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158 lines
9 KiB
C
158 lines
9 KiB
C
#ifndef CRYPTO_H
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#define CRYPTO_H
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extern cvar_t crypto_developer;
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extern cvar_t crypto_aeslevel;
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#define ENCRYPTION_REQUIRED (crypto_aeslevel.integer >= 3)
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extern int crypto_keyfp_recommended_length; // applies to LOCAL IDs, and to ALL keys
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#define CRYPTO_HEADERSIZE 31
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// AES case causes 16 to 31 bytes overhead
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// SHA256 case causes 16 bytes overhead as we truncate to 128bit
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#include "lhnet.h"
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#define FP64_SIZE 44
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#define DHKEY_SIZE 16
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typedef struct
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{
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unsigned char dhkey[DHKEY_SIZE]; // shared key, not NUL terminated
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char client_idfp[FP64_SIZE+1];
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char client_keyfp[FP64_SIZE+1]; // NULL if signature fail
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char server_idfp[FP64_SIZE+1];
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char server_keyfp[FP64_SIZE+1]; // NULL if signature fail
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qboolean authenticated;
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qboolean use_aes;
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void *data;
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}
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crypto_t;
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void Crypto_Init(void);
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void Crypto_Init_Commands(void);
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void Crypto_LoadKeys(void); // NOTE: when this is called, the SV_LockThreadMutex MUST be active
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void Crypto_Shutdown(void);
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qboolean Crypto_Available(void);
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void sha256(unsigned char *out, const unsigned char *in, int n); // may ONLY be called if Crypto_Available()
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const void *Crypto_EncryptPacket(crypto_t *crypto, const void *data_src, size_t len_src, void *data_dst, size_t *len_dst, size_t len);
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const void *Crypto_DecryptPacket(crypto_t *crypto, const void *data_src, size_t len_src, void *data_dst, size_t *len_dst, size_t len);
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#define CRYPTO_NOMATCH 0 // process as usual (packet was not used)
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#define CRYPTO_MATCH 1 // process as usual (packet was used)
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#define CRYPTO_DISCARD 2 // discard this packet
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#define CRYPTO_REPLACE 3 // make the buffer the current packet
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int Crypto_ClientParsePacket(const char *data_in, size_t len_in, char *data_out, size_t *len_out, lhnetaddress_t *peeraddress);
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int Crypto_ServerParsePacket(const char *data_in, size_t len_in, char *data_out, size_t *len_out, lhnetaddress_t *peeraddress);
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// if len_out is nonzero, the packet is to be sent to the client
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qboolean Crypto_ServerAppendToChallenge(const char *data_in, size_t len_in, char *data_out, size_t *len_out, size_t maxlen);
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crypto_t *Crypto_ServerGetInstance(lhnetaddress_t *peeraddress);
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qboolean Crypto_ServerFinishInstance(crypto_t *out, crypto_t *in); // also clears allocated memory
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const char *Crypto_GetInfoResponseDataString(void);
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// retrieves a host key for an address (can be exposed to menuqc, or used by the engine to look up stored keys e.g. for server bookmarking)
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// pointers may be NULL
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qboolean Crypto_RetrieveHostKey(lhnetaddress_t *peeraddress, int *keyid, char *keyfp, size_t keyfplen, char *idfp, size_t idfplen, int *aeslevel);
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int Crypto_RetrieveLocalKey(int keyid, char *keyfp, size_t keyfplen, char *idfp, size_t idfplen, qboolean *issigned); // return value: -1 if more to come, +1 if valid, 0 if end of list
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size_t Crypto_SignData(const void *data, size_t datasize, int keyid, void *signed_data, size_t signed_size);
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size_t Crypto_SignDataDetached(const void *data, size_t datasize, int keyid, void *signed_data, size_t signed_size);
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// netconn protocol:
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// non-crypto:
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// getchallenge >
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// < challenge
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// connect >
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// < accept (or: reject)
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// crypto:
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// getchallenge >
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// < challenge SP <challenge> NUL vlen <size> d0pk <fingerprints I can auth to> NUL NUL <other fingerprints I accept>
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//
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// IF serverfp:
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// d0pk\cnt\0\challenge\<challenge>\aeslevel\<level> NUL <serverfp> NUL <clientfp>
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// >
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// check if client would get accepted; if not, do "reject" now
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// require non-control packets to be encrypted require non-control packets to be encrypted
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// do not send anything yet do not send anything yet
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// RESET to serverfp RESET to serverfp
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// d0_blind_id_authenticate_with_private_id_start() = 1
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// < d0pk\cnt\1\aes\<aesenabled> NUL *startdata*
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// d0_blind_id_authenticate_with_private_id_challenge() = 1
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// d0pk\cnt\2 NUL *challengedata* >
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// d0_blind_id_authenticate_with_private_id_response() = 0
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// < d0pk\cnt\3 NUL *responsedata*
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// d0_blind_id_authenticate_with_private_id_verify() = 1
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// store server's fingerprint NOW
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// d0_blind_id_sessionkey_public_id() = 1 d0_blind_id_sessionkey_public_id() = 1
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//
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// IF clientfp AND NOT serverfp:
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// RESET to clientfp RESET to clientfp
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// d0_blind_id_authenticate_with_private_id_start() = 1
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// d0pk\cnt\0\challenge\<challenge>\aeslevel\<level> NUL NUL <clientfp> NUL *startdata*
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// >
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// check if client would get accepted; if not, do "reject" now
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// require non-control packets to be encrypted require non-control packets to be encrypted
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// d0_blind_id_authenticate_with_private_id_challenge() = 1
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// < d0pk\cnt\5\aes\<aesenabled> NUL *challengedata*
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//
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// IF clientfp AND serverfp:
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// RESET to clientfp RESET to clientfp
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// d0_blind_id_authenticate_with_private_id_start() = 1
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// d0pk\cnt\4 NUL *startdata* >
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// d0_blind_id_authenticate_with_private_id_challenge() = 1
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// < d0pk\cnt\5 NUL *challengedata*
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//
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// IF clientfp:
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// d0_blind_id_authenticate_with_private_id_response() = 0
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// d0pk\cnt\6 NUL *responsedata* >
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// d0_blind_id_authenticate_with_private_id_verify() = 1
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// store client's fingerprint NOW
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// d0_blind_id_sessionkey_public_id() = 1 d0_blind_id_sessionkey_public_id() = 1
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// note: the ... is the "connect" message, except without the challenge. Reinterpret as regular connect message on server side
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//
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// enforce encrypted transmission (key is XOR of the two DH keys)
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//
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// IF clientfp:
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// < challenge (mere sync message)
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//
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// connect\... >
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// < accept (ALWAYS accept if connection is encrypted, ignore challenge as it had been checked before)
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//
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// commence with ingame protocol
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// in short:
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// server:
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// getchallenge NUL d0_blind_id: reply with challenge with added fingerprints
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// cnt=0: IF server will auth, cnt=1, ELSE cnt=5
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// cnt=2: cnt=3
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// cnt=4: cnt=5
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// cnt=6: send "challenge"
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// client:
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// challenge with added fingerprints: cnt=0; if client will auth but not server, append client auth start
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// cnt=1: cnt=2
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// cnt=3: IF client will auth, cnt=4, ELSE rewrite as "challenge"
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// cnt=5: cnt=6, server will continue by sending "challenge" (let's avoid sending two packets as response to one)
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// other change:
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// accept empty "challenge", and challenge-less connect in case crypto protocol has executed and finished
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// statusResponse and infoResponse get an added d0_blind_id key that lists
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// the keys the server can auth with and to in key@ca SPACE key@ca notation
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// any d0pk\ message has an appended "id" parameter; messages with an unexpected "id" are ignored to prevent errors from multiple concurrent auth runs
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// comparison to OTR:
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// - encryption: yes
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// - authentication: yes
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// - deniability: no (attacker requires the temporary session key to prove you
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// have sent a specific message, the private key itself does not suffice), no
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// measures are taken to provide forgeability to even provide deniability
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// against an attacker who knows the temporary session key, as using CTR mode
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// for the encryption - which, together with deriving the MAC key from the
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// encryption key, and MACing the ciphertexts instead of the plaintexts,
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// would provide forgeability and thus deniability - requires longer
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// encrypted packets and deniability was not a goal of this, as we may e.g.
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// reserve the right to capture packet dumps + extra state info to prove a
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// client/server has sent specific packets to prove cheating)
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// - perfect forward secrecy: yes (session key is derived via DH key exchange)
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#endif
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