CAP prefix/clog
===============

Copyright (c) Soni L. \<fakedme plus irkv3 at gmail dot com>

This capability provides a mechanism for identifying and conveying a cryptographically secured list of messages to IRC clients.

This specification also suggests a mechanism by which IRC clients can sync logs, using the information provided by this capability.

Cap syntax
----------

The capability shall be specified as

    prefix/clog=hash_type,hash_type/tag,tag,tag

Example:

    prefix/clog=sha1,sha256/server-time

`server-time` is always implicitly specified, and should be omitted.

The `HASH` S2C command
----------------------

The `HASH` command shall be sent for hashes associated with a channel.

Each hash must be a cryptographic hash. Non-cryptographic hashes must be ignored. Broken hash algorithms should be avoided. MD5 is explicitly disallowed and must not be used.

The counter must be able to store numbers in the `0..2^62-1` range.

Syntax:

    HASH #channel :hash_type=counter/hash,type=counter/hash,...

Example:

    >>> JOIN #channel
    <<< JOIN #channel
    <<< NAMES etc
    <<< HASH #channel :sha1=20,something_long
    <<< HASH #channel :sha1=60,something_else sha256=70,another

Optionally, the server may include a server name with the HASH command:

    <<< :server1.example.com HASH #channel :etc
    <<< :server2.example.com HASH #channel :other

The `hash` message tag
----------------------

The `hash` mesaage tag shall be sent with every `PRIVMSG`, `TOPIC` and `NOTICE`.

Syntax:

    hash=type=counter/short_hash,type=counter/short_hash,...

The use of `short_hash` lowers bandwidth requirements. Consult your cryptography expert for best practices on using cryptography.

Example:

    TODO

The `SYNC` CTCP (informative)
-----------------------------

*This section is informative.*

The `SYNC` CTCP is a hypothetical CTCP for syncing logs.

Syntax:

    SYNC <tox-compatible public key> <port> <host> <host> <...> -[nospam+checksum]

This is a highly flexible command supporting ipv4, ipv6, hostname, tor, i2p and tox ID.

Messages sent over non-tox channels must be encrypted with the tox-compatible public key.