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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Known plaintext attack to CFB mode

How does a known plaintext attack on a block cipher in CFB mode work? I only see the following: If an attacker knows the plaintext $P_i$ he can recover the key $K_i = C_i \mathbin{\oplus} P_i$ from a ...
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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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44 views

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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1answer
75 views

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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35 views

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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1answer
156 views

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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211 views

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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1answer
101 views

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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1answer
92 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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2answers
103 views

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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17 views

Block size of 128 bit in (quantum) future [duplicate]

Is a block size of 128 bit enough to ward off expected attacks in the future (something like 30 years ahead) with the possible risk of quantum computers? Other formulation: If we were to create a ...
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49 views

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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2answers
145 views

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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1answer
53 views

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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3answers
429 views

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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3answers
129 views

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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2answers
109 views

Is CBC theoretically harder to brute force when compared with ECB?

Theoretically is CBC mode harder to bruteforce when compared with ECB? Assumptions We ignore computational cost for the XOR operations 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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1answer
64 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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2answers
154 views

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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2answers
117 views

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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1answer
80 views

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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1answer
162 views

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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1answer
77 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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65 views

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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105 views

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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166 views

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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114 views

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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1answer
117 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
110 views

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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77 views

Analyzing security flaws of cipher

I know using homebrew encryption can be very dangerous as it is very likely to have many flaws in its design. The following concept is just for learning purpose in case anybody is getting red flags ...
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104 views

Is my method symmetric encryption?

To obfuscate data I made up this method on the spot without planning since the goal wasn't real encryption. At first I though this cannot be real encryption but after revisiting the code and reading ...
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99 views

Why are there no MACs inspired by block cipher modes other than CBC and CFB?

I've been studying message authentication codes and I was wondering why a MAC can only be produced with AES in CBC and CFB mode and why not the other modes such as ECB, OFB and counter. Why are CBC ...
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240 views

Can we quantify strength of encryption scheme ?

Was wondering if we have any (or can we come up with) "units" for strength of encryption like in Physics. Most of our comparative analysis of encryption schemes are based on number of S boxes or ...
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213 views

DES generating the same ciphertext for different plaintexts and identical key

Is it possible to get the same output for DES while the inputs are different while using the same key? The key should not have to be a weak key. If yes could you give me a hint how to show how to do ...
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2answers
111 views

Can I simulate iterated AES-ECB with other block cipher modes?

I am trying to write some code using the Web Crypto API (http://www.w3.org/TR/WebCryptoAPI/#algorithm-overview) which provides only some of the block cipher modes for AES, intentionally excluding ...
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76 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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Why shouldn't I use ECB encryption?

I'm using Java to generate encrypted strings, and I get this warning at build time: ECB encryption mode should not be used So I'm wondering why I shouldn't use ECB and what I can use instead?
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What is the fixed point attribute of DES (when used with weak-keys)

I've heard in some lecture that the weak keys in DES implies the existence of $2^{32}$ fixed points in the algorithm, i.e. that $DES_k(x)=x$ for $2^{32}$ such $x$'s. I couldn't find anything about ...
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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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187 views

Why is authenticated CFB mode insecure?

I read that the following adaptation of the CFB block cipher mode into an authenticated mode is prone to chosen plaintext attacks, yet Im still unsure how to prove it: Let $P_1,P_2,\ldots P_n$ be the ...
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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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58 views

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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2answers
113 views

Block size vs key size confusion

I understand that if a block cipher has $k$-bit keys and $n$-bit input/output blocks, then if $k>n$, we can expect one message-ciphertext pair to narrow us down (I think?) to $2^{k-n}$ possible ...
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1answer
61 views

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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78 views

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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Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
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Condition on Vector Boolean Function to be Bijective

Suppose the vector boolean function be $$\begin{align} f:F^n_2 \longrightarrow F_2^n \\ (x_1,\dots ,x_n) \longrightarrow (x_2,\dots x_n,g) \\ \\ g:F^n_2 \longrightarrow F_2 \\ (x_1,\dots ,x_n) ...