Multiple encipherment of double-length keys

The multiple encipherment of a double-length key (*K) using two double-length *KEKs, *KEKa, and *KEKb is defined as follows:

e*KEKa(KL) || e*KEKb(KR) =
              eKEKaL(dKEKaR(eKEKaL(KL))) ||
              eKEKbL(dKEKbR(eKEKbL(KR)))

where:

• KL is the left 64 bits of *K
• KR is the right 64 bits of *K
• KEKaL is the left 64 bits of *KEKa
• KEKaR is the right 64 bits of *KEKa
• KEKbL is the left 64 bits of *KEKb
• KEKbR is the right 64 bits of *KEKb
• || means concatenation