NIST has approved two FPE algorithms FF1 and FF3, however, Voltage claims a patent on FF1 and potentially FF3. The Letter of Assurance issued by Voltage in 2013 states in general terms:
Voltage agrees that upon request it will make
available a non-exclusive license, under reasonable rates with or without compensation, to an unrestricted number of applicants on a worldwide basis with reasonable terms and conditions
I'm looking to clarify if which, if any, of these two FPE algorithms can be implemented without requiring a license.
Capital One has provided an open source Go implementation of FF1 and FF3. A Java implementation of FF1 and FF3 is also available but it has not been updated for FF3-1. Both provide a Apache v2 license. A C open source implementation is available with a MIT license for FF1 and FF3 (but not updated for FF3-1).