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(or Data Encryption Standard), a (symmetric) block cipher using a 64 bit block size, with keys of size 56 bit, the standard US block cipher from 1976 to 2001.

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S-Box and it's linearity

I am trying to figure out why it is necessary S-box's to be nonlinear. I have been searching for some materials but was not able to find out clear proof why it means that if we use S-box in DES, it ...
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1answer
105 views

AES and DES - reusing the same round keys

Both DES and AES use key expansion to generate the round keys (for Feistel network or for the AddRoundKey operation). Each round uses a different key. Why do we need that? Why we cannot use the same ...
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2answers
82 views

What is the key space of a 2-key Triple DES

I am assuming the 2-key triple DES is equivalent to double des. I know the key size is 2x56 = 112 bits. Is this the key size the same as the keyspace? e.g. would the keyspace be 112 bits (2^112)
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1answer
90 views

How to find fixed points for DES weak keys

Can someone explain me this please I am a bit confused? It's from a texbook I am reading (block cipher companion) it says that: each weak key has $2^{32}$ fixed points $m$ where $\operatorname{...
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2answers
99 views

How can I prove that a Feistel round is its own inverse for DES?

I'm having difficulty on proving the fact that each round of DES algorithm is its own inverse. Can someone put a concise explanation for it please? If a function, say $f$ ,is its own inverse than $f(...
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1answer
77 views

Double DES meet in the middle attack: probability that wrong key pair remains

My Question is based on poncho's answer in this post. If you're doing a meet-in-the-middle attack against 2DES with only on a plaintext-ciphertext pair $(P,C)$, I understand that the expected amount ...
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1answer
104 views

With DES, is ECB encryption mode equivalent to CBC with null IV for short data blocks?

I got to this by experimentation, but can someone maybe provide an explanation for this?
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1answer
47 views

Question about DES S-boxes from Encryption to Decryption [duplicate]

While working on a homework assignment, I came across an interesting dilemma that I want to delve more into. The question essentially said to flip the first bit in the key string and then see what S ...
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1answer
162 views

Is DES secure under CBC?

I know DES is outdated, but will is is secure in CBC mode? Can anyone help me understand why not?
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1answer
65 views

Initial Permutation of DES

I'm implementing DES, but I cannot understand example. Plaintext: 123456ABCD132536 After initial permutation: 14A7D67818CA18AD Plaintext is 64-bits hexadecimal, so each character is 4-bits. The ...
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1answer
30 views

DES- If LSB is removed, are the key B and C the same?

I believe that in DES every 8th bit is ignored of the key. That means B and C are same if the LSB is ignored. So, shouldn't encrypting a message by the key all Bs be able to be decrypted by key with ...
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2answers
47 views

When using DES, how large would the key space be if we only use letters as characters?

Would it be safe? Or is it susceptible to brute force attacks or something else?
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2answers
173 views

If $E_{k_1}(p_1) = c_1$, what is the probability that there exists key $k_2$ such that $E_{k_2}(p_1) = c_1$?

Let $k_1$ be a 56 bit DES key that performs $E_{k_1}(p_1) = c_1$. What is the probability that there exists another key $k_2$ such that $E_{k_2}(p_1) = c_1$?
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1answer
38 views

Matsui's paper on Linear Cryptanalysis of DES

I am trying to derive the best linear approximation for one round DES. I read the question and answer Regarding matsui's Paper on Linear Cryptanalysis of DES several times but still could ...
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2answers
162 views

understanding the block bits for DES

I'm trying to understand cryptographic protocols, and I've started with the DES algorithm. DES specs: it uses 64 bits for the plaintext, 56 bits for the key, with a result of the same 64 bits of ...
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1answer
44 views

what is the impact of smaller bit size sbox

There are multiple S-boxes type, as DES uses 4 bit S-box and AES uses 8 bit S-box. I want to know how this effect the security?? If we use 4 bit or 8 bit. apart from the DC attack. Both provides ...
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0answers
68 views

Showing that a cipher is not a perfect cipher

I was given this problem: Prove that the following ciphers are not perfect, using as few blocks as you can. There is no need to prove that the number of blocks is indeed minimal. DES AES-128 AES-256 ...
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1answer
106 views

Why does DES use a block size of 64 bit?

Why do we use 64 bit as block size for the DES algorithm? Is there a reason not to use another block size, for instance 72 bits?
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1answer
69 views

How are the PC-1 & PC-2 calculated for the DES block cipher?

How are the permuted choice tables - PC-1 and PC-2 - calculated for the DES block cipher algorithm?
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0answers
60 views

aside from DES has the NSA ever strengthened algorithms?

When DES was originally developed, the NSA changed the s-boxes. For decades people thought that their changes introduced a backdoor but then it was discovered that their changes actually strengthened ...
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0answers
63 views

How is pipelined DES different from sequential DES?

I implemented DES Coder in VHDL using ISE IDE by Xilinx in sequential architecture which was pretty easy and straightforward. Now my task is to do the same using pipelined architecture so that the ...
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1answer
156 views

I wanna know what exactly SP array does

Please only look at for loop in source code below, especially SP1,SP2,SP3....... Is it similar to what S-box does?(Ignore the other) ...
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2answers
2k views

Why is DES not an ideal cipher?

From Cryptography I on Coursera, Week 2, "Exhaustive Key Search Attacks": Now let's assume that DES is what's called an ideal cipher [...] Of course, DES is not a collection of 2^56 random ...
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1answer
41 views

What (if any) information can an eavesdropper infer in this scenario when using DES in OFB mode?

Assume that a company wants to use DES in order to encrypt messages to remotely control its manufacturing machines. The company uses different messages types of 8 ASCII characters length each. The ...
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1answer
240 views

Show number of affected blocks using CFB DES decryption of altered ciphertext

I have encrypted a file using -des -cfb and now I want to view how many blocks it contains once I decrypt it. I have done this on the Linux terminal. I know that 9 ...
3
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1answer
329 views

DES: how does Richard Outerbridge's Initial Permutation operate?

I know how initial permutation works, but I've never heard of this part. People say it's Richard Outerbridge's initial permutation and that it's faster than usual IP (initial permutation) and simple. ...
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1answer
1k views

8-bit CFB in DES and AES - error propagation

I have two questions for an assignment that I need to answer in relation to Error Propagation in 8-bit CFB mode for AES and DES encryption. The questions are as follows: If there is an error in ...
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4answers
1k views

Can I find the encryption key if I know the plain text and the encrypted text (DES and AES)?

If I have the plain text and its output after encryption with a key K1, is it algorithmically feasible to find K1? I am specifically interested in the cases of DES and AES encryption algorithms.
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0answers
112 views

Davies-Meyer with DES insecure

I'm stuck in coming up with a collision for a hash function $H$, which is built using a Davies-Meyer construction chained in a Merkle-Damgard fashion. I I guess its actually easy using the fact that ...
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1answer
379 views

Finding output given an S-box input of 8 bits

I'm given the following table: I'm told to find the output given an hexidecmal input of 2B. I know that 2B in binary = 001 01 011 So I took the first two and ...
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3answers
145 views

DES: histogram differences between plaintext and ciphertext

Using CrypTool I encrypted a plaintext with "DES CBC" and I genereated the histogram of plaintext and ciphertext. The histogram shows the relative frequency of each of the characters in the document. ...
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0answers
79 views

What values in the SDES algorithm change when we want to Decrypt?

So I am learning about SDES and I know how to use it to encrypt it. I know this is a symmetric algorithm which means it's basically the same thing to decrypt except a few things are reversed around. ...
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0answers
608 views

Triple DES encryption/decryption in nodejs

In Delphi , we are encrypting the password using TripleDESEncryption algorithm. We use the key as an array of byte [0..15]. Then the input string is converted is first saved to stream and then sends ...
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1answer
788 views

What is the main limitation of DES?

I know this question seems too general, not specific. Our professor asked this question today, and I have no idea how to answer it. Maybe it's the key size, maybe another thing? Any idea?
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1answer
131 views

Cracking truncated DES

Let's say we have a scheme in which 40 bits M are padded with 24 zeroes, encrypted using a secret DES key K, and the result truncated to the first 24 bits, C. If I wanted to determine a key that ...
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0answers
112 views

How many reversible gates would DES require?

How many reversible gates (said counting Toffoli and Controlled NOT, with free NOT) would be required to reversibly implement $(K,P)\mapsto(G,C)$ for the block cipher DES? $P$ is the plaintext, $C$ ...
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1answer
140 views

DES anti-fixed points for semi-weak keys

I am looking for some "real examples" of anti-fixed points for DES semi-weak keys. As I know, there are $2^{32}$ anti-fixed points for 4 of the 12 semi-weak keys each. One or two examples of these ...
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1answer
233 views

8th SharifCTF — What is the advisable way to recover the key of single round DES here?

I am participating in the 8th SharifCTF competition and have a related question: I have 1000 plaintext and its ciphertext, which has been encrypted with DES algorithm (only 1 round). Now, how can ...
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42 views

Find the Special DES key [duplicate]

I've given two pair of DES encryption plaintext-ciphertext as below: ...
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0answers
108 views

Why are binary operations used instead of S-boxes in the nonlinear F function?

Why are binary operations - such as AND, OR, XOR - used instead of S-boxes in the nonlinear F function? What would happen if a structure like the DES F function were used instead of the current ...
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1answer
858 views

How 3DES work in a simple way?

As I understand DES, It encrypt 64-bit plaintext block with 56-bit key (ECB). So if ...
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1answer
184 views

What are the subsequent inputs to the DES key schedule after round 1?

I've just been studying the DES crypto algorithm as presented by Christof Paar in his book entitled, Understanding Cryptography as well as his lecture. There is a diagram on page 68 of the text where ...
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1answer
1k views

Why do we use multiple rounds of encryption?

I understand that DES and AES use multiple rounds of encryption to secure the cipher text output, what is the real reason this is carried out? Is there a certain point performing multiple rounds ...
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1answer
290 views

Cryptographic methods that do not use prime numbers?

Does anyone know any cryptographic methods that do not use prime numbers? If so, which ones?
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1answer
184 views

What's the difference between substitution and permutation in DES? [duplicate]

What's the difference between substitution and permutation in DES? From my understanding substitution is replacing the data with new data and permutation is just rearranging the data?
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1answer
70 views

What if we increase the key length of DES and use ECB Mode, then will we get the different output as ECB mode encrypt with the same key?

I am looking for an answer as if we have DES having 64 bit key and we are encrypting an image it with ECB mode but it doesn't encrypt well. so if we change the key length then will it effect the ...
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1answer
183 views

DES and AES cryptography

I have a question that I can't answer: A plain text has been encrypted 3 times in a DES method with 3 different keys 56 bit each, after it the text was encrypted for the forth time using a AES ...
1
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1answer
122 views

weakness of a DES enhancement

The following key enhancement to DES was proposed in order to increase the complexity of finding the keys by exhaustive search. $$\text{DES}^V_{k,k_1}(M)=\text{DES}_k(M)\oplus k_1$$ where the keys’ ...
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1answer
201 views

DES 48-bit round keys replaced with 48-bit block keys

In a variant of DES with a 48*16 = 768-bit key, the sixteen 48-bit round keys scheduled for successive rounds in the encryption process for DES are replaced in this variant by successive 48-bit blocks ...
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1answer
2k views

Feistel cipher key generation and round function algorithms

I'm getting confused of what is the actual structure of the key generation and the round function algorithms that Feistel cipher uses. I have been reading many resources about block cipher. All ...