A digital signature is the most appropriate control to ensure integrity of online orders because it provides a way to verify the authenticity and integrity of the data sent by the sender. A digital signature is created by applying a cryptographic algorithm to the data and attaching the result to the data. The receiver can then use the sender’s public key to verify that the data has not been altered or tampered with during transmission. A digital signature also provides non-repudiation, which means that the sender cannot deny sending the data.

Data Encryption Standard (DES) is a symmetric encryption algorithm that can provide confidentiality of online orders, but not integrity. DES uses the same key to encrypt and decrypt the data, which means that anyone who has the key can modify the data without detection.

Public key encryption is an asymmetric encryption algorithm that can also provide confidentiality of online orders, but not integrity. Public key encryption uses a pair of keys: a public key and a private key. The sender encrypts the data with the receiver’s public key, and the receiver decrypts it with their own private key. However, public key encryption does not prevent anyone from modifying the encrypted data.

Multi-factor authentication is a control that can provide authentication and authorization of online orders, but not integrity. Multi-factor authentication requires the user to provide two or more pieces of evidence to prove their identity, such as a password, a token, or a biometric factor. Multi-factor authentication can prevent unauthorized access to online orders, but it does not protect the data from being modified after being sent.