derive_key
Description:
public Object derive_key (Object @base, ulong mech_type, Attributes attrs, Cancellable? cancellable = null) throws Error
  
  Derive a key from another key.
This call may block for an indefinite period.
If the attrs Attributes is floating, it is consumed.
Parameters:
| this | The session to use. | 
| mech_type | The mechanism to use for derivation. | 
| attrs | Additional attributes for the derived key. | 
| cancellable | Optional cancellation object, or  | 
| base | The key to derive from. | 
Returns:
| the new derived key or  |