# Bitwise cipher Cryptography

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.

• Did you ever find out what the instructor was looking for? May 30, 2016 at 13:43

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.

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!

• Sorry, I have edited the question. I am unable to find any relation between the two strings. Jan 31, 2016 at 4:44
• Then if your hint is "bitwise cipher", look through the materials your course has provided carefully for every mention of "bitwise" in relation to ciphers. Try those techniques! Jan 31, 2016 at 4:47
• I tried to take xor, or and and of both the strings but nothing worked out. Should I try to reduce the 'We need..' string to binary digits and work something out from there? Any help would be appreciated. Jan 31, 2016 at 4:48
• Read all of your course materials for each mention of what a "bitwise cipher" is, and then experiment with that. You need to learn the material! Jan 31, 2016 at 4:50
• This question is on another site and not in the course content, so I'm thinking maybe it is something which he has not covered in the course. Anyways, thanks for your help. Jan 31, 2016 at 5:08