[Questions]DAC private key length in factory data confusing

RE: [Questions]DAC private key length in factory data confusing

susepc — Tue, 18 Jun 2024 08:03:35 GMT

AHaug

Thanks for your strong support!

I'll close this ticket soon.

Chuan

RE: [Questions]DAC private key length in factory data confusing

AHaug — Tue, 18 Jun 2024 07:57:18 GMT

Hi,

No worries! :)

[quote user="susepc"] Can I use raw byte to store key not using byte string?[/quote]

This parameter is a byte string based on the Matter spec due to how octets, keys (which is an octet string AFAIK) and more are defined, so according to my understanding of the specification you will have to comply with the byte string format to avoid breaking the spec.

Ref: Matter Core Spec v 1.2, chapter 4.13.2.4, 6.5.10, 10.3.6

Kind regards,
Andreas

RE: [Questions]DAC private key length in factory data confusing

susepc — Tue, 18 Jun 2024 07:38:24 GMT

AHaug

Thanks for your great support!

Sorry to bother you again, I have one last question：

Can I use raw byte to store key not using byte string?

If not, please let me know the reason, thx!

Chuan

RE: [Questions]DAC private key length in factory data confusing

AHaug — Tue, 18 Jun 2024 07:05:22 GMT

Hi,

The byte string item is explained as:

Kind regards,
Andreas

RE: [Questions]DAC private key length in factory data confusing

susepc — Tue, 18 Jun 2024 03:14:18 GMT

AHaug

Thanks for your quickly response!

Does the last 4 bytes of data represent the dac_key field value length or the ASCII of "hex:"?

If it is the former, what is the role of this length?

RE: [Questions]DAC private key length in factory data confusing

AHaug — Mon, 17 Jun 2024 12:03:51 GMT

Ah, it makes sense that it is 68 Bytes.

The field is written in byte string format, i.e if the raw DAC key is 32 Bytes length, then the dac_key field value should have 32*2+len(hex:) => 64+4 => 68 Bytes.

Kind regards,
Andreas

RE: [Questions]DAC private key length in factory data confusing

AHaug — Mon, 17 Jun 2024 11:25:17 GMT

Hi,

I've had a look in the Matter 1.2 specification and I could not find a specific reason myself for why this was the case, so I've asked the developers for some input. I'll get back to you with a verification when I hear from them.

Kind regards,
Andreas