Krypton7

Website: http://overthewire.org/wargames/krypton/krypton7.html

According to the website page, this level is similar to the previous level, but with an unknown key length.

Let’s login using krypton6 credentials

Let’s create a working directory

Let’s try to find out the entropy of the random number generator. For that, we need to analyze the encryption using a known plaintext of a long length.

Reading the generated ciphertext

Observe that “EICTDGYIYZKTHNSIRFXYCPFUEOCKRN” is being repeated over and over again. The key length is 30 (length of the string above). Now, let’s try to encrypt some other known string in a similar fashion. Since the type of encryption is an addition, so if we add a fixed number to our original string, the same addition should be reflected in resultant cipher string.

Sure enough, the repeating string is now “FJDUEHZJZALUIOTJSGYZDQGVFPDLSO” which is exactly 1 offset from the previous string.

So we have obtained our key, we can now go ahead and decrypt the password.

So, we have our credentials!

Username: krypton7

Password: *************