derive child SK

derive_child_SK

The child key derivation function takes in the parent’s private key and the index of the child and returns the child private key.

Inputs

parent_SK, the secret key of the parent node, a big endian encoded integer index, the index of the desired child node, an integer 0 <= index < 2^32

Outputs

child_SK, the secret key of the child node, a big endian encoded integer

Procedure

0. compressed_lamport_PK = parent_SK_to_lamport_PK(parent_SK, index) 1. SK = HKDF_mod_r(compressed_lamport_PK) 2. return SK