<Dt> Keying option 3 </Dt> <Dd> All three keys are identical, i.e. K = K = K . </Dd> <Dd> This is backward compatible with DES, since two operations cancel out . ISO / IEC 18033 - 3 never allowed this option, and NIST no longer allows it . </Dd> <P> Each DES key is 8 odd - parity bytes, with 56 bits of key and 8 bits of error - detection . A key bundle requires 24 bytes for option 1, 16 for option 2, or 8 for option 3 . </P>

3des is based on which of the following