Add verbiage about the formats of SM and CM in ntor-v3

1 files changed, 38 insertions, 0 deletions

diff --git a/tor-spec.txt b/tor-spec.txt
index 3e13fcd..98f033d 100644
--- a/tor-spec.txt
+++ b/tor-spec.txt
@@ -33,6 +33,7 @@ Table of Contents
             5.1.4. The "ntor" handshake
             5.1.4.1. The "ntor-v3" handshake.
             5.1.5. CREATE_FAST/CREATED_FAST cells
+            5.1.6. Additional data in CREATE/CREATED cells
         5.2. Setting circuit keys
             5.2.1. KDF-TOR
             5.2.2. KDF-RFC5869
@@ -1488,6 +1489,43 @@ see tor-design.pdf.
 
    [Tor 0.3.1.1-alpha and later disable CREATE_FAST by default.]
 
+5.1.6. Additional data in CREATE/CREATED cells
+
+   Some handshakes (currently ntor-v3 defined above) allow the client or the
+   relay to send additional data as part of the handshake.  When used in a
+   CREATE/CREATED handshake, this additional data must have the following
+   format:
+
+        [Any number of times]:
+        EXTENSION
+            EXT_FIELD_TYPE     [one byte]
+            EXT_FIELD_LEN      [one byte]
+            EXT_FIELD          [EXT_FIELD_LEN bytes]
+
+    (`EXT_FIELD_LEN` may be zero, in which case EXT_FIELD is absent.)
+
+    All parties MUST reject messages that are not well-formed per the
+    rules above.
+
+    We do not specify specific TYPE semantics here; we leave those for
+    other proposals and specifications.
+
+    Parties MUST ignore extensions with `EXT_FIELD_TYPE` bodies they do not
+    recognize.
+
+    Unless otherwise specified in the documentation for an extension type:
+    * Each extension type SHOULD be sent only once in a message.
+    * Parties MUST ignore any occurrences all occurrences of an extension
+      with a given type after the first such occurrence.
+    * Extensions SHOULD be sent in numerically ascending order by type.
+
+    (The above extension sorting and multiplicity rules are only defaults;
+    they may be overridden in the description of individual extensions.)
+
+    Currently supported extensions are:
+
+        .....
+
 5.2. Setting circuit keys
 
 5.2.1. KDF-TOR