From a9d0d0d69b2ad85376bfa39c8df5273a94cb7f8b Mon Sep 17 00:00:00 2001 From: Csaba Kiraly Date: Tue, 12 Sep 2023 11:54:43 +0200 Subject: [PATCH] fix cross-connect key exchange Since key exchange can be started both ways simultaneously, and these might not get finalised with UDP transport, we can't be sure what encryption key will be used by the other side: - the one derived in the key-exchange started by us, - the one derived in the key-exchange started by the other node. To alleviate this issue, we store two decryption keys in each session. Signed-off-by: Csaba Kiraly --- .../private/eth/p2p/discoveryv5/encoding.nim | 33 +++++++++----- .../private/eth/p2p/discoveryv5/sessions.nim | 44 +++++++++++++++---- 2 files changed, 56 insertions(+), 21 deletions(-) diff --git a/libp2pdht/private/eth/p2p/discoveryv5/encoding.nim b/libp2pdht/private/eth/p2p/discoveryv5/encoding.nim index d879365..937fb07 100644 --- a/libp2pdht/private/eth/p2p/discoveryv5/encoding.nim +++ b/libp2pdht/private/eth/p2p/discoveryv5/encoding.nim @@ -229,8 +229,8 @@ proc encodeMessagePacket*(rng: var HmacDrbgContext, c: var Codec, # message var messageEncrypted: seq[byte] - var initiatorKey, recipientKey: AesKey - if c.sessions.load(toId, toAddr, recipientKey, initiatorKey): + var initiatorKey, recipientKey1, recipientKey2: AesKey + if c.sessions.load(toId, toAddr, recipientKey1, recipientKey2, initiatorKey): haskey = true messageEncrypted = encryptGCM(initiatorKey, nonce, message, @iv & header) discovery_session_lru_cache_hits.inc() @@ -425,8 +425,8 @@ proc decodeMessagePacket(c: var Codec, fromAddr: Address, nonce: AESGCMNonce, let srcId = NodeId.fromBytesBE(header.toOpenArray(staticHeaderSize, header.high)) - var initiatorKey, recipientKey: AesKey - if not c.sessions.load(srcId, fromAddr, recipientKey, initiatorKey): + var initiatorKey, recipientKey1, recipientKey2: AesKey + if not c.sessions.load(srcId, fromAddr, recipientKey1, recipientKey2, initiatorKey): # Don't consider this an error, simply haven't done a handshake yet or # the session got removed. trace "Decrypting failed (no keys)" @@ -436,15 +436,24 @@ proc decodeMessagePacket(c: var Codec, fromAddr: Address, nonce: AESGCMNonce, discovery_session_lru_cache_hits.inc() - let pt = decryptGCM(recipientKey, nonce, ct, @iv & @header) + var pt = decryptGCM(recipientKey2, nonce, ct, @iv & @header) if pt.isNone(): - # Don't consider this an error, the session got probably removed at the - # peer's side and a random message is send. - trace "Decrypting failed (invalid keys)" - c.sessions.del(srcId, fromAddr) - discovery_session_decrypt_failures.inc() - return ok(Packet(flag: Flag.OrdinaryMessage, requestNonce: nonce, - srcId: srcId)) + trace "Decrypting failed, trying other key" + pt = decryptGCM(recipientKey1, nonce, ct, @iv & @header) + if pt.isNone(): + # Don't consider this an error, the session got probably removed at the + # peer's side and a random message is send. + # This might also be a cross-connect. Not deleteing key, as it might be + # needed later, depending on message order. + trace "Decrypting failed (invalid keys)", address = fromAddr + #c.sessions.del(srcId, fromAddr) + discovery_session_decrypt_failures.inc() + return ok(Packet(flag: Flag.OrdinaryMessage, requestNonce: nonce, + srcId: srcId)) + + # Most probably the same decryption key will work next time. We should + # elevate it's priority. + c.sessions.swapr(srcId, fromAddr) let message = ? decodeMessage(pt.get()) diff --git a/libp2pdht/private/eth/p2p/discoveryv5/sessions.nim b/libp2pdht/private/eth/p2p/discoveryv5/sessions.nim index 46a5b3d..ffcb76f 100644 --- a/libp2pdht/private/eth/p2p/discoveryv5/sessions.nim +++ b/libp2pdht/private/eth/p2p/discoveryv5/sessions.nim @@ -9,6 +9,13 @@ ## https://github.com/ethereum/devp2p/blob/master/discv5/discv5-theory.md#session-cache ## +## A session stores encryption and decryption keys for P2P encryption. +## Since key exchange can be started both ways, and these might not get finalised with +## UDP transport, we can't be sure what encryption key will be used by the other side: +## - the one derived in the key-exchange started by us, +## - the one derived in the key-exchange started by the other node. +## To alleviate this issue, we store two decryption keys in each session. + {.push raises: [Defect].} import @@ -27,7 +34,7 @@ const type AesKey* = array[aesKeySize, byte] SessionKey* = array[keySize, byte] - SessionValue* = array[sizeof(AesKey) + sizeof(AesKey), byte] + SessionValue* = array[3 * sizeof(AesKey), byte] Sessions* = LRUCache[SessionKey, SessionValue] func makeKey(id: NodeId, address: Address): SessionKey = @@ -42,18 +49,37 @@ func makeKey(id: NodeId, address: Address): SessionKey = pos.inc(sizeof(address.ip.address_v6)) result[pos ..< pos+sizeof(address.port)] = toBytes(address.port.uint16) -func store*(s: var Sessions, id: NodeId, address: Address, r, w: AesKey) = - var value: array[sizeof(r) + sizeof(w), byte] - value[0 .. 15] = r - value[16 .. ^1] = w - s.put(makeKey(id, address), value) +func swapr*(s: var Sessions, id: NodeId, address: Address) = + var value: array[3 * sizeof(AesKey), byte] + let + key = makeKey(id, address) + entry = s.get(key) + if entry.isSome(): + let val = entry.get() + copyMem(addr value[0], unsafeAddr val[16], sizeof(AesKey)) + copyMem(addr value[16], unsafeAddr val[0], sizeof(AesKey)) + copyMem(addr value[32], unsafeAddr val[32], sizeof(AesKey)) + s.put(key, value) -func load*(s: var Sessions, id: NodeId, address: Address, r, w: var AesKey): bool = +func store*(s: var Sessions, id: NodeId, address: Address, r, w: AesKey) = + var value: array[3 * sizeof(AesKey), byte] + let + key = makeKey(id, address) + entry = s.get(key) + if entry.isSome(): + let val = entry.get() + copyMem(addr value[0], unsafeAddr val[16], sizeof(r)) + value[16 .. 31] = r + value[32 .. ^1] = w + s.put(key, value) + +func load*(s: var Sessions, id: NodeId, address: Address, r1, r2, w: var AesKey): bool = let res = s.get(makeKey(id, address)) if res.isSome(): let val = res.get() - copyMem(addr r[0], unsafeAddr val[0], sizeof(r)) - copyMem(addr w[0], unsafeAddr val[sizeof(r)], sizeof(w)) + copyMem(addr r1[0], unsafeAddr val[0], sizeof(r1)) + copyMem(addr r2[0], unsafeAddr val[sizeof(r1)], sizeof(r2)) + copyMem(addr w[0], unsafeAddr val[sizeof(r1) + sizeof(r2)], sizeof(w)) return true else: return false