ghoststring

ghoststring

A Go string wrapper type that is encrypted when stringified or JSONified. The following standard library interfaces are fulfilled:

• json.Marshaler
• json.Unmarshaler
• fmt.Stringer
• fmt.GoStringer
• encoding.TextMarshaler
• encoding.TextUnmarshaler
• encoding.BinaryMarshaler
• encoding.BinaryUnmarshaler

usage

Typical usage assumes at least two systems that share a key. For example, two or more web services may not directly communicate, but are passed data via state transfer through a browser session to which they both need access without leaking to the browser.

Each instance of GhostString requires a non-empty namespace which must match a registered Ghostifyer, e.g.:

Declare a type that uses a GhostString as a field:

type Message struct {
	Recipient string                  `json:"recipient"`
	Content   ghoststring.GhostString `json:"content"`
	Mood      ghoststring.GhostString `json:"mood"`
}

Load a secret key from somewhere that meets your security requirements, such as from a mounted kubernetes secret:

secretKeyBytes, err := os.ReadFile("/path/to/secret-key")
if err != nil {
	return err
}

Create a Ghostifyer with the secret key and namespace in use:

gh, err := ghoststring.NewAES256GCMSingleKeyGhostifyer("heck.example.org", string(secretKeyBytes))
if err != nil {
	return err
}

Register the Ghostifyer:

if err := ghoststring.SetGhostifyer(gh); err != nil {
	return err
}

Use the declared type as with any other struct type:

msg := &Message{
	Recipient: "morningstar@heck.example.org",
	Content: ghoststring.GhostString{
		Namespace: "heck.example.org",
		Str:       "We meet me at the fjord at dawn. Bring donuts, please.",
	},
	Mood: ghoststring.GhostString{
		Namespace: "heck.example.org",
		Str:       "giddy",
	},
}

When the type instance is encoded to JSON, the GhostString fields will automatically encode to a JSON string type:

{
  "recipient": "morningstar@heck.example.org",
  "content": "👻:NTNjZjdmMWZjNzU2NTY1ODFkN2E4ZDI4aGVjay5leGFtcGxlLm9yZzo60XHqdSEbswpPbKLrDUuBZCrtUQLjmJ1NxHsqHMgBJjrB10O7JC4rwiMZw+wf/BOJGmu9ZCpMjgMpu18/VgDBpLn4n1nBNw==",
  "mood": "👻:YmYzZDVjNDVhNTUyMTA1Mzg0ZWU0NjI0aGVjay5leGFtcGxlLm9yZzo6SML6iqmwSoDhX3b2SQXsMLJPMHHS"
}

In the event of an unrecognized namespace, the GhostString fields will be encoded as empty strings, e.g.:

msg := &Message{
	Recipient: "frith@heck.example.org",
	Content: ghoststring.GhostString{
		Namespace: "heck.example.org",
		Str:       "Next time I'm bringing the coffee.",
	},
	Mood: ghoststring.GhostString{
		Namespace: "wat.example.org",
		Str:       "zzz",
	},
}

Because the "wat.example.org" namespace isn't registered, the output will look like this:

{
  "recipient": "frith@heck.example.org",
  "content": "👻:NTNjZjdmMWZjNzU2NTY1ODFkN2E4ZDI4aGVjay5leGFtcGxlLm9yZzo60XHqdSEbswpPbKLrDUuBZCrtUQLjmJ1NxHsqHMgBJjrB10O7JC4rwiMZw+wf/BOJGmu9ZCpMjgMpu18/VgDBpLn4n1nBNw==",
  "mood": ""
}

Any system that needs to read the encrypted contents must decode the JSON into a type that uses GhostString for the matching fields in a process where a matching Ghostifyer has been registered. Other systems may treat the values as opaque strings.