Which cryptographic technique is used to ensure data integrity?

The correct answer is hashing, which is specifically designed to ensure data integrity by producing a fixed-size hash value from variable-sized input data. A hash function processes the input data and generates a unique hash as output. If even a single bit in the input data changes, the resulting hash will differ significantly, indicating that the data has been altered. This property makes hashing critical for validating the integrity of data in various applications, such as digital signatures and data verification processes.

In contrast, while encryption is focused on confidentiality—transforming data into a format that cannot be easily understood without the correct decryption key—hashing does not involve secrecy. Encoding is about data transformation for compatibility and readability rather than for security and integrity. Key exchange involves the secure sharing of keys for encryption and decryption purposes but does not relate directly to maintaining data integrity. Therefore, hashing stands out as the appropriate technique for ensuring data integrity.