == 2 then the path defined here must resolve to the same script_public_key in outputs[1].

*** account is the BIP44 account. A transaction can only come from a single account. Current Kaspa ecosystem only uses 0' (or 0x80000000) but support this is in anticipation of wider account-based support.

Transaction Input

Total bytes: 46

Field Size (bytes) Description
address_type 1 0x00 for RECEIVE or 0x01 for CHANGE address
address_index 4 The index of this address in the derivation path
value 8 The amount of KAS in sompi in this input
index 1 The index of this outpoint
prev_tx_id 32 The transaction ID in bytes

Transaction Output

Total bytes: 43 (max)

Field Size (bytes) Description
value 8 The amount of KAS in sompi that will go send to the address
script_public_key 35 Schnorr: 0x20 + public_key (32 bytes) + 0xac
ECDSA: 0x20 + public_key (33 bytes) + 0xab
P2SH: 0xaa, 0x20 + script_hash (32 bytes) + 0x87

Transaction Requirements

  • Fee = (total inputs amount) - (total outputs amount)
  • (total inputs amount) > (total outputs amount)
  • There must be at least 1 input
  • There must be exactly 1 or 2 outputs
    • If there is only 1 output, it is assumed to be the send address
    • If there are 2 outputs, the first output is assumed to be the send address and the second output is where the change will go
      • The script_public_key for the change must resolve to the same value that the change address type and index resolve to. This is validated in the ledger device.

Signature

Schnorr is used to sign transaction on the SECP-256k1 curve.

It is used to sign the SigHash.

Fee

The fee is the difference between the sum of input values and the sum of the output values.

Links