UPI Study › Courses › Ethics in Technology › Free lessons › Lesson 14.1 Free with a free account
Looking Back at DES — The Encryption Method That Dominated for Decades Before Being Replaced
Ethics in Technology · Chapter 14: Tomorrow's Technology: AI, Biotech, IoT, and the Connected FutureSection 14.1 · lesson 89 of 11615 min · free with a free account
Free preview
Create a free account to keep watching
It takes a minute and costs nothing. Your free account unlocks all of Chapter 1 and 3 more lessons of Ethics in Technology.
Lesson complete
Earn the 3 college credits for Ethics in Technology
Enrolling adds a quiz after each lesson, the graded work and the official transcript. Recommended for credit by NCCRS.
Next lesson: How Machines That Simulate Human Thinking Are Changing Every Industry — Artificial Intelligence, Machine Learning, Deep Learning, and Generative AI →← The Current Gold Standard in Encryption — How AES Protects Data WorldwideNext lesson: How Machines That Simulate Human Thinking Are Changing Every Industry — Artificial Intelligence, Machine Learning, Deep Learning, and Generative AI →
In this lesson
A shared standard, a shrinking security margin, and the transition to AES.
- Explain DES’s adoption and the reason a shared standard mattered.
- Describe its Feistel structure and 56-bit effective key.
- Explain practical brute-force search and the historical role of 3DES.
- Compare the retired DES family with today’s AES standard.
Free study notes
Get this lesson's notes by email
The key points and 4 practice questions with answers, in your inbox. One email, free.
One email. Unsubscribe in one click.
Transcript
Everything said in the video, section by section (1,817 words). Read along, or search it.
Tomorrow's Technology: AI, Biotech, IoT, and the Connected Future
Looking Back at DES
DES provides a useful historical example of an encryption standard. Its practical security margin changed over time. We will explain why it spread, then examine the two halves used in its Feistel structure. Its effective secret key contained fifty-six bits. The data block itself contained sixty-four bits, describing a different quantity. Those quantities describe different parts of the design, and should not be confused when comparing algorithms. Increasing computing resources eventually made searches through the possible DES keys practical for determined attackers. Triple DES extended the original design’s life by applying DES operations three times within one compound calculation. That bridge preserved compatibility with older implementations, but also carried processing costs and important limitations forward. AES supplied a different design, larger key choices, and efficient implementation after a public selection process. We will finish by connecting those historical transitions with the need to reassess deployed protection today.
A Common Standard
DES Helped Organizations Use a Shared, Reviewed Method
DES became an official United States encryption standard in nineteen seventy-seven. Its operating rules were publicly documented. A shared method offered organizations an alternative to inconsistent or proprietary encryption designs across their systems. Banks, businesses, and government agencies could implement the same reviewed algorithm for protecting sensitive electronic information. This common reference helped interoperability between different systems. Both sides could understand exactly which encryption method was being applied. Government endorsement and public review also supplied reasons for confidence, alongside the practical benefits of standardization. Its widespread adoption attracted extensive attention from researchers studying both its strengths and potential weaknesses. For roughly two decades, DES played a major role in the electronic security systems of its era. A defined algorithm still needed correct implementation and careful key protection to deliver the intended confidentiality. Standardization helped users coordinate, but could not freeze the security assessment forever as technology continued changing.
The Basic Quantities
DES’s Data Block and Effective Key Have Different Sizes
Separate the data block, its halves, the effective secret key, and the number of rounds. A DES block contains sixty-four bits, and the round calculation operates on two thirty-two-bit halves. The effective key contains fifty-six bits. Those determine the candidate values relevant to searching for that secret. A represented DES key may contain sixty-four bits, with eight additional bits used for parity checks. Those parity bits do not add cryptographic strength, because they do not create independent secret key choices. DES applies sixteen rounds, with a corresponding key schedule. The round keys are derived from the original secret. Two to the power of fifty-six describes the number of possible effective DES key values. It does not describe the block size, and a sixty-four-bit block does not imply a sixty-four-bit secret. These distinctions become especially important when comparing DES with the key sizes and strengths of later algorithms.
Feistel Structure
Each Round Computes New Halves from the Previous Pair
A Feistel network maintains two data halves and computes a new pair during each round. The previous right half is processed through the round function, together with the corresponding round key. The function result is combined with the previous left half through the exclusive-OR operation, or XOR. That combined value becomes the new right half. The previous right becomes the new left for the following round. This interchange prepares the new pair of halves for the following round of the calculation. The function and key influence the combined half. The other path carries the old right forward without that processing. Neither original half disappears; the structure preserves the information needed to recover the previous pair. DES repeats the round calculation sixteen times, with its defined surrounding permutations and final interchange. This description concerns the internal design, rather than instructions for attacking an implementation or recovering someone’s secrets.
Follow One Round
The Right Half Takes Two Paths
Follow the old right half along its two paths in the diagram of one round. One path sends it into the round function, where it is processed with the corresponding round key. The other path carries it forward unchanged to provide the value labeled as the new left. The old left half enters the exclusive-OR operation, alongside the value produced by the round function. Their combination forms the new right half. The two resulting labels describe the next pair of data halves. The picture emphasizes the relationships between inputs and outputs. It does not show every detail of the complete DES algorithm. A complete DES operation also includes its defined initial and final permutations, and the corresponding final interchange. Round keys are derived from the original secret, rather than independently chosen new secrets for every round. Understanding this one-round flow makes the reversal property easier to explain on the next slide.
Encryption and Decryption
Reverse the Round-Key Order to Recover the Original
An important Feistel property is that the same overall structure can support both encryption and decryption. For DES encryption, the algorithm applies its derived round keys from the first through the sixteenth. For decryption, it uses the corresponding sequence in reverse, beginning with the sixteenth and ending with the first. The defined permutations and interchange complete that process, allowing the original data block to be recovered. The round function itself does not need independent inversion. The whole cipher’s structure supports recovery of the original data. This reuse was helpful for hardware implementations of the period, avoiding entirely separate designs for both directions. However, ease of implementation says little about whether the key is large enough against available computing resources. A useful structure can therefore remain historically interesting. A particular cipher using it may nevertheless become unsuitable for new protection. The weakness we examine next concerns the practical search space of DES’s fifty-six-bit effective secret.
Why the Security Margin Changed
A Fixed Key Space Became Affordable to Search
A brute-force search tries candidate keys for protected data. The search continues until it identifies the correct secret. DES’s number of possible keys remained fixed, even while computing resources improved substantially over succeeding decades. Specialized hardware could test candidates much faster than before. This changed the time and cost of searching the key space. An effort that appeared impractical for many users in the nineteen seventies eventually became achievable by determined attackers. That change did not require the algorithm to shrink its key or alter its documented round structure. It changed the practical meaning of the existing key length relative to available attacking resources. The late-nineties demonstrations showed that recovering a DES key could be feasible without defeating every transformation individually. Algorithm analysis also matters, but exhaustive search alone supplied a clear reason to reject that short key. Treat security as an assessment of a design and its conditions, rather than a permanent label.
Public Demonstrations
Late-1990s Challenges Made the Problem Concrete
Public challenge results made the shrinking DES security margin concrete, rather than merely a prediction about future computers. In nineteen ninety-eight, the Electronic Frontier Foundation’s purpose-built hardware recovered a DES challenge key in fifty-six hours. The following year, its hardware joined distributed dot net in a combined challenge search. That nineteen ninety-nine effort recovered the challenge key in twenty-two hours and fifteen minutes. The reported times describe particular searches performed with particular resources. They are not a guarantee for every possible key. A search may encounter its correct candidate at different points, and available processing capacity also affects the duration. A well-resourced effort had demonstrated practical recovery of the short secret. That changed what users could reasonably assume about its protection. Continuing to rely on that key length therefore lacked the security margin users needed for new protection. The examples are historical evidence for migration, rather than a recommendation to deploy DES today.
The Interim Bridge
Triple DES Reused the Existing Cipher Three Times
Replacing a widely used standard required time and coordination. Organizations also needed changes to their existing deployed infrastructure. Triple DES served as an interim bridge by reusing the underlying DES operations in a compound construction. Its common encryption sequence encrypts with the first key, decrypts with the second, then encrypts with the third. A historical two-key version reused the first key for that third operation. The three-key version instead used independent keys. This design increased protection beyond single DES, without immediately abandoning all the existing design and implementation work. However, adding three fifty-six-bit key components does not produce one hundred sixty-eight bits of security strength. Three-key Triple DES contains that many effective key bits, but its assessed classical strength is about one hundred twelve bits. It also retains the original sixty-four-bit data block, which creates limits beyond the length of its keys. Understanding those distinctions explains why extending an old design was useful temporarily, but insufficient as a lasting solution.
Why the Bridge Ended
Triple DES Carried Costs and Limits Forward
Triple DES performs three underlying DES operations, so that reuse carries an additional processing cost. It also preserves the sixty-four-bit block size, making limits on protected data volumes an important consideration. The historical two-key version was disallowed for applying new protection before the later retirement of the three-key version. NIST withdrew the Triple DES recommendation on January first, two thousand twenty-four. That completed the transition for new approved protection. Under that policy, it is no longer an approved cipher for applying new cryptographic protection. That status is more precise than describing Triple DES as merely an algorithm still being phased out. NIST continues to permit certain processing of data already protected, including decryption, key unwrapping, and message-authentication verification. Recovering legacy information under those allowances is different from selecting Triple DES to encrypt newly generated data. The practical bridge had ended, while compatibility needs for historical data could still require carefully limited support.
The Ground-Up Replacement
AES Combines Larger Keys with a Different Structure
AES became the replacement standard in two thousand one. An open competition selected its different design after sustained evaluation. It supports keys of one hundred twenty-eight, one hundred ninety-two, or two hundred fifty-six bits. Its structure uses substitution, row shifting, column mixing, and key addition, rather than DES’s sixteen-round Feistel arrangement. The selection process considered both security and practical performance across different hardware and implementation settings. This supported use in systems ranging from larger servers to smaller devices, alongside its stronger key choices. AES is now widely deployed, while single DES and Triple DES are retired for new approved protection. The comparison distinguishes Triple DES’s nominal key material from its lower assessed security strength. A larger key is valuable, but modes, authentication, implementations, and key management remain necessary parts of protection. Replacing an aging design therefore involved a broader assessment than merely adding together more secret key bits.
Review and Apply
A Useful Standard Must Be Reassessed Over Time
For the first review question, connect DES’s adoption with a shared, documented, reviewed method across different organizations. For the second, explain how the round function processes the right half with its corresponding derived key. Its result combines with the old left, while the old right becomes the new left. For the third, describe how increasing computing resources made the fixed fifty-six-bit candidate space practically searchable. For the fourth, explain that Triple DES reused existing operations, but added processing costs and retained block-size limits. For the fifth, connect AES with larger keys and a different design. Public scrutiny and efficient implementation also supported its selection. Remember that the historical bridge is retired for applying new protection, even though limited legacy processing remains allowed. Reassessment should consider new attack methods and implementation flaws, as well as increases in available computing power. A useful migration plan responds to changing evidence before an important security margin disappears from deployed systems.
About Ethics in Technology at UPI Study
Ethics in Technology (Computer Science 195) is a self-paced online course of 116 video lessons in 15 chapters, from cybersecurity basics, privacy and surveillance to big data, hacking, malware, network defense, intellectual property, cybercrime, encryption, emerging technology and digital citizenship. It carries a NCCRS credit recommendation for 3 semester credits.
Every lesson transcript is free on pages like this one, and the videos are free with a free UPI Study account. Enrolling adds a practice quiz after each lesson, the graded work and final exam that earn the credit, lifetime access, and an official transcript on completion. UPI Study has helped over 130,000 students with college credits. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
Enroll now → Course details Download the syllabus All Computer Science courses
Compare: Cybersecurity vs Ethics in Technology · Which ethics course?
Why take it here
Why students take Ethics in Technology with UPI Study
Where the credit goes
Universities that work with NCCRS
Ethics in Technology carries a NCCRS credit recommendation. These universities work with NCCRS; some are UPI Study's signed partners. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
Thomas Edison State UniversitySigned partner
University of the PeopleSigned partner
Charter Oak State CollegeSigned partner
Strayer UniversitySigned partner
Columbia Southern UniversitySigned partner
Indiana TechSigned partner
Penn StateWorks with NCCRS
Southern New Hampshire UniversityWorks with NCCRS
SUNYWorks with NCCRS
+many more cooperating universitiesFind my college →Find my college → Not listed? Ask Athena in the corner of this page, or book a 15-minute call.
FAQ
Questions students ask us
About Looking Back at DES — The Encryption Method That Dominated for Decades Before Being Replaced
Why is DES no longer considered secure?
How does a Feistel network work?
Why does a 64-bit DES key give only 56 bits of security?
Is Triple DES still secure?
About the Ethics in Technology course
How many college credits is Ethics in Technology?
How much does Ethics in Technology cost and what is included?
Which universities accept UPI Study credits?
How long does Ethics in Technology take?
How are the exams done?
How do my credits reach my college?
Ready for the full course? Earn 3 credits in Ethics in Technology.
116 video lessons, a quiz after each one, and the graded work that earns the credit. Recommended for credit by NCCRS.
3 credits · NCCRSEnroll →