The specs of
RC5ParameterSpec.RC5ParameterSpec(int, int, int, byte) and RC5ParameterSpec.RC5ParameterSpec(int, int, int, byte, int)
constructors contain the following sentence: "Note that the size of the IV (block
size) must be twice the word size. The bytes that constitute the IV are those between iv and iv[2*(wordSize/8)-1] inclusive."
However dispite of obligatory "MUST" is used it's unclear what happens
when this rule is broken. The only case mentioned when constructors throw IAE is
"if iv is null."