In a special operation our unit was able to intercept encrypted chat messages from a group of spies who plan a secret meeting:


Ifmmp fwfszpof!
Fwj dtz htrnsl yt ymj Sjb Djfw'x ufwyd?
Ekgn, ul iuaxyk, oz'rr hk gckyusk!
Ylhssf nbfz? Aopz pz hu lujyfwalk jvuclyzpvu mvy ptwvyahua tlzzhnlz vusf
Ws Jwaa
R anvrwm hxd fn wnnm cx bnc dy j crvn oxa cqn wngc vnncrwp
S mkx'd Deocnkic kpdob 7
Hsle lmzfe esp qtcde Hpoypdolj zq esp xzyes?
Omz'f, uf'e yk mzzuhqdemdk
Znmny gbi
Hvoby Mci
Rpc ndj rdbt dc iwt 20iw?
De, Y xqlu qd unqc.
Fb, kyrk cvrmvj lj nzky fecp fev fgkzfe.
Usf wnwjqgfw escw al?
Hz ojj.
Cnawp, oaa ukq pdaj!

We also acquired this note from a secret agent:


Bitcoin encoding:

Can you decrypt the messages and find when the spies are meeting?

Hint 1:

Our intel says that each line in the note indicates a different time, possibly for the meeting, but we still need to decode it first.

Hint 2:

The forensics team just found out that there was something written in invisible ink on the other side of the note:


Continuing on from QuantumTwinkie's answer...

For the Bitcoin Encoding:

enter image description here

The Meeting will be on:

Sunday January 13, 2019 at 20:30

Useful Resources:


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  • $\begingroup$ Nice job! +1 ... $\endgroup$ – pirate Feb 13 '19 at 15:29
  • $\begingroup$ Explanation of how you got that table? $\endgroup$ – Barker Feb 15 '19 at 20:59
  • $\begingroup$ @Barker - What do you mean? I added some useful resources in the post, $\endgroup$ – LeppyR64 Feb 19 '19 at 12:07
  • 1
    $\begingroup$ Basically what Annosz's answer does. They go through how they went from the phrase "Bitcoin encoding" to the solution. Your answer just has the table out of nowhere and I didn't understand where it came from until I read Annosz's answer. $\endgroup$ – Barker Feb 19 '19 at 17:57

For the beginning

You start with rot25 for the first line, then continue down one rot for each line to get:
Hello everyone!
Are you coming to the New Year's party?
Yeah, of course, it'll be awesome!
Really guys? This is an encrypted conversion for important messages only
Ok Boss
I remind you we need to set up a time for the next meeting
I can't Tuesdays after 7
What about the first Wednesday of the month?
Can't, it's my anniversary
Mazal tov
Thank You
Can you come on the 20th?
No, I have an exam.
Ok, that leaves us with only one option.
Can everyone make it?
Me Too.
Great See you then!


I can assume that the "current date" is in Decembers as they are anticipating a New Years party. I am also guessing that it is before December 20th since that date is still in the question.

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  • 1
    $\begingroup$ They are planning the meeting for a specific date which you need to find (and it relates to the note). $\endgroup$ – pirate Feb 12 '19 at 14:21

We can suspect from Hint2:

The number 01011970 is reffering to the starting date of the Unix time, or POSIX time, 1970. 01. 01.
UNIX time is measured as seconds elapsed since this specific date.

Whit this information, we can deyrypt the note's front page

Bitcoin encoding refers to Base58 encoding. With a decoder, we can see the original information written on the notes:

3mM4jWTdh6qrGP -> 1546452000
3mM4japbLpuUij -> 1548009000
3mM4ENFbwtRhwk -> 1515529527
3mM4jYf77P5oVZ -> 1547411400
3mM4jWSeGPL3VR -> 1546282800

These, together with the back

must mean seconds: giving them to the UNIX start date we get the following times:

2019. January 2. 18:00:00
2019. January 20. 18:30:00
2018. January 9. 20:25:27
2019. January 13. 20:30:00
2018. December 31. 19:00:00

From the conversation, which was decoded by @QuantumTwinkie, we can

eliminate the dates that are not good for the meeting:

New Year's party is off, so not December 31.
Tuesdays after 7 pm are off, so not January 9.
Not the first Wednesday of the month, so not January 2.
The 20th is off, so not January 20.

The day of the meeting is

2019. January 13. 20:30:00

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  • $\begingroup$ I know @LeppyR64 was faster than me, but this is the first more complex puzzle I was able to solve on PSE, and I just didn't have the heart to delete it right away :( $\endgroup$ – Annosz Feb 13 '19 at 15:17
  • $\begingroup$ Great work! Congratulations! $\endgroup$ – LeppyR64 Feb 13 '19 at 15:24
  • $\begingroup$ Nice work! .... $\endgroup$ – pirate Feb 13 '19 at 15:31

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