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  • Using Public/Private keys in reverse

    - by Wizzarding
    Hi, I have a situation where I need to make some data available for reading by anyone from a specific device, where the data is pre-loaded on the device, but I cannot allow anyone to create their own device and populate it with their own data in the same format. I know this sounds a little crazy, but there is a good reason! I was planning to use Public Key cryptography, encrypting the data with a public key, but then publishing the private key to anyone who wants to read the data. However, after looking at the RSACryptoServiceProvider and how it works it looks like I cannot just publish the private key as the private key can be used to create the public key. Could someone confirm that suspicion, or give me some hints on how I might be able to make this work! Many Thanks.

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  • When encrypting data that is not an even multiple of the block size do I have to send a complete las

    - by WilliamKF
    If I am using a block cipher such as AES which has a block size of 128 bits, what do I do if my data is not an even multiple of 128 bits? I am working with packets of data and do not want to change the size of my packet when encrypting it, yet my data is not an even multiple of 128? Does the AES block cipher allow handling of a final block that is short without changing the size of my message once encrypted?

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  • rsync useful w/ encrypted files?

    - by barrycarter
    Is rsync efficient for transferring encrypted files? More specifically: I encrypt 'x' with my public key and call the result 'y'. I rsync 'y' to my backup server. 'x' changes slightly I encrypt the modified 'x' and rsync the modified 'y' to my backup server. Is this efficient? I know a small change in 'x' yields a large change in 'y', but is the change localized? Or has 'y' changed so thoroughly that rsync is not much better than scp? I currently backup my "critical" files by tarring/bzipping them nightly, then encrypting the .tar.bz file and rsync'ing it to my backup server. Many of the individual files don't change, but, of course, the tar file changes if even one of the files change. Is this efficient? Should I be encrypting and backing up each file individually? That way, unchanged files will take no time to rsync.

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  • How to implement copy protection of content in an open source application?

    - by Lococo
    I have an idea for an open source app -- the app would be free, but I would charge a small fee for data that a customer would order. For instance, let's say I'm writing a map application. I'd give the app away, make it open-source, but I would like to sell various maps to individual users. Is there a way to protect the data in such a way that makes it very difficult for someone to simply take the map they bought and distribute it to others? Is this feasible for an open source app?

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  • AES Key encoded byte[] to String and back to byte[]

    - by Tom Brito
    In the similar question "Conversion of byte[] into a String and then back to a byte[]" is said to not to do the byte[] to String and back conversion, what looks like apply to most cases, mainly when you don't know the encoding used. But, in my case I'm trying to save to a DB the javax.crypto.SecretKey data, and recoverd it after. The interface provide a method getEncoded() which returns the key data encoded as byte[], and with another class I can use this byte[] to recover the key. So, the question is, how do I write the key bytes as String, and later get back the byte[] to regenerate the key?

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  • BadPaddingException in Android encrypt

    - by DarthRoman
    Hi everyone, I am making an Android application, and I want to encrypt a String before sending it to a DataBase, and encrytpion is correct. The problem is when I am going to decrypt the String, because I get a BadPaddingException and I have no idea where the problem is. Here is the code: public final static String HEX = "36A52C8FB7DF9A3F"; public static String encrypt(String seed, String cleartext) throws Exception { byte[] rawKey = getRawKey(seed.getBytes()); byte[] result = encrypt(rawKey, cleartext.getBytes()); return toHex(result); } public static String decrypt(String seed, String encrypted) throws Exception { byte[] rawKey = getRawKey(seed.getBytes()); byte[] enc = toByte(encrypted); byte[] result = decrypt(rawKey, enc); return new String(result); } public static String toHex(String txt) { return toHex(txt.getBytes()); } public static String fromHex(String hex) { return new String(toByte(hex)); } public static byte[] toByte(String hexString) { int len = hexString.length()/2; byte[] result = new byte[len]; for (int i = 0; i < len; i++) result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue(); return result; } public static String toHex(byte[] buf) { if (buf == null) return ""; StringBuffer result = new StringBuffer(2*buf.length); for (int i = 0; i < buf.length; i++) { appendHex(result, buf[i]); } return result.toString(); } private static byte[] getRawKey(byte[] seed) throws Exception { KeyGenerator kgen = KeyGenerator.getInstance("AES"); SecureRandom sr = SecureRandom.getInstance("SHA1PRNG"); sr.setSeed(seed); kgen.init(128, sr); // 192 and 256 bits may not be available SecretKey skey = kgen.generateKey(); byte[] raw = skey.getEncoded(); return raw; } private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception { SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec); byte[] encrypted = cipher.doFinal(clear); return encrypted; } private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception { SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.DECRYPT_MODE, skeySpec); byte[] decrypted = cipher.doFinal(encrypted); return decrypted; } private static void appendHex(StringBuffer sb, byte b) { sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f)); } I encrypt and decrypt with this code: String encrypted = encrypt(HEX, "some text"); String decrypted = decrypt(HEX, encrypted); Can anyone help me please? Thank you very much!!

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  • List modification in Python

    - by user2945143
    We are given an algorithm to modify a list of numbers from 1 to 28. There are 5 steps in the algorithm. We have written functions for each step (all correct). We need to write a function that combines all 5 steps. The algorithm modifies the list to get a value. Each time you get a new value, you use the list created by the algorithm from the previous step. This is what we have gotten so far for the code: get_card_at_top_index(insert_top_to_bottom(triple_cut((move_joker_2( move_joker_1(deck)))))) When we run the code to generate the get_card_at_top_index, the first answer is correct. However, the rest are not. Instead of using from the new list, python uses the value that it generated from the last step. What did we do wrong? UPDATE: The other 5 codes passed the tests, they are correct. Code 1 (List) = list1 Code 2 (list1) = list2 Code 3 (list2) = list3 Code 4 (list3) = list4 Code 5 (list4) = list5 we generate a number from 5. We need to run the algorithm again to generate 25 more numbers. We will use list 5 start from step 1

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  • C# arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • Arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • mcrypt_encrypt fails to initialise

    - by mixkat
    I am trying to encrypt some data in PHP using the Rijndael cipher in CBC mode with a 256bit key but for some reason I get the following error message: mcrypt_encrypt() Module initialization failed My code: $hashKey = hash('sha256',$key); $iv = hash('sha256',$hashKey); // ------Cipher-------------key-------------Data-------------Mode---------IV-- $encryptedQuestion = base64_encode(mcrypt_encrypt('MCRYPT_RIJNDAEL_256', $hashKey , $_POST['question'], MCRYPT_MODE_CBC, $iv)); Can anyone see whats wrong with this?

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  • Storing an encrypted cookie with Rails

    - by J. Pablo Fernández
    I need to store a small piece of data (less than 10 characters) in a cookie in Rails and I need it to be secure. I don't want anybody being able to read that piece of data or injecting their own piece of data (as that would open up the app to many kinds of attacks). I think encrypting the contents of the cookie is the way to go (should I also sign it?). What is the best way to do it? Right now I'm doing this, which looks secure, but many things looked secure to people that knew much more than I about security and then it was discovered it wasn't really secure. I'm saving the secret in this way: encryptor = ActiveSupport::MessageEncryptor.new(Example::Application.config.secret_token) cookies[:secret] = { :value => encryptor.encrypt(secret), :domain => "example.com", :secure => !(Rails.env.test? || Rails.env.development?) } and then I'm reading it like this: encryptor = ActiveSupport::MessageEncryptor.new(Example::Application.config.secret_token) secret = encryptor.decrypt(cookies[:secret]) Is that secure? Any better ways of doing it? Update: I know about Rails' session and how it is secure, both by signing the cookie and by optionally storing the contents of the session server side and I do use the session for what it is for. But my question here is about storing a cookie, a piece of information I do not want in the session but I still need it to be secure.

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  • Crypto++ AES Decrypt how to?

    - by indigoOrange
    There are next to no noob guides to crypto++ out there. Or none that I've found anyway. What I want to do is decrypt an array of uchars I generate with another AES encrypter. Where would I start? I have the library built and linking grand. Do I need to set anything up or do I just call a function on my array (and if so what function) ? I'd really appreshiate some help from someone who knows this stuff. Thanks

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  • Crackers - How do they do it, how do we fight back?

    - by zedo
    As someone who is interested in learning more about the security side of technology, I ask you all the following questions: How is it that crackers crack software? What techniques are used to do so? I would imagine that the cracking methods depend upon the language the software is written in, right? Aside from using something like cloud-based security for SaaS ((software as a service) which isn't always an option), what choices does one have to prevent their software from being compromised?

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  • Java RSA Encrypt using .NET XML Key File - need help

    - by badMonkey
    In .net I have generated the following public key file: <RSAKeyValue> <Modulus>xTSiS4+I/x9awUXcF66Ffw7tracsQfGCn6g6k/hGkLquHYMFTCYk4mOB5NwLwqczwvl8HkQfDShGcvrm47XHKUzA8iadWdA5n4toBECzRxiCWCHm1KEg59LUD3fxTG5ogGiNxDj9wSguCIzFdUxBYq5ot2J4iLgGu0qShml5vwk=</Modulus> <Exponent>AQAB</Exponent> .NET is happy to encrypt using it's normal methods. I am trying to use this key to encode a string in Java and am running into an Arithmetic problem (exception) when I attempt to encrypt the string. The following is the code I am using to encrypt: byte[] modulusBytes = Base64.decode(this.getString(R.string.public_key_modulus)); byte[] exponentBytes = Base64.decode(this.getString(R.string.public_key_exponent)); BigInteger modulus = new BigInteger( modulusBytes ); BigInteger exponent = new BigInteger( exponentBytes); RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent); KeyFactory fact = KeyFactory.getInstance("RSA"); PublicKey pubKey = fact.generatePublic(rsaPubKey); Cipher cipher = Cipher.getInstance("RSA"); cipher.init(Cipher.ENCRYPT_MODE, pubKey); byte[] cipherData = cipher.doFinal( new String("big kitty dancing").getBytes() ); It is the final line in the code block that fails. I have looked at numerous examples and this is the best I could come up with. If it is not obvious, the R.string.public_key_modulus is a copy/paste of the text in the Modulus element, same applies for exponent.

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  • Understanding Security Certificates (and thier pricing)

    - by John Robertson
    I work at a very small company so certificate costs need to be absolutely minimal. However for some applications we do Need to have our customers get that warm fuzzy not-using-a-self-signed certificate feeling. Since creating a "certificate authority" with makecert really just means creating a public/private key pair, it seems pretty clear that creating a public/private key pair FROM such a "certificate authority" really just means generating a second public/private key pair and signing both with the private key that belongs to the "certificate authority". Since the keys are signed anyone can verify they came from the certificate authority I created, or if verisign gave me the pair they sign it with one of their own private keys, and anyone can use verisigns corresponding public key to confirm verisign as the source of the keys. Given this I don't understand when I go to verisign or godaddy why they have rates only for yearly plans, when all I really want from them is a single public/private key pair signed with one of their private keys (so that anyone else can use their public keys to confirm that, yes, they gave me that public/private key pair and they confirmed I was who I said I was so you can trust my public/private key pair as belonging to a legitimate third party). Clearly I am misunderstanding something, what is it? Does verisign retire their public/private key pairs periodically so that my verisign signed key pair "expires" and I need new ones?

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  • AES and CBC in PHP

    - by Kane
    I am trying to encrypt a string in php using AES-128 and CBC, but when I call mcrypt_generic_init() it returns false. $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '',MCRYPT_MODE_CBC, ''); $iv_size = mcrypt_enc_get_iv_size($cipher); $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND); $res = mcrypt_generic_init($cipher, 'aaaa', $iv); //'aaaa' is a test key Can someone tell me why is returning 0/false? I read the php documentation and seems correct (http://us.php.net/manual/en/mcrypt.examples.php)

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  • Java MessageDigest result does not stay constant

    - by user344146
    I've got this function for encrypting passwords in Java, but somehow when I call MessageDigest, it returns a different result every time even though I call it with the same password. I wonder if I am initializing it wrong somehow. public String encrypt (String password) { MessageDigest md = MessageDigest.getInstance("SHA-1"); md.reset(); md.update(password.getBytes(Charset.forName("utf-8")),0,password.length()); String res = md.digest().toString(); }

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  • How to go about signing text in a verifiable way from within ruby in a simple yet strong & portable

    - by roja
    Guys, I have been looking for a portable method to digitally sign arbitrary text which can be placed in a document and distributed while maintaining its verifiable origin. Here is an example: a = 'some text' a.sign(<private key>) # => <some signature in ASCII format> The contents of a can now be distributed freely. If a receiver wants to check the validity of said text they can do the following: b = 'some text' b.valid(<public key>, <signature supplied with text>) # => true/false Is there any library out there that already offers this kind of functionality? Ruby standard library contains SHA hashing code so at lest there is a portable way to perform the hashing but from that point I am struggling to find anything which fits purpose. Kind Regards, Roja

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  • How to find Key and IV value from .Net to PHP

    - by PHP-Prabhu
    Can any one please let me know is there any way to find a solution for the below stuffs. I need to find out the KEY and IV value from the below byte array. the byte array in .net and this has to be convert into KEY(string) and IV(string) via PHP. private static readonly byte[] Key = { 0xda, 0x3c, 0x35, 0x6f, 0xbd, 0xd, 0x87, 0xf0, 0x9a, 0x7, 0x6d, 0xab, 0x7e, 0x82, 0x36, 0xa, 0x1a, 0x5a, 0x77, 0xfe, 0x74, 0xf3, 0x7f, 0xa8, 0xaa, 0x4, 0x11, 0x46, 0x6b, 0x2d, 0x48, 0xa1 }; private static readonly byte[] IV = { 0x6d, 0x2d, 0xf5, 0x34, 0xc7, 0x60, 0xc5, 0x33, 0xe2, 0xa3, 0xd7, 0xc3, 0xf3, 0x39, 0xf2, 0x16 };

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  • Encrypt the file for security

    - by pavun_cool
    Actually I have a file . I am working in linux environment. I need to encrypt that file for secure purpose with giving the some password. The operation could be like zip , tar any compression. When I extract the file It should ask me password , only then it should get extracted Thanks in Advance

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  • How to encrypt a RSAKey using another RSAKey?

    - by Tom Brito
    I know its not the usual thing to do. But the specification I'm implementing is discribed this way, and I cannot run out. I was trying to encrypt the modulus and exponent of the private key, but the following test code raises an exception because the byte array is 1 byte larger then the maximum allowed by RSA block: import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.NoSuchAlgorithmException; import java.security.NoSuchProviderException; import java.security.interfaces.RSAPrivateKey; import java.security.interfaces.RSAPublicKey; import javax.crypto.Cipher; import org.apache.commons.lang.ArrayUtils; public class TEST { public static KeyPair generateKeyPair() throws NoSuchAlgorithmException, NoSuchProviderException { KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA", "BC"); keyPairGenerator.initialize(1024); return keyPairGenerator.generateKeyPair(); } public static void main(String[] args) throws Exception { KeyPair keyPair = generateKeyPair(); RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate(); System.out.println("Priv modulus len = " + privateKey.getModulus().bitLength()); System.out.println("Priv exponent len = " + privateKey.getPrivateExponent().bitLength()); System.out.println("Priv modulus toByteArray len = " + privateKey.getModulus().toByteArray().length); byte[] byteArray = privateKey.getModulus().toByteArray(); // the byte at index 0 have no value (in every generation it is always zero) byteArray = ArrayUtils.subarray(byteArray, 1, byteArray.length); System.out.println("byteArray size: " + byteArray.length); RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic(); Cipher cipher = Cipher.getInstance("RSA", "BC"); cipher.init(Cipher.ENCRYPT_MODE, publicKey); byte[] encryptedBytes = cipher.doFinal(byteArray); System.out.println("Success!"); } } (obs. its just a test, i would never encrypt the private key with its pair public key) The byte array is 128 bytes, the exactly maximum allowed by a RSA block, so why the exception? And how to fix it?

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