(Current time: )
After reading the rules, please enter your real name and the number written on the board to enter the contest.
(Hint hint: Now we're debugging, so you can enter anything as the magic number.)
Come up with an encryption algorithm (from numbers to numbers) that's easy to use but hard to break.
16:45
In 10min, please do the following:
Read the rules
Enter the number written on the board and click "I'm ready!"
Come up with 1 or 2 encryption algorithms for later
16:55 (the Encrypting Phase, signaled by a change of interface)
In 10min, please do the following:
Leave one message per algorithm for the decipherer. Here you're expected to describe the algorithm. If you decide to use the same algorithm, click the checkbox so that the message is copied.
(We suggest that you spend no more than 4min to leave the messages.)
Upon submitting the messages, you'll see 2 sets of four-digit numbers (9 in each). Encrypt them with your encryption algorithm(s). You must also encrypt them to four-digit numbers!
17:05 (the Decrypting Phase, signaled by a change of interface)
In 10min, please do the following:
You'll see 4 sets of encrypted numbers, along with the messages from the encryptor (who, we promise, is not you). Decrypt them.
17:15 (the Hacking Phase, signaled by a change of interface)
In 15min, please do the following:
You'll see 4 sets of encrypted numbers. In each set 8 of the 9 original numbers will be leaked to you. Identify the pattern and determine the last original number.
17:30
Award Ceremony
For each number correctly decrypted by the decipherer,
encryptor's score += 20, decipherer's score += 10
To encourage simplicity, there's a -x% modifier to their scores, where x is the length (in bytes) of the message.
If the decipherer gets the entire set correct, a +20% modifier will be applied to their scores.
For each set correctly hacked by the hacker,
hacker steals 100 from encryptor's score
Suppose Alice, Bob and Charlie are the contestants.
At 16:55, Alice described her algorithm in the message "AllDigits+1mod10". Then she received the numbers 1952 and 2473 (we'll assume there are just 2 numbers and one set). She encrypted them into 2063 and 3584.
At 17:05, Bob received 2063 and 3584, as well as Alice's message. He managed to understand it, and reduced every digit by 1 to retrieve 1952 and 2473. By submitting them, both Alice and Bob got credits.
At 17:15, Charlie received 2063 and 3584. He was also given all but one original number. Say, he knew that 3584 was originally 2473. After prolonged staring, he found the pattern -- each number was raised by 1! He concluded that the original number for 2063 should be 1952. Upon submitting the correct 1952, Charlie stole a lot of points from Alice.
Final score --- Alice: 20 * 9 * (100% - 16% + 20%) - 100 = 87.2; Bob: 10 * 9 * (100% - 16% + 20%) = 93.6; Charlie: 100.
You might think: it's even worse than encrypting everything to 0000, in which nobody gets points. But when there are more participants, this is a good deal!
0. Work as an individual. (See, we don't ask your team name.)
1. Generally, the encryptor should collaborate with the decipherer (and vise versa).
2. Describe your algorithm in a simple but clear fashion.
3. After encrypting, we will shuffle the numbers in the set, so don't depend your algorithm on their order.
4. We use cookies to backup your numbers, in case anything goes wrong. Please enable them if you haven't. Don't worry, they'll automatically disappear after 2 days.