The org.apache.commons.codec.binary.Base64 class is not part of the standard Android APIs. To fix the problem, just use the standard Base64 class that comes with Android by replacing these lines:
import org.apache.commons.codec.binary.Base64;
...
String retVal = Base64.encodeBase64String(digest);
by:
import android.util.Base64;
...
String retVal = Base64.encodeToString(digest, Base64.DEFAULT);