Cryptography Details

Draft

The cryptographic library used in KadNode is libsodium (a NaCl fork).

The secret/public key pair is generated by the crypto_sign_keypair method.

The authentication process is the task to verify that a node is in possession of a specific secret key.

For this we send a random 16 Byte string, the challenge, to the nodes IP address and DHT port that we want to authenticate.
"AUTH" (4 Bytes) + ID (20 Bytes) + 16 Bytes (Challenge)

We expect the node to send back the challenge, but encrypted (crypto_sign) with it's own secret key.
"AUTH" (4 Bytes) + ID (20 Bytes) + >16 Bytes (encrypted challenge)

If we can decrypt (crypto_sign_open) the message and get our random key, then we have verified that the other node has the secret key.

We send the challenge a few times before giving up.

Possible Problems:

• sending a challenge multiple times might be used for a DDoS when the sender address is spoofed!
  • send only one challenge per address per lookup?
• the address of the other side might change right after a successful authentication.
  • same attack vector for DNS