# Byte-at-a-time ECB decryption (Harder)

Take your oracle function from [#12](https://depp.brause.cc/cryptopals/02/12.md). Now generate a random count
of random bytes and prepend this string to every plaintext. You are
now doing:

    AES-128-ECB(random-prefix || attacker-controlled || target-bytes, random-key)

Same goal: decrypt the target-bytes.

## Stop and think for a second.

What's harder than challenge #12 about doing this? How would you
overcome that obstacle? The hint is: you're using all the tools you
already have; no crazy math is required.

Think "STIMULUS" and "RESPONSE".