Are there cryptographic scheme where encryption is sequential and take a long time (in a way that it can be quantified) while instead decryption with a secret key takes very short time?
Some sort of reverse time-lock encryption where it takes a long time to decrypt rather than encrypt?
(Either with symmetric or asymmetric)
One obvious way (which is a variant of the normal time-lock encryption technique) is to do RSA encryption, with a truly huge $e$.
That is, to encrypt, you compute $M^{3^\lambda} \bmod N$; by making $\lambda$ sufficiently large, you can make this take a long time.
To decrypt, you would have precomputed the values $(3^\lambda)^{-1} \bmod p-1$ and $(3^\lambda)^{-1} \bmod q-1$, which can be done in $O(\log \lambda)$ time; you proceed with RSA decryption in the standard way.
