Able to decrypt the message using different key - encryption

Question

I create following singleton class to encrypt and decrypt the string messages.
public class EncryptionHelper {
private Cipher ecipher;
private Cipher dcipher;
private SecretKey key;
private byte iv[] = { 8, 7, 6, 5, 4, 3, 2, 1 };
private static EncryptionHelper instance;
public static EncryptionHelper getInstance( String defKey ) {
synchronized( EncryptionHelper.class ) {
if ( null == instance ) {
try {
instance = new EncryptionHelper( defKey );
} catch( Exception e ) {
}
}
}
return instance;
}
private EncryptionHelper( String defKey )
throws Exception {
DESedeKeySpec keyspec = new DESedeKeySpec( defKey.getBytes() );
SecretKeyFactory keyfactory = SecretKeyFactory.getInstance( "TripleDES" );
key = keyfactory.generateSecret( keyspec );
ecipher = Cipher.getInstance( "TripleDES/CBC/PKCS5Padding" );
dcipher = Cipher.getInstance( "TripleDES/CBC/PKCS5Padding" );
ecipher.init( Cipher.ENCRYPT_MODE, key, new IvParameterSpec( iv ) );
dcipher.init( Cipher.DECRYPT_MODE, key, new IvParameterSpec( iv ) );
}
public String encrypt( String str ) {
try {
byte[] utf8 = str.getBytes( "UTF-8" );
byte[] enc = ecipher.doFinal( utf8 );
String val = Base64.getEncoder().encodeToString( enc );
return val;
} catch( UnsupportedEncodingException | IllegalBlockSizeException | BadPaddingException e ) {
}
return str;
}
public String decrypt( String str ) {
try {
byte[] dec = Base64.getDecoder().decode( str );
byte[] utf8 = dcipher.doFinal( dec );
return new String( utf8, "UTF8" );
} catch( IllegalBlockSizeException | BadPaddingException | IOException e ) {
}
return str;
}
}
When I tried to use encrypt and decrypt method of this class using two different program with different key as follows.
public static void main( String[] args ) {
EncryptionHelper encryptionHelper = EncryptionHelper.getInstance( "000000000000ffffffffffff" );
System.out.println( encryptionHelper.encrypt( "ABCDEFGH" ) );
}
Output is ::: n+0SEJQDXwfvpdMIdetNow==
and
public static void main( String[] args ) {
// Use different key to decrypt
EncryptionHelper encryptionHelper = EncryptionHelper.getInstance( "111111111111ffffffffffff" );
// Use output of previous call as input to decrypt
System.out.println( encryptionHelper.decrypt( "n+0SEJQDXwfvpdMIdetNow==" ) );
}
Output is ::: ABCDEFGH
As you can see I am using different keys while using encrypt and decrypt method but still the program is able to decrypt the exact value using wrong key.
Can you guys help me to know, why it is behaving like this, why I am able to decrypt using wrong key?

Answer 1

why I am able to decrypt using wrong key?
... because you are not using the second key, but the key that was used with the first call to getInstance
if you don't see that, answer the following question to yourself ... on your SECOND call to getInstance, when instance has already a value and is not NULL, how does defKey influence the instance? (hint: it doesn't)