    PublicKey publicKey = 
        KeyFactory.getInstance(&quot;RSA&quot;).generatePublic(new X509EncodedKeySpec(bytes));

For more info &lt;a href=&quot;http://docs.oracle.com/javase/tutorial/security/apisign/vstep2.html&quot;&gt;see this tutorial&lt;/a&gt;

For others who want to get private key instead of public key from byte array:

    PrivateKey privateKey = KeyFactory.getInstance(&quot;RSA&quot;).generatePrivate(new PKCS8EncodedKeySpec(privateKeyBytes));
					

Great answer. Thanks for the link. Just for complete, I found this https://stackoverflow.com/questions/5364338/converted-secret-key-into-bytes-how-to-convert-it-back-to-secrect-key

    SecretKey key2 = new SecretKeySpec(data, 0, data.length, &quot;DES&quot;);

and just worked very well.

I&#39;m running Windows 7 **with UAC enabled**. I&#39;ve always found it weird that [Eclipse][1] doesn&#39;t use an installer and doesn&#39;t use the AppData folder to store its data in Windows, but lately I&#39;ve had to reinstall it a couple times (hard drive problems) and I&#39;ve been wondering if I am really putting it in the best place.

I copy the eclipse folder to my `C:\Program Files\` directory and make a shortcut on my start menu, and then pin it to my taskbar. However, eclipse has problems so I go to properties, the compatibility tab, and enable &quot;Run as administrator&quot;. Then every time I open eclipse I have to hit yes on the UAC window, but everything works correctly, except for one side effect: my touchpad doesn&#39;t scroll any windows in eclipse. This is because the touchpad program is running as a normal user, so it can&#39;t modify eclipse running as administrator. So, then I have to close and reopen my touchpad software as an administrator.

Anyway, long story short... **Where is the best place to put the eclipse folder in Windows, and why?**

---

Edit: I just found [a possible suggestion][2], feel free to comment. Sounds like I can just run it as administrator once the first time and set up all my plugins and such, and then run it as a normal user for my normal tasks (coding). I can&#39;t believe I never thought of doing this, but I may stick to the Program Files directory and give this approach a try unless I get a better answer here.

---

[Ninite][3] places Eclipse in C:\eclipse. Ever since asking this question, that has been my install location for Eclipse. Eclipse still does not properly handle permissions when run out of the Program Files folder.


  [1]: http://www.eclipse.org/
  [2]: http://www.eclipsezone.com/eclipse/forums/t97323.html#92155438
  [3]: http://www.ninite.com/

What folder should I install Eclipse to on Windows?

While other questions have tackled the broader category of [sequences][1] and [modules][2], I ask this very specific question:

**&quot;What naming convention do you use for dictionaries and why?&quot;**

Some naming convention samples I have been considering:

    # &#39;value&#39; is the data type stored in the map, while &#39;key&#39; is the type of key
    value_for_key={key1:value1, key2,value2}
    value_key={key1:value1, key2,value2}
    v_value_k_key={key1:value1, key2,value2}

Don&#39;t bother answering the &#39;why&#39; with &quot;because my work tells me to&quot;, not very helpful. The reason driving the choice is more important. Are there any other good considerations for a dictionary naming convention aside from readability?

**EDIT:**

**Chosen answer:** value_key_map

**Reason for chosen answer:** Allows a code reviewer to quickly and easily figure out the key and value for a map, and the fact that it is a map without looking anywhere else.


  [1]: https://stackoverflow.com/questions/659415/python-sequence-naming-convention
  [2]: https://stackoverflow.com/questions/711884/python-naming-conventions-for-modules

Python Naming Conventions for Dictionaries/Maps/Hashes

I&#39;m wondering if it&#39;s possible to recover a RSA public key that I have converted to byte array previously.

    byte[] keyBytes = publicKey.getEncoded();

Thanks for the help.



How to recover a RSA public key from a byte[] array?

I'm wondering if it's possible to recover a RSA public key that I have converted to byte array previously.
<pre><code class="hljs language-ini">byte[] keyBytes = publicKey.getEncoded();
</code></pre>
Thanks for the help.

I know that `this` refers to a current object. But I do not know when I really need to use it. For example, will be there any difference if I use `x` instead of `this.x` in some of the methods? May be `x` will refer to a variable which is local for the considered method? I mean variable which is seen only in this method.

What about `this.method()`? Can I use it? Should I use it. If I just use `method()`, will it not be, by default, applied to the current object?

When should I use &quot;this&quot; in a class?

I&#39;ve had instances of our Java code catch a `NullPointerException`, but when I try to log the StackTrace (which basically ends up calling `Throwable.printStackTrace()` ), all I get is:

    java.lang.NullPointerException

Has anyone else come across this? I tried googling for &quot;java null pointer empty stack trace&quot; but didn&#39;t come across anything like this.

NullPointerException in Java with no StackTrace

After [answering][1] a question about how to [force-free objects in Java][2] (the guy was clearing a 1.5GB HashMap) with `System.gc()`, I was told it&#39;s bad practice to call `System.gc()` manually, but the comments were not entirely convincing. In addition, no one seemed to dare to upvote, nor downvote my answer.

I was told there that it&#39;s bad practice, but then I was also told that garbage collector runs don&#39;t systematically stop the world anymore, and that it could also effectively be used by the JVM only as a hint, so I&#39;m kind of at loss.

I do understand that the JVM usually knows better than you when it needs to reclaim memory. I also understand that worrying about a few kilobytes of data is silly. I also understand that even megabytes of data isn&#39;t what it was a few years back. But still, 1.5 gigabytes? And you _know_ there&#39;s like 1.5 GB of data hanging around in memory; it&#39;s not like it&#39;s a shot in the dark. Is `System.gc()` systematically bad, or is there some point at which it becomes okay?

So the question is actually double:

* Why is or isn&#39;t it bad practice to call `System.gc()`? Is it really merely a hint to the JVM under certain implementations, or is it always a full collection cycle? Are there really garbage collector implementations that can do their work without stopping the world? Please shed some light over the various assertions people have made in the comments to my [answer][3].
* Where&#39;s the threshold? Is it _never_ a good idea to call `System.gc()`, or are there times when it&#39;s acceptable? If so, what are those times?


  [1]: https://stackoverflow.com/a/2406360/3650944
  [2]: https://stackoverflow.com/questions/2406349/forcing-deallocation-of-large-cache-object-in-java/
  [3]: https://stackoverflow.com/a/2406360/3650944

Why is it bad practice to call System.gc()?

I&#39;m using Spring to define stages in my application. It&#39;s configured that the necessary class (here called `Configurator`) is injected with the stages.  
Now I need the List of Stages in another class, named `LoginBean`. The `Configurator` doesn&#39;t offer access to his List of Stages.

I cannot change the class `Configurator`.

My Idea:  
Define a new bean called Stages and inject it to `Configurator` and `LoginBean`.
My problem with this idea is that I don&#39;t know how to transform this property:

&lt;!-- language: xml --&gt;

    &lt;property ...&gt;
      &lt;list&gt;
        &lt;bean ... &gt;...&lt;/bean&gt;
        &lt;bean ... &gt;...&lt;/bean&gt;
        &lt;bean ... &gt;...&lt;/bean&gt;
      &lt;/list&gt;
    &lt;/property&gt;

into a bean.

Something like this does not work:

&lt;!-- language: xml --&gt;

    &lt;bean id=&quot;stages&quot; class=&quot;java.util.ArrayList&quot;&gt;

Can anybody help me with this?

How to define a List bean in Spring?

Why is the `catch(Exception)` almost always a bad Idea?

Why is the Catch(Exception) almost always a bad Idea?

How can I convert the hashed result, which is a byte array, to a string?

    byte[] bytePassword = Encoding.UTF8.GetBytes(password);

    using (MD5 md5 = MD5.Create())
    {
        byte[] byteHashedPassword = md5.ComputeHash(bytePassword);
    } 

I need to convert `byteHashedPassword` to a string. 

Converting a md5 hash byte array to a string

I understand how standard random number generators work. But when working with crytpography, the random numbers really have to be random. 

I know there are instruments that read [cosmic white noise][1] to help generate secure hashes, but your standard PC doesn&#39;t have this. 

How does a cryptographically secure random number generator  get its values with no repeatable patterns?


  [1]: http://en.wikipedia.org/wiki/Hardware_random_number_generator

How does a cryptographically secure random number generator work?

Given two different strings S1 and S2 (S1 != S2) is it possible that:
    
    SHA1(S1) == SHA1(S2)

is True?

 1. If yes - with what probability?  
 2. If not - why not?
 3. Is there a upper bound on the length of a input string, for which the probability of getting duplicates is 0? OR is the calculation of SHA1  (hence probability of duplicates) independent of the length of the string?

The goal I am trying to achieve is to hash some sensitive ID string (possibly joined together with some other fields like parent ID), so that I can use the hash value as an ID instead (for example in the database).

Example:

    Resource ID: X123
    Parent ID: P123

I don&#39;t want to expose the nature of my resource identifies to allow client to see &quot;X123-P123&quot;.

Instead I want to create a new column hash(&quot;X123-P123&quot;), let&#39;s say it&#39;s AAAZZZ. Then the client can request resource with id AAAZZZ and not know about my internal id&#39;s etc.



Is it possible to get identical SHA1 hash?

I am writing an app for BlackBerry that utilizes a BlackBerry smartcard reader. There is not much documentation on the subject, so I&#39;d really like if someone could give me starting examples.

Basically, there is one RSA private key on the card plus a certificate (for paired public key). I would like to be able to encrypt/decrypt data and also sign it as well. The final goal would be to establish an mutual-authenticated SSL connection using client certificate contained on the smartcard.

Here is the code I managed to come up with so far:

    SmartCardReader btReader = null;
    SmartCardReader[] readers = SmartCardReaderFactory.getInstalledReaders();
    for (int i = 0; i &lt; readers.length; i++) {
        SmartCardReader reader = readers[i];
        if (reader.getType().equalsIgnoreCase(&quot;bluetooth&quot;)) {
            btReader = reader;
            break;
        }
    }
    
    SmartCardReaderSession readerSession = reader.openSession();
    CryptoSmartCard card = (CryptoSmartCard) readerSession.getSmartCard();
    RSACryptoToken token = (RSACryptoToken) card.getCryptoToken(&quot;RSA&quot;);

This `token` looks promising - has some nice methods, but with &quot;cryptic&quot; arguments. What to do next?

Blackberry smartcard reader example

I need to hash some passwords with salt on postgresql, and I haven&#39;t been able to find any relevant documentation on how to get that done.  

So how can I hash passwords (with some salts) in postgresql?

How can I hash passwords in postgresql?

What&#39;s the difference between id_rsa.pub and id_dsa.pub?

It appears they are both encryption algorithms that require public and private keys.  Why would I pick one versus the other to provide encryption in my client server application?

What is the difference between DSA and RSA?

I need to encrypt some data using RSA in JavaScript. All of the libraries around ask for an exponent and a modulus, yet I get a single `public.key` file from my opponent. 

How do you retrieve the public `exponent` and `modulus` part from an RSA file?

RSA: Get exponent and modulus given a public key

I am working on a test harness for a SAML 1.1 Assertion Consumer Service.  The test must generate a signed SAMLResponse and submit it to the ACS encoded in Base64.  The ACS must be able to verify the signed message using the X509 public cert.

I am able to build the SAMLResponse, adding the necessary assertions, etc.  But when I try to sign the object I am running into problems.  Here is a snippet of my current code:

    String certPath = &quot;mycert.pem&quot;;
    File pubCertFile = new File(certPath);
    BufferedInputStream bis = null;
    try {
        bis = new BufferedInputStream(new FileInputStream(pubCertFile));
    } catch(FileNotFoundException e) {
        throw new Exception(&quot;Could not locate certfile at &#39;&quot; + certPath + &quot;&#39;&quot;, e);
    }
    CertificateFactory certFact = null;
    Certificate cert = null;
    try {
        certFact = CertificateFactory.getInstance(&quot;X.509&quot;);
        cert = certFact.generateCertificate(bis);
    } catch(CertificateException e) {
        throw new Exception(&quot;Could not instantiate cert&quot;, e);
    }
    bis.close();
    ArrayList&lt;Certificate&gt; certs = new ArrayList&lt;Certificate&gt;();
    certs.add(cert);
    
    String keyPath = &quot;mykey.pem&quot;;
    File privKeyFile = new File(keyPath);
    try {
        bis = new BufferedInputStream(new FileInputStream(privKeyFile));
    } catch(FileNotFoundException e) {
        throw new Exception(&quot;Could not locate keyfile at &#39;&quot; + keyPath + &quot;&#39;&quot;, e);
    }
    byte[] privKeyBytes = new byte[(int)privKeyFile.length()];
    bis.read(privKeyBytes);
    bis.close();
    KeyFactory keyFactory = KeyFactory.getInstance(&quot;RSA&quot;);
    KeySpec ks = new PKCS8EncodedKeySpec(privKeyBytes);
    RSAPrivateKey privKey = (RSAPrivateKey) keyFactory.generatePrivate(ks);
    
    samlResponse.sign(Signature.getInstance(&quot;SHA1withRSA&quot;).toString(), privKey, certs);

The error occurs on the second-to-last line.  I see the following in the console:

    java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: invalid key format


Though not customary or secure, but for sake of this thread, I am providing the public cert and private key that I am using.  I of course will re-create new ones once the problem is solved.  :)

    aj@mmdev0:~/$ cat mykey.pem
    -----BEGIN RSA PRIVATE KEY-----
    MIICXgIBAAKBgQDnbcLSlDFaDMhalcmQgclTFobpkHQHJtxMVGRlbv7zknttAVbY
    1jzGjJ6HVupndzDxA9tbiMjQujmGlS/8g5IEbVsR9o6dmcmbvujtEZ2rHZ82tMYP
    VAt2IoS/W/q2Rr1cAZ/zTKEmh0ZZjzCZFueLfrYPm3am5JLcXgVtbKwybQIDAQAB
    AoGBAJ441oettYgBUUFNQv8/HGtn7Vjl38277cVptTH8DuZr8WJ3Fe8tmWONZBzX
    eW6/eIBuyJvuCo1ZpFa0zJfxQ/Ph6QlQwdN50GNfh9RzSS6lDdfy8BRhc27sypXS
    L6c5ljB6ql+pp3DdxFhJMOs3ZmBJdeyWe7uFrkngtnM1nxZBAkEA+1hbV1Q305wa
    u8YMF1SlNIAfgLJ7buD43SEXle0egz405PFG8f8yDmvROwDiRceILGVrRbInd7Cb
    dvJKr34WOQJBAOu2+reG44rNuiXeGX1MYg6TlWYyABm7PrTrhPZkedodOQB8p7zD
    AqtDSK7RnDCoThndPW6kdNAeB+kG4ug5XdUCQHRDU8UajNRSkj8nhjJIkj6twWS7
    qsMIR7Wp+An+7C1TWg5I2UNZg2MOVnNPnlseyAuZQjy0AvOnetJTk16IGWkCQQCL
    FUbOr8rnhgiGe4yywDVDwJVw3aPtiuyvOCEWeabkqkWOIf+fg7m5cFQcwxXUKBsd
    a8vp0yQSAQZN24Bb4i2ZAkEA8xGJFlFDY9HREWZnDey5STgbUeT1wYkyKcDsUrp1
    kR/3BliGqSIfje+mSKDIZqaP+gai/8bIABYAsDP/t6+cuA==
    -----END RSA PRIVATE KEY-----
    
    aj@mmdev0:~/$ cat mycert.pem
    -----BEGIN CERTIFICATE-----
    MIID7zCCA1igAwIBAgIJAKrURaAaD6ulMA0GCSqGSIb3DQEBBQUAMIGsMQswCQYD
    VQQGEwJVUzERMA8GA1UECBMISWxsaW5vaXMxEDAOBgNVBAcTB0NoaWNhZ28xHDAa
    BgNVBAoTE0hvc3R3YXkgQ29ycG9yYXRpb24xITAfBgNVBAsTGFJlc2VhcmNoIGFu
    ZCBEZXZlbG9wbWVudDEYMBYGA1UEAxMPd3d3Lmhvc3R3YXkuY29tMR0wGwYJKoZI
    hvcNAQkBFg5hakBob3N0d2F5LmNvbTAeFw0xMDA3MTQwMjMyMDhaFw0xMTA3MTQw
    MjMyMDhaMIGsMQswCQYDVQQGEwJVUzERMA8GA1UECBMISWxsaW5vaXMxEDAOBgNV
    BAcTB0NoaWNhZ28xHDAaBgNVBAoTE0hvc3R3YXkgQ29ycG9yYXRpb24xITAfBgNV
    BAsTGFJlc2VhcmNoIGFuZCBEZXZlbG9wbWVudDEYMBYGA1UEAxMPd3d3Lmhvc3R3
    YXkuY29tMR0wGwYJKoZIhvcNAQkBFg5hakBob3N0d2F5LmNvbTCBnzANBgkqhkiG
    9w0BAQEFAAOBjQAwgYkCgYEA523C0pQxWgzIWpXJkIHJUxaG6ZB0BybcTFRkZW7+
    85J7bQFW2NY8xoyeh1bqZ3cw8QPbW4jI0Lo5hpUv/IOSBG1bEfaOnZnJm77o7RGd
    qx2fNrTGD1QLdiKEv1v6tka9XAGf80yhJodGWY8wmRbni362D5t2puSS3F4FbWys
    Mm0CAwEAAaOCARUwggERMB0GA1UdDgQWBBQI/4Inzs6OH5IquItuKhIrhPb24zCB
    4QYDVR0jBIHZMIHWgBQI/4Inzs6OH5IquItuKhIrhPb246GBsqSBrzCBrDELMAkG
    A1UEBhMCVVMxETAPBgNVBAgTCElsbGlub2lzMRAwDgYDVQQHEwdDaGljYWdvMRww
    GgYDVQQKExNIb3N0d2F5IENvcnBvcmF0aW9uMSEwHwYDVQQLExhSZXNlYXJjaCBh
    bmQgRGV2ZWxvcG1lbnQxGDAWBgNVBAMTD3d3dy5ob3N0d2F5LmNvbTEdMBsGCSqG
    SIb3DQEJARYOYWpAaG9zdHdheS5jb22CCQCq1EWgGg+rpTAMBgNVHRMEBTADAQH/
    MA0GCSqGSIb3DQEBBQUAA4GBAA388zZp6UNryC/6o44hj7wTBQdzFFM5cs3B668A
    ylAnnal+J8RMIeCHoMF4S7yFQtYdOiWeScgw3c7KXrhJK1X7fU3I+eb1t3Yp1cTI
    htyzw14AoiICFalmlVgTCsn3+uh6AXP02PTkR8osdEpUOlWap4uzSKYNKc7tLOFd
    4CkM
    -----END CERTIFICATE-----




Thanks!

Content Type	Original Author	Original Content on Stackoverflow
Question	kiewic	View Question on Stackoverflow
Solution 1 - Java	Bozho	View Answer on Stackoverflow
Solution 2 - Java	Marko Kotar	View Answer on Stackoverflow
Solution 3 - Java	Adrien	View Answer on Stackoverflow

How to recover a RSA public key from a byte[] array?

Java Problem Overview

Java Solutions

Solution 1 - Java

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Python Naming Conventions for Dictionaries/Maps/Hashes

What folder should I install Eclipse to on Windows?

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