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Quantum computers are not something you see in movies anymore. They are real. They are a major problem in how we keep things safe online. This includes our bank accounts, the way we talk to each other, and our identities.
Most of the ways we keep things secret today are based on one idea: some math problems are too hard for regular computers to figure out. Things like factoring numbers, solving logarithms, and getting private keys from public ones. It is hard for regular computers to do these things. That is what keeps our secrets safe.
Quantum computers can do these things much faster. A powerful Quantum computer can solve these problems in a few hours, whereas a regular computer would take thousands of years.
This has put the way we keep things safe online in a spot. There are three ways to keep things safe now:
- Classical Cryptography secures systems in use today.
- Quantum Cryptography uses quantum physics to secure communications.
- Post-quantum Cryptography builds encryption that can withstand quantum attacks.
It is really important to know the difference between these three ways. The choices we make today about how to keep things need to be good enough to stop the computers of tomorrow. We need to think about Quantum computers when we choose how to keep our secrets safe.
What is Classical Cryptography?
Classical cryptography is the practice of securing digital information using mathematical algorithms on conventional computers. It protects HTTPS connections, financial transactions, logins, and nearly all internet communication. Its security depends on computational hardness operations that are easy to perform but extremely difficult to reverse without a secret key.
How Does Classical Cryptography Work?
There are two fundamental types of classical cryptography: symmetric and asymmetric.
Symmetric Cryptography, one key is used for both encrypting and decrypting data. The most popular algorithm in this category is AES (Advanced Encryption Standard). It is quick and efficient and is the preferred method for encrypting large files, database encryption, and data-at-rest protection.
Asymmetric cryptography is based on a public/private key pair. This includes RSA, Diffie-Hellman, and Elliptic Curve Cryptography (ECC). A secure key exchange and digital signing are possible in asymmetric systems. They enable two unrelated parties to use a public network to communicate securely, which is impossible with symmetric encryption.
Completing the picture are hashing algorithms such as SHA-256. They check that the data is intact and ensure that the content is authentic, without the need to exchange keys. In combination, these three are the trust infrastructure of the modern internet: symmetric encryption, asymmetric cryptography, and hashing.
Classical cryptography is still used to secure communication in the world today. However, its long-term weakness is assuming that the classical computing paradigm will continue as the primary computing paradigm, which quantum computing is now challenging.
Also Read: Asymmetric vs. Symmetric Encryption: Differences
What is Quantum Cryptography
Quantum cryptography is a method of securing communication using the principles of quantum physics rather than mathematical complexity. It does not rely on hard-to-solve equations. Instead, it uses the behaviour of quantum particles, specifically the fact that measuring a quantum state alters it, to detect any attempt at eavesdropping.
What is Post-Quantum Cryptography?
When quantum cryptography is concerned with incorporating quantum physics to secure the message, it is post-quantum cryptography that deals with surviving quantum attacks.
And such a difference is decisive.
Post-quantum cryptography (PQC) aims at creating new encryption algorithms that will be resistant to attacks by even large-scale quantum computers coming into use. It does not need quantum equipment. Rather, it reinvents cryptographic mathematics to be immune to quantum computation.
This is the worry behind this change: “the mighty quantum computers will crack classical algorithms, such as RSA and ECC, with methods such as the Shor algorithm”. Tasks that previously would have required a thousand years with the classical computers would only take hours or minutes using the new machines.
The potential has compelled scientists to come up with completely novel cryptography techniques.
Post-quantum algorithms are based on mathematical problems that have been believed to be vulnerable to quantum attacks. These are lattice-based cryptography, hash-based signatures, multivariate polynomial problems, and code-based cryptography.
They are not based on integer factorisation or discrete logarithms, the type of problems that quantum computers are best at, unlike RSA.
The interesting aspect of PQC is that it is practical. It can operate on the current hardware and integrate with the current systems without necessitating quantum infrastructure. That is to say that organisations can begin making the transition now and not wait until quantum computers can grow up.
I consider post-quantum cryptography more of a preparation than a reaction. Encryption is not on the wish list to fail. We are re-architecturing it in such a way that we are not scaling our security with quantum computing.
How Does Quantum Cryptography Work?
The application that is most commonly used is Quantum Key Distribution (QKD). In QKD, the keys are sent through quantum particles, like photons. This disturbance cannot be avoided if one tries to trap or detect these particles while they are in transit. Both the sender and receiver can know if that is happening or not, so if someone is listening in, they will be easily spotted.
This means that quantum cryptography is thought to be unbreakable, not because it’s hard to compute but because it’s impossible to intercept without detection by physics. There is no silent surveillance. It is impossible to avoid leaving a trace if there is any infiltration.
However, quantum cryptography is currently limited in use. It needs to have special equipment, an environment that is controlled for transmission, and an infrastructure that includes fibre-optic cable or a satellite link. It is impractical for use on a broad level, due to its cost and complexity.
For this reason, quantum cryptography is isolated to specific high-security environments at the moment, like for government communications, financial institutions, and critical infrastructure, but not for general internet traffic.
Also Read: What Is Hybrid Cryptography? [The Practical Path to PQC]
Problems in Classical PKI
Classical PKI (Public Key Infrastructure) is the trust system behind every secure website certificate, signed software update, and corporate authentication tool. It has supported digital trust for decades. Solid in design, mature in deployment, and deeply embedded in global infrastructure.
The problem is that classical PKI was built for a world without quantum computers.
RSA and ECC are its foundation and its vulnerability. Both algorithms derive their security from mathematical problems that are hard for classical machines: factoring large integers and computing discrete logarithms. Classical computers cannot solve these in any practical timeframe. Quantum computers can.
A sufficiently powerful quantum machine running Shor’s algorithm would break RSA and ECC by solving those problems exponentially faster. Digital certificates, secure email signatures, VPN authentication, and code signing all of it rests on algorithms that would not survive a quantum attack.
There is a second, more immediate problem: long-term data exposure. Attackers can collect encrypted data today and store it. Once quantum capability arrives, they decrypt it. This harvest-now, decrypt-later strategy is already a concern for security teams protecting data with long-term sensitivity, such as government records, financial archives, and intellectual property.
Updating classical PKI is not a quick fix. It requires key replacement, certificate renewal, key rotation, and compatibility checks across sprawling infrastructure. It is a migration problem on a global scale, and the window to prepare is narrowing.
What Algorithms Power Each Era of Cryptography?
Each of the eras of cryptography has its own set of algorithms that it relies on. The choice of maths problems to rely on gives a clear indication of the evolution and direction of security thinking.
How Do the Algorithms Differ Across Classical, Quantum, and Post-Quantum?
The computational hardness is the basis of classical cryptography.
- RSA is responsible for public-key encryption and digital signatures.
- Diffie-Hellman is a method that supports secure key exchange.
- ECC is an efficient and highly secure alternative to RSA with smaller key sizes, suitable for mobile and limited devices.
- AES is the world-standard encryption for symmetric encryption. To ensure data integrity and authentication, hashing is done using SHA-256 and other variants.
These algorithms are based on the assumption that classical computers have been the upper bound of computing power and that this bound has remained for decades.
Rather, quantum cryptography makes no use of traditional encryption algorithms. Instead, it employs quantum mechanical procedures.
QKD protocols like BB84 are able to share a secret key between two parties by creating a shared secret key from quantum states. Security is NOT a function of math. It’s a function of physics. When you measure a quantum particle, you alter it, so there’s always a way to know if it’s been intercepted.
The post-quantum families of algorithms are completely new families that are highly resistant to both classical and quantum attacks. The most advanced are lattice-based cryptography methods, such as CRYSTALS-Kyber (key encapsulation) and Dilithium (digital signatures).
An alternative for signing operations is hash-based signatures, e.g. SPHINCS+. The classic McEliece cryptography is an example of code-based cryptography, which is based on the theory of error correcting codes. There is an additional diversity in multivariate polynomial cryptography.
Also Read: Quantum Computing Stats, Trends & Future 2026: Crucial Year for Quantum Security
None of these is based on integer factorisation or discrete logarithms, the exact problems quantum computers are designed to break.
During the transition period, all three are to be handled by systems concurrently. There are still classical algorithms in play. Post-quantum algorithms are being added on. Running both simultaneously solves the problem by filling the gap between the two systems without requiring changes to existing infrastructure.
Why Quantum Computing Is a Real Threat to Encryption
Quantum computing has been a far-off research project over the years. Very intriguing, yet none of the use is in everyday security judgments. Such perception is swiftly disappearing.
The danger is no longer figurative. It’s strategic.
The processing of information by quantum computers is not the same as that of classical machines. Rather than bits that are represented as 0 or 1, quantum bits, qubits, can be represented in multiple states at once. This enables some calculations to be done a thousand times faster than can be done by conventional computers.
And then there is encryption, and that is where I get concerned.
Such algorithms as RSA and ECC rely on mathematical problems, which are easy to solve but not easy to undo. Classical computers require an impractical amount of time to factorise large numbers or to compute discrete logarithms. That challenge is the foundation of contemporary encryption.
The equation is altered by quantum algorithms.
The algorithm by Shor, specifically, might enable sufficiently powerful quantum computers to effectively break RSA and ECC. Jobs that used to require classical machines to complete in thousands of years could be accomplished in hours. When this threshold is reached, it makes much of the modern-day public-key infrastructure vulnerable.
Today, attackers are able to gather encrypted information even before that occurs and store it to be decrypted at an opportune time. Government sensitive information, intellectual property, bookkeeping of the finances, anything of long value, has become a victim.
This is why the transition to post-quantum cryptography is rather a necessity than a luxury. We are not training to be in science fiction. We are gearing towards a technological milestone that is bound to happen and change the definition of digital security.
Also Read: Quantum-Safe Crypto: SEC’s Blueprint to Keep Your Digital Assets Quantum-Safe
How Smart Organizations Prepare for the Post-Quantum Shift
Most organisations say the same thing: we’ll move to post-quantum cryptography when the time comes.
That mindset is comfortable. And dangerous.
When quantum computers become capable of breaking RSA and ECC, the organisations that wait will be the ones scrambling. Post-quantum migration is not a weekend upgrade. It’s not a patch. It’s not a toggle switch. It’s a multi-year transformation that touches every layer of digital infrastructure.
Here is how smart organisations prepare before disruption hits.
Step 1: Gain Cryptographic Visibility
You can’t fix what you can’t see. Most organisations don’t know where encryption lives across their systems, and that’s the first problem to solve.
Cryptography is embedded everywhere: TLS certificates, VPN gateways, database encryption, API authentication, IoT firmware, code-signing systems, identity providers, and cloud workloads. Without a clear map of where each algorithm operates, there is no basis for a migration plan.
The starting point is a cryptographic inventory identifying every place RSA, ECC, or other vulnerable algorithms are in use, mapping dependencies between services and certificates, and classifying assets by risk exposure. Think of it as building a crypto bill of materials (CBOM). It is the foundation on which everything else rests.
Step 2: Build Crypto Agility
Most systems are tightly coupled to a specific encryption algorithm. That becomes a problem when the algorithm needs to change.
Hard-coding cryptography into an architecture means switching algorithms later feels like rebuilding an aircraft mid-flight. Smart organisations design for crypto agility instead of the ability to swap algorithms without redesigning the system around them.
In practice, that means abstracting cryptographic layers, using libraries that support plug-and-play algorithm replacement, and building toward hybrid cryptography running classical and post-quantum algorithms in parallel during the transition period.
The transition will not be binary. For a significant window, organisations will operate classical algorithms alongside post-quantum ones. Systems that cannot accommodate both will face a harder, more disruptive migration.
Step 3: Test for Real-World Performance
Post-quantum algorithms are not drop-in replacements. They carry trade-offs: larger key sizes, bigger signatures, higher bandwidth consumption, increased latency, and greater memory requirements.
Those constraints matter particularly for IoT devices, mobile applications, high-frequency trading systems, embedded hardware, and cloud APIs operating at scale. A solution that performs well in a lab environment can fail under real production load.
Testing should include controlled pilot deployments, latency and bandwidth benchmarking, device compatibility checks, certificate chain stress tests, and simulations of real traffic volumes. Performance problems discovered in testing are manageable. The same problems discovered post-migration are not.
Step 4: Prioritise by Risk and Data Sensitivity
Not all systems carry the same risk. Data with long-term sensitivity, government records, financial archives, legal documents, and intellectual property face the greatest exposure from harvest-now, decrypt-later attacks. Those assets need to move first.
Lower-risk systems can follow a slower migration timeline. Prioritising by sensitivity and exposure turns a sprawling infrastructure overhaul into a sequenced, manageable programme. It also allows teams to learn from early migrations before applying them on a wider scale.
Step 5: Treat It as Risk Hedging, Not a Panic Response
A storm shelter built during a hurricane offers little protection. The organisations that fare best are the ones that built it early.
Post-quantum preparation is risk hedging. The threat is real, the timeline is uncertain, and the cost of early action is far lower than the cost of reactive scrambling. Inventory now. Design for agility now. Test continuously. Improve incrementally.
The organisations treating post-quantum migration as a strategic initiative, not a future IT project, are the ones that will move through the transition with confidence rather than disruption.
Migrating to the PQC
- Post-quantum migration doesn’t have to be chaotic. It can be structured and strategic.
- The right certificate and PKI management approach make the transition controlled instead of reactive.
How the Transition Actually Happens
- Migration will be gradual, not instant
- Hybrid certificates (classical + PQC) will be used initially
- Systems will be upgraded based on risk and data sensitivity
- Automation simplifies discovery, renewal, and replacement
The Bigger Picture
- Classical cryptography secures today
- Post-quantum cryptography prepares for tomorrow
- Emerging quantum cryptography explores physics-based security
- All three will coexist during the transition phase
Conclusion
The shift to post-quantum cryptography is not a distant possibility; it’s an inevitable transition. Organisations that begin preparing today by building visibility, automation, and crypto-agility into their PKI infrastructure will move forward with confidence. Those who delay risk facing disruption when the change becomes urgent.
Now is the time to assess, plan, and modernise your cryptographic strategy.
Contact our team today to get expert guidance on migrating to quantum-ready security and to explore reliable, scalable PKI solutions tailored to your organisation’s needs. We’re here to help you transition smoothly and securely.
