And its devastating because it works so fast.
Lets assume the byte we gmail hacker for mac are modifying has the value Q (for Question Mark).
One of these methods is called Cipher Block Chaining or CBC.
If I have captured 10 blocks, I can break the 10th block.If I send it to Alice, and I send to Bob, someone can see that I sent the same recipe to both people.Once we know the value for the last byte (Byte 16) of the block N, we XOR the desired padding for a 2-byte pad into block N-1.Let me elaborate with an example.However, if we can sent the message to the Padding Oracle, and it returns Good Padding or Bad Padding then we can defeat the system.If we continue this, we can guess all 16 bytes of the last block.The IV should be random, but for the sake of this explanation, lets assume its all zeros.Or to put it another way, every time I encrypt my Beans and Franks recipe, the result is identical.I can send blocks 1 through.Congratulations you are now an expert in Padding Oracle Attacks.Im not going to throw a big complicated diagram in front of you.16*8 or 128-bit) blocks.Once you have that, you can decode the decrypted message.If each test takes a 1ms, then to crack 16000 characters takes milliseconds, which is 4096 seconds., or a little more than an hour.We can XOR the same value to both sides of the equation and the equation will still be true.All I have to do is change the previous block, and this changes the decrypted value of the message.Because of the way CBC-mode works, all I need to do is send 2 blocks.There is no information used from a previous block of data that affects the transformation.
Does this block have proper padding?