Today I discover a encryption method
Which
0 = 35
1 = 34
2 = 37
3 = 36
4 = 31
5 = 30
6 = 33
7 = 32
8 = 3d
9 = 3c
It's the encode of number 1 to 0 for the method
Can you please help me to find the name of the method?
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1If each number is __substituted__ by a fixed other value then it is a [substitution cipher](https://en.wikipedia.org/wiki/Substitution_cipher). – Steffen Ullrich Mar 01 '20 at 17:02
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I voted to reopen this question because it is not a vague unanswerable question like so many others. In fact, @Luc has clearly and concisely already answered it. – user10216038 Mar 02 '20 at 04:28
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It is not on topic here though, so no, it should remain closed. – Rory Alsop Mar 06 '20 at 10:38
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Ok, but it wasn't closed as "off topic", it was closed as duplicative. – user10216038 Mar 07 '20 at 21:42
1 Answers
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It's an xor cipher with 0x05 as key.
Looking in the ASCII table, the digit 0 is ASCII code 0x30. In binary, that is 110000. Your ciphertext result is 0x35, which is 110101 in binary. The difference is that third-to-last and last positions are flipped (1 becomes 0 or 0 becomes 1). This is indicative of an xor key 000101 (put a 1 in the positions that flip). Converting 000101 (or simply 101 since leading zeroes can be removed) back to (hexa)decimal, you get 5.
The shortcut to calculating the xor key given a ciphertext and plaintext byte, is to xor them together: 0x35 ^ 0x30 = 0x05
To confirm this, we can use any other value from your list:
0 0x30 ^ 5 = 0x35
1 0x31 ^ 5 = 0x34
2 0x32 ^ 5 = 0x37
...
9 0x39 ^ 5 = 0x3c
An easy way to convert between binary / hexadecimal / decimal is python: hex(0b110101) gives 0x35 and bin(0x35) gives 0b110101. Note that the 0b and 0x notations are just prefixes to indicate the number system (binary and hexadecimal, respectively).
Luc
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