Devise a simple algorithm which creates a file which contains nothing but its own checksum.
Let’s say it is CRC-32, so this file must be 4 bytes long.
Devise a simple algorithm which creates a file which contains nothing but its own
Share
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
Devise a simple algorithm which creates a file which contains nothing but its own checksum.
Let’s say it is CRC-32, so this file must be 4 bytes long.
There might be some smart mathematical way of finding it out (or proving that none exists), if you know how the algorithm works.
But since I’m lazy and CRC32 has only 2^32 values, I would brute force it. While waiting for the algorithm to go through all 2^32 values, I would use Google and Stack Overflow to find whether somebody has a solution to it.
In case of SHA-1, MD5 and other more-or-less cryptographically secure algorithms, I would get intimidated by the mathematicians who designed those algorithms and just give up.
EDIT 1: Brute forcing… This far I’ve found one; CC4FBB6A in big-endian encoding. There might still be more. I’m checking 4 different encodings: ASCII uppercase and lowercase, and binary big-endian and little-endian.
EDIT 2: Brute force done. Here are the results:
CC4FBB6A (big-endian)
FFFFFFFF (big-endian & little-endian)
32F3B737 (uppercase ASCII)
The code is here. On my overclocked C2Q6600 that takes about 1.5 hours to run. Now that program is single-threaded, but it would be easy to make it multi-threaded, which would give a nice linear scalability.