forked from I2P_Developers/i2p.www
Prop. 144 next key fixes and clarifications
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@@ -5,7 +5,7 @@ ECIES-X25519-AEAD-Ratchet
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:author: zzz, chisana
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:created: 2018-11-22
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:thread: http://zzz.i2p/topics/2639
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:lastupdated: 2020-04-22
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:lastupdated: 2020-04-25
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:status: Open
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:target: 0.9.46
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:implementedin: 0.9.46
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@@ -1939,68 +1939,89 @@ by initiating the key exchange; the diagram below shows that.
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When Alice ratchets, the same thing happens in reverse.
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The first tag set used after the NS/NSR handshake is tag set 0.
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When that tag set is almost exhausted, new keys must be exchanged to create tag set 1.
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When tag set 0 is almost exhausted, new keys must be exchanged in both directions to create tag set 1.
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After that, a new key is only sent in one direction.
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For tag set 2, Bob sends the ID of his old key and requests a new key from Alice.
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To create tag set 2, the tag sender sends a new key and the tag receiver sends the ID of his old key as an acknowledgement.
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Both sides do a DH.
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For tag set 3, Bob sends a new key and Alice sends the ID of her old key.
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To create tag set 3, the tag sender sends the ID of his old key and requests a new key from the tag receiver.
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Both sides do a DH.
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Subsequent tag sets are generated as for tag sets 2 and 3.
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The tag set number is (1 + Alice's key id + Bob's key id).
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The tag set number is (1 + sender key id + receiver key id).
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.. raw:: html
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{% highlight %}
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Alice Bob
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Tag Sender Tag Receiver
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(Tagset #0 almost empty)
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(generate new key #0)
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... use tag set #0 ...
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<-------------- Next Key, forward, request reverse, with key #0
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(repeat until next key received)
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(generate new key #0, do DH, create IB Tagset #1)
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(Tagset #0 almost empty)
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(generate new key #0)
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Next Key, reverse, with key #0 ------------------->
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(repeat until tag received on new tagset)
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Next Key, forward, request reverse, with key #0 -------->
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(repeat until next key received)
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(do DH, create OB Tagset #1)
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...
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(Tagset #1 almost empty)
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(resend key #0)
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(generate new key #0, do DH, create IB Tagset #1)
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<-------------- Next Key, forward, request reverse, id 0
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(repeat until next key received)
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<------------- Next Key, reverse, with key #0
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(repeat until tag received on new tagset)
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(generate new key #1, do DH, create IB Tagset #2)
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(do DH, create OB Tagset #1)
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Next Key, reverse, with key #1 ------------------->
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(repeat until tag received on new tagset)
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(do DH, create OB Tagset #2)
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...
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(Tagset #2 almost empty)
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(generate new key #1)
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... use tag set #1 ...
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<-------------- Next Key, forward, with key #1
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(repeat until next key received)
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(Tagset #1 almost empty)
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(generate new key #1)
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Next Key, forward, with key #1 -------->
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(repeat until next key received)
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(reuse key #0, do DH, create IB Tagset #2)
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<-------------- Next Key, reverse, id 0
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(repeat until tag received on new tagset)
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(do DH, create OB Tagset #2)
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... use tag set #2 ...
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(Tagset #2 almost empty)
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(reuse key #1)
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Next Key, forward, request reverse, id 1 -------->
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(repeat until next key received)
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(generate new key #1, do DH, create IB Tagset #3)
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<-------------- Next Key, reverse, with key #1
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(do DH, create OB Tagset #3)
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(reuse key #1, do DH, create IB Tagset #3)
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Next Key, reverse, id 1 ------------------->
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(repeat until tag received on new tagset)
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(do DH, create OB Tagset #3)
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Repeat the above patterns for tagsets
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2 and 3.
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Every even tagset, Bob resends his key
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and requests a reverse key from Alice.
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Every odd tagset, Bob sends a new key
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and Alice sends an ACK.
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... use tag set #3 ...
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After tag set 3, repeat the above
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patterns as shown for tag sets 2 and 3.
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To create a new even-numbered tag set, the sender sends a new key
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to the receiver. The receiver sends his old key ID
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back as an acknowledgement.
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To create a new odd-numbered tag set, the sender sends a reverse request
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to the receiver. The receiver sends a new reverse key to the sender.
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{% endhighlight %}
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@@ -2012,21 +2033,23 @@ the receiver should listen for tags in both tagsets, and delete the old tagset
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after a short time, about 3 minutes.
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Summary of tag set and key ID progression:
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Summary of tag set and key ID progression is in the table below.
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* indicates that a new key is generated.
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========== ============= ===========
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Tag Set ID Sender key ID Rcvr key ID
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========== ============= ===========
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0 n/a n/a
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1 0 0
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2 1 0
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3 1 1
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4 2 1
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5 2 2
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... ... ...
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65534 32767 32766
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65535 32767 32767
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========== ============= ===========
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============== ============= ===========
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New Tag Set ID Sender key ID Rcvr key ID
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============== ============= ===========
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0 n/a n/a
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1 0 * 0 *
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2 1 * 0
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3 1 1 *
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4 2 * 1
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5 2 2 *
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... ... ...
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65534 32767 * 32766
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65535 32767 32767 *
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========== ============= ===========
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DH INITIALIZATION KDF
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