Long-term archival

Some signatures must remain verifiable for decades or centuries: government records, patent filings, court evidence, archival scientific data, treaty documents, mortgage filings. The challenge: every cryptographic algorithm has a finite expected lifetime. SHA-1 is broken; SHA-256 will eventually be broken; RSA and ECDSA will fall to quantum computers. How do you keep signatures verifiable across algorithm generations?

Confium’s answer combines three layers:

  1. RFC 4998 Evidence Record Syntax (ERS) — periodically re-timestamp evidence with current algorithms.
  2. Composite signatures — include both classical and PQ components from day one.
  3. OTS anchoring — irrefutable time proof via Bitcoin.

When to choose this use case

  • You maintain records that must remain verifiable for 25+ years (regulatory archive, treaty documents, scientific data).
  • You’re operating a sovereign archive (national archives, patent offices, court systems).
  • You need to migrate archives as algorithms age without breaking existing verifications.
  • You want irrefutable time proof that survives institutional / jurisdictional change.

How Confium solves it

Threshold key lifecycle: generate, distribute, use, refresh, rotate, retire. 1 Generate DKG ceremony (no dealer) 2 Distribute Shares to N parties 3 Use T-of-N signing sessions 4 Refresh Herzberg monthly 5 Rotate Re-share + new party defeats long-term share aggregation secret created then destroyed secret never reconstructed add/remove signers ALL STATES AUDITED IN TRANSPARENCY LOG

A long-term archival deployment maintains evidence records that outlive any individual signing key. The lifecycle:

  1. Original signature at time T₀ with algorithm A (e.g. Ed25519 + ML-DSA-65 composite).
  2. Archival timestamps at T₀, T₁, T₂, … via RFC 3161 TSA.
  3. Algorithm renewal: when algorithm A is deprecated, the archive re-timestamps all evidence with algorithm B (the new standard). The original signature remains valid because we can prove it existed before A was broken.
  4. OTS anchoring at every renewal: Bitcoin proof that the re-timestamp happened at a specific time.

RFC 4998 Evidence Record

The Evidence Record wraps the original signature with a chain of archival timestamps:

EvidenceRecord ::= SEQUENCE {
    version                   INTEGER { v1(1) },
    digestAlgorithms          SEQUENCE OF AlgorithmIdentifier,
    cryptoInfos               [0] SEQUENCE OF CryptoInfo OPTIONAL,
    encryptionInfo            [1] EncryptionInfo OPTIONAL,
    archiveTimeStampSequence  ArchiveTimeStampSequence
}

ArchiveTimeStampSequence ::= SEQUENCE OF ArchiveTimeStampChain

Each ArchiveTimeStampChain covers a period; chains chain together to form the full evidence record. When the current chain’s algorithm gets old, a new chain is added with the new algorithm.

Composite signatures from day one

For new archival records, Confium produces composite signatures containing both classical (Ed25519, ECDSA-P256) and post-quantum (ML-DSA-65) components. Today both verify; tomorrow when classical falls to quantum, the PQ component still holds. No algorithm renewal needed for the quantum transition.

OTS anchoring

For the strongest time proof, every archival batch anchors in Bitcoin:

batch_root = Confium::Transparency.compute_root(recent_archives)

ots_proof = Confium::OTS.submit(
  hash: batch_root,
  calendar: "https://btc.calendar.confium.org",
)

# Store the OTS proof alongside the archive. Future verifiers can
# independently prove the batch existed at Bitcoin block height N.
archive_record.attach_ots_proof(ots_proof)

Bitcoin’s proof-of-work chain provides irrefutable time proof that survives institutional collapse, jurisdictional change, or even the dissolution of the issuing organization.

Algorithm renewal

When an algorithm gets deprecated (e.g. SHA-1 was deprecated in 2017, RSA-1024 in 2010):

  1. The archive computes a new hash of every record using the new algorithm (SHA-384, SHA-512, or future hash).
  2. Each new hash is timestamped by the TSA.
  3. The timestamp is itself anchored in Bitcoin.
  4. The evidence record is extended with a new ArchiveTimeStampChain.

The original record remains verifiable because we can prove: “At time T₀, this record existed with hash H using algorithm A. At time T_n, we renewed to hash H’ using algorithm A’. The chain of custody is intact.”

Sovereign archive example

A national archive deploying Confium might configure:

[archive]
backend = "lmdb"
path = "/var/lib/confium/archive"

[archive.signing]
algorithm = "composite"
components = ["ECDSA-P384", "Ed25519", "ML-DSA-65"]
require_pq_component = true

[archive.timestamping]
tsa_endpoint = "tsa://tsa.confium.org"
renewal_interval_days = 365
hash_algorithm_future = "SHA-512"  # used at next renewal

[archive.anchoring]
ots_calendar = "https://btc.calendar.confium.org"
anchor_interval_hours = 1

[archive.quorum]
threshold = 3
total = 5
attributes = { "archivist" => 2, "oversight" => 2, "regulator" => 1 }

Every archival event requires T-of-N quorum; every event anchors in transparency log + OTS.

See also