Christmas Tree Hash
100 points Hard

As Christmas approaches, Adam decides that he wants to improve his network security. He is inspired by the nearly identical Christmas Trees in his office with the only difference being the number on the star on top, and writes a hash function to generate a key. His instructions are found here: https://mega.nz/#!vawiwIBL!MNh3kyh12f_V8xtpHVCiBz5svr7Npvdhu6uzUkS08Tg - The trees in Adam's office can be found here (your input): https://mega.nz/#!PGw2SCDZ!yzI2DCX0ut-TR5WBDX2x_aqtNQezg9WTGcxcmHlNJNs - What is the encryption key generated by Adam's Christmas Tree Hash function?

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Rating 4.54
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Discussion

Well that took longer than I planned.

Tips: - Depending on what language/tool you're using you may want to calculate the exponents by hand - mine was about 60 out using normal libs, and even an online site I tried to verify at was getting the wrong result (but by a different margin to 60). - Make sure you work through the given examples (especially the ones showing intermediate results). They do help troubleshoot most things.

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I don't get how the binary string is made at step 4....if I convert each character to binary, then the first 16 bits is the 1st 2 char and then last 16 bits are the last 2 chars....but that would be: a = 0110110001100111 //lg b = 0110010001100111 //dg so obviously I don't get soemthing, but if someone could point me in a vague direction.....

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Never mind. It's 7 bit not 8 bit.

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365^5 + 52^10 + 7^20 where this came from?

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Poorly explained from step 6 onwards.

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kinda complex but Its was fun lol

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remeber there is a "-" before the new value ;).

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most of the difficulty of this CTF comes from understanding the instructions (not joking, you have to read the author's mind sometimes, heh)

there's a typo, in the line:<br /> 365^5 + 52^10 + 7^20 - 457981573849226022<br /> the minus was meant to be a plus:<br /> 365^5 + 52^10 + 7^20 + 457981573849226022

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Any hint about step 7 - how to convert -682335424444623097 to uehcysuxjh? I've already tried several conversions of -682335424444623097 to other values

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never mind - I've found how to convert

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That was a fun programming challenge! Also, that flag made me do a double take and then made me laugh pretty hard, lmao. Thanks for the challenge!

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