Understanding Encrypt-Decrypt of txt file by DES

Although insecure, it was highly influential in the advancement of modern cryptography. The publication of an NSA-approved encryption standard simultaneously understanding Encrypt-Decrypt of txt file by DES in its quick international adoption and widespread academic scrutiny.

This is mainly due to the 56-bit key size being too small. The origins of DES go back to the early 1970s. On 17 March 1975, the proposed DES was published in the Federal Register. Public comments were requested, and in the following year two open workshops were held to discuss the proposed standard. DES algorithm was, to the best of their knowledge, free from any statistical or mathematical weakness.

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NSA did not tamper with the design of the algorithm in any way. IBM invented and designed the algorithm, made all pertinent decisions regarding it, and concurred that the agreed upon key size was more than adequate for all commercial applications for which the DES was intended. Another member of the DES team, Walter Tuchman, stated “We developed the DES algorithm entirely within IBM using IBMers. The NSA did not dictate a single wire! The first offerings were disappointing, so NSA began working on its own algorithm. Then Howard Rosenblum, deputy director for research and engineering, discovered that Walter Tuchman of IBM was working on a modification to Lucifer for general use.

Understanding Encrypt-Decrypt of txt file by DES

NSA gave Tuchman a clearance and brought him in to work jointly with the Agency on his Lucifer modification. NSA worked closely with IBM to strengthen the algorithm against all except brute-force attacks and to strengthen substitution tables, called S-boxes. Conversely, NSA tried to convince IBM to reduce the length of the key from 64 to 48 bits. Ultimately they compromised on a 56-bit key. Some of the suspicions about hidden weaknesses in the S-boxes were allayed in 1990, with the independent discovery and open publication by Eli Biham and Adi Shamir of differential cryptanalysis, a general method for breaking block ciphers. Despite the criticisms, DES was approved as a federal standard in November 1976, and published on 15 January 1977 as FIPS PUB 46, authorized for use on all unclassified data.

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The algorithm is also specified in ANSI X3. Today X3 is known as INCITS and ANSI X3. Another theoretical attack, linear cryptanalysis, was published in 1994, but it was the Electronic Frontier Foundation’s DES cracker in 1998 that demonstrated that DES could be attacked very practically, and highlighted the need for a replacement algorithm. The introduction of DES is considered to have been a catalyst for the academic study of cryptography, particularly of methods to crack block ciphers. The DES can be said to have “jump-started” the nonmilitary study and development of encryption algorithms.

In the 1970s there were very few cryptographers, except for those in military or intelligence organizations, and little academic study of cryptography. There are now many active academic cryptologists, mathematics departments with strong programs in cryptography, and commercial information security companies and consultants. Biham and Shamir rediscover differential cryptanalysis, and apply it to a 15-round DES-like cryptosystem. Biham and Shamir report the first theoretical attack with less complexity than brute force: differential cryptanalysis. However, it requires an unrealistic 247 chosen plaintexts.

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The DESCHALL Project breaks a message encrypted with DES for the first time in public. DES key in 22 hours and 15 minutes. DES is reaffirmed for the fourth time as FIPS 46-3, which specifies the preferred use of Triple DES, with single DES permitted only in legacy systems. Within a year software improvements reduced the average time to 6. The successor of COPACOBANA, the RIVYERA machine, reduced the average time to less than a single day. The Open Source password cracking software hashcat added in DES brute force searching on general purpose GPUs. Systems have been built with 8 x 1080Ti GPUs which can recover a key in an average of under 2 days.

A chosen-plaintext attack utilizing a rainbow table can recover the DES key for a single specific chosen plaintext 1122334455667788 in 25 seconds. A new rainbow table has to be calculated per plaintext. A limited set of rainbow tables have been made available for download. The key is nominally stored or transmitted as 8 bytes, each with odd parity. Bits 8, 16,, 64 are for use in ensuring that each byte is of odd parity. Like other block ciphers, DES by itself is not a secure means of encryption, but must instead be used in a mode of operation.

FIPS-81 specifies several modes for use with DES. Further comments on the usage of DES are contained in FIPS-74. Decryption uses the same structure as encryption, but with the keys used in reverse order. This has the advantage that the same hardware or software can be used in both directions. This section needs additional citations for verification. The algorithm’s overall structure is shown in Figure 1: there are 16 identical stages of processing, termed rounds.

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The Feistel structure ensures that decryption and encryption are very similar processes—the only difference is that the subkeys are applied in the reverse order when decrypting. The rest of the algorithm is identical. The F-function scrambles half a block together with some of the key. The output from the F-function is then combined with the other half of the block, and the halves are swapped before the next round. Feistel structure which makes encryption and decryption similar processes.

Understanding Encrypt-Decrypt of txt file by DES

Understanding Encrypt-Decrypt of txt file by DES

Expansion: the 32-bit half-block is expanded to 48 bits using the expansion permutation, denoted E in the diagram, by duplicating half of the bits. 4 corresponding input bits, plus a copy of the immediately adjacent bit from each of the input pieces to either side. Key mixing: the result is combined with a subkey using an XOR operation. Substitution: after mixing in the subkey, the block is divided into eight 6-bit pieces before processing by the S-boxes, or substitution boxes. Each of the eight S-boxes replaces its six input bits with four output bits according to a non-linear transformation, provided in the form of a lookup table. Permutation: finally, the 32 outputs from the S-boxes are rearranged according to a fixed permutation, the P-box.

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This is designed so that, after permutation, the bits from the output of each S-box in this round are spread across four different S-boxes in the next round. The alternation of substitution from the S-boxes, and permutation of bits from the P-box and E-expansion provides so-called “confusion and diffusion” respectively, a concept identified by Claude Shannon in the 1940s as a necessary condition for a secure yet practical cipher. Figure 3 illustrates the key schedule for encryption—the algorithm which generates the subkeys. The key schedule for decryption is similar—the subkeys are in reverse order compared to encryption.

Apart from that change, the process is the same as for encryption. The same 28 bits are passed to all rotation boxes. Although more information has been published on the cryptanalysis of DES than any other block cipher, the most practical attack to date is still a brute-force approach. For any cipher, the most basic method of attack is brute force—trying every possible key in turn. The length of the key determines the number of possible keys, and hence the feasibility of this approach.

250,000 DES cracking machine contained 1,856 custom chips and could brute-force a DES key in a matter of days—the photo shows a DES Cracker circuit board fitted with several Deep Crack chips. In academia, various proposals for a DES-cracking machine were advanced. 20 million which could find a DES key in a single day. 1 million which would find a key within 7 hours. The next confirmed DES cracker was the COPACOBANA machine built in 2006 by teams of the Universities of Bochum and Kiel, both in Germany. Unlike the EFF machine, COPACOBANA consists of commercially available, reconfigurable integrated circuits.

The system can exhaustively search the entire 56-bit DES key space in about 26 hours and this service is offered for a fee online. IBM and the NSA and kept secret. There have also been attacks proposed against reduced-round versions of the cipher, that is, versions of DES with fewer than 16 rounds. Such analysis gives an insight into how many rounds are needed for safety, and how much of a “security margin” the full version retains. Differential-linear cryptanalysis was proposed by Langford and Hellman in 1994, and combines differential and linear cryptanalysis into a single attack. An enhanced version of the attack can break 9-round DES with 215.

8 chosen plaintexts and has a 229. By definition, this property also applies to TDES cipher. DES also has four so-called weak keys. There are also six pairs of semi-weak keys.

The keys are not really any weaker than any other keys anyway, as they do not give an attack any advantage. SDES has similar properties and structure as DES, but has been simplified to make it much easier to perform encryption and decryption by hand with pencil and paper. Some people feel that learning SDES gives insight into DES and other block ciphers, and insight into various cryptanalytic attacks against them. DES itself can be adapted and reused in a more secure scheme. On January 2, 1997, NIST announced that they wished to choose a successor to DES. The Legacy of DES – Schneier on Security”.

A brief history of the data encryption standard”. Security for computer networks, 2nd ed. Data Encryption Gurus: Tuchman and Meyer”. American Cryptology during the Cold War, 1945-1989. This version is differently redacted than the version on the NSA website. American National Standards Institute, ANSI X3.

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IEC 18033-3:2010 Information technology—Security techniques—Encryption algorithms—Part 3: Block ciphers”. Schimmler, “How to Break DES for Euro 8,980″. FIPS 81 – Des Modes of Operation”. FIPS 74 – Guidelines for Implementing and Using the NBS Data”. Cryptography and network security: principles and practice.

Think Complex Passwords Will Save You? Differential cryptanalysis of the data encryption standard. Linear Cryptanalysis Method for DES Cipher”. Advances in Cryptology — EUROCRYPT ’93. Investigation of a potential weakness in the DES algorithm, Private communications”.

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New Comparative Study Between DES, 3DES and AES within Nine Factors”. CS1 maint: Explicit use of et al. A Chosen-Plaintext Linear Attack on DES”. On the Complexity of Matsui’s Attack”.

An improvement of Davies’ attack on DES”. Advances in Cryptology — CRYPTO ’94. Advances in Cryptology — ASIACRYPT 2002. Introduction to Cryptography with Open-Source Software”. Cryptanalysis of Simplified Data Encryption Standard via Optimisation Heuristics”.

A Simplified Data Encryption Standard Algorithm”. Breaking of Simplified Data Encryption Standard Using Binary Particle Swarm Optimization”. Cryptography Research: Devising a Better Way to Teach and Learn the Advanced Encryption Standard”. Biham, Eli and Shamir, Adi, Differential Cryptanalysis of the Data Encryption Standard, Springer Verlag, 1993. Biham, Eli and Alex Biryukov: An Improvement of Davies’ Attack on DES. Biham, Eli, Orr Dunkelman, Nathan Keller: Enhancing Differential-Linear Cryptanalysis. Wiener: DES is not a Group.

Product Block Cipher System for Data Security, U. Gilmore, John, “Cracking DES: Secrets of Encryption Research, Wiretap Politics and Chip Design”, 1998, O’Reilly, ISBN 1-56592-520-3. On the Complexity of Matsui’s Attack. Matt Robshaw: Linear Cryptanalysis Using Multiple Approximations. Knudsen, Lars, John Erik Mathiassen: A Chosen-Plaintext Linear Attack on DES. The First Experimental Cryptanalysis of the Data Encryption Standard”.

National Bureau of Standards, Data Encryption Standard, FIPS-Pub. Chapter 3 of “Understanding Cryptography, A Textbook for Students and Practitioners”. Wikimedia Commons has media related to Data Encryption Standard. M9 1a8 8 0 1 0 0 16A8 8 0 0 0 9 1zm. Join Stack Overflow to learn, share knowledge, and build your career. M9 1a8 8 0 1 0 0 16A8 8 0 0 0 9 1zM8 15. How can I create my own key?

I was actually padding the password out to 256 bytes, not bits, which is too long. The following is some code I am using now that I have some more experience with this. Could you clarify: does calling kgen. I can specify a 16bit one which works for 128bit encryption which works. I have tried a 32bit one for 256bit encryption, but it did not work as expected.

If I understand correctly, you are trying to use a pre-arranged, 256-bit key, specified, for example, as an array of bytes. Be careful about padding a number, you may be making your AES less secure. Derive the key, given password and salt. 65536 and 256 are the key derivation iteration count and the key size, respectively. The key derivation function is iterated to require significant computational effort, and that prevents attackers from quickly trying many different passwords. The iteration count can be changed depending on the computing resources available.

The key size can be reduced to 128 bits, which is still considered “strong” encryption, but it doesn’t give much of a safety margin if attacks are discovered that weaken AES. Used with a proper block-chaining mode, the same derived key can be used to encrypt many messages. Store the ciphertext and the iv. Decrypt the message, given derived key and initialization vector. Java 7 included API support for AEAD cipher modes, and the “SunJCE” provider included with OpenJDK and Oracle distributions implements these beginning with Java 8. Based on the problem description, it sounds like the policy files are not correctly installed. Salts are necessary for PBKDF2, which is why the API for password-based encryption requires them as input for key derivation.

Without salts, a dictionary attack could be used, enabling a pre-computed list of the most likely symmetric encryption keys. Cipher IVs and key-derivation salts serve different purposes. First, that would be DES encryption, not AES. SunJCE doesn’t provide and PBE for AES. Second, enabling jasypt is a non-goal.

A package that purports to offer security without requiring an understanding of the underlying principles seems dangerous prima facie. For running this code, make sure you have the right Unlimited Strength Jurisdiction Policy Files in your JRE as stated in ngs. The salt is used to prevent dictionary attacks against the key in the event your encrypted data is compromised. A 16-byte random initialization vector is also applied so each encrypted message is unique. A look at the internals reveals a structure similar to erickson’s answer. Can you use that module without loading all of Spring? They don’t seem to have made jar files available for download.

Yes, you can use the module without Spring Security or the Spring framework. From looking at the pom, the only runtime dependency is apache commons-logging 1. Is it possible to set the key length to 128-bits? Modifying security folder in every PC is not an option for me.

IvanRF sorry, doesn’t look like it. The NULL_IV_GENERATOR used by the Spring utility is not secure. If the application doesn’t provide an IV, let the provider choose it, and query it after initialization. After reading through erickson’s suggestions, and gleaning what I could from a couple other postings and this example here, I’ve attempted to update Doug’s code with the recommended changes. Feel free to edit to make it better.