Merritt FixityAuthenticity for Managed Digital Assets

Univers i ty of Cal i forn ia Curation CenterC a l i fo r n i a D i g i t a l L i b ra r y

A p r i l 7 , 2 0 1 1

Fixity

A means for determining whether a digital resource is authentic; in other words, that it conforms to a known (and trusted) state• A guard against various preservation threats, such as

media degradation, software/hardware failure, natural disaster, and inadvertent or malicious human behavior

hn, http://www.flickr.com/photos/neumeyer/3729267245/

Pyroclastichawk, http://www.flickr.com/photos/neumeyer/3729267245/

Fixity

A means for determining whether a digital resource is authentic; in other words, that it conforms to a known (and trusted) state• Codified as an important element of an OAIS information

model in ISO 14721[http://public.ccsds.org/publications/archive/650x0b1.pdf]

• Identified as an important criterion for a TDR in the TRAC audit checklist[http://www.crl.edu/sites/default/files/attachments/pages/trac_0.pdf, B4.4]

Timothy Valentine, http://www.flickr.com/photos/el_ramon/4221629185/

Message digests

The goal of digital preservation management is to preserve information, but that information is always represented by bits• Bits can be verified for authenticity by comparison of

message digests (aka checksums)• Different digest types trade off computational efficiency

with cryptographic security– Adler-32, CRC-32– MD2, MD5– SHA-1, SHA-256, SHA-384, SHA-512

Marcin Wichary, http://www.flickr.com/photos/mwichary/2355783479/

Preservation management

Fixity is one component of any pro-active preservation management program• Persistent identifiers• Persistent storage• Fixity• Replication• Characterization• Discovery• Transformation• Annotation

Preservation management

Fixity is one component of Merritt’s pro-active preservation management http://merritt.cdlib.org

• Persistent identifiers• Persistent storage• Fixity• Replication• Characterization• Discovery• Transformation• Annotation

EZIDCAN/Pairtree/Dflat/ReDDFixityReplicationJHOVE2XTF

Version 2

Assumptions

• Digital resources may be managed in a variety of services and systems

• Fixity verification should be performed periodically• If the size of a resource doesn’t match, it is not

necessary to verify the checksum• The “known” size and digest value for a resource

may change over time

Litchfield District Council, http://www.flickr.com/photos/30084068@N08/3813864085/

Features

• The unit of verification is the item• Items are represented by URLs• Items are associated with a known size and

message digest value, and a status:– unverified, verified, size mismatch, digest mismatch, unavailable

• All items are verified periodically at a configurable interval

• “Free” link checking

Rafael Anderson Gonzalez Mendoza, http://www.flickr.com/photos/andercismo/2349098787/

Features

• Verification can be suspended and resumed gracefully

• Summary reports are issued after each complete iteration

• Items may be associated with one or more contexts, so they can be grouped together in context-sensitive query results

Aaron Smith, http://www.flickr.com/photos/theartguy/178700752/

http://www.flickr.com/photos/thecuriousoysters/4458657148/

Questions?

Feedback we’d like from you

• What is the appropriate periodicity of iteration? • Currently, any fixity violations are reported to UC3

staff, not to owners or curators– Are there use cases in which you would want to receive

notification directly?– Are there other kinds of desirable reporting of results?

Matti Mattila, http://www.flickr.com/photos/mattimattila/4863055461/

Feedback we’d like from you

• Do you anticipate using this service to verify non-Merritt content? Are you interested in deploying the service locally for this purpose?

• How often do anticipate your content changing?

http://www.flickr.com/photos/bala_/1420171699/

For more information

UC Curation Centerhttp://www.cdlib.org/uc3uc3@ucop.edu

Merritt repositoryhttp://merritt.cdlib.org/

UC3Stephen Abrams Margaret LowLisa Colvin David LoyPatricia Cruse Mark Reyes Scott Fisher Tracy Seneca Alex Genadinik Joan StarrErik Hetzner Marisa StrongGreg Janée Perry WillettJohn Kunze