[Cryptography] Shortening block cipher length...

[Natanael]

Den lör 10 juli 2021 03:13Phillip Hallam-Baker <phill at hallambaker.com>
skrev:

>
>
> On Thu, Jul 8, 2021 at 12:24 AM Sampo Syreeni <decoy at iki.fi> wrote:
>
>> On 2021-03-29, Peter Gutmann wrote:
>>
>> >> For that matter, what's wrong with Counter Mode?
>> >
>> > It turns any strong block cipher into the functional equivalent of
>> > RC4. So what you're saying there is "what's wrong with RC4"?
>>
>> Functional equilent of RC4, isn't the same as RC4, as a bad cipher.
>>
>> If you substitute a better cipher for RC4 in said construction,
>> suddently it can become secure as fuck.
>>
>
> I read 'functional equivalent of RC4' as being a stream cipher.
>
> This application absolutely cannot accept a stream cipher.
>

There are various constructions for format preserving encryption, intended
to work for encrypting stuff of arbitrary but fixed sizes (like database
fields with format restrictions) without changing their size. Suppose you
could use one of those to put together a 64 bit mode?

Or make your own Feistel network from hash functions truncated to 64 bit
outputs.

>
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