/******************************************************************************\
* This is a part of the Microsoft Source Code Samples.
* Copyright 1996 - 1998 Microsoft Corporation.
* All rights reserved.
* This source code is only intended as a supplement to
* Microsoft Development Tools and/or WinHelp documentation.
* See these sources for detailed information regarding the
* Microsoft samples programs.
\******************************************************************************/
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <wincrypt.h>
#ifdef USE_BLOCK_CIPHER
// defines for RC2 block cipher
#define ENCRYPT_ALGORITHMCALG_RC2
#define ENCRYPT_BLOCK_SIZE8
#else
// defines for RC4 stream cipher
#define ENCRYPT_ALGORITHMCALG_RC4
#define ENCRYPT_BLOCK_SIZE1
#endif
static BOOL CAPIDecryptFile(PCHAR szSource, PCHAR szDestination, PCHAR szPassword);
/*****************************************************************************/
void _cdecl main(int argc, char *argv[])
{
PCHAR szSource= NULL;
PCHAR szDestination = NULL;
PCHAR szPassword= NULL;
// Validate argument count.
if(argc != 3 && argc != 4) {
printf("USAGE: decrypt <source file> <dest file> [ <password> ]\n");
exit(1);
}
// Parse arguments.
szSource = argv[1];
szDestination = argv[2];
if(argc == 4) {
szPassword = argv[3];
}
if(!CAPIDecryptFile(szSource, szDestination, szPassword)) {
printf("Error encrypting file!\n");
exit(1);
}
exit(0);
}
/*****************************************************************************/
static BOOL CAPIDecryptFile(PCHAR szSource, PCHAR szDestination, PCHAR szPassword)
{
FILE *hSource = NULL;
FILE *hDestination = NULL;
INT eof = 0;
HCRYPTPROV hProv = 0;
HCRYPTKEY hKey = 0;
HCRYPTHASH hHash = 0;
PBYTE pbKeyBlob = NULL;
DWORD dwKeyBlobLen;
PBYTE pbBuffer = NULL;
DWORD dwBlockLen;
DWORD dwBufferLen;
DWORD dwCount;
BOOL status = FALSE;
// Open source file.
if((hSource = fopen(szSource,"rb")) == NULL) {
printf("Error opening Ciphertext file!\n");
goto done;
}
// Open destination file.
if((hDestination = fopen(szDestination,"wb")) == NULL) {
printf("Error opening Plaintext file!\n");
goto done;
}
// Get handle to the default provider.
if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) {
printf("Error %x during CryptAcquireContext!\n", GetLastError());
goto done;
}
if(szPassword == NULL) {
// Decrypt the file with the saved session key.
// Read key blob length from source file and allocate memory.
fread(&dwKeyBlobLen, sizeof(DWORD), 1, hSource);
if(ferror(hSource) || feof(hSource)) {
printf("Error reading file header!\n");
goto done;
}
if((pbKeyBlob = malloc(dwKeyBlobLen)) == NULL) {
printf("Out of memory or improperly formatted source file!\n");
goto done;
}
// Read key blob from source file.
fread(pbKeyBlob, 1, dwKeyBlobLen, hSource);
if(ferror(hSource) || feof(hSource)) {
printf("Error reading file header!\n");
goto done;
}
// Import key blob into CSP.
if(!CryptImportKey(hProv, pbKeyBlob, dwKeyBlobLen, 0, 0, &hKey)) {
printf("Error %x during CryptImportKey!\n", GetLastError());
goto done;
}
} else {
// Decrypt the file with a session key derived from a password.
// Create a hash object.
if(!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
printf("Error %x during CryptCreateHash!\n", GetLastError());
goto done;
}
// Hash in the password data.
if(!CryptHashData(hHash, szPassword, strlen(szPassword), 0)) {
printf("Error %x during CryptHashData!\n", GetLastError());
goto done;
}
// Derive a session key from the hash object.
if(!CryptDeriveKey(hProv, ENCRYPT_ALGORITHM, hHash, 0, &hKey)) {
printf("Error %x during CryptDeriveKey!\n", GetLastError());
goto done;
}
// Destroy the hash object.
CryptDestroyHash(hHash);
hHash = 0;
}
// Determine number of bytes to decrypt at a time. This must be a multiple
// of ENCRYPT_BLOCK_SIZE.
dwBlockLen = 1000 - 1000 % ENCRYPT_BLOCK_SIZE;
dwBufferLen = dwBlockLen;
// Allocate memory.
if((pbBuffer = malloc(dwBufferLen)) == NULL) {
printf("Out of memory!\n");
goto done;
}
// Decrypt source file and write to destination file.
do {
// Read up to 'dwBlockLen' bytes from source file.
dwCount = fread(pbBuffer, 1, dwBlockLen, hSource);
if(ferror(hSource)) {
printf("Error reading Ciphertext!\n");
goto done;
}
eof = feof(hSource);
// Decrypt data
if(!CryptDecrypt(hKey, 0, eof, 0, pbBuffer, &dwCount)) {
printf("Error %x during CryptDecrypt!\n", GetLastError());
goto done;
}
// Write data to destination file.
fwrite(pbBuffer, 1, dwCount, hDestination);
if(ferror(hDestination)) {
printf("Error writing Plaintext!\n");
goto done;
}
} while(!feof(hSource));
status = TRUE;
printf("OK\n");
done:
// Close files.
if(hSource) fclose(hSource);
if(hDestination) fclose(hDestination);
// Free memory.
if(pbKeyBlob) free(pbKeyBlob);
if(pbBuffer) free(pbBuffer);
// Destroy session key.
if(hKey) CryptDestroyKey(hKey);
// Destroy hash object.
if(hHash) CryptDestroyHash(hHash);
// Release provider handle.
if(hProv) CryptReleaseContext(hProv, 0);
return(status);
}