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
  • Running Codebase Checks
  • Rebuilding Generated Code
  • Updating Vendor Code

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 HTTP entrypoints described in section 4 of RFC 6962.
  • dnsclient/ has a library that allows access to CT Logs over DNS.
  • scanner/ holds a library for scanning the entire contents of an existing CT Log.
• 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.
• Command line tools:
  • ./client/ctclient allows interaction with a CT Log.
  • ./ctutil/sctcheck allows SCTs (signed certificate timestamps) from a CT Log to be verified.
  • ./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).
• Other libraries related to CT:
  • ctutil/ holds utility functions for validating and verifying CT data structures.
  • loglist/ has a library for reading v1 JSON lists of CT Logs.
  • loglist2/ has a library for reading v2 JSON lists of CT Logs.

Trillian CT Personality

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

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.

In order for the go generate command to work properly, the code must be checked out to the following location: $GOPATH/src/github.com/google/certificate-transparency-go

Running Codebase Checks

The scripts/presubmit.sh script runs various tools and tests over the codebase; please ensure this script passes before sending pull requests for review.

# Install golangci-lint
go get -u github.com/golangci/golangci-lint/cmd/golangci-lint
cd $GOPATH/src/github.com/golangci/golangci-lint/cmd/golangci-lint
go install -ldflags "-X 'main.version=$(git describe --tags)' -X 'main.commit=$(git rev-parse --short HEAD)' -X 'main.date=$(date)'"
cd -

# 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:
golangci-lint run

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:

• tools written in go can be installed with a single run of go install (courtesy of tools.go and go.mod).
• protoc tool: you'll need version 3.12.4 installed, and PATH updated to include its bin/ directory.

With tools installed, 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.