How can I decrypt a string using CryptUnprotectData - winapi

Question

I have been trying to decrypt some encrypted data (AES key encrypting chrome cookies) via the c++ CryptUnprotectData function for a short while now, but I cant seem to get it working. Currently the function will fail and return an error code of 13 (meaning "The parameter is incorrect."). Here is my code so far:
#include <iostream>
#include <Windows.h>
#include <wincrypt.h>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
std::string GetLastErrorAsString()
{
DWORD errorMessageID = ::GetLastError();
if(errorMessageID == 0) {
return std::string();
}
LPSTR messageBuffer = nullptr;
size_t size = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);
std::string message(messageBuffer, size);
LocalFree(messageBuffer);
return message;
}
int main()
{
string data = "(data I want to decode)";
cout << data;
DATA_BLOB DataBytes;
DataBytes.pbData = (BYTE*)data.data();
DataBytes.cbData = (DWORD)data.size()+1;
DATA_BLOB output;
output.pbData = NULL;
output.cbData = (DWORD)data.size();
CryptUnprotectData(&DataBytes, NULL, NULL, NULL, NULL, 0, &output);
cout << GetLastErrorAsString() << endl;
cout << output.pbData;
LocalFree(output.pbData);
return 0;
}
If anyone can provide any help, that would be greatly appreciated.
I have tried different variations of the data types the parameters are stored in, although it still returns this error.

Answer 1

I modified your code, which is as follows. It only implements simple decryption.
And the data is not encrypted, so CryptUnprotectData() does not return the correct value.
#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#include <string>
#include <vector>
#include <fstream>
#include <iostream>
using namespace std;
#define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
#pragma comment (lib, "Crypt32.lib")
int main()
{
// Decrypt data from DATA_BLOB DataOut to DATA_BLOB DataVerify.
//--------------------------------------------------------------------
// Declare and initialize variables.
string data = ("data I want to decode \n");
cout << data;
LPWSTR pDescrOut = NULL;
DATA_BLOB DataBytes;
BYTE* pbDataOutput = (BYTE*)data.data();
DWORD cbDataOutput = strlen((char*)pbDataOutput) + 1;
DataBytes.pbData = pbDataOutput;
DataBytes.cbData = cbDataOutput;
//DATA_BLOB DataVerify;
//--------------------------------------------------------------------
// The buffer DataOut would be created using the CryptProtectData
// function. If may have been read in from a file.
//--------------------------------------------------------------------
// Begin unprotect phase.
BOOL res = CryptUnprotectData(
&DataBytes,
&pDescrOut,
NULL, // Optional entropy
NULL, // Reserved
NULL, // Here, the optional
// prompt structure is not
// used.
0,
&DataBytes);
if (res==1)
{
printf("The decrypted data is: %s\n", DataBytes.pbData);
printf("The description of the data was: %s\n", pDescrOut);
}
else
{
printf("Decryption error!");
}
// LocalFree(DataVerify.pbData);
LocalFree(pDescrOut);
//LocalFree(DataBytes.pbData);
}
It is recommended to refer to Microsoft's official documentation when you add additional code.