Let me explain. I complete a tax return and generate the electronic copy. I note the FBI mark (let's say it starts CCIZGRT)
The client changes their mind about an expense so I then change an expense (and so the SE profits) and regenerate, noting the new FBI mark (starting CCSUKZ).
The client then calls to say actually the first number was right, so back the figure goes. When I regenerate the FBI mark again it is back to starting CCISGRT.
So my question is, is that because the software (IRIS but PTP also does it, can't comment on the rest) gives each return a unique code, then when I revert to one it has already seen it just dredges up that code again, or is it because the code somehow IS the tax return, as in you could put in the code and it would create the tax return entries?
Anyone know?
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It's an IR mark not an FBI mark.
No idea about your software but as far as I know its a generated code probably using something like base64 or some other blowfish type encryption most likely generated from a key
But I doubt very much you could decrypt it without knowing what that key is.
It's generated by the software based on the content of the return. Virtually any change (not just numbers) will result in a new IR mark. Putting the return back exactly to the original generates the same IR mark.
Here's what your software does to generate it:-
Application – Generates IRmark
a. Calculate IRmark over the Body of the document excluding the IRmark
element – This is best implemented by using one of the third party security
libraries that are available such as Apache or Phaos (sample Apache code is
included as a separate tech pack item). A library provides facilities to:
- canonicalise (c14n) the XML document
- generate a 160-bit binary secure hash from the canonicalise XML
using the SHA-1 algorithm
- encode the binary data using base-64 to produce a 28 character
string
Generating the IR Mark:-
https://assets.publishing.service.gov.uk/government/uploads/system/uploa...
And here's details of the Canonicalise step:-
https://www.w3.org/TR/2001/REC-xml-c14n-20010315
And what SHA-1 is all about:-
https://en.wikipedia.org/wiki/SHA-1