Lenstra, Arjen K.2011-03-292011-03-292011-03-292006https://infoscience.epfl.ch/handle/20.500.14299/65761The SafeWord Silver authentication token is a small hard- ware device. It generates one-time passwords consisting of 6 hexadecimal digits. In this note it is shown that if a few dozen consecutive passwords and the first digit of the next one are known for a particular SafeWord Silver token, its second and third digit can easily be determined. Fur- thermore, given 256 consecutive passwords, on average one of the 256 next passwords can be predicted. These observations hold for all tokens that were studied. It cannot be guaranteed, but must considered to be likely, that they hold for other SafeWord Silver tokens as well.recreational cryptanalysisone-time passwordstext::report