downloadbrowsewarsaw's Invisible Java Crackme

Download invisible.zip, 2 kb (password: crackmes.de)
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Is this the real code, or is it just fantasy...

Find the string you need to pass on the commandline for the program to print out "Correct!". Make sure that your answer works in the unmodified program, running on the official Java release from Oracle.

Difficulty: 4 - Needs special knowledge
Platform: Multiplatform
Language: Unspecified/other

Published: 01. Jul, 2014
Downloads: 185

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Solutions

Solution by boonz, published 07. jul, 2014; download (48 kb), password: crackmes.de or browse.

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Discussion and comments

warsaw
Author
02. Jul 2014
Note, this crackme is designed for Hotspot. It won't work properly on alternative JVM implementations.
boonz
02. Jul 2014
for (int i = 1; i < 32; i++) {
array[i] = (char) (array[i] ^ array[i * 123456 % 31] & 0x1F);
}

The hash function must be brute-forced because it takes the least 5 bits using binary AND which cannot be inversed?
warsaw
Author
06. Jul 2014
No brute forcing is required.

That operation is invertible.
marcoventuri
06. Jul 2014
sorry,i wrong solution
Dark_Prince
14. Sep 2014
What a nice solution! Well done boonz.

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