[int$length = 0],
[string$info = ""],
[string$salt = ""]
Name of selected hashing algorithm (i.e. "sha256", "sha512", "haval160,4", etc..) See hash_algos for a list of supported algorithms.
Non-cryptographic hash functions are not allowed.
Input keying material (raw binary). Cannot be empty.
Desired output length in bytes. Cannot be greater than 255 times the chosen hash function size.
If length is 0, the output length will default to the chosen hash function size.
Application/context-specific info string.
Salt to use during derivation.
While optional, adding random salt significantly improves the strength of HKDF.
Returns a string containing a raw binary representation of the derived key (also known as output keying material - OKM); or false on failure.
Exceptions and Errors
An E_WARNING will be raised if key is empty, algo is unknown/non-cryptographic, length is less than 0 or too large (greater than 255 times the size of the hash function).