@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|}
+ @verb{|N N C P P 0x00 0x00 0x03|}
@item Payload type @tab
unsigned integer @tab
- 0 (file), 1 (freq), 2 (mail), 3 (transition)
+ 0 (file), 1 (freq), 2 (exec), 3 (transition), 4 (exec-fat)
+@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
Path has fixed size because of hiding its actual length -- it is
valuable metadata. Payload is appended to the header -- it is not stored
-as XDR field, because most XDR libraries will store all that data in the
-memory.
+as XDR field, because XDR has no ability to pass more than 4 GiB of
+opaque data. Moreover most XDR libraries store fields in the memory in
+practice.
Depending on the packet's type, payload could store:
@itemize
@item File contents
@item Destination path for freq
-@item @url{http://zlib.net/, zlib} compressed email
+@item @url{https://facebook.github.io/zstd/, Zstandard} compressed exec body
@item Whole encrypted packet we need to relay on
+@item Uncompressed exec body
+@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
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 | BLOCK 0 | BLOCK 1 ... | 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 0x05|}
@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/,
-BLAKE2b-256} MAC is appended to the ciphertext.
+All following encryption is done in AEAD mode using
+@url{https://cr.yp.to/chacha.html, ChaCha20}-@url{https://en.wikipedia.org/wiki/Poly1305, Poly1305}
+algorithms. Data is divided on 128 KiB blocks. Each block is encrypted with
+increasing nonce counter.
-After the headers comes an encrypted payload size and MAC of that size.
+Authenticated and encrypted size come after the header:
@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.
@end multitable
-Next comes the actual encrypted payload with corresponding MAC.
+Then comes the actual payload.
Each node has static @strong{exchange} and @strong{signature} keypairs.
When node A want to send encrypted packet to node B, it:
@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:
- @enumerate
- @item "Size" encryption (for Twofish) key
- @item "Size" authentication (for BLAKE2b-MAC) key
- @item Payload encryption key
- @item Payload authentication key
- @end enumerate
-@item encrypts size, appends its ciphertext to the header
-@item appends MAC tag over that ciphertext
-@item encrypts and appends payload ciphertext
-@item appends MAC tag over that payload ciphertext
+@item derives 32-bytes AEAD encryption key with BLAKE3 derivation
+ function. Source key is the derived ephemeral key. Context is
+ @verb{|N N C P E 0x00 0x00 0x05|} magic number
+@item encrypts size, appends its authenticated ciphertext to the header
+@item encrypts each payload block, appending its authenticated ciphertext
@item possibly appends any kind of "junk" noise data to hide real
- payload's size from the adversary
+ payload's size from the adversary (generated using BLAKE3 XOF, with
+ the key derived from the ephemeral one and context string of
+ @verb{|N N C P E 0x00 0x00 0x05 <SP> P A D|})
@end enumerate