How quantum computers will affect blockchain technology

Key points:

• Chinese researchers claim to have discovered a new way to crack the Rivest-Shamir-Adleman 2048-bit (RSA-2048) signature algorithm.
• RSA is a cryptographic technique that encrypts the information using a public key and decrypts the information using a private key.
• It would take an average computer 300 trillion years to crack an RSA-2048 encryption key, as it must find the prime factor of a number with 617 decimal places and 2048 binary bits.
• Chinese researchers appear to have combined "classical lattice reduction factorization techniques with quantum approximation optimization algorithms," which have successfully factored 48-bit numbers using a 10-qubit quantum computer. 
• Ethereum co-founder Vitalik Buterin previously explained that one of the long-term goals is to make the blockchain quantization-resistant. In theory, this involves forking the network to use higher-order encryption algorithms that require larger qubits to break.

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Chinese researchers claim to have discovered a new way to crack the Rivest-Shamir-Adleman 2048-bit (RSA-2048) signature algorithm that is presented in blockchains and other security protocols, according to a recent publication. RSA is a cryptographic technique that encrypts the information using a public key and decrypts the information using a private key.

To crack the RSA-2048 algorithm, like other algorithms in the RSA family of numbers, one must find the prime factor of a number with 617 decimal places and 2048 binary bits. Experts estimate that it would take an average computer 300 trillion years to crack an RSA-2048 encryption key. However, the Chinese researchers say in their paper that the encryption could be reversed using a 372-qubit quantum computer, or the basic unit of information that acts as a proxy for computing power.

For comparison: the latest quantum computer, the IBM Osprey, has a processing power of 433 qubits. Previously, experts calculated that factoring RSA-2048 with a quantum computer would require 13,436 qubits, using a quantum factorization method known as Shor's algorithm.

Unlike classical computers, which operate on a binary base of 0s or 1s, quantum computers use qubits that can assume infinite states at temperatures as low as -273 °C (-459.4 °F) by using a liquid gas coolant. A quantum computer would thus be able to map out all possible solutions to a cryptographic problem and try all of them simultaneously, increasing efficiency on astronomical scales.

Classical vs quantum computing comparison. Source - Towards Data Science

According to American cryptographer Bruce Schneier, Chinese researchers appear to have combined "classical lattice reduction factorization techniques with quantum approximation optimization algorithms," which have successfully factored 48-bit numbers using a 10-qubit quantum computer. Schneier commented: "While there is always a potential problem with scaling something like this by a factor of 50, there aren't any obvious obstacles."

Roger Grimes, an expert on security issues, stated:

“Apparently what happened is another guy who had previously announced he was able to break traditional asymmetric encryption using classical computers … but reviewers found a flaw in his algorithm and that guy had to retract his paper. But this Chinese team realized that the step that killed the whole thing could be solved by small quantum computers. So they tested and it worked.”

Schneier also cautions that the algorithm relies on a recent factorization paper by Peter Schnorr, in which his algorithm works well on small bits, but cannot handle larger sizes without a specific explanation. "Thus, if the Chinese paper does rely on this non-scalable Schnorr technique, the technique in this Chinese paper will not be scaled either," Schneier wrote.

“In general, the smart bet is on the new techniques not working. But someday, that bet will be wrong.”

Quantum computers are also limited by operational factors such as heat loss and the requirement for complex -273 °C (-459.4 °F) cooling infrastructure. Therefore, the nominal number of qubits required to invert a cryptography algorithm may be much higher than theoretical estimates.

Although the researchers have not yet done so, the method could theoretically be extended to other RSA-2048 protocols used in information technology, such as HTTPS, email, web browsing, two-factor authentication, and more. Ethereum co-founder Vitalik Buterin previously explained that one of the long-term goals is to make the blockchain quantization-resistant. In theory, this involves forking the network to use higher-order encryption algorithms that require larger qubits to break.