alexxnica/spiped

Spiped is a utility for creating symmetrically encrypted and authenticated pipes between socket addresses.

spiped

Official signed releases are published at:

www.tarsnap.com/spiped.html

spiped (pronounced "ess-pipe-dee") is a utility for creating symmetrically encrypted and authenticated pipes between socket addresses, so that one may connect to one address (e.g., a UNIX socket on localhost) and transparently have a connection established to another address (e.g., a UNIX socket on a different system). This is similar to ssh -L functionality, but does not use SSH and requires a pre-shared symmetric key.

spipe (pronounced "ess-pipe") is a utility which acts as an spiped protocol client (i.e., connects to an spiped daemon), taking input from the standard input and writing data read back to the standard output.

Note that spiped:

1. Requires a strong key file: The file specified via the -k option should have at least 256 bits of entropy. (dd if=/dev/urandom bs=32 count=1 is your friend.)

2. Requires strong entropy from /dev/urandom. (Make sure your kernel's random number generator is seeded at boot time!)

3. Does not provide any protection against information leakage via packet timing: Running telnet over spiped will protect a password from being directly read from the network, but will not obscure the typing rhythm.

4. Can significantly increase bandwidth usage for interactive sessions: It sends data in packets of 1024 bytes, and pads smaller messages up to this length, so a 1 byte write could be expanded to 1024 bytes if it cannot be coalesced with adjacent bytes.

5. Uses a symmetric key -- so anyone who can connect to an spiped "server" is also able to impersonate it.

Example usage

To set up an encrypted and authenticated pipe for sending email between two systems (in the author's case, from many systems around the internet to his central SMTP server, which then relays email to the rest of the world), one might run

dd if=/dev/urandom bs=32 count=1 of=keyfile
spiped -d -s '[0.0.0.0]:8025' -t '[127.0.0.1]:25' -k keyfile

on a server and after copying keyfile to the local system, run

spiped -e -s '[127.0.0.1]:25' -t $SERVERNAME:8025 -k keyfile

at which point mail delivered via localhost:25 on the local system will be securely transmitted to port 25 on the server.

You can also use spiped to protect SSH servers from attackers: Since data is authenticated before being forwarded to the target, this can allow you to SSH to a host while protecting you in the event that someone finds an exploitable bug in the SSH daemon -- this serves the same purpose as port knocking or a firewall which restricts source IP addresses which can connect to SSH. On the SSH server, run

dd if=/dev/urandom bs=32 count=1 of=/etc/ssh/spiped.key
spiped -d -s '[0.0.0.0]:8022' -t '[127.0.0.1]:22' -k /etc/ssh/spiped.key

then copy the server's /etc/ssh/spiped.key to ~/.ssh/spiped_HOSTNAME_key on your local system and add the lines

Host HOSTNAME
ProxyCommand spipe -t %h:8022 -k ~/.ssh/spiped_%h_key

to the ~/.ssh/config file. This will cause ssh HOSTNAME to automatically connect using the spipe client via the spiped daemon; you can then firewall off all incoming traffic on port tcp/22.

For a detailed list of the command-line options to spiped and spipe, see the man pages.

Security requirements

The user is responsible for ensuring that:

1. The key file contains 256 or more bits of entropy.

2. The same key file is not used for more than 2^64 connections.

3. Any individual connection does not transmit more than 2^64 bytes.

Building

The official releases should build and install on almost any POSIX-compliant operating system, using the included Makefiles:

make BINDIR=/path/to/target/directory install

See the BUILDING file for more details (e.g. how to install man pages).

Testing

A small test suite can be run with:

make test

Code layout

spiped/*        -- Code specific to the spiped utility.
  main.c        -- Command-line parsing, initialization, and event loop.
  dispatch.c    -- Accepts connections and hands them off to protocol code.
spipe/*	        -- Code specific to the spipe utility.
  main.c        -- Command-line parsing, initialization, and event loop.
  pushbits.c    -- Copies data between standard input/output and a socket.
proto/*	        -- Implements the spiped protocol.
  _conn.c       -- Manages the lifecycle of a connection.
  _handshake.c  -- Performs the handshaking portion of the protocol.
  _pipe.c       -- Performs the data-shuttling portion of the protocol.
  _crypt.c      -- Does the cryptographic bits needed by _handshake and _pipe.
lib/dnsthread   -- Spawns a thread for background DNS (re)resolution.
libcperciva/*   -- Library code from libcperciva

More info

For more details about spiped, read the DESIGN.md file.