// (c) 2020-2022 ZeroTier, Inc. -- currently proprietary pending actual release and licensing. See LICENSE.md. // ZSSP: ZeroTier Secure Session Protocol // FIPS compliant Noise_IK with Jedi powers and built-in attack-resistant large payload (fragmentation) support. use std::io::{Read, Write}; use std::ops::Deref; use std::sync::atomic::{AtomicU64, Ordering}; use std::sync::{Mutex, RwLock}; use crate::aes::{Aes, AesGcm}; use crate::hash::{hmac_sha512, HMACSHA384, SHA384}; use crate::p384::{P384KeyPair, P384PublicKey, P384_PUBLIC_KEY_SIZE}; use crate::random; use crate::secret::Secret; use zerotier_utils::gatherarray::GatherArray; use zerotier_utils::memory; use zerotier_utils::ringbuffermap::RingBufferMap; use zerotier_utils::unlikely_branch; use zerotier_utils::varint; /// Minimum size of a valid physical ZSSP packet or packet fragment. pub const MIN_PACKET_SIZE: usize = HEADER_SIZE + AES_GCM_TAG_SIZE; /// Minimum physical MTU for ZSSP to function. pub const MIN_TRANSPORT_MTU: usize = 1280; /// Minimum recommended interval between calls to service() on each session, in milliseconds. pub const SERVICE_INTERVAL: u64 = 10000; /// Setting this to true enables kyber1024 post-quantum forward secrecy. /// /// Kyber1024 is used for data forward secrecy but not authentication. Authentication would /// require Kyber1024 in identities, which would make them huge, and isn't needed for our /// threat model which is data warehousing today to decrypt tomorrow. Breaking authentication /// is only relevant today, not in some mid to far future where a QC that can break 384-bit ECC /// exists. /// /// This is normally enabled but could be disabled at build time for e.g. very small devices. /// It might not even be necessary there to disable it since it's not that big and is usually /// faster than NIST P-384 ECDH. const JEDI: bool = true; /// Maximum number of fragments for data packets. const MAX_FRAGMENTS: usize = 48; // hard protocol max: 63 /// Maximum number of fragments for key exchange packets (can be smaller to save memory, only a few needed) const KEY_EXCHANGE_MAX_FRAGMENTS: usize = 2; // enough room for p384 + ZT identity + kyber1024 + tag/hmac/etc. /// Start attempting to rekey after a key has been used to send packets this many times. /// /// This is 1/4 the NIST recommended maximum and 1/8 the absolute limit where u32 wraps. /// As such it should leave plenty of margin against nearing key reuse bounds w/AES-GCM. const REKEY_AFTER_USES: u64 = 536870912; /// Maximum random jitter to add to rekey-after usage count. const REKEY_AFTER_USES_MAX_JITTER: u32 = 1048576; /// Hard expiration after this many uses. /// /// Use of the key beyond this point is prohibited. If we reach this number of key uses /// the key will be destroyed in memory and the session will cease to function. A hard /// error is also generated. const EXPIRE_AFTER_USES: u64 = (u32::MAX - 1024) as u64; /// Start attempting to rekey after a key has been in use for this many milliseconds. const REKEY_AFTER_TIME_MS: i64 = 1000 * 60 * 60; // 1 hour /// Maximum random jitter to add to rekey-after time. const REKEY_AFTER_TIME_MS_MAX_JITTER: u32 = 1000 * 60 * 10; // 10 minutes /// Version 0: AES-256-GCM + NIST P-384 + optional Kyber1024 PQ forward secrecy const SESSION_PROTOCOL_VERSION: u8 = 0x00; /// Secondary key type: none, use only P-384 for forward secrecy. const E1_TYPE_NONE: u8 = 0; /// Secondary key type: Kyber1024, PQ forward secrecy enabled. const E1_TYPE_KYBER1024: u8 = 1; /// Size of packet header const HEADER_SIZE: usize = 16; /// Size of AES-GCM keys (256 bits) const AES_KEY_SIZE: usize = 32; /// Size of AES-GCM MAC tags const AES_GCM_TAG_SIZE: usize = 16; /// Size of HMAC-SHA384 MAC tags const HMAC_SIZE: usize = 48; /// Size of a session ID, which behaves a bit like a TCP port number. /// /// This is large since some ZeroTier nodes handle huge numbers of links, like roots and controllers. const SESSION_ID_SIZE: usize = 6; /// Number of session keys to hold at a given time (current, previous, next). const KEY_HISTORY_SIZE: usize = 3; // Packet types can range from 0 to 15 (4 bits) -- 0-3 are defined and 4-15 are reserved for future use const PACKET_TYPE_DATA: u8 = 0; const PACKET_TYPE_NOP: u8 = 1; const PACKET_TYPE_KEY_OFFER: u8 = 2; // "alice" const PACKET_TYPE_KEY_COUNTER_OFFER: u8 = 3; // "bob" // Key usage labels for sub-key derivation using NIST-style KBKDF (basically just HMAC KDF). const KBKDF_KEY_USAGE_LABEL_HMAC: u8 = b'M'; // HMAC-SHA384 authentication for key exchanges const KBKDF_KEY_USAGE_LABEL_HEADER_CHECK: u8 = b'H'; // AES-based header check code generation const KBKDF_KEY_USAGE_LABEL_AES_GCM_ALICE_TO_BOB: u8 = b'A'; // AES-GCM in A->B direction const KBKDF_KEY_USAGE_LABEL_AES_GCM_BOB_TO_ALICE: u8 = b'B'; // AES-GCM in B->A direction const KBKDF_KEY_USAGE_LABEL_RATCHETING: u8 = b'R'; // Key input for next ephemeral ratcheting // AES key size for header check code generation const HEADER_CHECK_AES_KEY_SIZE: usize = 16; /// Aribitrary starting value for master key derivation. /// /// It doesn't matter very much what this is but it's good for it to be unique. It should /// be changed if this code is changed in any cryptographically meaningful way like changing /// the primary algorithm from NIST P-384 or the transport cipher from AES-GCM. const INITIAL_KEY: [u8; 64] = [ // macOS command line to generate: // echo -n 'ZSSP_Noise_IKpsk2_NISTP384_?KYBER1024_AESGCM_SHA512' | shasum -a 512 | cut -d ' ' -f 1 | xxd -r -p | xxd -i 0x35, 0x6a, 0x75, 0xc0, 0xbf, 0xbe, 0xc3, 0x59, 0x70, 0x94, 0x50, 0x69, 0x4c, 0xa2, 0x08, 0x40, 0xc7, 0xdf, 0x67, 0xa8, 0x68, 0x52, 0x6e, 0xd5, 0xdd, 0x77, 0xec, 0x59, 0x6f, 0x8e, 0xa1, 0x99, 0xb4, 0x32, 0x85, 0xaf, 0x7f, 0x0d, 0xa9, 0x6c, 0x01, 0xfb, 0x72, 0x46, 0xc0, 0x09, 0x58, 0xb8, 0xe0, 0xa8, 0xcf, 0xb1, 0x58, 0x04, 0x6e, 0x32, 0xba, 0xa8, 0xb8, 0xf9, 0x0a, 0xa4, 0xbf, 0x36, ]; pub enum Error { /// The packet was addressed to an unrecognized local session (should usually be ignored) UnknownLocalSessionId(SessionId), /// Packet was not well formed InvalidPacket, /// An invalid parameter was supplied to the function InvalidParameter, /// Packet failed one or more authentication (MAC) checks FailedAuthentication, /// New session was rejected via Host::check_new_session_attempt or Host::accept_new_session. NewSessionRejected, /// Rekeying failed and session secret has reached its hard usage count limit MaxKeyLifetimeExceeded, /// Attempt to send using session without established key SessionNotEstablished, /// Packet ignored by rate limiter. RateLimited, /// The other peer specified an unrecognized protocol version UnknownProtocolVersion, /// Caller supplied data buffer is too small to receive data DataBufferTooSmall, /// Data object is too large to send, even with fragmentation DataTooLarge, /// An unexpected I/O error such as a buffer overrun occurred (possible bug) UnexpectedIoError(std::io::Error), } impl From for Error { #[cold] #[inline(never)] fn from(e: std::io::Error) -> Self { Self::UnexpectedIoError(e) } } impl std::fmt::Display for Error { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { match self { Self::UnknownLocalSessionId(id) => f.write_str(format!("UnknownLocalSessionId({})", id.0).as_str()), Self::InvalidPacket => f.write_str("InvalidPacket"), Self::InvalidParameter => f.write_str("InvalidParameter"), Self::FailedAuthentication => f.write_str("FailedAuthentication"), Self::NewSessionRejected => f.write_str("NewSessionRejected"), Self::MaxKeyLifetimeExceeded => f.write_str("MaxKeyLifetimeExceeded"), Self::SessionNotEstablished => f.write_str("SessionNotEstablished"), Self::RateLimited => f.write_str("RateLimited"), Self::UnknownProtocolVersion => f.write_str("UnknownProtocolVersion"), Self::DataBufferTooSmall => f.write_str("DataBufferTooSmall"), Self::DataTooLarge => f.write_str("DataTooLarge"), Self::UnexpectedIoError(e) => f.write_str(format!("UnexpectedIoError({})", e.to_string()).as_str()), } } } impl std::error::Error for Error {} impl std::fmt::Debug for Error { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { std::fmt::Display::fmt(self, f) } } /// Result generated by the packet receive function, with possible payloads. pub enum ReceiveResult<'a, H: Host> { /// Packet is valid, no action needs to be taken. Ok, /// Packet is valid and a data payload was decoded and authenticated. /// /// The returned reference is to the filled parts of the data buffer supplied to receive. OkData(&'a mut [u8]), /// Packet is valid and a new session was created. /// /// The session will have already been gated by the accept_new_session() method in the Host trait. OkNewSession(Session), /// Packet appears valid but was ignored e.g. as a duplicate. Ignored, } /// 48-bit session ID (most significant 16 bits of u64 are unused) #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)] #[repr(transparent)] pub struct SessionId(u64); impl SessionId { /// The nil session ID used in messages initiating a new session. /// /// This is all 1's so that ZeroTier can easily tell the difference between ZSSP init packets /// and ZeroTier V1 packets. pub const NIL: SessionId = SessionId(0xffffffffffff); #[inline] pub fn new_from_u64(i: u64) -> Option { if i < Self::NIL.0 { Some(Self(i)) } else { None } } #[inline] pub fn new_from_reader(r: &mut R) -> std::io::Result> { let mut tmp = 0_u64.to_ne_bytes(); r.read_exact(&mut tmp[..SESSION_ID_SIZE])?; Ok(Self::new_from_u64(u64::from_le_bytes(tmp))) } #[inline] pub fn new_random() -> Self { Self(random::next_u64_secure() % Self::NIL.0) } } impl From for u64 { #[inline(always)] fn from(sid: SessionId) -> Self { sid.0 } } /// State information to associate with receiving contexts such as sockets or remote paths/endpoints. /// /// This holds the data structures used to defragment incoming packets that are not associated with an /// existing session, which would be new attempts to create sessions. Typically one of these is associated /// with a single listen socket, local bound port, or other inbound endpoint. pub struct ReceiveContext { initial_offer_defrag: Mutex, 1024, 128>>, incoming_init_header_check_cipher: Aes, } /// Trait to implement to integrate the session into an application. /// /// Templating the session on this trait lets the code here be almost entirely transport, OS, /// and use case independent. pub trait Host: Sized { /// Arbitrary opaque object associated with a session, such as a connection state object. type AssociatedObject; /// Arbitrary object that dereferences to the session, such as Arc>. type SessionRef: Deref>; /// A buffer containing data read from the network that can be cached. /// /// This can be e.g. a pooled buffer that automatically returns itself to the pool when dropped. /// It can also just be a Vec or Box<[u8]> or something like that. type IncomingPacketBuffer: AsRef<[u8]>; /// Remote physical address on whatever transport this session is using. type RemoteAddress; /// Rate limit for attempts to rekey existing sessions in milliseconds (default: 2000). const REKEY_RATE_LIMIT_MS: i64 = 2000; /// Get a reference to this host's static public key blob. /// /// This must contain a NIST P-384 public key but can contain other information. In ZeroTier this /// is a byte serialized identity. It could just be a naked NIST P-384 key if that's all you need. fn get_local_s_public(&self) -> &[u8]; /// Get SHA384(this host's static public key blob). /// /// This allows us to avoid computing SHA384(public key blob) over and over again. fn get_local_s_public_hash(&self) -> &[u8; 48]; /// Get a reference to this hosts' static public key's NIST P-384 secret key pair. /// /// This must return the NIST P-384 public key that is contained within the static public key blob. fn get_local_s_keypair_p384(&self) -> &P384KeyPair; /// Extract the NIST P-384 ECC public key component from a static public key blob or return None on failure. /// /// This is called to parse the static public key blob from the other end and extract its NIST P-384 public /// key. SECURITY NOTE: the information supplied here is from the wire so care must be taken to parse it /// safely and fail on any error or corruption. fn extract_p384_static(static_public: &[u8]) -> Option; /// Look up a local session by local session ID or return None if not found. fn session_lookup(&self, local_session_id: SessionId) -> Option; /// Rate limit and check an attempted new session (called before accept_new_session). fn check_new_session_attempt(&self, rc: &ReceiveContext, remote_address: &Self::RemoteAddress) -> bool; /// Check whether a new session should be accepted. /// /// On success a tuple of local session ID, static secret, and associated object is returned. The /// static secret is whatever results from agreement between the local and remote static public /// keys. fn accept_new_session( &self, receive_context: &ReceiveContext, remote_address: &Self::RemoteAddress, remote_static_public: &[u8], remote_metadata: &[u8], ) -> Option<(SessionId, Secret<64>, Self::AssociatedObject)>; } /// ZSSP bi-directional packet transport channel. pub struct Session { /// This side's session ID (unique on this side) pub id: SessionId, /// An arbitrary object associated with session (type defined in Host trait) pub associated_object: H::AssociatedObject, send_counter: Counter, // Outgoing packet counter and nonce state psk: Secret<64>, // Arbitrary PSK provided by external code ss: Secret<48>, // Static raw shared ECDH NIST P-384 key header_check_cipher: Aes, // Cipher used for header MAC (fragmentation) state: RwLock, // Mutable parts of state (other than defrag buffers) remote_s_public_hash: [u8; 48], // SHA384(remote static public key blob) remote_s_public_p384: [u8; P384_PUBLIC_KEY_SIZE], // Remote NIST P-384 static public key defrag: Mutex, 8, 8>>, } struct SessionMutableState { remote_session_id: Option, // The other side's 48-bit session ID keys: [Option; KEY_HISTORY_SIZE], // Buffers to store current, next, and last active key key_ptr: usize, // Pointer used for keys[] circular buffer offer: Option>, // Most recent ephemeral offer sent to remote last_remote_offer: i64, // Time of most recent ephemeral offer (ms) } impl Session { /// Create a new session and send an initial key offer message to the other end. /// /// * `host` - Interface to application using ZSSP /// * `local_session_id` - ID for this side of the session, must be locally unique /// * `remote_s_public` - Remote side's public key/identity /// * `offer_metadata` - Arbitrary meta-data to send with key offer (empty if none) /// * `psk` - Arbitrary pre-shared key to include as initial key material (use all zero secret if none) /// * `associated_object` - Arbitrary object to put into session /// * `mtu` - Physical wire MTU /// * `current_time` - Current monotonic time in milliseconds pub fn new( host: &H, mut send: SendFunction, local_session_id: SessionId, remote_s_public: &[u8], offer_metadata: &[u8], psk: &Secret<64>, associated_object: H::AssociatedObject, mtu: usize, current_time: i64, ) -> Result { if let Some(remote_s_public_p384) = H::extract_p384_static(remote_s_public) { if let Some(ss) = host.get_local_s_keypair_p384().agree(&remote_s_public_p384) { let send_counter = Counter::new(); let remote_s_public_hash = SHA384::hash(remote_s_public); let header_check_cipher = Aes::new(kbkdf512(ss.as_bytes(), KBKDF_KEY_USAGE_LABEL_HEADER_CHECK).first_n::()); if let Ok(offer) = send_ephemeral_offer( &mut send, send_counter.next(), local_session_id, None, host.get_local_s_public(), offer_metadata, &remote_s_public_p384, &remote_s_public_hash, &ss, None, None, mtu, current_time, ) { return Ok(Self { id: local_session_id, associated_object, send_counter, psk: psk.clone(), ss, header_check_cipher, state: RwLock::new(SessionMutableState { remote_session_id: None, keys: [None, None, None], key_ptr: 0, offer: Some(offer), last_remote_offer: i64::MIN, }), remote_s_public_hash, remote_s_public_p384: remote_s_public_p384.as_bytes().clone(), defrag: Mutex::new(RingBufferMap::new(random::xorshift64_random() as u32)), }); } } } return Err(Error::InvalidParameter); } /// Send data over the session. /// /// * `send` - Function to call to send physical packet(s) /// * `mtu_buffer` - A writable work buffer whose size also specifies the physical MTU /// * `data` - Data to send #[inline] pub fn send( &self, mut send: SendFunction, mtu_buffer: &mut [u8], mut data: &[u8], ) -> Result<(), Error> { debug_assert!(mtu_buffer.len() >= MIN_TRANSPORT_MTU); let state = self.state.read().unwrap(); if let Some(remote_session_id) = state.remote_session_id { if let Some(key) = state.keys[state.key_ptr].as_ref() { // Total size of the armored packet we are going to send (may end up being fragmented) let mut packet_len = data.len() + HEADER_SIZE + AES_GCM_TAG_SIZE; // This outgoing packet's nonce counter value. let counter = self.send_counter.next(); // Create initial header for first fragment of packet and place in first HEADER_SIZE bytes of buffer. create_packet_header( mtu_buffer, packet_len, mtu_buffer.len(), PACKET_TYPE_DATA, remote_session_id.into(), counter, )?; // Get an initialized AES-GCM cipher and re-initialize with a 96-bit IV built from remote session ID, // packet type, and counter. let mut c = key.get_send_cipher(counter)?; c.reset_init_gcm(CanonicalHeader::make(remote_session_id, PACKET_TYPE_DATA, counter.to_u32()).as_bytes()); // Send first N-1 fragments of N total fragments. if packet_len > mtu_buffer.len() { let mut header: [u8; 16] = mtu_buffer[..HEADER_SIZE].try_into().unwrap(); let fragment_data_mtu = mtu_buffer.len() - HEADER_SIZE; let last_fragment_data_mtu = mtu_buffer.len() - (HEADER_SIZE + AES_GCM_TAG_SIZE); loop { let fragment_data_size = fragment_data_mtu.min(data.len()); let fragment_size = fragment_data_size + HEADER_SIZE; c.crypt(&data[..fragment_data_size], &mut mtu_buffer[HEADER_SIZE..fragment_size]); data = &data[fragment_data_size..]; set_header_check_code(mtu_buffer, &self.header_check_cipher); send(&mut mtu_buffer[..fragment_size]); debug_assert!(header[15].wrapping_shr(2) < 63); header[15] += 0x04; // increment fragment number mtu_buffer[..HEADER_SIZE].copy_from_slice(&header); if data.len() <= last_fragment_data_mtu { break; } } packet_len = data.len() + HEADER_SIZE + AES_GCM_TAG_SIZE; } // Send final fragment (or only fragment if no fragmentation was needed) let gcm_tag_idx = data.len() + HEADER_SIZE; c.crypt(data, &mut mtu_buffer[HEADER_SIZE..gcm_tag_idx]); mtu_buffer[gcm_tag_idx..packet_len].copy_from_slice(&c.finish_encrypt()); set_header_check_code(mtu_buffer, &self.header_check_cipher); send(&mut mtu_buffer[..packet_len]); // Check reusable AES-GCM instance back into pool. key.return_send_cipher(c); return Ok(()); } else { unlikely_branch(); } } else { unlikely_branch(); } return Err(Error::SessionNotEstablished); } /// Check whether this session is established. pub fn established(&self) -> bool { let state = self.state.read().unwrap(); state.remote_session_id.is_some() && state.keys[state.key_ptr].is_some() } /// Get information about this session's security state. /// /// This returns a tuple of: the key fingerprint, the time it was established, the length of its ratchet chain, /// and whether Kyber1024 was used. None is returned if the session isn't established. pub fn status(&self) -> Option<([u8; 16], i64, u64, bool)> { let state = self.state.read().unwrap(); if let Some(key) = state.keys[state.key_ptr].as_ref() { Some((key.secret_fingerprint, key.establish_time, key.ratchet_count, key.jedi)) } else { None } } /// This function needs to be called on each session at least every SERVICE_INTERVAL milliseconds. /// /// * `host` - Interface to application using ZSSP /// * `send` - Function to call to send physical packet(s) /// * `offer_metadata' - Any meta-data to include with initial key offers sent. /// * `mtu` - Physical MTU for sent packets /// * `current_time` - Current monotonic time in milliseconds /// * `force_rekey` - Re-key the session now regardless of key aging (still subject to rate limiting) pub fn service( &self, host: &H, mut send: SendFunction, offer_metadata: &[u8], mtu: usize, current_time: i64, force_rekey: bool, ) { let state = self.state.read().unwrap(); if (force_rekey || state.keys[state.key_ptr] .as_ref() .map_or(true, |key| key.lifetime.should_rekey(self.send_counter.previous(), current_time))) && state .offer .as_ref() .map_or(true, |o| (current_time - o.creation_time) > H::REKEY_RATE_LIMIT_MS) { if let Some(remote_s_public_p384) = P384PublicKey::from_bytes(&self.remote_s_public_p384) { if let Ok(offer) = send_ephemeral_offer( &mut send, self.send_counter.next(), self.id, state.remote_session_id, host.get_local_s_public(), offer_metadata, &remote_s_public_p384, &self.remote_s_public_hash, &self.ss, state.keys[state.key_ptr].as_ref(), if state.remote_session_id.is_some() { Some(&self.header_check_cipher) } else { None }, mtu, current_time, ) { drop(state); let _ = self.state.write().unwrap().offer.replace(offer); } } } } } impl ReceiveContext { pub fn new(host: &H) -> Self { Self { initial_offer_defrag: Mutex::new(RingBufferMap::new(random::xorshift64_random() as u32)), incoming_init_header_check_cipher: Aes::new( kbkdf512(host.get_local_s_public_hash(), KBKDF_KEY_USAGE_LABEL_HEADER_CHECK).first_n::(), ), } } /// Receive, authenticate, decrypt, and process a physical wire packet. /// /// * `host` - Interface to application using ZSSP /// * `remote_address` - Remote physical address of source endpoint /// * `data_buf` - Buffer to receive decrypted and authenticated object data (an error is returned if too small) /// * `incoming_packet_buf` - Buffer containing incoming wire packet (receive() takes ownership) /// * `mtu` - Physical wire MTU for sending packets /// * `current_time` - Current monotonic time in milliseconds #[inline] pub fn receive<'a, SendFunction: FnMut(&mut [u8])>( &self, host: &H, remote_address: &H::RemoteAddress, mut send: SendFunction, data_buf: &'a mut [u8], incoming_packet_buf: H::IncomingPacketBuffer, mtu: usize, current_time: i64, ) -> Result, Error> { let incoming_packet = incoming_packet_buf.as_ref(); if incoming_packet.len() < MIN_PACKET_SIZE { unlikely_branch(); return Err(Error::InvalidPacket); } let counter = u32::from_le(memory::load_raw(incoming_packet)); let packet_type_fragment_info = u16::from_le(memory::load_raw(&incoming_packet[14..16])); let packet_type = (packet_type_fragment_info & 0x0f) as u8; let fragment_count = ((packet_type_fragment_info.wrapping_shr(4) + 1) as u8) & 63; let fragment_no = packet_type_fragment_info.wrapping_shr(10) as u8; // & 63 not needed if let Some(local_session_id) = SessionId::new_from_u64(u64::from_le(memory::load_raw(&incoming_packet[8..16])) & 0xffffffffffffu64) { if let Some(session) = host.session_lookup(local_session_id) { if verify_header_check_code(incoming_packet, &session.header_check_cipher) { let canonical_header = CanonicalHeader::make(local_session_id, packet_type, counter); if fragment_count > 1 { if fragment_count <= (MAX_FRAGMENTS as u8) && fragment_no < fragment_count { let mut defrag = session.defrag.lock().unwrap(); let fragment_gather_array = defrag.get_or_create_mut(&counter, || GatherArray::new(fragment_count)); if let Some(assembled_packet) = fragment_gather_array.add(fragment_no, incoming_packet_buf) { drop(defrag); // release lock return self.receive_complete( host, remote_address, &mut send, data_buf, canonical_header.as_bytes(), assembled_packet.as_ref(), packet_type, Some(session), mtu, current_time, ); } } else { unlikely_branch(); return Err(Error::InvalidPacket); } } else { return self.receive_complete( host, remote_address, &mut send, data_buf, canonical_header.as_bytes(), &[incoming_packet_buf], packet_type, Some(session), mtu, current_time, ); } } else { unlikely_branch(); return Err(Error::FailedAuthentication); } } else { unlikely_branch(); return Err(Error::UnknownLocalSessionId(local_session_id)); } } else { unlikely_branch(); // we want data receive to be the priority branch, this is only occasionally used if verify_header_check_code(incoming_packet, &self.incoming_init_header_check_cipher) { let canonical_header = CanonicalHeader::make(SessionId::NIL, packet_type, counter); if fragment_count > 1 { let mut defrag = self.initial_offer_defrag.lock().unwrap(); let fragment_gather_array = defrag.get_or_create_mut(&counter, || GatherArray::new(fragment_count)); if let Some(assembled_packet) = fragment_gather_array.add(fragment_no, incoming_packet_buf) { drop(defrag); // release lock return self.receive_complete( host, remote_address, &mut send, data_buf, canonical_header.as_bytes(), assembled_packet.as_ref(), packet_type, None, mtu, current_time, ); } } else { return self.receive_complete( host, remote_address, &mut send, data_buf, canonical_header.as_bytes(), &[incoming_packet_buf], packet_type, None, mtu, current_time, ); } } else { unlikely_branch(); return Err(Error::FailedAuthentication); } }; return Ok(ReceiveResult::Ok); } /// Called internally when all fragments of a packet are received. /// /// NOTE: header check codes will already have been validated on receipt of each fragment. AEAD authentication /// and decryption has NOT yet been performed, and is done here. #[inline] fn receive_complete<'a, SendFunction: FnMut(&mut [u8])>( &self, host: &H, remote_address: &H::RemoteAddress, send: &mut SendFunction, data_buf: &'a mut [u8], canonical_header_bytes: &[u8; 12], fragments: &[H::IncomingPacketBuffer], packet_type: u8, session: Option, mtu: usize, current_time: i64, ) -> Result, Error> { debug_assert!(fragments.len() >= 1); // The first 'if' below should capture both DATA and NOP but not other types. Sanity check this. debug_assert_eq!(PACKET_TYPE_DATA, 0); debug_assert_eq!(PACKET_TYPE_NOP, 1); if packet_type <= PACKET_TYPE_NOP { if let Some(session) = session { let state = session.state.read().unwrap(); for p in 0..KEY_HISTORY_SIZE { let key_ptr = (state.key_ptr + p) % KEY_HISTORY_SIZE; if let Some(key) = state.keys[key_ptr].as_ref() { let mut c = key.get_receive_cipher(); c.reset_init_gcm(canonical_header_bytes); let mut data_len = 0; // Decrypt fragments 0..N-1 where N is the number of fragments. for f in fragments[..(fragments.len() - 1)].iter() { let f = f.as_ref(); debug_assert!(f.len() >= HEADER_SIZE); let current_frag_data_start = data_len; data_len += f.len() - HEADER_SIZE; if data_len > data_buf.len() { unlikely_branch(); key.return_receive_cipher(c); return Err(Error::DataBufferTooSmall); } c.crypt(&f[HEADER_SIZE..], &mut data_buf[current_frag_data_start..data_len]); } // Decrypt final fragment (or only fragment if not fragmented) let current_frag_data_start = data_len; let last_fragment = fragments.last().unwrap().as_ref(); if last_fragment.len() < (HEADER_SIZE + AES_GCM_TAG_SIZE) { unlikely_branch(); return Err(Error::InvalidPacket); } data_len += last_fragment.len() - (HEADER_SIZE + AES_GCM_TAG_SIZE); if data_len > data_buf.len() { unlikely_branch(); key.return_receive_cipher(c); return Err(Error::DataBufferTooSmall); } c.crypt( &last_fragment[HEADER_SIZE..(last_fragment.len() - AES_GCM_TAG_SIZE)], &mut data_buf[current_frag_data_start..data_len], ); let aead_authentication_ok = c.finish_decrypt(&last_fragment[(last_fragment.len() - AES_GCM_TAG_SIZE)..]); key.return_receive_cipher(c); if aead_authentication_ok { // Select this key as the new default if it's newer than the current key. if p > 0 && state.keys[state.key_ptr] .as_ref() .map_or(true, |old| old.establish_counter < key.establish_counter) { drop(state); let mut state = session.state.write().unwrap(); state.key_ptr = key_ptr; for i in 0..KEY_HISTORY_SIZE { if i != key_ptr { if let Some(old_key) = state.keys[key_ptr].as_ref() { // Release pooled cipher memory from old keys. old_key.receive_cipher_pool.lock().unwrap().clear(); old_key.send_cipher_pool.lock().unwrap().clear(); } } } } if packet_type == PACKET_TYPE_DATA { return Ok(ReceiveResult::OkData(&mut data_buf[..data_len])); } else { unlikely_branch(); return Ok(ReceiveResult::Ok); } } } } // If no known key authenticated the packet, decryption has failed. return Err(Error::FailedAuthentication); } else { unlikely_branch(); return Err(Error::SessionNotEstablished); } } else { unlikely_branch(); // To greatly simplify logic handling key exchange packets, assemble these first. // Handling KEX packets isn't the fast path so the extra copying isn't significant. const KEX_BUF_LEN: usize = MIN_TRANSPORT_MTU * KEY_EXCHANGE_MAX_FRAGMENTS; let mut kex_packet = [0_u8; KEX_BUF_LEN]; let mut kex_packet_len = 0; for i in 0..fragments.len() { let mut ff = fragments[i].as_ref(); debug_assert!(ff.len() >= MIN_PACKET_SIZE); if i > 0 { ff = &ff[HEADER_SIZE..]; } let j = kex_packet_len + ff.len(); if j > KEX_BUF_LEN { return Err(Error::InvalidPacket); } kex_packet[kex_packet_len..j].copy_from_slice(ff); kex_packet_len = j; } let kex_packet_saved_ciphertext = kex_packet.clone(); // save for HMAC check later // Key exchange packets begin (after header) with the session protocol version. if kex_packet[HEADER_SIZE] != SESSION_PROTOCOL_VERSION { return Err(Error::UnknownProtocolVersion); } match packet_type { PACKET_TYPE_KEY_OFFER => { // alice (remote) -> bob (local) if kex_packet_len < (HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE + AES_GCM_TAG_SIZE + HMAC_SIZE + HMAC_SIZE) { return Err(Error::InvalidPacket); } let payload_end = kex_packet_len - (AES_GCM_TAG_SIZE + HMAC_SIZE + HMAC_SIZE); let aes_gcm_tag_end = kex_packet_len - (HMAC_SIZE + HMAC_SIZE); let hmac1_end = kex_packet_len - HMAC_SIZE; // Check the second HMAC first, which proves that the sender knows the recipient's full static identity. if !hmac_sha384_2( host.get_local_s_public_hash(), canonical_header_bytes, &kex_packet[HEADER_SIZE..hmac1_end], ) .eq(&kex_packet[hmac1_end..kex_packet_len]) { return Err(Error::FailedAuthentication); } // Check rate limits. if let Some(session) = session.as_ref() { if (current_time - session.state.read().unwrap().last_remote_offer) < H::REKEY_RATE_LIMIT_MS { return Err(Error::RateLimited); } } else { if !host.check_new_session_attempt(self, remote_address) { return Err(Error::RateLimited); } } // Key agreement: alice (remote) ephemeral NIST P-384 <> local static NIST P-384 let (alice_e0_public, e0s) = P384PublicKey::from_bytes(&kex_packet[(HEADER_SIZE + 1)..(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)]) .and_then(|pk| host.get_local_s_keypair_p384().agree(&pk).map(move |s| (pk, s))) .ok_or(Error::FailedAuthentication)?; // Initial key derivation from starting point, mixing in alice's ephemeral public and the e0s. let mut key = Secret(hmac_sha512(&hmac_sha512(&INITIAL_KEY, alice_e0_public.as_bytes()), e0s.as_bytes())); // Decrypt the encrypted part of the packet payload and authenticate the above key exchange via AES-GCM auth. let mut c = AesGcm::new( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_ALICE_TO_BOB).first_n::(), false, ); c.reset_init_gcm(canonical_header_bytes); c.crypt_in_place(&mut kex_packet[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..payload_end]); if !c.finish_decrypt(&kex_packet[payload_end..aes_gcm_tag_end]) { return Err(Error::FailedAuthentication); } // Parse payload and get alice's session ID, alice's public blob, metadata, and (if present) Alice's Kyber1024 public. let (offer_id, alice_session_id, alice_s_public, alice_metadata, alice_e1_public, alice_ratchet_key_fingerprint) = parse_key_offer_after_header(&kex_packet[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..kex_packet_len], packet_type)?; // We either have a session, in which case they should have supplied a ratchet key fingerprint, or // we don't and they should not have supplied one. if session.is_some() != alice_ratchet_key_fingerprint.is_some() { return Err(Error::FailedAuthentication); } // Extract alice's static NIST P-384 public key from her public blob. let alice_s_public_p384 = H::extract_p384_static(alice_s_public).ok_or(Error::InvalidPacket)?; // Key agreement: both sides' static P-384 keys. let ss = host .get_local_s_keypair_p384() .agree(&alice_s_public_p384) .ok_or(Error::FailedAuthentication)?; // Mix result of 'ss' agreement into master key. key = Secret(hmac_sha512(key.as_bytes(), ss.as_bytes())); // Authenticate entire packet with HMAC-SHA384, verifying alice's identity via 'ss' secret that was // just mixed into the key. if !hmac_sha384_2( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_HMAC).first_n::<48>(), canonical_header_bytes, &kex_packet_saved_ciphertext[HEADER_SIZE..aes_gcm_tag_end], ) .eq(&kex_packet[aes_gcm_tag_end..hmac1_end]) { return Err(Error::FailedAuthentication); } // Alice's offer has been verified and her current key state reconstructed. // Perform checks and match ratchet key if there's an existing session, or gate (via host) and // then create new sessions. let (new_session, ratchet_key, ratchet_count) = if let Some(session) = session.as_ref() { // Existing session identity must match the one in this offer. if !session.remote_s_public_hash.eq(&SHA384::hash(&alice_s_public)) { return Err(Error::FailedAuthentication); } // Match ratchet key fingerprint and fail if no match, which likely indicates an old offer packet. let alice_ratchet_key_fingerprint = alice_ratchet_key_fingerprint.as_ref().unwrap(); let mut ratchet_key = None; let mut ratchet_count = 0; let state = session.state.read().unwrap(); for k in state.keys.iter() { if let Some(k) = k.as_ref() { if secret_fingerprint(k.ratchet_key.as_bytes())[..16].eq(alice_ratchet_key_fingerprint) { ratchet_key = Some(k.ratchet_key.clone()); ratchet_count = k.ratchet_count; break; } } } if ratchet_key.is_none() { return Ok(ReceiveResult::Ignored); // old packet? } (None, ratchet_key, ratchet_count) } else { if let Some((new_session_id, psk, associated_object)) = host.accept_new_session(self, remote_address, alice_s_public, alice_metadata) { let header_check_cipher = Aes::new( kbkdf512(ss.as_bytes(), KBKDF_KEY_USAGE_LABEL_HEADER_CHECK).first_n::(), ); ( Some(Session:: { id: new_session_id, associated_object, send_counter: Counter::new(), psk, ss, header_check_cipher, state: RwLock::new(SessionMutableState { remote_session_id: Some(alice_session_id), keys: [None, None, None], key_ptr: 0, offer: None, last_remote_offer: current_time, }), remote_s_public_hash: SHA384::hash(&alice_s_public), remote_s_public_p384: alice_s_public_p384.as_bytes().clone(), defrag: Mutex::new(RingBufferMap::new(random::xorshift64_random() as u32)), }), None, 0, ) } else { return Err(Error::NewSessionRejected); } }; // Set 'session' to a reference to either the existing or the new session. let existing_session = session; let session = existing_session.as_ref().map_or_else(|| new_session.as_ref().unwrap(), |s| &*s); // Generate our ephemeral NIST P-384 key pair. let bob_e0_keypair = P384KeyPair::generate(); // Key agreement: both sides' ephemeral P-384 public keys. let e0e0 = bob_e0_keypair.agree(&alice_e0_public).ok_or(Error::FailedAuthentication)?; // Key agreement: bob (local) static NIST P-384, alice (remote) ephemeral P-384. let se0 = bob_e0_keypair.agree(&alice_s_public_p384).ok_or(Error::FailedAuthentication)?; // Mix in the psk, the key to this point, our ephemeral public, e0e0, and se0, completing Noise_IK. // // FIPS note: the order of HMAC parameters are flipped here from the usual Noise HMAC(key, X). That's because // NIST/FIPS allows HKDF with HMAC(salt, key) and salt is allowed to be anything. This way if the PSK is not // FIPS compliant the compliance of the entire key derivation is not invalidated. Both inputs are secrets of // fixed size so this shouldn't matter cryptographically. key = Secret(hmac_sha512( session.psk.as_bytes(), &hmac_sha512( &hmac_sha512(&hmac_sha512(key.as_bytes(), bob_e0_keypair.public_key_bytes()), e0e0.as_bytes()), se0.as_bytes(), ), )); // At this point we've completed Noise_IK key derivation with NIST P-384 ECDH, but now for hybrid and ratcheting... // Generate a Kyber encapsulated ciphertext if Kyber is enabled and the other side sent us a public key. let (bob_e1_public, e1e1) = if JEDI && alice_e1_public.len() > 0 { if let Ok((bob_e1_public, e1e1)) = pqc_kyber::encapsulate(alice_e1_public, &mut random::SecureRandom::default()) { (Some(bob_e1_public), Some(Secret(e1e1))) } else { return Err(Error::FailedAuthentication); } } else { (None, None) }; // Create reply packet. let mut reply_buf = [0_u8; KEX_BUF_LEN]; let reply_counter = session.send_counter.next(); let mut reply_len = { let mut rp = &mut reply_buf[HEADER_SIZE..]; rp.write_all(&[SESSION_PROTOCOL_VERSION])?; rp.write_all(bob_e0_keypair.public_key_bytes())?; rp.write_all(&offer_id)?; rp.write_all(&session.id.0.to_le_bytes()[..SESSION_ID_SIZE])?; varint::write(&mut rp, 0)?; // they don't need our static public; they have it varint::write(&mut rp, 0)?; // no meta-data in counter-offers (could be used in the future) if let Some(bob_e1_public) = bob_e1_public.as_ref() { rp.write_all(&[E1_TYPE_KYBER1024])?; rp.write_all(bob_e1_public)?; } else { rp.write_all(&[E1_TYPE_NONE])?; } if ratchet_key.is_some() { rp.write_all(&[0x01])?; rp.write_all(alice_ratchet_key_fingerprint.as_ref().unwrap())?; } else { rp.write_all(&[0x00])?; } KEX_BUF_LEN - rp.len() }; create_packet_header( &mut reply_buf, reply_len, mtu, PACKET_TYPE_KEY_COUNTER_OFFER, alice_session_id.into(), reply_counter, )?; let reply_canonical_header = CanonicalHeader::make(alice_session_id.into(), PACKET_TYPE_KEY_COUNTER_OFFER, reply_counter.to_u32()); // Encrypt reply packet using final Noise_IK key BEFORE mixing hybrid or ratcheting, since the other side // must decrypt before doing these things. let mut c = AesGcm::new( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_BOB_TO_ALICE).first_n::(), true, ); c.reset_init_gcm(reply_canonical_header.as_bytes()); c.crypt_in_place(&mut reply_buf[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..reply_len]); let c = c.finish_encrypt(); reply_buf[reply_len..(reply_len + AES_GCM_TAG_SIZE)].copy_from_slice(&c); reply_len += AES_GCM_TAG_SIZE; // Mix ratchet key from previous session key (if any) and Kyber1024 hybrid shared key (if any). if let Some(ratchet_key) = ratchet_key { key = Secret(hmac_sha512(ratchet_key.as_bytes(), key.as_bytes())); } if let Some(e1e1) = e1e1.as_ref() { key = Secret(hmac_sha512(e1e1.as_bytes(), key.as_bytes())); } // Authenticate packet using HMAC-SHA384 with final key. Note that while the final key now has the Kyber secret // mixed in, this doesn't constitute session authentication with Kyber because there's no static Kyber key // associated with the remote identity. An attacker who can break NIST P-384 (and has the psk) could MITM the // Kyber exchange, but you'd need a not-yet-existing quantum computer for that. let hmac = hmac_sha384_2( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_HMAC).first_n::<48>(), reply_canonical_header.as_bytes(), &reply_buf[HEADER_SIZE..reply_len], ); reply_buf[reply_len..(reply_len + HMAC_SIZE)].copy_from_slice(&hmac); reply_len += HMAC_SIZE; let key = SessionKey::new(key, Role::Bob, current_time, reply_counter, ratchet_count + 1, e1e1.is_some()); let mut state = session.state.write().unwrap(); let _ = state.remote_session_id.replace(alice_session_id); let next_key_ptr = (state.key_ptr + 1) % KEY_HISTORY_SIZE; let _ = state.keys[next_key_ptr].replace(key); drop(state); // Bob now has final key state for this exchange. Yay! Now reply to Alice so she can construct it. send_with_fragmentation(send, &mut reply_buf[..reply_len], mtu, &session.header_check_cipher); if new_session.is_some() { return Ok(ReceiveResult::OkNewSession(new_session.unwrap())); } else { return Ok(ReceiveResult::Ok); } } PACKET_TYPE_KEY_COUNTER_OFFER => { // bob (remote) -> alice (local) if kex_packet_len < (HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE + AES_GCM_TAG_SIZE + HMAC_SIZE) { return Err(Error::InvalidPacket); } let payload_end = kex_packet_len - (AES_GCM_TAG_SIZE + HMAC_SIZE); let aes_gcm_tag_end = kex_packet_len - HMAC_SIZE; if let Some(session) = session { let state = session.state.read().unwrap(); if let Some(offer) = state.offer.as_ref() { let (bob_e0_public, e0e0) = P384PublicKey::from_bytes(&kex_packet[(HEADER_SIZE + 1)..(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)]) .and_then(|pk| offer.alice_e0_keypair.agree(&pk).map(move |s| (pk, s))) .ok_or(Error::FailedAuthentication)?; let se0 = host .get_local_s_keypair_p384() .agree(&bob_e0_public) .ok_or(Error::FailedAuthentication)?; let mut key = Secret(hmac_sha512( session.psk.as_bytes(), &hmac_sha512( &hmac_sha512(&hmac_sha512(offer.key.as_bytes(), bob_e0_public.as_bytes()), e0e0.as_bytes()), se0.as_bytes(), ), )); let mut c = AesGcm::new( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_BOB_TO_ALICE).first_n::(), false, ); c.reset_init_gcm(canonical_header_bytes); c.crypt_in_place(&mut kex_packet[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..payload_end]); if !c.finish_decrypt(&kex_packet[payload_end..aes_gcm_tag_end]) { return Err(Error::FailedAuthentication); } // Alice has now completed Noise_IK with NIST P-384 and verified with GCM auth, but now for hybrid... let (offer_id, bob_session_id, _, _, bob_e1_public, bob_ratchet_key_id) = parse_key_offer_after_header( &kex_packet[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..kex_packet_len], packet_type, )?; if !offer.id.eq(&offer_id) { return Ok(ReceiveResult::Ignored); } let e1e1 = if JEDI && bob_e1_public.len() > 0 && offer.alice_e1_keypair.is_some() { if let Ok(e1e1) = pqc_kyber::decapsulate(bob_e1_public, &offer.alice_e1_keypair.as_ref().unwrap().secret) { Some(Secret(e1e1)) } else { return Err(Error::FailedAuthentication); } } else { None }; let mut ratchet_count = 0; if bob_ratchet_key_id.is_some() && offer.ratchet_key.is_some() { key = Secret(hmac_sha512(offer.ratchet_key.as_ref().unwrap().as_bytes(), key.as_bytes())); ratchet_count = offer.ratchet_count; } if let Some(e1e1) = e1e1.as_ref() { key = Secret(hmac_sha512(e1e1.as_bytes(), key.as_bytes())); } if !hmac_sha384_2( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_HMAC).first_n::<48>(), canonical_header_bytes, &kex_packet_saved_ciphertext[HEADER_SIZE..aes_gcm_tag_end], ) .eq(&kex_packet[aes_gcm_tag_end..kex_packet_len]) { return Err(Error::FailedAuthentication); } // Alice has now completed and validated the full hybrid exchange. let counter = session.send_counter.next(); let key = SessionKey::new(key, Role::Alice, current_time, counter, ratchet_count + 1, e1e1.is_some()); let mut reply_buf = [0_u8; HEADER_SIZE + AES_GCM_TAG_SIZE]; create_packet_header( &mut reply_buf, HEADER_SIZE + AES_GCM_TAG_SIZE, mtu, PACKET_TYPE_NOP, bob_session_id.into(), counter, )?; let mut c = key.get_send_cipher(counter)?; c.reset_init_gcm(CanonicalHeader::make(bob_session_id.into(), PACKET_TYPE_NOP, counter.to_u32()).as_bytes()); reply_buf[HEADER_SIZE..].copy_from_slice(&c.finish_encrypt()); key.return_send_cipher(c); set_header_check_code(&mut reply_buf, &session.header_check_cipher); send(&mut reply_buf); drop(state); let mut state = session.state.write().unwrap(); let _ = state.remote_session_id.replace(bob_session_id); let next_key_ptr = (state.key_ptr + 1) % KEY_HISTORY_SIZE; let _ = state.keys[next_key_ptr].replace(key); let _ = state.offer.take(); return Ok(ReceiveResult::Ok); } } // Just ignore counter-offers that are out of place. They probably indicate that this side // restarted and needs to establish a new session. return Ok(ReceiveResult::Ignored); } _ => return Err(Error::InvalidPacket), } } } } /// Outgoing packet counter with strictly ordered atomic semantics. #[repr(transparent)] struct Counter(AtomicU64); impl Counter { #[inline(always)] fn new() -> Self { // Using a random value has no security implication. Zero would be fine. This just // helps randomize packet contents a bit. Self(AtomicU64::new(random::next_u32_secure() as u64)) } /// Get the value most recently used to send a packet. #[inline(always)] fn previous(&self) -> CounterValue { CounterValue(self.0.load(Ordering::SeqCst)) } /// Get a counter value for the next packet being sent. #[inline(always)] fn next(&self) -> CounterValue { CounterValue(self.0.fetch_add(1, Ordering::SeqCst)) } } /// A value of the outgoing packet counter. /// /// The used portion of the packet counter is the least significant 32 bits, but the internal /// counter state is kept as a 64-bit integer. This makes it easier to correctly handle /// key expiration after usage limits are reached without complicated logic to handle 32-bit /// wrapping. Usage limits are below 2^32 so the actual 32-bit counter will not wrap for a /// given shared secret key. #[repr(transparent)] #[derive(Copy, Clone)] struct CounterValue(u64); impl CounterValue { #[inline(always)] pub fn to_u32(&self) -> u32 { self.0 as u32 } } /// "Canonical header" for generating 96-bit AES-GCM nonce and for inclusion in HMACs. /// /// This is basically the actual header but with fragment count and fragment total set to zero. /// Fragmentation is not considered when authenticating the entire packet. A separate header /// check code is used to make fragmentation itself more robust, but that's outside the scope /// of AEAD authentication. #[derive(Clone, Copy)] #[repr(C, packed)] struct CanonicalHeader(u64, u32); impl CanonicalHeader { #[inline(always)] pub fn make(session_id: SessionId, packet_type: u8, counter: u32) -> Self { CanonicalHeader( (u64::from(session_id) | (packet_type as u64).wrapping_shl(48)).to_le(), counter.to_le(), ) } #[inline(always)] pub fn as_bytes(&self) -> &[u8; 12] { memory::as_byte_array(self) } } /// Alice's KEY_OFFER, remembered so Noise agreement process can resume on KEY_COUNTER_OFFER. struct EphemeralOffer { id: [u8; 16], // Arbitrary random offer ID creation_time: i64, // Local time when offer was created ratchet_count: u64, // Ratchet count starting at zero for initial offer ratchet_key: Option>, // Ratchet key from previous offer key: Secret<64>, // Shared secret in-progress, at state after offer sent alice_e0_keypair: P384KeyPair, // NIST P-384 key pair (Noise ephemeral key for Alice) alice_e1_keypair: Option, // Kyber1024 key pair (agreement result mixed post-Noise) } /// Create and send an ephemeral offer, returning the EphemeralOffer part that must be saved. fn send_ephemeral_offer( send: &mut SendFunction, counter: CounterValue, alice_session_id: SessionId, bob_session_id: Option, alice_s_public: &[u8], alice_metadata: &[u8], bob_s_public_p384: &P384PublicKey, bob_s_public_hash: &[u8], ss: &Secret<48>, current_key: Option<&SessionKey>, header_check_cipher: Option<&Aes>, // None to use one based on the recipient's public key for initial contact mtu: usize, current_time: i64, ) -> Result, Error> { // Generate a NIST P-384 pair. let alice_e0_keypair = P384KeyPair::generate(); // Perform key agreement with the other side's static P-384 public key. let e0s = alice_e0_keypair.agree(bob_s_public_p384).ok_or(Error::InvalidPacket)?; // Generate a Kyber1024 pair if enabled. let alice_e1_keypair = if JEDI { Some(pqc_kyber::keypair(&mut random::SecureRandom::get())) } else { None }; // Get ratchet key for current key if one exists. let (ratchet_key, ratchet_count) = if let Some(current_key) = current_key { (Some(current_key.ratchet_key.clone()), current_key.ratchet_count) } else { (None, 0) }; // Random ephemeral offer ID let id: [u8; 16] = random::get_bytes_secure(); // Create ephemeral offer packet (not fragmented yet). const PACKET_BUF_SIZE: usize = MIN_TRANSPORT_MTU * KEY_EXCHANGE_MAX_FRAGMENTS; let mut packet_buf = [0_u8; PACKET_BUF_SIZE]; let mut packet_len = { let mut p = &mut packet_buf[HEADER_SIZE..]; p.write_all(&[SESSION_PROTOCOL_VERSION])?; p.write_all(alice_e0_keypair.public_key_bytes())?; p.write_all(&id)?; p.write_all(&alice_session_id.0.to_le_bytes()[..SESSION_ID_SIZE])?; varint::write(&mut p, alice_s_public.len() as u64)?; p.write_all(alice_s_public)?; varint::write(&mut p, alice_metadata.len() as u64)?; p.write_all(alice_metadata)?; if let Some(e1kp) = alice_e1_keypair { p.write_all(&[E1_TYPE_KYBER1024])?; p.write_all(&e1kp.public)?; } else { p.write_all(&[E1_TYPE_NONE])?; } if let Some(ratchet_key) = ratchet_key.as_ref() { p.write_all(&[0x01])?; p.write_all(&secret_fingerprint(ratchet_key.as_bytes())[..16])?; } else { p.write_all(&[0x00])?; } PACKET_BUF_SIZE - p.len() }; // Create ephemeral agreement secret. let key = Secret(hmac_sha512( &hmac_sha512(&INITIAL_KEY, alice_e0_keypair.public_key_bytes()), e0s.as_bytes(), )); let bob_session_id = bob_session_id.unwrap_or(SessionId::NIL); create_packet_header(&mut packet_buf, packet_len, mtu, PACKET_TYPE_KEY_OFFER, bob_session_id, counter)?; let canonical_header = CanonicalHeader::make(bob_session_id, PACKET_TYPE_KEY_OFFER, counter.to_u32()); // Encrypt packet and attach AES-GCM tag. let gcm_tag = { let mut c = AesGcm::new( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_ALICE_TO_BOB).first_n::(), true, ); c.reset_init_gcm(canonical_header.as_bytes()); c.crypt_in_place(&mut packet_buf[(HEADER_SIZE + 1 + P384_PUBLIC_KEY_SIZE)..packet_len]); c.finish_encrypt() }; packet_buf[packet_len..(packet_len + AES_GCM_TAG_SIZE)].copy_from_slice(&gcm_tag); packet_len += AES_GCM_TAG_SIZE; // Mix in static secret. let key = Secret(hmac_sha512(key.as_bytes(), ss.as_bytes())); // HMAC packet using static + ephemeral key. let hmac = hmac_sha384_2( kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_HMAC).first_n::<48>(), canonical_header.as_bytes(), &packet_buf[HEADER_SIZE..packet_len], ); packet_buf[packet_len..(packet_len + HMAC_SIZE)].copy_from_slice(&hmac); packet_len += HMAC_SIZE; // Add secondary HMAC to verify that the caller knows the recipient's full static public identity. let hmac = hmac_sha384_2(bob_s_public_hash, canonical_header.as_bytes(), &packet_buf[HEADER_SIZE..packet_len]); packet_buf[packet_len..(packet_len + HMAC_SIZE)].copy_from_slice(&hmac); packet_len += HMAC_SIZE; if let Some(header_check_cipher) = header_check_cipher { send_with_fragmentation(send, &mut packet_buf[..packet_len], mtu, header_check_cipher); } else { send_with_fragmentation( send, &mut packet_buf[..packet_len], mtu, &Aes::new(kbkdf512(&bob_s_public_hash, KBKDF_KEY_USAGE_LABEL_HEADER_CHECK).first_n::()), ); } Ok(Box::new(EphemeralOffer { id, creation_time: current_time, ratchet_count, ratchet_key, key, alice_e0_keypair, alice_e1_keypair, })) } /// Populate all but the header check code in the first 16 bytes of a packet or fragment. #[inline(always)] fn create_packet_header( header: &mut [u8], packet_len: usize, mtu: usize, packet_type: u8, recipient_session_id: SessionId, counter: CounterValue, ) -> Result<(), Error> { let fragment_count = ((packet_len as f32) / (mtu - HEADER_SIZE) as f32).ceil() as usize; debug_assert!(header.len() >= HEADER_SIZE); debug_assert!(mtu >= MIN_TRANSPORT_MTU); debug_assert!(packet_len >= MIN_PACKET_SIZE); debug_assert!(fragment_count > 0); debug_assert!(fragment_count <= MAX_FRAGMENTS); debug_assert!(packet_type <= 0x0f); // packet type is 4 bits if fragment_count <= MAX_FRAGMENTS { // Header indexed by bit: // [0-31] counter // [32-63] header check code (computed later) // [64-111] recipient's session ID (unique on their side) // [112-115] packet type (0-15) // [116-121] number of fragments (0..63 for 1..64 fragments total) // [122-127] fragment number (0, 1, 2, ...) memory::store_raw((counter.to_u32() as u64).to_le(), header); memory::store_raw( (u64::from(recipient_session_id) | (packet_type as u64).wrapping_shl(48) | ((fragment_count - 1) as u64).wrapping_shl(52)) .to_le(), &mut header[8..], ); Ok(()) } else { unlikely_branch(); Err(Error::DataTooLarge) } } /// Break a packet into fragments and send them all. fn send_with_fragmentation( send: &mut SendFunction, packet: &mut [u8], mtu: usize, header_check_cipher: &Aes, ) { let packet_len = packet.len(); let mut fragment_start = 0; let mut fragment_end = packet_len.min(mtu); let mut header: [u8; 16] = packet[..HEADER_SIZE].try_into().unwrap(); loop { let fragment = &mut packet[fragment_start..fragment_end]; set_header_check_code(fragment, header_check_cipher); send(fragment); if fragment_end < packet_len { debug_assert!(header[15].wrapping_shr(2) < 63); header[15] += 0x04; // increment fragment number fragment_start = fragment_end - HEADER_SIZE; fragment_end = (fragment_start + mtu).min(packet_len); packet[fragment_start..(fragment_start + HEADER_SIZE)].copy_from_slice(&header); } else { debug_assert_eq!(fragment_end, packet_len); break; } } } /// Set 32-bit header check code, used to make fragmentation mechanism robust. #[inline] fn set_header_check_code(packet: &mut [u8], header_check_cipher: &Aes) { debug_assert!(packet.len() >= MIN_PACKET_SIZE); let mut check_code = 0u128.to_ne_bytes(); header_check_cipher.encrypt_block(&packet[8..24], &mut check_code); packet[4..8].copy_from_slice(&check_code[..4]); } /// Verify 32-bit header check code. #[inline] fn verify_header_check_code(packet: &[u8], header_check_cipher: &Aes) -> bool { debug_assert!(packet.len() >= MIN_PACKET_SIZE); let mut header_mac = 0u128.to_ne_bytes(); header_check_cipher.encrypt_block(&packet[8..24], &mut header_mac); memory::load_raw::(&packet[4..8]) == memory::load_raw::(&header_mac) } /// Parse KEY_OFFER and KEY_COUNTER_OFFER starting after the unencrypted public key part. fn parse_key_offer_after_header( incoming_packet: &[u8], packet_type: u8, ) -> Result<([u8; 16], SessionId, &[u8], &[u8], &[u8], Option<[u8; 16]>), Error> { let mut p = &incoming_packet[..]; let mut offer_id = [0_u8; 16]; p.read_exact(&mut offer_id)?; let alice_session_id = SessionId::new_from_reader(&mut p)?; if alice_session_id.is_none() { return Err(Error::InvalidPacket); } let alice_session_id = alice_session_id.unwrap(); let alice_s_public_len = varint::read(&mut p)?.0; if (p.len() as u64) < alice_s_public_len { return Err(Error::InvalidPacket); } let alice_s_public = &p[..(alice_s_public_len as usize)]; p = &p[(alice_s_public_len as usize)..]; let alice_metadata_len = varint::read(&mut p)?.0; if (p.len() as u64) < alice_metadata_len { return Err(Error::InvalidPacket); } let alice_metadata = &p[..(alice_metadata_len as usize)]; p = &p[(alice_metadata_len as usize)..]; if p.is_empty() { return Err(Error::InvalidPacket); } let alice_e1_public = match p[0] { E1_TYPE_KYBER1024 => { if packet_type == PACKET_TYPE_KEY_OFFER { if p.len() < (pqc_kyber::KYBER_PUBLICKEYBYTES + 1) { return Err(Error::InvalidPacket); } let e1p = &p[1..(pqc_kyber::KYBER_PUBLICKEYBYTES + 1)]; p = &p[(pqc_kyber::KYBER_PUBLICKEYBYTES + 1)..]; e1p } else { if p.len() < (pqc_kyber::KYBER_CIPHERTEXTBYTES + 1) { return Err(Error::InvalidPacket); } let e1p = &p[1..(pqc_kyber::KYBER_CIPHERTEXTBYTES + 1)]; p = &p[(pqc_kyber::KYBER_CIPHERTEXTBYTES + 1)..]; e1p } } _ => &[], }; if p.is_empty() { return Err(Error::InvalidPacket); } let alice_ratchet_key_fingerprint = if p[0] == 0x01 { if p.len() < 16 { return Err(Error::InvalidPacket); } Some(p[1..17].try_into().unwrap()) } else { None }; Ok(( offer_id, alice_session_id, alice_s_public, alice_metadata, alice_e1_public, alice_ratchet_key_fingerprint, )) } /// Was this side the one who sent the first offer (Alice) or countered (Bob). /// Note that role is not fixed. Either side can take either role. It's just who /// initiated first. enum Role { Alice, Bob, } /// Key lifetime manager state and logic (separate to spotlight and keep clean) struct KeyLifetime { rekey_at_or_after_counter: u64, hard_expire_at_counter: u64, rekey_at_or_after_timestamp: i64, } impl KeyLifetime { fn new(current_counter: CounterValue, current_time: i64) -> Self { Self { rekey_at_or_after_counter: current_counter.0 + REKEY_AFTER_USES + (random::next_u32_secure() % REKEY_AFTER_USES_MAX_JITTER) as u64, hard_expire_at_counter: current_counter.0 + EXPIRE_AFTER_USES, rekey_at_or_after_timestamp: current_time + REKEY_AFTER_TIME_MS + (random::next_u32_secure() % REKEY_AFTER_TIME_MS_MAX_JITTER) as i64, } } #[inline(always)] fn should_rekey(&self, counter: CounterValue, current_time: i64) -> bool { counter.0 >= self.rekey_at_or_after_counter || current_time >= self.rekey_at_or_after_timestamp } #[inline(always)] fn expired(&self, counter: CounterValue) -> bool { counter.0 >= self.hard_expire_at_counter } } /// A shared symmetric session key. struct SessionKey { secret_fingerprint: [u8; 16], // First 128 bits of a SHA384 computed from the secret establish_time: i64, // Time session key was established establish_counter: u64, // Counter value at which session was established lifetime: KeyLifetime, // Key expiration time and counter ratchet_key: Secret<64>, // Ratchet key for deriving the next session key receive_key: Secret, // Receive side AES-GCM key send_key: Secret, // Send side AES-GCM key receive_cipher_pool: Mutex>>, // Pool of initialized sending ciphers send_cipher_pool: Mutex>>, // Pool of initialized receiving ciphers ratchet_count: u64, // Number of new keys negotiated in this session jedi: bool, // True if Kyber1024 was used (both sides enabled) } impl SessionKey { /// Create a new symmetric shared session key and set its key expiration times, etc. fn new(key: Secret<64>, role: Role, current_time: i64, current_counter: CounterValue, ratchet_count: u64, jedi: bool) -> Self { let a2b: Secret = kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_ALICE_TO_BOB).first_n_clone(); let b2a: Secret = kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_AES_GCM_BOB_TO_ALICE).first_n_clone(); let (receive_key, send_key) = match role { Role::Alice => (b2a, a2b), Role::Bob => (a2b, b2a), }; Self { secret_fingerprint: secret_fingerprint(key.as_bytes())[..16].try_into().unwrap(), establish_time: current_time, establish_counter: current_counter.0, lifetime: KeyLifetime::new(current_counter, current_time), ratchet_key: kbkdf512(key.as_bytes(), KBKDF_KEY_USAGE_LABEL_RATCHETING), receive_key, send_key, receive_cipher_pool: Mutex::new(Vec::with_capacity(2)), send_cipher_pool: Mutex::new(Vec::with_capacity(2)), ratchet_count, jedi, } } #[inline] fn get_send_cipher(&self, counter: CounterValue) -> Result, Error> { if !self.lifetime.expired(counter) { Ok(self .send_cipher_pool .lock() .unwrap() .pop() .unwrap_or_else(|| Box::new(AesGcm::new(self.send_key.as_bytes(), true)))) } else { // Not only do we return an error, but we also destroy the key. let mut scp = self.send_cipher_pool.lock().unwrap(); scp.clear(); self.send_key.nuke(); Err(Error::MaxKeyLifetimeExceeded) } } #[inline] fn return_send_cipher(&self, c: Box) { self.send_cipher_pool.lock().unwrap().push(c); } #[inline] fn get_receive_cipher(&self) -> Box { self.receive_cipher_pool .lock() .unwrap() .pop() .unwrap_or_else(|| Box::new(AesGcm::new(self.receive_key.as_bytes(), false))) } #[inline] fn return_receive_cipher(&self, c: Box) { self.receive_cipher_pool.lock().unwrap().push(c); } } /// Shortcut to HMAC data split into two slices. fn hmac_sha384_2(key: &[u8], a: &[u8], b: &[u8]) -> [u8; 48] { let mut hmac = HMACSHA384::new(key); hmac.update(a); hmac.update(b); hmac.finish() } /// HMAC-SHA512 key derivation function modeled on: https://csrc.nist.gov/publications/detail/sp/800-108/final (page 12) /// Cryptographically this isn't really different from HMAC(key, [label]) with just one byte. fn kbkdf512(key: &[u8], label: u8) -> Secret<64> { Secret(hmac_sha512(key, &[0, 0, 0, 0, b'Z', b'T', label, 0, 0, 0, 0, 0x02, 0x00])) } /// Get a hash of a secret key that can be used as a public fingerprint. fn secret_fingerprint(key: &[u8]) -> [u8; 48] { let mut tmp = SHA384::new(); tmp.update("fp".as_bytes()); tmp.update(key); tmp.finish() } #[cfg(test)] mod tests { use std::collections::LinkedList; use std::sync::{Arc, Mutex}; use zerotier_utils::hex; #[allow(unused_imports)] use super::*; struct TestHost { local_s: P384KeyPair, local_s_hash: [u8; 48], psk: Secret<64>, session: Mutex>>>>, session_id_counter: Mutex, queue: Mutex>>, key_id: Mutex<[u8; 16]>, this_name: &'static str, other_name: &'static str, } impl TestHost { fn new(psk: Secret<64>, this_name: &'static str, other_name: &'static str) -> Self { let local_s = P384KeyPair::generate(); let local_s_hash = SHA384::hash(local_s.public_key_bytes()); Self { local_s, local_s_hash, psk, session: Mutex::new(None), session_id_counter: Mutex::new(1), queue: Mutex::new(LinkedList::new()), key_id: Mutex::new([0; 16]), this_name, other_name, } } } impl Host for Box { type AssociatedObject = u32; type SessionRef = Arc>>; type IncomingPacketBuffer = Vec; type RemoteAddress = u32; const REKEY_RATE_LIMIT_MS: i64 = 0; fn get_local_s_public(&self) -> &[u8] { self.local_s.public_key_bytes() } fn get_local_s_public_hash(&self) -> &[u8; 48] { &self.local_s_hash } fn get_local_s_keypair_p384(&self) -> &P384KeyPair { &self.local_s } fn extract_p384_static(static_public: &[u8]) -> Option { P384PublicKey::from_bytes(static_public) } fn session_lookup(&self, local_session_id: SessionId) -> Option { self.session.lock().unwrap().as_ref().and_then(|s| { if s.id == local_session_id { Some(s.clone()) } else { None } }) } fn check_new_session_attempt(&self, _: &ReceiveContext, _: &Self::RemoteAddress) -> bool { true } fn accept_new_session( &self, _: &ReceiveContext, _: &u32, _: &[u8], _: &[u8], ) -> Option<(SessionId, Secret<64>, Self::AssociatedObject)> { loop { let mut new_id = self.session_id_counter.lock().unwrap(); *new_id += 1; return Some((SessionId::new_from_u64(*new_id).unwrap(), self.psk.clone(), 0)); } } } #[allow(unused_variables)] #[test] fn establish_session() { let mut data_buf = [0_u8; (1280 - 32) * MAX_FRAGMENTS]; let mut mtu_buffer = [0_u8; 1280]; let mut psk: Secret<64> = Secret::default(); random::fill_bytes_secure(&mut psk.0); let alice_host = Box::new(TestHost::new(psk.clone(), "alice", "bob")); let bob_host = Box::new(TestHost::new(psk.clone(), "bob", "alice")); let alice_rc: Box>> = Box::new(ReceiveContext::new(&alice_host)); let bob_rc: Box>> = Box::new(ReceiveContext::new(&bob_host)); //println!("zssp: size of session (bytes): {}", std::mem::size_of::>>()); let _ = alice_host.session.lock().unwrap().insert(Arc::new( Session::new( &alice_host, |data| bob_host.queue.lock().unwrap().push_front(data.to_vec()), SessionId::new_random(), bob_host.local_s.public_key_bytes(), &[], &psk, 1, mtu_buffer.len(), 1, ) .unwrap(), )); let mut ts = 0; for test_loop in 0..256 { for host in [&alice_host, &bob_host] { let send_to_other = |data: &mut [u8]| { if std::ptr::eq(host, &alice_host) { bob_host.queue.lock().unwrap().push_front(data.to_vec()); } else { alice_host.queue.lock().unwrap().push_front(data.to_vec()); } }; let rc = if std::ptr::eq(host, &alice_host) { &alice_rc } else { &bob_rc }; loop { if let Some(qi) = host.queue.lock().unwrap().pop_back() { let qi_len = qi.len(); ts += 1; let r = rc.receive(host, &0, send_to_other, &mut data_buf, qi, mtu_buffer.len(), ts); if r.is_ok() { let r = r.unwrap(); match r { ReceiveResult::Ok => { //println!("zssp: {} => {} ({}): Ok", host.other_name, host.this_name, qi_len); } ReceiveResult::OkData(data) => { //println!("zssp: {} => {} ({}): OkData length=={}", host.other_name, host.this_name, qi_len, data.len()); assert!(!data.iter().any(|x| *x != 0x12)); } ReceiveResult::OkNewSession(new_session) => { println!( "zssp: {} => {} ({}): OkNewSession ({})", host.other_name, host.this_name, qi_len, u64::from(new_session.id) ); let mut hs = host.session.lock().unwrap(); assert!(hs.is_none()); let _ = hs.insert(Arc::new(new_session)); } ReceiveResult::Ignored => { println!("zssp: {} => {} ({}): Ignored", host.other_name, host.this_name, qi_len); } } } else { println!( "zssp: {} => {} ({}): error: {}", host.other_name, host.this_name, qi_len, r.err().unwrap().to_string() ); panic!(); } } else { break; } } data_buf.fill(0x12); if let Some(session) = host.session.lock().unwrap().as_ref().cloned() { if session.established() { { let mut key_id = host.key_id.lock().unwrap(); let security_info = session.status().unwrap(); if !security_info.0.eq(key_id.as_ref()) { *key_id = security_info.0; println!( "zssp: new key at {}: fingerprint {} ratchet {} kyber {}", host.this_name, hex::to_string(key_id.as_ref()), security_info.2, security_info.3 ); } } for _ in 0..4 { assert!(session .send( send_to_other, &mut mtu_buffer, &data_buf[..((random::xorshift64_random() as usize) % data_buf.len())] ) .is_ok()); } if (test_loop % 8) == 0 && test_loop >= 8 && host.this_name.eq("alice") { session.service(host, send_to_other, &[], mtu_buffer.len(), test_loop as i64, true); } } } } } } }