A block cipher is an encryption algorithm which encrypts fixed-size blocks of plaintext to same-sized blocks of ciphertext. For good ciphers every bit of the ciphertext block depends on every bit of the plaintext block and every bit of the key.

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Inverse of a function $f_k(x) := f (x ⊕ k) ⊕ k$

$f : \{0, 1\}^4 → \{0, 1\}^4$ Given a function $f_k(x) := f (x ⊕ k) ⊕ k$, what is the inverse function $f_k^{-1}$? I could not figure out how this would be done. Thanks.
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How to secure a mental poker protocol? [closed]

I would like to implement a mental poker protocol in a secure fashion. How should I go about that without (preferably) infringing on the Mental Poker Framework patent?
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Is a strong block cipher usable as a strong sponge function?

From the literature, it looks like the security proofs of sponge functions depend on how well they approximate a random permutation, Since a block cipher also ideally behaves like a random permutation ...
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block cipher algorithms with variable block lengths

Rijndael supports block lengths of 128, 192 and 256. AES does not but Rijndael does. What other algorithms support variable block lengths? Or is Rijndael unique in that regard?
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how to calculate non linearity of AES S-box?

S-box has to satisfy different design criteria. How to calculate non-linearity , propagation criteria for an AES S-box?
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Encrypting twice with different modes?

I was using a SOCKS5 proxy today (tunneled through SSH) and I began to wonder what the effect of encrypting twice (TLS over encrypted SOCKS5 in this case) would have on the security of the transmitted ...
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Is AES a linear hash?

So, having read a variety of documentations on AES encryption, I came to the unknowledgeable conclusion that the key schedule applied to the array of chunks, and not just the 14 cycles on a single ...
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CAST-256 (CAST6) versions or S-Boxes

Are there different versions of CAST-256 - also known as CAST6 - available? Are there different S-Boxes available for CAST-256? If there are different versions or S-Boxes what identifier should I use ...
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Active Sbox count in PRESENT Cipher [on hold]

Can any one please tell me how to calculate active Sbox directly or is there any c code for it?
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The number of surviving key after “Meet in the middle stage” in 3-subset MITM attack

In 3-subset Meet in the middle attack, how can we calculate the number of surviving key after meet in the middle stage? and how can we calculate the complexity of Key testing stage? I have read about ...
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NRPAD and FPAD padding schemes (Korean Seed?)

I've got an API spec that specifies NRPAD and FPAD as possible padding schemes. I see these being used together with the Korean SEED algorithm. The SEED specification however is void of any padding ...
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Bit level permutation

Could anyone explain how secure is bit level permutation? What is the most serious threat against the security of this kind of cipher? Thank you
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Problem understanding the construction of block cipher distinguishers

I know a block cipher distinguisher is an algorithm which can predict with high probability whether a system is a random permutation or a block cipher by asking a few queries to the system. My ...
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How to prove Security of Onion Layers of encryption?

CryptDB has Onion layers of Encryption to provide wider functionality from weaker forms of encryption. How do we prove such things are indeed secure ? Intuitively It seems ok. Are there any parallels ...
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Block cipher encryption of decryption with the same key

With block chipers can I assume that Enc(k,Dec(k,m))=m Meaning if I decrypt something with a key k and then encrypt the result with the same key k, do I get what ...
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Block Cipher vs Stream Cipher in Web Application [closed]

I'm doing research about "Cryptographic attack methods in Web Application" so I have some questions to ask you guys: Block Cipher vs Stream Cipher, which is more common used in Web Application? How ...
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Block Cipher Modes

I have a question here asking the following: Why do block ciphers need the use of blocking modes? To encrypt messages larger than the size of the block. To avoid having the same block ...
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Pseudo Random Generator with fixed Hamming Weight [closed]

I'm searching for way to generate secure pseudo random sequence with a fixed Hamming weight using a seed. I found below code but I need a seed to generate a sequence ... (and need know if is possible ...
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1answer
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File Encryption/Decryption in ECB mode [duplicate]

Possible Duplicate: Removing Padded Value in Decrypted Message I tried to encrypt and decrypt a file in ECB mode using AES Algorithm but I encountered one problem during decryption, I don't ...
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Why is there a strong distinction between stream and block ciphers? [duplicate]

If I don't err, in the literature a stream cipher is one in which each plaintext bit is processed individually, commonly via xor-ing with one bit of a random or pseudo-random bit stream, while a block ...
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Found a way to crack AES-128, what now?

I have just found a way to crack AES-128 in a reasonable time (1-2 days). How do I publish and prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they ...