How to recover circuit output from two files

I know that jsnark uses prepFiles() to generate .arith and .in files, but how can verifiers recover the circuit outputs from these two files?
For example, a prover generates a rsa circuit, uses pubkey to encrypt a plaintext and provides two files.
A verifier can easily use runLibsnark() for verification, but how can he get the pubkey value and cipherText from the two files?