What is the key length of Triple DES?

• A. 128 bits.
• B. 192 bits.
• C. 168 bits.
• D. 256 bits.

Answer: (C)

Triple DES gains its key length from applying DES three times with three separate keys. Each DES key provides 56 bits of secret material (the 64-bit DES key includes 8 parity bits, which don’t add to secrecy). Using three independent keys gives 56 + 56 + 56 = 168 bits of secret key length. In memory you’ll see 64 bits per DES key due to parity, which totals 192 bits of key material stored, but the actual secret strength remains 168 bits. In practice, the effective security is around 112 bits because of meet-in-the-middle attacks, but the formal key length is 168 bits. The other options do not match this DES-based three-key construction.