The difference between MAC and Digital Signatures, one uses symmetric keys and the other asymmetric keys (provided by the CA). To achieve non-repudiation one must trust a service (a certificate generated by a trusted third party (TTP) called certificate authority (CA)) which prevents an entity from denying previous commitments or actions (e.g. Thus just providing message integrity and authentication, but not non-repudiation. A misconception is that encrypting, per se, provides authentication "If the message decrypts properly then it is authentic" - Wrong! MAC can be subject to several types of attacks, like: message reordering, block substitution, block repetition. Message Authentication Codes (MAC), useful when the communicating parties have arranged to use a shared secret that they both possess, does not give non-repudiation. The common method to provide non-repudiation in the context of digital communications or storage is Digital Signatures, a more powerful tool that provides non-repudiation in a publicly verifiable manner. Because of this, data integrity is best asserted when the recipient already possesses the necessary verification information, such as after being mutually authenticated. Even with this safeguard, it is possible to tamper with data in transit, either through a man-in-the-middle attack or phishing. A data hash such as SHA2 usually ensures that the data will not be changed undetectably. Proof of data integrity is typically the easiest of these requirements to accomplish. An authentication that the data is available under specific circumstances, or for a period of time: data availability.An authentication that can be said to be genuine with high confidence.A service that provides proof of the integrity and origin of data.In digital security, non-repudiation means: Similarly, the owner of a computer account must not allow others to use it, such as by giving away their password, and a policy should be implemented to enforce this. For example, a secure area may use a key card access system where non-repudiation would be violated if key cards were shared or if lost and stolen cards were not immediately reported. In general, non-repudiation involves associating actions or changes with a unique individual.
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