What is DES (Data Encryption Standard)? DES Algorithm Explained

Introduction

Nowadays, our daily life and activities are mainly based on the Internet. From storing personal information like photos, videos, and others to using various banking and financial applications, we rely on the Internet for almost everything.

These activities put our critical data at increasing risk. We must keep sensitive data away from any unauthorised access. Data confidentiality is the key here. It is where data encryption comes in.

If you use a computer to store critical data, you must wonder, “What is encryption in the computer?” This blog will explore data encryption and Data Encryption Standards.

What Is Data Encryption Standard (DES)?

Before delving further, the first thing to know is “what is DES in cryptography”. The Data Encryption Standard, or DES, is an algorithm for data encryption. It uses symmetric keys of 56-bit size.

The DES algorithm is an archetypal block cipher. It converts a plaintext bit of fixed length into a ciphertext bit string, keeping its length unchanged. The block size for DES is 64-bit.

From the very beginning, DES also received criticism due to 56-bit encryption being too short and a little insecure for modern applications. However, it played an integral role in the advancement of cryptography.

Past Record of DES Algorithm

Various countries worldwide quickly adopted DES after IBM developed it in the early 1970s. 

In 1972, the National Bureau of Standards (US) felt the need for an encryption standard to protect classified information. Around 1973, the Atalla Corporation invented a hardware security module, the first of its kind. It also boosted the need for an international encryption standard.

In 1974, IBM, a competitor to Atalla Corporation, proposed a cipher named DES. The IBM developed DES on an earlier algorithm called Horst Feistel’s Lucifer cipher. Horst Feistel, an IBM cryptographer, developed the Lucifer cipher in 1971. 

In 1976, DES became an encryption standard approved by the US government, followed by its authorisation in 1977 to be used on all unclassified data. DES received a reaffirmation as a standard in 1983, 1988, 1993 and 1999.

2002 AES or Advanced Encryption Standard ousted DES as the accepted standard. In 2005, the NIST withdrew the DES algorithm and only approved Triple DES until 2030 for sensitive government information.

What Is Triple DES Algorithm?

Triple DES, first proposed in 1981 by Merkle and Hellman, is a block cipher that uses a threefold DES algorithm. The Triple DES (TDES or 3DES) uses three keys – K1, K2 and K3. Using three keys is encryption, decryption and encryption again, for K1, K2 and K3, respectively.

Also, there is a double-key version of Triple DES.

The most notable uses of Triple DES include the electronic payment industry. Various Microsoft products also use it to protect user content and system data. Applications like Firefox also use Triple DES for encrypting website authentication login credentials.

Step-by-Step Guide to Initial Permutation

The Initial Permutation or IP process occurs only once, that too before the first round. This is an adjustment process. It is more or less a jugglery of bit positions of the original text block. 

For example, the IP process replaces the first bit with the 58th bit of original text, the second bit with the 50th bit, the third with the 42nd bit, and so on.

After the IP process is complete, the permuted 64-bit text block is divided into two half blocks, each consisting of 32 bits. These two blocks are Left Plain Text (LPT) and Right Plain Text (RPT).

Step 1: Key Transformation

Before the process begins, every 8th bit of the initial DES’s 64-bit key is eliminated. Hence, the bit positions eliminated are 8, 16, 24, 32, 40, 48, 56 and 64, thus, forming a 56-bit key.

Now, the Key Transformation includes generating a sub-key containing 48-bit positions from the 56-bit key. The 56-bit key divides into two halves, each of which is 28-bit. Depending on the number of the round, these halves get shifted by a position or two. For example, for the 1st,2nd,9th and 16th rounds, each of the two halves shifts by one position. For the remaining ones, they shift by two. 

The process produces a 48-bit key. During the shifting procedure, some bits in the 56-bit key are lost. And thus, it forms the 48-bit key. This process is called compression permutation.

Step 2: Expansion Permutation

After IP, we had two halves — LPT and RPT. During this process, i.e., the expansion permutation, the RPT is expanded into 48-bit from 32-bit. The 32-bit RPT first divides into eight blocks. Each of these blocks contains 4 bits. Then an extra two bits are added to each 4-bit block resulting in 6-bit blocks.

After this, the bits undergo a permutation procedure to form 48-bit data. Further, an XOR function applies to the 48-bit RPT and the 48-bit key acquired from the compression permutation procedure.

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What Are the Steps of the DES Algorithm?

The DES algorithm is a complex process involving several steps in both encryption and decryption.

Steps for Encryption

The encryption process consists of the steps discussed below:

Step 1: Starts when the Initial Permutation function acquires the 64-bit plain text.

Step 2: The plain text block goes through the Initial Permutation or IP.

Step 3: A successful IP produces two permuted half blocks. These two are called LPT and RPT.

Step 4: This step takes 16 rounds of the encryption process. Both the LPT and RPT go through this procedure. The encryption procedure consists of five stages. These are-

• S-box Permutation
• Key Transformation
• P-box Permutation
• Expansion Permutation
• XOR and Swapping

Step 5: The two half blocks (RPT and LPT) are combined again. The newly merged block goes through a Final Permutation (FP) procedure.

Step 6: As a result, a 64-bit ciphertext is produced.

Steps for Decryption

The steps for the decryption of data are following:

Step 1: Use the 16 round keys in reverse order.

Step 2: Apply the steps for encryption to the ciphertext.

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Implementing and Testing Process for DES

The DES implementation process consists of the following steps.

• First, choose a security provider of the many available. It is one of the most crucial stages of the implementation to select one. Sometimes, choosing the security provider depends on the language you are using.
• The next step involves generating a key. You can either create a key yourself or can use a KeyGenerator.

After completing the implementation, it is necessary to test the encryption to confirm its appropriate implementation.

What Are the Practical Applications of the DES Algorithm?

The uses of the DES algorithm include:

• When a comparatively less secure encryption can do the job, DES is a perfect choice.
• DES can generate random numbers.
• Also, DES produces a Triple DES algorithm and uses three DES keys in the procedure.

What Are the Various Modes in Which DES Operates?

There are five dive different modes of DES operation used widely. 

• Electronic Codebook (ECB)

Here, the encryption and decryption process of each 64-bit block occurs independently.

• Cipher Feedback (CFB)

For this mode of operation, the previous ciphertext is used as the encryption algorithm’s input. The pseudorandom output then goes through an XOR function with the plaintext, creating the successive ciphertext.

• Cipher Block Chaining (CBC)

Each of the 64-bit blocks depends on the preceding block. Also, it makes use of an Initialization Vector.

• Counter (CTR)

Every plaintext block goes through an XOR function with an encrypted counter. Then, for each succeeding block, the counter is further boosted.

• Output Feedback (OFB)

OFB is very much like CFB. There is a slight difference between these two. The encryption algorithm’s input here is the output of the previous DES.

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Comparing DES and AES Algorithms

AES, or Advanced Encryption Standard, replaced DES as the accepted standard. There are several differences between the two. The table below shows some of the significant dissimilarities between them.

DES Algorithm – Pros and Cons 

Advantages

• Cryptographers have been using DES since 1977. The Brute Force attack is the only vulnerability in the DES algorithm until now.
• DES was approved as a federal encryption standard for a long time.
• The 168-bit key used by Triple DES is tough to crack.

Disadvantages

• The 56-bit key has made DES vulnerable. Deep Cracker, a machine that cracks DES, is available for sale.
• With the advent of AES, which is a lot more complex, DES has fallen out of favour.
• DES works a lot slower in software than it works on hardware.

Why Learn an Encryption Standard That Has Become Irrelevant?

Although DES has lost ground and is no longer the gold standard of encryption standards,  you can still learn a lot by understanding DES. DES was the first encryption standard and the core of all the latest encryption standards. To have proper in-depth knowledge about data encryption, it’s always best to start from the very beginning.

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Conclusion

This thorough discussion on “What is encryption in cybersecurity?” reveals that DES was and probably still is the stepping stone in cybersecurity. However, it is only a minor part of an extensive field of study, with much more to learn.

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