how to correct convert char to byte in C++ - c++

Question

I have some problem.
I write next code.
z=recv(conn,buff,512,0);//"Hi VahagnAAAAAAA" - but encrypted for example "zЖWЙЇ%ЂАЊ"S]яАAЧ0АбЯ.Щk5S¤Oц", length 32
BYTE messageLen = (BYTE)strlen(buff);// messageLen = 32
BYTE encryptedMessage[32];
memcpy(encryptedMessage, buff, messageLen);//!!!!!!!!!!!
DWORD encryptedMessageLen = messageLen;
CryptDecrypt(hSessionKeyRSA_2,NULL,TRUE,0,encryptedMessage, &encryptedMessageLen);
cout<<encryptedMessage<<endl;
I recv to buffer char array 32 length.
Where I copy encrypted text
"zЖWЙЇ%ЂАЊ"S]яАAЧ0АбЯ.Щk5S¤Oц"
to byte array, on the encryptedMessage have next value
"zЖWЙЇ%ЂАЊ"S]яАAЧ0АбЯ.Щk5S¤OцMMMMMMMMMMMMMMMMMMM"
where I decrypted I don't get start text, I get
"Ik VqagnеAAcS]‰МММММММММММ ММММММММ"
How I can fix it? please help me.
UPDATE
Client main()
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
const char* servername="127.0.0.1";
Sleep(2000);
setlocale(LC_ALL, "Russian");
WSADATA wsaData;
struct hostent *hp;
unsigned int addr;
struct sockaddr_in server;
int wsaret=WSAStartup(0x101,&wsaData);
if(wsaret)
return 0;
SOCKET conn;
conn=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(conn==INVALID_SOCKET)
return 0;
if(inet_addr(servername)==INADDR_NONE)
{
hp=gethostbyname(servername);
}
else
{
addr=inet_addr(servername);
hp=gethostbyaddr((char*)&addr,sizeof(addr),AF_INET);
}
if(hp==NULL)
{
closesocket(conn);
return 0;
}
server.sin_addr.s_addr=*((unsigned long*)hp->h_addr);
server.sin_family=AF_INET;
server.sin_port=htons(20248);
if(connect(conn,(struct sockaddr*)&server,sizeof(server)))
{
closesocket(conn);
return 0;
}
std::cout<<"Connected to server";
char buff[512];
memset(buff,'\0',512);
int z;
z=recv(conn,(char*)exportRSAKey,140,0);//Import RSA key
z=recv(conn,(char*)exportAESKey,140,0);//Import AES key
z=recv(conn,buff,512,0);//Get encryption text
importKey();//import key to client
BYTE messageLen = (BYTE)strlen(buff);
BYTE encryptedMessage[33];
memcpy(encryptedMessage, buff, messageLen);
DWORD encryptedMessageLen = messageLen;
CryptDecrypt(hSessionKeyRSA_2,NULL,FALSE,0,encryptedMessage, &encryptedMessageLen);
cout<<encryptedMessage<<endl;
// buff[z]=0;
}
Import key to client
if (CryptAcquireContext(&hCryptProv_RSA_2, NULL, MS_ENH_RSA_AES_PROV, PROV_RSA_AES, 0))
{
printf("A cryptographic provider has been acquired.\r\n");
}
else
{
DWORD d = GetLastError();
return -1;
}
int iii = CryptImportKey(hCryptProv_RSA_2,(BYTE *)&exportAESKey,140,NULL,NULL,&hSessionKeyRSA_2);
if(CryptSetKeyParam(hSessionKeyRSA_2, KP_IV, exportRSAKey, 0))
{
cout<<"ok";
}
Server main()
std::cout<<"Client connected... "<<pParam<<std::endl;
char buff[512];
CString cmd;
CString params;
int n;
int x;
BOOL auth=false;
SOCKET client=(SOCKET)pParam;
strcpy(buff,"#Server Ready.\r\n");
char keybuff[1024];
createRSAPublicKey();//create enc_dec key
//keybuff = exportRSAKey;
//memset(rec,'\0',512);
const char *p = reinterpret_cast<const char*>(exportRSAKey);
send(client,p,140,0);//send RSA
const char *pp = reinterpret_cast<const char*>(exportAESKey);
send(client,pp,140,0);//Send AES
const char *ppp = reinterpret_cast<const char*>(encryptedMessage);
send(client,ppp,512,0);//Send encrypt text
createRSAPublicKey()
BOOL createRSAPublicKey()
{
if (CryptAcquireContext(&hCryptProv_AES, NULL, MS_ENH_RSA_AES_PROV, PROV_RSA_AES, 0))
{
printf("A cryptographic provider has been acquired.\r\n");
}
else
{
DWORD d = GetLastError();
return -1;
}
HCRYPTKEY hSessionKey_AES;
if (!CryptGenKey(hCryptProv_AES, CALG_AES_256, CRYPT_EXPORTABLE, &hSessionKey_AES))
{
DWORD d = GetLastError();
return -1;
}
// Create RSA key to encrypt AES one
HCRYPTKEY hSessionKey;
if (!CryptGenKey(hCryptProv_AES, AT_KEYEXCHANGE, 1024 << 16, &hSessionKey))
{
DWORD d = GetLastError();
return -1;
}
// Export key
DWORD keylen;
BOOL ok = CryptExportKey(hSessionKey_AES, hSessionKey, SIMPLEBLOB, 0, exportRSAKey, &keylen);
if (ok == FALSE)
{
DWORD d = GetLastError();
return -1;
}
BYTE *encKey = (BYTE *)malloc(keylen);
ok = CryptExportKey(hSessionKey_AES, hSessionKey, SIMPLEBLOB, 0, exportAESKey, &keylen);
if (ok == FALSE)
{
DWORD d = GetLastError();
return -1;
}
else
printf("A cryptographic key export succeeded.\r\n");
BYTE messageLen = (BYTE)strlen(mess);
memcpy(encryptedMessage, mess, messageLen);
DWORD encryptedMessageLen = messageLen;
CryptEncrypt(hSessionKey_AES, NULL, TRUE, 0, encryptedMessage, &encryptedMessageLen, sizeof(encryptedMessage));
}

Answer 1

You are using strlen() to get the length of buff, but recv() does not null-terminate the buffer unless a null terminator was actually transmitted and read. You should instead be using the return value of recv(), which is the number of bytes actually read:
z=recv(conn,buff,512,0);
messageLen = z;//(BYTE)strlen(buff);
That being said, TCP is a byte stream, it has no concept of message boundaries. There is no 1-to-1 relationship between send() and recv() in TCP, like there is in UDP, so recv() above could read as little as 1 byte or as many as 512 bytes, and buff could contain a full message, a partial message, pieces of multiple messages, etc. You can't just blindly read and expect to receive everything in one go. You need to take all of that into account.
Design your TCP protocol to delimit messages, either with a preceding header that specifies the message length, or a trailing delimiter that never appears in the message body. Call recv() as many times as it takes, buffering any received data, and only process/decrypt complete messages that are in your buffer, leaving partial message data in the buffer to be completed by later reads.
Try something more like this:
Client main()
int readBuffer(SOCKET s, void *buffer, int buflen)
{
unsigned char *pbuf = (unsigned char*) buffer;
int total = 0;
while (total < buflen)
{
int num = recv(s, pbuf+total, buflen-total, 0);
if (num < 0)
return SOCKET_ERROR;
if (num == 0)
return 0;
total += num;
}
return total;
}
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
const char* servername="127.0.0.1";
setlocale(LC_ALL, "Russian");
WSADATA wsaData;
memset(&wsaData, 0, sizeof(wsaData));
int wsaret = WSAStartup(0x101, &wsaData);
if (wsaret != 0)
return 0;
struct sockaddr_in server;
memset(&server, 0, sizeof(server));
server.sin_addr.s_addr = inet_addr(servername);
if (server.sin_addr.s_addr == INADDR_NONE)
{
struct hostent *hp = gethostbyname(servername);
if (hp == NULL)
return 0;
server.sin_addr = *((in_addr*)hp->h_addr);
}
server.sin_family = AF_INET;
server.sin_port = htons(20248);
SOCKET conn = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (conn == INVALID_SOCKET)
return 0;
if (connect(conn, (struct sockaddr*)&server, sizeof(server)) != 0)
{
closesocket(conn);
return 0;
}
std::cout << "Connected to server";
if (readBuffer(conn, exportRSAKey, 140) <= 0) //Import RSA key
{
closesocket(conn);
return 0;
}
if (readBuffer(conn, exportAESKey, 140) <= 0) //Import AES key
{
closesocket(conn);
return 0;
}
importKey();//import key to client
DWORD messageLen;
if (readBuffer(conn, &messageLen, sizeof(messageLen)) <= 0) //Get encryption text length
{
closesocket(conn);
return 0;
}
messageLen = ntohl(messageLen);
std::vector<BYTE> buff(messageLen);
if (messageLen > 0)
{
if (readBuffer(conn, &buff[0], messageLen) <= 0) //Get encryption text
{
closesocket(conn);
return 0;
}
if (!CryptDecrypt(hSessionKeyRSA_2, NULL, FALSE, 0, &buff[0], &messageLen))
{
closesocket(conn);
return 0;
}
}
std::cout << std::string((char*)buff.data(), messageLen) << std::endl;
}
Server main()
int sendBuffer(SOCKET s, void *buffer, int buflen)
{
unsigned char *pbuf = (unsigned char*) buffer;
int total = 0;
while (total < buflen)
{
int num = send(s, pbuf+total, buflen-total, 0);
if (num < 0)
return SOCKET_ERROR;
if (num == 0)
return 0;
total += num;
}
return total;
}
...
SOCKET client = (SOCKET)pParam;
std::cout << "Client connected... " << pParam << std::endl;
...
createRSAPublicKey();//create enc_dec key
...
if (sendBuffer(client, exportRSAKey, 140) <= 0) //send RSA
{
closesocket(client);
return;
}
if (sendBuffer(client, exportAESKey, 140) <= 0) //Send AES
{
closesocket(client);
return;
}
...
DWORD tmpMessageLen = htonl(messageLen);
if (sendBuffer(client, &tmpMessageLen, sizeof(tmpMessageLen)); //Send encrypt text length
{
closesocket(client);
return;
}
if (sendBuffer(client, encryptedMessage, messageLen) <= 0) //Send encrypt text
{
closesocket(client);
return;
}
...