Encrypt Decrypt String

Introduction

The purpose of this article to try to help the beginner to learn how to encrypt and decrypt files using a symmetric key algorithm (e.g., RC2, RC4, DES, Triple-DES, and AES) by building an application with Visual C++ that uses the CAPICOM component. The Platform SDK redistributable ships a COM component called CAPICOM. CAPI stands for Crypto API. When we download this component, Capicom.dll, we must install it on our machine. Because it installs by default in the Program Files directory, we must traverse the CAPICOM folder on the command line until we find the Capicom.dll in the directory listing. At that point, we use the 'regsvr32 Capicom.dll' command to get a 'succeeded' box. To build this application, simply use Visual C++ Express 2005 or 2008, or use Visual Studio. Remember to choose the Win32 Console application icon when starting the process and to choose 'empty project' in the application settings box. Copy and paste this code, build the solution, and deploy the executable.

Decrypt File Online

The source code file uses four headers that predefine methods that deal with strings, and files that deal with strings. The <fstream> template is for file I/O. And because we are not using the Crypto API but the CAPICOM component, we must initialize the COM library, and at some point, uninitialize it. Import Capicom.dll. I used quotation marks after the import statement in my source code file after I copied and pasted the DLL into the same directory as the source. It can help to avoid file path errors when building the solution. Here is the source code, which will be explained:

The line in the source code (ifstream in(pszFile, ios::in ios::binary ios::ate); means that we open the file in binary mode. Problems would result if we were to use any mapping of carriage returns and line feeds, because the data is in binary and we don't know what it means. So once a file is in binary data, it cannot be mapped by CR-LF to anything else. For the beginner, CR-LF means hit the ENTER key to have the cursor drop down one line and move to the far left. We see that in this operation, a COM object wraps an encrypted data block. But we must first check and see if the file will open. If it won't, we have to output an error message to the console. We also need to know the size of the file: the option ios::ate makes the open operation point the file pointer to the end of the file. When we are at the end of the file, we can determine the file size:

If I'm at the end of the file, and I know the file size, then I can allocate a buffer. Notice these parts of the code: in.seekg(0, ios::beg); -- in.read(buf, size); in other words, go to the beginning of the file and read it into a buffer. When the file is read into the buffer, we can create an instance of the object to encrypt it:

Little snitch sale. Because this is a COM API, we will take our buffer and wrap it up into a bstr_t. Note the line of code: Auto tune 5 download.

This line asks the encrypted data object for a pointer to the algorithm:

Now that we have a pointer to the encryption algorithm, we tell the algorithm that we are going to use the symmetrical AES algorithm and that we will use the maximum key length. After that, we tell the encryptor what password we will use to encrypt the data with. Subsequent to the choice of cipher block, key length, and password, we then wrap what we got off the command line into a bstr_t object:

It is good practice to encode the encrypted data with base64 encoding. Now examine an example of the use of the CAPI.exe on the command line:

Here is a partial view of the encrypted text:

Here is a partial view of the file, MyFile.txt.encrypted.decrypted:

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Build Capi.exe and try on the text above to see if you get the same encrypted text.

C# Encrypt Decrypt Text