Note
Network deployment completed. See [SPEC] for the official specification.
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:
Add and Change commands:
example.i2p=b64destination#!key1=val1#key2=val2 ...
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.
References
| [SPEC] | http://i2p2.de/spec/subscription |