RE: Un-encrypting data on the iSeries

You can't decrypt a hash value. A hash value is basically just a fixed
length signature for a set of data and you'd use it to verify that the
contents of the data haven't changed. 

For example, let's say I'm sending you a file with an order number, a
bunch of line items, and an amount due. I could feed all of this into
the hash algorithm we agreed on (MD5 and SHA1 are the most common) in
the order we agreed on. The result would be a series of bytes that I'd
also send with the file (these strings are typically shown in hex format
since un-printable characters are typically generated). Once you get the
file, you could run the same data through the hash algorithm we agreed
on and you should come up with the same series of bytes. If there's a
difference, you know that the file has either been changed or part of it
was lost in transmission.

If you need to be able to encrypt and decrypt data, you'll have to use
an algorithm (such as AES, 3DES, or RC4) that allows decryption. The
current recommendation is to use AES (3DES is a good second) and the
CIPHER MI can do this. There's an example of AES in the archives but
you'll need to read the entire thread since the code I posted has an
error in it that I was seeking help on. Also, the example does not
handle salting (this is random bytes you add to make sure that the same
clear text generates different cipher text) and I didn't find a way to
specify the padding to use for the clear text so if the transmitting
system uses padding on the clear text (PKCS #5 is a common method),
you'll need to remove that yourself.

Matt 

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of
michaelsoucy@xxxxxxxxxxx
Sent: Thursday, June 30, 2005 10:20 AM
To: RPG400-L@xxxxxxxxxxxx
Subject: Un-encrypting data on the iSeries


I need some help with trying to un-encrypting part of a data file that I
have on the iSeries.  The data is encrypted using something  called
"FIPS SHA1".  From the very little I understand about this it's a hash
algorithm.  Is there any routines out there or APIs for the iSeries that
will allow me to un-encrypt the data?  Any help would be greatly
appreciated.

Michael Soucy
michaelsoucy@xxxxxxxxxxx