Certificate Transparency: Go Code

This repository holds Go code related to Certificate Transparency (CT). The repository requires Go version 1.9.

• Repository Structure
• Trillian CT Personality
• Working on the Code
  • Rebuilding Generated Code
  • Updating Vendor Code
  • Running Codebase Checks

Repository Structure

The main parts of the repository are:

• Encoding libraries:
  • asn1/ and x509/ are forks of the upstream Go encoding/asn1 and crypto/x509 libraries. We maintain separate forks of these packages because CT is intended to act as an observatory of certificates across the ecosystem; as such, we need to be able to process somewhat-malformed certificates that the stricter upstream code would (correctly) reject. Our x509 fork also includes code for working with the pre-certificates defined in RFC 6962.
  • tls holds a library for processing TLS-encoded data as described in RFC 5246.
  • x509util provides additional utilities for dealing with x509.Certificates.
• CT client libraries:
  • The top-level ct package (in .) holds types and utilities for working with CT data structures defined in RFC 6962.
  • client/ and jsonclient/ hold libraries that allow access to CT Logs via entrypoints described in section 4 of RFC 6962.
  • scanner/ holds a library for scanning the entire contents of an existing CT Log.
• Command line tools:
  • ./client/ctclient allows interaction with a CT Log
  • ./scanner/scanlog allows an existing CT Log to be scanned for certificates of interest; please be polite when running this tool against a Log.
  • ./x509util/certcheck allows display and verification of certificates
  • ./x509util/crlcheck allows display and verification of certificate revocation lists (CRLs).
• CT Personality for Trillian:
  • trillian/ holds code that allows a Certificate Transparency Log to be run using a Trillian Log as its back-end -- see below.

Trillian CT Personality

The trillian/ subdirectory holds code and scripts for running a CT Log based on the Trillian general transparency Log.

The main code for the CT personality is held in trillian/ctfe; this code responds to HTTP requests on the CT API paths and translates them to the equivalent gRPC API requests to the Trillian Log.

This obviously relies on the gRPC API definitions at github.com/google/trillian; the code also uses common libraries from the Trillian project for:

• exposing monitoring and statistics via an interface and corresponding Prometheus implementation (github.com/google/trillian/monitoring/...)
• dealing with cryptographic keys (github.com/google/trillian/crypto/...).

The trillian/integration/ directory holds scripts and tests for running the whole system locally. In particular:

• trillian/integration/ct_integration_test.sh brings up local processes running a Trillian Log server, signer and a CT personality, and exercises the complete set of RFC 6962 API entrypoints.
• trillian/integration/ct_hammer_test.sh brings up a complete system and runs a continuous randomized test of the CT entrypoints.

These scripts require a local database instance to be configured as described in the Trillian instructions.

Working on the Code

Developers who want to make changes to the codebase need some additional dependencies and tools, described in the following sections. The Travis configuration for the codebase is also useful reference for the required tools and scripts, as it may be more up-to-date than this document.

Rebuilding Generated Code

Some of the CT Go code is autogenerated from other files:

• Protocol buffer message definitions are converted to .pb.go implementations.
• A mock implementation of the Trillian gRPC API (in trillian/mockclient) is created with GoMock.

Re-generating mock or protobuffer files is only needed if you're changing the original files; if you do, you'll need to install the prerequisites:

• mockgen tool from https://github.com/golang/mock
• protoc, Go support for protoc (see documentation linked from the protobuf site)

and run the following:

go generate -x ./...  # hunts for //go:generate comments and runs them

Updating Vendor Code

The codebase includes a couple of external projects under the vendor/ subdirectory, to ensure that builds use a fixed version (typically because the upstream repository does not guarantee back-compatibility between the tip master branch and the current stable release). See instructions in the Trillian repo for how to update vendored subtrees.

Running Codebase Checks

The scripts/presubmit.sh script runs various tools and tests over the codebase.

# Install gometalinter and all linters
go get -u github.com/alecthomas/gometalinter
gometalinter --install

# Run code generation, build, test and linters
./scripts/presubmit.sh

# Run build, test and linters but skip code generation
./scripts/presubmit.sh  --no-generate

# Or just run the linters alone:
gometalinter --config=gometalinter.json ./...