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
