I will say however that, while CBC has its own problems, ECB should never be used unless you are encrypting one block of data, which is 16 bytes for AES, otherwise this will happen.Ĭonfidentiality - no adversary can learn the content of the encrypted messageĪuthenticity - any attempt to tamper with the data will be detected I suggest you take a look at the Wikipedia page to understand more about this. Now of course, MAC algorithms are much more complex, as are ciphers, so this is just a simple example, but it should get the point across.Īs for CBC and ECB are two modes of encryption. If that encryption used a type of authentication, such as a message appended to it which is somehow derived from the decrypted message, then you could easily tell if it has been tampered with, and no one could modify without you knowing, unless they know that they key is "sekrit". They didn't know what number it would change into, but they knew it would be enough to confuse our troops. Changing just one part of the encrypted text may end up changing just one part of the decrypted text, in this case it changes the number 4 to the number 9. A tiny difference, but enough that they may win the battle. They can't make it say whatever they want, but maybe they can make it say "attack at 9 PM" instead. But what if they can modify it? They might not know what they are turning it into, but if they modify just a tiny bit, they can have it decrypt in slightly predictable ways. Without knowing "sekrit", they will have no idea when we will attack. Now, if the enemy catches the encrypted message, they can't read it. With the wrong key of course, even if the key they try is one character off, like "sikrit", it will decrypt to total gibberish. If I send an encrypted message to my army, "8F0ajc8a Op", then with the right key, "sekrit", it may decrypt to "attack at 4 PM". Both have the same result, ensuring that, unless you know the key, you cannot tamper with the data without the other party knowing. An alternative scheme, called HMACs which uses hashes are typically used instead. A CMAC is a type of message authentication code(MAC) which uses block ciphers to ensure that a message has not been tampered with. Authenticity means you can cryptographically verify that the data has not been tampered with. Confidentiality means the data cannot be decrypted without a known key.
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