public void decryptData(String encryptedData)
{
String encryptedFile = "C:\\Program Files\\Apache Group\\jakarta-tomcat-4.1.27\\webapps\\cs5890project\\WEB-INF\\encryptedpaymentfile.xml";
String decryptedFile = "C:\\Program Files\\Apache Group\\jakarta-tomcat-4.1.27\\webapps\\cs5890project\\WEB-INF\\decryptedpaymentfile.xml";

// Testing the provider for TripleDES encryption support.
try {
Cipher testCipher = Cipher.getInstance("DESede");
}//try
catch(Exception e) {
// JCE provider not installed on this system.
// Installing the JCE provider.
System.err.println("INSTALLING PROVIDER: SunJCE");
Provider sunjceprov = new com.sun.crypto.provider.SunJCE();
Security.addProvider(sunjceprov);
System.err.println("PROVIDER INSTALLED... CONTINUING");
}//catch

// Creating a new XmlEncryption Object for decryption
XmlEncryption bXmlEnc = new XmlEncryption();
// Decrypting the XML Encrypted file String
String bFileString = bXmlEnc.getDecryptedData(encryptedData.toString());  //Encrypted data which was in the form of StringBuffer is written to a File

System.out.println("bFileString is " + bFileString);

try
{
File xmlFile = new File(decryptedFile);
BufferedWriter out = new BufferedWriter(new FileWriter(xmlFile));

StringBuffer stringBuffer = new StringBuffer(bFileString);

out.write(stringBuffer.toString()); // Decrypted data is returned as a String, this is written to a file
out.close();

System.out.println("Decrypted Xml File built successfully");
}
catch(Exception e)
{
e.printStackTrace();
}
}

Actual Decryption in the XmlEncryption class

//Decrypting the XML Encrypted file
public String getDecryptedData(String encString) {
String decString = "";

try {
//get the encrypted XML file string parsed into a Document object
ByteArrayInputStream bais = new ByteArrayInputStream(encString.getBytes());
Document encDoc = docBuilder.parse(bais);
//Get a list of all the EncryptedData tags
NodeList nl = encDoc.getElementsByTagName("EncryptedData");
//Load, decrypt and replace each EncryptedData tag in the Document object

for(int i=0;i<nl.getLength();i++) {
//Loading an element
Node edata = nl.item(i);
//Extracting the values of Algorithm, KeyName,
//Type(of encryption) and CipherValue
String algo = null;
String keyname = null;
String encType = null;
String ciphervalue = null;
//Setting the values
edata.normalize();
//Setting the value of encType
encType = edata.getAttributes().getNamedItem("Type").getNodeValue();
//Setting the values of the remaining parameters
NodeList algoNL = edata.getChildNodes();
for(int j=0;j<algoNL.getLength();j++) {
        //Setting the value of algo
       if(algoNL.item(j).getNodeName().equals("EncryptionMethod"))
      algo = algoNL.item(j).getAttributes().
      getNamedItem("Algorithm").getNodeValue();
     //Setting the value of keyname
    if(algoNL.item(j).getNodeName().equals("ds:KeyInfo")) {
           NodeList knNL = algoNL.item(j).getChildNodes();
          for(int k=0;k<knNL.getLength();k++) {
                if(knNL.item(k).getNodeName().equals("KeyName"))
                keyname = (knNL.item(k).getFirstChild().
                getNodeValue());
                                                                                                }
                                                        }
//Setting the value of ciphervalue
if(algoNL.item(j).getNodeName().equals("CipherData")) {
NodeList cvNL = algoNL.item(j).getChildNodes();

          for(int v=0;v<cvNL.getLength();v++) {
         if(cvNL.item(v).getNodeName().equals
         ("CipherValue"))
         ciphervalue = (cvNL.item(v).getFirstChild().
         getNodeValue());
                                                                   }
                                                                                                 }
}

if (algo.equals("http://www.w3.org/2001/04/xmlenc#tripledes-cbc"))
algo = "DESede";
//Reading the key file and generating/setting decKey
this.generateDecKey(keyname, algo);
//Decrypt the cipher
String decbit = Decrypt(ciphervalue,this.decKey,algo).trim();
//Replacement Logic
//For replacing an entire XML file
if(encType.equals(
"http://www.isi.edu/in-notes/iana/assignments/media-types/text/xml"))
decString = decbit;

}
catch(org.xml.sax.SAXParseException spe) {
  spe.printStackTrace();
}
decString = (getString((XmlDocument)encDoc));
}
}
}
catch(Exception e) {
e.printStackTrace();
}
return decString;
}// End getDecryptedData()

// This is where the actual JCA/JCE data decryption takes place.

private String Decrypt(String encString, Key decKey, String algo) {
// Decoding the Base 64 Encoded IV+cipher String into a byte array
byte[] g = getBase64Decoded(encString);
int glen = g.length;
// Separating the IV from the byte array
byte [] iv = new byte[8];
for(int t=0;t<8;t++)
iv[t] = g[t];
// Separating the cipher from the byte array
byte [] Enc = new byte[glen-8];
for(int p=8;p<glen;p++)
Enc[p-8] = g[p];
// This will hold the decrypted String
String decString = null;
// Decrypting the cipher and setting decString:
try {
IvParameterSpec ivps = new IvParameterSpec(iv);
AlgorithmParameters aparam = AlgorithmParameters.getInstance(algo);
aparam.init(ivps);
Cipher cipherObj = Cipher.getInstance(algo+"/CBC/NoPadding");
cipherObj.init(Cipher.DECRYPT_MODE, decKey, aparam);
decString = new String(cipherObj.update(Enc));
}
catch(Exception e) {
System.out.println("Problem in Decrypt()");
e.printStackTrace();
}
return decString;
}//End Decrypt

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

<EncryptedData xmlns="http://www.w3.org/2001/04/xmlenc#" Id="Test" Type="http://www.isi.edu/in-notes/iana/assignments/media-types/text/xml">
<EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#tripledes-cbc" />
<ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<KeyName>theKey</KeyName>
</ds:KeyInfo>
<CipherData>
<CipherValue>W/HrN6WyPC7ieE41K9UVOPTD1Y0lX8/62zuxp1Z+dTekAoa+6HG6A9BxSyUABOKY
cbxEx35BOrRu1J0P8EGe7mpoNWTufilvz4PkN8cI5DtnWvhamix6Dseju1au0izD
qVViSPjRrDTmMUM+hItji/O5vQMHDZ4nVulrras8NlrDaTbBzq6ZMP0lpzHjFia+
ij+Xj06+N7ojM6qDpFqEGz43PqG61XGzD4jSp3l3M5y4qggZ/R7XVB0D30iktggm
IFC3HwEp9PaKhdEZlvbOlRODN8sLXU+hOGIRKgFjSSZkgINwb9hyEG3ZNzvgyL2A
e0ZQerfPMKwo6sGXPP+cNuqM5Ilp/fsHlN1fF2LtGk7Qyq60U9WPYk8OQtZVy37R
AkxmVXG/ctXwwiavo5HdSd8EMcxTI/GwLXyyfqD16Jd4Z+8dWNU8kHtCtnqJZKcN
o7re+PwzZiCqrVHzFFknc1wW0uydItc3UyVylFPWzr1OJPi40fMyx3lUlmhFxviZ
GsBMuEB++hCul4ksDrjaM+iVxbrYcuJ5Ibw+3tfyVUp2ihfi130s8jYhq3vhvDuk
rk6kb/a5pJ71+0RkLBboFIPQDCkMPBGG/gaMWl0TXle4v7Rfp4fvx8JFAscI13bz
KMkcR73XBoNGLX190rEBT3V8vUtcKDU0TfmJB7GBUgX4lO4ltAwBTjUVmxxFHahj
3KuzFy1MLvXSmVRVx6R9TWwoqe6tOETw7BxsRMAhisAiQFeudOiFisel7ue3fTcP
Qhh+j9IDvTmfgix0K6yf/Q7Yz/6MPJD4I1aMPuHslBC1uMoIBhlvwCsaTLCYRbgM
3WuXZ15iE+o4toEgGravnPbFs080bUlkVDLFv3i6Eb56jkx5RlVILhXtajkNwPaf
JW/Ex2Px9+tObfK20N0Rb++a6lcXvWRBcYN3i8N7ON8vKp7hhZeDIpIvfQ7afOJN
O4GQaNpSJyTooCtr5fehjOGPCv3aH890Nvk0LfVxGA4TfhldezusIW3AHBSi45Vg
xXMNguYshVpVOa3fUxyyVkA/UTge9HJQXixEdFTBAm4JSR33DrBlwg==</CipherValue>
</CipherData>
</EncryptedData>

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

<creditcardpayment xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" payerid="123456789">
<paymentamount>800</paymentamount>
<paymentdate>2004/04/15</paymentdate>
<paymentdesc>This is payment for student fee</paymentdesc>
<customer>

<firstname>ZAHEER</firstname>
<lastname>SHAIK</lastname>
<address>

<street1>7575 W 106 th St</street1>
<street2>Apt 297</street2>
<city>Overland park</city>
<state>KS</state>
<zip>66212</zip>
</address>
</customer>
<creditcardinfo>
<cardnumber>1234567891234567</cardnumber>
<cardtype>Discover</cardtype>
<expirydate>12/31/2004</expirydate>
<securitycode>123</securitycode>
</creditcardinfo>
</creditcardpayment>

References :

http://www-106.ibm.com/developerworks/library/x-encrypt2/