Is CBC-MAC collision resistant?
This example also shows that a CBC-MAC cannot be used as a collision-resistant one-way function: given a key it is trivial to create a different message which “hashes” to the same tag.
How does CBC-MAC work?
What CBC-MAC does is simply take the last block of ciphertext that is output and calls that the MAC. So your MAC should be the size of the block cipher which is probably not 4 bits. If you’re using 3DES it would be 64 bits.
What prevents length extension attacks in CBC-MAC?
1 Answer. In its plain form, CBC-MAC is vulnerable to “length extension attack”, where you just add some blocks at the end. So in order to stop people from doing that, you need to somehow mark the final block as indeed the final block. And not treat it like any other block.
Is AES-CBC still secure?
AES-CBC remains the most common mode in general use, but AES-GCM is increasing in popularity. Given the advantages of GCM, this trend is only likely to continue. From a cryptographic perspective, though, both AES-CBC and AES-GCM are highly secure.
What is difference between MAC and Message Digest?
A Message Digest is simply a hash of a message. It’s the output of a cryptographic hash function applied to input data, which is referred to as a message. A Message Authentication Code (MAC) is a piece of information that proves the integrity of a message and cannot be counterfeited easily.
How is CBC-MAC secure for variable length messages?
There are three main ways of modifying CBC-MAC so that it is secure for variable length messages: 1) Input-length key separation; 2) Length-prepending; 3) Encrypt last block. In such a case, it may also be recommended to use a different mode of operation, for example, CMAC or HMAC to protect the integrity of variable-length messages.
How to calculate the CBC-MAC of a message m?
To calculate the CBC-MAC of message m, one encrypts m in CBC mode with zero initialization vector and keeps the last block. The following figure sketches the computation of the CBC-MAC of a message comprising blocks
What’s the difference between CBC and CBC MAC?
A quick reminder. CBC-MAC is very similar to the classic CBC mode for encryption, with a few major differences. First, the Initialization Vector (IV) is a fixed value, usually zero. Second, CBC-MAC only outputs the last block of the ciphertext — this single value forms the MAC.
Is there way to encrypt last block in CBC-MAC?
This problem cannot be solved by adding a message-size block to the end. There are three main ways of modifying CBC-MAC so that it is secure for variable length messages: 1) Input-length key separation; 2) Length-prepending; 3) Encrypt last block.