//example teal code taken from https://developer.algorand.org/tutorials/writing-simple-smart-contract/
// Check the Fee is resonable 
// In this case 10,000 microalgos
txn Fee
int 10000
<=

// Check the length of the passphrase is correct 
arg 0
len 
int 73
==
&&

// The sha256 value of the passphrase
arg 0
sha256
byte base64 30AT2gOReDBdJmLBO/DgvjC6hIXgACecTpFDcP1bJHU=
==
&&

// Make sure the CloseRemainderTo is not set
txn CloseRemainderTo
txn Receiver 
==
&&