CRYPTO1 - The Bytelandian Cryptographer (Act I)

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The infamous Bytelandian Bit-eating Fanatic Organisation (BBFO for short) plans to launch an all-out denial-of-service attack on the Bytelandian McDecimal's fast food network by blocking the entrance to every restaurant with a camel (the purpose being to rid the Organisation of unhealthy competition, obviously). In a sly and perfidious move, the head cryptographer of BBFO decided to disclose the date and time of the planned attack to the management of McDecimal's, but in encrypted form (ha ha). He calculated the number of seconds from midnight 1970.01.01 GMT to the moment of attack, squared it, divided it by 4000000007 and sent the remainder by e-mail to McDecimal's. This made the original date impossible to decode.

Or did it?

*   *   *

You work as the head algorthimist at McDecimal's HQ and know nothing of what is happening in Byteland. Things are not going well. You are playing a quiet game of hearts against your computer and wondering why on earth Management are considering making you redundant. Suddenly, the CEO bursts into your office, saying:

- Look here, young man[lady]! I have this number and those guys claim it is supposed to be some date. I am giving you one second to tell me what it all means!

I am afraid you have no choice. You can't ask any further questions.
You just have to answer, now.


The encrypted timestamp.


The decrypted GMT time and date of attack, somewhere between 1970 and 2030, using standard 26 character formatting.



Sun Jun 13 16:20:39 2004

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Rodrigo Salazar: 2010-01-29 08:56:49

Last edit: 2010-01-31 04:35:57
schiermike: 2010-01-21 14:23:30

encryption seems to be f(x) = x^2 mod p
the output of the example is Sun Jun 13 16:20:39 2004, which lets x be 1087136439, but then f(x) would be 2933335865 and not 1749870067 as indicated by the input!

Stay Puft: 2010-01-21 15:27:10

long is not 64bit on the test machine. Use long long.

Vo Duy Khang: 2009-02-23 12:15:00

This problem has 1 test case for each running isn't it?

Added by:adrian
Time limit:1s
Source limit:10000B
Memory limit:1536MB
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