"Thee packets that are chosen needeth not fear purgatory, for thee shall be safe with my blessing. Confess thy sins and moveth into heaven."

Sanctum 1:1

This is a very small, reviewable, capable, experimental and fully privilege seperated VPN daemon capable of transporting encrypted network traffic between two peers.

WARNING: This code uses an experimental AEAD cipher based on Keccak-f[1600,24] to provide confidentiality and integrity for transmitted session keys during the key exchange.

Due to its privilege separated design, sanctum guarantees that all of its important assets are separated from the processes that talk to the internet or handle non-cryptography related things.

Whats with the weird mythology around this project?

It's fun, but it doesn't make it less of a serious project.

There are several processes that make up a sanctum instance:

Each process can run as its own user.

Each process is sandboxed and only has access to the system calls required to perform its task.

The processes share packets between each other in a very well defined way.

For incoming packets:

purgatory-rx (black) -> confess (decryption) -> heaven-tx (red)

For outgoing packets:

heaven-rx (red) -> bless (encrypt) -> purgatory-tx (black)

When the processes start they will remove any of the queues they do not need for operating.

As an example of why this is important, it is impossible for a packet that arrives on the plaintext interface to be moved to the ciphertext interface without passing the encryption process.

A sanctum instance is responsible for sending its RX key to the other side. It does this by periodically generating a new key uniformly at random and wrapping it with a secret derived from the underlying shared secret between both parties.

See docs/keys.md for details on the session key and shared secrets.

Note that sanctum only supports symmetrical keying and does not implement any asymmetrical key exchange method.

Your shared secret must be handled with great care and must be rotated often. When using a cathedral you can use the Ambry distribution to update shared secrets.

The encrypted traffic is encapsulated with ESP in tunnel mode, using incrementing 64-bit sequence numbers. The traffic is either encrypted with AES256-GCM or Agelas and are encrypted under keys exchanged as described above.

In both cases a 96-bit nonce constructed as follows is used:

nonce = 32-bit salt from key exchange || 64-bit packet counter

You can select what cipher to use by specifying a CIPHER environment variable at compile time with either:

• nyfe-agelas (Agelas as provided by Nyfe).
• openssl-aes-gcm (AES256-GCM via OpenSSL its low level API).
• intel-aes-gcm (AES256-GCM via Intel its highly performant libisal_crypto lib).

Sanctum supports unidirectional tunnels, this is called the pilgrim or shrine mode.

In pilgrim mode, sanctum will be able to send encrypted traffic to its shrine peer. It will however never send an RX key to its peer (a shrine).

In shrine mode, sanctum will be able to verify and decrypt the arriving traffic but will never receive a TX key from its peer.

This allows one-way traffic to flow from a pilgrim to the shrine with a strong guarantee that the shrine cannot send data back (there are no keys).

A cathedral is a sanctum mode that can run on a machine somewhere and will relay packets between tunnel end-points without being able to read, inject or modify packets.

Peers can use a cathedral to move to a peer-to-peer end-to-end encrypted connection if both peers are behind a not too restrictive NAT.

A cathedral may also be used as an Ambry distribution point for shared secret rollover.

Please read docs/cathedral.md for more.

A default build requires pkg-config and libssl-dev.

$ git clone https://github.com/jorisvink/sanctum
$ cd sanctum
$ make
# make install

If this is to complicated for you, this isn't your software.

Sanctum builds on MacOS 13+, OpenBSD 6.8+ and Linux-y things like Ubuntu 22.04.

Sanctum uses a configuration file. Find an example of a simple configuration below.

# Name of this sanctum instance.
instance laptop

# Path to the shared secret.
secret /etc/sanctum/laptop_secret.key

# The control socket for pontifex.
run control as joris
control /tmp/sanctum-control joris

# The tunnel configuration
tunnel 1.0.0.1/30 1422

# Add additional routes over the tunnel
route 2.0.0.0/24

# The local address to which sanctum binds.
local x.x.x.x:2333

# Optional peer address, ignore if you have a peer that
# moves networks a lot.
peer y.y.y.y:2333

# The encryption and decryption processes.
run bless as _bless
run confess as _confess

# Run the internal io processes as one user.
run heaven-rx as _heaven
run heaven-tx as _heaven

# Run the external io processes as another.
run purgatory-rx as _purgatory
run purgatory-tx as _purgatory

# Run chapel for the key exchange as yet another user.
run chapel as _chapel