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Go Keyless

Build Status GoDoc

Keyless SSL implementation in Go

Go Keyless is an implementation CloudFlare's Keyless SSL Protocol in Go. It is provided as an upgrade to the previous C implementation.

Protocol

The CloudFlare Keyless SSL client communicates to the server via a binary protocol over a mutually authenticated TLS 1.2 tunnel. Messages are in binary format and identified by a unique ID.

Messages consist of a fixed length header, and a variable length body. The body of the message consists of a sequence of items in TLV (tag, length, value) messages.

All messages with major version 1 will conform to the following format. The minor version is currently set to 0 and is reserved for communicating policy information.

Header:

0 - - 1 - - 2 - - 3 - - 4 - - - - 6 - - 7 - - 8
| Maj | Min |   Length  |          ID           |
|                    Body                       |
|     Body     | <- 8 + Length

Item:

0 - - 1 - - 2 - - 3 - - 4 - - - - 6 - - 7 - - 8
| Tag |   Length  |          Data               |
|           Data             | <- 3 + Length

All numbers are in network byte order (big endian).

The following tag values are possible for items:

0x01 - Certificate Digest,
0x02 - Server Name Indication,
0x03 - Client's IP address,
0x11 - Opcode,
0x12 - Payload,

A requests contains a header and the following items:

0x01 - length: 32 bytes, data: SHA256 of RSA modulus
0x02 - length: variable, data: SNI string
0x03 - length: 4 or 16 bytes, data: IPv4/6 address
0x11 - length: 1, data: opcode describing operation
0x12 - length: variable, data: payload to sign or encrypt

The following opcodes are supported in the opcode item:

0x01 - operation: RSA decrypt payload 
0x02 - operation: RSA sign MD5SHA1
0x03 - operation: RSA sign SHA1
0x04 - operation: RSA sign SHA224
0x05 - operation: RSA sign SHA256
0x06 - operation: RSA sign SHA384
0x07 - operation: RSA sign SHA512
0x08 - operation: RSA raw decrypt payload
0x12 - operation: ECDSA sign MD5SHA1
0x13 - operation: ECDSA sign SHA1
0x14 - operation: ECDSA sign SHA224
0x15 - operation: ECDSA sign SHA256
0x16 - operation: ECDSA sign SHA384
0x17 - operation: ECDSA sign SHA512

Responses contain a header with a matching ID and only two items:

0x11 - length: 1, data: opcode describing operation status
0x12 - length: variable, data: payload response

The following opcodes are supported in the opcode item:

0xF0 - operation: success, payload: modified payload
0xFF - operation: RSA decrypt payload, payload:

On an error, these are the possible 1-byte payloads:

0x01 - cryptography failure
0x02 - key not found - no matching certificate ID
0x03 - read error - disk read failure
0x04 - version mismatch - unsupported version incorrect
0x05 - bad opcode - use of unknown opcode in request
0x06 - unexpected opcode - use of response opcode in request
0x07 - format error - malformed message
0x08 - internal error - memory or other internal error

Defines and further details of the protocol can be found in kssl.h

Image

Key Management

The Keyless SSL server is a TLS server and therefore requires cryptographic keys. All requests are mutually authenticated, so both the client and the server need a TLS 1.2 compatible key pair. The client must present a client certificate that can be verified against the CA that the keyless server is configured to use.

The server will need a valid key and certificate pair in PEM format. The following options are required and take a path to these files. These two parameters set up the certificate (and associated private key) that will be presented by the server when a client connects.

 --server-cert 
 --server-key

The private keys that this server is able to use should be stored in PEM format in a directory denoted by the option:

--private-key-directory

In order to authenticate the client's certificate, a custom CA file is required. This CA file available is provided by CloudFlare and specified with:

--ca-file

Deploying

Installing

Package Installation

Instructions for installing Go Keyless from .deb and .rpm packages can be found at https://pkg.cloudflare.com.

Source Installation

Compiling Go Keyless requires Go 1.5. Binary distributions can be found at golang.org/dl, under go1.5.

Installing the appropriate package for your operating system should leave you with a working Go installation and a properly set GOPATH.

$ go get -u github.com/cloudflare/gokeyless/...
$ go install github.com/cloudflare/gokeyless/cmd/gokeyless/...

Running

Command-line Arguments

This is the keyserver for Keyless SSL. It consists of a single binary file gokeyless that has the following command-line options:

  • -port (optional) The TCP port on which to listen for connections. These connections must be TLSv1.2. Defaults to 2407.
  • -ca-file Path to a PEM-encoded file containing the CA certificate(s) used to sign client certificates presented on connection.
  • -cert, -key Path to PEM-encoded files containing the certificate and private key that are used when a connection is made to the server. These must be signed by an authority that the client side recognizes.
  • --private-key-directory Path to a directory containing private keys which the keyserver provides decoding service against. The key files must end with ".key" and be PEM-encoded. There should be no trailing / on the path.
  • -loglevel (optional) Level of logging as defined here. Defaults to LevelInfo.
  • -pid-file (optional) Path to a file into which the PID of the keyserver. This file is only written if the keyserver starts successfully.

License

See the LICENSE file for details. Note: the license for this project is not 'open source' as described in the Open Source Definition.