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Questions tagged [tweakable-cipher]

A block cipher is a family of permutations where the key selects a particular permutation from that family. With a tweakable blockcipher both key and tweak are used to select a permutation. So tweak and key are related.

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Is tweakable block-cipher based on the Merkle-Damgård construction secure if $F$ is a PRP

Assume $F$ is a pseudo-random permutation (PRP) then the tweakable block-cipher based on the Merkle-Damgård construction (take this as the way I understand, here is the equation): $F_k[t](m) := F_{...
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Should a tweak value be secret like a key or visible like an IV?

In tweakable block ciphers the tweak acts some ways like part of the key and in other ways, acts like an initialization vector. Should the the tweak remain secret like the key or visible like the an ...
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Is it problematic to use PBKDF2-HMAC-SHA256 to derive a 512-bit XTS key?

PBKDF2 should only be used to generate a larger output than the hash function it uses if the output is used in such a way that it has a flat keyspace. As far as I am aware, XTS does not have a flat ...
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Some simple questions about tweakable ciphers

I have read a few papers on tweakable ciphers (didn't understand them well, though) and looked at many of the questions and answers on this exchange: What is a tweakable block cipher, Tweakable Block ...
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What is the difference between a dual cipher and a tweak?

I have looked at the idea of dual ciphers but I cannot convince myself I really understand them. I think I just need a very simple worked example. I was given the definition: Two ciphers $E$ and $E′$...
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Can tweaking a cipher have the same or similar effect as changing the key?

If we encrypt a message $m$ with (say) $AES$ and key $k$ we get ciphertext $c$. And if we encrypt the same message $m$ but with $k^*$ we get ciphertext $c^*$: 1) $AES[E_k(m)] = c$ and $AES[E_{k^*}(m)]...
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Maximum number of blocks that can be safely encrypted using a block cipher with a counter

Assume that we have a block cipher with a key size of $\ell_{K}$ bits, a tweak size of $\ell_{T}$ bits, and a block size of $\ell_{X}$ bits. Formally, the encryption of a given block of data is $$E(K, ...
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Is it possible for this tweakable block cipher scheme to be secure for more than $2^\frac{n}{2}$ blocks? $2^{n}$ blocks?

In the title, $n$ is the block size in bits and will not be used to denote it in the body of this question unless otherwise stated. Imagine that we have $\mathbb{K} \in \{0, 1\}^{\ell_{K}}$, $\mathbb{...
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How to determine which tweak was used

Imagine the following situation: you have a tweakable block cipher you have a plain text block you have a cipher text block you have the key which was used to encrypt the plain text block I have ...
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Tweakable Even-Mansour scheme where the block size is twice the key size?

We have the functions $E(K, T, X)$ and $D(K, T, X)$ where for both it is the case that $\{0, 1\}^{\ell_{K}} \times \{0, 1\}^{\ell_{T}} \times \{0, 1\}^{\ell_{X}} \rightarrow \{0, 1\}^{\ell_{X}}$. The ...
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Does XEX mode specify how the whitening value is generated?

When the term "XEX" or the phrase "XOR-encrypt-XOR" is used, does it refer only to the scheme $CT = E_{K}(PT \oplus T) \oplus T$/$PT = E_{K}(CT \oplus T) \oplus T$ (where $T$ is the whitening/tweak ...
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Maximum length of a XEX-encrypted scheme?

Suppose that: $\widetilde{E}: \mathcal{K} \times \mathcal{T} \times \mathcal{PT} \rightarrow \mathcal{CT}$ and $\widetilde{D}: \mathcal{K} \times \mathcal{T} \times \mathcal{CT} \rightarrow \mathcal{...
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Difference between Tweak and nonce

What are diffrences between tweak and nonce? I only know that nonce is used only once but tweak can be used for more than one time.but still by this diffrence I can't diffrentiate tweak and nonce
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What is the difference between lightweight tweakable block cipher and tweakable block cipher?

What is the difference between lightweight tweakable block cipher and tweakable block cipher? For example, lightweight tweakable block cipher is SKINNY family, and tweakable block cipher is Threefish ...
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tweakable block cipher and ideal block cipher

Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ?
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How to select a 'tweak' used in FE1 mode format preserving encryption?

I'm experimenting with this library Botan which includes a module for format preserving encryption based on FE1 mode. The parameters for the Encrypt method are as follows ...
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Adding tweak to a block cipher

I know there are XEX, XTS and other ways to add tweak to block cipher without modifying cipher itself. However they are quite slow and/or complex. If we assume we have a secure block cipher round ...
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Is a tweakable block cipher still considered deterministic in nature?

"a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks, with an unvarying transformation that is specified by a symmetric key. - Wikipedia " But with a ...
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Tweakable encryption algorithms vs Key wrapping

I have read many articles about Key wrapping and tweakable cipher modes. However, I don't understand the main difference between them? What you recommend for Key storage and Key Archive.
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Should tweak be unique per message?

Since tweaks are like IV,Salt for block cipher inputs . Should they be unique for each message ? If they are to be unique per message then what is the advantage of giving tweak directly into the ...
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Is this EAX extension weakening the (provable) security of EAX?

I would like to insert a key deriving function into EAX mode, in order to hamper brute-force attacks for a key-size restricted cipher (56 bits). The modification inserts an identical multi-block ...
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what are the uses of tweaks in block ciphers?

Few block cipher modes has additional parameter , tweaks , especially the ones that are format preserving . Now the comments section of this blog entry says such tweaks can be used for BIN numbers, ...
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What is a tweakable block cipher?

Pretty simple question - but I can't seem to find much information about it. What exactly is a tweakable block cipher? How do they differ from traditional block ciphers? What is the 'tweak'? Is it ...
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Can I build a secure tweakable block cipher from a normal one by adding key and tweak?

Let (E,D) be a secure block cipher. Consider the following tweakable block cipher: ...