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fix: do not propagate unsigned encrypted messages #5129

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merged 1 commit into from
Jan 20, 2023
Merged

fix: do not propagate unsigned encrypted messages #5129

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52 changes: 35 additions & 17 deletions comms/dht/src/inbound/decryption.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -224,8 +224,10 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
node_identity: Arc<NodeIdentity>,
message: DhtInboundMessage,
) -> Result<DecryptedDhtMessage, DecryptionError> {
// Perform initial checks on message validity
let validated_msg = Self::initial_validation(message)?;

// The message is unencrypted and valid
if !validated_msg.header().flags.is_encrypted() {
return Self::success_not_encrypted(validated_msg).await;
}
Expand All @@ -237,22 +239,14 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
validated_msg.message().dht_header.message_tag
);

let dht_header = validated_msg.header();

let e_pk = dht_header
.ephemeral_public_key
.as_ref()
// No ephemeral key with ENCRYPTED flag set
.ok_or( DecryptionError::EphemeralKeyNotProvidedForEncryptedMessage)?;

if !validated_msg.message().dht_header.destination.is_unknown() &&
validated_msg
.message()
.dht_header
.destination
.public_key()
.map(|pk| pk != node_identity.public_key())
.unwrap_or(false)
// The message is encrypted, so see if it is for us
if validated_msg
.message()
.dht_header
.destination
.public_key()
.map(|pk| pk != node_identity.public_key())
.unwrap_or(false)
{
debug!(
target: LOG_TARGET,
Expand All @@ -264,6 +258,13 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
return Ok(DecryptedDhtMessage::failed(validated_msg.into_message()));
}

// The message is encrypted and for us, so derive its encryption key
let dht_header = validated_msg.header();
let e_pk = dht_header
.ephemeral_public_key
.as_ref()
// This has already been checked, but we need it to avoid an unwrap
.ok_or( DecryptionError::EphemeralKeyNotProvidedForEncryptedMessage)?;
let shared_secret = CommsDHKE::new(node_identity.secret_key(), e_pk);
let message = validated_msg.message();

Expand Down Expand Up @@ -310,6 +311,7 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
message.tag,
message.dht_header.message_tag
);
// Decrypt and verify the message
match Self::attempt_decrypt_message_body(&shared_secret, &message.body) {
Ok(message_body) => {
debug!(
Expand Down Expand Up @@ -346,13 +348,21 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
}

/// Performs message validation that should be performed by all nodes. If an error is encountered, the message is
/// invalid and should never have been sent.
/// invalid and should never have been propagated.
///
/// These failure modes are detectable by any node, so it is generally safe to ban an offending peer.
fn initial_validation(message: DhtInboundMessage) -> Result<ValidatedDhtInboundMessage, DecryptionError> {
// Messages must not be empty
if message.body.is_empty() {
return Err(DecryptionError::EncryptedMessageEmptyBody);
}

if message.dht_header.flags.is_encrypted() {
// An encrypted message needs:
// - a destination
// - an ephemeral public key used for DHKE
// - an encrypted message signature

// Check if there is no destination specified and discard
if message.dht_header.destination.is_unknown() {
return Err(DecryptionError::EncryptedMessageNoDestination);
Expand All @@ -363,10 +373,17 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
return Err(DecryptionError::EphemeralKeyNotProvidedForEncryptedMessage);
}

// An encrypted message signature is required
if message.dht_header.message_signature.is_empty() {
return Err(DecryptionError::MessageSignatureNotProvidedForEncryptedMessage);
}

Ok(ValidatedDhtInboundMessage::new(message, None))
} else if message.dht_header.message_signature.is_empty() {
// An unencrypted message does not require a message signature
Ok(ValidatedDhtInboundMessage::new(message, None))
} else {
// But if it has one, it must be valid!
let message_signature: MessageSignature =
ProtoMessageSignature::decode(message.dht_header.message_signature.as_slice())
.map_err(|_| DecryptionError::MessageSignatureClearTextDecodeFailed)?
Expand All @@ -393,6 +410,7 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
let encrypted_message_signature = Some(&dht_header.message_signature)
.filter(|b| !b.is_empty())
// This should not have been sent/propagated
// This is already checked elsewhere, but we need it to avoid an unwrap
.ok_or( DecryptionError::MessageSignatureNotProvidedForEncryptedMessage)?;

// obtain key signature for authenticated decrypt signature
Expand Down