[Questions]DAC private key length in factory data confusing

Question

Dear sir: 
 The DAC private key is generated using P256, and the key length is 256 bits, which is 32 bytes. 
 As below link, why is 68 bytes planned in the factory data? 
 developer.nordicsemi.com/.../nrfconnect_factory_data_configuration.html

dac_key 
 DAC private key 
 68 B 
 byte string 
 mandatory 
 The private key associated with the Device Attestation Certificate (DAC). This key should be encrypted and maximum security should be guaranteed while generating and providing it to factory data.

AHaug · Accepted Answer

Hi, 
 No worries! :) 
 susepc said: Can I use raw byte to store key not using byte string? 
 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

AHaug · Answer

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

AHaug · Answer

Hi, 
 The byte string item is explained as: 
 
 Kind regards, Andreas

[Questions]DAC private key length in factory data confusing

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