Pairing Accessory is failing

Hi,

I am trying to use this library, but I am unable to pair with the Apple Home app on the iPhone. I followed the demo code. First, if I use the latest hex.pm package (0.4.8), ThousandIsland refuses to start because HAP.HAPSessionTransport.sockname/1 is undefined or private. I noticed this was fixed in the recent commits, so I used the git repo in mix.exs instead.

Now, when I try to pair, Apple Home does request details (as visible in the console), but the HAP.PairSetup GenServer crashes due to bad IV length.

Here are the logs:

12:42:54.688 [info] POST /pair-setup

12:42:54.698 [info] Sent 200 in 9ms

12:42:54.751 [info] POST /pair-setup

12:42:54.752 [info] Sent 200 in 1ms

12:42:54.758 [info] POST /pair-setup

12:42:54.761 [error] GenServer HAP.PairSetup terminating
** (stop) {:badarg, {~c"aead.c", 111}, ~c"Bad IV length"}
    (crypto 5.2) crypto.erl:1023: :crypto.crypto_one_time_aead(:chacha20_poly1305, <<140, 134, 89, 123, 121, 178, 138, 33, 27, 220, 164, 31, 200, 248, 154, 52, 178, 117, 38, 128, 158, 119, 53, 41, 228, 79, 0, 123, 2, 90, 19, 142>>, "PS-Msg05", <<142, 52, 148, 112, 87, 220, 56, 54, 225, 232, 91, 209, 194, 240, 6, 138, 18, 142, 101, 140, 36, 61, 108, 156, 5, 170, 90, 213, 64, 203, 101, 216, 34, 224, 19, 185, 58, 129, 84, 154, 58, 171, 121, 190, 205, 111, 10, 141, 32, 5, ...>>, "", <<151, 111, 233, 169, 209, 103, 60, 53, 218, 80, 101, 129, 96, 93, 141, 149>>, false)
    (hap 0.4.8) lib/hap/crypto/cha_cha_20.ex:24: HAP.Crypto.ChaCha20.decrypt_and_verify/4
    (hap 0.4.8) lib/hap/pair_setup.ex:97: HAP.PairSetup.handle_call/3
    (stdlib 5.0.2) gen_server.erl:1113: :gen_server.try_handle_call/4
    (stdlib 5.0.2) gen_server.erl:1142: :gen_server.handle_msg/6
    (stdlib 5.0.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3

I tried experimenting with the :crypto.crypto_one_time_aead function, but every variation I try gives me the same Bad IV Length error, even though the lengths described in the Erlang manual are what I'm using.

I am using a Mac with Elixir installed from brew. I also tried it in a ARM Alpine Linux VM, and it gave the same error.

Erlang/OTP 26 [erts-14.0.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit] [dtrace]

Elixir 1.15.7 (compiled with Erlang/OTP 26)

OpenSSL 3.1.4 24 Oct 2023 (Library: OpenSSL 3.1.4 24 Oct 2023)

I'm guessing I'm doing something wrong, or there's some recent bug?

Also, slightly off-topic, but I cannot find the HomeKit Accessory Protocol Specification PDF anywhere. Did Apple remove it? Their help pages say it's available for hobbyists, but I can't find it anywhere on their website.

These are all 'known issues', though some of them are pretty new and not fixed yet:

You're right - 0.4.8 is long in the tooth and I should cut a new release that incorporates Bandit 1.0 compatibility
The crash you're seeing in aead.c has something to do (I thought, anyway) with newer macOS hosts & the changes to openssl thereon. The fact that you're seeing it in an ARM linux VM is new to me though. I wonder if it's related to OpenSSL 3 on any platform? Builds on GitHub Actions work fine, but I'm not sure what libraries are present there.
Even once you get all of this working, the pairing process still sometimes fails on the iOS side with no useful information provided. This is unfortunately 'just the way it is' with their implementation, and it can usually be solved by waiting a while for some internal iOS cache to expire, changing the id of your HAP device, or just waiting for a new phase of the moon.
Apple seem to have pulled their public copies of the HAP spec about a year ago. I don't want to share it here but if you hit me up on Slack (@mtrudel on the Elixir slack) I'll point you in the right direction.

I'll endeavour to get the OpenSSL error characterized and fixed later this week, and one that's done i'll cut a new 0.4.9 release. Thanks for reminding me!

mtrudel / hap

Pairing Accessory is failing #97