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8

Can anyone explain why CBC-MAC is not secure for variable length message? For the previous question I'll quote Matthew Green's post from 2013: 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 ...


7

Yes, the basic idea of hardcoding a public key is secure. It is sometimes recommended as an alternative to the complexity TLS and PKI bring – otherwise it can be easy to skip a crucial step and end up with little or no security. However, the "encrypt a secret for server" scheme has some weaknesses compared to TLS. The clearest is lack of forward secrecy ...


2

I am trying to better understand authentication. Lets say I have posted my 128-bit AES symmetric key on some forum, encrypted asymmetrically to my friend using 256-bit ECC (25519). The forum isn't controlled by us so this key message could potentially be tampered with. Well first of all, note that encrypting with curve25519 isn't as trivial as ...


1

If the key is send beforehand it is not required but highly recommended to sign it. Otherwise anybody could post an AES key, encrypted using the public encryption key of your friend. In that case your friend may only find out after receiving the right messages. Furthermore, your friend may not be able to distinguish between an invalid key and an invalid ...



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