Password Hashing Security Using Scrypt & Argon2 I am developing an app where the following cryptographic system will be in place:


Elliptic Curve key exchange (curve: secp521r1)
Double Scrypt the shared secret with different salts
Pass this result through Argon2 with another salt
Encrypt the data using AES 256 and the key from Argon2 (and an IV)


I was wondering whether at the password hashing and KDF stage there was any weaknesses of using double Scrypt then Argon2?? If so, what would be the solution to improve the security of the hashing?? Thanks
This home-made construction is pointless and unnecessarily complex, Complexity is often the source of vulnerabilities. In this case, for example, I’ll wager you’re not securely handling the intermediate variables as you chain the multiple password hashes together.

Simply use argon2 only and increase the work factors. “Double scrypt” is fairly meaningless as scrypt also has work factor parameters which can simply be increased.