//base64 decode to binary data
byte[] fieldBytes = org.keyczar.util.Base64Coder.decode(ed.getField_data());
String sessionData = ed.getSession_data();
decrypter = new Crypter(new KeyczarHardCodedReader());
verifier = new Verifier(new KeyczarHardCodedVerifier());
SignedSessionDecrypter sessionDecrypter = new SignedSessionDecrypter(decrypter, verifier, sessionData);
byte[] plainText = sessionDecrypter.decrypt(fieldBytes);