require 'openssl'

ALGORITHM = 'AES-256-CBC'

puts 'Enter key to decrypt with (in hexadecimal):'
hex_key = gets.chomp

puts 'Enter message to decrypt (in hexadecimal):'
hex_message = gets.chomp

cipher = OpenSSL::Cipher.new(ALGORITHM)

key = [hex_key].pack('H*')
message = [hex_message].pack('H*')

cipher.decrypt
cipher.key = key

message = cipher.update(message)
message << cipher.final

puts "Decrypted message: #{message}"