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<!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&amp; aInput, const TDesC&amp; aFilename, const TDesC&amp; 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-&gt;NewEncryptLC();

         // Create a buffer of appropriate size to hold the ciphertext
         HBufC8* ciphertextTemp = HBufC8::NewLC(encryptor-&gt;MaxFinalOutputLength(aInput.Length()));
         TPtr8 ciphertext = ciphertextTemp-&gt;Des();         

         // Encrypt the input data into the ciphertext buffer
         encryptor-&gt;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 &lt;&lt; encryption-&gt;EncryptionData();

         // Store the ciphertext
         writeStream &lt;&lt; ciphertext;

         // Commit the stream
         writeStream.CommitL();

         // Free memory (writeStream, encryption, encryptor, ciphertextTemp)
         CleanupStack::PopAndDestroy(4, &amp;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&amp; aFilename, const TDesC&amp; 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-&gt;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-&gt;MaxFinalOutputLength(ciphertext-&gt;Length()));
         TPtr8 plaintext = plaintextBuf-&gt;Des();

         // Decrypt the data
         decryptor-&gt;ProcessFinalL(*ciphertext, plaintext);

         // Free memory (readStream, encryptionData, encryption, decryptor, ciphertext, plaintext)
         CleanupStack::Pop(plaintextBuf); // don't free this
         CleanupStack::PopAndDestroy(5, &amp;readStream);
         CleanupStack::PushL(plaintextBuf);

         // Return plaintext to the caller
         return plaintextBuf;
         }
        </codeblock> </section>
</conbody></concept>