We Need To Stop Using Private Keys and Move To Storing Seed Values

Sometime, soon, we need to talk seriously about our migration away from RSA, ECDSA and EdDSA towards methods such as Dilithium, Falcon and SPHINCS+ [1]. But how do we migrate? Well, Shor’s algorithm defines that with a public key (pk), we will be able to derive the private key (sk). In the case of ECDSA, the public key is derived directly from the private key:

pk=sk.G

and where sk is typically just a random 256-bit value, and G is the base point on the curve. Thus, once the public key is cracked, the private key is revealed completely. We thus cannot use the private key to create a new quantum-robust key pair, as someone could discover the private key in the future and generate the same Dilithium, Falcon or SPHINCS+ keys. For EdDSA, we create the private key from a random seed value:

sk=SHA512(seed)[:32]

and where sk is then a 256-bit value, and G is the base point on the curve. In the wallet, we thus only have to store the seed, and not the private key. Now, when Shor’s algorithm breaks the public key (pk) to discover the private key (sk), the attacker will not be able to determine the seed value used, as SHA512 is a quantum-robust method.

The great advantage of using a seed is also that Dilithium, Falcon and SPHINCS+ can use a…