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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BKSQ Block Cipher implementation [on hold]

has anyone a working implementation of BKSQ block cipher? (preferably in c)
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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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Block Ciphers - Standardize plain text

I need to use AES-128 to encrypt a plain text about 720 bits. Is it correct to say that – in this case – the plain text will be divided in 5 blocks of 128, the result will be equal 640 bits, and the ...
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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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How are subkeys, in Feistel block ciphers, derived for each round?

I'm bit confused about the subkeys that are used in Feistel ciphers. I know that all the subkeys ki are derived from the main key K, but how? Say I have a simplified Feistel block cipher of i rounds, ...
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Turning a 64 bit block cipher into a 128 bit block cipher

There are quite a few block cipher modes of operation that require 128 bits. There are also modes of operation where a higher block size than 128, e.g. a block size of 256 bit would even be practical. ...
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Distinguishing attack on stream cipher created from a block cipher in counter mode

A block cipher in counter mode creates a key stream by: $$z_i = E_K(IV || i)$$ Where $IV$ is some chosen initialisation vector (with some length $l$ less that $n$ bits) and $i$ is the binary ...
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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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security in format preserving encryption

In format preserving encryption an attacker knows the format and data type of the plain text. The format of the plain text and cipher text are same. usually cipher text are unreadable form. then how ...
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98 views

Can AES be considered as Perfectly Secure?

I am studying about the AES encryption standard, and as I know from the theory there is no known weaknesses today about this block-cipher. I would like to find out or at least to understand what ...
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Operation modes of block ciphers how are used?

I am studying about different operation modes of block ciphers my question isn't something specific to that, but is how these operation modes are used in cryptography? I have this picture here ...
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Is it practical to use a stream cipher in a block cipher mode?

My idea is to use a stream cipher encrypting 16 bytes at a time as a primative block cipher in a mode of operation such as CBC mode. Is this practical or useful in any way?
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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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Would this method allow fast authenticated encryption using only a single encryption operation per block?

[This approach is flawed. A different speculative approach using an RNG instead of the cipher as a source of entropy was posted as a separate question] Assume $E$ is a block cipher, $C_0 = IV$ and ...
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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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Recovering key length from transposition block cipher ciphertext

First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ...
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Reciprocal block ciphers

I'm interested in the property of involution in block ciphers and how one would go about constructing one. Creating a cipher where $E_K(E_K(M))=M$ for any $M$ and $K$ isn't an obvious task and the use ...
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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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313 views

Block cipher does not provide security by itself

What is this statement all about? When I look at a block cipher it seems pretty hard to break it and the mathematics behind insure a good complexity. It may refer to key generation, initialization ...
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Reducing the keyspace for a brute force attack on a chained 64-bit xor

I have a block of data which I know is encrypted using a chained 64-bit xor (sorry if that makes no sense, I'm not familiar with crypto lingo). I know a little bit about what the plaintext should look ...
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48 views

Why must the sender and receiver be synchronised in synchronous stream ciphers?

I would like to know why the sender and receiver must be synchronized in synchronous stream ciphers as said in synchronous stream cipher. Why is there no synchronization between the sender and ...
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1answer
86 views

Plaintext block chaining, bad idea why?

Ahead of the question, little warning. Question is not about what are the better options. Question is why it is bad idea? Ok, suppose we have plaintext $p$, which divided into blocks: ...
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Are keys generated by the user or block cipher algorithms themselves? [closed]

We know block cipher algorithms. In the block cipher algorithms, Key Scheduling is the one crucial part. I see that in some simulation programs of the AES,DES,TripleDES encryption algorithms. In ...
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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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Required key size for an ideal cipher with a 32 bit block size

For an ideal block cipher, what size key would be required when the cipher has a 32-bit block size?
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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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Is it safe to encrypt random data using ECB mode?

If I have 48 random bytes, is it safe to encrypt them using ECB mode? Or is there still a good reason to use another mode like CTR, CBC, etc.? Context is this: I am creating something like a TLS ...
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Cryptography system by combining a block cipher and a stream cipher

I have to come up with a design for a cryptography system by combining a block cipher and a stream cipher. I can't seem to come up with anything on my own. Can someone point me in the right direction ...
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Is the SEED blockcipher still secure?

I did found an old question which answers exactly this but it is from 2 years ago and i was wondering if there were any changes. I have not been able to find any new information on the cipher and am ...
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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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Coding of unsigned int to prevent guessing next ID

Suppose we are assigning records an unsigned integer ID from a N-bit space (say 32-bit) in a sequential manner. Is there a way we can code this ID before showing it to the public such that someone ...
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Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
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Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
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Why are twofish or other algorithms not NIST approved, are they still safe?

NIST has a total of 3 approved block ciphers on their website: AES, TDES and skipjack. I get why those are on there (though personally I find TDES a bit iffy) but from my understanding Twofish and ...
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Why are modes of operation used, what attacks do they prevent?

I know you always need to use a mode of operation when using a block cipher, AES for example, and Wikipedia has a good explanation for what modes of operation are Now I know if i do not use a mode of ...
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Is the 1st Encrypted Block Less Secure Than Subsequent Ones?

It's my understanding that Electronic Code Book (ECB) produces similar cypher text for similar plaintext inputs which is not a good thing. To get around that, Cypher Block Chaining (CBC) can be used ...
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Known plaintext, unknown 128 bit block cipher

I have an encrypted configuration file from an embedded device which I'm trying to decrypt. The file seems to be encrypted in 128bit blocks, as changing a single option causes a 16 byte block to ...
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Is CBC theoretically harder to brute force when compared with ECB?

Theoretically – is CBC mode harder to bruteforce when compared with ECB when assuming: we ignore computational cost for the XOR operations, and the IV is made public?
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What are the steps to decrypt a TLS 1.1 record?

My question is related to another question in Cryptography about TLS 1.1 and 1.2. I have read both RFC 2246 The TLS Protocol Version 1.0 and RFC 4346 The TLS Protocol Version 1.1. What I know is that ...
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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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Which characters to take into account when calculating unicity distance?

I need to calculate the unicity distance of a block cipher. Assuming I know that the plaintext is an English message I considered using 53 as the size of the alphabet, since the message could contain ...
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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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Definition of ciphertext security

If I got it right, chosen ciphertext security implies also CPA security. In other words, attacker can submit plaintexts to the challenger (along with ciphertexts). I do not understand why ...
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Why does the DES crypto algorithm NOT use 2 rounds?

Now, if we were to go round by round, you could give a distinct reason for not using a single round since after just one round, the right half of the text comes directly, as-is, to form the left half ...
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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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Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit?

In reading through the original GCM specification (McGrew & Viega '05), the composition of the 128 bit Initialization Vector as a concatenation of a 96b nonce and a 32b unsigned wrapping counter ...
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BEAST attack confusion

I understand that BEAST is a CPA using javascript injected onto the browser's webpage. Apparently the thing that BEAST exploits is the fact that the IVs are predictable. What I'm confused about is why ...
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What cryptanalysis is possible against two independent keystreams XORed against plaintext?

If a wise person was unsure about which commercial cryptography standards are truly secure from the fascist powers that be, it would seem the obvious option for companies and individuals is to now use ...
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Combining a keystream generator with a block cipher

I understand that: A stream cipher's security is diluted if the same key is used more than once. This is fixed by using an additional initialization vector in the keystream's computation. A block ...
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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 ...