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    <p>Most Java <code>Key</code> instances are represented as a string of bytes resulting from their <a href="http://java.sun.com/javase/6/docs/api/java/security/Key.html#getEncoded()" rel="noreferrer"><code>getEncoded()</code></a> method. This is what needs to be stored in order to reconstruct the key later.</p> <p>However, to store a key safely in electronic form, it should be encrypted. Of course, encrypting the key would require another key (or password)&hellip; and so you have an infinite regress. A Java <code>KeyStore</code> can be used to store <code>SecretKey</code> objects in this manner, and that is useful when you have many secret keys that are all protected by a single "master" password. But for protecting a single key, it doesn't make a lot of sense.</p> <p>One alternative is to present the key to the user in a form that can be stored in some safe manner (in many applications, that might be on a slip of paper in their wallet). This could be as simple as displaying the bytes of the key encoded in hexadecimal, Base-64, or other text encoding, and asking the user to write it down.</p> <p>Another approach is to allow the user to choose a memorable password, and generate a key with that, using an algorithm like PBKDF2. The salt (and maybe the iteration count) used for key derivation would need to be recorded somewhere though. Another drawback is that people tend to choose from a relatively limited number of passwords out of the total available. So keys derived from passwords may be easier guess than than the key size suggests.</p> <hr> <p>Here is an illustration of the basic technique for persisting and reconstituting a secret key.</p> <pre><code>byte[] encoded = aesKey.getEncoded(); /* Now store "encoded" somewhere. For example, display the key and ask the user to write it down. */ String output = Base64.getEncoder().withoutPadding().encodeToString(encoded); System.out.println("Keep it secret, keep it safe! " + output); ... /* At some point, you need to reconstitute the key. Let's say the user enters it as a base-64 number that you convert to bytes. */ String input = ... ; byte[] encoded = Base64.getDecoder().decode(input); SecretKey aesKey = new SecretKeySpec(encoded, "AES"); </code></pre>
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    1. POEasy way to store/restore encryption key for decrypting string in java
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    1. COThanks for explanation. But How can I call the key instead of genenerating one(KeyGenerator.getInstance("AES").generateKey(); )? I can now print out the key with getEncoded(), user will write it down. But how I call the key back ?
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    2. COI'm seeing inconsistent reads with the new BigInteger(input, 16).toByteArray() portion of this code. More often than not its reading in 17bytes and giving me an 'invalid aes key length: 17 bytes' error when i try to use it. What might cause this?
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    3. CO@sapatos if the high bit of the key is set, `BigInteger` will add a zero byte to the beginning of the byte array to prevent it from being interpreted as a negative number. Maybe instead of `new BigInteger(1, encoded)`, you should allow the string to be a negative number: `new BigInteger(encoded)`
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