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Transaction Info and Sighash Using Minsc

Introduction

Minsc is a powerful tool for Bitcoin scripting, developed by Shesek.
You can do some really cool things with Minsc, like CTV-based Vault and HTLC.
In this guide we will use Minsc to check transaction details and compute sighash.

We'll explore two simplified Minsc templates:

P2WPKH template - For basic Pay-to-Witness-Public-Key-Hash transactions.
P2WSH template - For more complex Pay-to-Witness-Script-Hash transactions.

Important: This guide uses testnet/signet examples only. Never use mainnet private keys in Minsc templates.

1. Set Up Your Variables

We will define private key and output details. We can use any form of key, but in our example we will use an extended private key.

Open p2wpkh template in the browser:

https://min.sc/v0.3/#gist=4f3a74b78978ea2a650b96f5a72352ce

Declare private key:

$tprv = tprv8ZgxMBicQKsPe2ueBRfzTzgpt7gnRZdwo4rEPKsLmmpGHQxZscNKv45nsgfohcoWgturdL3c2J7FakV8adSk3huTA1RSWJEXFukwkJWF3gC;

Declare bip32 key derivation index:

$derivationIndex = 0;


Declare output address:

$outputAddr = tb1qwtcm09rg8eez7ep0x4tkqkrtasa0mytufw7xzz;


And the amount of the output:

$amount = 0.85208938 BTC;


We will add an assert to ensure that the derived address matches the expected output. This step is crucial because it verifies that the private key derivation is correct and aligns with the expected output address, preventing potential errors when signing transactions. Note the derivation path is 84h/1h/0h/0/derivationIndex, we can adjust it to our needs.

assert::eq(address(wpkh($tprv/84h/1h/0h/0/$derivationIndex)), $outputAddr);

2. Load the Transaction

Define the transaction using the tx() function.

$tx = tx(0x020000000001012dbbe91eceb76830221374c1a0d0080fc88f01ad2cc121b07bb06b0a27cb3abff200000000ffffffff0240420f0000000000220020e2f55cdc156913d6fc86f4ab684d54c113a1ad04d7cdec2f8f706a5bc64edc78d5a27b00000000001600147022f7802b1c8f495b191e014849a217de3235f802483045022100a905549b19b5ef3563bda630d3050aa318d56dd7101ce647eff5bba3b7d947660220213c1c9890410374a6271bc69e48e94ea4ea4f6bd8cdfc375d29c9239edf7f930121039c66ff2131622270d5eee20cd45fac7457912b16704d1cd17156957771c18a1400000000);

This represents the raw Bitcoin transaction.

3. Remove Witness Data

Since signatures cover transaction data without witnesses, we create a witness-stripped transaction:

$tx_no_witness = tx::with_witness($tx, [ 0: [] ]);

4. Compute the Sighash

The sighash is a hash of the transaction data that must be signed. Let compute it using:

$sighash = tx::sighash($tx_no_witness, 0, [ $outputAddr:$amount ], SIGHASH_ALL);

Sighash command:

  • Targets input index 0.
  • Uses the given output address and amount.
  • Specifies SIGHASH_ALL (signing the entire transaction).

5. Generate the Signature

Sign the transaction hash using the derived private key:

$signature = ecdsa::sign($tprv/84h/1h/0h/0/$derivationIndex, $sighash) + SIGHASH_ALL;
  • Note that bitcoin signature are not deterministic, therefor your signature will be different.

6. Full Template Example (p2wpkh)

Template: p2wpkh

// template for signet p2wpkh

// replace key (test only!), index, output address & amount
// you can find your output address & amount using: https://boss2025.xyz/api/tx/yourtxid
$tprv = tprv8ZgxMBicQKsPe2ueBRfzTzgpt7gnRZdwo4rEPKsLmmpGHQxZscNKv45nsgfohcoWgturdL3c2J7FakV8adSk3huTA1RSWJEXFukwkJWF3gC; 
$derivationIndex = 999;
$outputAddr = tb1qwtcm09rg8eez7ep0x4tkqkrtasa0mytufw7xzz;
$amount = 0.85208938 BTC;

// uncomment this, if assert, verify key and index
//assert::eq(address(wpkh($tprv/84h/1h/0h/0/$derivationIndex)), $outputAddr);

$tx = tx(0x020000000001012dbbe91eceb76830221374c1a0d0080fc88f01ad2cc121b07bb06b0a27cb3abff200000000ffffffff0240420f0000000000220020e2f55cdc156913d6fc86f4ab684d54c113a1ad04d7cdec2f8f706a5bc64edc78d5a27b00000000001600147022f7802b1c8f495b191e014849a217de3235f802483045022100a905549b19b5ef3563bda630d3050aa318d56dd7101ce647eff5bba3b7d947660220213c1c9890410374a6271bc69e48e94ea4ea4f6bd8cdfc375d29c9239edf7f930121039c66ff2131622270d5eee20cd45fac7457912b16704d1cd17156957771c18a1400000000);

$tx_no_witness = tx::with_witness($tx, [ 0: [] ]);

$sighash = tx::sighash($tx_no_witness, 0, [ $outputAddr:$amount ], SIGHASH_ALL);

$signature = ecdsa::sign($tprv/84h/1h/0h/0/$derivationIndex, $sighash) + SIGHASH_ALL;

7. Expected Output (p2wpkh)

// Defined variables:

$tprv = tprv8ZgxMBicQKsPe2ueBRfzTzgpt7gnRZdwo4rEPKsLmmpGHQxZscNKv45nsgfohcoWgturdL3c2J7FakV8adSk3huTA1RSWJEXFukwkJWF3gC // seckey

$derivationIndex = 999 // int

$outputAddr = tb1qwtcm09rg8eez7ep0x4tkqkrtasa0mytufw7xzz // address

$amount = 85208938 // int

$tx = tx [
  "version": 2,
  "inputs": [
    [
      "prevout": bf3acb270a6bb07bb021c12cad018fc80f08d0a0c17413223068b7ce1ee9bb2d:242,
      "witness": [ 0x3045022100a905549b19b5ef3563bda630d3050aa318d56dd7101ce647eff5bba3b7d947660220213c1c9890410374a6271bc69e48e94ea4ea4f6bd8cdfc375d29c9239edf7f9301, 0x039c66ff2131622270d5eee20cd45fac7457912b16704d1cd17156957771c18a14 ]
    ]
  ],
  "outputs": [
    tb1qut64ehq4dyfadlyx7j4ksn25cyf6rtgy6lx7ctu0wp49h3jwm3uqrw4sqj:0.01 BTC,
    tb1qwq300qptrj85jkcercq5sjdzzl0ryd0cvxk8wh:0.08102613 BTC
  ]
] // transaction

$tx_no_witness = tx [
  "version": 2,
  "inputs": [
    bf3acb270a6bb07bb021c12cad018fc80f08d0a0c17413223068b7ce1ee9bb2d:242
  ],
  "outputs": [
    tb1qut64ehq4dyfadlyx7j4ksn25cyf6rtgy6lx7ctu0wp49h3jwm3uqrw4sqj:0.01 BTC,
    tb1qwq300qptrj85jkcercq5sjdzzl0ryd0cvxk8wh:0.08102613 BTC
  ]
] // transaction

$sighash = 0xdf2bbe5674893a76cfcd86d7099e680105250feabf031301e64cc4523d56ce1f // bytes

$signature = 0x3044022006fb261e2eb52c2adc7495123b868dac3ff6623eb5753ef34f3ddd3600c8423002201da932213cb2dd037ac787a461a6042dbb9f8287526f95874f6dad6c9611501c01 // bytes

8. Full Template Example (p2wsh)

Template: p2wsh

// template for signet p2wsh

// update your key (test only)
$tprv = tprv8ZgxMBicQKsPe2ueBRfzTzgpt7gnRZdwo4rEPKsLmmpGHQxZscNKv45nsgfohcoWgturdL3c2J7FakV8adSk3huTA1RSWJEXFukwkJWF3gC;
$amount = 0.01 BTC;

$tx = tx(0x02000000000101d62234a2ce378e85baad2d0499c60dbc3037b29da2cf4d4e796e52a6fd264d570000000000ffffffff0200e1f50500000000220020421305d3c9f5faee4f8fa7dc79f54c5eb2971ff4819cfac68fcb219c14f8aed5fb8d435500000000160014f1a65dab1d878c0ae057a5d3cc1b7d31f494d774024830450221008e9582cf252ed3b9f05c38a017c675ae8c55f0aba3bc9c1dfddb0fbbe3b17c3f022002d4c28e687597aa89445a78afdee34d96852493c140b573fa8b157edc3a704901210250e42d3f14ed353ffb49c8a041bab867dadbbb987a41007c7424aa7c5cad90ca00000000);


$tx_no_witness = tx::with_witness($tx, [ 0: [] ]);

$sk0 = bytes(derived($tprv/84h/1h/0h/0/0));
$sk1 = bytes(derived($tprv/84h/1h/0h/0/1));
$pk1 = bytes(derived(pubkey($tprv/84h/1h/0h/0/0)));
$pk2 = bytes(derived(pubkey($tprv/84h/1h/0h/0/1)));

$sighash = tx::sighash($tx_no_witness, 0, [ wsh(`2 $pk1 $pk2 2 OP_CHECKMULTISIG`):$amount], SIGHASH_ALL);

9. Expected Output (p2wsh)

// Defined variables:

$tprv = tprv8ZgxMBicQKsPe2ueBRfzTzgpt7gnRZdwo4rEPKsLmmpGHQxZscNKv45nsgfohcoWgturdL3c2J7FakV8adSk3huTA1RSWJEXFukwkJWF3gC // seckey

$amount = 1000000 // int

$tx = tx [
  "version": 2,
  "inputs": [
    [
      "prevout": 574d26fda6526e794e4dcfa29db23730bc0dc699042dadba858e37cea23422d6:0,
      "witness": [ 0x30450221008e9582cf252ed3b9f05c38a017c675ae8c55f0aba3bc9c1dfddb0fbbe3b17c3f022002d4c28e687597aa89445a78afdee34d96852493c140b573fa8b157edc3a704901, 0x0250e42d3f14ed353ffb49c8a041bab867dadbbb987a41007c7424aa7c5cad90ca ]
    ]
  ],
  "outputs": [
    tb1qggfst57f7hawunu05lw8na2vt6efw8l5sxw04350evsec98c4m2s9vg9ql:1 BTC,
    tb1q7xn9m2cas7xq4czh5hfucxmax86ff4m5pj7ce8:14.30490619 BTC
  ]
] // transaction

$tx_no_witness = tx [
  "version": 2,
  "inputs": [
    574d26fda6526e794e4dcfa29db23730bc0dc699042dadba858e37cea23422d6:0
  ],
  "outputs": [
    tb1qggfst57f7hawunu05lw8na2vt6efw8l5sxw04350evsec98c4m2s9vg9ql:1 BTC,
    tb1q7xn9m2cas7xq4czh5hfucxmax86ff4m5pj7ce8:14.30490619 BTC
  ]
] // transaction

$sk0 = 0x490e081f444ec00e525a1eab9976505f0e4b0c9e3878c1b05015859adc0deae0 // bytes

$sk1 = 0x7c8a7a16352b924ae807a3ccf19b5b6be453ca3e5263b8fc338ba5e9ba65dd6a // bytes

$pk1 = 0x03df653824ac6a3e8bcca1372e9b36241acc654a2d0cc94c76cb4cf613447391c7 // bytes

$pk2 = 0x03eda350a58a973f31466663b348b8340c94251ee0c5d01cbaeaa5e17e4d6c8e14 // bytes

$sighash = 0xc90832d5fe9abcf36a8be02b7fce0e37e5c2428b865448fb55ee2e5f9cafec17 // bytes