do you know about CBC-MAC? I have iv ,MAC and Transaction but no key. and I should change Transaction without change cipher text. do you know how this is possible at all? In addition, I do not have cipher text to find key. information:
Transaction:to=9714163002&from=9711412111&amount=10000000 IV: qes/2BpH9BvVN7f6jFy43g== (base64) MAC: NEhKNEtaR3lDdzRtWHJJTg== (base64)
9714163002 should exchange to something other than 1234567890 and what I should find and submit is:
Transaction: IV: MAC:
The main text of the challenge is as follows:
Consider the following method for digital signature.
A. The text P should be downloaded
B. CBC text is encrypted with a secret key
C. Discard all code blocks except the last block
D. The last bulk should be considered as the MAC-CBC digital signature of the text.
The above method can easily detect any unauthorized changes in the text, because if any changes MAC-CBC will not correspond to the text. Suppose this system is used in banking transactions And any transaction will be valid if the signature is correct. You as the attacker Could you hear a message:
Transaction:to=9714163002&from=9711412111&amount=10000000 IV: qes/2BpH9BvVN7f6jFy43g== MAC: NEhKNEtaR3lDdzRtWHJJTg==
IV and MAC are coded base64. If you can change the number 9714163002 with your participant number in the above message, the amount will be credited to your account, but the problem is that the transaction must have a valid CBCMAC and you do not have the key. Find a way to reach your goal without a key. Send your answer to the address of the question. Note that the destination must be your participant number.