Rating:
**Description**: The aliens saw us break PhaseStream 3 and have proposed a quick fix to protect their new cipher.
**Stars**: 2/5
**Downloadable**:
output.txt - encrypted file
phasestream4.py - encryption algorithm
**Goal**: To find a vulnerability of the algorithm and decrypt the flag
**Solution**:
Similar as for [PhaseStream 3](), we need to use same Crib Dragging technique but this time we do not have a plaintext for the first encrypted blob.
We know the flag format of course, if we input as a known plaintext, we will receive first 5 characters of the plaintext used in the first encryption.
From there some googling will take us to this quite from Mother Theresa: "I alone cannot change the world, but I can cast a stone across the waters to create many ripples."
If we use it as a key, we get our flag:
