Score:0

Crypto

How can I decode a XOR cipher with a string key I know?

unno

6/19/23, 2:47 PM

I have a text that has been XORed with the key "77U" (I am sure of this as it is a file created by a code I have, so I have seen every entry getting XORed by 77U.

However, none of the online decryptors I have tried are giving me any valuable results (error, or something gibberish), some don't have the option to put a string as a key so I tried converting it to ASCII but I still don't get any good results.

For trial purposes, that is part of the file I want to decrypt:

D>9,?9m=(#)$#*Gb|ub}mw|zwm

Some characters are being altered by the website so here is a screenshot:

Any help would be appreciated!

132

0 + 0

encryption

xor

decryption

Peter Mortensen

6/21/23, 12:37 PM

This is referenced in [a meta question](https://meta.stackexchange.com/questions/376440/broken-feed-for-the-cryptography-site).

Peter Mortensen

6/21/23, 12:45 PM

Is the listed part of the file supposed to be valid printable characters or is it essentially binary data? Or [UTF-16](https://en.wikipedia.org/wiki/UTF-16) where UTF-8 is expected?

Score:0

Crypto

vnd

6/19/23, 9:33 PM

Welcome unno!

You can use Python to define decryption function:

def decrypt(encrypted: bytes, key: bytes):
    result = []
    
    for i in range(len(encrypted)):
        result.append(encrypted[i] ^ key[i % len(key)])

    return bytes(result)

In this case I believe the text was encrypted with a single character of decimal ASCII code 77 (letter M):

% python3 -i xor.py
>>> encrypted = b"D>9,?9m=(#)$#*Gb|ub}mw|zwm"
>>> key = bytes([77, ])
>>> decrypt(encrypted, key)
b'\tstart pending\n/18/0 :17: '

Other online decoders should work as well once you specify 'M' (or 0x4D in hexadecimal representation) as a key.

0 + 0

unno

6/20/23, 6:31 AM

What about the U? Why did you just take 77 instead of 77U?

unno

6/20/23, 6:48 AM

Moreover, when I pasted the 3 lines in the uploaded screenshot I got ""Syntax Error: cannot mix bytes and nonbytes literals""

unno

6/20/23, 6:49 AM

for reference, here is the full file: https://pastebin.com/baFm7EqC

vnd

6/20/23, 10:20 AM

You probably get SyntaxError because text has quotation marks inside and you paste it without escaping. You need to escape it first, load from file or use triple-quotes like this: >>> b"""text " is " here"""

vnd

6/20/23, 10:25 AM

Regarding U, it often stands for Unicode. As for values <128 Unicode is same as ASCII, I've just tried 77 as a decimal value and it seemed like the text deciphered with this key was something meaningful.

unno

6/20/23, 10:41 AM

any idea how can I load it entirely from the file as I am having trouble pasting it since it is really big and I am getting "The text contains control characters, which could allow the pasted content to perform arbitrary commands. To confirm and Paste, you can use ⇧⌘⏎."

unno

6/20/23, 10:41 AM

so it might be ruining some parts.

vnd

6/20/23, 11:13 AM

Try: >>> encrypted = open("file.txt", "rb").read()

unno

6/20/23, 11:50 AM

Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/134293/discussion-between-unno-and-vnd).

unno

6/20/23, 11:52 AM

thank you so much this is working!

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How can I decode a XOR cipher with a string key I know?

TH: ฉันจะถอดรหัสรหัส XOR ด้วยคีย์สตริงที่ฉันรู้ได้อย่างไร

RO: Cum pot decoda un cifr XOR cu o cheie șir pe care o cunosc?

RU: Как я могу расшифровать шифр XOR с помощью известного мне строкового ключа?

VI: Làm cách nào tôi có thể giải mã mật mã XOR bằng khóa chuỗi mà tôi biết?

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