One of the core effective key lengths listed for 3DES is 112 bits.

• A. 56 bits
• B. 112 bits
• C. 110 bits
• D. 168 bits

Answer: (B)

Triple DES uses DES three times with up to three 56-bit keys, which naively suggests a very large key space. But the measured security isn’t the raw key length—it's the effective key length, which accounts for practical attacks. The best-known attack on triple DES, a meet-in-the-middle approach, reduces the work needed to break the scheme to about 2^112 operations rather than 2^168. That means, in practice, the security of triple DES is considered around 112 bits, even though the nominal key length could be 168 bits if you use three independent keys. The other options don’t reflect this practical strength: 56 bits is the single-DES length, 110 bits isn’t a standard cryptographic key length, and 168 bits represents the raw key length, not the commonly cited effective security.