Eve enters Mallet room in a hurry.
Mallet! Mallet! I need your skills. Do you fancy some free games?
My skills? So that means that you want to steal those games, eh? I like the idea, I'm open to all kind of evilness!
Of course Mallet, we're going to steal some games from Bob! I was drinking some coffee near Alice room when I heard something interesting... She got a message from Bob telling her that he'll buy her some of their wishlisted games, but needed her email to send them through steam.
So you want to intercept the message from Alice and change the email to one we own. It seems easy, I mean even you could do that!
No Mallet, since our last prank they use some kind of magic to make their messages unreadable!
Don't panic Eve, we'll get the games!


Some hours later Mallet intercept the following message from Alice to Bob: f99a4fcbea31e7188d40def79f919594764fa4d58f33c520
Mmm... so it's true that they are using some cryptography at last. It seems I'll have some work to do, it'll be difficult but at least I know that her email is alice.ron.rivest@mit.com.
I just need to change it to one of my mails, like mallet.ron.rivest@mit.co !


Mallet head to his evil site to tamper the message back to Bob.


Giveaway will finish in 6 days.

We have 8 solvers and 4 entries by now, so the chances are good! Giveaway is a not bundle (in my opinion awesome) steam package for level 0+, so no requisites apart from resolving the puzzle!


Hint 1: The message received by Mallet uses a crypto algorithm that is vulnerable to Frequency analysis when it gets reused.
Hint 2: graphic hint

5 years ago*

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Mission accomplished!

5 years ago
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Sorry Bob, they forced me to do it!

5 years ago
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Don't do puzzles so have a bump!

View attached image.
5 years ago
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Poor Alice, so many interceptors.. Bump!

5 years ago
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Bump :3

5 years ago
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Bump for solved!

5 years ago
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Bump for solved, I like such puzzles.

5 years ago
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Bump for not even going to try, goodluck everyone else

5 years ago
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Bump for solved. This is kinda hard.

5 years ago
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Man, one of those puzzles I really wanna get but I have no idea how to approach it... hmmm...

5 years ago
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We have now 6 brave solvers and 2 entries :D

5 years ago
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Bump for I was one of the 6 :)

5 years ago
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Bump for solved!

5 years ago
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Shameless bump :3

5 years ago
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Bump for mallet

5 years ago
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Morning bump.

Right now we have 8 solvers and 4 entries!

5 years ago
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my brains are going to explode if i keep trying to solve this.....

Or this is too complicated, or i am making it too complicated.

Edit: I think i almost got there, but maybe i'm looking at the wrong clue... so i give up. ¯\(ツ)

5 years ago*
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Tomorrow I'll post a hint to make it a little easier :P

5 years ago
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Hint 1: The message received by Mallet uses a crypto algorithm that is vulnerable to Frequency analysis when it gets reused.

5 years ago
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Bump for I believe I know what to do,
Sadly I couldn't find a tool yet to solve this. My google foo is filing me :(

5 years ago
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Hint 2: graphic hint

5 years ago
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Less than 1 day left!

5 years ago
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I give up. I tried everything i can. I think i got a lot of it done, but in the end nothing worked to lead me to the giveaway and i spent too many hours in this.

I hope you'll post the method to get to the giveaway when it ends. i'm very curious to know what i did wrong. xD

Good luck to everyone that made it! ;)

5 years ago
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Solution:

The first thing to do is look at the italic letters to get otp, that stands for One Time Pad. This is a basic type of stream cipher where the "key" (the pad) must not be reused, that's why it's called One Time Pad.
That's because the nature of the algorithm that makes it vulnerable if the pad is repeated due to Frequency Analysis and the possibility to remove the pad using two or more messages.

But that it's not needed to solve the puzzle. There are two options to solve it, one involves knowing how OTP works and the other simple addition or substract between characters to alter.

The good way to solve it is using bitwise xor (second hint), so let's do it:

Plain message: alice.ron.rivest@mit.com
Encrypted message: f9 9a 4f cb ea 31 e7 18 8d 40 de f7 9f 91 95 94 76 4f a4 d5 8f 33 c5 20
Hexa value for plain message: 61 6c 69 63 65 2e 72 6f 6e 2e 72 69 76 65 73 74 40 6d 69 74 2e 63 6f 6d 
bitwise xor: 98f626a88f1f9577e36eac9ee9f4e6e03622cda1a150aa4d

So we have the pad, now we can use OTP with out tampered message.

plain message: mallet.ron.rivest@mit.co
hexa value: 6d 61 6c 6c 65 74 2e 72 6f 6e 2e 72 69 76 65 73 74 40 6d 69 74 2e 63 6f 
PAD: 98 f6 26 a8 8f 1f 95 77 e3 6e ac 9e e9 f4 e6 e0 36 22 cd a1 a1 50 aa 4d
bitwise xor: f5974ac4ea6bbb058c0082ec808283934262a0c8d57ec922

The correct answer is: f5974ac4ea6bbb058c0082ec808283934262a0c8d57ec922

5 years ago
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