SPOJ Problem Set (classical)
17. The Bytelandian Cryptographer (Act I)
Problem code: CRYPTO1
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
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
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