(or message authentication code), a short piece of information used to authenticate a message, and the algorithm to create and check such information, using a secret key.

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566 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
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3answers
309 views

Realize a MAC using a Pseudo-random function?

Given a pseudo-random function and assuming that we do not have any other tools, How can we construct a MAC? I believe this can be done. Would like to know if there is more than one way of doing ...
3
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1answer
339 views

What type of hash functions provides non-malleability of hash digests?

I want to use a hash function for commitments. I don't want an attacker to construct a commitment related to a previously published (but still unopened) commitment. A simple deterministic commitment ...
3
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1answer
1k views

ANSI X9.9 Cryptography Standards

I'm trying to create a ISO8583 Rev93 message. What is the standard way of generating MAC key in ANSI X9.9 DES-CBC encryption algorithm is used to encrypt the ...
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1answer
294 views

How safe is it to derive MAC key from a hashed password?

Imagine I have a blob that I want to encrypt-then-MAC. Now, what I can realistically ask my users for (out of UX considerations) is just an encryption password. Naturally, I bcrypt original password ...
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1answer
181 views

What are the consequences of a MAC tag collision?

I've seen some proofs of MAC security that are based on the extremely-unlikely event that two MAC tags collide (ie, they are equal for distinct messages). Suppose that this extremely unlikely event ...
14
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1answer
979 views

Is H(k||length||x) a secure MAC construction?

If $H$ is a typical secure hash function, then $(k,x) \mapsto H(k \mid\mid x)$ is not a secure MAC construction, because given a known plaintext $x_1$ and its MAC $m_1$, an attacker can extend $k ...
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2answers
3k views

What is the purpose of four different secrets shared by client and server in SSL/TLS?

I was looking through the working of SSL V3, and found that a connection state is defined by a set of things, including client write mac secret, server write mac secret, server write key, client ...
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1answer
3k views

Why is it insecure to use a randomized IV for CBC-MAC instead of an all-zero IV?

A fixed length CBC-MAC uses an all-zero block as the initialization vector. Suppose that we used a randomized IV instead, and sent the IV along with the tag. So if the message $m$ will be $m = b_1 || ...
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2answers
1k views

Encrypt-then-MAC Confidentiality, Integrity and Authenticity

Does Encrypt-then-MAC provide equal confidentiality, integrity and authenticity as other constructs such as EAX? If yes, how do I go about using it? My current understanding is: E = ...
9
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3answers
754 views

UMAC: to what extent is it in use today?

Inspired slightly by the Encrypt-then-MAC question. The most obvious message authentication code is probably HMAC or RFC 2104 which is basically a hash of the input, an xor with a key... you get the ...