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prop. 144 key/tagset id clarifications

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zzz
2020-04-14 13:43:56 +00:00
parent d8d34ed2c8
commit 8529010684
1 changed files with 51 additions and 7 deletions
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i2p2www/spec/proposals/144-ecies-x25519-aead-ratchet.rst
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@@ -5,7 +5,7 @@ ECIES-X25519-AEAD-Ratchet
:author: zzz, chisana
:created: 2018-11-22
:thread: http://zzz.i2p/topics/2639
:lastupdated: 2020-04-04
:lastupdated: 2020-04-14
:status: Open
.. contents::
@@ -1891,13 +1891,38 @@ After the final handshake KDF on bound sessions, Bob and Alice must run the Nois
resulting CipherState to create independent symmetric and tag chain keys for inbound and outbound sessions.
KEY AND TAG SET IDS
~~~~~~~~~~~~~~~~~~~~~~~~~
Key and tag set ID numbers are used to identify keys and tag sets.
Key IDs are used in NextKey blocks to identify the key sent or used.
Tag set IDs are used (with the message number) in ACK blocks to identify the message being acked.
Both key and tag set ids apply to the tag sets for a single direction.
In the first tag sets used for a session in each direction, the tag set ID is 0.
No NextKey blocks have been sent, so there are no key IDs.
To begin a DH ratchet, the sender transmits a new NextKey block with a key ID of 0.
The receiver replies with a new NextKey block with a key ID of 0.
The sender then starts using a new tag set with a tag set ID of 1.
Subsequent tag sets are generated similarly.
For all tag sets used after NextKey exchanges, the tag set number is (1 + Alice's key ID + Bob's key ID).
Key and tag set IDs start at 0 and increment sequentially.
The maximum key and tag set ID is 65535.
When a tag set is almost exhausted, the tag set sender must initiate a NextKey exchange.
When tag set 65535 is almost exhausted, the tag set sender must initiate a new session
by sending a New Session message.
DH RATCHET MESSAGE FLOW
~~~~~~~~~~~~~~~~~~~~~~~~~
The next key exchange for a tag set must be initiated by the
sender of those tags (the owner of the outbound tag set).
The receiver (owner of the inbound tag set) will respond.
For a typical HTTP session, Bob will send more messages and will ratchet first
For a typical HTTP GET traffic at the application layer, Bob will send more messages and will ratchet first
by initiating the key exchange; the diagram below shows that.
When Alice ratchets, the same thing happens in reverse.
@@ -1911,7 +1936,7 @@ For tag set 3, Bob sends a new key and Alice sends the ID of her old key.
Both sides do a DH.
Subsequent tag sets are generated as for tag sets 2 and 3.
The tag set number is (1 + bob's key id + alice's key id).
The tag set number is (1 + Alice's key id + Bob's key id).
.. raw:: html
@@ -1975,6 +2000,21 @@ the receiver should listen for tags in both tagsets, and delete the old tagset
after a short time, about 3 minutes.
Summary of tag set and key ID progression:
========== ============= ===========
Tag Set ID Sender key ID Rcvr key ID
========== ============= ===========
0 n/a n/a
1 0 0
2 1 0
3 1 1
4 2 1
5 2 2
...
========== ============= ===========
DH INITIALIZATION KDF
~~~~~~~~~~~~~~~~~~~~~~~
@@ -2629,10 +2669,10 @@ Key ID = 0.
Notes
``````
- Key ID is an incrementing counter, starting at 0.
The ID must not change unless the key changes.
It may not be strictly necessary, but it's useful for debugging.
Signal does not use a key ID.
Key ID is an incrementing counter for the local key used for that tag set, starting at 0.
The ID must not change unless the key changes.
It may not be strictly necessary, but it's useful for debugging.
Signal does not use a key ID.
Issues
@@ -2670,6 +2710,10 @@ Multiple acks may be present to ack multiple messages.
Notes
``````
The tag set ID and N uniquely identify the message being acked.
In the first tag sets used for a session in each direction, the tag set ID is 0.
No NextKey blocks have been sent, so there are no key IDs.
For all tag sets used after NextKey exchanges, The tag set number is (1 + Alice's key ID + Bob's key ID).
Issues