Re: [dm-crypt] bits vs bytes

Arno Wagner
2020-03-31T06:43:39Z

On Tue, Mar 31, 2020 at 07:35:16 CEST, JT Morée wrote:
>
> On Monday, March 30, 2020, 6:43:11 PM MST, Arno Wagner <arno@wagner.name> wrote:
> > Not in a cryptographic context. You could also want to etch them
>
> is that because the 512 bits is not the size of the key but instead a
> measurement of one component that goes into generating the key?

Well, block-ciphers have gotten to respect CPU operations recently,
so they are starting to use bytes internally ti increase efficiency.
But look at classic DES, and every but pretty much gets treated by
itself or bits get grpuped in ways that have nothing to do with byte
boundaries. Or look at RSA and whether you have a 4096 bit, 4095 bit
or 4097 bit modulus makes no difference. Of course you usually
go for multiples of 8, but that is just to accomodate a specific
implementation (computers with 8 bit bytes), not anything that is
part of the algebra of the cipher.

Just accept it, it makes sense form a mathematical viewpoint.
Otherwise you would need to multiply by 8 in a lot of places.
And you could also use nibbles (4 bit) words (16 bits),
long words (32 bits) or quadwords (64 bits) as "units". The
byte is not really specuial.

Regards,
Arno

--
Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@wagner.name
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