How much does the availability of x86-64 CPUs affect the time needed to crack passwords?
Solar Designer: I am sorry to disappoint you, but this is not a major change for John. As far as John is concerned, Intel’s MMX was already 64-bit. It was not a true 64-bit architecture (most importantly, there was no 64-bit addressing), but in order to implement bitslice DES, only bitwise operations were needed – and those were available. The only things which change for John the Ripper on x86 with the availability of x86-64 CPUs are the ability to generate 64-bit code from C source (MMX code had to be hand-written or generated with self-made scripts), the availability of more 64-bit registers (15 usable instead of just 8), and the lack of an AND-NOT operation with x86-64. While the extra registers provide some speedup for bitslice DES, the existing MMX code is hand-optimized whereas the x86-64 code is currently being generated by C compilers. Overall, x86/MMX and x86-64 builds of John deliver similar performance, with differences for most hash types being within 20% (on the same CPU)
