Which algorithm is a block cipher with 128-bit blocks widely used today?

• A. DES
• B. AES
• C. ECB Mode
• D. Padding

Answer: (B)

Block ciphers process data in fixed-size blocks, and the one that is widely used today operates on 128-bit blocks. This algorithm—AES—became the standard because it provides strong security with efficient performance in both hardware and software, and it supports key lengths of 128, 192, or 256 bits. Its design is robust against common cryptographic attacks, which is why it’s trusted for securing communications and data around the world.

DES is an older block cipher that uses 64-bit blocks and shorter keys, which makes it insecure by today’s standards. ECB mode is not a cipher itself; it’s a mode of operation that describes how to apply a block cipher to data, but the mode does not define the underlying algorithm. Padding is a technique used to fill the final block when the plaintext isn’t a multiple of the block size, not a cipher.