It operates on 64-bit blocks of data, using a 56-bit key plus 8 bits for parity, which are not used in the encryption process.. The DES encryption process involves multiple rounds of a s
Trang 21 Team Member:
No Full name ID Class Signature
1 Dao Tuan Minh 20070749 MIS2020B
¢ Background of cryptographic methods leading up to DES
« Overview of DES development and adoption as a federal standard
¢ Purpose and scope of the article
2 Technical Overview of DES
« Description of symmetric key cryptography
¢ Detailed explanation of DES structure:
¢ Block cipher mechanism
¢ Key generation and management
e Feistel network structure
¢ Encryption and decryption process in DES
3 Historical Context and Significance
« The role of DES in the evolution of digital security
¢ Adoption by U.S government and global impact
¢ Early challenges and controversies
Trang 3¢ Modern applications and relevance:
« Continued use in legacy systems
« Role in educational and training settings
5 Limitations and Security Concerns
¢ Analysis of the 56-bit key vulnerability
¢ Historical and modern perspectives on DES security
¢ Discussion of notable attacks and brute-force vulnerabilities
6 The Transition to Advanced Encryption Standard (AES)
¢ Reasons for the transition
« Comparison of DES and AES
¢ Impact of the transition on digital security
7 DES in the Modern Cryptography Landscape
¢ Current status of DES in encryption protocols
¢ DES's role in understanding and teaching cryptography
¢ Reflection on DES's legacy and influence on modern encryption methods
8 Conclusion
¢ Summary of DES's historical importance
¢ Reflection on the evolution of encryption standards
e Future outlook and lessons learned from the DES era
DATA ENCRYPTION STANDARD
Trang 41 Introduction
Background of Cryptographic Methods Leading Up to DES
Before the advent of the Data Encryption Standard (DES), cryptographic methods had evolved significantly through history, primarily driven by military and diplomatic needs Early cryptographic practices were manual, like the Caesar cipher used in ancient Rome However, with the onset of World War II, the complexity of cryptographic systems increased dramatically The German Enigma machine and the Allied efforts to crack it, notably by Alan Turing and his team at Bletchley Park, marked a pivotal point in the history of cryptography These efforts were characterized by the transition from manual to mechanical and then to early electronic cryptographic techniques
In the 1950s and 1960s, as electronic communication became more common, there was a
growing need for secure data transmission in the commercial sector The limitations of existing cryptographic methods, such as their vulnerability to increasing computational power and their infeasibility for large-scale commercial applications, led to the search for a more robust, standardized encryption method This need was particularly felt in the banking industry, which required a secure means of electronic fund transfers
Overview of DES Development and Adoption as a Federal Standard
The development of DES was initiated in the early 1970s The U.S National Bureau of Standards (NBS), now the National Institute of Standards and Technology (NIST), recognized the need for a standardized encryption method In 1973, NBS solicited proposals for a federal encryption standard IBM submitted a design named Lucifer, which had been developed by cryptographer Horst Feistel After consultations with the National Security Agency (NSA), modifications were made to strengthen its security, particularly reducing the key size to 56 bits
In 1977, after rigorous scrutiny and public debate over its security, particularly regarding the key size, DES was officially adopted as Federal Information Processing Standards (FIPS) Publication
46 by the NBS This marked a significant moment in cryptographic history, as DES became the first encryption standard to be adopted by the U.S government for non-classified information Its adoption also influenced global cryptographic practices, setting a precedent for the development
of encryption standards worldwide
Trang 52 Technical Overview of DES
Description of Symmetric Key Cryptography
Symmetric key cryptography, also known as secret key cryptography, is a type of encryption where a single key is used for both encryption and decryption of messages This key is shared between the sender and the receiver and must be kept secret from unauthorized parties The primary characteristic of symmetric key cryptography is its reliance on this shared secret key, which is used to transform plaintext into ciphertext and vice versa
The effectiveness of symmetric cryptography lies in the encryption algorithm and the secrecy of the key If the key is compromised, the security of the encrypted data is also compromised Therefore, secure key distribution and management are critical aspects of symmetric
cryptography
Key Features of Symmetric Key Cryptography
¢ Speed and Efficiency: Symmetric key algorithms are generally faster and less computationally intensive than asymmetric key algorithms (which use separate keys for
encryption and decryption) This makes them suitable for encrypting large volumes of data
¢ Key Management: The biggest challenge in symmetric key cryptography is the secure distribution and management of the secret key Both the sender and receiver must have
access to the key, and it must be protected from unauthorized access at all times
¢« Applications: Symmetric key cryptography is widely used for securing data in transit and
at rest, such as in file encryption, secure communications, and in various internet security
protocols
DES as a Symmetric Key Algorithm
The Data Encryption Standard (DES) is a classic example of a symmetric key algorithm It operates on 64-bit blocks of data, using a 56-bit key (plus 8 bits for parity, which are not used in the encryption process) The same key is used for both encryption and decryption
The DES encryption process involves multiple rounds of a specific set of operations on the plaintext, including permutation (rearranging bits) and substitution (replacing bits with other bits), based on the key These operations are structured in what is known as a Feistel network
The DES algorithm can be summarized in the following steps:
1 Initial Permutation: The plaintext block undergoes an initial permutation that rearranges its bits
Trang 62 Round Function: The block is then subjected to a series of 16 rounds of processing In each round, the block is divided into two halves The right half goes through a round function that involves expansion, key mixing (using a subkey generated from the main key), substitution (using S-boxes), and permutation, then combined with the left half using an XOR operation The halves are then swapped
3 Final Permutation: After all rounds are completed, the halves are swapped back and
combined, followed by a final permutation
Trang 7Detailed Explanation of DES Structure
Block Cipher Mechanism
The Data Encryption Standard (DES) employs a block cipher mechanism, which means it encrypts data in fixed-size blocks In the case of DES, the block size is 64 bits This approach contrasts with stream ciphers, which encrypt data bit by bit
¢ Fixed Block Size: DES processes 64-bit blocks of plaintext and ciphertext Each block is handled independently during the encryption or decryption process
¢ Operation Modes: DES can be used in various modes of operation, such as Electronic Codebook (ECB), Cipher Block Chaining (CBC), and others, each offering different security properties and applications
Key Generation and Management
¢ 56-bit Key: DES utilizes a 56-bit key, which is the comerstone of the entire encryption and decryption process The original key is 64 bits, but 8 bits are used for parity checks, effectively leaving a 56-bit key for encryption
¢ Key Scheduling: DES generates 16 subkeys from the main 56-bit key Each subkey is
used in one of the 16 rounds of the encryption/decryption process This subkey generation involves permuting and shifting operations
¢ Security Implications: The length and management of the key are crucial for the security of DES The relatively short key length of 56 bits became a security vulnerability with advancements in computing power, leading to the ability to perform brute-force attacks,
Feistel Network Structure
DES utilizes a Feistel network, a common structure used in many block cipher algorithms This structure is named after Horst Feistel of IBM, who played a key role in its development The Feistel network enables the encryption and decryption processes to be very similar, differing only in the order of applying the subkeys
¢ 16 Rounds of Processing: Each 64-bit block of data goes through 16 rounds of processing in DES In each round, the block is divided into two halves
¢ Round Function: In each round, the right half of the block is expanded and goes through
a series of operations—mixing with a subkey (derived from the main key), substitution, and permutation The result is then combined with the left half using an XOR operation Finally, the halves are swapped
Trang 8Substitution and Permutation: The core of the Feistel structure in DES involves substitution (using S-boxes) and permutation (P-boxes) The S-boxes provide non- linearity (making it hard to reverse the encryption without the key), and the P-boxes provide diffusion (spreading the influence of a single plaintext bit over many ciphertext bits)
Initial and Final Permutations: The process begins with an initial permutation of the input block and ends with a final permutation of the output block after the 16 rounds
Trang 9Encryption and Decryption Process in DES
The Data Encryption Standard (DES) encryption and decryption processes are complex, involving multiple rounds of operations on the data Both processes are quite similar, with the main difference being the order in which the keys are applied
Encryption Process in DES
1 Initial Permutation: The 64-bit plaintext block is first subjected to an initial permutation (IP), which rearranges the bits to produce a permuted input
2 16 Rounds of Processing: The main part of the DES encryption process consists of 16 identical rounds Each round includes the following steps:
Splitting: The 64-bit block is split into two 32-bit halves, referred to as the left
half (L) and the right half (R)
Expansion: The right half (R) is expanded from 32 bits to 48 bits using an expansion permutation (E) This step increases the size of the half block to match
the key size
Key Mixing: The expanded right half is then combined with a round-specific 48- bit key (derived from the main 56-bit DES key) using the XOR operation These
subkeys are generated by the key schedule; in each round, a different subkey is
used
Substitution: Following the XOR operation, the block passes through a series of substitution boxes (S-boxes) Each 48-bit block is divided into eight 6-bit blocks, and each is substituted by a 4-bit block according to the S-boxes This step is crucial for the security of DES as it introduces non-linearity
Permutation: The output from the S-boxes undergoes a permutation (P), which rearranges the bits to produce a 32-bit output
Combination: Finally, the output of the permutation step is XORed with the left half (L) of the input After this, the halves are swapped The right half becomes the new left half, and the combined output becomes the new right half
3 Final Permutation: After the 16th round, a final permutation (FP) is applied to the combined output This permutation is the inverse of the initial permutation and produces the 64-bit ciphertext block
Decryption Process in DES
Trang 10Decryption in DES is very similar to encryption but requires the subkeys to be applied in the reverse order
1 Initial Permutation: The 64-bit ciphertext block undergoes the initial permutation, just
like in the encryption process
2 16 Rounds of Processing: The decryption process also consists of 16 rounds, but the round keys are applied in reverse order (1.e., the key used in the last round of encryption
is used in the first round of decryption, and so on)
« The same steps as in encryption are followed (expansion, key mixing with the XOR operation, substitution, permutation, and combination), but using the
reversed order of subkeys
3 Final Permutation: After the 16 rounds, a final permutation (the inverse of the initial
permutation) is applied to produce the original plaintext
Key Takeaway
The DES algorithm's encryption and decryption processes are similar, differing only in the order
of key application The security of DES relies heavily on the complexity of these processes, particularly the use of S-boxes for substitution, which are designed to be resistant to various cryptanalytic attacks However, due to advancements in computational capabilities and inherent limitations in its key size, DES is now considered vulnerable to brute-force attacks, leading to its replacement by more advanced encryption standards
Trang 113 Historical Context and Significance
The Role of DES in the Evolution of Digital Security
DES played a foundational role in the field of digital security, serving as one of the first encryption standards to be widely adopted across various industries Prior to DES, encryption was primarily the domain of government and military agencies, with little in the way of standardized practices for commercial and private use DES's introduction marked the beginning
of a new era where digital security became a focus for civilian communications, data storage,
and electronic transactions
As a pioneering cryptographic algorithm, DES influenced the design of many subsequent encryption methods Its widespread adoption also sparked significant research interest in the field of cryptanalysis, leading to a deeper understanding of how to both attack and defend cryptographic systems
Adoption by U.S Government and Global Impact
The U.S government's adoption of DES as a federal standard in 1977 legitimized the use of encryption for protecting sensitive but unclassified information This move also had a profound global impact, as it set a benchmark for what constituted an acceptable level of security at the time International organizations and governments began to look at DES as a model for their own encryption needs, thereby standardizing certain cryptographic practices worldwide
The influence of DES extended beyond its technical specifications; it became a symbol of the
struggle between privacy advocates and government agencies over the control of cryptography Its adoption led to the development of an ecosystem of products and services designed to meet
the DES standard, contributing to the growth of the cybersecurity industry
Early Challenges and Controversies
¢ Key Length Debate: From the outset, there were controversies surrounding the 56-bit key length of DES Critics argued that the key was too short to withstand brute-force attacks, suggesting that the NSA had deliberately weakened the algorithm to ensure that it could decrypt DES-encrypted messages This debate was not just technical but also political, as it touched on the broader issue of the public's right to use strong encryption
¢ Susceptibility to Differential Cryptanalysis: DES was also the subject of intense
academic scrutiny, which led to the discovery of more sophisticated attacks In the early 1990s, researchers Eli Biham and Adi Shamir revealed differential cryptanalysis, a
method they believed the NSA already knew about when they advised IBM to make
certain changes to the original Lucifer cipher This revelation brought about renewed skepticism regarding the NSA's involvement in the weakening of the cipher
Trang 12¢ Escalation of Computational Power: As computational power escalated, the feasibility
of brute-force attacks against DES became a practical concern By the late 1990s, it was
demonstrated that DES could be cracked within days, and later, within hours, using
dedicated hardware
Conclusion
DES's historical role extends beyond its technical contributions; it catalyzed a broader public
dialogue on encryption policy, the right to privacy, and the balance of power between citizens and the state Even as newer, more secure algorithms have taken its place, the lessons learned from the controversies and challenges of DES continue to influence the development and standardization of encryption technologies today The story of DES underscores the importance
of anticipating the future impact of technological advancements on current security measures