Conditional decryption
&quot;Conditional decryption&quot; title could be confusing.
A ciphertex verification was demonstrated at Bitcoin workshop Financial Crypto 2016, to be a valid solution of a Sudoku instance. No third (another) party required.
Technically, we prove satisfiability of an R1CS system with a SNARK proof, and &quot;computation on an encrypted value&quot; could be expressed as R1CS equations, leading to just one single proof. One could also create &quot;some secret plaintext is less than parameter AND this ciphertext is valid for that plaintex and some secret key&quot; circuit.
Sure one could make a comparator circuit with a parameter (100 in your example), in hope to get a secret in logarithmic number of verification queries, alledgely rendering encryption useless. However, there is no oracle with SNARKs, only one single snark-proof for specific parameter value (for example, =100). If a prover would create too many comparator snark-proofs himself, he will break his encryption.