Encrypt and decrypt a String in java

Question

I am new to cryptography. I wish to learn how to encrypt and decrypt the text in a file... when I refer the related articles in net. I had a doubt that whether the encrypted text will be same for single text when encryption is done multiple times on the same text? Can anyone please clear my doubt?

Answer 1

    public String encrypt(String str) {
        try {
            // Encode the string into bytes using utf-8
            byte[] utf8 = str.getBytes("UTF8");

            // Encrypt
            byte[] enc = ecipher.doFinal(utf8);

            // Encode bytes to base64 to get a string
            return new sun.misc.BASE64Encoder().encode(enc);
        } catch (javax.crypto.BadPaddingException e) {
        } catch (IllegalBlockSizeException e) {
        } catch (UnsupportedEncodingException e) {
        } catch (java.io.IOException e) {
        }
        return null;
    }

    public String decrypt(String str) {
        try {
            // Decode base64 to get bytes
            byte[] dec = new sun.misc.BASE64Decoder().decodeBuffer(str);

            // Decrypt
            byte[] utf8 = dcipher.doFinal(dec);

            // Decode using utf-8
            return new String(utf8, "UTF8");
        } catch (javax.crypto.BadPaddingException e) {
        } catch (IllegalBlockSizeException e) {
        } catch (UnsupportedEncodingException e) {
        } catch (java.io.IOException e) {
        }
        return null;
    }
}

Here's an example that uses the class:

try {
    // Generate a temporary key. In practice, you would save this key.
    // See also Encrypting with DES Using a Pass Phrase.
    SecretKey key = KeyGenerator.getInstance("DES").generateKey();

    // Create encrypter/decrypter class
    DesEncrypter encrypter = new DesEncrypter(key);

    // Encrypt
    String encrypted = encrypter.encrypt("Don't tell anybody!");

    // Decrypt
    String decrypted = encrypter.decrypt(encrypted);
} catch (Exception e) {
}