This step-by-step article describes how to encrypt a string
by using CryptoAPI in Microsoft Visual Basic 6.0. It also describes how to
decrypt the string by using the
CryptoServiceProvider classes in Microsoft Visual Basic .NET or in Microsoft Visual
Basic 2005. This article discusses the code for the encryption process in
Visual Basic 6.0. It also discusses the code for the decryption process in
Visual Basic .NET or in Visual Basic 2005.
The encryption process code
and the decryption process code have the following structures:
- Encryption process code - When you develop encryption code by using Visual Basic 6.0, the
code is structured in one project group that is named EncryptGroup. This
project group contains the following individual projects:
- CryptWrap.vbp - The CryptWrap.vbp project contains a Visual Basic class file
that is named clsCryptoAPI.cls.
- Encrypt.vbp - The Encrypt.vbp project contains a form that is named
frmEncFiles.frm.
- Decryption process code - When you develop decryption code by using Visual Basic .NET or
in Visual Basic 2005, the code is structured in one solution that is named
DecryptInVBNET. This solution contains one Microsoft Windows application
project that is named DecryptInVBNET.vbproj. This project contains one Windows
Form that is named Form1.vb.
Requirements
This
article assumes that you are familiar with the following topics:
- Cryptography
- Using APIs in Visual Basic 6.0
- Using the CryptoServiceProvider classes in Visual Basic .NET or in Visual Basic 2005
The
following list outlines the recommended hardware, software, network
infrastructure, and service packs that you need:
- Microsoft Windows Server 2003, Microsoft Windows 2000, or
Microsoft Windows XP
- Microsoft Visual Basic 6.0 and Microsoft Visual Basic .NET
and Microsoft Visual Basic 2005
Code for encryption and for decryption
This article describes the code that is included in the
CryptographySample.exe package.
The following file is available for
download from the Microsoft Download Center:
For
additional information about how to download Microsoft Support files, click the
following article number to view the article in the Microsoft Knowledge Base:
119591
(http://support.microsoft.com/kb/119591/
)
How to Obtain Microsoft Support Files from Online Services
Microsoft scanned this file for viruses. Microsoft used the most
current virus-detection software that was available on the date that the file
was posted. The file is stored on security-enhanced servers that help to
prevent any unauthorized changes to the file.
Note To use the downloaded sample code, follow the steps in the
"
Instructions to run the code"
section.
Encryption in Visual Basic 6.0
This section describes the important steps in the encryption
process. It also describes the Visual Basic code that is used for these
steps.
CryptWrap DLL
The CryptWrap DLL is included with the code that you downloaded in
the "
Code for encryption and for
decryption" section. The CryptWrap DLL is a wrapper that wraps
around the API calls. The CryptWrap DLL is in the CryptWrap.vbp project that is
in the EncryptGroup project group.
The encryption process requires the
CryptWrap DLL. The Encrypt project uses the CryptWrap DLL to call the functions
that perform the actual encryption.
CryptoWrap DLL
The CryptoWrap DLL is coded by using an ActiveX DLL project
template. The CryptoWrap DLL is in the clsCryptoAPI.cls file that is in the
EncryptGroup project group.
The code of the CryptoWrap DLL contains
the following:
- Declarations of variables and of constants that the
CryptoWrap DLL uses.
- Declarations of subroutines and of functions for the Cryptography API function from the Advapi32.dll library file in terms of
Visual Basic 6.0.
- Declarations of properties, of functions, and of
subroutines.
- A password that is assigned to a module-level variable in
the code from the calling program.
Note This password is used to derive the key that the CryptoEncrypt function uses to encrypt the string.
The CryptoWrap DLL uses the SHA1 algorithm for hashing and uses
the RC2 algorithm for encryption.
Variables declaration
This section describes the important variables that are declared
in the clsCryptoAPI.cls file.
Together with the typical variables
that you may use for string input and for string output, some other constants
are declared in the encryption process code. These other constants are used to
call API functions in the CryptWrap.vbp project. Descriptions of some of these
other constants appear in the following sample code:
Private Const ALG_CLASS_ANY As Long = 0
Private Const ALG_TYPE_ANY As Long = 0
Private Const ALG_CLASS_HASH As Long = 32768
Private Const ALG_TYPE_BLOCK As Long = 1536
Private Const ALG_CLASS_DATA_ENCRYPT As Long = 24576
Private Const ALG_SID_RC2 As Long = 2
Private Const ALG_SID_SHA1 As Long = 4
' Hash algorithms
Private Const CALG_SHA1 As Long = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_SHA1
' Block ciphers
Private Const CALG_RC2 As Long = ALG_CLASS_DATA_ENCRYPT Or ALG_TYPE_BLOCK Or ALG_SID_RC2
' CryptSetProvParam
Private Const PROV_RSA_FULL As Long = 1
' used when acquiring the provider
Private Const CRYPT_VERIFYCONTEXT As Long = &HF0000000
' Microsoft provider data
Private Const MS_DEFAULT_PROVIDER As String = _
"Microsoft Base Cryptographic Provider v1.0"
' used to specify not to use any salt value while deriving the key
Private Const CRYPT_NO_SALT As Long = &H10 The Wincrypt.h header file on your computer contains the definitions of
all these other constants. You can use the Wincrypt.h header file directly in
your C or C++ project code. However, in the Visual Basic 6.0 program that you
downloaded in the "
Code for encryption and for
decryption" section, the constants that the encryption process uses
are declared and are initialized in the clsCryptoAPI.cls file. These constants
are the same constants that are declared in the Wincrypt.h file on your
computer.
API declaration in Visual Basic 6.0
The important API functions that are declared in the
clsCryptoAPI.cls file are the following:
- GetLastError - The GetLastError function retrieves the calling thread's last error code value.
The following code is an example of the GetLastError function:Private Declare Function GetLastError Lib "kernel32" () As Long
- CryptAcquireContext - The CryptAcquireContext function is used to acquire a handle to a specified key container
in a specified cryptographic service provider (CSP). The phProv parameter receives the handle to the specified key container. You
can use this handle to call other API functions.
The following code
is an example of the CryptAcquireContext function: Private Declare Function CryptAcquireContext Lib "advapi32.dll" _
Alias "CryptAcquireContextA" (ByRef phProv As Long, _
ByVal pszContainer As String, ByVal pszProvider As String, _
ByVal dwProvType As Long, ByVal dwFlags As Long) As Long - CryptCreateHash - The CryptCreateHash function is used to initiate the hashing of a stream of data. The
CryptCreateHash function returns to the caller a handle to a CSP hash object.
This handle can also be used in later calls to the CryptHashData function to hash the session key. The phHash parameter receives the handle of the new hash object.
The following code is an example of the CryptCreateHash function: Private Declare Function CryptCreateHash Lib "advapi32.dll" _
(ByVal hProv As Long, ByVal algid As Long, _
ByVal hkey As Long, ByVal dwFlags As Long, _
ByRef phHash As Long) As Long - CryptHashData - The CryptHashData function adds data to a specified hash object. The pbData parameter contains the data to be hashed.
The following
code is an example of the CryptHashData function: Private Declare Function CryptHashData Lib "advapi32.dll" _
(ByVal hhash As Long, ByVal pbData As String, _
ByVal dwDataLen As Long, ByVal dwFlags As Long) As Long - CryptDestroyHash - The CryptDestroyHash function destroys the hash object that the hHash parameter references.
The following code is an example
of the CryptDestroyHash function: Private Declare Function CryptDestroyHash Lib "advapi32.dll" _
(ByVal hhash As Long) As Long - CryptReleaseContext - The CryptReleaseContext function is used to release a handle to a CSP and to a key
container. The hProv parameter is the handle to the CSP. The value of the hProv parameter is obtained by calling the CryptAcquireContext API function.
The following code is an example of the CryptReleaseContext function: Private Declare Function CryptReleaseContext Lib "advapi32.dll" _
(ByVal hProv As Long, ByVal dwFlags As Long) As Long - CryptDeriveKey - The CryptDeriveKey function generates a cryptographic key that is derived from base
data. The CryptDeriveKey function always generates the same key for the same base data if
you use the same CSP and the same algorithms every time that you call the CryptDeriveKey function for the same base data.
The base data can be a
password. You can hash the password and then call this function to obtain a
handle to the key. The phKey parameter receives the handle to the key that is used for the
encryption.
The following code is an example of the CryptDeriveKey function: Private Declare Function CryptDeriveKey Lib "advapi32.dll" _
(ByVal hProv As Long, ByVal algid As Long, _
ByVal hBaseData As Long, ByVal dwFlags As Long, _
ByRef phKey As Long) As Long - CryptDestroyKey - The CryptDestroyKey function releases the handle that the hKey parameter references. The following code is an example of the CryptDestroyKey function:
Private Declare Function CryptDestroyKey Lib "advapi32.dll" _
(ByVal hkey As Long) As Long - CryptEncrypt - The CryptEncrypt function is used to encrypt data. The key that the CSP module
holds designates the algorithm that is used to encrypt the data. The hKey parameter references this key. The following code is an example
of the CryptEncrypt function:
Private Declare Function CryptEncrypt Lib "advapi32.dll" _
(ByVal hkey As Long, ByVal hhash As Long, ByVal Final As Long, _
ByVal dwFlags As Long, ByVal pbData As String, _
ByRef pdwDataLen As Long, ByVal dwBufLen As Long) As Long
The
CopyMemory subroutine is also declared in the clsCryptoAPI.cls file. The
CopyMemory subroutine copies a block of memory from one location to another
location. The
CopyMemory subroutine takes the following parameters:
- dest - The dest parameter is the destination where the content is copied
to.
- source - The source parameter is the source where the content is copied from.
- bytes - The bytes parameter is the size of the content to be copied from the source
to destination.
The following code is an example of the
CopyMemory subroutine:
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(dest As Any, source As Any, ByVal bytes As Long) Important functions
This section describes some important functions that are declared
in the clsCryptoAPI.cls file.
The Encrypt program calls the
Encrypt function to encrypt a string. The following code is an example of
the
Encrypt function:
Public Function Encrypt(Optional intHashType As Integer = 1, _
Optional intCipherType As Integer = 1) As Boolean
Encrypt = CryptoEncrypt(intHashType, intCipherType)
End Function This function has two optional parameters. The
intHashType parameter specifies the hashing algorithm to be used to derive
the key. The
intCipherType parameter specifies the cipher type that the Encrypt program uses
to encrypt the string.
Note The cipher type is also known as the
encryption
algorithm.
Because these parameters are optional, they are
initialized to their default values. Therefore, if the calling program does not
provide the values for these parameters, the
Encrypt function uses the default values.
The
Encrypt function calls the
CryptoEncrypt function. The
CryptoEncrypt function is a private function of the CryptoWrap DLL that
performs the actual encryption. The following code is an example of the
CryptoEncrypt function:
Private Function CryptoEncrypt(intHashType As Integer, _
intCipherType As Integer) As BooleanThe
CryptoEncrypt function is the main function in the CryptoWrap DLL. The
CryptoEncrypt function encrypts the string.
Encryption process
The following steps describe the encryption process:
- The CryptoEncrypt function starts the encryption process by calling the GetProvider function.
Note The GetProvider function is a private function. - The GetProvider function calls the CryptAcquireContext API function to obtain the handle of the CSP.
- The GetProvider function calls the CryptCreateHash API function to obtain a handle of the hash object.
- The CryptHashData API function hashes the password text by using the handle that
the GetProvider function obtained in step 3.
- The CryptoEncrypt function calls the CryptDeriveKey API function, and then the CryptDeriveKey API function use the handles that the GetProvider function obtained in steps 2 and 3 to derive the key for
encryption.
- The CryptoEncrypt function calls the CryptDestroyHash API function to destroy the hash object.
- A variable initialization statement allocates sufficient
space for the buffer where the encrypted string will be stored. For example,
the following string will allocate sufficient space:
lngEnctBuffLen=lngEncDataLength*2
- The CryptoEncrypt function calls the CryptEncrypt API function. The input for the CryptEncrypt API function is the key that the CryptDeriveKey API function derived in step 5 and the string that you want to
encrypt.
- The CryptEncrypt API function stores the encrypted string by overwriting the input
string in the buffer.
- The CryptoEncrypt function calls the CryptDestroyKey API function to destroy the key.
- The CryptoEncrypt function calls the CryptDestroyHash API function to destroy the hash object.
Encrypt program
The Encrypt program is included with the code that you downloaded
in the "
Code for encryption and for
decryption" section. The Encrypt program creates the user interface
for the encryption process. It uses the CryptWrap DLL to encrypt strings. This
Encrypt program is in the Encrypt project that is a part of the EncryptGroup
project group.
User interface
The user interface of the Encrypt program contains the following
text boxes:
- Enter full path\filename for a file to
encrypt
- Name and location of encrypted
file
Note This text box is read-only.
The user interface of the Encrypt program also contains the
following buttons:
After you type the correct information in the
Enter full
path\filename for a file to encrypt box, the path of the file where
the encrypted string will be stored appears in the
Name and location of
encrypted file box.
To start the encryption process, click
Encrypt. After the encryption process has completed, you
receive a message box that indicates whether the encryption process has
succeeded.
To quit the Encrypt program, click
Exit.
Important function
The following function is declared in the frmEncFiles.frm file of
the Encrypt program:
Private Sub Encrypt_File()
This function is called when you click
Encrypt. This
function call does the following:
- Creates an object of the clsCryptoAPI class in the CryptoWrap DLL.
- Performs the basic validation tasks, such as verifying the
existence of the file.
- Initializes the password field and the InputData field of
the clsCryptoAPI class object.
- Calls the Encrypt function of the clsCryptoAPI class object.
Note In the clsCryptoAPI class object, the intHashType parameter is set to the SHA1 algorithm value 4, and the intCipherType parameter is set to the RC2 algorithm value 2. - Populates the OutputData field of the clsCryptoAPI class object.
The program receives the encrypted string and then stores it in
the output file. You then receive a message box that indicates whether the
encryption process has succeeded.
DecryptInVBNET program
The DecryptInVBNET program is included with the code that you
downloaded in the "
Code for encryption and for
decryption" section. The DecryptInVBNET program creates the user
interface for the decryption. It also uses the Microsoft Visual Studio .NET or
Microsoft Visual Studio 2005 CSPs for the decryption
process.
User interface
The user interface of the DecryptInVBNET program contains the
following text boxes:
- Enter full path\filename for a file to
decrypt
- Name and location of decrypted
file
Note This text box is read-only.
The user interface of the DecryptInVBNET program also contains
the following buttons:
After you type the correct information in the
Enter full
path\filename for a file to decrypt box, the path of the file where
the decrypted string will be stored appears in the
Name and location of
decrypted file box.
To start the decryption process, click
Decrypt. After the decryption process has completed, you
receive a message box that indicates whether the decryption process has
succeeded.
To quit the DecryptInVBNET program, click
Exit.
Important function
The following function is declared in the Form1.vb file of the
DecryptInVBNET program:
Private Sub Decrypt_File()
This function is called when you click
Decrypt. This
function call does the following:
- Creates an object of the CspParameter class. This object is used to pass the parameter to the CSP that
performs the cryptographic computations.
- Creates an object of PasswordDeriveBytes class. This object is used to derive a key from the specified
password.
Note For simplicity, the password is hard-coded in the
program. - Calls the CryptDeriveKey method of the PasswordDeriveBytes class. This method gives the key as the output data. The key is
based on the input data.
This program uses the SHA1 algorithm for hashing and uses the
RC2 algorithm for encryption. It also creates an object of the
RC2CryptoServiceProvider class. This object is used in the decryption process.
The code then initializes the key and the initialization vector field
of the
RC2CryptoServiceProvider object. The
RC2CryptoServiceProvider object is a wrapper to access the CSP implementation of the RC2
algorithm.
The code also calls the
CreateDecryptor method. The
CreateDecryptor method creates a symmetric decryptor object by using the current
key and the current initialization vector.
Finally, the
TransformFinalBlock method of the
ICryptoTransform class does the decryption by giving the value of the
input parameter as
encrypted string and by giving the length of the encrypted string. After the
TransformFinalBlock method has completed, you receive a message box that indicates
whether the decryption process has succeeded. If the decryption process has
succeeded, the program writes the decrypted string in the output file.
Instructions to run the code
See the "
Code for encryption and
for decryption" section for information about how to download and
then save the program files to the C:\ folder on your computer.
Encrypt program
- Open the EncryptGroup project group in Visual Basic 6.0. To
do this, double-click the EncryptGroup.vbg file. The
EncryptGroup.vbg file is located in the C:\CryptographySample\EncryptInVB6
folder.
- On the Run menu in Visual Basic 6.0, click
Start With Full Compile. A Windows Form that is named Form1
appears. Form1 is the user interface for the Encrypt program.
- In the Enter full path\filename for a file to
encrypt box, type the path of the file that you want to encrypt. To
use the sample file that is included with the Encrypt program, type the
following:
c:\CryptographySample\input.txt
- Press TAB. The name of the file where the encrypted string
will be stored appears in the Name and location of encrypted
file box.
Note In this example, the path of the encrypted file is
C:\CryptographySample\Input.enc. - Click Encrypt. The Encrypt
Files message box appears.
- Click OK.
- Click Exit to quit the
application.
The encrypted string appears in the
C:\CryptographySample\Input.enc file.
DecryptInVBNET program
- Open the DecryptInVBNET solution in Microsoft Visual Studio
.NET 2002. To do this, double-click the DecryptInVBNET.sln
file. The DecryptInVBNET.sln file is located in the
C:\CryptographySample\DecryptInVBNET folder.
Note If you are using Microsoft Visual Studio .NET 2003 or Microsoft
Visual Studio 2005, you receive a dialog box that prompts you to upgrade the
project and the solution to Microsoft Visual Studio .NET 2003 or Microsoft
Visual Studio 2005. Click Yes. - On the Debug menu in Visual Studio .NET or
in Visual Studio 2005, click Start. A Windows Form that is
named Form1 appears. Form1 is the user interface for the DecryptInVBNET
program.
- In the Enter full path\filename for a file to
decrypt box, type the path of the file that you want to decrypt. To
use the sample file that is included with the DecryptInVBNET program, type the
following:
c:\CryptographySample\input.enc
- Press TAB. The name of the file where the decrypted string
will be stored appears in the Name and location of decrypted
file box.
Note In this example, the path of the decrypted file is
C:\CryptographySample\Input.dec. - Click Decrypt. The
DecryptInVBNET message box appears.
- Click OK.
- Click Exit to quit the
application.
The decrypted string appears in the
C:\CryptographySample\Input.dec file.
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