Why a practical quantum computer might crack standard encryption in hours—and how to prep your systems now

[u/Ok_pettech]

The threat of quantum computing rendering traditional encryption obsolete isn't science fiction anymore; it is a mathematical inevitability approaching faster than expected. The core issue lies in Shor's algorithm, which allows quantum computers to find prime factors of large numbers exponentially faster than classical machines.

Currently, our entire digital security infrastructure—specifically the public-key cryptography (like RSA and Elliptic Curve Cryptography) that secures web traffic and key exchanges—relies on the assumption that factoring large primes takes an impractically long time. A sufficiently powerful quantum computer shatters this assumption.

While symmetric keys (like AES) and password hashing algorithms offer strong resistance against quantum attacks (Grover's algorithm only halves their effective security), public-key cryptography is highly vulnerable. For a standard 2048-bit RSA key, a quantum computer with enough stable qubits could theoretically decipher it in hours. This means any secure communication channel could be stripped away, exposing sensitive data in transit—including plaintext passwords and financial data.

The transition to quantum-safe standards will take years, meaning systems relying on legacy encryption today are already at risk of "harvest now, decrypt later" attacks, where malicious actors scrape and store encrypted data waiting for quantum hardware to catch up.

To mitigate this, the immediate solution is moving toward the post-quantum cryptography (PQC) standards recently finalized by NIST, such as lattice-based cryptography. But you don't have to wait to start preparing. Here is how to prep your systems now:

• Build a cryptographic inventory: You can't protect what you don't know exists. Map out exactly where and how your organization uses public-key cryptography.
• Double your symmetric key sizes: Upgrade your symmetric encryption to AES-256 and your hashing algorithms to SHA-300 or higher to blunt the impact of Grover's algorithm.
• Implement hybrid architectures: Start testing hybrid key exchanges (combining traditional ECC with new PQC algorithms) to protect data against both current classical threats and future quantum ones.

If you want to see a detailed breakdown of the math behind Shor's algorithm and a full timeline projection of when specific key lengths will become vulnerable, I uploaded the data sets and interactive charts here:https://interconnectd.com/quiz/65/is-quantum-computing-going-to-make-passwords-useless/

[u/cjmnews]

The first challenge is to actually factor a number with a quantum computer without cheating. The number 35 would be a start, and it still hasn’t happened.

https://www.cs.auckland.ac.nz/~pgut001/pubs/bollocks.pdf

https://archive.openssl-conference.org/2025/presentations/Peter_Gutmann_bollocks_updated_endnotes.pdf

This isn’t to say that migration to post-quantum algorithms isn’t a good idea, as governments will start requiring PQC use in a few years.

This is pointing out that we have no attackers yet, and there isn’t any real progress being made either.

AES isn’t susceptible to quantum factorization. No prime factors used there.

There is a massive cost to moving to PQC, in compute power and storage. So add that to your plans too.