[Docs] Better docs for CT functions (#267)

Renamed Sunlight to Static CT, and added pointers to the RFC 6962 to Checkpoint conversion

Author: mhutchinson

README.md

@@ -24,6 +24,10 @@ provided in the respective directories:
 The [`log checkpoint`](./log/README.md#checkpoint-format) represents a commitment to the
 state of a transparent log.
 
+### RFC 6962 / Certificate Transparency Interoperability
+
+For interoperability with classic RFC 6962 logs, the [`note`](./note) package provides tools to convert Signed Tree Heads (STHs) to the checkpoint format and verify their signatures. See [`note_rfc6962.go`](./note/note_rfc6962.go) for details.
+
 ## Support
 * Mailing list: https://groups.google.com/forum/#!forum/trillian-transparency
 - Slack: https://transparency-dev.slack.com/ ([invitation](https://transparency.dev/slack/))

log/README.md

@@ -86,6 +86,14 @@ If you plan to use `otherdata` in your log, see the section on [merging checkpoi
 The first signature on a checkpoint should be from the log which issued it, but there MUST NOT
 be more than one signature from a log identity present on the checkpoint.
 
+## RFC 6962 (Certificate Transparency) Interoperability
+
+If you need to work with classic RFC 6962 CT logs, you can convert their JSON Signed Tree Heads (STHs) to this checkpoint format.
+
+The conversion and verification tools are located in the [`note`](../note) package:
+*   [`note.RFC6962STHToCheckpoint`](../note/note_rfc6962.go) converts an STH to a signed checkpoint.
+*   [`note.NewRFC6962Verifier`](../note/note_rfc6962.go) creates a verifier for these checkpoint signatures.
+
 ## Example
 
 An annotated example signed checkpoint in this format is shown below:

log/checkpoint.go

@@ -14,6 +14,9 @@
 
 // Package log provides basic support for the common log checkpoint and proof
 // format described by the README in this directory.
+//
+// For converting classic RFC 6962 Signed Tree Heads (STH) to this checkpoint
+// format, see note.RFC6962STHToCheckpoint in the github.com/transparency-dev/formats/note package.
 package log
 
 import (

note/note_rfc6962.go

@@ -48,7 +48,7 @@ func RFC6962VerifierString(logURL string, pubK crypto.PublicKey) (string, error)
 	return fmt.Sprintf("%s+%08x+%s", name, hash, base64.StdEncoding.EncodeToString(append([]byte{algRFC6962STH}, pubSer...))), nil
 }
 
-// NewRFC6962Verifier creates a note verifier for Sunlight/RFC6962 checkpoint signatures.
+// NewRFC6962Verifier creates a note verifier for Static CT/RFC6962 checkpoint signatures.
 func NewRFC6962Verifier(vkey string) (note.Verifier, error) {
 	name, vkey, _ := strings.Cut(vkey, "+")
 	hash16, key64, _ := strings.Cut(vkey, "+")
@@ -90,7 +90,7 @@ type signedTreeHead struct {
 }
 
 // RFC6962STHToCheckpoint converts the provided RFC6962 JSON representation of a CT Signed Tree Head structure to
-// a sunlight style signed checkpoint.
+// a Static CT style signed checkpoint.
 // The passed in verifier must be an RFC6929Verifier containing the correct details for the log which signed the STH.
 func RFC6962STHToCheckpoint(j []byte, v note.Verifier) ([]byte, error) {
 	var sth signedTreeHead
@@ -134,11 +134,11 @@ func rfc6962Keyhash(name string, logID [32]byte) uint32 {
 	return binary.BigEndian.Uint32(r)
 }
 
-// rfc6962LogName returns a sunlight checkpoint compatible log name from the
+// rfc6962LogName returns a Static CT checkpoint compatible log name from the
 // passed in CT log root URL.
 //
 // "For example, a log with submission prefix https://rome.ct.example.com/2024h1/ will use rome.ct.example.com/2024h1 as the checkpoint origin line"
-// (see https://github.com/C2SP/C2SP/blob/main/sunlight.md#checkpoints)
+// (see https://github.com/C2SP/C2SP/blob/main/static-ct-api.md#checkpoints)
 func rfc6962LogName(logURL string) string {
 	logURL = strings.ToLower(logURL)
 	logURL = strings.TrimPrefix(logURL, "http://")

note/note_verifier_test.go

@@ -82,7 +82,7 @@ func TestNewVerifier(t *testing.T) {
 			name: "ECDSA works",
 			key:  sigStoreKey,
 		}, {
-			name: "Sunlight works",
+			name: "Static CT works",
 			key:  "ct.googleapis.com/logs/us1/argon2024+7deb49d0+BTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABB25bKnLaZTFXOa2pgO70rjcVEMXKJkMBgFQHZ1kwFlGK9zIAx0FtC2oCfeZQe0E++VXuiYE9hFSzhRlOy92K8A=",
 		},
 	} {