ACE – Auditing Control Environment University of Maryland Institute for Advanced Computer Studies

Digital Objects: Properties Mutable Sensitive to accidental changes One bit change can destroy an entire file No storage medium is safe forever Unpredictable Never moved, always copied

Risks in Archiving Malicious changes Corruption Hardware faults Software faults Authenticity Failure recognition window

Detecting Changes How do we ensure a file has not changed over time? Compare against another copy? Expensive operation No guarantee which is correct Solution: Secure Cryptographic Hashing

Hashing 101 Entire file run through an algorithm to generate a fixed size, but large number. Dogs and Shakespeare Large number is the hash value Later, rerun the algorithm and compare hash values Secure hashing is a one-way operation Passwords Unsecure hash example: divide by 10

Simple Solution Store hash values with the files? Problems: Easy to change one? Can change both… Unauthorized additions, deletions

ACE IMS: Integrity Management Server 3rd-party service Present hash values, issued tokens Timestamps Validation through IMS Round aggregation Witness values published

ACE AM: Audit Manager Registers data holdings Holds issued tokens Audits files on a periodic basis Three layers of checking File hash against token Token against IMS record IMS Witness challenge