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 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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289 views

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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2answers
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Multiple encryption of part of block

Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones: Block 1: Byte 0 - 7 Block 2: Byte ...
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87 views

How do I communicate the value of the initialization vector to the end user? Should it be part of the encrypted message?

I am taking a cryptography class and our first homework is to implement a 32-bit block cipher. I implemented a simple block-cipher that uses CBC. Currently, my implementation reads both the 32-bit IV ...
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CBC with a fixed or random IV

I have two probably quite naive questions: 1) Why, exactly, is it so bad to have a fixed (or predictable) IV in CBC mode? An example would be great! 2) Given 1), why is a random IV better? And if ...
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127 views

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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173 views

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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BKSQ Block Cipher implementation [closed]

has anyone a working implementation of BKSQ block cipher? (preferably in c)
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Understanding Meet-in-the-Middle attack on block ciphers

I understand how to implement a Meet-in-the-Middle attack on 2DES/3DES, by computing for one half all possible keys and storing the outcome and then subsequently do the same for the other half but ...
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Why is a Feistel network bijective?

EDIT: Fixed for clarity of intention I was reading "The FFX Mode of Operation for Format-Preserving Encryption" when I came across Figure 1 (see below). It's obvious why it's reversible (top-down ...
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RFC 5297 implementation [duplicate]

I am looking for an implementation of RFC 5297 algorithm using javascript. I would like to see how to wrap a key on client side web browser, like Mozilla's fxa-auth-client (That uses a xor to wrap) ...
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Does it make sense to have multiple values of authentication and cipher offsets while encrypting a packet?

Consider a packet with N segments. cofsset(cipher offset - from where one must cipher) lies in arbitrary Segment "A". aoffset (authentication offset - from where one must authenticate) lies in ...
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Recover keys using statistical saturation attack

I am having trouble here performing this attack on a block cipher. This is my block cipher, it is a toy with really bad diffusion just for the sake of performing a successful attack ...
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0answers
40 views

Memory requirement in light weight block ciphers cryptanalysis

If we have a light weight block cipher where the block length is different than the key length. Let's say the block has a length of 64 bits while the key is 80 bits. For an attack to be successful, ...
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23 views

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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50 views

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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78 views

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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1answer
86 views

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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1answer
101 views

Calculation of time needed to crack DES with my CPU

I have a laptop that has the CPU and the RAMs shown below in the images. My question is that, using this CPU and the RAMs, how much time would it take for me to crack an old school DES algorithm ...
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1answer
124 views

Which block cipher mode does the experts use? [closed]

I want to know which "block cipher mode of operation" does the experts use? I don't want to use ECB or CBC because add padding and padding mess up my code. So which one does the experts use. /Thanks ...
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1answer
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Double the key in block cipher - which approach is better?

Assume than you have a block cipher $E(k,m)$ for which the only attack exists has complexity of $2^{64}$. You consider to double the key size by either: $E'_1(k_1,k_2) := k_1 \oplus E(k_2,m)$ ...
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3answers
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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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1answer
120 views

credit card number encryption using aes-ctr mode

I want to encrypt credit card numbers. I want to apply AES-CTR mode. Is it suitable for that? How can I store nonce and counter values for an individual credit card number? How can I send the ...
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109 views

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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1answer
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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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1answer
79 views

Which Block cipher mode should I use? [closed]

Which of the Block cipher mode is MOST secure? I dont care about the performance just the most secure
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176 views

Would this method deliver a perfectly non-malleable encryption for at least two blocks? [closed]

Disclaimer: the algorithms I present here (and in other messages) are used as a hands-on way to learn about developing crypto algorithms, (and might also be of interest for other curious people), not ...
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1answer
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Would this method allow fast authenticated encryption using only a single encryption and RNG operation per block? [closed]

The most promising of the 4 approaches described here (version 4) has been posted as a separate question. This post should be considered for archiving and historical purposes only. Disclaimer: the ...
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4answers
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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 ...