[TLS] Re: Record layer padding

[Simon Josefsson <simon@xxxxxxxxxxxxx>]

<Pasi.Eronen@xxxxxxxxx> writes:

>> Even more: If I am understand it correctly, implementations are
>> encouraged to do so in order to foil traffic analysis-based cracking
>> attempts.
>
> Well, "encouraged" is perhaps an overstatement: as far as I know,
> most existing TLS implementations don't this. (When some versions
> of GnuTLS shipped with this feature enabled, it was discovered
> that Symbian TLS implementation didn't like receiving that 
> extra padding -- a bug that hadn't been discovered in probably 5+
> years, suggesting that nobody else sends such records. There were
> some messages on the list back in November, I think.)

GnuTLS still pad records randomly, for security reasons, and has done so
since basically forever as far as I know.  I see no reason to disable it
by default.  There has been relatively few reports about problems caused
by this, and only from Symbian TLS users.

What has changed since it was discovered that record padding was
problematic in some environments is that we offer a mechanism for
applications to disable it.  We recommend that application authors use
the defaults (i.e., record padding enabled), and only that users disable
it on their own initiative, and further, that they only do so on a
per-IP or per-account basis if possible.

I would encourage all implementers to enable record padding.

/Simon


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