Pervasively we would include the length of the MAC in the length prefix
for cipher text packets. As a result, the MAC would eat into the total
payload size. To remedy this, we now exclude the MAC from the length
prefix for cipher text packets, and instead account for the length of
the MAC on the packet when reading messages.
This commit fixes a bug in our key derivation for the final step of the
key exchange. In our code we were swapping the order of the salt and
input keyeing material to the HKDF function. This was triggered by the
argument order of the golang implementation we’re currently using has
the “secret” of IKM argument first, instead of second as defined within
rfc5869.
To fix this, we simply need to swap function arguments in two places:
within the split() function and during key rotation.
This bug was discovered by Rusty Russell, thanks!
This commit modifies the opening brontide handshake to use
libsecp256k1's public ECDH API throughout the handshake rather than the
current method which just returns the x-coordinate of the generated
point.
This change was made in order to align the current spec draft with the
aforementioned library since it’s very popular within the pace and
strives to only expose safe API’s to end users.
This commit modifies the current implementation to more closely match
what’s currently specified within the spec.
The encrypted+MAC’d packet length is no longer included as the
associated data for the encryption/decryption of transport messages.
This isn’t required as if an active attacker swaps out the encrypted
length in the byte string, the decryption+MAC check will simply fail as
the nonce won’t be in proper sequence.
This commit implements key rotation for brontide as-per the current
draft of the LN p2p crypto spec. Key rotation is currently performed
every 1000 messages encrypted/decrypted with a cipherState object. Key
rotation is performed by evaluating the HKDF (extracting exactly 64
bytes) with the current chaining key, and cipher key. The key rotation
is to attempted after each nonce increment making implementation easy
as the current nonce value will already be within the local scope.
This commit modifies the current implementation of the p2p crypto
protocol to further constrain the max allowed payload size. With this
change we now use 16-bits (2-bytes) for the maximum payload length.
This change puts us closer to strict adherence of the Noise spec, and
simplifies the memory management w.r.t implementing the current version
of our scheme.
Note that this doesn’t restrict the size of messages that are able to
be sent over the wire within the LN p2p protocol. Larger message can
safely be encapsulated within the crypt messages via fragmentation that
will detected take place if a larger message is detected.
This commit introduces Brontide: an authenticated key agreement
protocol in three acts. Brontide is the successor to lndc within lnd,
and ultimately within the greater Lighting Network. Brontide uses the
Noise_XK handshake for initial key agreement, then implements an AEAD
scheme which encrypts+authenticates both packets, and the lengths of
the packets on the wire. The initial authentication handshake preserves
the responder’s identity by never transmitting it to the initiator and
performing mutual authentication via an incremental Triple-DH based on
ECDH of secp256k1 and an HKDF which uses SHA-256.
Bronzed isn’t yet integrated within the wider daemon yet. Full
integration will land in a future pull request.
