### Phase stream 3
#### Problem
- Given the output.txt file, get the flag- The source file for encryption is also given.
#### Solution
- If we read about AES-CTR , we can find out that AES-CTR uses the AES block  cipher to create a stream cipher.- Also, the key along with IV(Initialization vector) is used to generate the encoding blocks first.- Then these blocks are 'xor'ed with plain text to output the encoded text.- Now, if we use the same key, then the generated encoding blocks will be same, so basically, only the plain text is varying.- So, enc(test) = test ^ block and enc(flag) = flag ^ block.- This means, block = enc(flag) ^ flag = enc(test) ^ test.- => flag = enc(test) ^ test ^ enc(flag) (as ^ is a commutative operation)- As, we know all the 3 things, we can decrypt the flag with decrypt.py.- Flag : `CHTB{r3u53d_k3Y_4TT4cK}`