This method is known as creating a digital signature of the message. It ensures the integrity of the message by verifying that it has not been tampered with in transit. The process involves hashing the message and encrypting the hash value with the sender's private key. Any changes to the message will result in a different hash value1. This method is used in DomainKeys Identified Mail (DKIM), which verifies an email's domain and helps show that the email has not been tampered with in transit2.
References:
Understanding Digital Signatures | CISA
Using DomainKeys Identified Mail (DKIM) in your organisation

The IS audit manager should specifically review the detailed evidence of the successes and weaknesses of all contingency testing to substantiate the conclusions of the audit of the corporate disaster recovery test. This is because the detailed evidence can provide the audit manager with a clear and objective picture of how well the disaster recovery plan was executed, what issues or gaps were encountered, and what recommendations or actions were taken to address them. The detailed evidence can also help the audit manager to verify the accuracy, completeness, and validity of the audit findings, as well as to evaluate the adequacy and effectiveness of the disaster recovery controls.
The other options are not as specific or relevant as the detailed evidence of all contingency testing. Overviews of interviews between data center personnel and the auditor may provide some useful information, but they are not sufficient to substantiate the conclusions without supporting evidence from the actual testing. Prior audit reports involving other corporate disaster recovery audits may provide some benchmarking or comparison data, but they are not directly related to the current audit scope and objectives. Summary memos reflecting audit opinions regarding noted weaknesses may provide some high-level insights, but they are not enough to substantiate the conclusions without detailed evidence to back them up.
References:
ISACA, CISA Review Manual, 27th Edition, 2019, p. 2411
Disaster Recovery Audit Work Program2

The most effective method of destroying sensitive data stored on electronic media is physical destruction, which involves breaking, shredding, melting, or incinerating the media to make it unreadable and unrecoverable. Degaussing, random character overwrite, and low-level formatting are methods of sanitizing or erasing data from electronic media, but they do not guarantee complete destruction of data and may leave some traces that can be recovered by advanced techniques. Therefore, physical destruction is the most secure and reliable method of data disposal for sensitive data. References: CISA Review Manual (Digital Version), Chapter 5: Protection of Information Assets, Section 5.4: Data Disposal