Hello, I just found up-to-date RFC 2440: http://www.ietf.org/internet-drafts/draft-ietf-openpgp-rfc2440bis-14.txt
Here is 5.12:
5.12. User Attribute Packet (Tag 17)
The User Attribute packet is a variation of the User ID packet. It
is capable of storing more types of data than the User ID packet
which is limited to text. Like the User ID packet, a User Attribute
packet may be certified by the key owner ("self-signed") or any
other key owner who cares to certify it. Except as noted, a User
Attribute packet may be used anywhere that a User ID packet may be
used.
While User Attribute packets are not a required part of the OpenPGP
standard, implementations SHOULD provide at least enough
compatibility to properly handle a certification signature on the
User Attribute packet. A simple way to do this is by treating the
User Attribute packet as a User ID packet with opaque contents, but
an implementation may use any method desired.
The User Attribute packet is made up of one or more attribute
subpackets. Each subpacket consists of a subpacket header and a
body. The header consists of:
- the subpacket length (1, 2, or 5 octets)
- the subpacket type (1 octet)
and is followed by the subpacket specific data.
The only currently defined subpacket type is 1, signifying an image.
An implementation SHOULD ignore any subpacket of a type that it does
not recognize. Subpacket types 100 through 110 are reserved for
private or experimental use.
> The important sentence is the last one: there are 11 types to play with.I suggest to take pick one type between 100 and 110 and use it to store extra information. Since we may want to add various data, I suggest to store them as a series of named proprieties.
The attribute format could look like this: - Magic number identifying this experimental attribute - UTF-8 Name of property 1 - Data length for property 1 - Data of property 1 - UTF-8 Name of property 2 - Data length for property 2 - Data of property 2 - etc... And the content might look like this: First name=David Last name=Srbecky Country=Czech Republic City=Usti nad Labem Telephone=+65 536 1024 ICQ=#128-256-512 Homepage url=http://www.gnupg.org/ Prefers encrypted mail=true Prefers signed mail=true Preferred encapsulation=MIME PGP key url=http://www.gnupg.org/dsrbecky/pgp.keyAs this attribute will contain a lot of text, it should be encapsulated in Compressed Data Packet (Tag 8).
So, what do you think? David
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