[Cryptography] a question on consensus over algorithmic agility

[ianG]

On 27/06/2014 14:31 pm, Peter Fairbrother wrote:
> On 26/06/14 11:33, ianG wrote:
> [...]
>> Take your favourite two block ciphers.  Independent keys, XOR the
>> output.  This provides the strength of both, together.
> 
> 
> For a keyed hash, maybe [1] - but for a cipher, how do you decrypt?


CTR mode.  Feed counter (eg. block number) in as the 'plaintext' into
each cipher.  Take each cipher's output and XOR them together.  Then XOR
that with your real plaintext.

https://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Counter_.28CTR.29

Do exactly the same for decrypt.  Don't ever use the same key/counter
combination for different packets ;-) but that is true of CTR mode anyway.


iang