Which aspect of cryptography ensures that a message has not been altered during transmission?

The aspect of cryptography that ensures a message has not been altered during transmission is origin authentication. This process involves verifying that a message originated from a specific sender and has not been tampered with or modified en route. It typically employs techniques such as digital signatures or message authentication codes (MACs) to confirm both the identity of the sender and the integrity of the message.

When origin authentication is implemented, even if a malicious actor intercepts the message, they would not be able to alter it without invalidating the authentication mechanism, alerting the intended recipient to a possible integrity violation.

The other options focus on different functions within the realm of cryptography. Encryption primarily addresses the confidentiality of data, ensuring that only authorized parties can read the contents. Confidentiality protects sensitive information from interception, while obfuscation makes data harder to understand but does not inherently provide guarantees against alteration or verification of the sender's identity. Therefore, origin authentication is specifically geared toward confirming the integrity and authenticity of the message, which makes it the correct choice in this context.