Bitwise cipher Cryptography

Question

I'm doing an online cryptography course. There is a question in which it is given that the encrypted text for;

OwBPAAQXAE9UC0FVBQxODgZSCUUMAQwCCApYRBJZBR0LDhoAGApPHQAUAQNZRAJPGwQbDQBDDREKQA==

Is

We need to use more complex systems to safely communicate.

They are asking the decrypted text for

JQtPDRMLFBtPAxNBBgEXT0lUBABPHQgfFANFRDlvJEkNChlICRdPBxJSBU9UHRFFVgYIQwhECAwbBxcXRAxJFAlFBEkaCwhUTBAcCxJSBU9THQxNEx0cCgoABwAWQEE7EE9JChdPGh8LEElQCRcJARMfDQFHRAAAFAAaFABTCUU3ITNSCx9FFgBUHwYAQwtFGBIKCw9SEAdFRAxFBRoPBAwADQsLTgoXHU9UC0FDBAwPFwwAGA0KTgIbFAdFFhVFDh1CQwhOCEUZBwIXRBlFFhJBVh0BQw5FGEUbBgRSCQpTFwBHE0kIEQZNTAYGHgkXFhtFHBUOVj0GBklGAAQITggBRBwBCRFMRRFeEQ==

What I have figured out:

After converting

We need to use more complex systems to safely communicate.

To base64, I got another string with the same length as the string they have given, so now I have to find a relationship between both these strings. But, I have been unable to find any relationship so far. The hint given in the question is bitwise cipher. Any help would be appreciated.

String they have given;

OwBPAAQXAE9UC0FVBQxODgZSCUUMAQwCCApYRBJZBR0LDhoAGApPHQAUAQNZRAJPGwQbDQBDDREKQA==

String I get after converting

We need to use more complex systems to safely communicate."

To base64:

V2UgbmVlZCB0byB1c2UgbW9yZSBjb21wbGV4IHN5c3RlbXMgdG8gc2FmZWx5IGNvbW11bmljYXRlLg==

I am unable to find a relationship between the above two strings.

Answer 1

The phrase "bitwise cipher" is most likely XOR'ing the base64 of the plaintext with a key of the same length. This is the most basic kind of symmetric cipher.

Try XOR'ing the base64 of the plaintext with the ciphertext they give you to get the "key". Then XOR this key with the challenge text to decrypt it.

And yes, I am aware this is an old question and the course is probably over by now.

Answer 2

Quit working with the JQ... string.

First, take the Ow... string, and work out a series of steps that result in the desired cleartext.

Then apply those same steps to the JQ... string!