We need to check all files to/from customers on uniqueness based on SHA1 hash.
functionality :
a. Calculate SHA1 hash of a file
b. is this hash already present in a specified named list?
c. If not in list, add it to the named list
d. If hash does occur, exception handling
e. Named list cleanup (days validity of the hash)
How can this be done in a MFT workflow?
Are there already functions/tasks in MFT we can use for his?

Gerard,

GAMFT has the capability of running local commands. Utilizing that functionality, you can take a file that has been uploaded or currently exists and pass that into the local command to generate the MD5 or SHA1 hash of the file, returning that value to the GAMFT Workflow.

Now, it's just a matter of doing comparisons against your specified named list. Search a Table, CSV, XML, etc... compare against value generated and you have your conditions identified.

Named list cleanup can be done separately.

*Side Note*
You could also create a custom task that does this for you as well. Pass the file name into the custom task and it returns the SHA1 value for you.

Either way, you have the information you need for processing.