Which statement best explains why ECB can be unsafe for many real datasets?

• A. Identical plaintext blocks encrypt to identical ciphertext blocks
• B. It requires an initialization vector
• C. It provides integrity protection
• D. It uses a stream of random numbers

Answer: (A)

ECB encrypts data by dividing it into fixed-size blocks and encrypting each block with the same key independently. Because each block is treated separately, identical plaintext blocks produce identical ciphertext blocks. This reveals any repeated patterns, structure, or redundancy in the data, which an attacker can exploit to infer information about the plaintext. That pattern leakage is why ECB is unsafe for many real datasets.

The other points don’t fit ECB. It doesn’t use an initialization vector, since IVs are used in other modes to add randomness and break determinism. It doesn’t provide integrity protection—encryption alone doesn’t authenticate data. And it isn’t a stream cipher; ECB isn’t driven by a stream of random numbers.