The greatest threat to a record is not destruction, but alteration. As society moves from physical paper to born-digital records, the archival profession faces a problem of authenticity. How can archivists prove that a digital file created today remains unchanged fifty years from now? This challenge has led many to look to blockchain as a way to maintain the chain of custody.
Defining the Ledger
Blockchain is a form of Distributed Ledger Technology (DLT). Unlike a database controlled by a single administrator, a DLT replicates across a network of independent nodes. The system groups transactions into blocks, which are linked together using cryptographic hashing.
A hash function acts as a unique digital fingerprint. If even a bit of data in a file changes, its resulting hash changes. By recording these hashes in an immutable chain, the system creates a permanent, timestamped record of a file’s existence and state at a given moment.
Verifiable Chain of Custody
In archival diplomatics, the chain of custody is the continuous record of a document’s ownership and handling. It is what transforms a piece of information into a record with evidentiary value. Institutions manage the chain of custody through paper receipts and signed logs. However, people can easily copy and manipulate digital records, making audit logs vulnerable to tampering.
Blockchain enables the documentation of transfers of custody between creators, repositories, and vendors in a mathematically verifiable manner. By recording a file’s hash and metadata on a ledger, an archives can create an immutable audit trail that exists independently of the file itself.
On-Chain vs. Off-Chain
A common misconception is that organizations can use blockchain to store the actual records. For archives, this is neither practical nor scalable. Storing large archival datasets, such as high-resolution video or massive database exports, on a blockchain is expensive and leads to storage bloat.
Instead, the most viable archival model is the off-chain approach. The actual records and their rich metadata remain in a Trusted Digital Repository (TDR), while the ledger records only the cryptographic hashes and essential provenance events. Doing so allows the blockchain to serve as a lean integrity-verification layer without compromising the performance of the primary storage system.
Question of Trust
The archival community operates on trust, which sits in tension with the trustless nature of public blockchains like Bitcoin. Public ledgers often rely on Proof-of-Work systems, which incur high environmental and energy costs. Furthermore, decentralizing a public ledger may conflict with the strict governance requirements of a government or corporate archives.
For institutional use, permissioned or private ledgers are more appropriate. In these models, only vetted participants, such as a network of university libraries or a consortium of archives, can validate transactions. This approach shifts the trust from a single IT department to a distributed network of peers. However, this raises a philosophical question: does blockchain enhance trust, or does it simply shift trust from archivists to code?
Integration with Preservation Standards
Blockchain must operate with existing digital preservation standards, specifically the Open Archival Information System (OAIS) reference model. A blockchain could potentially automate the Ingest and Administration functions of OAIS using smart contracts. These are self-executing scripts that could enforce access restrictions or verify the integrity of a package during a migration event.
However, hurdles remain. The legal admissibility of blockchain-based records is still being tested in many jurisdictions. While a hash provides strong proof of integrity, it cannot verify the truth of the information in the file; it only confirms that the file remains unchanged. There is also the risk of technological obsolescence. If the blockchain protocol becomes obsolete in twenty years, the immutable proof it provides may become inaccessible, creating a new kind of digital dark age.
The Right to Erasure
The very immutability that makes blockchain attractive for integrity creates complexity for privacy. Laws like GDPR grant individuals the right to erasure. If someone accidentally or maliciously records personal data on an immutable ledger, it cannot be deleted, reinforcing the need for an off-chain model. By storing personal data in traditional systems and hashing it on-chain, institutions can delete it. In contrast, the hash, which is not personally identifiable, remains as a historical marker of the record’s former existence.
Trust, but Verify
Blockchain supports archival judgment. It provides mathematical receipts that support the human-led chain of custody. By treating blockchain as a verification layer rather than a storage solution, archives can bridge the gap between diplomatics and the demands of the digital future.
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