Deriving a key from a password programmatically

We are going to implement the kdf program, which will derive a key from a password.

Our key derivation program will take two command-line arguments:

1. Password
2. Hex-encoded salt

We are not going to take the N, r, and brute-force-resistant Scrypt parameters because because we want to simplify our example program and its usage. Instead, we are going to use OWASP-recommended settings.

OpenSSL 3.0 provides the following APIs for key derivation:

• The PKCS5_PBKDF2_HMAC(), PKCS5_PBKDF2_HMAC_SHA1(), and EVP_PBE_scrypt() legacy functions, specific to particular KDFs.
• The EVP_PKEY API. This API is intended for use with asymmetric cryptography and contains the EVP_PKEY_derive() function. That function is mostly intended for non-password-based key derivation during key exchange operations in secure network protocols, such as Diffie-Hellman key exchange, but also supports password-based key derivation using the Scrypt...