commit 176c9001f962848751bedfff9bade4aa58319714 Author: Nick Mathewson <nickm@torproject.org> Date: Thu Feb 17 10:53:20 2022 -0500 ntor3, rend3: clarify extension field defaults. These patch changes describe new default behaviors for extension field lists, as appear in ntor3 and in many places throughout the ntor3 protocol. In general: * Unrecognized extensions MUST be ignored. Additionally, all the following rules apply _unless otherwise stated in the documentation for an extension. * Extensions are sent in sorted order. * Extensions should only be sent once in a message * If you receive multiple copies of an extension, only the first one counts. This comes out of discussions on tor!525. --- proposals/332-ntor-v3-with-extra-data.md | 28 ++++++++++++++++++---------- rend-spec-v3.txt | 26 +++++++++++++++++++++++++- 2 files changed, 43 insertions(+), 11 deletions(-) diff --git a/proposals/332-ntor-v3-with-extra-data.md b/proposals/332-ntor-v3-with-extra-data.md index 4e55713..8e6dedc 100644 --- a/proposals/332-ntor-v3-with-extra-data.md +++ b/proposals/332-ntor-v3-with-extra-data.md @@ -338,20 +338,28 @@ We use the following meta-encoding for the contents of client and server messages. [Any number of times]: - TYPE [one byte] - LEN [one byte] - BODY [LEN bytes] - -We do not specify specific TYPE semantics here; we leave those for -other proposals. + EXTENSION + EXT_FIELD_TYPE [one byte] + EXT_FIELD_LEN [one byte] + EXT_FIELD [EXT_FIELD_LEN bytes] All parties MUST reject messages that are not well-formed per the rules above. -To avoid partitioning, clients MUST reject messages with TYPEs that -they do not recognize. (Therefore, whenever we specify a new server -message TYPE, we must say that it can only be included if the client -signals that it understands it.) +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.) # A.3 How much space is available? diff --git a/rend-spec-v3.txt b/rend-spec-v3.txt index 6a120eb..1a0b945 100644 --- a/rend-spec-v3.txt +++ b/rend-spec-v3.txt @@ -1548,9 +1548,17 @@ Table of contents: authentication key. The EXT_FIELD_TYPE, EXT_FIELD_LEN, EXT_FIELD entries are reserved for - future extensions to the introduction protocol. Extensions with + extensions to the introduction protocol. Extensions with unrecognized EXT_FIELD_TYPE values must be ignored. + 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 descriptions of individual extensions.) + The HANDSHAKE_AUTH field contains the MAC of all earlier fields in the cell using as its key the shared per-circuit material ("KH") generated during the circuit extension protocol; see tor-spec.txt @@ -1685,6 +1693,10 @@ Table of contents: Older versions of Tor send back an empty INTRO_ESTABLISHED cell instead. Services must accept an empty INTRO_ESTABLISHED cell from a legacy relay. + The same rules for multiplicity, ordering, and handling unknown types + apply to the extension fields here as described [EST_INTRO] above. + + 3.2. Sending an INTRODUCE1 cell to the introduction point. [SEND_INTRO1] In order to participate in the introduction protocol, a client must @@ -1737,6 +1749,10 @@ Table of contents: INTRODUCE2 cell with exactly the same contents to the service, and sends an INTRODUCE_ACK response to the client. + The same rules for multiplicity, ordering, and handling unknown types + apply to the extension fields here as described [EST_INTRO] above. + + 3.2.2. INTRODUCE_ACK cell format. [INTRO_ACK] An INTRODUCE_ACK cell has the following fields: @@ -1755,6 +1771,10 @@ Table of contents: [00 02] -- Bad message format [00 03] -- Can't relay cell to service + The same rules for multiplicity, ordering, and handling unknown types + apply to the extension fields here as described [EST_INTRO] above. + + 3.3. Processing an INTRODUCE2 cell at the hidden service. [PROCESS_INTRO2] Upon receiving an INTRODUCE2 cell, the hidden service host checks whether @@ -1831,6 +1851,10 @@ Table of contents: shared key with the hidden service client. * A set of shared keys to use for end-to-end encryption. + The same rules for multiplicity, ordering, and handling unknown types + apply to the extension fields here as described [EST_INTRO] above. + + 3.3.1. Introduction handshake encryption requirements [INTRO-HANDSHAKE-REQS] When decoding the encrypted information in an INTRODUCE2 cell, a