Step 1: Know your sources.
Looking into Wikipedia or, at least, other discussions on the unsolved D'Agapeyeff cipher, you will find an example of similar cipher. It's a polybius square, where every letter is encrypted with two digits. As seen by the shape of the puzzle, you can understand that it should be read by columns, ending at 30000. Join it as that, than split by two's. You shall get:
53 81 96 90 76 79 77 90 82 79 89 94 73 90 97 76 90 93 78 70 86 73 74 50 90 38 75 90 78 82 90 81 90 82 78 97 70 89 73 90 93 79 83 73 90 75 79 90 95 74 73 81 88 90 81 96 83 98 90 93 79 77 89 83 90 95 73 90 97 81 83 73 90 97 77 93 86 90 86 81 74 83 73 74 99 90 38 84 90 76 79 77 90 86 81 94 73 90 74 73 81 89 89 76 90 83 73 93 79 83 73 83 90 75 86 78 82 90 97 73 82 82 81 85 73 90 76 79 77 90 82 86 79 77 89 83 90 82 73 96 83 90 75 86 73 82 73 90 55 78 75 93 79 78 96 90 76 79 77 90 86 81 94 73 90 83 78 82 93 79 94 73 74 73 83 90 78 97 97 73 83 78 81 75 73 89 76 90 75 79 90 81 90 96 73 72 90 81 83 83 74 73 82 82 90 75 79 90 74 73 89 78 73 94 73 90 75 86 73 97 90 84 74 79 97 90 75 86 78 82 90 70 74 78 94 81 75 73 90 88 73 76 90 75 86 81 75 90 78 82 90 96 79 72 90 70 77 95 89 78 82 86 73 83 99 90 39 96 89 76 90 79 96 73 90 72 78 96 96 73 74 90 72 78 89 89 90 85 73 75 90 75 86 73 90 70 74 78 91 73 99 90 30 89 73 81 82 73 90 93 89 81 78 97 90 95 73 84 79 74 73 90 70 77 95 89 78 82 86 78 96 85 90 76 79 77 74 90 81 96 82 72 73 74 99 90 49 63 49 65 75 49 33 62 79 37 87 34 76 85 74 49 74 77 72 73 86 64 31 64 92 32 78 93 37 70 85 62 31 65 52 47 71 82 61 32 49 95 44 43 68 47 88 32 96 91 68 83 00 00
Step 2: Spaces
Analyse the frequencies: 90 is met here 62 times; the next number only 42 times. Thus, assume that 90 is space (you can also see that it is distributed evenly by Ctrl-F to find 90).
Step 3: Your everyday letter-guessing.
53 81 96 _ 76 79 77 _ 82 79 89 94 73 _ 97 76 _ 93 78 70 86 73 74 50 _ 38 75 _ 78 82 _ 81 _ 82 78 97 70 89 73 _ 93 79 83 73 _ 75 79 _ 95 74 73 81 88 _ 81 96 83 98 _ 93 79 77 89 83 _ 95 73 _ 97 81 83 73 _ 97 77 93 86 _ 86 81 74 83 73 74 99 _ 38 84 _ 76 79 77 _ 86 81 94 73 _ 74 73 81 89 89 76 _ 83 73 93 79 83 73 83 _ 75 86 78 82 _ 97 73 82 82 81 85 73 _ 76 79 77 _ 82 86 79 77 89 83 _ 82 73 96 83 _ 75 86 73 82 73 _ 55 78 75 93 79 78 96 _ 76 79 77 _ 86 81 94 73 _ 83 78 82 93 79 94 73 74 73 83 _ 78 97 97 73 83 78 81 75 73 89 76 _ 75 79 _ 81 _ 96 73 72 _ 81 83 83 74 73 82 82 _ 75 79 _ 74 73 89 78 73 94 73 _ 75 86 73 97 _ 84 74 79 97 _ 75 86 78 82 _ 70 74 78 94 81 75 73 _ 88 73 76 _ 75 86 81 75 _ 78 82 _ 96 79 72 _ 70 77 95 89 78 82 86 73 83 99 _ 39 96 89 76 _ 79 96 73 _ 72 78 96 96 73 74 _ 72 78 89 89 _ 85 73 75 _ 75 86 73 _ 70 74 78 91 73 99 _ 30 89 73 81 82 73 _ 93 89 81 78 97 _ 95 73 84 79 74 73 _ 70 77 95 89 78 82 86 78 96 85 _ 76 79 77 74 _ 81 96 82 72 73 74 99 _ 49 63 49 65 75 49 33 62 79 37 87 34 76 85 74 49 74 77 72 73 86 64 31 64 92 32 78 93 37 70 85 62 31 65 52 47 71 82 61 32 49 95 44 43 68 47 88 32 96 91 68 83 00 00
I assumed that 76 79 77 was "the". It wasn't. Still, It all looks positively like text. Keep trying. The single letter 81 is certainly an "A". Then I made two steps: 1) I replaced all the symbols with frequency 1 with stars to avoid messing with them; 2) I found the word "and". Still wasn't sure about the direction. Until...
75 79 _ a _ n 73 72 _ a d d 74 73 82 82 _
Wait, isn't it...
a d d 74 73 82 82 _
Yep. This is definitely 'address'. We're getting the right way.
Step 4: The pad.
Now for the original part (I bow to WillTech here, for it is really nicely done). After deciphering all you can, you will probably get:
Can you solve my cipher? It is a simple code to break and, could be made much harder. If you have really decoded this message you should send these Bitcoin you have discovered immediately to a new address to relieve them from this private key that is now published. Only one winner will get the prize. Please claim before publishing your answer. 49634965t493362o378734ygr49ruweh6431649232ic37pg623165524771s613249b44436847k32nz68d0000
(this last part is not fully deciphered yet).
Well, remember it was a polybius square? If you actually draw it (10x10 with 0's in the end) and fill with what you have, you will get:
*1234567890
1__________
2__________
3_______IOP
4__________
5__C_B____?
6__________
7_wertyuiop
8asdfghjkl_
9z_cvbnm,.
0__________
You should see two standard keyboard layouts, one uppercase and one lowercase. The rest is deciphered by filling in the formerly unknown uppercase letters and numbers in the grid (numbers will be in row 6).
Step 5: Just the answer.
Can you solve my cipher? It is a simple code to break and, could be made much harder. If you have really decoded this message you should send these Bitcoin you have discovered immediately to a new address to relieve them from this private key that is now published. Only one winner will get the prize. Please claim before publishing your answer. L3L5tLE2oUjRygrLruweh4Q4xWicUpg2Q5XJqs1WLbFD8JkWnz8d**
(Note: the two * at the end are from the trailing 00 00 and are not part of the bitcoin key) After some manipulations with cryptocurrency you may check the last transaction on this wallet happened about an hour ago, when I finally installed Penguin OS.
