[DUG] Sending a file and verifying the data

[Alister Christie]

This popped up on DelphiFeeds.com today
http://delphi.about.com/od/objectpascalide/a/delphi-md5-hash.htm

Alister Christie
Computers for People
Ph: 04 471 1849 Fax: 04 471 1266
http://www.salespartner.co.nz
PO Box 13085
Johnsonville
Wellington 



John Bird wrote:
> 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
>
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