I am trying to see specific cases of attacks in the CBC mode, in particular, I am investigating some attacks such as Example of a cut-and-paste attack on CBC. Here I have posted something similar and I have received great answers that are also very clear. But I have tried to look for more examples cut-and-paste attack and I have come across the following that I would like to solve and understand as well as possible:
An attacker intercepts the following encrypted text (encoded in hexadecimal):
He knows that plain text is the ASCII coding of the message "A Alice 10,000" (excluding quotes). The attacker also knows that CBC mode encryption was used with a random IV that uses AES as the cipher of underlying block. Show that the attacker can change the encrypted text to decrypt "A Alice 90,000" .What is the resulting encrypted text (encoded in hexadecimal)? This shows that CBC does not provide integrity.
We have to modify the encrypted text so that it decrypts what the exercise asks for, I suppose we have to change, in the plain text that is encoded using ASCII the character or characters that correspond to the number 1 by the number 9, to do this I don't need to know the initialization vector and the key? How could I solve this exercise easily?