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

2. 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

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

4. 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

5. 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

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

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

8. 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