@node Modes of operation
@unnumbered Modes of operation

See also this page @ref{Режимы работы, on russian}.

There are three modes of operation and two modes of data confidentiality
protection.

Three modes of operation provide various trade-off between
resource-consumption and effectiveness.

@table @asis

@item Default mode.

Data packets are encrypted and authenticated and sent immediately. This
is the most effective mode with minimal overhead and delays.

@verbatim
         +-----------+   +-----+         +---------+    +------+
         |  DATA     |   |DATA |         |  DATA   |    | DATA |
         +-----------+   +-----+         +---------+    +------+

---------------------------------------------------------------------------------------> t
@end verbatim

@item @ref{Noise} mode.

This mode hides packet's lengths. It consumes more traffic as a rule.

@verbatim
 +------const------+        +------const------+    +------const------+
/                   \      /                   \  /                   \

+------+------------+      +---------+---------+  +-------------+-----+
| DATA | NOISE      |      | DATA    | NOISE   |  | DATA        |NOISE|
+------+------------+      +---------+---------+  +-------------+-----+

---------------------------------------------------------------------------------------> t
@end verbatim

@item @ref{CPR} mode.

This mode also hides packets timestamps. It can increase delays and
insert dummy noised packets.

@verbatim
 +------const------+             +------const------+             +------const------+
/                   \           /                   \           /                   \

+------+------------+           +---------+---------+           +-------------------+
| DATA | NOISE      |<--const-->| DATA    | NOISE   |<--const-->|       NOISE       |
+------+------------+           +---------+---------+           +-------------------+

---------------------------------------------------------------------------------------> t
@end verbatim

@end table

Confidentiality protection modes are also trade-off between
effectiveness and resource-consumption.

@table @asis

@item @ref{Transport, Default} mode.

Encryption and authentication is done using well-known algorithms. This
is very effective mode. It generates packets undistinguishable from the
noise.

@verbatim
+---------------------------------------------------------+
|                       PACKET                            |
|                                                         |
|  +-----+ +---------------------------+   +-------+      |
|  | TAG |/         CIPHERTEXT          \ /  NONCE  \     |
|  +-----+|-----------------------------||-----------|    |
|         |                             ||           |    |
+---------------------------------------------------------+
          |                             ||           |
          |-----------------------------||-----------|
          |          ENCRYPTION         ||    MAC    |
          +------------+---+------------++-----------+
          |    DATA    |PAD|    ZEROS   ||  SERIAL   |
          +------------+---+------------++-----------+
@end verbatim

@item @ref{Encless, Encryptionless} mode.

This mode does not use any encryption function. Chaffing-and-Winnowing
encoding is used over AONT (all-or-nothing) package instead. This mode
consumes much more traffic and resources. It also generated
undistinguishable from the noise packets.

@verbatim
+----------------------------------------------------+
|                  PACKET                            |
|                                                    |
|     +---------------------------+  +---------+     |
|    /         CIPHERTEXT          \/   NONCE   \    |
|    |-----------------------------||-----------|    |
|    |                             ||           |    |
+----------------------------------------------------+
     |                             ||           |
     |--------+--------------------||-----------|
     |Chaffing|        AONT        ||    MAC    |
     +--------+---+---+------------++-----------+
     |    DATA    |PAD|    ZEROS   ||  SERIAL   |
     +------------+---+------------++-----------+
@end verbatim

@end table