[DUG] Sending a file and verifying the data

[John Bird]

I wish to send a data file either as an email attachment or via FTP and wish 
to be able to ensure:

1 -  it is not altered in transport.

2 - It came from where it is supposed to have come from.

Its a new area for me - what I have figured out so far is to say generate a 
hash for the file - using say SHA1 or SHA2 and append that on the file as a 
check.  Or to be even cleverer for the second part do the sort of trick when 
passwords are sent over a network with generating a unique session string 
(which never leaves the server),  and hash the combination of both. file and 
session string  This gives something that can be checked back to the server 
when the file arrives - ie no-one else could generate the same hash.

Can anyone suggest any web sites to read up more on - or give ideas on how 
they would do this?

Best hashes to use?

If SHA hashes are the way to go, anyone know of Delphi implementations?

John