<h1 id="chronicle"><img src="https://paragonie.com/static/images/chronicle-logo.svg" width="50" /> Chronicle</h1>
Chronicle is a self-hostable microservice, built with Slim Framework,
which enables authorized users to commit arbitrary data to an immutable,
append-only public ledger.
Chronicle is superior to "blockchain" solutions for most real-world
technical problems that don't involve proofs-of-work or Byzantine fault
More precisely, Chronicle is a self-hostable microservice exposing an append-only,
cryptographically-secure hash chain data structure that accepts arbitrary
data from authorized clients through an HTTP API, secured by Sapient,
that can be used as a building block for building a cryptographic audit trail
similar to Certificate Transparency.
> Chronicle will make you question the need for blockchain technology.
Chronicle was developed by Paragon Initiative Enterprises
as part of our continued efforts to make the Internet more secure.
Getting Started with Chronicle (Documentation)
Client-Side Software that Interacts with Chronicle
What does Chronicle do?
Chronicle allows trusted clients to send data to be included in an immutable,
auditable, cryptographic permanent record.
Furthermore, Chronicle has cross-signing and many-to-one replication built-in,
which, when used, greatly enhances the auditability and availability of the
data written to your local Chronicle instance.
What problems do Chronicle solve?
Chain of Custody
If you have sensitive information, you can write metadata about client access
times to a private Chronicle in order to have verifiable, tamper-resistant
proof that specific records were accessed by specific user accounts at a
Proof of Knowledge
By inserting an encrypted message and then revealing the key at a later date,
you can provide strong evidence of prior knowledge.
Userbase Consistency Verification
For building a secure code delivery system,
committing some metadata and a SHA256 or BLAKE2 hash of each update file to
a publicly verifiable Chronicle allows users to compile a whitelist of known
update files to help block trojan horse malware (in the event of a compromised
For best results, combine with cryptographic signatures (which may also be
registered in the Chronicle) and reproducible builds.
Auditable Security Event Logging
Because of Chronicle's cryptographically assured append-only properties, and
its use of modern elliptic curve digital signatures,
Chronicle is a good fit for integrating with SIEM solutions and internal SOCs.
How does it work?
All communications are secured with Sapient.
Sapient ensures that all published messages are signed with Ed25519. All messages
are committed to a hash chain data structure backed by BLAKE2b, which we call
Blakechain for short.
There are two hashes for each message:
The hash of the current message, whose BLAKE2b key is the previous message's
block. This is just called `currhash` internally.
The summary hash, which is a BLAKE2b hash of all message hashes to date,
concatenated together in order. This is called `summaryhash` internally.
The rationale for using the previous message's hash was to add a degree of domain
separation in the event that a BLAKE2b collision attack is ever discovered. The
keying should reduce the likelihood of any practical attacks, especially if the
chain is updated rapidly.