Re: Parser abilities, and MDCs (Re: pointers to openpgp-interopknowledge base?)

[pgut001@cs.auckland.ac.nz (Peter Gutmann)]

disastry@saiknes.lv writes:

>rfc2440b03>4.2.1. Old-Format Packet Lengths
>rfc2440b03>[snip]
>rfc2440b03>   The meaning of the length-type in old-format packets is:
>rfc2440b03>   3 - The packet is of indeterminate length.  The header is 1 octet
>rfc2440b03>       long, and the implementation must determine how long the packet
>rfc2440b03>       is. If the packet is in a file, this means that the packet
>rfc2440b03>       extends until the end of the file. In general, an implementation
>rfc2440b03>       SHOULD NOT use indeterminate length packets except where theend
>rfc2440b03>       of the data will be clear from the context,
>
>it does not talks about compression, so I think it should be the same for any
>packet type

In general indefinite-length packets are a pain, you can avoid them in all
cases except compressed-data where you don't know the length in advance (and
maybe a few oddball streaming applications).  Although the standard doesn't say
it, common sense would dictate using the definite-length encoding for all but
compressed data.

>rfc2440b03>4.2.3. Packet Length Examples
>rfc2440b03>[snip]
>rfc2440b03>   An implementation MAY use Partial Body Lengths for data packets,be
>                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>rfc2440b03>   they literal, compressed, or encrypted. The first partial length
>                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>rfc2440b03>   MUST be at least 512 octets long. Partial Body Lengths MUST NOT be
>rfc2440b03>   used for any other packet types.
>
>so it is ok for all data packets..

Urgh, I hope no-one interprets it that way.  The partial-length encoding is
incredibly painful to use with its silly power-of-two restriction (you can't
just say "This is what I've got so far, the next lot starts here" but have to
chop it up into little power-of-two length pieces just to fit the *&#^$&#*
length-encoding mechanism).  GPG uses the definite-length format where it can
and 0xA3 where it can't (compressed data), something I agree with 
wholeheartedly.

Peter.