One aspect of RSA that may help it become relevant again is that the key size can be arbitrary by utilizing multiple primes (RSA-MP[1]) and therefore increase the qubit requirement for a successful quantum attack. This could lead to a situation where large RSA keys would remain secure for decades longer than ECC keys, and if quantum computers hit a growth wall then those RSA keys could remain secure forever.
RSA-MP would then serve as a hedge (by either ending up completely secure, or buying time) against novel* PQC algorithms being broken. The cost being large public keys, large ciphertexts, slow decryption and very slow keygen.
Another option is to come up with enormous safe primes for good old DH. This would result is very fast keygen, and decryption performance will equal encryption - but will probably be worse than RSA anyway. The biggest public DH safe prime I'm aware of is 16384 bits (unofficially released by someone who worked on some DH standard which ended on 8192 bits).
* McEliece is not novel but did not see as much scrutiny as RSA. And has huge public keys - so might as well be paired with RSA?
Comments
One aspect of RSA that may help it become relevant again is that the key size can be arbitrary by utilizing multiple primes (RSA-MP[1]) and therefore increase the qubit requirement for a successful quantum attack. This could lead to a situation where large RSA keys would remain secure for decades longer than ECC keys, and if quantum computers hit a growth wall then those RSA keys could remain secure forever.
RSA-MP would then serve as a hedge (by either ending up completely secure, or buying time) against novel* PQC algorithms being broken. The cost being large public keys, large ciphertexts, slow decryption and very slow keygen.
Another option is to come up with enormous safe primes for good old DH. This would result is very fast keygen, and decryption performance will equal encryption - but will probably be worse than RSA anyway. The biggest public DH safe prime I'm aware of is 16384 bits (unofficially released by someone who worked on some DH standard which ended on 8192 bits).
* McEliece is not novel but did not see as much scrutiny as RSA. And has huge public keys - so might as well be paired with RSA?
[1] <https://www.degruyter.com/document/doi/10.1515/JMC.2008.006/...>