Implementing The Exponential Backoff Algorithm To Thwart Dictionary Attacks
Introduction
Recently there was a forum post regarding using the exponential backoff algorithm to prevent or at the very least slow down dictionary attacks. A dictionary attack is when a perpetrato...
Published Nov 17, 2011
Version 1.0
devnullNZ
Nimbostratus
NimbostratusIn the first iteration of the bit shift, it appears that tcl ends up trying to do a negative shift
i.e.
prev_attempts =0
so
set new_lockout [expr (1 << ($prev_attempts -1))]
evaluates to:
expr (1 << (0-1))
which is classed as undefined, being a negative number.
Should we be adding a rule to catch that prior to evaluating the expression?