[Cryptography] Whitening Algorithm

Ray Dillinger bear at sonic.net
Fri Jul 24 17:24:24 EDT 2015



On 07/23/2015 04:06 PM, Dave Horsfall wrote:
> On Thu, 23 Jul 2015, Ray Dillinger wrote:
> 
>> As a lightweight CSPRNG suitable for devices of modest compute power, I 
>> recommend the 'Spritz' algorithm developed by Rivest & Schuldt.  
>> Although it's fairly new, it seems quite good.
> 
> Bruce Schneier doesn't seem to like it, but thinks it's clever anyway:
> 
>     https://www.schneier.com/blog/archives/2014/10/spritz_a_new_rc.html
> 
> ``Spritz is Rivest and Schuldt's redesign of RC4. It retains all of the
>   problems that RC4 had. It's built on a 256-element array of bytes, 
>   making it less than ideal for modern 32-bit and 64-bit CPUs. It's not very 
>   fast. (It's 50% slower than RC4, which was already much slower than 
>   algorithms like AES and Threefish.) It has a long key setup. But it's a 
>   very clever design.''
> 

All this is true, but if you are implementing it for a device
that natively speaks 8-bit bytes (which a lot of embedded devices
do) it ain't bad.  And it's among the easiest cryptographic things
for a programmer to get right.

				Bear

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