iRule hashing + trim

Try this for your hash variable:

set variableHash [sha512 $variable]
set lastTenHash [string range $variableHash [expr [string length $variableHash] - 10] end]

For your response you would need to do a

HTTP::collect [HTTP::header Content-Length]

in your when HTTP_RESPONSE event and then in the HTTP_RESPONSE_DATA event you would need to inspect the HTTP::payload for your string probably using scan. Be weary, that this will collect the whole payload of every response which could be a performance hit to the application.

https://devcentral.f5.com/wiki/iRules.HTTP_RESPONSE_DATA.ashx