Here&#x27;s my attempt at explanatory comments - the ScriptPubkey is a program (written in Bitcoin Script) which is attached to an output of a Bitcoin transaction - parameters must be provided that make it return &quot;true&quot;.<p><pre><code>    # Compute the SHA256 of the value on the top of the stack (spender input),
    # then add the result to the top of the stack
    OP_SHA256
    # Check whether this value is equal to Y, the hash of the key under which
    # the solution was encrypted. 
    &lt;Y&gt; OP_EQUAL
    # If the correct key was provided, add the seller&#x27;s public key to the stack
    OP_IF
      &lt;Seller Pubkey&gt;
    # Otherwise, if it has been 100 blocks or more, add the buyer&#x27;s public key
    # to the stack so they may refund themselves if the seller does not complete
    # the protocol 
    OP_ELSE
      &lt;block_height+100&gt; OP_CHECKLOCKTIMEVERIFY OP_DROP
      &lt;Buyer Pubkey&gt;
    OP_ENDIF
    # Verify the signature against the public key on the top of the stack
    OP_CHECKSIG</code></pre>