gistfile1.txt

OP_IF // Normal redeem path

    // Require initiator's secret to be a known length that the redeeming
    // party can audit.  This is used to prevent fraud attacks between two
    // currencies that have different maximum data sizes.
    OP_SIZE
    secretSize
    OP_EQUALVERIFY

    // Require initiator's secret to be known to redeem the output.
    OP_SHA256
    secretHash
    OP_EQUALVERIFY

    // Verify their signature is being used to redeem the output.  This
    // would normally end with OP_EQUALVERIFY OP_CHECKSIG but this has been
    // moved outside of the branch to save a couple bytes.
    OP_DUP
    OP_HASH160
    addrTo

OP_ELSE // Refund path

    // Verify locktime and drop it off the stack (which is not done by
    // CLTV).
    locktime
    OP_CHECKLOCKTIMEVERIFY
    OP_DROP

    // Verify our signature is being used to redeem the output.  This would
    // normally end with OP_EQUALVERIFY OP_CHECKSIG but this has been moved
    // outside of the branch to save a couple bytes.
    OP_DUP
    OP_HASH160
    addrFrom

OP_ENDIF

// Complete the signature check.
OP_EQUALVERIFY
OP_CHECKSIG