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It's an average normal everyday day. You find a piece of mail in your mail box. It doesn't look like the rest of them:

The puzzle

The text reads

VVJHRU5UISBQbGVhc2U gYXR0YXRjaCBvdXIgbmV4dCBsaW ZlIGFuZCB5b3VyIHB1YmxpYyBrZXk gYW5kIHJldHVybiB0byB1cyB3aXR oaW4gdGhlIG5leHQgNyBkYXlzISB ZT1VSIExJRkUgSVMgSU4gREFO R0VSISBUaGVyZSBzaG91bGQgYmUg YSBwYXBlciBpbiB0aGUgYmluIHdpdGg gdGhlIGtleXMgd3JpdHRlbiBvbiB0aGV tIHRpdGxlZCBDdmIgI1MzIENmeS4gU mV0dXJuIGl0IHRvIHRoZSBidWlsZGlu ZyBub3J0aCBvZiB0aGUgb25lIG9uIHRo ZSBzdGFtcC4=

What should you do?

Some helpful websites:

pastebin.com i.imgur.com/.png

Hint:

What to do? Maybe the message might help

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  • 1
    $\begingroup$ Just a warning, that last character is a dead give away about the encoding. $\endgroup$ – Kai Qing Mar 16 '18 at 23:28
  • $\begingroup$ @KaiQing I'm aware, I did a second challenge and it is much more difficult than this one $\endgroup$ – pfg Mar 16 '18 at 23:28
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    $\begingroup$ It's a good one though. The initial encoding is not at all indicative of the difficulty of the rest of the puzzle. good job $\endgroup$ – Kai Qing Mar 16 '18 at 23:31
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A few observations on the photo at CvdNbvV:

I extracted the EXIF data but there didn't seem to be anything of value. The text in the left column gets distorted at certain places. The text in the left and right columns have different font sizes.

Leads me to believe:

The left columns pixels may have been distorted as a result of steganography.

Following on from Fifth_H0r5eman's answer. The LSB decoded image reveals the last bit of the QR code.

I have observed that the QR code has been split into 8 pieces. Now the pieces must be rearranged to form the original QR code.
The first 6 pieces are down the left column, separated by horizontal green lines once decoded. The last two are in the bottom right corner.
LSB decoded image

Following on from Deans reassembled QR code and hint 2.

It might be the case that the building on the stamp is actually the one located at "46.4295878,4.6621564" and not the one shown in the picture as these co-ordinates were deduced from the stamp.

If that is the case then the building north of this is the Les 'Marronniers Bar Restaurant' which is stated on the building, or 'Teixeira Ribeiro Joao-Marco' which it is labeled as on the map.
If we take it to be the latter, it translates in French to 'About me Joao-Marco' according to Google Translate.

Partial Answer Guess

Who: Joao-Marco
What to do: Send the public key located on paste bin and the next step in Conway's Game of Life of the logo in the top left corner of the original piece of mail.
Why: ??

Revised guess after riddle change

Send the public key located on paste bin and the next step in Conway's Game of Life of the logo in the top left corner of the original piece of mail.
Address to Joao-Marco at 20 Avenue Charles de Gaulle, 71250 Cluny, France

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  • $\begingroup$ Where should the letter be addressed $\endgroup$ – pfg Mar 16 '18 at 3:00
  • $\begingroup$ So if it is the latter, then it should be addressed to 20 Avenue Charles de Gaulle, 71250 Cluny, France $\endgroup$ – tyobrien Mar 16 '18 at 4:03
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    $\begingroup$ If you have a PGP key pair, shouldn't you be sending an encrypted email? $\endgroup$ – LeppyR64 Mar 16 '18 at 11:53
  • $\begingroup$ @LeppyR64 It's an RSA key pair - how will you encrypt it if you don't know their public key $\endgroup$ – pfg Mar 16 '18 at 18:39
  • $\begingroup$ @pfg - I have no idea. Never used one, just thought that's what they were for. Turns out it was irrelevant. $\endgroup$ – LeppyR64 Mar 16 '18 at 19:23
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Partial answer

Definitely correct stuff...

Text is

base64 encoded

Which produces:

URGENT! Please attatch our next life and your public key and return to us within the next 7 days! YOUR LIFE IS IN DANGER! There should be a paper in the bin with the keys written on them titled Cvb #S3 Cfy. Return it to the building north of the one on the stamp.

Based on the hint,

we can try https://pastebin.com/CvbS3Cfy which leads to some heavily obfuscated javascript. Running it however throws a syntax error caused by some embedded brainf-ck:
--[----->+<]>----.[--->+<]>+.-[--->++++<]>.-[--->+<]>+++.---[->+++<]>.+[--->+++++<]>+.[--->++++<]>--.+[--->++++<]>+.

Executing that produces bwHpGyJe, which leads to https://pastebin.com/bwHpGyJe, which contains an RSA public/private key pair...


Other notes and observations...

The stamp appears to be

based off this stock photo:
stamp stock image

Except that it has been squared off, and

has been made partially greyscale. The saturated/desaturated regions create these shapes:
colour grid
Not sure how much information you can compress into an 8x7 grid, but it's likely important (possibly also related to the game of life, see below). Of course it's also plausibly just an artifact from whichever stock image site OP nabbed the image from initially (there's a different watermark in the centre to the shutterstock one I showed above, but I can't quite make out what it says).

Probably less relevant, but

the image on the stamp is of Château de Gien, in France. The body text says to deliver our message to "the building North of the one on the stamp", but looking at google maps, there's little of obvious interest to the north of Gien Castle.

Finally, commenters below have noted that the image in the top left

is a glider from Conway's Game of Life, which is possibly hinted at in the body text ("our next life"). It also may relate to the grid layout of colours on the stamp, though at the very least running that configuration doesn't seem to do anything special... Of course the glider is also a common hacker emblem, so it may just be thematic.

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  • $\begingroup$ Part way there. $\endgroup$ – pfg Mar 15 '18 at 5:07
  • $\begingroup$ The image in the top left is a glider from Conway's game of life, so it might be a hint that the game of life is involved in some later step? $\endgroup$ – Carmeister Mar 15 '18 at 7:22
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    $\begingroup$ On that basis 'our next life' would be imgur.com/a/o0yjF $\endgroup$ – chrism Mar 15 '18 at 10:30
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    $\begingroup$ Good find on the greyscale parts. The left column is all colour, so the rows may be ASCII with colour = 0; greyscale = 1. (If so, the seven rows spell CvdNbvV. There's nothing associated with that code on pastebin, but imgur has a Lorem Ipsum page, which may or may not be useful.) $\endgroup$ – M Oehm Mar 15 '18 at 12:06
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    $\begingroup$ @MOehm, the lorem ipsum page (imgur.com/CvdNbvV) seems to have a part of a QR code to the left, some of which is grayed-out. Also, a bit meta- but its upload timestamp coincides with the question. So the QR pattern may be related to the patterns mentioned above (I now see Alconja have already observed the pattern) $\endgroup$ – etov Mar 15 '18 at 14:04
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Following Vlad's answer:

The QR code pieces slightly overlap in places, creating this QR code (sorry it's kinda ugly): qr


This translates to:

@46.4295878,4.6621564,21z

Using the first two numbers as latitude and longitude get me to this address:
building

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  • $\begingroup$ A hint has been added on where to go from here $\endgroup$ – pfg Mar 16 '18 at 0:12
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Using a LSB decoder:

Gives a second half to the QR code on the Lorem Ipsum image

However I cannot seem to piece the image together well enough to to read it...

The parts I have seem to be out of proportion to one another (Or at least the grey does).

enter image description here

From Dean's Answer and the comment from OP there, I have tried:

deconstructing the Public and Private RSAs (I'm not hugely familiar with how they work exactly I admit... and have found the public exponent to be 10001, with a modulus of 74aeaca203a5a2b7612b93c2b14543987e0eaa16c0024f57a29713a7bff11cbd9966e0008affd2f577ccbfc86208e896cd7c705a46d5db073561db7476aae167 (Hex obviously).

From the fact we are given:

The public AND private key, I thought perhaps they would allow a piece of text to be encrypted and decrypted into another, but no such luck there. I am now struggling to find a piece of the translated message text that has not been used...

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I ran

one step of Conway's Game of Life ("our next life")

on the black dots

above the QR code

in the

imgur lorem ipsum page (imgur.com/CvdNbvV)

which resulted in

this shape:
01100000000
10110000100
10000100000
01010110010
00010100011
01111111011
10000100010
01000101010
01011101100

I don't see much in there, except

It looks like there might be a "j" on the far right.

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  • $\begingroup$ Nice idea to use the ROT13(Tnzr bs Yvsr) on the black dots. $\endgroup$ – Phylyp Mar 15 '18 at 14:30

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