Encryption hides information from unauthorized observers by transforming a readable message, called plaintext, into ciphertext: data that appears as random noise. The recipient uses the appropriate key to recover the original message. section 1.2 section 4.0
A simple symmetric-encryption exchange works in three stages:
- Alice supplies a message and a secret key to ENCRYPT, producing the encrypted message. section 1.2
- She sends the encrypted message across an untrusted path; passive observers should not learn the underlying content. section 1.2
- Bob supplies the encrypted message and the same secret key to DECRYPT, recovering the original message. section 1.2
Alice’s letter to Bob
A messenger carries Alice’s letter through dangerous territory. Alice encrypts the letter before handing it over, so the messenger carries only noisy-looking data; Bob decrypts it after receiving the message.
