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The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:18:28
Peter Gutmann (pgut001@cs.auckland.ac.nz)
Thu, 25 Feb 1999 16:20:33 (NZDT)
nisse@lysator.liu.se (Niels Möller) writes:
>pgut001@cs.auckland.ac.nz (Peter Gutmann) writes:
>>ASN.1, if used properly, is an extremely elegant and powerful notation for
>>describing data formats.
>I'm not so sure about this... I once tried to write a grammer for ASN.1, for a
>LR parser generator. I.e., parsing the type descriptions, not just the encoded
>data objects. I failed. I'm not even convinced that ASN.1 is unambigous.
The original (1988) ASN.1 wasn't machine-parseable at all (and many would say
the macro notation wasn't even human-parseable), it was mostly fixed in the
1993 version but you still occasionally need to embed compiler directives into
the ASN.1 to fix up ambiguities, and the features which have been added to
replace the macro notation (stuff like extended forms of the constraint
notation) are a bit more rigorous but still can't be easily handled
automatically.
Although people complain about this, it isn't really a shortcoming compared to
other techniques since ASN.1 is a lot more than just a bit-bagging mechanism.
Other bit-bagging schemes (eg one-byte tag, 32-bit length, data) can appear
simpler but you pay for the format simplicity by the fact that the programmer
has to explicitly know about and add code to handle each field, whereas with
ASN.1 the parser will handle and unpack everything for you. I found it a *lot*
more work to write a PGP message processor than a PKCS #7 one.
Peter.
The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:18:28