[openssl-project] to fully overlap or not to

[Matt Caswell]

On 28/02/18 16:32, Viktor Dukhovni wrote:
> 
> 
>> On Feb 28, 2018, at 11:25 AM, Viktor Dukhovni <openssl-users at dukhovni.org> wrote:
>>
>>> I'd like to request more opinions on
>>> https://github.com/openssl/openssl/pull/5427. Key dispute question is
>>> whether or not following fragment should work
>>>
>>>   unsigned char *inp = buf, *out = buf;
>>>
>>>   for (i = 0; i < sizeof(buf); i++) {
>>>       EVP_EncryptUpdate(ctx, out, &outl, inp++, 1);
>>> 	out += outl;
>>>   }
>>
>> This should work.
> 
> On second thought, perhaps not.  A block cipher cannot provide output
> synchronously on byte boundaries.
> 

It should still work IMO. With a block size of 16 you should get 15
invocations of EVP_EncryptUpdate where outl is set to 0 afterwards,
followed by 1 invocation where outl is set to 16 afterwards. This should
still be the case for in-place encryption.

Matt