wirenboard/atecc-util

Ephemeral ECDH

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#11 opened on Mar 9, 2021

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enhancementgood first issue

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Description

I tried to calculate a shared secret using ephemeral ECDH exchange using slot 0xFFFF/65535 (TempKey). The communication is between a client with atecc608a chip and a host with a temporary ECC key generated with Python.

A working sample code can be found here: https://github.com/rrottmann/atecc-ecdh-python/blob/master/ecdh_device.py

Now I try to do the same with atecc-util. I can generate the public key for the TempKey slot but cannot calculate the shared secret:

$ ./atecc -b1 -c "ecc-gen 65535 tmpecc.pub"
$ xxd tmpecc.pub
#00000000: 2df2 ff52 d5db 7edd 147a 6da7 fd5b 45c3  -..R..~..zm..[E.
#00000010: 506e f9ac 57a4 6a35 6713 b082 2bc4 e57a  Pn..W.j5g...+..z
#00000020: 029d 7cf5 51b4 3940 22ff 4c1b 3800 4edc  ..|.Q.9@".L.8.N.
#00000030: 7336 b384 efc5 b332 ef06 a9f0 3e4e 7f99  s6.....2....>N..
$ ./atecc -b1 -c "ecdh 65535 tmpecc.pub ecdh.secret"
#Command atcab_ecdh is failed with status 0xf4

Any idea why this fails? Should TempKey work with atecc-util?

Contributor guide

Research direction
Investigate the error status 0xF4 returned by atcab ecdh. Check the ATECC608A datasheet for ECDH command execution when using TempKey (slot 0xFFFF). Verify that the public key is correctly formatted and that the TempKey is properly configured (e.g., not locked or used in previous operations). Trace the library code to see how it handles the TempKey slot.
Tech stack
c
Domain
apibackend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Needs investigation
Prerequisites
GitCECDHATECC chip knowledge
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40