LLARP v0

LLARP (Low Latency Anon Routing Protocol) is a protocol for anonymizing senders and
recipiants of encrypted messages sent over the internet without a centralied
trusted party.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

basic structures:

all structures are key, value dictionaries encoded with bittorrent encoding
notation:

a + b is a concatanated with b

a ^ b is a bitwise XOR b

x[a:b] is a memory slice of x from index a to b

BE(x) is bittorrent encode x

BD(x) is bittorrent decode x

{ a: b, y: z } is a dictionary with two keys a and y
    who's values are b and z respectively

[ a, b, c ... ] is a list containing a b c and more items in that order

"<description>" is a bytestring who's contents and length is described by the
    quoted value <description>

"<value>" * N is a bytestring containing the <value> concatenated N times.

cryptography:

see crypto_v0.txt

---

wire protocol

see iwp-v0.txt

---

datastructures:

all datastructures are assumed version 0 if they lack a v value
otherwise version is provided by the v value

all ip addresses can be ipv4 via hybrid dual stack ipv4 mapped ipv6 addresses,
i.e ::ffff.8.8.8.8. The underlying implementation MAY implement ipv4 as native
ipv4 instead of using a hybrid dual stack.

net address:

net addresses are a variable length byte string, if between 7 and 15 bytes it's
treated as a dot notation ipv4 address (xxx.xxx.xxx.xxx)
if it's exactly 16 bytes it's treated as a big endian encoding ipv6 address.

address info (AI)

An address info (AI) defines a publically reachable endpoint

{
  c: transport_rank_uint16,
  d: "<transport dialect name>",
  e: "<32 bytes public encryption key>",
  i: "<net address>",
  p: port_uint16,
  v: 0
}

example iwp address info:

{
  c: 1,
  d: "iwp",
  e: "<32 bytes of 0x61>",
  i: "123.123.123.123",
  p: 1234,
  v: 0
}

bencoded form:

d1:ci1e1:d3:iwp1:e32:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa1:d3:iwp1:i15:123.123.123.1231:pi1234e1:vi0ee

Exit Info (XI)

An exit info (XI) defines a exit address that can relay exit traffic to the 
internet.

{
  a: "<net address exit address>",
  b: "<net address exit netmask>",
  k: "<32 bytes public encryption/signing key>",
  v: 0
}


Exit Route (XR)

An exit route (XR) define an allocated exit address and any additional
information required to access the internet via that exit address.

{
  a: "<16 bytes big endian ipv6 gateway address>",
  b: "<16 bytes big endian ipv6 netmask>",
  c: "<16 bytes big endian ipv6 source address>",
  l: lifetime_in_seconds_uint64,
  v: 0
}

router contact (RC)

router's full identity

{
  a: [ one, or, many, AI, here ... ],
  k: "<32 bytes public long term identity signing key>",
  n: "<optional max 32 bytes router nickname>",
  p: "<32 bytes public path encryption key>",   
  u: last_updated_seconds_since_epoch_uint64,
  v: 0,
  x: [ Exit, Infos ],
  z: "<64 bytes signature using identity key>"
}

service info (SI)

public information blob for a hidden service

e is the long term public encryption key
s is the long term public signing key
v is the protocol version
x is a nounce value for generating vanity addresses that can be omitted

if x is included it MUST be equal to 16 bytes

{
  e: "<32 bytes public encryption key>",
  s: "<32 bytes public signing key>",
  v: 0,
  x: "<optional 16 bytes nonce for vanity>"
}

service address (SA)

the "network address" of a hidden service, which is computed as the blake2b
256 bit hash of the public infomration blob.

HS(BE(SI))

when in string form it's encoded with z-base32 and uses the .loki tld

introduction (I)

a descriptor annoucing a path to a hidden service

k is the rc.k value of the router to contact
p is the path id on the router that is owned by the service
v is the protocol version
x is the timestamp seconds since epoch that this introduction expires at

{
  k: "<32 bytes public identity key of router>",
  l: advertised_path_latency_ms_uint64, (optional)
  p: "<16 bytes path id>",
  v: 0,
  x: time_expires_seconds_since_epoch_uint64
}

introduction set (IS)

a signed set of introductions for a hidden service
a is the service info of the publisher
i is the list of introductions that this service is advertising with
k is the public key to use when doing encryption to this hidden service
n is a 16 byte null padded utf-8 encoded string tagging the hidden service in 
  a topic searchable via a lookup (optional)
v is the protocol version
w is an optinal proof of work for DoS protection (slot for future)
z is the signature of the entire IS where z is set to zero signed by the hidden
service's signing key.

{
  a: SI,
  i: [ I, I, I, ... ],
  k: "<1218 bytes sntrup4591761 public key block>",
  n: "<16 bytes service topic (optional)>", 
  v: 0,
  w: optional proof of work,
  z: "<64 bytes signature using service info signing key>"
}


---

Encrypted frames:


Encrypted frames are encrypted containers for link message records like LRCR.

32 bytes hmac, h
32 bytes nounce, n
32 bytes ephmeral sender's public encryption key, k
remaining bytes ciphertext, x

decryption:

0) verify hmac

S = PKE(n, k, our_RC.K)
verify h == MDS(n + k + x, S)

If the hmac verification fails the entire parent message is discarded

1) decrypt and decode

new_x = SD(S, n[0:24], x)
msg = BD(new_x)

If the decoding fails the entire parent message is discarded

encryption:

to encrypt a frame to a router with public key B.k

0) prepare nounce n, ephemeral keypair (A.k, s) and derive shared secret S

A.k, s = ECKG()
n = RAND(32)
S = PKE(p, A.k, B.k, n)

1) encode and encrypt

x = BE(msg)
new_x = SE(S, n[0:24], x)

2) generate message authentication

h = MDS(n + A.k + new_x, S)

resulting frame is h + n + A.k + new_x


---

link layer messages:

the link layer is responsible for anonymising the source and destination of
routing layer messages.

any link layer message without a key v is assumed to be version 0 otherwise
indicates the protocol version in use.



link introduce message (LIM)

This message MUST be the first link message sent before any others. This message
identifies the sender as having the RC contained in r. The recipiant MUST
validate the RC's signature and ensure that the public key in use is listed in
the RC.a matching the ipv6 address it originated from.

{
  a: "i",
  n: "<32 bytes nonce for key exhcange>",
  p: uint64_milliseconds_session_period,
  r: RC,
  v: 0,
  z: "<64 bytes signature of entire message by r.k>"
}

the link session will be kept open for p milliseconds after which
the session MUST be renegotiated.

link relay commit message (LRCM)

request a commit to relay traffic to another node.

{
  a: "c",
  c: [ list, of, encrypted, frames ],
  v: 0
}

c and r MUST contain dummy records if the hop length is less than the maximum
hop length.

link relay commit record (LRCR)

record requesting relaying messages for 600 seconds to router
on network who's i is equal to RC.k and decrypt data any messages using
PKE(n, rc.K, c) as symettric key for encryption and decryption.

if l is provided and is less than 600 and greater than 10 then that lifespan 
is used (in seconds) instead of 600 seconds.

if w is provided and fits the required proof of work then the lifetime of
the path is extended by w.y seconds

{
  c: "<32 byte public encryption key used for upstream>",
  i: "<32 byte RC.k of next hop>",
  l: uint_optional_lifespan,
  n: "<32 bytes nounce for key exchange>",
  r: "<16 bytes rx path id>",
  t: "<16 bytes tx path id>",
  v: 0,
  w: proof of work
}

w if provided is a dict with the following struct 

{
  t: time_created_seconds_since_epoch,
  v: 0,
  y: uint32_seconds_extended_lifetime,
  z: "<32 bytes nonce>"
}

the validity of the proof of work is that given 

h = HS(BE(w))
 
h has log_e(y) prefixed bytes being 0x00

this proof of work requirement is subject to change 

if i is equal to RC.k then any LRDM.x values are decrypted and interpreted as
routing layer messages. This indicates that we are the farthest hop in the path.

link relay upstream message (LRUM)

sent to relay data via upstream direction of a previously created path.

{
  a: "u",
  p: "<16 bytes path id>",
  v: 0,
  x: "<N bytes encrypted x1 value>",
  y: "<32 bytes nonce>"
}

x1 = SD(k, y, x)

if we are the farthest hop, process x1 as a routing message
otherwise transmit a LRUM to the next hop

{
  a: "u",
  p: p,
  v: 0,
  x: x1,
  y: y ^ HS(k)
}

link relay downstream message (LRDM)

sent to relay data via downstream direction of a previously created path.

{
  a: "d",
  p: "<16 bytes path id>",
  v: 0,
  x: "<N bytes encrypted x1 value>",
  y: "<32 bytes nonce>"
}

if we are the creator of the path decrypt x for each hop key k

x = SD(k, y, x)

otherwise transmit LRDM to next hop

x1 = SE(k, y, x)

{
  a: "d",
  p: p,
  v: 0,
  x: x1,
  y: y ^ HS(k)
}

link immediate dht message (LIDM):

transfer one or more dht messages directly without a previously made path.

{
  a: "m",
  m: [many, dht, messages],
  v: 0
}


link stateless relay message (LSRM)

statelessly relay a link message.

{
  a: "r",
  c: r_counter_uint8,
  d: "<32 bytes rc.K of destination>",
  s: "<32 bytes rc.K of source>",
  v: 0,
  x: "<N bytes encrypted link message>",
  y: "<24 bytes nounce>",
  z: "<64 bytes signature>"
}

ONLY exchanged over ethernet, if recieved from an IP link it MUST be discarded.

relay an encrypted link message from source s to destination d.
check signature z using public key s and discard if invalid signature.

if d is equal to ourRC.k then decrypt x via SD(KE(d, s), y, x) and process it as
a link message. if the inner decrypted link message is a LRCM forward all
following LRUM, LRDM and LRSM to s via a LSRM. LIDM and LSRM are discarded.

if d is not equal to ourRC.k then forward it to an ethernet peer that is cloeser
to d than you are. if you are closer to d than all of your other ethernet peers
then increment c and send to the ethernet peer with the lowest detected latency
that isn't the peer that this message was recieved from but ONLY if c is less
than 128. if c is equal to or greater than 128 then the message is discarded.

---

routing layer:

the routing layer provides inter network communication between the LLARP link
layer and ip (internet protocol) for exit traffic or ap (anonymous protocol) for
hidden services. replies to messages are sent back via the path they
originated from inside a LRDM. all routing messages have an S value which
provides the sequence number of the message so the messages can be ordered.

ipv4 addresses are allowed via ipv4 mapped ipv6 addresses, i.e. ::ffff.10.0.0.1

path confirm message (PCM)

sent as the first message down a path after it's built to confirm it was built

always the first message sent

{
  A: "P",
  L: uint64_milliseconds_path_lifetime,
  S: 0,
  T: uint64_milliseconds_sent_timestamp,
  V: 0
}

path latency message (PLM)

a latency measurement message, reply with a PLM response if we are the far end
of a path.

variant 1, request, generated by the path creator:

{
  A: "L",
  S: uint64_sequence_number,
  V: 0
}

variant 2, response, generated by the endpoint that recieved the request.

{
  A: "L",
  S: uint64_sequence_number,
  T: uint64_timestamp_recieved,
  V: 0
}

obtain exit address message (OXAM)

sent to an exit router to obtain a NAT ip address for ip exit traffic.
replies are sent down the path that messages originate from.

{
  A: "X",
  I: "<32 bytes signing public key for future communication>",
  S: uint64_sequence_number,
  T: uint64_transaction_id,
  V: 0,
  X: lifetime_of_address_mapping_in_seconds_uint64,
  Z: "<64 bytes signature using I>"
}

grant exit address messsage (GXAM)

sent in response to an OXAM to grant an ip for exit traffic from an external
ip address used for exit traffic.

{
  A: "G",
  E: XR,
  I: "<32 bytes signing public key of requester>",
  S: uint64_sequence_number,
  T: transaction_id_uint64,
  V: 0,
  Z: "<64 bytes signature using exit info's signing key>"
}

E contains an exit route that was granted to the requester that can be used with
IP exit traffic.

The requester will now have any ip traffic going to address S forwarded to them
via the path that originally sent the OXAM and any TDFM will is recieved on the
same path will be forwarded out to the internet, given that they have
valid signatures and addresses.


reject exit address message (RXAM)

sent in response to an OXAM to indicate that exit traffic is not allowed or
was denied.

{
  A: "J",
  B: backoff_milliseconds_uint64,
  I: "<32 bytes signing public key of requester>",
  R: "<optional reject metadata>",
  S: uint64_sequence_number,
  T: transaction_id_uint64,
  V: 0,
  Z: "<64 bytes signature signed by exit info's signing key>"
}

B is set to a backoff value.
R contains additional metadata text describing why the exit was rejected.


discarded data fragment message (DDFM)

sent in reply to TDFM when we don't have a path locally or are doing network
congestion control. indcates a TDFM was discarded.

{
  A: "D",
  P: "<16 bytes path id>",
  S: uint64_sequence_number_of_fragment_dropped,
  V: 0
}

transfer data fragment message (TDFM)

transfer data between paths.

{
  A: "T",
  P: "<16 bytes path id>",
  S: uint64_sequence_number,
  T: hidden_service_frame,
  V: 0
}

transfer data to another path with id P on the local router place a random 32
byte and T values into y and z values into a LRDM message (respectively) and
send it in the downstream direction. if this path does not exist on the router
it is replied to with a DDFM.



hidden service data (HSD)

data sent anonymously over the network to a recipiant from a sender.
sent inside a HSFM encrypted with a shared secret.

{
  a: protocol_number_uint,
  d: "<N bytes payload>",
  i: Introduction for reply,
  n: uint_message_sequence_number,
  o: N seconds until this converstation plans terminate,
  s: SI of sender,
  t: "<16 bytes converstation tag present only when n is 0>",
  v: 0
}


hidden service frame (HSF)

TODO: document this better

intro message (variant 1)

start a new session

{
  A: "H",
  C: "<1048 bytes ciphertext block>",
  D: "<N bytes encrypted HSD>",
  N: "<32 bytes nonce for key exchange>",
  V: 0,
  Z: "<64 bytes signature of entire message using sender's signing key>"
}

alice (A) wants to talk to bob (B) over the network, both have hidden services
set up and are online on the network. 

A and B are both SI.
A_sk is alice's private signing key.

for alice (A) to send the string "beep" to bob (B), alice picks an introduction
to use on one of her paths (I_A) such that I_A is aligning with one of bobs's 
paths (I_B)

alice generates:

T = RAND(16)

m = {
  a: 0,
  d: "beep",
  i: I_A,
  n: 0,
  s: A,
  t: T,
  v: 0
}

X = BE(m)

C, K = PQKE_A(I_B.k)
N = RAND(32)
D = SE(X, K, N)

M = {
  A: "T",
  P: I_B.P,
  S: uint64_sequence_number,
  T: {
    A: "H",
    C: C,
    D: D,
    N: N,
    V: 0,
    Z: "\x00" * 64
  },
  V: 0
}

Z = S(A_sk, BE(M))

alice transmits a TDFM to router with public key I_B.K via her path that ends 
with router with public key I_B.k

{
  A: "T",
  P: I_B.P,
  S: uint64_sequence_number,
  T: {
    A: "H",
    C: C,
    D: D,
    N: N,
    V: 0,
    Z: Z
  },
  V: 0
}

the shared secret (S) for further message encryption is:

S = HS(K + PKE(A, B, sk, N))

given sk is the local secret encryption key used by the current hidden service

please note:
signature verification can only be done after decryption

TODO: explain bob's side too (it's invsere of alice's process)

data from a previously made session (variant 2)

transfer data on a session previously made

{
  A: "H",
  D: "<N bytes encrypted HSD>",
  N: "<32 bytes nonce for symettric cipher>",
  T: "<16 bytes converstation tag>",
  V: 0,
  Z: "<64 bytes signature using sender's signing key>"
}


transfer ip traffic message (TITM)

transfer ip traffic for exit

{
  A: "E",
  S: uint64_sequence_number,
  V: 0,
  X: "<N bytes ip packet>",
  Y: "<16 bytes nounce>",
  Z: "<64 bytes signature using previously provided signing key>"
}

X is parsed as an IP packet and the source addresss is extracted.
Next we find the corrisponding signing key for a previously granted exit address
and use it to validate the siganture of the entire message. If the signing key
cannot be found or the signature is invalid this message is dropped, otherwise
the X value is sent on the appropriate exit network interface.

When we recieve an ip packet from the internet to an exit address, we put it
into a TITM, signed with the exit info's signing key and send it downstream the
corrisponding path in an LRDM.

update exit path message (UXPM)

sent from a new path by client to indicate that a previously established exit
should use the new path that this message came from.

{
  A: "U",
  S: uint64_sequence_number,
  T: transaction_id_uint64,
  V: 0,
  Y: "<16 bytes nounce>",
  Z: "<64 bytes signature using previously provided signing key>"
}

T is the transaction ID from the GXAM

close exit path message (CXPM)

client sends a CXPM when the exit is no longer needed.
The address used in exit MAY be reused later.

{
  A: "C",
  S: uint64_sequence_number,
  T: transaction_id_uint64,
  V: 0,
  Y: "<16 bytes nounce>",
  Z: "<64 bytes signagure using previously provided signing key>"
}

DHT message holder message:

wrapper message for sending many dht messages down a path.

{
  A: "M",
  M: [many, dht, messages, here],
  S: uint64_sequence_number,
  V: 0
}