Final answer:
The method used to protect the integrity of a message is hashing. Hashing takes an input message and generates a unique hash digest which can be used to verify that the message has not been altered. Encryption methods also protect messages, but they focus on confidentiality, not integrity.
Step-by-step explanation:
The method used to protect the integrity of a message is hashing. Hashing involves taking the input message and running it through a hash function to produce a fixed-size string of characters, which is typically a sequence of numbers and letters. This string, known as a hash digest, is unique to the original message. If even a single character in the message is changed, the resulting hash will be dramatically different. This property makes hashing an effective way to detect any alterations to the original message, thereby protecting its integrity.
While methods like symmetric encryption, asymmetric encryption, and stream cipher can also be used to protect messages, they focus more on confidentiality rather than integrity. Encryption transforms the original message into a scrambled form to prevent unauthorized access, but integrity verification typically relies on hashing techniques such as SHA-256 or MD5.