Replace encryption library

[sobolev-alexey]

Currently used encryption library secp256k1 generates private keys of 32 byte (256 bit) size. The length can't be increased to more secure 2048 bit size.

I recommend to use node-rsa library with adjustable key size. You can find completed and tested implementation in this file

You also won't need to use an additional eciesjs library for encryption/decryption. This functionality is provided by node-rsa