openssl_free_key()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

释放密钥资源

说明

openssl_free_key(resource $key_identifier): void

openssl_free_key()从内存中释放和指定的$key_identifier相关联的密钥。

参数

$key_identifier

返回值

没有返回值。

I just checked the code for PHP 7.1 and in there openssl_free_key is an alias for opnessl_pkey_free (PHP_FALIAS). 
This supports Richards assumption. 
I would also suggest to not use the alias,
but use the openssl_pkey_free function in new code.
This is because it is more descriptive about what its intend is and is the same structure as similar function in the openssl section.

openssl_free_key and openssl_pkey_free are probably aliases.
And the preferred one is probably openssl_pkey_free.