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transmission/libtransmission/handshake.c

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/*
* This file Copyright (C) 2007-2008 Charles Kerr <charles@rebelbase.com>
*
* This file is licensed by the GPL version 2. Works owned by the
* Transmission project are granted a special exemption to clause 2(b)
* so that the bulk of its code can remain under the MIT license.
* This exemption does not extend to derived works not owned by
* the Transmission project.
*
* $Id$
*/
#include <assert.h>
#include <errno.h>
#include <inttypes.h>
#include <limits.h> /* UCHAR_MAX */
#include <string.h>
#include <stdio.h>
#include <event.h>
#include "transmission.h"
#include "bencode.h"
#include "clients.h"
#include "crypto.h"
#include "handshake.h"
#include "peer-io.h"
#include "peer-mgr.h"
#include "torrent.h"
#include "trevent.h"
#include "utils.h"
/* enable LibTransmission extension protocol */
#define ENABLE_LTEP */
/* enable fast peers extension protocol */
/* #define ENABLE_FASTPEER */
/***
****
***/
#define HANDSHAKE_NAME "\023BitTorrent protocol"
enum
{
/* BitTorrent Handshake Constants */
HANDSHAKE_NAME_LEN = 20,
HANDSHAKE_FLAGS_LEN = 8,
HANDSHAKE_SIZE = 68,
PEER_ID_LEN = 20,
INCOMING_HANDSHAKE_LEN = 48,
/* Encryption Constants */
PadA_MAXLEN = 512,
PadB_MAXLEN = 512,
PadC_MAXLEN = 512,
PadD_MAXLEN = 512,
VC_LENGTH = 8,
KEY_LEN = 96,
CRYPTO_PROVIDE_PLAINTEXT = 1,
CRYPTO_PROVIDE_CRYPTO = 2
};
#ifdef ENABLE_LTEP
#define HANDSHAKE_HAS_LTEP( bits ) ( ( (bits)[5] & 0x10 ) ? 1 : 0 )
#define HANDSHAKE_SET_LTEP( bits ) ( (bits)[5] |= 0x10 )
#else
#define HANDSHAKE_HAS_LTEP( bits ) ( 0 )
#define HANDSHAKE_SET_LTEP( bits ) ( (void)0 )
#endif
#ifdef ENABLE_FASTPEER
#define HANDSHAKE_HAS_FASTEXT( bits ) ( ( (bits)[7] & 0x04 ) ? 1 : 0 )
#define HANDSHAKE_SET_FASTEXT( bits ) ( (bits)[7] |= 0x04 )
#else
#define HANDSHAKE_HAS_FASTEXT( bits ) ( 0 )
#define HANDSHAKE_SET_FASTEXT( bits ) ( (void)0 )
#endif
/* http://www.azureuswiki.com/index.php/Extension_negotiation_protocol
these macros are to be used if both extended messaging and the
azureus protocol is supported, they indicate which protocol is preferred */
#define HANDSHAKE_GET_EXTPREF( reserved ) ( (reserved)[5] & 0x03 )
#define HANDSHAKE_SET_EXTPREF( reserved, val ) ( (reserved)[5] |= 0x03 & (val) )
struct tr_handshake
{
unsigned int havePeerID : 1;
unsigned int haveSentBitTorrentHandshake : 1;
tr_peerIo * io;
tr_crypto * crypto;
struct tr_handle * handle;
uint8_t myPublicKey[KEY_LEN];
uint8_t mySecret[KEY_LEN];
uint8_t state;
tr_encryption_mode encryptionMode;
uint16_t pad_c_len;
uint16_t pad_d_len;
uint16_t ia_len;
uint32_t crypto_select;
uint32_t crypto_provide;
uint8_t myReq1[SHA_DIGEST_LENGTH];
uint8_t peer_id[PEER_ID_LEN];
handshakeDoneCB doneCB;
void * doneUserData;
};
/**
***
**/
enum
{
/* incoming */
AWAITING_HANDSHAKE,
AWAITING_PEER_ID,
AWAITING_YA,
AWAITING_PAD_A,
AWAITING_CRYPTO_PROVIDE,
AWAITING_PAD_C,
AWAITING_IA,
/* outgoing */
AWAITING_YB,
AWAITING_VC,
AWAITING_CRYPTO_SELECT,
AWAITING_PAD_D,
};
/**
***
**/
#define dbgmsg(handshake, fmt...) tr_deepLog( __FILE__, __LINE__, tr_peerIoGetAddrStr( handshake->io ), ##fmt )
static const char* getStateName( short state )
{
const char * str = "f00!";
switch( state ) {
case AWAITING_HANDSHAKE: str = "awaiting handshake"; break;
case AWAITING_PEER_ID: str = "awaiting peer id"; break;
case AWAITING_YA: str = "awaiting ya"; break;
case AWAITING_PAD_A: str = "awaiting pad a"; break;
case AWAITING_CRYPTO_PROVIDE: str = "awaiting crypto_provide"; break;
case AWAITING_PAD_C: str = "awaiting pad c"; break;
case AWAITING_IA: str = "awaiting ia"; break;
case AWAITING_YB: str = "awaiting yb"; break;
case AWAITING_VC: str = "awaiting vc"; break;
case AWAITING_CRYPTO_SELECT: str = "awaiting crypto select"; break;
case AWAITING_PAD_D: str = "awaiting pad d"; break;
}
return str;
}
static void
setState( tr_handshake * handshake, short state )
{
dbgmsg( handshake, "setting to state [%s]", getStateName(state) );
handshake->state = state;
}
static void
setReadState( tr_handshake * handshake, int state )
{
setState( handshake, state );
}
static uint8_t *
buildHandshakeMessage( tr_handshake * handshake,
int * setme_len )
{
uint8_t * buf = tr_new0( uint8_t, HANDSHAKE_SIZE );
uint8_t * walk = buf;
const uint8_t * torrentHash = tr_cryptoGetTorrentHash( handshake->crypto );
const uint8_t * peerId = tr_getPeerId( );
memcpy( walk, HANDSHAKE_NAME, HANDSHAKE_NAME_LEN );
walk += HANDSHAKE_NAME_LEN;
memset( walk, 0, HANDSHAKE_FLAGS_LEN );
HANDSHAKE_SET_LTEP( walk );
HANDSHAKE_SET_FASTEXT( walk );
walk += HANDSHAKE_FLAGS_LEN;
memcpy( walk, torrentHash, SHA_DIGEST_LENGTH );
walk += SHA_DIGEST_LENGTH;
memcpy( walk, peerId, PEER_ID_LEN );
walk += PEER_ID_LEN;
assert( strlen( ( const char* )peerId ) == PEER_ID_LEN );
assert( walk-buf == HANDSHAKE_SIZE );
*setme_len = walk - buf;
return buf;
}
static void
tr_handshakeDone( tr_handshake * handshake, int isConnected );
enum
{
HANDSHAKE_OK,
HANDSHAKE_ENCRYPTION_WRONG,
HANDSHAKE_BAD_TORRENT,
HANDSHAKE_PEER_IS_SELF,
};
static int
parseHandshake( tr_handshake * handshake,
struct evbuffer * inbuf )
{
uint8_t name[HANDSHAKE_NAME_LEN];
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
uint8_t hash[SHA_DIGEST_LENGTH];
dbgmsg( handshake, "payload: need %d, got %d", (int)HANDSHAKE_SIZE, (int)EVBUFFER_LENGTH(inbuf) );
if( EVBUFFER_LENGTH(inbuf) < HANDSHAKE_SIZE )
return READ_MORE;
/* confirm the protocol */
tr_peerIoReadBytes( handshake->io, inbuf, name, HANDSHAKE_NAME_LEN );
if( memcmp( name, HANDSHAKE_NAME, HANDSHAKE_NAME_LEN ) )
return HANDSHAKE_ENCRYPTION_WRONG;
/* read the reserved bytes */
tr_peerIoReadBytes( handshake->io, inbuf, reserved, HANDSHAKE_FLAGS_LEN );
/* torrent hash */
tr_peerIoReadBytes( handshake->io, inbuf, hash, sizeof(hash) );
assert( tr_peerIoHasTorrentHash( handshake->io ) );
if( !tr_torrentExists( handshake->handle, hash )
|| memcmp( hash, tr_peerIoGetTorrentHash(handshake->io), SHA_DIGEST_LENGTH ) )
{
dbgmsg( handshake, "peer returned the wrong hash. wtf?" );
return HANDSHAKE_BAD_TORRENT;
}
/* peer_id */
tr_peerIoReadBytes( handshake->io, inbuf, handshake->peer_id, sizeof(handshake->peer_id) );
tr_peerIoSetPeersId( handshake->io, handshake->peer_id );
/* peer id */
handshake->havePeerID = TRUE;
dbgmsg( handshake, "peer-id is [%*.*s]", PEER_ID_LEN, PEER_ID_LEN, handshake->peer_id );
if( !memcmp( handshake->peer_id, tr_getPeerId(), PEER_ID_LEN ) ) {
dbgmsg( handshake, "streuth! we've connected to ourselves." );
return HANDSHAKE_PEER_IS_SELF;
}
/**
*** Extensions
**/
if( HANDSHAKE_HAS_LTEP( reserved ) )
{
tr_peerIoEnableLTEP( handshake->io, 1 );
dbgmsg(handshake,"using ltep" );
}
if( HANDSHAKE_HAS_FASTEXT( reserved ) )
{
tr_peerIoEnableFEXT( handshake->io, 1 );
dbgmsg(handshake,"using fext" );
}
return HANDSHAKE_OK;
}
/***
****
**** OUTGOING CONNECTIONS
****
***/
/* 1 A->B: Diffie Hellman Ya, PadA */
static void
sendYa( tr_handshake * handshake )
{
int len;
const uint8_t * public_key;
struct evbuffer * outbuf = evbuffer_new( );
uint8_t pad_a[PadA_MAXLEN];
/* add our public key (Ya) */
public_key = tr_cryptoGetMyPublicKey( handshake->crypto, &len );
assert( len == KEY_LEN );
assert( public_key );
evbuffer_add( outbuf, public_key, len );
/* add some bullshit padding */
len = tr_cryptoRandInt( PadA_MAXLEN );
tr_cryptoRandBuf(pad_a, len);
evbuffer_add( outbuf, pad_a, len );
/* send it */
setReadState( handshake, AWAITING_YB );
tr_peerIoWriteBuf( handshake->io, outbuf );
/* cleanup */
evbuffer_free( outbuf );
}
static uint32_t
getCryptoProvide( const tr_handshake * handshake )
{
uint32_t provide = 0;
switch( handshake->encryptionMode )
{
case TR_ENCRYPTION_REQUIRED:
case TR_ENCRYPTION_PREFERRED:
provide |= CRYPTO_PROVIDE_CRYPTO;
break;
case TR_CLEAR_PREFERRED:
provide |= CRYPTO_PROVIDE_CRYPTO | CRYPTO_PROVIDE_PLAINTEXT;
break;
}
return provide;
}
static uint32_t
getCryptoSelect( const tr_handshake * handshake, uint32_t crypto_provide )
{
uint32_t choices[4];
int i, nChoices=0;
switch( handshake->encryptionMode )
{
case TR_ENCRYPTION_REQUIRED:
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
break;
case TR_ENCRYPTION_PREFERRED:
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
choices[nChoices++] = CRYPTO_PROVIDE_PLAINTEXT;
break;
case TR_CLEAR_PREFERRED:
choices[nChoices++] = CRYPTO_PROVIDE_PLAINTEXT;
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
break;
}
for( i=0; i<nChoices; ++i )
if( crypto_provide & choices[i] )
return choices[i];
return 0;
}
static int
readYb( tr_handshake * handshake, struct evbuffer * inbuf )
{
int isEncrypted;
const uint8_t * secret;
uint8_t yb[KEY_LEN];
struct evbuffer * outbuf;
size_t needlen = HANDSHAKE_NAME_LEN;
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
isEncrypted = memcmp( EVBUFFER_DATA(inbuf), HANDSHAKE_NAME, HANDSHAKE_NAME_LEN );
if( isEncrypted ) {
needlen = KEY_LEN;
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
}
dbgmsg( handshake, "got a %s handshake", (isEncrypted ? "encrypted" : "plaintext") );
tr_peerIoSetEncryption( handshake->io, isEncrypted ? PEER_ENCRYPTION_RC4
: PEER_ENCRYPTION_NONE );
if( !isEncrypted ) {
setState( handshake, AWAITING_HANDSHAKE );
return READ_AGAIN;
}
/* compute the secret */
evbuffer_remove( inbuf, yb, KEY_LEN );
secret = tr_cryptoComputeSecret( handshake->crypto, yb );
memcpy( handshake->mySecret, secret, KEY_LEN );
/* now send these: HASH('req1', S), HASH('req2', SKEY) xor HASH('req3', S),
* ENCRYPT(VC, crypto_provide, len(PadC), PadC, len(IA)), ENCRYPT(IA) */
outbuf = evbuffer_new( );
/* HASH('req1', S) */
{
uint8_t req1[SHA_DIGEST_LENGTH];
tr_sha1( req1, "req1", 4, secret, KEY_LEN, NULL );
evbuffer_add( outbuf, req1, SHA_DIGEST_LENGTH );
}
/* HASH('req2', SKEY) xor HASH('req3', S) */
{
int i;
uint8_t req2[SHA_DIGEST_LENGTH];
uint8_t req3[SHA_DIGEST_LENGTH];
uint8_t buf[SHA_DIGEST_LENGTH];
tr_sha1( req2, "req2", 4, tr_cryptoGetTorrentHash(handshake->crypto), SHA_DIGEST_LENGTH, NULL );
tr_sha1( req3, "req3", 4, secret, KEY_LEN, NULL );
for( i=0; i<SHA_DIGEST_LENGTH; ++i )
buf[i] = req2[i] ^ req3[i];
evbuffer_add( outbuf, buf, SHA_DIGEST_LENGTH );
}
/* ENCRYPT(VC, crypto_provide, len(PadC), PadC
* PadC is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
{
uint8_t vc[VC_LENGTH] = { 0, 0, 0, 0, 0, 0, 0, 0 };
tr_cryptoEncryptInit( handshake->crypto );
tr_peerIoSetEncryption( handshake->io, PEER_ENCRYPTION_RC4 );
tr_peerIoWriteBytes( handshake->io, outbuf, vc, VC_LENGTH );
tr_peerIoWriteUint32( handshake->io, outbuf, getCryptoProvide( handshake ) );
tr_peerIoWriteUint16( handshake->io, outbuf, 0 );
}
/* ENCRYPT len(IA)), ENCRYPT(IA) */
{
int msglen;
uint8_t * msg = buildHandshakeMessage( handshake, &msglen );
tr_peerIoWriteUint16( handshake->io, outbuf, msglen );
tr_peerIoWriteBytes( handshake->io, outbuf, msg, msglen );
handshake->haveSentBitTorrentHandshake = 1;
tr_free( msg );
}
/* send it */
tr_cryptoDecryptInit( handshake->crypto );
setReadState( handshake, AWAITING_VC );
tr_peerIoWriteBuf( handshake->io, outbuf );
/* cleanup */
evbuffer_free( outbuf );
return READ_DONE;
}
static int
readVC( tr_handshake * handshake, struct evbuffer * inbuf )
{
const uint8_t key[VC_LENGTH] = { 0, 0, 0, 0, 0, 0, 0, 0 };
const int key_len = VC_LENGTH;
uint8_t tmp[VC_LENGTH];
/* note: this works w/o having to `unwind' the buffer if
* we read too much, but it is pretty brute-force.
* it would be nice to make this cleaner. */
for( ;; )
{
if( EVBUFFER_LENGTH(inbuf) < VC_LENGTH ) {
dbgmsg( handshake, "not enough bytes... returning read_more" );
return READ_MORE;
}
memcpy( tmp, EVBUFFER_DATA(inbuf), key_len );
tr_cryptoDecryptInit( handshake->crypto );
tr_cryptoDecrypt( handshake->crypto, key_len, tmp, tmp );
if( !memcmp( tmp, key, key_len ) )
break;
evbuffer_drain( inbuf, 1 );
}
dbgmsg( handshake, "got it!" );
evbuffer_drain( inbuf, key_len );
setState( handshake, AWAITING_CRYPTO_SELECT );
return READ_AGAIN;
}
static int
readCryptoSelect( tr_handshake * handshake, struct evbuffer * inbuf )
{
uint32_t crypto_select;
uint16_t pad_d_len;
const size_t needlen = sizeof(uint32_t) + sizeof(uint16_t);
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
tr_peerIoReadUint32( handshake->io, inbuf, &crypto_select );
handshake->crypto_select = crypto_select;
dbgmsg( handshake, "crypto select is %d", (int)crypto_select );
if( ! ( crypto_select & getCryptoProvide( handshake ) ) )
{
dbgmsg( handshake, "peer selected an encryption option we didn't provide" );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
tr_peerIoReadUint16( handshake->io, inbuf, &pad_d_len );
dbgmsg( handshake, "pad_d_len is %d", (int)pad_d_len );
if( pad_d_len > 512 )
{
dbgmsg( handshake, "encryption handshake: pad_d_len is too long" );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
handshake->pad_d_len = pad_d_len;
setState( handshake, AWAITING_PAD_D );
return READ_AGAIN;
}
static int
readPadD( tr_handshake * handshake, struct evbuffer * inbuf )
{
const size_t needlen = handshake->pad_d_len;
uint8_t * tmp;
dbgmsg( handshake, "pad d: need %d, got %d", (int)needlen, (int)EVBUFFER_LENGTH(inbuf) );
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
tmp = tr_new( uint8_t, needlen );
tr_peerIoReadBytes( handshake->io, inbuf, tmp, needlen );
tr_free( tmp );
tr_peerIoSetEncryption( handshake->io,
handshake->crypto_select );
setState( handshake, AWAITING_HANDSHAKE );
return READ_AGAIN;
}
/***
****
**** INCOMING CONNECTIONS
****
***/
static int
readHandshake( tr_handshake * handshake, struct evbuffer * inbuf )
{
uint8_t pstrlen;
uint8_t * pstr;
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
uint8_t hash[SHA_DIGEST_LENGTH];
dbgmsg( handshake, "payload: need %d, got %d", (int)INCOMING_HANDSHAKE_LEN, (int)EVBUFFER_LENGTH(inbuf) );
if( EVBUFFER_LENGTH(inbuf) < INCOMING_HANDSHAKE_LEN )
return READ_MORE;
pstrlen = EVBUFFER_DATA(inbuf)[0]; /* peek, don't read. We may be
handing inbuf to AWAITING_YA */
if( pstrlen == 19 ) /* unencrypted */
{
tr_peerIoSetEncryption( handshake->io, PEER_ENCRYPTION_NONE );
if( handshake->encryptionMode == TR_ENCRYPTION_REQUIRED )
{
dbgmsg( handshake, "peer is unencrypted, and we're disallowing that" );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
}
else /* encrypted or corrupt */
{
tr_peerIoSetEncryption( handshake->io, PEER_ENCRYPTION_RC4 );
if( tr_peerIoIsIncoming( handshake->io ) )
{
dbgmsg( handshake, "I think peer is sending us an encrypted handshake..." );
setState( handshake, AWAITING_YA );
return READ_AGAIN;
}
tr_cryptoDecrypt( handshake->crypto, 1, &pstrlen, &pstrlen );
if( pstrlen != 19 )
{
dbgmsg( handshake, "I think peer has sent us a corrupt handshake..." );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
}
evbuffer_drain( inbuf, 1 );
/* pstr (BitTorrent) */
pstr = tr_new( uint8_t, pstrlen+1 );
tr_peerIoReadBytes( handshake->io, inbuf, pstr, pstrlen );
pstr[pstrlen] = '\0';
if( strcmp( (char*)pstr, "BitTorrent protocol" ) ) {
tr_free( pstr );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
tr_free( pstr );
/* reserved bytes */
tr_peerIoReadBytes( handshake->io, inbuf, reserved, sizeof(reserved) );
/**
*** Extension negotiation
**/
if( HANDSHAKE_HAS_LTEP( reserved ) )
{
tr_peerIoEnableLTEP( handshake->io, 1 );
dbgmsg( handshake,"using ltep" );
}
if( HANDSHAKE_HAS_FASTEXT( reserved ) )
{
tr_peerIoEnableFEXT( handshake->io, 1 );
dbgmsg( handshake,"using fext" );
}
/* torrent hash */
tr_peerIoReadBytes( handshake->io, inbuf, hash, sizeof(hash) );
if( tr_peerIoIsIncoming( handshake->io ) )
{
if( !tr_torrentExists( handshake->handle, hash ) )
{
dbgmsg( handshake, "peer is trying to connect to us for a torrent we don't have." );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
else
{
assert( !tr_peerIoHasTorrentHash( handshake->io ) );
tr_peerIoSetTorrentHash( handshake->io, hash );
}
}
else /* outgoing */
{
assert( tr_peerIoHasTorrentHash( handshake->io ) );
if( memcmp( hash, tr_peerIoGetTorrentHash(handshake->io), SHA_DIGEST_LENGTH ) )
{
dbgmsg( handshake, "peer returned the wrong hash. wtf?" );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
}
/**
*** If this is an incoming message, then we need to send a response handshake
**/
if( !handshake->haveSentBitTorrentHandshake )
{
int msgSize;
uint8_t * msg = buildHandshakeMessage( handshake, &msgSize );
tr_peerIoWrite( handshake->io, msg, msgSize );
tr_free( msg );
handshake->haveSentBitTorrentHandshake = 1;
}
setReadState( handshake, AWAITING_PEER_ID );
return READ_AGAIN;
}
static int
readPeerId( tr_handshake * handshake, struct evbuffer * inbuf )
{
int peerIsGood;
char client[128];
if( EVBUFFER_LENGTH(inbuf) < PEER_ID_LEN )
return READ_MORE;
/* peer id */
tr_peerIoReadBytes( handshake->io, inbuf, handshake->peer_id, PEER_ID_LEN );
tr_peerIoSetPeersId( handshake->io, handshake->peer_id );
handshake->havePeerID = TRUE;
tr_clientForId( client, sizeof( client ), handshake->peer_id );
dbgmsg( handshake, "peer-id is [%s] ... isIncoming is %d", client, tr_peerIoIsIncoming( handshake->io ) );
/* if we've somehow connected to ourselves, don't keep the connection */
peerIsGood = memcmp( handshake->peer_id, tr_getPeerId(), PEER_ID_LEN ) ? 1 : 0;
dbgmsg( handshake, "isPeerGood == %d", peerIsGood );
tr_handshakeDone( handshake, peerIsGood );
return READ_DONE;
}
static int
readYa( tr_handshake * handshake, struct evbuffer * inbuf )
{
uint8_t ya[KEY_LEN];
uint8_t *walk, outbuf[KEY_LEN + PadB_MAXLEN];
const uint8_t *myKey, *secret;
int len;
dbgmsg( handshake, "in readYa... need %d, have %d", (int)KEY_LEN, (int)EVBUFFER_LENGTH( inbuf ) );
if( EVBUFFER_LENGTH( inbuf ) < KEY_LEN )
return READ_MORE;
/* read the incoming peer's public key */
evbuffer_remove( inbuf, ya, KEY_LEN );
secret = tr_cryptoComputeSecret( handshake->crypto, ya );
memcpy( handshake->mySecret, secret, KEY_LEN );
tr_sha1( handshake->myReq1, "req1", 4, secret, KEY_LEN, NULL );
dbgmsg( handshake, "sending B->A: Diffie Hellman Yb, PadB" );
/* send our public key to the peer */
walk = outbuf;
myKey = tr_cryptoGetMyPublicKey( handshake->crypto, &len );
memcpy( walk, myKey, len );
walk += len;
len = tr_cryptoRandInt( PadB_MAXLEN );
tr_cryptoRandBuf( walk, len );
walk += len;
setReadState( handshake, AWAITING_PAD_A );
tr_peerIoWrite( handshake->io, outbuf, walk-outbuf );
return READ_AGAIN;
}
static int
readPadA( tr_handshake * handshake, struct evbuffer * inbuf )
{
uint8_t * pch;
dbgmsg( handshake, "looking to get past pad a... & resync on hash('req',S) ... have %d bytes", (int)EVBUFFER_LENGTH(inbuf) );
/**
*** Resynchronizing on HASH('req1',S)
**/
pch = memchr( EVBUFFER_DATA(inbuf),
handshake->myReq1[0],
EVBUFFER_LENGTH(inbuf) );
if( pch == NULL ) {
dbgmsg( handshake, "no luck so far.. draining %d bytes", (int)EVBUFFER_LENGTH(inbuf) );
evbuffer_drain( inbuf, EVBUFFER_LENGTH(inbuf) );
return READ_MORE;
}
dbgmsg( handshake, "looking for hash('req',S) ... draining %d bytes", (int)(pch-EVBUFFER_DATA(inbuf)) );
evbuffer_drain( inbuf, pch-EVBUFFER_DATA(inbuf) );
if( EVBUFFER_LENGTH(inbuf) < SHA_DIGEST_LENGTH )
return READ_MORE;
if( memcmp( EVBUFFER_DATA(inbuf), handshake->myReq1, SHA_DIGEST_LENGTH ) ) {
dbgmsg( handshake, "draining one more byte" );
evbuffer_drain( inbuf, 1 );
return READ_AGAIN;
}
dbgmsg( handshake, "found it... looking setting to awaiting_crypto_provide" );
setState( handshake, AWAITING_CRYPTO_PROVIDE );
return READ_AGAIN;
}
static int
readCryptoProvide( tr_handshake * handshake, struct evbuffer * inbuf )
{
/* HASH('req2', SKEY) xor HASH('req3', S), ENCRYPT(VC, crypto_provide, len(PadC)) */
int i;
uint8_t vc_in[VC_LENGTH];
uint8_t req2[SHA_DIGEST_LENGTH];
uint8_t req3[SHA_DIGEST_LENGTH];
uint8_t obfuscatedTorrentHash[SHA_DIGEST_LENGTH];
uint16_t padc_len = 0;
uint32_t crypto_provide = 0;
const size_t needlen = SHA_DIGEST_LENGTH /* HASH('req1',s) */
+ SHA_DIGEST_LENGTH /* HASH('req2', SKEY) xor HASH('req3', S) */
+ VC_LENGTH
+ sizeof(crypto_provide)
+ sizeof(padc_len);
tr_torrent * tor = NULL;
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
/* TODO: confirm they sent HASH('req1',S) here? */
evbuffer_drain( inbuf, SHA_DIGEST_LENGTH );
/* This next piece is HASH('req2', SKEY) xor HASH('req3', S) ...
* we can get the first half of that (the obufscatedTorrentHash)
* by building the latter and xor'ing it with what the peer sent us */
dbgmsg( handshake, "reading obfuscated torrent hash..." );
evbuffer_remove( inbuf, req2, SHA_DIGEST_LENGTH );
tr_sha1( req3, "req3", 4, handshake->mySecret, KEY_LEN, NULL );
for( i=0; i<SHA_DIGEST_LENGTH; ++i )
obfuscatedTorrentHash[i] = req2[i] ^ req3[i];
if(( tor = tr_torrentFindFromObfuscatedHash( handshake->handle, obfuscatedTorrentHash )))
{
dbgmsg( handshake, "got INCOMING connection's encrypted handshake for torrent [%s]", tor->info.name );
tr_peerIoSetTorrentHash( handshake->io, tor->info.hash );
if( !tr_torrentAllowsPex( tor ) &&
tr_peerMgrPeerIsSeed( handshake->handle->peerMgr,
tor->info.hash,
tr_peerIoGetAddress( handshake->io, NULL )))
{
dbgmsg( handshake, "a peer has tried to reconnect to us!" );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
}
else
{
dbgmsg( handshake, "can't find that torrent..." );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
/* next part: ENCRYPT(VC, crypto_provide, len(PadC), */
tr_cryptoDecryptInit( handshake->crypto );
tr_peerIoReadBytes( handshake->io, inbuf, vc_in, VC_LENGTH );
tr_peerIoReadUint32( handshake->io, inbuf, &crypto_provide );
handshake->crypto_provide = crypto_provide;
dbgmsg( handshake, "crypto_provide is %d", (int)crypto_provide );
tr_peerIoReadUint16( handshake->io, inbuf, &padc_len );
dbgmsg( handshake, "padc is %d", (int)padc_len );
handshake->pad_c_len = padc_len;
setState( handshake, AWAITING_PAD_C );
return READ_AGAIN;
}
static int
readPadC( tr_handshake * handshake, struct evbuffer * inbuf )
{
uint16_t ia_len;
const size_t needlen = handshake->pad_c_len + sizeof(uint16_t);
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
evbuffer_drain( inbuf, handshake->pad_c_len );
tr_peerIoReadUint16( handshake->io, inbuf, &ia_len );
dbgmsg( handshake, "ia_len is %d", (int)ia_len );
handshake->ia_len = ia_len;
setState( handshake, AWAITING_IA );
return READ_AGAIN;
}
static int
readIA( tr_handshake * handshake, struct evbuffer * inbuf )
{
int i;
const size_t needlen = handshake->ia_len;
struct evbuffer * outbuf;
uint32_t crypto_select;
dbgmsg( handshake, "reading IA... have %d, need %d", (int)EVBUFFER_LENGTH(inbuf), (int)needlen );
if( EVBUFFER_LENGTH(inbuf) < needlen )
return READ_MORE;
dbgmsg( handshake, "reading IA..." );
/* parse the handshake ... */
i = parseHandshake( handshake, inbuf );
dbgmsg( handshake, "parseHandshake returned %d", i );
if( i != HANDSHAKE_OK ) {
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
/**
*** B->A: ENCRYPT(VC, crypto_select, len(padD), padD), ENCRYPT2(Payload Stream)
**/
tr_cryptoEncryptInit( handshake->crypto );
outbuf = evbuffer_new( );
dbgmsg( handshake, "sending vc" );
/* send VC */
{
uint8_t vc[VC_LENGTH];
memset( vc, 0, VC_LENGTH );
tr_peerIoWriteBytes( handshake->io, outbuf, vc, VC_LENGTH );
}
/* send crypto_select */
crypto_select = getCryptoSelect( handshake, handshake->crypto_provide );
if( crypto_select ) {
dbgmsg( handshake, "selecting crypto mode '%d'", (int)crypto_select );
tr_peerIoWriteUint32( handshake->io, outbuf, crypto_select );
} else {
dbgmsg( handshake, "peer didn't offer an encryption mode we like." );
evbuffer_free( outbuf );
tr_handshakeDone( handshake, FALSE );
return READ_DONE;
}
dbgmsg( handshake, "sending pad d" );
/* ENCRYPT(VC, crypto_provide, len(PadC), PadC
* PadD is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
{
const int len = 0;
tr_peerIoWriteUint16( handshake->io, outbuf, len );
}
/* maybe de-encrypt our connection */
if( crypto_select == CRYPTO_PROVIDE_PLAINTEXT )
tr_peerIoSetEncryption( handshake->io, PEER_ENCRYPTION_NONE );
dbgmsg( handshake, "sending handshake" );
/* send our handshake */
{
int msgSize;
uint8_t * msg = buildHandshakeMessage( handshake, &msgSize );
tr_peerIoWriteBytes( handshake->io, outbuf, msg, msgSize );
handshake->haveSentBitTorrentHandshake = 1;
tr_free( msg );
}
/* send it out */
tr_peerIoWriteBuf( handshake->io, outbuf );
evbuffer_free( outbuf );
/* we've completed the BT handshake... pass the work on to peer-msgs */
tr_handshakeDone( handshake, TRUE );
return READ_DONE;
}
/***
****
****
****
***/
static ReadState
canRead( struct bufferevent * evin, void * arg )
{
tr_handshake * handshake = (tr_handshake *) arg;
struct evbuffer * inbuf = EVBUFFER_INPUT ( evin );
ReadState ret;
dbgmsg( handshake, "handling canRead; state is [%s]", getStateName(handshake->state) );
switch( handshake->state )
{
case AWAITING_HANDSHAKE: ret = readHandshake ( handshake, inbuf ); break;
case AWAITING_PEER_ID: ret = readPeerId ( handshake, inbuf ); break;
case AWAITING_YA: ret = readYa ( handshake, inbuf ); break;
case AWAITING_PAD_A: ret = readPadA ( handshake, inbuf ); break;
case AWAITING_CRYPTO_PROVIDE: ret = readCryptoProvide( handshake, inbuf ); break;
case AWAITING_PAD_C: ret = readPadC ( handshake, inbuf ); break;
case AWAITING_IA: ret = readIA ( handshake, inbuf ); break;
case AWAITING_YB: ret = readYb ( handshake, inbuf ); break;
case AWAITING_VC: ret = readVC ( handshake, inbuf ); break;
case AWAITING_CRYPTO_SELECT: ret = readCryptoSelect ( handshake, inbuf ); break;
case AWAITING_PAD_D: ret = readPadD ( handshake, inbuf ); break;
default: assert( 0 );
}
return ret;
}
static void
fireDoneFunc( tr_handshake * handshake, int isConnected )
{
const uint8_t * peer_id = isConnected && handshake->havePeerID
? handshake->peer_id
: NULL;
(*handshake->doneCB)( handshake,
handshake->io,
isConnected,
peer_id,
handshake->doneUserData );
}
static void
tr_handshakeDone( tr_handshake * handshake, int isOK )
{
dbgmsg( handshake, "handshakeDone: %s", isOK ? "connected" : "aborting" );
tr_peerIoSetIOFuncs( handshake->io, NULL, NULL, NULL, NULL );
fireDoneFunc( handshake, isOK );
tr_free( handshake );
}
void
tr_handshakeAbort( tr_handshake * handshake )
{
tr_handshakeDone( handshake, FALSE );
}
static void
gotError( struct bufferevent * evbuf UNUSED, short what, void * arg )
{
tr_handshake * handshake = (tr_handshake *) arg;
/* if the error happened while we were sending a public key, we might
* have encountered a peer that doesn't do encryption... reconnect and
* try a plaintext handshake */
if( ( ( handshake->state == AWAITING_YB ) || ( handshake->state == AWAITING_VC ) )
&& ( handshake->encryptionMode != TR_ENCRYPTION_REQUIRED )
&& ( !tr_peerIoReconnect( handshake->io ) ) )
{
int msgSize;
uint8_t * msg;
dbgmsg( handshake, "handshake failed, trying plaintext..." );
msg = buildHandshakeMessage( handshake, &msgSize );
handshake->haveSentBitTorrentHandshake = 1;
setReadState( handshake, AWAITING_HANDSHAKE );
tr_peerIoWrite( handshake->io, msg, msgSize );
tr_free( msg );
}
else
{
dbgmsg( handshake, "libevent got an error what==%d, errno=%d (%s)",
(int)what, errno, tr_strerror(errno) );
tr_handshakeDone( handshake, FALSE );
}
}
/**
***
**/
tr_handshake*
tr_handshakeNew( tr_peerIo * io,
tr_encryption_mode encryptionMode,
handshakeDoneCB doneCB,
void * doneUserData )
{
tr_handshake * handshake;
handshake = tr_new0( tr_handshake, 1 );
handshake->io = io;
handshake->crypto = tr_peerIoGetCrypto( io );
handshake->encryptionMode = encryptionMode;
handshake->doneCB = doneCB;
handshake->doneUserData = doneUserData;
handshake->handle = tr_peerIoGetHandle( io );
tr_peerIoSetTimeoutSecs( io, 15 );
tr_peerIoSetIOFuncs( handshake->io, canRead, NULL, gotError, handshake );
if( tr_peerIoIsIncoming( handshake->io ) )
setReadState( handshake, AWAITING_HANDSHAKE );
else if( encryptionMode != TR_CLEAR_PREFERRED )
sendYa( handshake );
else {
int msgSize;
uint8_t * msg = buildHandshakeMessage( handshake, &msgSize );
handshake->haveSentBitTorrentHandshake = 1;
setReadState( handshake, AWAITING_HANDSHAKE );
tr_peerIoWrite( handshake->io, msg, msgSize );
tr_free( msg );
}
return handshake;
}
const struct in_addr *
tr_handshakeGetAddr( const struct tr_handshake * handshake, uint16_t * port )
{
assert( handshake );
assert( handshake->io );
return tr_peerIoGetAddress( handshake->io, port );
}
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