Revise channel negotiation a bit more.

1 files changed, 28 insertions, 33 deletions

diff --git a/spec/tor-spec/negotiating-channels.md b/spec/tor-spec/negotiating-channels.md
index c4652f5..9948b53 100644
--- a/spec/tor-spec/negotiating-channels.md
+++ b/spec/tor-spec/negotiating-channels.md
@@ -72,30 +72,20 @@ it's a waste of resources.
 
 ## Negotiating versions with VERSIONS cells {#VERSIONS-cells}
 
-There are multiple instances of the Tor link connection protocol.  Any
-connection negotiated using the "certificates up front" handshake (see
-[Channels](./channels.md)) is "version 1".  In any connection where both parties
-have behaved as in the "renegotiation" handshake, the link protocol
-version must be 2.  In any connection where both parties have behaved
-as in the "in-protocol" handshake, the link protocol must be 3 or higher.
-
-To determine the version, in any connection where the "renegotiation"
-or "in-protocol" handshake was used (that is, where the responder
-sent only one certificate at first and where the initiator did not
-send any certificates in the first negotiation), both parties MUST
-send a VERSIONS cell.  In "renegotiation", they send a VERSIONS cell
-right after the renegotiation is finished, before any other cells are
-sent.  In "in-protocol", the initiator sends a VERSIONS cell
-immediately after the initial TLS handshake, and the responder
-replies immediately with a VERSIONS cell. (As an exception to this rule,
-if both sides support the "in-protocol" handshake, either side may send
-VPADDING cells at any time.)
+There are multiple instances of the Tor channel protocol.
+
+Once the TLS handshake is complete,
+both parties send a VERSIONS cell
+to negotiate which one they will use.
 
 The payload in a VERSIONS cell is a series of big-endian two-byte
-integers.  Both parties MUST select as the link protocol version the
+integers.
+Both parties MUST select as the link protocol version the
 highest number contained both in the VERSIONS cell they sent and in the
-versions cell they received.  If they have no such version in common,
-they cannot communicate and MUST close the connection.  Either party MUST
+versions cell they received.
+If they have no such version in common,
+they cannot communicate and MUST close the connection.
+Either party MUST
 close the connection if the versions cell is not well-formed (for example,
 if the payload contains an odd number of bytes).
 
@@ -103,22 +93,26 @@ Any VERSIONS cells sent after the first VERSIONS cell MUST be ignored.
 (To be interpreted correctly, later VERSIONS cells MUST have a CIRCID_LEN
 matching the version negotiated with the first VERSIONS cell.)
 
-Since the version 1 link protocol does not use the "renegotiation"
-handshake, implementations MUST NOT list version 1 in their VERSIONS
-cell.  When the "renegotiation" handshake is used, implementations
-MUST list only the version 2.  When the "in-protocol" handshake is
-used, implementations MUST NOT list any version before 3, and SHOULD
-list at least version 3.
+> (The
+> [obsolete v1 channel protocol](./obsolete-channels.md#v1-handshake)
+> does note VERSIONS cells.
+> Implementations MUST NOT list version 1 in their VERSIONS cells.
+> The
+> [obsolete v2 channel protocol](./obsolete-channels.md#v2-handshake)
+> can only be used after renegotiation;
+> implementations MUST NOT list version 2 in their VERSIONS cells
+> unless they have renegotiated the TLS session.)
 
-Link protocols differences are:
+The currently specified [Link](./subprotocol-versioning.md#link) protocols are:
 
 | Version | Description
 | ------- | -----------
-| 1       | The "certs up front" handshake.
-| 2       | Uses the renegotiation-based handshake. Introduces variable-length cells.
+| 1       | (Obsolete) The ["certs up front"](./obsolete-channels.md#v1-handshake) handshake.
+| 2       | (Obsolete) Uses the [renegotiation-based handshake](./obsolete-channels.md#v2-handshake). Introduces variable-length cells.
 | 3       | Uses the in-protocol handshake.
 | 4       | Increases circuit ID width to 4 bytes.
-| 5       | Adds support for link padding and negotiation (padding-spec.txt).
+| 5       | Adds support for [link padding](../padding-spec) and negotiation.
+
 
 <a id="tor-spec.txt-4.2"></a>
 
@@ -149,8 +143,9 @@ Relevant certType values are:
 | 6        | Ed25519 AUTHENTICATE cell key, signed with ed25519 signing key.
 | 7        | Ed25519 identity, signed with RSA identity.
 
-The certificate format for certificate types 1-3 is DER encoded
-X509.  For others, the format is as documented in cert-spec.txt.
+The certificate format for certificate types 1-3 is DER encoded X509.
+For others, the format is as documented in [a later section](./cert-spec.md)
+
 Note that type 7 uses a different format from types 4-6.
 
 A CERTS cell may have no more than one certificate of each CertType.