Number
112
Author
zzz
Created
Thread
http://zzz.i2p/topics/1704
Last updated
Status
Closed

Overview

This proposal is about extending the address subscription feed with commands, to enable name servers to broadcast entry updates from hostname holders. Implemented in 0.9.26.

Motivation

Right now, the hosts.txt subscription servers just send data in a hosts.txt format, which is as follows:

example.i2p=b64destination

There are several problems with this:

  • Hostname holders cannot update the Destination associated with their hostnames (in order to e.g. upgrade the signing key to a stronger type).
  • Hostname holders cannot relinquish their hostnames arbitrarily; they must give the corresponding Destination private keys directly to the new holder.
  • There is no way to authenticate that a subdomain is controlled by the corresponding base hostname; this is currently only enforced individually by some name servers.

Design

This proposal adds a number of command lines to the hosts.txt format. With these commands, name servers can extend their services to provide a number of additional features. Clients that implement this proposal will be able to listen for these features through the regular subscription process.

All command lines must be signed by the corresponding Destination. This ensures that changes are only made at the request of the hostname holder.

Security implications

This proposal has no implications on anonymity.

There is an increase in the risk associated with losing control of a Destination key, as someone who obtains it can use these commands to make changes to any associated hostnames. But this is no more of a problem than the status quo, where someone who obtains a Destination can impersonate a hostname and (partially) take over its traffic. The increased risk is also balanced our by giving hostname holders the ability to change the Destination associated with a hostname, in the event that they believe the Destination has been compromised; this is impossible with the current system.

Specification

New line types

This proposal adds two new types of lines:

  1. Add and Change commands:

    example.i2p=b64destination#!key1=val1#key2=val2 ...
    
  2. Remove commands:

    #!key1=val1#key2=val2 ...
    

Ordering

A feed is not necessarily in-order or complete. For example, a change command may be on a line before an add command, or without an add command.

Keys may be in any order. Duplicate keys are not allowed. All keys and values are case-sensitive.

Common keys

Required in all commands:

sig
B64 signature, using signing key from the destination

References to a second hostname and/or destination:

oldname
A second hostname (new or changed)
olddest
A second b64 destination (new or changed)
oldsig
A second b64 signature, using signing key from nolddest

Other common keys:

action
A command
name
The hostname, only present if not preceded by example.i2p=b64dest
dest
The b64 destination, only present if not preceded by example.i2p=b64dest
date
In seconds since epoch
expires
In seconds since epoch

Commands

All commands except the "Add" command must contain an "action=command" key/value.

For compatibility with older clients, most commands are preceded by example.i2p=b64dest, as noted below. For changes, these are always the new values. Any old values are included in the key/value section.

Listed keys are required. All commands may contain additional key/value items not defined here.

Add hostname

Preceded by example.i2p=b64dest
YES, this is the new host name and destination.
action
NOT included, it is implied.
sig
signature

Example:

example.i2p=b64dest#!sig=b64sig

Change hostname

Preceded by example.i2p=b64dest
YES, this is the new host name and old destination.
action
changename
oldname
the old hostname, to be replaced
sig
signature

Example:

example.i2p=b64dest#!action=changename#oldname=oldhostname#sig=b64sig

Change destination

Preceded by example.i2p=b64dest
YES, this is the old host name and new destination.
action
changedest
olddest
the old dest, to be replaced
oldsig
signature using olddest
sig
signature

Example:

example.i2p=b64dest#!action=changedest#olddest=oldb64dest#oldsig=b64sig#sig=b64sig

Add hostname alias

Preceded by example.i2p=b64dest
YES, this is the new (alias) host name and old destination.
action
addname
oldname
the old hostname
sig
signature

Example:

example.i2p=b64dest#!action=addname#oldname=oldhostname#sig=b64sig

Add destination alias

(Used for crypto upgrade)

Preceded by example.i2p=b64dest
YES, this is the old host name and new (alternate) destination.
action
adddest
olddest
the old dest
oldsig
signature using olddest
sig
signature using dest

Example:

example.i2p=b64dest#!action=adddest#olddest=oldb64dest#oldsig=b64sig#sig=b64sig

Add subdomain

Preceded by subdomain.example.i2p=b64dest
YES, this is the new host subdomain name and destination.
action
addsubdomain
oldname
the higher-level hostname (example.i2p)
olddest
the higher-level destination (for example.i2p)
oldsig
signature using olddest
sig
signature using dest

Example:

subdomain.example.i2p=b64dest#!action=addsubdomain#oldname=example.i2p#olddest=oldb64dest#oldsig=b64sig#sig=b64sig

Update metadata

Preceded by example.i2p=b64dest
YES, this is the old host name and destination.
action
update
sig
signature

(add any updated keys here)

Example:

example.i2p=b64dest#!action=update#k1=v1#k2=v2#sig=b64sig

Remove hostname

Preceded by example.i2p=b64dest
NO, these are specified in the options
action
remove
name
the hostname
dest
the destination
sig
signature

Example:

#!action=removeall#name=example.i2p#dest=b64destsig=b64sig

Remove all with this destination

Preceded by example.i2p=b64dest
NO, these are specified in the options
action
removeall
name
the old hostname, advisory only
dest
the old dest, all with this dest are removed
sig
signature

Example:

#!action=removeall#name=example.i2p#dest=b64destsig=b64sig

Signatures

All commands must contain a signature key/value "sig=b64signature" where the signature for the other data, using the destination signing key.

For commands including an old and new destination, there must also be an oldsig=b64signature, and either oldname, olddest, or both.

In an Add or Change command, the public key for verification is in the Destination to be added or changed.

In some add or edit commands, there may be an additional destination referenced, for example when adding an alias, or changing a destination or host name. In that case, there must be a second signature included and both should be verified. The second signature is the "inner" signature and is signed and verified first (excluding the "outer" signature). The client should take any additional action necessary to verify and accept changes.

oldsig is always the "inner" signature. Sign and verify without the 'oldsig' or 'sig' keys present. sig is always the "outer" signature. Sign and verify with the 'oldsig' key present but not the 'sig' key.

Input for signatures

To generate a byte stream to create or verify the signature, serialize as follows:

  • Remove the "sig" key
  • If verifying with oldsig, also remove the "oldsig" key
  • For Add or Change commands only, output example.i2p=b64dest
  • If any keys remain, output "#!"
  • Sort the options by UTF-8 key, fail if duplicate keys
  • For each key/value, output key=value, followed by (if not the last key/value) a '#'

Notes

  • Do not output a newline
  • Output encoding is UTF-8
  • All destination and signature encoding is in Base 64 using the I2P alphabet
  • Keys and values are case-sensitive
  • Host names must be in lower-case

Compatibility

All new lines in the hosts.txt format are implemented using leading comment characters, so all older I2P versions will interpret the new commands as comments.

When I2P routers update to the new specification, they will not re-interpret old comments, but will start listening to new commands in subsequent fetches of their subscription feeds. Thus it is important for name servers to persist command entries in some fashion, or enable etag support so that routers can fetch all past commands.