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57 votes

Is Triple DES still considered safe to use?

Well, yes and no. Triple DES using 3 different keys is still considered secure because there are no known attack which completely break its security to a point where it is feasible nowadays to crack ...
Lery's user avatar
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47 votes
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How was the special DES key 0E329232EA6D0D73 found?

That value 0E329232EA6D0D73 was found by brute force. I would be surprised if there was a significantly better method: that would be tantamount to a cryptanalytic break of DES, very different from the ...
fgrieu's user avatar
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33 votes
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Why is double encryption that's equivalent to single encryption no better than single encryption?

This is simply saying that if a cryptosystem has a functional composition that is $$ h_{k}(x) = f_{k_1}(g_{k_2}(x)) $$ then you can find a key for single encryption that works as the double encryption....
kelalaka's user avatar
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29 votes
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Can neural cryptanalysis be applied to AES?

No. Neuro-Cryptanalysis fails on serious ciphers, including DES and AES. Sebastien Dourlens's Neuro-differential cryptanalysis of DES (in sections 5.4.2 and 5.4.3 of his 1996 mémoire) learns an S-box. ...
fgrieu's user avatar
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17 votes
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Why is DES not an ideal cipher?

DES uses a 56-bit key (formally, a 64-bit key, out of which 8 bits are simply ignored), so it represents a family of exactly $2^{56}$ permutations(*). If you were to select a permutation at random ...
Thomas Pornin's user avatar
15 votes

Converting normal alphabets to 64 bit plain text

What's asked requires choices not explicit in the question: 1. Character encoding into bytes The most common and recommendable convention nowadays is UTF-8, which encodes any character as a sequence ...
fgrieu's user avatar
  • 142k
14 votes

For a typical n-bit symmetric key, how many keys would be considered too weak to use?

I understand that all zeros or all ones would be weak for any cipher. This isn't actually true. For good cipher there are no weak keys. And certain ciphers, e.g. DES, have a list of weak keys. But ...
axapaxa's user avatar
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13 votes

Is DES secure under CBC?

No, it will be insecure. There are two reasons; Due to the smaller key size 56-bit; DES was tested for brute-force attack since published. DES_CHALL, 96 days to find the CES challenge key in 1997. ...
kelalaka's user avatar
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13 votes

What is DES-EDE3-CBC?

At least in the context of PKCS#5 (which is commonly seen through the encryption of PEM files), DES-EDE3-CBC is Triple DES with three keys, used in CBC mode, with unspecified padding. Yes, “EDE” means ...
Gilles 'SO- stop being evil''s user avatar
12 votes

S-box basic question

Good question and yes, it would appear that data is lost. And technically, something clearly must disappear as 6 don't go into 4. But consider the overall architecture of DES: Trace the flow of the ...
Paul Uszak's user avatar
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12 votes

Is Triple DES still considered safe to use?

NIST just recently (11/27/2017) put out a bulletin that Triple-DES will be deprecated in the future, and will be disallowed in protocols like TLS and IPsec, with a future deprecation timeline to be ...
untra's user avatar
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12 votes

Cryptographic methods that do not use prime numbers?

There is none. All cryptography involves the number 2, which is prime, whenever dealing with information in strings of bits—or in esoteric cases like ROT13, well, there's a prime number right there, ...
Squeamish Ossifrage's user avatar
11 votes
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Why is the DES s-box non-linear? Why does it make the cracking of the cipher more difficult?

It is of course possible to write DES or any block cipher as a system of non-linear equations involving the plaintext bits, the ciphertext bits, and the key bits, which hold with probability 1. In ...
J.D.'s user avatar
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11 votes

Feistel-Network - why wire crossing?

Let's look at a picture of a generic feistel cipher Notice that no keying material is used during or after that final swap. So, we can conclude that the final swap does not impact security at all. ...
mikeazo's user avatar
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11 votes
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Can I find the encryption key if I know the plain text and the encrypted text (DES and AES)?

The most cost-effective way to do this is to try each key and see if it works. The expected number of trials is $2^{55}$ with DES, $2^{127}$ with AES-128, and $2^{255}$ with AES-256. You can speed ...
Squeamish Ossifrage's user avatar
11 votes
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In the RSA DES challenges, how did the contestants know they had found the right key considering they weren't given any plaintext?

One can still access the challenge rules from the archive.org Each contest is based on a specified cipher. A brief piece of printable ASCII text (containing byte values in hexadecimal notation from ...
kelalaka's user avatar
  • 49k
11 votes

Why use complex encryption algorithms?

We use more complex encryption algorithms than XOR with a random or pseudo-random keystream for a number of reasons: In order to get a short secret key in symmetric encryption. XOR with a true ...
fgrieu's user avatar
  • 142k
11 votes

Converting normal alphabets to 64 bit plain text

First of all you should not use DES, it is not secure and, arguably, never has been secure as the key size of 56 bits is well below 128 bits. The strength of the key after analysis is even less than ...
Maarten Bodewes's user avatar
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10 votes

AES vs DES S-boxes

A good source for this kind of questions is the book The Design of Rijndael by Joan Daemen and Vincent Rijmen. On page 35 they write about their choice for the used S-box $S_{RD}$: Design criteria ...
itsme's user avatar
  • 101
9 votes

Feistel-Network - why wire crossing?

It's there to facilitate a simple implementation. As there is no key addition applied afterwards, the final swapping of the halves does not contribute towards security. The Feistel cipher entry on ...
Ella Rose's user avatar
  • 19.7k
9 votes

DES strength and weakness

The wikipedia article @SEJPM links to is about as high level of an overview as you can really get. We can elaborate on some of the points. DES is weak against Brute force in this day and age. ...
Ella Rose's user avatar
  • 19.7k
9 votes

S-box basic question

DES uses a Feistel network. The S-box results gets XOR-ed with the other half so no information is lost. It doesn't need to be invertible.
Meir Maor's user avatar
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9 votes
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How to find fixed points for DES weak keys

I answer in hopefully didactic order. What does the author mean by the intermediate texts exactly? The intermediate texts after $n$ rounds are the 64-bit quantities $L_n\mathbin\|R_n$, numbering ...
fgrieu's user avatar
  • 142k
8 votes
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What is the main limitation of DES?

According to Introduction to Modern Cryptography by Katz and Lindell, in the section titled Security of DES on page 218 in the second edition. After almost 30 years of intensive study, the best ...
mikeazo's user avatar
  • 38.7k
8 votes
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Would DES be secure with 128 bit keys?

No, DES* (which I'll call your "DES modified to use 128 bit keys") would not be as secure as AES; two reasons spring immediately to mind: Block size; DES* would still have 64 bit blocks; most block ...
poncho's user avatar
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7 votes
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In differential cryptanalysis for DES, why is F(0...0) assumed to be always 0...0?

The question arises from a misunderstanding: The attack described in the paper does not work with actual inputs and outputs, but with differences between them. Hence Differential Cryptanalysis. ...
Emiswelt's user avatar
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7 votes
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How can I calculate the avalanche effect in symmetric algorithms?

You appear to be under the impression that AES should score better than DES, because AES is stronger than DES. The issue is that your test is extremely crude; any decent block cipher will pass the ...
poncho's user avatar
  • 148k
7 votes
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DES and Feistel Cipher

A "permutation", by definition, must have the same domain and range, i.e., the same possible inputs and possible outputs. You can look at it as either as a bijective function from some domain onto the ...
Matt Timmermans's user avatar
7 votes
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How can semi-weak DES keys be leveraged to attack DES?

The answer is that they cannot. DES weak keys will be chosen with such a small probability that they don't matter at all. The only reason that weak keys are of interest is when you want to use a block ...
Yehuda Lindell's user avatar

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