Decoder and Decoding

noun

• The kind of intellectual who converts messages from a code to plain text.
  • synonyms: decipherer
• A machine that converts a coded text into ordinary language. .

noun

• The activity of making clear or converting from code into plain text.
  • usage: "a secret key or password is required for decryption"
  • synonyms: decryption, decipherment

verb

• Convert code into ordinary language.
  • synonyms: decode, decrypt, decipher