The I2P Network Protocol (I2NP), which is sandwiched between I2CP and the various I2P transport protocols, manages the routing and mixing of messages between routers, as well as the selection of what transports to use when communicating with a peer for which there are multiple common transports supported.
Common header to all I2NP messages, which contains important information like a checksum, expiration date, etc.
1 byte Integer specifying the type of this message, followed by a 4 byte Integer specifying the message-id. After that there is an expiration Date, followed by a 2 byte Integer specifying the length of the message payload, followed by a Hash, which is truncated to the first byte. After that the actual message data follows.
{% filter escape %}
Standard (16 bytes):
+----+----+----+----+----+----+----+----+
|type| msg-id | expiration
+----+----+----+----+----+----+----+----+
| size |chks|
+----+----+----+----+----+----+----+----+
Short (SSU, 5 bytes):
+----+----+----+----+----+
|type| short expiration |
+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
type :: Integer
length -> 1 byte
purpose -> identifies the message type (see table below)
msg-id :: Integer
length -> 4 bytes
purpose -> uniquely identifies this message (for some time at least)
This is usually a locally-generated random number, but for
outgoing tunnel build messages it may be derived from
the incoming message. See below.
expiration :: Date
8 bytes
date this message will expire
short expiration :: Integer
4 bytes
date this message will expire (seconds since the epoch)
size :: Integer
length -> 2 bytes
purpose -> length of the payload
chks :: Integer
length -> 1 byte
purpose -> checksum of the payload
SHA256 hash truncated to the first byte
data :: Data
length -> $size bytes
purpose -> actual message contents
{% endfilter %}
One Record in a set of multiple records to request the creation of one hop in the tunnel. For more details see the tunnel overview and the tunnel creation specification.
TunnelId to receive messages on, followed by the Hash of our RouterIdentity. After that the TunnelId and the Hash of the next router's RouterIdentity follow.
{% filter escape %}
Cleartext:
+----+----+----+----+----+----+----+----+
| receive_tunnel | our_ident |
+----+----+----+----+ +
| |
+ +
| |
+ +
| |
+ +----+----+----+----+
| | next_tunnel |
+----+----+----+----+----+----+----+----+
| next_ident |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| layer_key |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| iv_key |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| reply_key |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| reply_iv |
+ +
| |
+----+----+----+----+----+----+----+----+
|flag| request_time | send_msg_id
+----+----+----+----+----+----+----+----+
| |
+----+ +
| 29 bytes padding |
+ +
| |
+ +----+----+
| |
+----+----+----+----+----+----+
ElGamal encrypted:
+----+----+----+----+----+----+----+----+
| toPeer |
+ +
| |
+----+----+----+----+----+----+----+----+
| encrypted data ... |
~ ~
| |
+----+----+----+----+----+----+----+----+
ElGamal and AES encrypted:
+----+----+----+----+----+----+----+----+
| encrypted data ... |
~ ~
| |
+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
unencrypted:
receive_tunnel :: TunnelId
length -> 4 bytes
our_ident :: Hash
length -> 32 bytes
next_tunnel :: TunnelId
length -> 4 bytes
next_ident :: Hash
length -> 32 bytes
layer_key :: SessionKey
length -> 32 bytes
iv_key :: SessionKey
length -> 32 bytes
reply_key :: SessionKey
length -> 32 bytes
reply_iv :: data
length -> 16 bytes
flag :: Integer
length -> 1 byte
request_time :: Integer
length -> 4 bytes
Hours since the epoch, i.e. current time / 3600
send_message_id :: Integer
length -> 4 bytes
padding :: Data
length -> 29 bytes
source -> random
total length: 222
ElGamal encrypted:
toPeer :: First 16 bytes of the SHA-256 Hash of the peer's router identity
length -> 16 bytes
encrypted_data :: ElGamal-2048 encrypted data (see notes)
length -> 512
total length: 528
ElGamal and AES encrypted:
encrypted_data :: ElGamal and AES encrypted data
length -> 528
total length: 528
{% endfilter %}
{% filter escape %}
unencrypted:
+----+----+----+----+----+----+----+----+
| |
+ +
| |
+ SHA-256 Hash of following bytes +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| random data... |
~ ~
| |
+ +----+
| |ret |
+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
unencrypted:
bytes 0-31 : SHA-256 Hash of bytes 32-527
bytes 32-526 : random data
byte 527 : reply
encrypted:
bytes 0-527: AES-encrypted record(note: same size as BuildRequestRecord)
total length: 528
{% endfilter %}
{% filter escape %}
unencrypted:
+----+----+----+----+----+----+----+----+
| Delivery Instructions |
~ ~
~ ~
| |
+----+----+----+----+----+----+----+----+
| I2NP Message |
~ ~
~ ~
| |
+----+----+----+----+----+----+----+----+
| Clove ID | Expiration
+----+----+----+----+----+----+----+----+
| Certificate |
+----+----+----+----+----+----+----+
{% endfilter %}
unencrypted: Delivery Instructions :: as defined here Length varies but is typically 39, 43, or 47 bytes I2NP Message :: Any I2NP Message Clove ID :: 4 byte Integer Expiration :: Date (8 bytes) Certificate :: Always NULL in the current implementation (3 bytes total, all zeroes)
| Message | Type |
|---|---|
| DatabaseStore | 1 |
| DatabaseLookup | 2 |
| DatabaseSearchReply | 3 |
| DeliveryStatus | 10 |
| Garlic | 11 |
| TunnelData | 18 |
| TunnelGateway | 19 |
| Data | 20 |
| TunnelBuild | 21 |
| TunnelBuildReply | 22 |
| VariableTunnelBuild | 23 |
| VariableTunnelBuildReply | 24 |
An unsolicited database store, or the response to a successful Database Lookup Message
An uncompressed LeaseSet or a compressed RouterInfo
with reply token: +----+----+----+----+----+----+----+----+ | SHA256 Hash as key | + + | | + + | | + + | | +----+----+----+----+----+----+----+----+ |type| reply token | reply tunnel- +----+----+----+----+----+----+----+----+ Id | SHA256 of the gateway RouterInfo | +----+ + | | + + | | + + | | + +----+----+----+----+----+----+----+ | | data ... +----+--------\\ with reply token == 0: +----+----+----+----+----+----+----+----+ | SHA256 Hash as key | + + | | + + | | + + | | +----+----+----+----+----+----+----+----+ |type| 0 | data ... +----+-------------------+---------\\
key:
32 bytes
SHA256 hash
type:
1 byte
type identifier
mapping:
0 RouterInfo
1 LeaseSet
reply token:
4 bytes
If greater than zero, a Delivery Status Message
is requested with the Message ID set to the value of the Reply Token.
A floodfill router is also expected to flood the data to the closest floodfill peers
if the token is greater than zero.
reply tunnelId:
4 byte Tunnel ID
only included if reply token > 0
This is the tunnel ID of the inbound gateway of the tunnel the response should be sent to
reply gateway:
32 bytes
Hash of the routerInfo entry to reach the gateway
only included if reply token > 0
This is the router hash of the inbound gateway of the tunnel the response should be sent to
data:
If type == 0, data is a 2-byte integer specifying the number of bytes that follow, followed by a gzip-compressed RouterInfo.
If type == 1, data is an uncompressed LeaseSet.
A request to look up an item in the network database. The response is either a DatabaseStore or a DatabaseSearchReply.
{% filter escape %}
+----+----+----+----+----+----+----+----+
| SHA256 hash as the key to look up |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
| SHA256 hash of the routerInfo |
+ who is asking, or the gateway to +
| send the reply to |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
|flag| reply tunnelId |size | |
+----+----+----+----+----+----+----+ +
| SHA256 of $key1 to exclude |
+ +
| |
+ +
| |
+ +----+
| | |
+----+----+----+----+----+----+----+ +
| SHA256 of $key2 to exclude |
+ +
~ ~
+ +----+
| | |
+----+----+----+----+----+----+----+ +
| |
+ +
| Session key if reply encryption |
+ was requested +
| |
+ +----+
| |tags|
+----+----+----+----+----+----+----+----+
| |
+ +
| Session tags if reply encryption |
+ was requested +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
key:
32 bytes
SHA256 hash of the object to lookup
from:
32 bytes
If deliveryFlag == 0, the SHA256 hash of the routerInfo entry this request came from (and to which the reply should be sent)
If deliveryFlag == 1, the SHA256 hash of the reply tunnel gateway (to which the reply should be sent)
flags:
1 byte
bit order: 76543210
bit 0: deliveryFlag
0 => send reply directly
1 => send reply to some tunnel
bit 1: encryptionFlag
Through release 0.9.5, must be set to 0
As of release 0.9.6, ignored
As of release 0.9.7:
0 => send unencrypted reply
1 => send AES encrypted reply using enclosed key and tag
bits 7-2:
Through release 0.9.5, must be set to 0
As of release 0.9.6, ignored, set to 0 for compatibility with future uses and with older routers
reply tunnelId:
4 byte Tunnel ID
only included if deliveryFlag == 1
tunnelId of the tunnel to send the reply to
size:
2 byte Integer
valid range: 0-512
number of peers to exclude from the Database Search Reply Message
excludedPeers:
$size SHA256 hashes of 32 bytes each (total $size*32 bytes)
If the lookup fails, these peers are requested to be excluded from the list in
the Database Search Reply Message.
If excludedPeers includes a hash of all zeroes, the request is exploratory, and
the Database Search Reply Message is requested to list non-floodfill routers only.
reply key:
32 byte SessionKey
Only included if encryptionFlag == 1, only as of release 0.9.7
tags:
1 byte Integer
valid range: 1-32 (typically 1)
The number of reply tags that follow
Only included if encryptionFlag == 1, only as of release 0.9.7
reply tags:
One or more 32 byte SessionTags (typically one)
Only included if encryptionFlag == 1, only as of release 0.9.7
{% endfilter %}
The response to a failed Database Lookup Message
A list of router hashes closest to the requested key
{% filter escape %}
+----+----+----+----+----+----+----+----+
| SHA256 hash as query key |
+ +
| |
+ +
| |
+ +
| |
+----+----+----+----+----+----+----+----+
|num | peer hash $1 |
+----+ +
| |
+ +
| |
+ +
| |
+ +----+----+----+----+----+----+----+
| | |
+----+.... $num peer hashes
+ +----+----+----+----+----+----+----+
| | from |
+----+ +
| |
+ +
| |
+ +
| |
+ +----+----+----+----+----+----+----+
| |
+----+
{% endfilter %}
{% filter escape %}
key:
32 bytes
SHA256 of the object being searched
num:
1 byte Integer
number of peer hashes that follow, 0-255
peer hash ($num entries) :
32 bytes
SHA256 of the RouterIdentity that the other router thinks is close to the key
from:
32 bytes
SHA256 of the RouterInfo of the router this reply was sent from
{% endfilter %}
A simple message acknowledgment. Generally created by the message originator, and wrapped in a Garlic Message with the message itself, to be returned by the destination.
The ID of the delivered message, and the creation or arrival time.
{% filter escape %}
+----+----+----+----+----+----+----+----+----+----+----+----+
|msg-id | time stamp |
+----+----+----+----+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
msg-id:
4 bytes
unique ID of the message we deliver the DeliveryStatus for (see common I2NP header for details)
time stamp: Date
8 bytes
time the message was successfully created or delivered
{% endfilter %}
Used to wrap multiple encrypted I2NP Messages
When decrypted, a series of Garlic Cloves.
{% filter escape %}
encrypted:
+----+----+----+----+----+----+----+----+
| length | data |
+----+----+----+----+ +
| |
~ ~
~ ~
| |
+----+----+----+----+----+----+----+----+
unencrypted data:
+----+----+----+----+----+----+----+----+
|num | clove 1 |
+----+ +
| |
~ ~
~ ~
| |
+----+----+----+----+----+----+----+----+
| clove 2 ... |
~ ~
~ ~
| |
+----+----+----+----+----+----+----+----+
| Certificate | Message ID |
+----+----+----+----+----+----+----+----+
Expiration |
+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
Encrypted:
length:
4 byte Integer
number of bytes that follow 0 - 64 KB
data:
$length bytes
ElGamal encrypted data
Unencrypted data:
num:
1 byte Integer number of Garlic Cloves to follow
clove: A Garlic Clove
Certificate :: Always NULL in the current implementation (3 bytes total, all zeroes)
Message ID :: 4 byte Integer
Expiration :: Date (8 bytes)
{% endfilter %}
A message sent from a tunnel's gateway or participant to the next participant or endpoint. The data is of fixed length, containing I2NP messages that are fragmented, batched, padded, and encrypted.
{% filter escape %}
+----+----+----+----+----+----+----+----+
| tunnnelID | data |
+----+----+----+----+ |
| |
~ ~
~ ~
| |
+ +----+----+----+----+
| |
+----+----+----+----+
{% endfilter %}
{% filter escape %}
tunnelId:
4 byte Tunnel ID
identifies the tunnel this message is directed at
data:
1024 bytes
payload data.. fixed to 1024 bytes
{% endfilter %}
Wraps another I2NP message to be sent into a tunnel at the tunnel's inbound gateway.
{% filter escape %}
+----+----+----+----+----+----+--\\----+
| tunnelId | length | data...|
+----+----+----+----+----+----+--\\----+
{% endfilter %}
{% filter escape %}
tunnelId:
4 byte Tunnel ID
identifies the tunnel this message is directed at
length:
2 byte Integer
length of the payload
data:
$length bytes
actual payload of this message
{% endfilter %}
Used by Garlic Messages and Garlic Cloves to wrap arbitrary data.
A length Integer, followed by opaque data.
{% filter escape %}
+----+----+----+----+----+---//--+
| length | data... |
+----+----+----+----+----+---//--+
{% endfilter %}
{% filter escape %}
length:
4 bytes
length of the payload
data:
$length bytes
actual payload of this message
{% endfilter %}
{% filter escape %}
+----+----+----+----+----+----+----+----+
| Record 0 ... |
| |
+----+----+----+----+----+----+----+----+
| Record 1 ... |
.....
+----+----+----+----+----+----+----+----+
| Record 7 ... |
| |
+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
Just 8 Build Request Records attached together
Record size: 528 bytes
Total size: 8*528 = 4224 bytes
{% endfilter %}
{% filter escape %}
same format as TunnelBuild message, with Build Response Records
{% endfilter %}
{% filter escape %}
+----+----+----+----+----+----+----+----+
|num | BuildRequestRecords...
+----+----+----+----+----+----+----+----+
{% endfilter %}
{% filter escape %}
Same format as TunnelBuildMessage, except for the addition of an "num" field in front and $num number of Build Request Records instead of 8
num:
1 byte Integer
Valid values: 1-8
Record size: 528 bytes
Total size: 1 + $num*528
{% endfilter %}
{% filter escape %}
+----+----+----+----+----+----+----+----+
|num | BuildResponseRecords...
+----+----+----+----+----+----+----+----+
{% endfilter %}