6. General Concerns post-quantum cryptography

While TLS is secure against today’s classical computers, the asymmetric cryptography in TLS is unfortunately vulnerable to future attacks from quantum computers. Given the importance of TLS, preparing for the transition to post-quantum cryptography needs to start now.  Asymmetric cryptography in TLS is vulnerable in two places:

Key exchange: the server and client exchange cryptographic messages use asymmetric key exchange algorithms (such as RSA and ECDH) to derive a symmetric key. The symmetric key then encrypts the rest of the session.  This 256-bit key is what turns plaintext into unreadable ciphertext. For a third party to decrypt the ciphertext using brute force, turning it back to plaintext, they would need to figure out 2×256 ( 4 Billion x 4 Billion x 4 Billion x 4 Billion x 4 Billion x 4 Billion x 4 Billion x 4 Billion) different number combinations. Currently, it would take the world’s strongest supercomputer millions of years to crack that key and break encryption. A powerful quantum computer could reduce this time significantly. A recent study from MIT showed that a 2048-bit RSA key— another widely used encryption key — could potentially be broken by a powerful quantum computer in 8 hours. While both the integer factorization problem and the general discrete logarithm problem are believed to be hard in classical computation models, it has been shown that neither problem is hard in the quantum computation model. So even data that is secure today isn’t safe from being stolen today and decrypted tomorrow when quantum computing is accessible.

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