Licstar has a tool which can encrypt any text file by simple XOR encryption. The main procedure for this tool is as below.
for(int i = 0; i < contentLength; i += keyLength) {
for(int j = 0; j < keyLength && i + j < contentLength; j++) {
fprintf(f, "%.2x", content[i + j] ^ key[j]);
}
}
One day, Doraemonok found the tool and encrypt a source code "source.cpp" by it. If you submit original "source.cpp" you can get Accepted,
but unfortunately, you only have the encypted "source.cpp" and you do not know the key. The length of key is no more than 30.
The encrypted "source.cpp" in hex is as below.
71060c02241a11224f52144754595f6a1d515d08003b521733060c49614f0e4d4f4e4713595e44641b4f6a415f7f4970724f42412e0007
674707094710591079555f6c41076f4e5a3c54420863445c671464471310101064554f310e1c6f5a133c1b420b68525577544e0d130c1
05e7f55057c4a476f0970724f4241684f55674f4e4713565f42645d0639154e245247725f5941234f4967015547581b1b19640e6577414
e6f525a724f4241684f55674f4e5c3910101064554f77414e6f525a2f654241684f55674f4e1a3910101064086577414e6f5d55060707412
b0011224f0c02555f4255641c1c77141d2a1e1f211c4e412701193e4f08084110595e27070a36120721155a26070741240a1b201b06475
c5610442c1c1c7702012b1754584f4241681f00331c4645635c555137104f24140c221b0e7202074d681b1d22014e1e5c4510472d19037
7060b3b523b114f584c614d5c7c654e47131040453006477535062a5211371642083b4f27280d0f2f5c45775f2a125c67515e0b0715050e
0c2e3a15576e5464471310101f6b210732410f3a06123d1d1141270955330707141340425f26190a3a41546f1e13311c16003a4f14290b
4e035c425155291a01380a646f525a721d07153d1d1b675f556d4e3a3a