Sentinel Hardware Keys Developer's Guide - Customer Connection ...

Chapter 7 – Implementing Secure Licensing
Contents Glossary Index Troubleshooting
Tip: The query/response table is written into the design header file when you
build a license template containing an AES feature. 1
Query Frequently
If you rely on a single call at the beginning of your code, it is relatively easy
for a skilled hacker to isolate the call and defeat your protection. Another
potential problem with querying only once is that a user could remove the
Sentinel Key after starting the application. The key could then be used to
run another copy of the application. 2
Query Randomly
174 Sentinel Hardware Keys Developer’s Guide
You must design the protection strategy to have the application pick the
challenge from the query/response table randomly. This makes it difficult to
anticipate what the challenge will be. Once you choose a challenge, use this
one challenge repeatedly for some period of time (such as each time the program
is run, or once a day). If your application uses a different challenge
every time, then it will cycle through all available challenges in a faster time
frame. This speeds up the time it takes to listen to every possible challenge.
Add Noise to your Query Checks
Generate random queries and then dismiss the results. This generates a
large amount of unused data among the useful data. Anyone trying to
record your communications with the key will need to record large amounts
of data and have trouble deciphering what is meaningful.
Generate New Tables Frequently
Each time you create an update to your application, regenerate the query/
response table. If an attacker has been able to record all the challenges used
1. The query/response table will be generated for a CodeCover feature when you select the
Include CodeCover features check box under the Build Options tab.
2. To address this, you may also like to use the SFNTSetHeartbeat API function which will
release the license after specified idle period.