PHP Function - sodium_crypto_generichash_final

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A function is a piece of code that performs some action and returns the result. In PHP, a function must be defined by using the keyword function and then specifying all of the arguments that the function should take (inside the parentheses). Arguments are used to pass information into the function. The order of the arguments does not matter.

PHP functions can be passed either named or positional arguments. Named arguments are separated by commas and can be added after the positional arguments. A named argument cannot override an already unpacked argument in the same call to the function. When passing named arguments, it is important to use escapeshellarg() or escapeshellcmd() so that the user does not execute arbitrary commands.

php function sodium_crypto_generichash_final takes two integer values as input: the length of the password hash in bytes and the salt to add to the password before hashing. The function then returns the derived password hash, or false on failure. This function provides low-level access to libsodium's crypto_pwhash key derivation function.

This function also supports authenticated asymmetric encryption/decryption, similar to OpenSSL's openssl_public_encrypt and openssl_private_decrypt functions. This allows the sender to sign a message with their private key and encrypt it with their public key so only the recipient can read the encrypted text. The sender will also need to generate a nonce value ($nonce) to add to the message, which must be stored/transmitted alongside the encrypted message to prevent replay attacks.