After soaking for a bit on the adverts without issue on multiple nodes,
I added more hardware crypto.
Supported nodes is unchanged in this PR addition, but if others can verify,
they can easily be added.
Some info on the CC310: https://docs.nordicsemi.com/r/bundle/ps_nrf9151/page/cryptocell.html
**Added:**
- AES-128 packet encryption/decryption now use hardware crypto
- HMAC-SHA-256 authentication now uses hardware crypto
- ACK hash computation and channel ID derivation now use hardware crypto
- RNG (random number generator) now uses hardware crypto rather than
radio noise + weak software RNG (which can have issues if there's
no surrounding radio noise.) NIST SP 800-90B certified.
- Runs hardware self-tests on startup
- Runs continuous health tests during operation
- Uses thermal noise/shot noise for randomness
**Unchanged:**
- calcSharedSecret remains software - it would be a split hw/sw solution
and added complexity for likely not a lot of gains. This only happens
when establishing a new contact, so not too frequent to be worth it.
- ed25519_create_keypair remains software. This is only called when a
node is first initialized. It does use the hardware RNG change, however,
so better randomization.
Tested on (so far):
- Heltec t096
Build test on:
- Heltec t096 companion ble
- t1000e companion ble
- RAK 4631 repeater
- RAK 3401 companion BLE
- Heltec v3 companion wifi
Address review feedback:
- Move the alignment check before the HMAC-SHA256 computation to skip
expensive crypto on obviously malformed packets
- Update MACThenDecrypt header comment to document block-alignment as a
reason for returning zero
Add validation that ciphertext length is a multiple of CIPHER_BLOCK_SIZE
before calling decrypt(). The decrypt() function processes data in 16-byte
AES blocks, rounding up non-aligned input, which can write up to 8 bytes
past the caller's stack buffer. This can be triggered by crafted packets
that pass the 2-byte HMAC check (1-in-65536 chance per attempt), enabling
a persistent denial-of-service attack against repeaters and other nodes.
Liam Cottle