"Anytime that I need to encrypt blocks of data in ECB mode, I can always use many threads simultaneously, but I always encrypt plaintext blocks separately for security purposes. The difference between the two is that with CBC, I need to add XOR to each plaintext block to the block that was previously produced. With ECB it's the simplest mode of encryption. The result is then encrypted using a cipher algorithm in the usual way. CBC is a little different because the initialization vector needs to be created randomly by the sender."

"When it comes to ECB and CBC data, I like to see if there may be encryption weaknesses using ECB mode encoding an image for example. If I don't use the proper protocols for encryption, the ECB mode cannot hide/blur the plaintext image. In cases like these, I would change the initialization vector after using the secret key a number of times. It's almost the same as needing to change your password on a regular basis. If the vector is used too many times, this would make the system vulnerable to plaintext attacks."

Essentially, the hiring manager wants to know if you understand the differences between ECB and CBC, which deal with encrypting ciphertext. They'll ask questions similar to these; Are ciphertext blocks decrypted separately? Is it possible to encrypt and decrypt simultaneous threads? Other questions that may come up are how can an image be encrypted, what's the standard protocol to do so, or perhaps; What's the difference between ciphertext and plaintext? These are more advanced questions that will likely occur later in the interview, once the interviewer has confirmed your basic qualifications