The Day Hackers Broke the Data Encryption Standard

On June 17, 1997, a group of hackers successfully cracked the Data Encryption Standard (DES), a widely used encryption method that was once considered unbreakable. This breakthrough exposed vulnerabilities in digital security and led to significant changes in encryption technology.

Explanation of the Data Encryption Standard (DES)

The Data Encryption Standard (DES) is a symmetric-key block cipher that encrypts data in 64-bit blocks using a 56-bit key. It was developed by IBM in the early 1970s based on an earlier cipher called LUCIFER. DES operates using a Feistel network structure, which ensures that encryption and decryption follow similar processes. Later, in 1977, was adopted as a Federal Information Processing Standard (FIPS) for securing sensitive but unclassified government data.  The National Bureau of Standards (NBS), with input from the National Security Agency (NSA), selected DES due to its balanced Feistel network structure and 16-round encryption process. However, its 56-bit key size was controversial, as experts feared it was too short and vulnerable to brute-force attacks. Despite concerns, DES became widely used in banking, government, and commercial applications.

Overall Structure

DES is the archetypal block cipher—an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another ciphertext bitstring of the same length. DES consists of 16 rounds of encryption, each involving substitution and permutation operations. The process includes:

1. Initial Permutation (IP): Rearranges the bits of the plaintext. It has no cryptographic significance, but was included in order to facilitate loading blocks in of mid-1970s 8-bit based hardware
   

2. 16 Feistel Rounds: Each round applies a key-dependent transformation. The ⊕ symbol denotes the exclusive-OR (XOR) operation. 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. After the final round, the halves are swapped; this is a feature of the Feistel structure which makes encryption and decryption similar processes.

3. Final Permutation (FP): Reverses the initial permutation to produce the ciphertext.
   

Feistel Function (F-Function)

Each round of DES applies the Feistel function, which consists of:

• Expansion (E): Expands the 32-bit half-block to 48 bits.

• Key Mixing: XORs the expanded block with a 48-bit subkey.

• Substitution (S-Boxes): Uses 8 substitution boxes (S-boxes) to reduce the 48-bit input to 32 bits.

• Permutation (P-Box): Rearranges the bits to increase diffusion.

Key Schedule

DES generates 16 subkeys from the 56-bit main key:

1. Permuted Choice 1 (PC-1): Reduces the key to 56 bits. 56 bits of the key are selected from the initial 64, the remaining eight bits are either discarded or used as parity check bits.

2. Key Splitting: Divides the key into two 28-bit halves. Each half is thereafter treated separately.

3. Key Rotation: Shifts each half left by 1 or 2 bits per round.(denoted by "<<<" in the diagram)

4. Permuted Choice 2 (PC-2): Selects 48 bits for each round.

Successors to DES

Due to its vulnerabilities, DES was replaced by Triple DES (3DES) and later by the Advanced Encryption Standard (AES) for stronger security.

Today, encryption standards have evolved significantly. The most widely used encryption methods include:

• AES (Advanced Encryption Standard): The successor to DES, offering 128-bit, 192-bit, and 256-bit key sizes, making it highly secure.

• RSA (Rivest-Shamir-Adleman): A popular asymmetric encryption method using 4096-bit keys for secure communications.

• Post-Quantum Cryptography (PQC): New encryption standards designed to resist attacks from quantum computers, finalized by NIST in 2024.

• Zero-Knowledge Protocols: Used for privacy-focused applications, ensuring data security without revealing sensitive information.

Encryption continues to evolve to counter emerging cyber threats. 

How Did They Do It?

The hackers behind the DES attack in 1997 were a team of programmers, students, and cryptography enthusiasts worked together, led by Rocke Verser, a programmer from Colorado. Later, in 1998, the Electronic Frontier Foundation (EFF) built a specialized machine called Deep Crack, which could break a DES key in just a few days. This demonstrated that DES was no longer secure, leading to the adoption of stronger encryption standards like AES (Advanced Encryption Standard).

The hackers used a brute force attack to break the Data Encryption Standard (DES). Specifically, they performed an exhaustive key search, where they systematically tried every possible 56-bit key until they found the correct one.

Since DES had 72 quadrillion possible keys, this process would normally take an impractical amount of time. However, the hackers accelerated the attack by distributing the workload across multiple computers, allowing them to test keys much faster. Later, the Electronic Frontier Foundation (EFF) built a specialized machine called Deep Crack, which could break DES in just a few days.

What Is a Brute Force Attack?

A brute force attack is a hacking method that relies on trial and error to crack passwords, encryption keys, or login credentials. Attackers systematically try every possible combination until they find the correct one. While simple, this method remains effective, especially against weak passwords.

Types of Brute Force Attacks

Hackers use different variations of brute force attacks, including:

• Simple brute force attacks: Manually guessing passwords based on common choices like "password123" or "admin."

• Dictionary attacks: Using a list of commonly used passwords or words to attempt access.

• Hybrid brute force attacks: Combining dictionary attacks with random character variations.

• Reverse brute force attacks: Starting with a known password and testing it against multiple usernames.

• Credential stuffing: Using previously leaked username-password pairs to gain unauthorized access.

How to Prevent Brute Force Attacks

To protect against brute force attacks, security experts recommend:

• Using strong, complex passwords with a mix of letters, numbers, and symbols.

• Enabling multi-factor authentication (MFA) for an extra layer of security.

• Limiting login attempts to prevent automated attacks.

• Using CAPTCHAs to block bots from repeatedly guessing passwords.

Brute force attacks remain a persistent cybersecurity threat, but with proper security measures, they can be mitigated.

How Was the Issue Addressed?

This event proved that DES was no longer secure for protecting sensitive data. Banks, governments, and businesses that relied on DES had to reconsider their security measures. The U.S. government had restricted stronger encryption for fear of misuse, but this incident demonstrated that stronger encryption was necessary.

Following this event, security experts pushed for more advanced encryption methods. The Advanced Encryption Standard (AES) was later introduced, offering stronger protection and replacing DES in most applications. Companies also began using longer key lengths and multi-layered security approaches to prevent similar attacks.

This historic moment reshaped digital security, proving that encryption must continuously evolve to stay ahead of cyber threats.