BOLT 2&7: Cleaner separation of concerns wrt announcement signatures (b…

…itcoin#97)

* BOLT 2&7: Cleaner separation of concerns wrt announcement signatures

So far we did not have any indication on what to do if a node does not
allow announcing the channel and we had a mix of concerns in the
`funding_locked` message, which would also transfer the signatures
needed for the announcement. This is a proposal about splitting the
signatures into their own message, so that simple omission is an
opt-out of announcements, and it does not mix announcement/gossip
stuff into the peer-protocol.

(It also ended up adding a localfeatures flag to opt-into the channel-announcement, and thus creating BOLT 9)

00-introduction.md

@@ -20,6 +20,7 @@ This is version 0.
 6. [BOLT #6](06-irc-announcements.md): Interim Node and Channel Discovery
 7. [BOLT #7](07-routing-gossip.md): P2P Node and Channel Discovery
 8. [BOLT #8](08-transport.md): Encrypted and Authenticated Transport
+9. [BOLT #9](09-features.md): Assigned Feature Flags
 
 ## Glossary and Terminology Guide
 

02-peer-protocol.md

@@ -248,8 +248,6 @@ This message indicates that the funding transaction has reached the `minimum-dep
 2. data:
     * [8:temporary-channel-id]
     * [8:channel-id]
-    * [64:announcement-node-signature]
-    * [64:announcement-bitcoin-signature]
     * [33:next-per-commitment-point]
 
 The `channel-id` is the unique description of the funding transaction.
@@ -261,8 +259,6 @@ index which pays to the channel.
 This `channel-id` is used in all messages referring to the channel
 from this point onwards.
 
-`announcement-node-signature` and `announcement-bitcoin-signature` are the optional signature for `channel_announcement` as described in [BOLT #7](07-routing-gossip.md#the-channel_announcement-message).
-
 #### Requirements
 
 The sender MUST wait until the funding transaction has reached
@@ -289,14 +285,6 @@ re-transmit `funding_locked` if the `channel-id` changes.
 If the recipient has received previous `funding_locked` message, it
 MUST ignore it in favor of the new `funding_locked`.
 
-The sender MUST set `announcement-node-signature` and `announcement-bitcoin-signature` to the signatures for the
-`channel_announcement` message, or all zeroes if it does not want the
-channel announced.
-
-The recipient SHOULD fail the channel if the `announcement-node-signature` and `announcement-bitcoin-signature`s are incorrect (and not all zeroes).
-The recipient SHOULD queue the `channel_announcement` message for its
-peers if it has sent and received a non-zero `announcement-node-signature` and `announcement-bitcoin-signature`.
-
 #### Rationale
 
 If the `minimum-depth` is very low (such as 1), it's possible that
@@ -443,8 +431,7 @@ reason to pay a premium for rapid processing.
 
 ## Normal Operation
 
-Once both nodes have exchanged `funding_locked`, the channel can be
-used to make payments via Hash TimeLocked Contracts.
+Once both nodes have exchanged `funding_locked` (and optionally `announcement_signatures`), the channel can be used to make payments via Hash TimeLocked Contracts.
 
 Changes are sent in batches: one or more `update` messages are sent before a
 `commit_sig` message, as in the following diagram:

07-routing-gossip.md

@@ -13,6 +13,23 @@ There can only be one valid `channel_announcement` for any channel,
 but multiple `node_announcement` messages are possible (to update node
 information), and at least two `channel_update` messages are expected.
 
+## The `announcement_signatures` message
+This is a direct message between two endpoints of a channel and serves as an opt-in mechanism to allow the announcement of the channel to the rest of the network.
+It contains the necessary signatures by the sender to construct the `channel_announcement` message.
+
+1. type: 259 (`announcement_signatures`)
+2. data:
+    * [8:channel-id]
+    * [64:node-signature]
+    * [64:bitcoin-signature]
+
+The willingness of the endpoints to announce the channel is signaled during the connection setup by setting the first bit (`0x01`) in the `localfeatures` field.
+Should both endpoints have signaled that they'd like to publish the channel (`localfeatures & 0x01 == 0x01`) then the `announcement_signatures` message MUST directly sent following the `funding_locked` message that established the corresponding channel.
+The `announcement_signatures` message is created by constructing a `channel_announcement` message corresponding to the newly established channel, and sign it with the secrets matching their `node-id` and `bitcoin-key`, and send them using an `announcement_signatures`.
+The recipient MAY fail the channel if the `node-signature` or `bitcoin-signature` is incorrect.
+The recipient SHOULD queue the `channel_announcement` message for its peers if it has sent and received a valid `announcement_signatures` message.
+If either endpoints does not signal (`localfeatures & 0x01 == 0x00`) then `announcement_signatures` MUST NOT be sent.
+
 ## The `channel_announcement` message
 
 This message contains ownership information about a channel.  It ties

09-features.md

@@ -0,0 +1,16 @@
+# BOLT #9: Assigned Feature Flags
+
+This document tracks the assignment of `localfeatures` and `globalfeatures` flags in the `init` message ([BOLT #1](01-messaging.md)), as well as the `features` field in the `channel_announcement` message and `node_announcement` message ([BOLT #7](07-routing-gossip.md)).
+They are tracked separately since new flags will likely be added over time.
+
+The `features` flags in the routing messages are a subset of the `globalfeatures` flags, since the `localfeatures` are by definition only of interest to direct peers.
+
+## Assigned `localfeatures` flags
+
+This flags may only be used in the `init` message.
+
+| Bits | Description                                     | Link                                                                |
+|------|-------------------------------------------------|---------------------------------------------------------------------|
+| 1    | The sending node wishes to announce the channel | [BOLT #7](07-routing-gossip.md#the-announcement_signatures-message) |
+
+## Assigned `globalfeatures` flags