RTMPdump（libRTMP）源代码分析 4： 连接第一步——握手（Hand Shake）

注：此前写了一些列的分析RTMPdump（libRTMP）源代码的文章，在此列一个列表：

RTMPdump 源代码分析 1： main()函数

RTMPDump（libRTMP）源代码分析 2：解析RTMP地址——RTMP_ParseURL()

RTMPdump（libRTMP） 源代码分析 3： AMF编码

RTMPdump（libRTMP）源代码分析 4： 连接第一步——握手（Hand Shake）

RTMPdump（libRTMP） 源代码分析 5： 建立一个流媒体连接 （NetConnection部分）

RTMPdump（libRTMP） 源代码分析 6： 建立一个流媒体连接 （NetStream部分 1）

RTMPdump（libRTMP） 源代码分析 7： 建立一个流媒体连接 （NetStream部分 2）

RTMPdump（libRTMP） 源代码分析 8： 发送消息（Message）

RTMPdump（libRTMP） 源代码分析 9： 接收消息（Message）（接收视音频数据）

RTMPdump（libRTMP） 源代码分析 10： 处理各种消息（Message）
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在这里分析一下RTMPdump（libRTMP）连接到支持RTMP协议的服务器的第一步：握手（Hand Shake）。

RTMP连接的过程曾经分析过：RTMP流媒体播放过程

在这里不再细说，分析一下位于handshake.h文件里面实现握手（HandShake）功能的函数：

注意：handshake.h里面代码量很大，但是很多代码都是为了处理RTMP的加密版协议的，例如rtmps；因此在这里就不做过多分析了，我们只考虑普通的RTMP协议。

static int
HandShake(RTMP * r, int FP9HandShake)
{
int i, offalg = 0;
int dhposClient = 0;
int digestPosClient = 0;
int encrypted = r->Link.protocol & RTMP_FEATURE_ENC;

RC4_handle keyIn = 0;
RC4_handle keyOut = 0;

int32_t *ip;
uint32_t uptime;

uint8_t clientbuf[RTMP_SIG_SIZE + 4], *clientsig=clientbuf+4;
uint8_t serversig[RTMP_SIG_SIZE], client2[RTMP_SIG_SIZE], *reply;
uint8_t type;
getoff *getdh = NULL, *getdig = NULL;

if (encrypted || r->Link.SWFSize)
FP9HandShake = TRUE;
else
//普通的
FP9HandShake = FALSE;

r->Link.rc4keyIn = r->Link.rc4keyOut = 0;

if (encrypted)
{
clientsig[-1] = 0x06;	/* 0x08 is RTMPE as well */
offalg = 1;
}
else
//0x03代表RTMP协议的版本（客户端要求的）
//数组竟然能有“-1”下标
//C0中的字段(1B)
clientsig[-1] = 0x03;

uptime = htonl(RTMP_GetTime());
//void *memcpy(void *dest, const void *src, int n);
//由src指向地址为起始地址的连续n个字节的数据复制到以dest指向地址为起始地址的空间内
//把uptime的前4字节（其实一共就4字节）数据拷贝到clientsig指向的地址中
//C1中的字段(4B)
memcpy(clientsig, &uptime, 4);

if (FP9HandShake)
{
/* set version to at least 9.0.115.0 */
if (encrypted)
{
clientsig[4] = 128;
clientsig[6] = 3;
}
else
{
clientsig[4] = 10;
clientsig[6] = 45;
}
clientsig[5] = 0;
clientsig[7] = 2;

RTMP_Log(RTMP_LOGDEBUG, "%s: Client type: %02X", __FUNCTION__, clientsig[-1]);
getdig = digoff[offalg];
getdh  = dhoff[offalg];
}
else
{
//void *memset(void *s, int ch, size_t n);将s中前n个字节替换为ch并返回s；
//将clientsig[4]开始的4个字节替换为0
//这是C1的字段
memset(&clientsig[4], 0, 4);
}

/* generate random data */
#ifdef _DEBUG
//将clientsig+8开始的1528个字节替换为0（这是一种简单的方法）
//这是C1中的random字段
memset(clientsig+8, 0, RTMP_SIG_SIZE-8);
#else
//实际中使用rand()循环生成1528字节的伪随机数
ip = (int32_t *)(clientsig+8);
for (i = 2; i < RTMP_SIG_SIZE/4; i++)
*ip++ = rand();
#endif

/* set handshake digest */
if (FP9HandShake)
{
if (encrypted)
{
/* generate Diffie-Hellmann parameters */
r->Link.dh = DHInit(1024);
if (!r->Link.dh)
{
RTMP_Log(RTMP_LOGERROR, "%s: Couldn't initialize Diffie-Hellmann!",
__FUNCTION__);
return FALSE;
}

dhposClient = getdh(clientsig, RTMP_SIG_SIZE);
RTMP_Log(RTMP_LOGDEBUG, "%s: DH pubkey position: %d", __FUNCTION__, dhposClient);

if (!DHGenerateKey((DH *)r->Link.dh))
{
RTMP_Log(RTMP_LOGERROR, "%s: Couldn't generate Diffie-Hellmann public key!",
__FUNCTION__);
return FALSE;
}

if (!DHGetPublicKey((DH *)r->Link.dh, &clientsig[dhposClient], 128))
{
RTMP_Log(RTMP_LOGERROR, "%s: Couldn't write public key!", __FUNCTION__);
return FALSE;
}
}

digestPosClient = getdig(clientsig, RTMP_SIG_SIZE);	/* reuse this value in verification */
RTMP_Log(RTMP_LOGDEBUG, "%s: Client digest offset: %d", __FUNCTION__,
digestPosClient);

CalculateDigest(digestPosClient, clientsig, GenuineFPKey, 30,
&clientsig[digestPosClient]);

RTMP_Log(RTMP_LOGDEBUG, "%s: Initial client digest: ", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, clientsig + digestPosClient,
SHA256_DIGEST_LENGTH);
}

#ifdef _DEBUG
RTMP_Log(RTMP_LOGDEBUG, "Clientsig: ");
RTMP_LogHex(RTMP_LOGDEBUG, clientsig, RTMP_SIG_SIZE);
#endif
//发送数据报C0+C1
//从clientsig-1开始发，长度1536+1，两个包合并
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。发送握手数据C0+C1");
//-----------------------------
if (!WriteN(r, (char *)clientsig-1, RTMP_SIG_SIZE + 1))
return FALSE;
//读取数据报，长度1，存入type
//是服务器的S0，表示服务器使用的RTMP版本
if (ReadN(r, (char *)&type, 1) != 1)	/* 0x03 or 0x06 */
return FALSE;
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。接收握手数据S0");
//-----------------------------
RTMP_Log(RTMP_LOGDEBUG, "%s: Type Answer   : %02X", __FUNCTION__, type);
//客户端要求的版本和服务器提供的版本不同
if (type != clientsig[-1])
RTMP_Log(RTMP_LOGWARNING, "%s: Type mismatch: client sent %d, server answered %d",
__FUNCTION__, clientsig[-1], type);
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。成功接收握手数据S0，服务器和客户端版本相同");
//-----------------------------
//客户端和服务端随机序列长度是否相同
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。接收握手数据S1");
//-----------------------------
if (ReadN(r, (char *)serversig, RTMP_SIG_SIZE) != RTMP_SIG_SIZE)
return FALSE;

/* decode server response */
//把serversig的前四个字节赋值给uptime
memcpy(&uptime, serversig, 4);
//大端转小端
uptime = ntohl(uptime);

RTMP_Log(RTMP_LOGDEBUG, "%s: Server Uptime : %d", __FUNCTION__, uptime);
RTMP_Log(RTMP_LOGDEBUG, "%s: FMS Version   : %d.%d.%d.%d", __FUNCTION__, serversig[4],
serversig[5], serversig[6], serversig[7]);

if (FP9HandShake && type == 3 && !serversig[4])
FP9HandShake = FALSE;

#ifdef _DEBUG
RTMP_Log(RTMP_LOGDEBUG, "Server signature:");
RTMP_LogHex(RTMP_LOGDEBUG, serversig, RTMP_SIG_SIZE);
#endif

if (FP9HandShake)
{
uint8_t digestResp[SHA256_DIGEST_LENGTH];
uint8_t *signatureResp = NULL;

/* we have to use this signature now to find the correct algorithms for getting the digest and DH positions */
int digestPosServer = getdig(serversig, RTMP_SIG_SIZE);

if (!VerifyDigest(digestPosServer, serversig, GenuineFMSKey, 36))
{
RTMP_Log(RTMP_LOGWARNING, "Trying different position for server digest!");
offalg ^= 1;
getdig = digoff[offalg];
getdh  = dhoff[offalg];
digestPosServer = getdig(serversig, RTMP_SIG_SIZE);

if (!VerifyDigest(digestPosServer, serversig, GenuineFMSKey, 36))
{
RTMP_Log(RTMP_LOGERROR, "Couldn't verify the server digest");	/* continuing anyway will probably fail */
return FALSE;
}
}

/* generate SWFVerification token (SHA256 HMAC hash of decompressed SWF, key are the last 32 bytes of the server handshake) */
if (r->Link.SWFSize)
{
const char swfVerify[] = { 0x01, 0x01 };
char *vend = r->Link.SWFVerificationResponse+sizeof(r->Link.SWFVerificationResponse);

memcpy(r->Link.SWFVerificationResponse, swfVerify, 2);
AMF_EncodeInt32(&r->Link.SWFVerificationResponse[2], vend, r->Link.SWFSize);
AMF_EncodeInt32(&r->Link.SWFVerificationResponse[6], vend, r->Link.SWFSize);
HMACsha256(r->Link.SWFHash, SHA256_DIGEST_LENGTH,
&serversig[RTMP_SIG_SIZE - SHA256_DIGEST_LENGTH],
SHA256_DIGEST_LENGTH,
(uint8_t *)&r->Link.SWFVerificationResponse[10]);
}

/* do Diffie-Hellmann Key exchange for encrypted RTMP */
if (encrypted)
{
/* compute secret key */
uint8_t secretKey[128] = { 0 };
int len, dhposServer;

dhposServer = getdh(serversig, RTMP_SIG_SIZE);
RTMP_Log(RTMP_LOGDEBUG, "%s: Server DH public key offset: %d", __FUNCTION__,
dhposServer);
len = DHComputeSharedSecretKey((DH *)r->Link.dh, &serversig[dhposServer],
128, secretKey);
if (len < 0)
{
RTMP_Log(RTMP_LOGDEBUG, "%s: Wrong secret key position!", __FUNCTION__);
return FALSE;
}

RTMP_Log(RTMP_LOGDEBUG, "%s: Secret key: ", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, secretKey, 128);

InitRC4Encryption(secretKey,
(uint8_t *) & serversig[dhposServer],
(uint8_t *) & clientsig[dhposClient],
&keyIn, &keyOut);
}

reply = client2;
#ifdef _DEBUG
memset(reply, 0xff, RTMP_SIG_SIZE);
#else
ip = (int32_t *)reply;
for (i = 0; i < RTMP_SIG_SIZE/4; i++)
*ip++ = rand();
#endif
/* calculate response now */
signatureResp = reply+RTMP_SIG_SIZE-SHA256_DIGEST_LENGTH;

HMACsha256(&serversig[digestPosServer], SHA256_DIGEST_LENGTH,
GenuineFPKey, sizeof(GenuineFPKey), digestResp);
HMACsha256(reply, RTMP_SIG_SIZE - SHA256_DIGEST_LENGTH, digestResp,
SHA256_DIGEST_LENGTH, signatureResp);

/* some info output */
RTMP_Log(RTMP_LOGDEBUG,
"%s: Calculated digest key from secure key and server digest: ",
__FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, digestResp, SHA256_DIGEST_LENGTH);

#ifdef FP10
if (type == 8 )
{
uint8_t *dptr = digestResp;
uint8_t *sig = signatureResp;
/* encrypt signatureResp */
for (i=0; i<SHA256_DIGEST_LENGTH; i+=8)
rtmpe8_sig(sig+i, sig+i, dptr[i] % 15);
}
#if 0
else if (type == 9))
{
uint8_t *dptr = digestResp;
uint8_t *sig = signatureResp;
/* encrypt signatureResp */
for (i=0; i<SHA256_DIGEST_LENGTH; i+=8)
rtmpe9_sig(sig+i, sig+i, dptr[i] % 15);
}
#endif
#endif
RTMP_Log(RTMP_LOGDEBUG, "%s: Client signature calculated:", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, signatureResp, SHA256_DIGEST_LENGTH);
}
else
{
//直接赋值
reply = serversig;
#if 0
uptime = htonl(RTMP_GetTime());
memcpy(reply+4, &uptime, 4);
#endif
}

#ifdef _DEBUG
RTMP_Log(RTMP_LOGDEBUG, "%s: Sending handshake response: ",
__FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, reply, RTMP_SIG_SIZE);
#endif
//把reply中的1536字节数据发送出去
//对应C2
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。发送握手数据C2");
//-----------------------------
if (!WriteN(r, (char *)reply, RTMP_SIG_SIZE))
return FALSE;

/* 2nd part of handshake */
//读取1536字节数据到serversig
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。读取握手数据S2");
//-----------------------------
if (ReadN(r, (char *)serversig, RTMP_SIG_SIZE) != RTMP_SIG_SIZE)
return FALSE;

#ifdef _DEBUG
RTMP_Log(RTMP_LOGDEBUG, "%s: 2nd handshake: ", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, serversig, RTMP_SIG_SIZE);
#endif

if (FP9HandShake)
{
uint8_t signature[SHA256_DIGEST_LENGTH];
uint8_t digest[SHA256_DIGEST_LENGTH];

if (serversig[4] == 0 && serversig[5] == 0 && serversig[6] == 0
&& serversig[7] == 0)
{
RTMP_Log(RTMP_LOGDEBUG,
"%s: Wait, did the server just refuse signed authentication?",
__FUNCTION__);
}
RTMP_Log(RTMP_LOGDEBUG, "%s: Server sent signature:", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, &serversig[RTMP_SIG_SIZE - SHA256_DIGEST_LENGTH],
SHA256_DIGEST_LENGTH);

/* verify server response */
HMACsha256(&clientsig[digestPosClient], SHA256_DIGEST_LENGTH,
GenuineFMSKey, sizeof(GenuineFMSKey), digest);
HMACsha256(serversig, RTMP_SIG_SIZE - SHA256_DIGEST_LENGTH, digest,
SHA256_DIGEST_LENGTH, signature);

/* show some information */
RTMP_Log(RTMP_LOGDEBUG, "%s: Digest key: ", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, digest, SHA256_DIGEST_LENGTH);

#ifdef FP10
if (type == 8 )
{
uint8_t *dptr = digest;
uint8_t *sig = signature;
/* encrypt signature */
for (i=0; i<SHA256_DIGEST_LENGTH; i+=8)
rtmpe8_sig(sig+i, sig+i, dptr[i] % 15);
}
#if 0
else if (type == 9)
{
uint8_t *dptr = digest;
uint8_t *sig = signature;
/* encrypt signatureResp */
for (i=0; i<SHA256_DIGEST_LENGTH; i+=8)
rtmpe9_sig(sig+i, sig+i, dptr[i] % 15);
}
#endif
#endif
RTMP_Log(RTMP_LOGDEBUG, "%s: Signature calculated:", __FUNCTION__);
RTMP_LogHex(RTMP_LOGDEBUG, signature, SHA256_DIGEST_LENGTH);
if (memcmp
(signature, &serversig[RTMP_SIG_SIZE - SHA256_DIGEST_LENGTH],
SHA256_DIGEST_LENGTH) != 0)
{
RTMP_Log(RTMP_LOGWARNING, "%s: Server not genuine Adobe!", __FUNCTION__);
return FALSE;
}
else
{
RTMP_Log(RTMP_LOGDEBUG, "%s: Genuine Adobe Flash Media Server", __FUNCTION__);
}

if (encrypted)
{
char buff[RTMP_SIG_SIZE];
/* set keys for encryption from now on */
r->Link.rc4keyIn = keyIn;
r->Link.rc4keyOut = keyOut;

/* update the keystreams */
if (r->Link.rc4keyIn)
{
RC4_encrypt((RC4_KEY *)r->Link.rc4keyIn, RTMP_SIG_SIZE, (uint8_t *) buff);
}

if (r->Link.rc4keyOut)
{
RC4_encrypt((RC4_KEY *)r->Link.rc4keyOut, RTMP_SIG_SIZE, (uint8_t *) buff);
}
}
}
else
{
//int memcmp(const void *buf1, const void *buf2, unsigned int count); 当buf1=buf2时，返回值=0
//比较serversig和clientsig是否相等
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。比较握手数据签名");
//-----------------------------
if (memcmp(serversig, clientsig, RTMP_SIG_SIZE) != 0)
{
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。握手数据签名不匹配！");
//-----------------------------
RTMP_Log(RTMP_LOGWARNING, "%s: client signature does not match!",
__FUNCTION__);
}
}
//握手----------------
r->dlg->AppendCInfo("建立连接：第1次连接。握手成功");
//-----------------------------
RTMP_Log(RTMP_LOGDEBUG, "%s: Handshaking finished....", __FUNCTION__);
return TRUE;
}

rtmpdump源代码（Linux）：http://download.csdn.net/detail/leixiaohua1020/6376561

rtmpdump源代码（VC 2005 工程）：http://download.csdn.net/detail/leixiaohua1020/6563163