@unnumbered Packet format
All packets are
-@url{https://en.wikipedia.org/wiki/External_Data_Representation,
-XDR}-encoded structures.
+@url{https://tools.ietf.org/html/rfc4506, XDR}-encoded structures.
@menu
* Plain packet: Plain.
@section Plain packet
Plain packet contains either the whole file, or file request (freq), or
-transition packet or email message. It is called "plain", because it
+transition packet or exec message. It is called "plain", because it
contains plaintext, but plain packets would never be stored on your hard
drive.
@verbatim
HEADER
-+-------------------------------+--...---+
-| MAGIC | TYPE | PATHLEN | PATH | PAYLOAD|
-+-------------------------------+--...---+
++--------------------------------------+--...---+
+| MAGIC | TYPE | NICE | PATHLEN | PATH | PAYLOAD|
++--------------------------------------+--...---+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
-@headitem @tab XDR type @tab Value
+@headitem @tab XDR type @tab Value
@item Magic number @tab
8-byte, fixed length opaque data @tab
@verb{|N N C P P 0x00 0x00 0x01|}
@item Payload type @tab
unsigned integer @tab
- 0 (file), 1 (freq), 2 (mail), 3 (transition)
+ 0 (file), 1 (freq), 2 (exec), 3 (transition)
+@item Niceness @tab
+ unsigned integer @tab
+ 1-255, preferred packet @ref{Niceness, niceness} level
@item Path length @tab
unsigned integer @tab
actual length of @emph{path} field's payload
@itemize
@item UTF-8 encoded destination path for file transfer
@item UTF-8 encoded source path for file request
- @item UTF-8 encoded, space separated, email recipients list
+ @item UTF-8 encoded, zero byte separated, exec's arguments
@item Node's id the transition packet must be relayed on
@end itemize
@end multitable
@itemize
@item File contents
@item Destination path for freq
-@item @url{http://zlib.net/, zlib} compressed email
+@item @url{http://zlib.net/, zlib} compressed exec body
@item Whole encrypted packet we need to relay on
@end itemize
+Also depending on packet's type, niceness level means:
+
+@itemize
+@item Preferable niceness level for files sent by freq
+@item @env{NNCP_NICE} variable's value passed during @ref{CfgExec} invocation.
+@end itemize
+
@node Encrypted
@section Encrypted packet
Each encrypted packet has the following header:
@verbatim
- +------------ HEADER -------------+ +-------- ENCRYPTED --------+
- / \ / \
-+-------------------------------------+------------+----...-----------+------+
-| MAGIC | NICE | SENDER | EPUB | SIGN | SIZE | MAC | CIPHERTEXT | MAC | JUNK |
-+------------------------------/------\------------+----...-----------+------+
- / \
- +-------------------------------------+
- | MAGIC | NICE | RCPT | SENDER | EPUB |
- +-------------------------------------+
+ +------------ HEADER --------------------+ +-------- ENCRYPTED --------+
+ / \ / \
++--------------------------------------------+------------+----...-----------+------+
+| MAGIC | NICE | SENDER | RCPT | EPUB | SIGN | SIZE | MAC | CIPHERTEXT | MAC | JUNK |
++-------------------------------------/------\------------+----...-----------+------+
+ / \
+ +-------------------------------------+
+ | MAGIC | NICE | SENDER | RCPT | EPUB |
+ +-------------------------------------+
@end verbatim
@multitable @columnfractions 0.2 0.3 0.5
-@headitem @tab XDR type @tab Value
+@headitem @tab XDR type @tab Value
@item Magic number @tab
8-byte, fixed length opaque data @tab
- @verb{|N N C P E 0x00 0x00 0x01|}
+ @verb{|N N C P E 0x00 0x00 0x03|}
@item Niceness @tab
unsigned integer @tab
1-255, packet @ref{Niceness, niceness} level
@item Sender @tab
32-byte, fixed length opaque data @tab
Sender node's id
+@item Recipient @tab
+ 32-byte, fixed length opaque data @tab
+ Recipient node's id
@item Exchange public key @tab
32-byte, fixed length opaque data @tab
Ephemeral curve25519 public key
ed25519 signature for that packet's header
@end multitable
-Signature is calculated over the following structure:
-
-@itemize
-@item Magic number
-@item Niceness
-@item Recipient (32-byte recipient node's id)
-@item Sender
-@item Exchange public key
-@end itemize
+Signature is calculated over all previous fields.
-All following encryption is done using
-@url{https://www.schneier.com/academic/twofish/, Twofish} algorithm with
-256-bit key in
-@url{https://en.wikipedia.org/wiki/Counter_mode#Counter_.28CTR.29, CTR}
-mode of operation with zero initialization vector (because each
-encrypted packet has ephemeral exchange key). @url{https://blake2.net/,
+All following encryption is done using @url{https://cr.yp.to/chacha.html,
+ChaCha20} algorithm. Data is splitted on 128 KiB blocks. Each block is
+encrypted with increasing nonce counter. @url{https://blake2.net/,
BLAKE2b-256} MAC is appended to the ciphertext.
After the headers comes an encrypted payload size and MAC of that size.
@multitable @columnfractions 0.2 0.3 0.5
-@headitem @tab XDR type @tab Value
+@headitem @tab XDR type @tab Value
@item Size @tab
unsigned hyper integer @tab
Payload size.
@item takes remote node's exchange public key and performs
Diffie-Hellman computation on this remote static public key and
private ephemeral one
-@item derived ephemeral key is used as an input to
- @url{https://en.wikipedia.org/wiki/HKDF, HKDF}-BLAKE2b-256 KDF
-@item derives four session keys using
- @url{https://en.wikipedia.org/wiki/HKDF, HKDF}-BLAKE2b-256 KDF:
+@item derive the keys:
@enumerate
- @item "Size" encryption (for Twofish) key
- @item "Size" authentication (for BLAKE2b-MAC) key
- @item Payload encryption key
- @item Payload authentication key
+ @item initialize @url{https://blake2.net/, BLAKE2Xb} XOF with
+ derived ephemeral key and 224-byte output length
+ @item feed @verb{|N N C P E 0x00 0x00 0x03|} magic number to XOF
+ @item read 32-bytes of "size" encryption key (for ChaCha20)
+ @item read 64-bytes of "size" authentication key (for BLAKE2b-MAC)
+ @item read 32-bytes of payload encryption key
+ @item read 64-bytes of payload authentication key
+ @item optionally read 32-bytes pad generation key (for ChaCha20)
@end enumerate
@item encrypts size, appends its ciphertext to the header
@item appends MAC tag over that ciphertext