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Transport Layer: Communicating with Trusted Server T

This document explains how data is transported from the untrusted logger (U) to the trusted server (T) in the private-verifiable scheme.

Overview

Per Section 4 of A New Approach to Secure Logging, the logger must coordinate three protocol phases with the trusted server:

  1. Log Initialization – Deliver the initial commitment (A₀, B₀), along with an opening message capturing the first entry and tags.
  2. Log Closure – Notify T when the log closes, providing the final aggregate tags.
  3. Final Verification – Supply the full log so T can validate the T-chain aggregates against its stored metadata.

Our implementation splits the initialization into two messages:

  • InitCommitment: commits to key seeds and update policy.
  • OpenMessage: confirms the LOG_OPENED entry, its index, and both aggregate tags.
┌─────────────┐                           ┌─────────────┐
│   Logger U  │                           │  Server T   │
│ (untrusted) │                           │  (trusted)  │
└─────────────┘                           └─────────────┘
       │                                         │
       │  1a. InitCommitment (A₀, B₀, meta)     │
       │────────────────────────────────────────>│
       │  1b. OpenMessage (LOG_OPENED tags)     │
       │────────────────────────────────────────>│
       │                                         │
       │  (U appends log entries…)               │
       │                                         │
       │  2. CloseMessage (μ_V,f, μ_T,f)         │
       │────────────────────────────────────────>│
       │                                         │
       │  3. Log file (records)                  │
       │────────────────────────────────────────>│
       │                                         │
       │  4. Verification result                 │
       │<────────────────────────────────────────│

Transport Implementations

Folder Transport (development/testing)

Stores metadata alongside logs on disk.

/shared/securelog/
  commitments/
    app-log-001.gob   # InitCommitment
  opens/
    app-log-001.gob   # OpenMessage
  closures/
    app-log-001.gob   # CloseMessage
  logs/
    app-log-001/
      logs.dat        # Entries
      anchors.idx     # Anchors
      tail.dat        # Tail state (μ_V, μ_T)

Logger usage

transport, _ := securelog.NewFolderTransport("/shared/securelog")
logDir := "/shared/securelog/logs/app-log-001"
store, _ := securelog.OpenFileStore(logDir)

logger, _ := securelog.NewRemoteLogger(
    securelog.Config{AnchorEvery: 100},
    store,
    transport,
    "app-log-001",
)

NewRemoteLogger automatically:

  1. Calls InitProtocol, which appends LOG_OPENED and returns (InitCommitment, OpenMessage).
  2. Sends both to T via SendCommitment and SendOpen.

Closing the logger sends the CloseMessage; FolderTransport.VerifyLog loads all three messages and checks the T-chain.

HTTP Transport (production)

Endpoints expected by Server:

  • POST /api/v1/logs/register – InitCommitment
  • POST /api/v1/logs/open – OpenMessage
  • POST /api/v1/logs/close – CloseMessage
  • POST /api/v1/logs/{id}/verify – records for final verification

Example logger setup:

store, _ := securelog.OpenFileStore("/var/log/myapp")
transport := securelog.NewHTTPTransport("https://trust.example.com")
logger, err := securelog.NewRemoteLogger(cfg, store, transport, "myapp-log-001")

Local Transport (in-process)

For integration tests where U and T run in the same process:

trusted := securelog.NewTrustedServer()
transport := securelog.NewLocalTransport(trusted, store)
logger, _ := securelog.NewRemoteLogger(cfg, store, transport, "test-log")

SendCommitment, SendOpen, and SendClosure map directly to TrustedServer methods.

Custom Transport

Implement the interface:

type Transport interface {
    SendCommitment(InitCommitment) error
    SendOpen(OpenMessage) error
    SendClosure(CloseMessage) error
    SendLogFile(logID string, records []Record) (bool, error)
}

Security Notes

  • TLS with mutual auth: ensure commitment/open/close messages are protected.
  • Key protection: (A₀, B₀) and OpenMessage must be transmitted securely.
  • Delay-detection: OpenMessage allows T to detect total deletion and verify the first entry’s tags.
  • Tail state: the store writes only current aggregates (tail.dat, tail table); verifiers recompute from LOG_OPENED onward.

Ensure any new transport preserves the three-phase protocol: commitment, open, close, plus final verification.