code review 10140046: asn1: Improved encoding/decoding for OID types

asn1: Improved encoding/decoding for OID types

The first identifier in an Object Identifer must be between 0 and 2
inclusive. The range of values that the second one can take depends
on the value of the first one.
The two first identifiers are not necessarily encoded in a single octet,
but in a varint.

[gedimitr, 2013-06-10 20:52:41]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[agl1, 2013-06-10 21:00:56]

Why do you believe that the first two values need to be a varint? I believed
that it was restricted to a single byte.

(I don't have the ASN.1 spec of course, I use [1], the same as everyone else it
appears)

[1] http://luca.ntop.org/Teaching/Appunti/asn1.html

[gedimitr, 2013-06-10 21:17:21]

Hi,

X.690 is explicit about it:
"
8.19.2 The contents octets shall be an (ordered) list of encodings of
subidentifiers (see 8.19.3 and 8.19.4)
concatenated together.
Each subidentifier is represented as a series of (one or more) octets...
...
8.19.4 The numerical value of the first subidentifier is derived from
the values of the first two object identifier
components in the object identifier value being encoded, using the
formula: (X*40) + Y
"

Also, in the example that is provided in the same chapter, 2 octets
are needed for the first subidentifier:
OID {2 100 3} gets encoded as 0x0603813403 (tag and length included)

ITU used to charge for downloading its standards, but now all of them
can be downloaded free of charge:
https://www.itu.int/rec/T-REC-X.690/en

BRs,
Gerasimos

2013/6/11  <agl@golang.org>:
> Why do you believe that the first two values need to be a varint? I
> believed that it was restricted to a single byte.
>
> (I don't have the ASN.1 spec of course, I use [1], the same as everyone
> else it appears)
>
> [1] http://luca.ntop.org/Teaching/Appunti/asn1.html
>
> https://codereview.appspot.com/10140046/

[agl1, 2013-06-10 22:14:54]

*** Submitted as https://code.google.com/p/go/source/detail?r=fe447e02dc0b ***

asn1: Improved encoding/decoding for OID types

The first identifier in an Object Identifer must be between 0 and 2
inclusive. The range of values that the second one can take depends
on the value of the first one.
The two first identifiers are not necessarily encoded in a single octet,
but in a varint.

R=golang-dev, agl
CC=golang-dev
https://codereview.appspot.com/10140046

Committer: Adam Langley <agl@golang.org>