Hackthissite/Basic/Level6
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- Level: Basic::6
- URL: http://www.hackthissite.org/missions/basic/6/
- Exercise: An encryption system has been set up, which uses an unknown algorithm to change the text given. Requirements: Persistence, some general cryptography knowledge. Network Security Sam has encrypted his password. The encryption system is publically available and can be accessed with this form. Please enter a string to have it encrypted. You have recovered his encrypted password. It is:a7e34:l=. Decrypt the password and enter it below to advance to the next level.
- Solution:
We have to understand how the encryption works. Enter some letters: a, b, c, ... and some numbers: 1, 2, 3. You will notice that the increment seems to be the same. By using an ASCII conversion table (http://www.asciitable.com/), you will notice that we have following scheme:
- Each position is converted in ASCII number.
- Each position is then transformed with: +0 for the first position, +1 for the second one, +2 for the third one, etc.
- New ASCII after transform are then converted into characters.
To get the solution, we apply the reverse scheme. Here is the scheme:
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Encrypted | a | 7 | e | 3 | 4 | : | l | = |
| ASCII | 97 | 55 | 101 | 51 | 52 | 58 | 108 | 61 |
| Transform | -0 | -1 | -2 | -3 | -4 | -5 | -6 | -7 |
| Result after transform | 97 | 54 | 99 | 48 | 48 | 53 | 102 | 54 |
| ASCII (after transform) | a | 6 | c | 0 | 0 | 5 | f | 6 |