Difference between revisions of "Messages Format"
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E PPRZ_CHECKSUM_B (sum[ck_a]) | E PPRZ_CHECKSUM_B (sum[ck_a]) | ||
==Secure Paparazzi (S-PPRZ) for serial and transparent modem communication== | ==Secure Paparazzi (S-PPRZ) for serial and transparent modem communication== | ||
The overhead is | Secure Paparazzi link ([https://github.com/paparazzi/pprzlink/tree/hacl-c pprzlink]) uses [https://en.wikipedia.org/wiki/Symmetric-key_algorithm symmetric key encryption] with [https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant Chacha20] cipher. | ||
'''s-pprzlink''' uses a formally verified cryptographic library [https://github.com/mitls/hacl-star HACL*] developed by the [http://prosecco.inria.fr/ Prosecco] team at [https://www.inria.fr/en/centre/paris INRIA Paris] in collaboration with Microsoft Research, as part of [https://github.com/project-everest Project Everest]. | |||
Because certain data have to be send in plaintext (such as the message counter), '''s-pprzlink''' uses ''Authenticated Encryption with Associated Data'' (AEAD) algorithm to authenticate such data before use. Authentication means that any unauthorized change in data is detected upon decryption. Authentication is important because if we decide to send SENDER_ID or DESTINATION_ID in plaintext - so the receiver can decide whether to decrypt the message - we don't want it to be tampered with. '''s-pprzlink''' uses a modified [https://github.com/GaloisInc/gec Galois Embedded Crypto] algorithm, refer there for more details about the algorithm itself. | |||
The cryptographic overhead during regular communication is 20 bytes (4 bytes of the counter, 16 bytes of the authentication tag), plus the necessary key exchange at the beginning of communication. | |||
===S-Pprzlink v1.0=== | ===S-Pprzlink v1.0=== | ||
Revision as of 19:41, 3 November 2017
Introduction
Messages Format and how to use them
For the message definitions see http://docs.paparazziuav.org/latest/paparazzi_messages.html
Types
Paparazzi "PPRZ" standard message for direct serial connection
Pprzlink v1.0
PPRZ-message: ABCxxxxxxxDE
byte: | value:
0 PPRZ_STX (0x99)
1 LENGTH (PPRZ_STX->PPRZ_CHECKSUM_B)
2 SENDER_ID
3 MSG_ID
4..(N-2) MSG_PAYLOAD (messages.xml)
N-1 PPRZ_CHECKSUM_A (sum[B->C])
N PPRZ_CHECKSUM_B (sum[ck_a])
Pprzlink v2.0
Note that there is currently no explicit way to recognize whether the protocol is v1.0 or 2.0 so it has to be known before the communication.
PPRZ-message: ABCxxxxxxxDE
A PPRZ_STX (0x99)
B LENGTH (A->E)
C PPRZ_DATA
0 SOURCE (~sender_ID)
1 DESTINATION (can be a broadcast ID)
2 CLASS/COMPONENT
bits 0-3: 16 class ID available
bits 4-7: 16 component ID available
3 MSG_ID
4 MSG_PAYLOAD
. DATA (messages.xml)
D PPRZ_CHECKSUM_A (sum[B->C])
E PPRZ_CHECKSUM_B (sum[ck_a])
Secure Paparazzi (S-PPRZ) for serial and transparent modem communication
Secure Paparazzi link (pprzlink) uses symmetric key encryption with Chacha20 cipher.
s-pprzlink uses a formally verified cryptographic library HACL* developed by the Prosecco team at INRIA Paris in collaboration with Microsoft Research, as part of Project Everest.
Because certain data have to be send in plaintext (such as the message counter), s-pprzlink uses Authenticated Encryption with Associated Data (AEAD) algorithm to authenticate such data before use. Authentication means that any unauthorized change in data is detected upon decryption. Authentication is important because if we decide to send SENDER_ID or DESTINATION_ID in plaintext - so the receiver can decide whether to decrypt the message - we don't want it to be tampered with. s-pprzlink uses a modified Galois Embedded Crypto algorithm, refer there for more details about the algorithm itself.
The cryptographic overhead during regular communication is 20 bytes (4 bytes of the counter, 16 bytes of the authentication tag), plus the necessary key exchange at the beginning of communication.
S-Pprzlink v1.0
PPRZ-message: ABCxxxxxxxDE byte: | value: 0 PPRZ_STX (0x99) 1 LENGTH (PPRZ_STX->PPRZ_CHECKSUM_B) 2-5 COUNTER (4 bytes) 6 encrypted SENDER_ID 7 encrypted MSG_ID 8..(N-16) encrypted MSG_PAYLOAD (messages.xml) (N-15)..(N-2) TAG (16 bytes) N-1 PPRZ_CHECKSUM_A (sum[B->C]) N PPRZ_CHECKSUM_B (sum[ck_a])
| byte | Value | Type |
|---|---|---|
| 0 | PPRZ_STX (0x99) | Header |
| 1 | length N (PPRZ_STX->checksum B) | Header |
| 2 | counter LSB 1 | Authenticated data |
| 3 | counter LSB 2 | Authenticated data |
| 4 | counter LSB 3 | Authenticated data |
| 5 | counter LSB 4 | Authenticated data |
| 6 | sender ID | Encrypted payload |
| 7 | message ID | Encrypted payload |
| 8..(N-16) | (optional) message payload (0-234 bytes) | Encrypted payload |
| (N-15)..(N-2) | tag (16 bytes) | Authentication tag |
| N-1 | checksum A | Header |
| N | checksum B | Header |
S-Pprzlink v2.0
In this case we decrypt only packets with matching DESTINATION (or broadcast), to avoid decrypting unwanted data.
PPRZ-message: ABCxxxxxxxDE
A PPRZ_STX (0x99)
B LENGTH (A->E)
C PPRZ_DATA
0 SOURCE (~sender_ID)
1 DESTINATION (can be a broadcast ID)
2-5 COUNTER (4 bytes)
// ciphertext start
6 CLASS/COMPONENT
bits 0-3: 16 class ID available
bits 4-7: 16 component ID available
7 MSG_ID
8 MSG_PAYLOAD
. DATA (messages.xml)
// ciphertext end
8-19 TAG (12 bytes)
D PPRZ_CHECKSUM_A (sum[B->C])
E PPRZ_CHECKSUM_B (sum[ck_a])
XBee API format
XBee-message: ABCDxxxxxxxE
A XBEE_START (0x7E)
B LENGTH_MSB (D->D)
C LENGTH_LSB
D XBEE_PAYLOAD
0 XBEE_TX16 (0x01) / XBEE_RX16 (0x81)
1 FRAME_ID (0) / SRC_ID_MSB
2 DEST_ID_MSB / SRC_ID_LSB
3 DEST_ID_LSB / XBEE_RSSI
4 TX16_OPTIONS (0) / RX16_OPTIONS
5 PPRZ_DATA
0 SENDER_ID
1 MSG_ID
2 MSG_PAYLOAD
. DATA (messages.xml)
E XBEE_CHECKSUM (sum[D->D])
ID is AC_ID for aircraft, 0x100 for ground station
Telemetry storage format for data logger
TLM-message: ABCDEFGHxxxxxxxI
A PPRZ_STX (0x99)
B LENGTH (H->H)
C SOURCE (0=uart0, 1=uart1, 2=i2c0, ...)
D TIMESTAMP_LSB (100 microsecond raster)
E TIMESTAMP
F TIMESTAMP
G TIMESTAMP_MSB
H PPRZ_DATA
0 SENDER_ID
1 MSG_ID
2 MSG_PAYLOAD
. DATA (messages.xml)
I CHECKSUM (sum[B->H])