A simple c program that takes a base64 encoded string containing data protected with CryptProtectData and calls CryptUnprotectData on it

unprotect.c

/*
 * To build run the following commands (ensure that the path to vcvars64.bat matches with your build environment)
 * call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat"
 * cl /EHsc unprotect.c /link Advapi32.lib Crypt32.lib
*/

#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void base64_decode(char* input, BYTE** output, DWORD* outputSize) {
    DWORD decodedSize;
    CryptStringToBinaryA(input, 0, CRYPT_STRING_BASE64, NULL, &decodedSize, NULL, NULL);
    *output = (BYTE*)malloc(decodedSize);
    CryptStringToBinaryA(input, 0, CRYPT_STRING_BASE64, *output, &decodedSize, NULL, NULL);
    *outputSize = decodedSize;
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        printf("Usage: %s base64_encoded_data\n", argv[0]);
        return 1;
    }

    BYTE* base64DecodedData;
    DWORD base64DecodedSize;
    
    // Decode base64 encoded data
    base64_decode(argv[1], &base64DecodedData, &base64DecodedSize);

    DATA_BLOB input;
    DATA_BLOB output;

    // Initialize input data
    input.pbData = base64DecodedData;
    input.cbData = base64DecodedSize;

    BOOL result = CryptUnprotectData(&input, NULL, NULL, NULL, NULL, 0, &output);

    if (result) {
        printf("Decryption successful!\n");

        // The decrypted data is in the output structure
        printf("Decrypted Data: %.*s\n", output.cbData, (char*)output.pbData);

        // Clean up the output data
        LocalFree(output.pbData);
    } else {
        printf("Decryption failed. Error code: %d\n", GetLastError());
    }

    // Clean up the base64 decoded data
    free(base64DecodedData);

    return 0;
}