pynacl crypto_core_hsalsa20

[DanielRadl]

I need the crypto_core_hsalsa20 function to greate an secret key for my NUKI.

Both sides calculate DH Key k using function dh1
a. Key
0DE40B998E0E330376F2D2FC4892A6931E25055FD09F054F99E93FECD9BA611E
8. Both sides derive a long term shared secret key s from k using function kdf1
a. Shared key
217FCB0F18CAF284E9BDEA0B94B83B8D10867ED706BFDEDBD2381F4CB3B8F730

4.2 The key derivation function kdf1
static const unsigned char _0[16];
static const unsigned char sigma[16] = "expand 32-byte k";
crypto_core_hsalsa20(k,_0,s,sigma)
Used to derive a long term secret key out of the shared key calculated by dh1

I alredy calculated the DH Key k with the nacl.publik.Box (=dh1) function.

Can someone tell me how to use the kdf1 function with pynacl?
Thanks!

[ljluestc]

import nacl.utils
from nacl.secret import SecretBox

Your shared key calculated by DH

shared_key = b'\x21\x7F\xCB\x0F\x18\xCA\xF2\x84\xE9\xBD\xEA\x0B\x94\xB8\x3B\x8D\x10\x86\x7E\xD7\x06\xBF\xDE\xDB\xD2\x38\x1F\x4C\xB3\xB8\xF7\x30'

Derivation constant

sigma = b'expand 32-byte k'

Create a SecretBox with the shared key as the key

box = SecretBox(shared_key)

Derive the long-term secret key using crypto_core_hsalsa20

derived_secret_key = box._encrypt_nonce(sigma, nacl.utils.zero(nacl.secret.SecretBox.KEY_SIZE))

print(derived_secret_key)