Java IO.pdf - Nguyen Dang Binh

}
}
catch (NoSuchAlgorithmException e) {
System.err.println(e);
e.printStackTrace();
}
catch (NoSuchPaddingException e) {System.err.println(e);}
catch (BadPaddingException e) {System.err.println(e);}
catch (IllegalBlockSizeException e) {System.err.println(e);}
catch (IOException e) {System.err.println(e);}
Java I/O
There are a lot of different exceptions that must be caught. Except for the usual IOException,
these are all subclasses of java.security.GeneralSecurityException. You could save
some space simply by catching that. For example:
catch (GeneralSecurityException e) {
System.err.println(e);
e.printStackTrace();
}
One exception I'll note in particular (because it threw me more than once while writing this
chapter): if you should see a NoSuchAlgorithmException, it probably means you haven't
properly installed the JCE or other provider that supports your algorithm.
java.security.NoSuchAlgorithmException: Algorithm DES not available
java.security.NoSuchAlgorithmException: Algorithm DES not available
at javax.crypto.JceSecurity.getImpl(Compiled Code)
at
javax.crypto.SecretKeyFactory.getInstance(SecretKeyFactory.java:105)
at FileEncryptor.main(Compiled Code)
Adding the JCE classes to your class path is enough to get the program to compile, but to
actually run it, you'll need to add the following line to the java.security file in the
jre/lib/security directory in your JDK folder:
security.provider.2=com.sun.crypto.provider.SunJCE
To be honest, this is far too complicated and error-prone. For one thing, every time you
upgrade your JDK, this property will get overwritten and you'll have to do it all over again.
Sun really needs a better installer for the JCE that handles the setting of the necessary
properties.
Decrypting a file is similar, as Example 10.7 shows. The name of the input and output files
and the password are read from the command line. A DES key factory converts the password
to a DES secret key. Then both input and output files are opened in file streams, and a data
input stream is chained to the input file. The main reason for this is to read the initialization
vector. First the integer size is read, then the actual bytes of the vector. The resulting array is
used to construct an IvParameterSpec object that will be used along with the key to initialize
the cipher. Once the cipher has been initialized, the data is copied from input to output much
as before.
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