quic_record_rx.h
/*
* Copyright 2022-2024 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#ifndef OSSL_QUIC_RECORD_RX_H
# define OSSL_QUIC_RECORD_RX_H
# include <openssl/ssl.h>
# include "internal/quic_wire_pkt.h"
# include "internal/quic_types.h"
# include "internal/quic_predef.h"
# include "internal/quic_record_util.h"
# include "internal/quic_demux.h"
# ifndef OPENSSL_NO_QUIC
/*
* QUIC Record Layer - RX
* ======================
*/
typedef struct ossl_qrx_st OSSL_QRX;
typedef struct ossl_qrx_args_st {
OSSL_LIB_CTX *libctx;
const char *propq;
/* Demux which owns the URXEs passed to us. */
QUIC_DEMUX *demux;
/* Length of connection IDs used in short-header packets in bytes. */
size_t short_conn_id_len;
/*
* Maximum number of deferred datagrams buffered at any one time.
* Suggested value: 32.
*/
size_t max_deferred;
/* Initial reference PN used for RX. */
QUIC_PN init_largest_pn[QUIC_PN_SPACE_NUM];
/* Initial key phase. For debugging use only; always 0 in real use. */
unsigned char init_key_phase_bit;
} OSSL_QRX_ARGS;
/* Instantiates a new QRX. */
OSSL_QRX *ossl_qrx_new(const OSSL_QRX_ARGS *args);
/*
* Frees the QRX. All packets obtained using ossl_qrx_read_pkt must already
* have been released by calling ossl_qrx_release_pkt.
*
* You do not need to call ossl_qrx_remove_dst_conn_id first; this function will
* unregister the QRX from the demuxer for all registered destination connection
* IDs (DCIDs) automatically.
*/
void ossl_qrx_free(OSSL_QRX *qrx);
/* Setters for the msg_callback and msg_callback_arg */
void ossl_qrx_set_msg_callback(OSSL_QRX *qrx, ossl_msg_cb msg_callback,
SSL *msg_callback_ssl);
void ossl_qrx_set_msg_callback_arg(OSSL_QRX *qrx,
void *msg_callback_arg);
/*
* Secret Management
* =================
*
* A QRX has several encryption levels (Initial, Handshake, 0-RTT, 1-RTT) and
* two directions (RX, TX). At any given time, key material is managed for each
* (EL, RX/TX) combination.
*
* Broadly, for a given (EL, RX/TX), the following state machine is applicable:
*
* WAITING_FOR_KEYS --[Provide]--> HAVE_KEYS --[Discard]--> | DISCARDED |
* \-------------------------------------[Discard]--> | |
*
* To transition the RX side of an EL from WAITING_FOR_KEYS to HAVE_KEYS, call
* ossl_qrx_provide_secret (for the INITIAL EL, use of
* ossl_quic_provide_initial_secret is recommended).
*
* Once keys have been provisioned for an EL, you call
* ossl_qrx_discard_enc_level to transition the EL to the DISCARDED state. You
* can also call this function to transition directly to the DISCARDED state
* even before any keys have been provisioned for that EL.
*
* The DISCARDED state is terminal for a given EL; you cannot provide a secret
* again for that EL after reaching it.
*
* Incoming packets cannot be processed and decrypted if they target an EL
* not in the HAVE_KEYS state. However, there is a distinction between
* the WAITING_FOR_KEYS and DISCARDED states:
*
* - In the WAITING_FOR_KEYS state, the QRX assumes keys for the given
* EL will eventually arrive. Therefore, if it receives any packet
* for an EL in this state, it buffers it and tries to process it
* again once the EL reaches HAVE_KEYS.
*
* - In the DISCARDED state, the QRX assumes no keys for the given
* EL will ever arrive again. If it receives any packet for an EL
* in this state, it is simply discarded.
*
* If the user wishes to instantiate a new QRX to replace an old one for
* whatever reason, for example to take over for an already established QUIC
* connection, it is important that all ELs no longer being used (i.e., INITIAL,
* 0-RTT, 1-RTT) are transitioned to the DISCARDED state. Otherwise, the QRX
* will assume that keys for these ELs will arrive in future, and will buffer
* any received packets for those ELs perpetually. This can be done by calling
* ossl_qrx_discard_enc_level for all non-1-RTT ELs immediately after
* instantiating the QRX.
*
* The INITIAL EL is not setup automatically when the QRX is instantiated. This
* allows the caller to instead discard it immediately after instantiation of
* the QRX if it is not needed, for example if the QRX is being instantiated to
* take over handling of an existing connection which has already passed the
* INITIAL phase. This avoids the unnecessary derivation of INITIAL keys where
* they are not needed. In the ordinary case, ossl_quic_provide_initial_secret
* should be called immediately after instantiation.
*/
/*
* Provides a secret to the QRX, which arises due to an encryption level change.
* enc_level is a QUIC_ENC_LEVEL_* value. To initialise the INITIAL encryption
* level, it is recommended to use ossl_quic_provide_initial_secret instead.
*
* You should seek to call this function for a given EL before packets of that
* EL arrive and are processed by the QRX. However, if packets have already
* arrived for a given EL, the QRX will defer processing of them and perform
* processing of them when this function is eventually called for the EL in
* question.
*
* suite_id is a QRL_SUITE_* value which determines the AEAD function used for
* the QRX.
*
* The secret passed is used directly to derive the "quic key", "quic iv" and
* "quic hp" values.
*
* secret_len is the length of the secret buffer in bytes. The buffer must be
* sized correctly to the chosen suite, else the function fails.
*
* This function can only be called once for a given EL, except for the INITIAL
* EL, which can need rekeying when a connection retry occurs. Subsequent calls
* for non-INITIAL ELs fail, as do calls made after a corresponding call to
* ossl_qrx_discard_enc_level for that EL. The secret for a non-INITIAL EL
* cannot be changed after it is set because QUIC has no facility for
* introducing additional key material after an EL is setup. QUIC key updates
* are managed semi-automatically by the QRX but do require some caller handling
* (see below).
*
* md is for internal use and should be NULL.
*
* Returns 1 on success or 0 on failure.
*/
int ossl_qrx_provide_secret(OSSL_QRX *qrx,
uint32_t enc_level,
uint32_t suite_id,
EVP_MD *md,
const unsigned char *secret,
size_t secret_len);
/*
* Informs the QRX that it can now discard key material for a given EL. The QRX
* will no longer be able to process incoming packets received at that
* encryption level. This function is idempotent and succeeds if the EL has
* already been discarded.
*
* Returns 1 on success and 0 on failure.
*/
int ossl_qrx_discard_enc_level(OSSL_QRX *qrx, uint32_t enc_level);
/*
* Packet Reception
* ================
*/
/* Information about a received packet. */
struct ossl_qrx_pkt_st {
/*
* Points to a logical representation of the decoded QUIC packet header. The
* data and len fields point to the decrypted QUIC payload (i.e., to a
* sequence of zero or more (potentially malformed) frames to be decoded).
*/
QUIC_PKT_HDR *hdr;
/*
* Address the packet was received from. If this is not available for this
* packet, this field is NULL (but this can only occur for manually injected
* packets).
*/
const BIO_ADDR *peer;
/*
* Local address the packet was sent to. If this is not available for this
* packet, this field is NULL.
*/
const BIO_ADDR *local;
/*
* This is the length of the datagram which contained this packet. Note that
* the datagram may have contained other packets than this. The intended use
* for this is so that the user can enforce minimum datagram sizes (e.g. for
* datagrams containing INITIAL packets), as required by RFC 9000.
*/
size_t datagram_len;
/* The PN which was decoded for the packet, if the packet has a PN field. */
QUIC_PN pn;
/*
* Time the packet was received, or ossl_time_zero() if the demuxer is not
* using a now() function.
*/
OSSL_TIME time;
/* The QRX which was used to receive the packet. */
OSSL_QRX *qrx;
/*
* The key epoch the packet was received with. Always 0 for non-1-RTT
* packets.
*/
uint64_t key_epoch;
/*
* This monotonically increases with each datagram received.
* It is for diagnostic use only.
*/
uint64_t datagram_id;
};
/*
* Tries to read a new decrypted packet from the QRX.
*
* On success, *pkt points to a OSSL_QRX_PKT structure. The structure should be
* freed when no longer needed by calling ossl_qrx_pkt_release(). The structure
* is refcounted; to gain extra references, call ossl_qrx_pkt_up_ref(). This
* will cause a corresponding number of calls to ossl_qrx_pkt_release() to be
* ignored.
*
* The resources referenced by (*pkt)->hdr, (*pkt)->hdr->data and (*pkt)->peer
* have the same lifetime as *pkt.
*
* Returns 1 on success and 0 on failure.
*/
int ossl_qrx_read_pkt(OSSL_QRX *qrx, OSSL_QRX_PKT **pkt);
/*
* Decrement the reference count for the given packet and frees it if the
* reference count drops to zero. No-op if pkt is NULL.
*/
void ossl_qrx_pkt_release(OSSL_QRX_PKT *pkt);
/* Increments the reference count for the given packet. */
void ossl_qrx_pkt_up_ref(OSSL_QRX_PKT *pkt);
/*
* Returns 1 if there are any already processed (i.e. decrypted) packets waiting
* to be read from the QRX.
*/
int ossl_qrx_processed_read_pending(OSSL_QRX *qrx);
/*
* Returns 1 if there are any unprocessed (i.e. not yet decrypted) packets
* waiting to be processed by the QRX. These may or may not result in
* successfully decrypted packets once processed. This indicates whether
* unprocessed data is buffered by the QRX, not whether any data is available in
* a kernel socket buffer.
*/
int ossl_qrx_unprocessed_read_pending(OSSL_QRX *qrx);
/*
* Returns the number of UDP payload bytes received from the network so far
* since the last time this counter was cleared. If clear is 1, clears the
* counter and returns the old value.
*
* The intended use of this is to allow callers to determine how much credit to
* add to their anti-amplification budgets. This is reported separately instead
* of in the OSSL_QRX_PKT structure so that a caller can apply
* anti-amplification credit as soon as a datagram is received, before it has
* necessarily read all processed packets contained within that datagram from
* the QRX.
*/
uint64_t ossl_qrx_get_bytes_received(OSSL_QRX *qrx, int clear);
/*
* Sets a callback which is called when a packet is received and being validated
* before being queued in the read queue. This is called after packet body
* decryption and authentication to prevent exposing side channels. pn_space is
* a QUIC_PN_SPACE_* value denoting which PN space the PN belongs to.
*
* If this callback returns 1, processing continues normally.
* If this callback returns 0, the packet is discarded.
*
* Other packets in the same datagram will still be processed where possible.
*
* The callback is optional and can be unset by passing NULL for cb.
* cb_arg is an opaque value passed to cb.
*/
typedef int (ossl_qrx_late_validation_cb)(QUIC_PN pn, int pn_space,
void *arg);
int ossl_qrx_set_late_validation_cb(OSSL_QRX *qrx,
ossl_qrx_late_validation_cb *cb,
void *cb_arg);
/*
* Forcibly injects a URXE which has been issued by the DEMUX into the QRX for
* processing. This can be used to pass a received datagram to the QRX if it
* would not be correctly routed to the QRX via standard DCID-based routing; for
* example, when handling an incoming Initial packet which is attempting to
* establish a new connection.
*/
void ossl_qrx_inject_urxe(OSSL_QRX *qrx, QUIC_URXE *e);
/*
* Decryption of 1-RTT packets must be explicitly enabled by calling this
* function. This is to comply with the requirement that we not process 1-RTT
* packets until the handshake is complete, even if we already have 1-RTT
* secrets. Even if a 1-RTT secret is provisioned for the QRX, incoming 1-RTT
* packets will be handled as though no key is available until this function is
* called. Calling this function will then requeue any such deferred packets for
* processing.
*/
void ossl_qrx_allow_1rtt_processing(OSSL_QRX *qrx);
/*
* Key Update (RX)
* ===============
*
* Key update on the RX side is a largely but not entirely automatic process.
*
* Key update is initially triggered by receiving a 1-RTT packet with a
* different Key Phase value. This could be caused by an attacker in the network
* flipping random bits, therefore such a key update is tentative until the
* packet payload is successfully decrypted and authenticated by the AEAD with
* the 'next' keys. These 'next' keys then become the 'current' keys and the
* 'current' keys then become the 'previous' keys. The 'previous' keys must be
* kept around temporarily as some packets may still be in flight in the network
* encrypted with the old keys. If the old Key Phase value is X and the new Key
* Phase Value is Y (where obviously X != Y), this creates an ambiguity as any
* new packet received with a KP of X could either be an attempt to initiate yet
* another key update right after the last one, or an old packet encrypted
* before the key update.
*
* RFC 9001 provides some guidance on handling this issue:
*
* Strategy 1:
* Three keys, disambiguation using packet numbers
*
* "A recovered PN that is lower than any PN from the current KP uses the
* previous packet protection keys; a recovered PN that is higher than any
* PN from the current KP requires use of the next packet protection
* keys."
*
* Strategy 2:
* Two keys and a timer
*
* "Alternatively, endpoints can retain only two sets of packet protection
* keys, swapping previous keys for next after enough time has passed to
* allow for reordering in the network. In this case, the KP bit alone can
* be used to select keys."
*
* Strategy 2 is more efficient (we can keep fewer cipher contexts around) and
* should cover all actually possible network conditions. It also allows a delay
* after we make the 'next' keys our 'current' keys before we generate new
* 'next' keys, which allows us to mitigate against malicious peers who try to
* initiate an excessive number of key updates.
*
* We therefore model the following state machine:
*
*
* PROVISIONED
* _______________________________
* | |
* UNPROVISIONED --|----> NORMAL <----------\ |------> DISCARDED
* | | | |
* | | | |
* | v | |
* | UPDATING | |
* | | | |
* | | | |
* | v | |
* | COOLDOWN | |
* | | | |
* | | | |
* | \---------------| |
* |_______________________________|
*
*
* The RX starts (once a secret has been provisioned) in the NORMAL state. In
* the NORMAL state, the current expected value of the Key Phase bit is
* recorded. When a flipped Key Phase bit is detected, the RX attempts to
* decrypt and authenticate the received packet with the 'next' keys rather than
* the 'current' keys. If (and only if) this authentication is successful, we
* move to the UPDATING state. (An attacker in the network could flip
* the Key Phase bit randomly, so it is essential we do nothing until AEAD
* authentication is complete.)
*
* In the UPDATING state, we know a key update is occurring and record
* the new Key Phase bit value as the newly current value, but we still keep the
* old keys around so that we can still process any packets which were still in
* flight when the key update was initiated. In the UPDATING state, a
* Key Phase bit value different to the current expected value is treated not as
* the initiation of another key update, but a reference to our old keys.
*
* Eventually we will be reasonably sure we are not going to receive any more
* packets with the old keys. At this point, we can transition to the COOLDOWN
* state. This transition occurs automatically after a certain amount of time;
* RFC 9001 recommends it be the PTO interval, which relates to our RTT to the
* peer. The duration also SHOULD NOT exceed three times the PTO to assist with
* maintaining PFS.
*
* In the COOLDOWN phase, the old keys have been securely erased and only one
* set of keys can be used: the current keys. If a packet is received with a Key
* Phase bit value different to the current Key Phase Bit value, this is treated
* as a request for a Key Update, but this request is ignored and the packet is
* treated as malformed. We do this to allow mitigation against malicious peers
* trying to initiate an excessive number of Key Updates. The timeout for the
* transition from UPDATING to COOLDOWN is recommended as adequate for
* this purpose in itself by the RFC, so the normal additional timeout value for
* the transition from COOLDOWN to normal is zero (immediate transition).
*
* A summary of each state:
*
* Epoch Exp KP Uses Keys KS0 KS1 If Non-Expected KP Bit
* ----- ------ --------- ------ ----- ----------------------
* NORMAL 0 0 Keyset 0 Gen 0 Gen 1 → UPDATING
* UPDATING 1 1 Keyset 1 Gen 0 Gen 1 Use Keyset 0
* COOLDOWN 1 1 Keyset 1 Erased Gen 1 Ignore Packet (*)
*
* NORMAL 1 1 Keyset 1 Gen 2 Gen 1 → UPDATING
* UPDATING 2 0 Keyset 0 Gen 2 Gen 1 Use Keyset 1
* COOLDOWN 2 0 Keyset 0 Gen 2 Erased Ignore Packet (*)
*
* (*) Actually implemented by attempting to decrypt the packet with the
* wrong keys (which ultimately has the same outcome), as recommended
* by RFC 9001 to avoid creating timing channels.
*
* Note that the key material for the next key generation ("key epoch") is
* always kept in the NORMAL state (necessary to avoid side-channel attacks).
* This material is derived during the transition from COOLDOWN to NORMAL.
*
* Note that when a peer initiates a Key Update, we MUST also initiate a Key
* Update as per the RFC. The caller is responsible for detecting this condition
* and making the necessary calls to the TX side by detecting changes to the
* return value of ossl_qrx_get_key_epoch().
*
* The above states (NORMAL, UPDATING, COOLDOWN) can themselves be
* considered substates of the PROVISIONED state. Providing a secret to the QRX
* for an EL transitions from UNPROVISIONED, the initial state, to PROVISIONED
* (NORMAL). Dropping key material for an EL transitions from whatever the
* current substate of the PROVISIONED state is to the DISCARDED state, which is
* the terminal state.
*
* Note that non-1RTT ELs cannot undergo key update, therefore a non-1RTT EL is
* always in the NORMAL substate if it is in the PROVISIONED state.
*/
/*
* Return the current RX key epoch for the 1-RTT encryption level. This is
* initially zero and is incremented by one for every Key Update successfully
* signalled by the peer. If the 1-RTT EL has not yet been provisioned or has
* been discarded, returns UINT64_MAX.
*
* A necessary implication of this API is that the least significant bit of the
* returned value corresponds to the currently expected Key Phase bit, though
* callers are not anticipated to have any need of this information.
*
* It is not possible for the returned value to overflow, as a QUIC connection
* cannot support more than 2**62 packet numbers, and a connection must be
* terminated if this limit is reached.
*
* The caller should use this function to detect when the key epoch has changed
* and use it to initiate a key update on the TX side.
*
* The value returned by this function increments specifically at the transition
* from the NORMAL to the UPDATING state discussed above.
*/
uint64_t ossl_qrx_get_key_epoch(OSSL_QRX *qrx);
/*
* Sets an optional callback which will be called when the key epoch changes.
*
* The callback is optional and can be unset by passing NULL for cb.
* cb_arg is an opaque value passed to cb. pn is the PN of the packet.
* Since key update is only supported for 1-RTT packets, the PN is always
* in the Application Data PN space.
*/
typedef void (ossl_qrx_key_update_cb)(QUIC_PN pn, void *arg);
int ossl_qrx_set_key_update_cb(OSSL_QRX *qrx,
ossl_qrx_key_update_cb *cb, void *cb_arg);
/*
* Relates to the 1-RTT encryption level. The caller should call this after the
* UPDATING state is reached, after a timeout to be determined by the caller.
*
* This transitions from the UPDATING state to the COOLDOWN state (if
* still in the UPDATING state). If normal is 1, then transitions from
* the COOLDOWN state to the NORMAL state. Both transitions can be performed at
* once if desired.
*
* If in the normal state, or if in the COOLDOWN state and normal is 0, this is
* a no-op and returns 1. Returns 0 if the 1-RTT EL has not been provisioned or
* has been dropped.
*
* It is essential that the caller call this within a few PTO intervals of a key
* update occurring (as detected by the caller in a call to
* ossl_qrx_key_get_key_epoch()), as otherwise the peer will not be able to
* perform a Key Update ever again.
*/
int ossl_qrx_key_update_timeout(OSSL_QRX *qrx, int normal);
/*
* Key Expiration
* ==============
*/
/*
* Returns the number of seemingly forged packets which have been received by
* the QRX. If this value reaches the value returned by
* ossl_qrx_get_max_epoch_forged_pkt_count() for a given EL, all further
* received encrypted packets for that EL will be discarded without processing.
*
* Note that the forged packet limit is for the connection lifetime, thus it is
* not reset by a key update. It is suggested that the caller terminate the
* connection a reasonable margin before the limit is reached. However, the
* exact limit imposed does vary by EL due to the possibility that different ELs
* use different AEADs.
*/
uint64_t ossl_qrx_get_cur_forged_pkt_count(OSSL_QRX *qrx);
/*
* Returns the maximum number of forged packets which the record layer will
* permit to be verified using this QRX instance.
*/
uint64_t ossl_qrx_get_max_forged_pkt_count(OSSL_QRX *qrx,
uint32_t enc_level);
# endif
#endif
