3.3 HISTORY LESSON

EXERCISE 3.3 HISTORY LESSON

Do some research online about DES and 3DES. What is the block size of DES? What is its key size? How does 3DES strengthen DES?

---

The block size of DES is $64$ bits.

The key size of DES is $56$ bits.

3DES strengthens DES by increasing its key size. When using Keying Option 1 (read more here) 3DES will have $3$ independent keys each of size $56$ bits. Thus the key size for 3DES is $3\times 56=168$ bits. But it is still vulnerable to meet-in-the-middle attack, but the attack requires $2^{2\times 56}$ steps.