This example works for me in powershell (using nitropy 0.4.39 and nk3 firmware v1.5.0, writing to slot 2): nitropy.exe nk3 secrets add-challenge-response 2 ABCDEFGHIJKLMNOPQRSTUVWXYZ234567 Of course you want to use a good random secret in practice. The example secret shown is just to reflect all base32 symbols.