Periodic payment smart signature can be used multiple times within the same block

[jordan-public]

Subject of the issue

The example smart signature https://github.com/algorand/pyteal/blob/master/examples/signature/periodic_payment.py can be called twice in the same block, thus double-paying the intended amount.

Your environment

Same as the example.

Steps to reproduce

1. When calling from the client using "acl.send_transaction(lstx)", repeat this twice.
2. In the block where Txn.first_valid() % tmpl_period == Int(0), this transaction gets executed twice.

Expected behaviour

Single paying (some code should prevent the transaction from running twice within a block).
This could be an assertion that last succesful transaction was more than a block ago.

Actual behaviour

Double-paying within the same period.

[jasonpaulos]

@jordan-public the lease field prevents the second transaction from being accepted by the network. See this article for more info: https://developer.algorand.org/articles/leased-transactions-securing-advanced-smart-contract-design/

[jordan-public]

Oops, I had removed it not understanding what it was for. Maybe you can mention this in the sample explanation. Thanks, Jordan

…

On Dec 6, 2021, at 9:03 PM, Jason Paulos ***@***.***> wrote: @jordan-public <https://github.com/jordan-public> the lease field prevents the second transaction from being accepted by the network. See this article for more info: https://developer.algorand.org/articles/leased-transactions-securing-advanced-smart-contract-design/ <https://developer.algorand.org/articles/leased-transactions-securing-advanced-smart-contract-design/> — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#143 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEUT77RJCMEKBWDA4JMBFJTUPVTPFANCNFSM5JQAP6PQ>. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.