Regarding your code, your problem is that your input is hex-encoded, but you decode it as bytes.
A simple fix would be replacing this line:
let cryptedInput = toByteSeq(encryptedInput)
... with this:
let cryptedInput = cast[seq[byte]](parseHexStr(encryptedInput))
and importing std/strutils for the parseHexStr. Mind you that casting is
generally frowned upon, but so is copying memory from unsafeAddrs like you seem
to be already doing.
