Questions tagged [des]

(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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How to perform the initial permutations 64-Bit DES to derive $K$?

Perform DES encryption on the first 64-bit plaintext only, what are these 0's and 1's? Do they mean that I need to use this ...
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Does anyone know of any tools that can decrypt CTR, CFB, and OFB modes in DES? [closed]

I have the key, ciphertext, and IV for all 3 messages. Don't really know what I'm doing with programming it and haven't found any working tools online for them.
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Chosen plain-text Attack on DES-X with roughly $2^{64}$ DES operations

Here is the quote from P. Rogaway,The security of DESX "the effective key length of DESX with respect to key search is at least 55 + 63 - lg(m) bits" where m is the number of chosen plaintext/...
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How to figure out DES mode used given plaintext and ciphertext?

In DES, I'm given the following exercise. - How can I find out which part of the plaintext each ciphertext message corresponds to, and which mode they were each encrypted with?
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Would Triple DES-X with 7 keys be much slower than standard Triple DES?

Since a single hardware pass of an XOR with a 64 bit key is very fast, would Triple DES-X using seven 64 bit keys used in the following manner be virtually identical in terms of code size, memory ...
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Bitslice DES decryption

I would like to implement fast DES decryption using Bitslice technique. Without bitslice DES technique, I have already done decrpytion in this source code by changing the for loop from 15 to 0. In ...
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In DES what happens if the 32-bit swap at the end is not performed while decrypting?

I know that the swap at the end of DES is so that the same algorithm can be used for encryption and decryption, but I'm wondering what happens if one does not include the swap at the end. What is the ...
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Struggling to understand CFB mode (with DES)

I'm really struggling to understand CFB mode (with DES if that matters). I realise after searching around here that these modes are now obsolete but I need to understand them for class. From wikipedia,...
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Number of cryptographic operations required to perform a MitM for 4DES

Suppose DES is applied 4 times with 4 different 56-bit keys ($k_1$ to $k_4$). By using meet-in-the-middle attack, what is the number of cryptographic operations required for known-plaintext attack? ...
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Is there a feasible way to reconstruct the key from the (Triple-)DES round key?

Assume there is a closed source application which uses Triple-DES with a fixed/hardcoded key to decrypt large amounts of data. Someone managed to extract the round keys from a process memory dump and ...
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Why didn't people redesign the key scheduling algorithm of DES to use longer keys instead of using 3-DES?

To overcome short key length of DES, Triple DES was devised. What would go wrong or why didn't people redesign the key scheduling algorithm to use longer keys?
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Differential cryptanalysis for DES reduced to Four Rounds and about S/N

I'm reading the paper "Differential Cryptanalysis of the Data Encryption Standard(2009)" and I was stuck in a certain part while reading it. In chapter 4, they explained about differential ...
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2Des is double secure of DES?

I read this question in my book (that doesn't have a response). 2DES is doubly more secure than DES? I know that 2DES can be attacked from meet in the middle ...
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Double 3DES/TDES Encryption

If 3DES/TDES (officially TDEA or Triple DEA - Triple Data Encryption Algorithm) encryption is used twice, using 6 different keys K1-...
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what if the S-boxes in DES were “optimal”

if we assume that the s-boxes in DES were optimal. that is for each s-box, every cell in the DDT equals to 4. is there a differential characteristic in a good probability?
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Does the Initialization Vector in DES have to be 8 bytes long?

I was experimenting around with DES and decided to implement an IV (Initialization Vector) for it. I noticed that in DES, which is 56 bits and 8 parity bits, the IV would be 8 bytes in length. Does ...
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DES/CBC : incorrect first 8 bytes [duplicate]

Question about DES-CBC : how to know IV if I have key, input buffer (plaintext), output buffer (encrypted) and decrypted result where first 8 bytes are incorrect but all other bytes are correct ?"
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What to pad DES key with? [closed]

As a bit of practice, I'm reinventing the wheel by implementing DES in python. Before I even got beyond the first function, I came across a problem... With key <...
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2DES and 3DES against a DES build with complimentary

I saw this complicated question and I am not really sure about it, would appreciate your view on it. Is the following build stronger than 2DES or 3DES with 2 different keys (or even normal DES)? $...
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How was PC2 designed?

I am trying to understand DES. Can anyone explain the table given in one of the answer DES Key Schedule Algorithm. My question is from where the first entry of Ks comes from. i.e ...
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DES P box design criteria

I hope somebody can help me to find out how DES P box has designed. I am doing DES by hand so I want to know how these numbers are arranged?
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Weakness in double encryption [duplicate]

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "If double encryption is equivalent to single encryption,...
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Why is double encryption that's equivalent to single encryption no better than single encryption?

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "if a cryptosystem is such that double encryption is ...
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Lineary of Sbox in DES

I'm not a mathematician, and i would like to understand in the most concise way (if possible) why choosing linear S-Box functions makes the DES algorithm attackable. Thanks
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Property of a good cipher system

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about DES algorithm the authors say that: "In a good cipher system, each bit of the ciphertext ...
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Why use complex encryption algorithms? [duplicate]

I have recently gotten interested in cryptography, so I looked some things up. I thought, why even use AES or DES or any other complex way for encrypting data when there are far simpler ways, like ...
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Effect of longer key on DES security

I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short. I am trying to depict how DES would ...
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One way secure DES key transfer to defend against attacker [closed]

I have a question about cryptanalysis. A transmit message to B with radio waves, A use modulator to transmit bytes with radio, B obviously use demodulator. A encrypts and B decrypts the messages ...
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In DES : Matsui's notation(LC) vs Biham's notation(DC)

I'm doing linear attack for 8 rounds DES. And I just wondering about the difference between matsui's notation and Biham's notation. In Matsui's paper, numbers bits from 0 to 63 from right to left. In ...
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Calculating DES key knowing message before and after encryption [duplicate]

I've 8 bytes before encryption (for example: 01 02 03 04 05 06 07 08) and 8 bytes after DES encryption: ...
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Attacking Double DES (OFB Mode) given the initialization vector and not much else? [closed]

I'm given a Plaintext/Ciphertext pair, a Ciphertext to break, and the IV. One thing of note is that the same IV is used for both DES Encryptions, so $$C = E_{K_2}(E_{K_1}(P, IV), IV)$$ I have limited ...
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Can I change the S-box and P-box in DES?

I am a newbie to crypto and just one quick question on the s-box and p-box of DES. I understood that the s-box is where the security comes from and NSA has somehow decided how it should be filled in. ...
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How DES/AES can guarantee by feeding different secret keys, the encrypted outputs are different?

I am learning the meet-in-the-middle on DES attack. I understood the basic logic behind how it is performed; however, one further question is: why can we guarantee to find one and only one pair of k1 ...
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I'm studying about differential cryptanalysis in DES. I need to make the DDT through python [duplicate]

I just made DES algorithm(encryption, decryption) using python. And I want to attack 1,2 4,8 .. round DES. For that, I need to make the DDT code. Could you guys help me to make the DDT? Thank you.
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Block cipher information leakage using same key

This is from a previous exam question and I'm not really sure how to approach this properly We're using a block-cipher mode that encrypts $C_i$ = $E_k$ ($P_i$ $\oplus$ $C_{i-1}$ $\oplus$ $P_{...
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Meet-in-the-middle attack (different block cipher modes)

Does a meet-in-the-middle attack on depend on the used modes for block ciphers? encryption: $C_i$ = $D_{K2}$($D_{K1}$($E_{K1}$($P_i$ $\oplus$ $C''_{i-1}$))) $\oplus$ $C'_{i-1}$ and $IV_1$ = $C''_0$ = ...
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DES - Weakness in Sbox

In the book "Introduction to Cryptography with Coding Theory ", in the chapter about the Differential Cryptanalysis for Four Rounds for DES algorithm, the authors say: There is a weakness in the ...
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Why is DES secure against differential cryptanalysis

I was wondering, why DES is secure against Differential Attacks. Some of the S-Boxes have a very bad Differential Uniformity, only one has a DU of 4, 3 have a DU of 6 and the others are much worse. ...
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Meet-in-the-middle attack (on custom encryption scheme) [duplicate]

This is a question I had from an exercise session. Exercise: First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$. Then we do DES in ECB decryption mode using $K_1$. And then DES ...
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Symmetric encryption construction (meet-in-the-middle attack)

This is a question I had from an exercise session. First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$. Then we do DES in ECB decryption mode using $K_1$. And then DES in CBC ...
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DES parity bits

The key is nominally stored or transmitted as 8 bytes, each with odd parity. According to ANSI X3.92-1981 (Now, known as ANSI INCITS 92-1981), section 3.5: One bit in each 8-bit byte of ...
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Can $AES_{k1}(m)$ be equal to $AES_{k2}(m)$? [duplicate]

Context: We have a generic bloc cipher composed of an encryption function $E_k$ and a decryption function $D_k$ operating on blocs of $n$ bits. For a key $k$ fixed, we can see $E_k$ as a pseudo-...
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What are the separate single DES keys from a triple DES key?

Suppose my 192 bit triple DES key (in hex) is 0123456789ABCDEFFEDCBA987654321089ABCDEF01234567 What are the keys for the separate single DES operations? In this ...
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good OmegaP for characteristic to use in differential cryptanalysis on DES

how to choose a good OmegaP(input difference) for the characteristic used in differential crypt-analysis on DES?
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Is there any encryption algorithm that, with small change in input will produce big change in the encrypted output?

As stated in the title, I'm looking for an encryption algorithm with the characteristics that, when inputs are slightly different, the encrypted output will be VERY much different, to the point that ...
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differential cryptanalysis on the second round of 4-variant DES

I am using differential cryptanalysis to attack the second key of a 4-variant DES and I am using Shamir and biham book as a reference . they say that we should choose two input Xor P3 and P4 that ...
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Security of a block cipher if double encryption $E_{K_2} \circ E_{K_1}$ is always single encryption $E_{f(K_1,K_2)}$

If there always existed a $k_3$ such that $\operatorname{DES}(k_2, \operatorname{DES}(k_1, M)) = \operatorname{DES}(k_3, M)$, how would that affect the security of $\operatorname{DES}$?
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Getting the s-box input from its output in differential cryptanalysis on DES

If we try to get K4 using differential cryptanalysis on 4-variant DES, how can we get the input of a certain S-box if we know it's output? This seems hard to do since the substitution operation is ...
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Is it possible for an attacker to determine the original input to the S-Boxes in DES?

I am learning about DES, a Feistel 64-bit block cipher with 16 rounds. Is it possible that an intruder can determine the original input to the S-Boxes?
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triple-des simple questtion [duplicate]

Why do we use encrypt-decrypt-encrypt (EDE) in 3DES, rather than encrypting three times? in this link, we use EDE Mode usually. when we use one key, in this case, Encryption -> Decryption result ...

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