is AES key random? | 易学教程

问题

AES key may be generate by this code

KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);

but

If I have a "very reliable" method of generating random numbers can I use it in such a way

SecureRandom rnd = new SecureRandom();
byte[] key = new byte[16];
rnd.nextBytes(key);

is key obtained by this method reliable ?

or it ONLY must generated by some SPECIAL algorithm

回答1:

The AES key can be any 128 bits. It should be be practically unguessable, whatever the method of creating it.

For Example:

SecureRandom sr = new SecureRandom()

key = new byte[16];
iv = new byte[16];

sr.nextBytes(key);
sr.nextBytes(iv);

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key,"AES"), new IvParameterSpec(IV));

SecretKeySpec, by the way, is just a thin wrapper around a byte[] --- it does not transform the key in any way. No "special algorithm".

回答2:

To add to the other answers ... I believe that the reason that the basic Random functions aren't secure are two reasons:

Slight statistical biases that are acceptable for non-security related situations, but narrow the distributions unacceptably for security applications.
They are seeded by the system DATETIME. Even knowing WHEN you generated your key - to a poor accuracy of +/- 6 months - would significantly reduce the brute force search space.

回答3:

You can add a random algorithm using SecureRandom :

    KeyGenerator keyGen = KeyGenerator.getInstance("AES");
    SecureRandom random = new SecureRandom(); // cryptograph. secure random 
    keyGen.init(random); 
    SecretKey secretKey = keyGen.generateKey();

回答4:

It sounds like you're trying to generate an AES key based on a password.

If this is the case, you can use javax.crypto.SecretKeyFactory's generateSecret method, passing in a javax.crypto.spec.PBEKeySpec as the parameter. The PBEKeySpec allows to to specify the password as an argument to its constructor.

来源：https://stackoverflow.com/questions/10252449/is-aes-key-random

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