Merritt Fixity Authenticity for Managed Digital Assets University of California Curation Center California Digital Library April 7, 2011

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, Pyroclastichawk,

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 [ Identified as an important criterion for a TDR in the TRAC audit checklist [ B4.4] Timothy Valentine,

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,

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 Persistent identifiers Persistent storage Fixity Replication Characterization Discovery Transformation Annotation EZID CAN/Pairtree/Dflat/ReDD Fixity Replication JHOVE2 XTF 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,

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,

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,

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,

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?

For more information UC Curation Center Merritt repository UC3 Stephen AbramsMargaret Low Lisa ColvinDavid Loy Patricia Cruse Mark Reyes Scott Fisher Tracy Seneca Alex GenadinikJoan Starr Erik Hetzner Marisa Strong Greg Janée Perry Willett John Kunze