<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-3385079E-84F4-534F-B937-BD3A568D71BC" xml:lang="en"><title>Password

Based Encryption (PBE) example code</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>This example covers: </p>

<ul>

<li id="GUID-79A33AFC-B814-586D-93BC-D152C08DC7FD"><p> <xref href="GUID-3385079E-84F4-534F-B937-BD3A568D71BC.dita#GUID-3385079E-84F4-534F-B937-BD3A568D71BC/GUID-29272282-2325-55CD-B583-E9E50D344C14">Encrypting some data with a password and writing it to a file</xref>  </p> </li>

<li id="GUID-72DFC0FF-5E9E-581E-9589-544E349413D1"><p> <xref href="GUID-3385079E-84F4-534F-B937-BD3A568D71BC.dita#GUID-3385079E-84F4-534F-B937-BD3A568D71BC/GUID-432A4D99-0AD1-5E1E-8E09-ED47FFC0C353">Reading the data back from the file and decrypting it with the same password.</xref>  </p> </li>

</ul>

<p> <i>This example code is for reference only - it would be better to use:</i>  </p>

<ul>

<li id="GUID-450F0BEB-EA72-5A93-8722-CB10DF2DD0FC"><p> <xref href="GUID-598B6698-3518-50CA-98DE-D85CB255BA2D.dita">Secure

stream example code</xref>  </p> </li>

<li id="GUID-95E469DF-F6D4-5F1A-9A6F-A3759DC51308"><p> <xref href="GUID-36BCDD1F-3713-5DF0-8D8A-CF093694B636.dita">Secure

store example code</xref>  </p> </li>

</ul>

<section id="GUID-29272282-2325-55CD-B583-E9E50D344C14"><title>Encrypting

data with a password and writing it to a file</title> <ul>

<li id="GUID-92C03164-30E8-5B3E-91FA-667D344DC8A6"><p> <xref href="GUID-9E3ADEB4-C000-525D-B220-2BAFF5DC6B0C.dita">Supporting

code for this example</xref>  </p> </li>

</ul> <codeblock id="GUID-A2587573-A051-57DF-BC36-76585CB14F99" xml:space="preserve">

void CPBEExample::WriteEncryptedDataL(const TDesC8& aInput, const TDesC& aFilename, const TDesC& aPassword)

         {

         // Open a stream to the output file

         RFileWriteStream writeStream;

         User::LeaveIfError(writeStream.Replace(iFs, aFilename, EFileShareExclusive | EFileWrite));

         CleanupClosePushL(writeStream);

         // Create a CPBEncryptElement object, passing details of the encryption we

         // are using and the user's password

         CPBEncryptElement* encryption = CPBEncryptElement::NewLC(aPassword, ECipherDES_CBC);

         // This is used to create a CPBEncryptor object

         CPBEncryptor* encryptor = encryption->NewEncryptLC();

         // Create a buffer of appropriate size to hold the ciphertext

         HBufC8* ciphertextTemp = HBufC8::NewLC(encryptor->MaxFinalOutputLength(aInput.Length()));

         TPtr8 ciphertext = ciphertextTemp->Des();         

         // Encrypt the input data into the ciphertext buffer

         encryptor->ProcessFinalL(aInput, ciphertext);

         // Store encryption data.  This contains details of the encryption used (e.g.,

         // cipher, key size) as well as things like the salt.  This must be stored

         // along with the encrypted data, otherwise it is not possible to decrypt it

         // again!

         writeStream << encryption->EncryptionData();

         // Store the ciphertext

         writeStream << ciphertext;

         // Commit the stream

         writeStream.CommitL();

         // Free memory (writeStream, encryption, encryptor, ciphertextTemp)

         CleanupStack::PopAndDestroy(4, &writeStream);

         }

            </codeblock> </section>

<section id="GUID-432A4D99-0AD1-5E1E-8E09-ED47FFC0C353"><title>Reading data

from a file and decrypting it</title> <ul>

<li id="GUID-70128A46-1AAB-59E8-9F03-68885091D54B"><p> <xref href="GUID-9E3ADEB4-C000-525D-B220-2BAFF5DC6B0C.dita">Supporting

code for this example</xref>  </p> </li>

</ul> <codeblock id="GUID-110E47B5-D63D-5041-ADC9-5A8DA1305712" xml:space="preserve">

HBufC8* CPBEExample::ReadEncryptedDataLC(const TDesC& aFilename, const TDesC& aPassword)

         {

         // Open a stream to the input file

         RFileReadStream readStream;

         User::LeaveIfError(readStream.Open(iFs, aFilename, EFileRead));

         CleanupClosePushL(readStream);

         // Read the encryption data from the file

         CPBEncryptionData* encryptionData = CPBEncryptionData::NewLC(readStream);

         // Recreate the CPBEncryptElement object, using the encryption data from the

         // file and the user's password.  This will leave with KErrBadPassphrase if

         // the password is wrong.

         CPBEncryptElement* encryption = CPBEncryptElement::NewLC(*encryptionData, aPassword);

         // This is used to create a CPBDecryptor object

         CPBDecryptor* decryptor = encryption->NewDecryptLC();

         // Read the ciphertext

         HBufC8* ciphertext = HBufC8::NewLC(readStream, KMaxTInt);

         // Allocate a buffer for the plaintext (this will be returned to the caller)

         HBufC8* plaintextBuf = HBufC8::NewLC(decryptor->MaxFinalOutputLength(ciphertext->Length()));

         TPtr8 plaintext = plaintextBuf->Des();

         // Decrypt the data

         decryptor->ProcessFinalL(*ciphertext, plaintext);

         // Free memory (readStream, encryptionData, encryption, decryptor, ciphertext, plaintext)

         CleanupStack::Pop(plaintextBuf); // don't free this

         CleanupStack::PopAndDestroy(5, &readStream);

         CleanupStack::PushL(plaintextBuf);

         // Return plaintext to the caller

         return plaintextBuf;

         }

        </codeblock> </section>

</conbody></concept>