(Non-conformance) Stateless Cookie Exchange
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Stale
- Tech stack
- c
- Domain
- networking, security
Research direction
Read the linked DTLS 1.2 RFC section 4.2.1 and inspect the attached handshake trace alongside the duplicate-packet log. Trace how TinyDTLS records and checks the initial ClientHello sequence number; done means the ClientKeyExchange record in the trace is not discarded as a duplicate and the stateless cookie exchange retains no initial ClientHello state.
Written by the indexing model from the issue text.
Description
Description
- Type: Non-conformance Bug
- Priority: Minor
Non-conformance Bug
Version: development branch
Expected behavior
The DTLS 1.2 RFC specifies the following requirement regarding stateless cookie exchange :
The DTLS server SHOULD generate cookies in such a way that they can be verified without retaining any per-client state on the server.
Actual behavior
TinyDTLS stores the record sequence number of the initial ClientHello and discards any subsequent records that duplicate this sequence number. However, in a truly stateless exchange, no information from the initial ClientHello should be retained. In the attached handshake trace, the record containing the ClientKeyExchange message uses the same record sequence number as the initial ClientHello. As shown in the log below, this results in the record being discarded.
Log
May 15 13:08:00 INFO received message (117 bytes), starting with 'handshake', epoch 0
May 15 13:08:00 INFO handshake message epoch 0
May 15 13:08:00 INFO got 'handshake' epoch 0 sequence 0 (42 bytes)
May 15 13:08:00 DEBG dtls_handle_message: FOUND PEER
May 15 13:08:00 DEBG bitfield is ffffffffffffffff sequence base 1 rseqn 0
May 15 13:08:00 DEBG Drop: duplicate packet arrived (bitfield)```- Dominant language
- C
- Stars
- 122
- Forks
- 67
- Avg merge
- 6d 8h
- Merged PRs (30d)
- 5
Getting set up
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First steps
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- Open a pull request that references the issue number.
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