Integrity of Documents and Messages Detection of corrupted documents and messages Detection of bit errors caused by unreliable transmission links or faulty storage media Solution: Message Digest acting as a unique fingerprint for the document(similar function as CRC) Protection against unauthorized modification Without protection a forger could create both an alternative document and its corresponding correct message digest Symmetric Key solution: Message Authentication Code (MAC) formed by using a keyed message digest function Asymmetric Key Solution: Digital Signature formed by encrypting the message digest with the document author's private keyIntegrity of Documents and Messages • Detection of corrupted documents and messages – Detection of bit errors caused by unreliable transmission links or faulty storage media. – Solution: Message Digest acting as a unique fingerprint for the document (similar function as CRC). • Protection against unauthorized modification – Without protection a forger could create both an alternative document and its corresponding correct message digest. – Symmetric Key Solution: Message Authentication Code (MAC) formed by using a keyed message digest function. – Asymmetric Key Solution: Digital Signature formed by encrypting the message digest with the document author‘ s private key