13 replies to this topic

[Ohm]

Here's something to get us started. This is not a difficult challenge, I really just wanted something to put here while I prepare something more interesting.

I've encrypted a secret message below. Decrypt it to complete the challenge.

NVGhpcyBpcyBteSBzZWNyZXQgbWVzc2FnZQo

[DanielG]

Usually challenges like this have a hint in the form of a small (cryptic) accompanying text, or just a title as a hint.
Also, should we just solve this and post it here, or do we use some sort of [spoiler] tag to not spoil it for other people who want to solve it.

I haven't solved it yet but I think I'm baseing it on correct assumptions.

[Ohm]

OK, let's try a hint.

[Seal]

This is going to be fun. Thanks Ohm!

[Swerve]

OK, here is where I've got to:

Spoiler

I figure it's BASE64 from the hint given.

When I goto an online Base64 decoder, it produces a binary file.

When I open the binary file in Notepad++, it shows this:

5Q¡¥Ì¥ÌµäÍ•É•Ðµ•ÍÍ…”(

Which I assume is wrong.

If anyone has completed the challenge please feel free to give us a hint.

I don't think Ohm should be expected to help people who are stuck as he's done enough by creating these for us.

[DanielG]

Lol Swerve, that's how far I got without a hint, but he states we should "Decrypt it". So we're just halfway there.

[Ohm]

I've posted a second hint in the hints thread.

[zandi]

i'll get started on this asap, i need something other than schoolwork to focus on.

and maybe i'll get to toy around with some math, too.

[SchippStrich]

This is probably incredibly incorrect but are the first two characters: -R

In case you are wondering how the hell I got this, here is what I did;
I took each character from the ciphertext and found their corresponding decimal value.
I used this chart : http://email.about.c...se64enctabl.htm
I did this for 4 characters and calculated the six bit value for each.
001011 010101 001010 100001
After that I grouped the values into 3 byte groups.
00101101 01010010 10100001
And then I converted the bytes into their ASCII character equivalent.

I derived the idea from this: http://email.about.c...64_encoding.htm
The reason I did not try the third character is because I was getting this: í
So then I figured I was wrong.

Edited by schippystrich, 03 October 2009 - 06:13 AM.

[DanielG]

It really is simpler than you'd expect.

answer:

Spoiler

VGhpcyBpcyBteSBzZWNyZXQgbWVzc2FnZQo= decoded is "This is my secret message" (note the padded = to make the string length a multiple of 4).

My mistake was trusting that the supplied Base64 string was correct.
But you need to remove the first character (the N) and then you'll have the correct string.

Edited by DanielG, 03 October 2009 - 01:06 PM.

[Ohm]

You got it

Spoiler

This really works because base64 encodes 6 bits of the message in every character of the encoded form. By adding another digit to the front of the encoded message, you then throw off the boundary of the characters. Now, characters of the message are spread over multiple characters in the output, making it very difficult to see what's going on. It's security through obscurity, but it'll fool any casual observers and is dirt cheap.

[SchippStrich]

So I kind of had the right idea?

[bcrscahh198987]

I thought you wanted somebody to write a code that will undo it.

But that's too much work.

[megabraker]

I had it 'this is my secret message'