Tag Info

New answers tagged

1

Here are some advantages and disadvantages for each of the three classes of MACs, which I know about: Based on block cipher There are constructions where the security of the MAC is proven in terms of the security definition of a block cipher. This means as long as the block cipher is secure, the MAC will be secure. There are constructions where encryption ...


1

Unsurprisingly, any secure MACs are a secure choice. Assessing their relative security beyond how many bits of security they offer isn't possible in general. However, there are some differences that don't depend on the protocol: Unmodified CBC-MAC is only secure for fixed length messages, otherwise it allows some forgeries. Block cipher based MACs allow ...


2

Small addition: You do not lose integrity when using encrypt-then-MAC. Since encryption is an injection, distinct plaintexts produce distinct ciphertexts, so plaintext forgery implies ciphertext forgery, which is hard if encrypt-then-MAC is secure.


6

Using a MAC on the plaintext may potentially leak information about the plaintext (MAC algorithms do not necessarily ensure confidentiality of the data they are applied to, although some MAC algorithms like HMAC seem pretty safe). If you want to avoid this (theoretical) problem, then you should encrypt the MAC on the plaintext (i.e. MAC-then-encrypt, not ...


3

I am wondering if using Skein or the Keccak hash algorithm in this construction (as a stream cipher) is secure: In the case of Skein and Keccak it should be secure. However, both of those have defined their own cipher modes which you should IMO prefer. (For compatibility, if not security.) The Skein one is defined in section 4.10 of the paper. It uses ...


1

If you replace $H$ with a MAC that is build using $H$, i.e. NMAC, then it will be provably secure. Encryption will be $C_i = MAC_k(IV | i) \oplus P_i$. You are guaranteed by the MAC security property (existential forgery) that an adversary cannot generate any of the key stream on his own and so you are left with a secure stream cipher. Just using $H$ by ...



Top 50 recent answers are included