Re: AES counter mode

On 6/2/2013 2:24 AM, Peter Gutmann wrote:
> Kostantinos Koukopoulos <[email protected]> writes:
>
>> I'm looking to implement encryption and transmission of large datasets (in
>> the order of a couple of gigabytes) with the following requirements:
>>
>> a) the encryption of each block shouldn't depend on the completed encryption
>> and transmission of other blocks (i.e. parallel encryption)
>>
>> b) encryption and transmission may be stopped and it should be possible to
>> resume the encryption using as small a saved state as possible (e.g. the key,
>> the IV/nonce and the sequence of previously encrypted blocks).
>>
>> If I'm not mistaken AES CTR mode would be suitable for this task. Is it
>> possible with cryptlib? I haven't found any information about AES CTR and
>> cryptlib so far.
>>
>> Is there perhaps some other way that I could implement (a) and (b) that would
>> be possible and/or straightforward with cryptlib?
> Implementing counter mode is pretty simple when you've got ECB mode, you just
> encrypt the counter in ECB mode and XOR with the data.  However, it's very,
> very easy to get counter mode wrong, which means a simple XOR is all anyone
> needs in order to recover the encrypted data.  AES-CTR is the logical
> successor to RC4 in terms of both functionality and ease-of-misuse, so you
> have to be extremely careful to get it right.  I wouldn't use it myself
> because it's too easy to get wrong.  You can do the same as you require with
> CBC, provided you stop and start at a 16-byte boundary.
>
> Peter.

I realize it's been over a year since this was discussed, but I 
downloaded the 3.4.3 beta to check.  I see that the AES CTR routines are 
there, but they aren't hooked into the crypto kernel framework.   There 
is also no CRYPT_MODE_CTR available in cryptlib.h

Is AES CTR supported?  Is aes_ctr_crypt() functional, or does it need work?




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