Use of Electronic Signatures to Secure VISTA Data

Statement of Problem

The crux of the issue is the ability to store data on patients and be able to detect if the patient data has been changed intentionally or unintentionally since it was entered. Compounding this issue is the need for different people at different points in time to be able to see the data that was entered. This means that the data creator's token cannot be used as a way to secure the data against future modification. The system has to also support document retraction and reassignment, which override the data creator's authority on the document.

An example is in order: how do you know if the text of a TIU note is the same as what the original user entered?

Implementation in FOIA VISTA

Various parts of FOIA VISTA accomplish this using the encryption and decryption functionality. The encryption algorithm used is a stream cipher (I am not exactly sure which one). For TIU documents, the cipher algorithm uses the document's checksum of document contents as one of the vectors in the algorithm to encrypt the signer's name and title. If the document is modified outside of TIU, the user will see gibberish for these two fields.

For example, this is a typical signature:

/es/ DOCTOR MCDUCK, MD
ENT PHYSICIAN
Signed: 02/27/2013 09:34

If the document is changed outside of TIU, it may look like this (this example isn't real as I do not have access to the algorithm):

/es/ lks&*(*% *(*&@#$*&
A#@^*(ssDASDF
Signed: 02/27/2013 09:34

Other VISTA packages, notably Radiology, implement the same functionality, using other vectors for encryption.