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fix cross-connect key exchange

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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 <csaba.kiraly@gmail.com>
This commit is contained in:
Csaba Kiraly 2023-09-12 11:54:43 +02:00
parent 304f0c089d
commit a9d0d0d69b
No known key found for this signature in database
GPG Key ID: 0FE274EE8C95166E
2 changed files with 56 additions and 21 deletions
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33
libp2pdht/private/eth/p2p/discoveryv5/encoding.nim
View File

@ -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())

44
libp2pdht/private/eth/p2p/discoveryv5/sessions.nim
View File

@ -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