twogen.h

#ifndef QUIC_KUSWITCH_TWOGEN_H
#define QUIC_KUSWITCH_TWOGEN_H
 
#include "tls/handshake/core/tls/initial.h"
 
/* RFC 9001 6.3/6.5: an endpoint keeps the current 1-RTT keys and, after a key
 * update, the immediately prior keys, so packets in flight under the old key
 * can still be decrypted until the retention period ends. A received packet's
 * Key Phase bit selects which generation decrypts it. */

typedef struct {
  quic_initial_keys cur; 
  quic_initial_keys old; 
  u64 generation;        
  int have_old;          
} quic_kuswitch_state;
 
/* Initialise at generation 0 with the first 1-RTT keys; no old key yet. */
void quic_kuswitch_init(
    quic_kuswitch_state* state, const quic_initial_keys* gen0);
 
/* RFC 9001 6.3: advance to the next generation. The current keys become old
 * (retained), and next becomes current; generation increments. */
void quic_kuswitch_rotate(
    quic_kuswitch_state* state, const quic_initial_keys* next);
 
/* RFC 9001 6.3: choose the keys that decrypt a packet carrying recv_phase_bit.
 * Returns 1 with *keys set when a matching generation is available, 0 when the
 * bit asks for an old generation that is not (or no longer) retained. */
int quic_kuswitch_key_for_phase(
    const quic_kuswitch_state* state,
    int                        recv_phase_bit,
    const quic_initial_keys**  keys);
 
/* RFC 9001 6.5: drop the retained old key once its retention period ends. */
void quic_kuswitch_discard_old(quic_kuswitch_state* state);
 
#endif