Archived:AES buffer encryption of files using Symbian C++

Comments

(no comments yet)

Log in or Join to leave comments.

Archived: This article is archived because it is not considered relevant for third-party developers creating commercial solutions today. If you think this article is still relevant, let us know by adding the template {{ReviewForRemovalFromArchive|user=~~~~|write your reason here}}.

Article Metadata

---

Code Example

Source file: Media:BufEnEx.zip

---

Tested with

Devices(s): Nokia N95, Nokia N78

---

Compatibility

Platform(s): S60 3rd Edition FP1, S60 3rd Edition FP2

---

Article

Keywords: AES Encryption, Symbian Cryptography API

Created: User:Nokia Developer KB (03 Apr 2009)

Last edited: hamishwillee (29 Jun 2012)

Description

According to the Advanced Encryption Standard (AES), a block of data can be encrypted and decrypted using the Archived:Symbian Cryptography APIs classes CAESEncryptor and CAESDecryptor, respectively. However, these classes can convert a data block of 16 bytes only and its not possible to encrypt/decrypt larger data blocks. For this purpose, the classes CBufferedEncryptor and CBufferedDecryptor can be used. These classes are intialised with an encryptor/decrytor class object, depending on the mode of operation, and a subclass of CPadding.

Solution

This example code encrypts a plain text file using AES encryption.

 _LIT( KPlainInputFileName, "C:\\Data\\PlainInput.txt" );
 _LIT( KEncryptedOutputFileName, "C:\\Data\\EnOutput.txt" );
 _LIT8(KAESKey,"1234567890abcdef");   <br>
 //Reading the plain text from the file
 RFs fsSession;
 User::LeaveIfError(fsSession.Connect());
 RFile file;
 User::LeaveIfError(file.Open(fsSession,KPlainInputFileName,EFileShareExclusive|EFileRead));
 TInt plainTextsize;
 file.Size(plainTextsize); 
 HBufC8* plainText = HBufC8::NewLC(plainTextsize);
 TPtr8 plainTextPtr = plainText->Des();
 file.Read(plainTextPtr);
 file.Close();	<br>
 //Initializing the encrytor and padding objects
 CPaddingSSLv3* encryptPadding = CPaddingSSLv3::NewL(16);
 CAESEncryptor* aesEncryptor = CAESEncryptor::NewL(KAESKey);	
 CBufferedEncryptor* bufEncryptor  = CBufferedEncryptor::NewL(aesEncryptor, encryptPadding);<br>			 
 HBufC8* encryptData = HBufC8::NewLC(bufEncryptor->MaxFinalOutputLength(plainTextPtr.Size()));			 
 TPtr8 encryptDataPtr = encryptData->Des();<br>		 
 //Encrypting the text and writing into an output file			 
 bufEncryptor->ProcessFinalL(plainTextPtr,encryptDataPtr);<br>		 
 TInt err=file.Open(fsSession,KEncryptedOutputFileName,EFileShareExclusive|EFileWrite);
 if (err==KErrNotFound) // file does not exist - create it
     err=file.Create(fsSession,KEncryptedOutputFileName,EFileShareExclusive|EFileWrite);
 file.Write(encryptDataPtr);			 
 file.Close();
 CleanupStack::PopAndDestroy2);//encryptData,plainText                       
 fsSession.Close();

This example code decrypts the file encrypted using the above code.

 _LIT( KEncryptedOutputFileName, "C:\\Data\\EnOutput.txt" );
 _LIT( KPlainOutputFileName, "C:\\Data\\PlainOutput.txt" );
 _LIT8(KAESKey,"1234567890abcdef");  <br>
 //Reading the encrypted text from the file
 RFs fsSession;
 User::LeaveIfError(fsSession.Connect());
 RFile file;
 User::LeaveIfError(file.Open(fsSession,KEncryptedOutputFileName,EFileShareExclusive|EFileRead));
 TInt fileSize;
 file.Size(fileSize);<br>				 
 HBufC8* encryptData = HBufC8::NewLC(fileSize);
 TPtr8 encryptDataPtr = encryptData->Des();
 file.Read(encryptDataPtr);	
 file.Close();<br>
 //Initializing the encrytor and padding objects
 CPaddingSSLv3* decryptPadding = CPaddingSSLv3::NewL(16);
 CAESDecryptor* aesDecryptor = CAESDecryptor::NewL(KAESKey);	
 CBufferedDecryptor* bufDecryptor = CBufferedDecryptor::NewL(aesDecryptor, decryptPadding);<br>
 HBufC8* decryptedText = HBufC8::NewLC(bufDecryptor->MaxFinalOutputLength(encryptDataPtr.Size()));			 
 TPtr8 decryptedTextPtr = decryptedText->Des();<br>
 //Decrypting the text and writing the output into a file.	
 bufDecryptor->ProcessFinalL(encryptDataPtr,decryptedTextPtr);	<br>
 TInt err=file.Open(fsSession,KPlainOutputFileName,EFileShareExclusive|EFileWrite);
 if (err==KErrNotFound) // file does not exist - create it
 err=file.Create(fsSession,KPlainOutputFileName,EFileShareExclusive|EFileWrite);
 file.Write(decryptedTextPtr); 
 file.Close();<br>
 CleanupStack::PopAndDestroy(2); // encryptData,decryptedText  
 fsSession.Close();

Example application

File:BufEnEx.zip