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mu-tunnel

Service which allows tunneling of HTTP requests between semantic.works stacks securely using the OpenPGP standard.

API

mu-tunnel only takes requests from other services on the /out endpoint using POST.

The POST body should be a JSON object with the following properties:

  • peer: The identity of the destination stack. This is the email address associated with the PGP key for that stack.
  • url: The URL that a request should be forwarded to in the destination stack. This includes the protocol, the hostname, the path and any query parameters if desired.
  • method: The method to use for the request.
  • headers (optional): A JSON object mapping HTTP headers to their value.
  • body (optional): The base64 encoded request body.

The response to this request will be the same as if the endpoint specified in url was contacted directly and requires no special parsing or treatment.

An example request:

{
  "peer": "[email protected]",
  "url": "http://service/endpoint",
  "method": "POST",
  "headers": {
    "Content-Type": "text/plain",
    "Accept": "application/vnd.api+json"
  },
  "body": "cXdmcGFyc3R6eGNkZnBncnN0ZndwdHR2Y2Rxd2ZzdHBmYnRnc2R2YXI="
}

The /secure endpoint is where encrypted messages from peers arrive and should not be used by other services.

Config

Keys are stored in armored form in /config/keys/.

The configuration file is stored at /config/config.json.

The configuration object has the following properties:

  • self: An object containing information about this tunnel node:
    • identity: The identity of this node and the private key used by this node.
    • file: The file storing this node’s private key. This key should be passphrase-protected.
    • passphrase: The passphrase to decrypt this node’s private key.
  • peers: An array of peer objects:
    • identity: The identity of this peer and its public key.
    • file: The file storing this peer’s public key.
    • address (optional): The external endpoint where this peer can be reached to forward requests. If not present, this tunnel cannot initiate messages to this peer, only receive them.
    • allowed (optional): An array of strings indicating the path prefixes this peer is allowed to request. If not present, all incoming requests are rejected.

An example configuration file:

{
  "self": {
    "identity": "[email protected]",
    "file": "producer.asc",
    "passphrase": "hunter2"
  },
  "peers": [
    { "identity": "[email protected]",
      "file": "consumer1.asc",
      "allowed": ["http://identifier/sync/files", "http://identifier/files/"]
    },
    { "identity": "[email protected]",
      "file": "consumer2.asc",
      "address": "http://tunnel-consumer2/secure"
    }
  ]
}

HTTPS

This service must be ran over HTTPS for strong security. Without HTTPS messages can easily be intercepted and replayed at a later date, due to PGPs one-pass nature.

Scripts

This service includes mu-cli scripts for key and configuration management:

  • gen-privkey: Generate a new elliptic curve GPG key for use with mu-tunnel
  • gen-pubkey: Convert a private GPG key file into a public GPG key file.
  • config-self: Configure this tunnel service by changing the settings of the key.
  • config-peer: Configure the peers this service connects to.

Keys

RSA and other algorithms over integer fields can be quite slow, as they require very large keys. Elliptic curves offer similar security with smaller key sizes (256 bits instead of 4096 bits) and are thus much faster.

Therefore it is recommended to use elliptic curve keys with this service. Modern versions of gpg support elliptic curves, but the --expert flag must be passed to generate these keys.

Curve25519 is a widely used elliptic curve which is also rigid, unlike the NIST curves. It is thus a good choice.

The following are instructions to manually generate keys. However, the included mu-cli scripts can also be used for this (and should be easier to use).

To generate a new GPG key:

gpg --expert --full-generate-key

Follow the instructions and do not use a (sign only) or (set your own capabilities) key. Elliptic curves may be selected by choosing ECC and ECC.

To export a private key to a file:

gpg --export-secret-keys --armor [email protected] > privatekey.asc

To export a public key to a file:

gpg --export --armor [email protected] > publickey.asc