More than a decade ago, I was giving an introductory presentation on quantum cryptography, as I had done many times before. I discussed the basic concepts of quantum physics, quantum computers, and quantum cryptography. I ended it with the promise that when quantum computing went mainstream that most of our current digital encryption secrets, which rely on hard-to-solve large prime-number equations, would be immediately revealed to the world.Most secrets have been protected with some form of asymmetric encryption ever since Whitfield Diffie, Mark Hellman and Ralph Merkle publicly revealed the concept in 1976 in their seminal paper called New Directions in Cryptography. Think RSA, SSL, TLS and HTTPS. We\u2019re talking most websites, digitally signed downloads, online financial transactions, your VPN, smartcards, and most wireless networks\u2014all capable of being broken an instant.Modern day secure communications rely on the fact that traditional digital computers cannot easily factor multi-factor equations involving large prime numbers. If a computer could do that, and quantum computers can, then it would be game over for any secrets encrypted by that protection.It\u2019s been theorized that most of the world\u2019s major nation-states have been recording and storing much of the world\u2019s encrypted network traffic for future decryption, just waiting for that day of reckoning to come. America will be able to read Russia\u2019s and China\u2019s top-secret communications and vice-versa. I wrote about this threat nearly eight years ago in a column.Back to my talk many years ago: When I took questions at the end of the presentation, I was asked how long I thought it would be until quantum computers would be good enough to break all those secrets. I said \u201c10 years. Most quantum physics experts think it\u2019s only 10 years off.\u201d \u00a0As I walked off stage, industry luminary Bruce Schneier was walking on to follow me. He casually said to me as he walked on by without breaking stride, \u201cHow long have you been saying 10 years?\u201dI had probably been saying 10 years as the answer for at least 10 years. Bruce made me realize that none of us really knew the answer. The running joke in quantum physics circles is that quantum computers are always 10 years off.How quantum computers workWell, it\u2019s not 10 years away anymore. According to Dr. Mark Jackson, theoretical physicist and scientific lead of business development at Cambridge Quantum Computing (CQC), we might be four to five years away, and in certain areas, limited commercial application\u2014quantum chemistry, for example\u2014might even be possible by the middle of 2021. What\u2019s changed? Well, we now have many quantum computers, devices and software with enough sophistication to be useful without something called \u201cerror correction.\u201dQuantum computers can slay traditional digital computers because of how they work. Obviously, quantum computers rely on quantum mechanics (a subject too big and complex to cover here), but here is the advantage in a nutshell. A digital computer is binary. Each transistor or logic gate within its central processing unit (CPU) is capable of holding only one \u201cstate\u201d at one time. It can either be \u201copen\u201d or \u201cclosed,\u201d energized or not, be a \u201c1\u201d or a \u201c0.\u201d Hence, the word binary.Quantum computers are based on something called quantum bits (qubits or qbits). Each qubit can be both states at the same time. Thus, one qubit is equivalent to two binary logic gates. Qubits get exponential as you add them. Two qubits can hold four simultaneous states, three qubits can hold eight simultaneous states, and so on.A relatively modest quantum computer, then, could break all our previous public\/private key pair secrets but would require effective error correction.How and when quantum computers can break public key cryptographyWe\u2019ve been waiting a long time for quantum computing to become a reality. How long? At least since 1959 when\u00a0Dr. Richard Feynman gave a lecture on it. Many quantum computing experts consider Dr. Peter Shor\u2019s algorithm released in 1994 as being the real start of quantum computing.Shor\u2019s algorithm showed that quantum-based computing could rapidly decrypt most traditional forms of asymmetric encryption. More than two decades later, the promise (and threat) of quantum computing is nearly here--not just theoretical models, but multiple, working quantum computers, software, networks, and other communication devices.One of the biggest challenges is getting qubits stable enough, long enough, without errors to be useful in serious computing. I use the non-technical terms \u201cperfect\u201d and \u201cimperfect.\u201d \u201cTo break public-key crypto, you\u2019d indeed need thousands of \u2018logical\u2019 or \u2018encoded\u2019 qubits,\u201d says Scott Aaronson, professor of computer science at the University of Texas at Austin, and director of its Quantum Information Center.\u00a0\u201cIn the real world, because of the need for error-correction and the large overheads of existing fault-tolerance schemes, that could easily translate into millions of high-quality physical qubits.\u201dSo where are we in the quantum computing lifecycle? According to Dr. Jackson, it would take a quantum computer with \u201conly\u201d 49 perfect qubits to outperform traditional binary computers. This is known as \u201cquantum supremacy,\u201d the seminal moment when quantum computers finally become more powerful than binary computers. It\u2019s like IBM\u2019s Deep Blue supercomputer beating world chess champion Gary Kasparov in 1997.To crack most current public key encryption, it would take a quantum computer with at least 4,000 perfect qubits or many times that number if the qubits were imperfect. How close are we to a perfect 4,000 qubits? It depends on who you ask. Dr. Jackson is confident that we\u2019ll have perfect 4,000-qubit quantum computers in the next five years. He has some evidence to support his claim, although we are nowhere near 4,000 perfect qubits.In March 2018, Google announced an imperfect 72-qubit computer. Google\u2019s current (publicly known) implementation makes a mistake about once every 200 calculations. When you\u2019re doing billions of calculations a second, that error rate is an unusable disaster. Tens if not hundreds of billions of dollars are being spent around the world trying to make more stable quantum computers. Some say that the jump needed to get to 4,000-qubits is not as daunting as it once was.Dr. Jackson, who is directly working with quantum computers says, \u201cWe have gone from nine to 72 qubits in just one year, so it\u2019s not crazy at all that we could get 4,000 in another five [years]. Given that the US government finally got on board a few months ago, I think that\u2019s now a conservative estimate.\u201dA greater number of knowledgeable sources still think we still don\u2019t know when the quantum break of public key crypto will be. Schneier, who has written about quantum cryptography for a long time, when told of the 5-year claim, says \u201cI don't buy it. No one knows about the unforeseen implementation problems.\u201dDr. Aaronson was also skeptical. He wrote, \u201cI\u2019ll be astonished if that happens in five years. I can\u2019t say it\u2019s impossible, but I expect it to take quite a bit longer. I\u2019ll be happy if, in three to five years, Google, IBM and others succeed in their current efforts to build noisy 70-qubit [quantum computers], and if they start to outperform classical computers at some (mostly artificial) tasks.\u00a0Even if so, that\u2019s still a long way from threatening public-key cryptography, because of the need for error-correction and the large overheads of existing fault-tolerance schemes, that could easily translate into [requiring] millions of high-quality physical qubits.\u201dClearly, the jury is out on when quantum computers can break public-key crypto, but it is no longer the stuff of science fiction.The National Security Agency (NSA) has not admitted that a quantum break is coming anytime soon, but they have said now is the time to start preparing. Specifically, in a related FAQ they wrote, \u201cThe NSA believes the time is right now right\u2026. Consistent advances in quantum computing are being made.... The NSA is looking to all NSA vendors and operators to implement standards-based, quantum resistant cryptography to protect their data and communications.\u201dThe emerging quantum computing industryA growing number of companies and organizations\u2014at least 44 known entities\u2014are attempting to build quantum computer. The four globally prominent American companies are Google, IBM, Intel and Microsoft. A growing number of startups appear to be making progress, too. One of them, Dr. Jackson\u2019s firm, CQC, is currently working with Google and IBM, among others.Many of these companies are using similar technologies, a few are using their own methods, and a few others are using multiple methods at the same time in the race to be the winner. In the past few months, IBM and Google have established business development units showing that the focus is turning from the theoretical to the commercial.The presence of so many competing companies spending billions of dollars is important. When billions of dollars across many companies and countries begins to flow, it\u2019s a virtual certainty that the killer application is at hand. Think cloud computing as an example. For years, cloud was just a discredited buzzword, until it wasn\u2019t. Same thing here.Common quantum computing methods include superconducting, ion trapping and Majorana fermions. Superconducting and ion trapping are resulting in the greatest number of qubits right now. Superconducting requires very cold temperatures, close to absolute zero (nearly -460F or -273C), and the resulting qubits can be fragile and unstable.The less mature Majorana fermion method being used by Microsoft is currently resulting in fewer qubits than the other methods but appears to be far less fragile. Dr. Jackson described the Majorana fermion method like tying braids of hair. They can be jostled about by the external environment, but their quantum state remains the same. Dr. Jackson says, \u201cIf we could get them to work at scale, they would be the clear winners. But we know less about them.\u201dThe race is an international one, and it is widely believed the Chinese are very competitive, if not leading. As Dr. Jackson puts it, \u201cThey are heavily committed to it and have virtually no budget constraints.\u201d The Chinese have even claimed to have performed quantum communications using a satellite, but there is some skepticism about this claim.Cambridge Quantum ComputingCQC formed four years ago, when the focus on investment started to shift from university laboratories to private firms such as Microsoft, Google and IBM. They are active in the building of tools that enable quantum computers to become effective. They have recently designed and tested a novel device that works in the encryption space providing theoretically unhackable protection.CQC has a proprietary quantum programming language and compiler, which they call \u201ct|ket.\u201d. Dr. Jackson says the language is somewhat C-like. The compiler is platform agnostic and works with all types of quantum computers based on many different platforms. It works to split computing effort between a traditional digital CPU and the new quantum processing unit, or QPU.Dr. Jackson says that just like a traditional graphical processing unit, or GPU, handles the intensive graphical loads or a traditional numeric processor unit (NPU) handles the heavy mathematical loads for a regular digital computer, a QPU will handle the quantum stuff.CQC\u2019s compiler hands off the workloads that traditional digital computers do well to the regular CPU and hands off the specialized quantum computing needs to the QPU. Then the results are re-synthesized into a common output stream. \u201cYou won\u2019t be needing to throw away your digital computers anytime soon. We still need them,\u201d says Dr. Jackson. This is great news because I was wondering how we were going to carry around computers needing super cool temperatures.Verifiably random number generatorsCQC also builds hardware, including a \u201cverifiably\u201d quantum random number generator. Traditional digital computers have never been able to generate truly random numbers. It\u2019s just impossible. Traditional computers are driven by very stable and naturally predictable quartz clocks that determine how fast and when a CPU can move information into and out of the CPU\u2019s registers. Every clock tick is the same amount of time as before. This means the ultimate \u201csource of truth\u201d behind any traditional random number generator is predictable (i.e., not truly random).Randomness in a traditional computer is really someone\u2019s approximation of randomness. The lack of true randomness has been the downfall of many encryption solutions, which start with a randomly generated number. So, not only do we need truly random number generators, we also need to verify that they are truly random to completely trust them.The National Institute of Standards & Technology (NIST) discussed the need for truly random number generators in the April 2018 issue of Nature magazine. Turns out quantum computing is also really good at generating verified random numbers. The earliest verifiable quantum random number generators were very big (the size of a building at 200 meters long) and fairly slow.How random numbers can save cryptography in a post-quantum worldCQC has delivered a hardware-based, \u201cpizza box\u201d prototype unit called IronBridge, about the size of a VCR, that is expected to generate about 4 million random bits per second \u2013 enough to be commercially viable for powering encryption protocols that provide quantum security today. Wow! All of those numbers are verified as being truly random by the mathematics and physics theorem Bell\u2019s Inequality.Who cares about getting these types of truly random numbers? Well, anyone hoping to protect data and information after quantum computing breaks the traditional methods. This includes governments, technology firms and any company who need to protect their valuable intellectual property, research and information.For nearly two decades, I used to say that the day of quantum reckoning was 10 years away with the same commitment given the ideas of flying cars and underwater cities. I and others didn\u2019t really believe it was coming anytime soon.Today, it\u2019s closer than ever before. We have working quantum computers and the number of qubits is growing fast. It\u2019s no longer a hype-driven pipe dream. Nation-states and companies big and small are making substantive progress against the few remaining problems. It\u2019s still just a matter of time, so start measuring the arrival of quantum computing in months or years instead of decades. For more advice, check out my book,\u00a0Cryptography Apocalypse.