_lengthOctets(self,
payloadLen)
Return an octet string that is suitable for the BER/DER
length element if the relevant payload is of the given
size (in bytes).
encode(self)
_decodeLen(self,
idx,
str)
Given a string and an index to a DER LV,
this function returns a tuple with the length of V
and an index to the first byte of it.