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  • Cycles/byte calculations

    - by matskn
    Hi ! In Crypto communities it is common to measure algorithm performance in cycles/byte. My question is, which parameters in the CPU architecture are affecting this number? Except the clockspeed ofcourse :)

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  • How can I turn a string of text into a BigInteger representation for use in an El Gamal cryptosystem

    - by angstrom91
    I'm playing with the El Gamal cryptosystem, and my goal is to be able to encipher and decipher long sequences of text. I have come up with a method that works for short sequences, but does not work for long sequences, and I cannot figure out why. El Gamal requires the plaintext to be an integer. I have turned my string into a byte[] using the .getBytes() method for Strings, and then created a BigInteger out of the byte[]. After encryption/decryption, I turn the BigInteger into a byte[] using the .toByteArray() method for BigIntegers, and then create a new String object from the byte[]. This works perfectly when i call ElGamalEncipher with strings up to 129 characters. With 130 or more characters, the output produced is garbled. Can someone suggest how to solve this issue? Is this an issue with my method of turning the string into a BigInteger? If so, is there a better way to turn my string of text into a BigInteger and back? Below is my encipher/decipher code. public static BigInteger[] ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) { // returns a BigInteger[] cipherText // cipherText[0] is c // cipherText[1] is d BigInteger[] cipherText = new BigInteger[2]; BigInteger pText = new BigInteger(plaintext.getBytes()); // 1: select a random integer k such that 1 <= k <= p-2 BigInteger k = new BigInteger(p.bitLength() - 2, sr); // 2: Compute c = g^k(mod p) BigInteger c = g.modPow(k, p); // 3: Compute d= P*r^k = P(g^a)^k(mod p) BigInteger d = pText.multiply(r.modPow(k, p)).mod(p); // C =(c,d) is the ciphertext cipherText[0] = c; cipherText[1] = d; return cipherText; } public static String ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) { //returns the plaintext enciphered as (c,d) // 1: use the private key a to compute the least non-negative residue // of an inverse of (c^a)' (mod p) BigInteger z = c.modPow(a, p).modInverse(p); BigInteger P = z.multiply(d).mod(p); byte[] plainTextArray = P.toByteArray(); String output = null; try { output = new String(plainTextArray, "UTF8"); } catch (Exception e) { } return output; }

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  • Simple caesar cipher in java

    - by Max Canlas
    Hey I'm making a simple caesar cipher in Java using the formula [x- (x+shift-1) mod 127 + 1] I want to have my encrypted text to have the ASCII characters except the control characters(i.e from 32-127). How can I avoid the control characters from 0-31 applying in the encrypted text. Thank you.

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  • Example about crypto/rand in Go

    - by nevalu
    Could put a little example about the use of crypto/rand [1]? The function Read has as parameter an array of bytes. Why? If it access to /dev/urandom to get the random data. func Read(b []byte) (n int, err os.Error) [1] http://golang.org/pkg/crypto/rand/

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  • C# RSA Cryptographic Algorithm

    - by karthik
    Hi, Is C# 'RSACryptoServiceProvider' cryptographic algorithm is a part of Microsoft- CryptoAPI? Any advantage we have for normal asymmetric encryption by using CryptoAPI over 'RSACryptoServiceProvider' in .Net? I cannot understand the difference between them?And which one is best and safty? Could you please help? Thanks Karthik

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  • Verify Authenticode signature as being from our company for automatic updater

    - by James Johnston
    I am implementing an automatic update feature and need some advice on how to do this securely using best practices. I would like to use the downloaded file's Authenticode signature to verify that it is safe to run (i.e. originates from our company and hasn't been tampered with). My question is very similar to question #2008519. The bottom-line question: what's the best, most secure way to check Authenticode signatures for an automatic update feature? What fields in the certificate should be checked? Requirements being: (1) check signature is valid, (2) check it's my signature, (3) old clients can still update when my certificate expires and I get a new one. Here's some background information / ideas from my research: I believe this could be broken into two steps: Verify that the signature is valid. I believe this should be easy using WinVerifyTrust as outlined in http://msdn.microsoft.com/en-us/library/aa382384(VS.85).aspx - I don't expect problems here. Verify that the signature corresponds to our company, and not another company. This seems to be a more difficult question to answer: One possibility is to check some of the strings in the signature. Could be obtained via code at MS KB article #323809, but this article doesn't make recommendations on what fields should be checked for this type of application (or any other, for that matter). Question #1072540 also illustrates how to get some certificate info, but again doesn't recommend what fields to actually check. My concern is that the strings might not be the best check: what if another person is able to obtain a certificate with the same name, for example? Or if there's a valid reason for us to change the strings in the future? The person at question #2008519 has a very similar requirement. His need for a "TrustedByUs" function is identical to mine. However, he goes about doing the check by comparing public keys. While this would work in the short-term, it seems like it won't work for an automatic update feature. This is because code signing certificates are only valid for 2 - 3 years max. Therefore, in the future, when we buy a new certificate in 2 years, the old clients wouldn't be able to update any more due to the change in public key.

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  • Can a product that uses BouncyCastle be exported from the UK

    - by swisstony
    We are doing work for a company, based in the UK, who are planning on developing an application that uses the BouncyCastle.Crypto.dll. They intend to make their product (including the crypto dll) available for download over the Internet. Are there UK restrictions on the export of crypto software that would prevent them from doing this? From Wikipedia, I understand it's okay to export it from the US, but not sure about the UK.

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  • simple yet secure encrypt / decrypt asp to asp.net

    - by Michael
    First post here. I have a asp/vb6 web app that logs in a user I want to encrypt the users identity field and pass(querystring) it to a asp.net app and then decrypt it to do a db lookup. I've google'd it of course and found rot13, not secure enough. I've also found some hits on MD5 / RC4 but did not find any good examples of encrypt / decrypt. Thanks, Michael

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  • Why doesn't my implementation of ElGamal work for long text strings?

    - by angstrom91
    I'm playing with the El Gamal cryptosystem, and my goal is to be able to encipher and decipher long sequences of text. I have come up with a method that works for short sequences, but does not work for long sequences, and I cannot figure out why. El Gamal requires the plaintext to be an integer. I have turned my string into a byte[] using the .getBytes() method for Strings, and then created a BigInteger out of the byte[]. After encryption/decryption, I turn the BigInteger into a byte[] using the .toByteArray() method for BigIntegers, and then create a new String object from the byte[]. This works perfectly when i call ElGamalEncipher with strings up to 129 characters. With 130 or more characters, the output produced from ElGamalDecipher is garbled. Can someone suggest how to solve this issue? Is this an issue with my method of turning the string into a BigInteger? If so, is there a better way to turn my string of text into a BigInteger and back? Below is my encipher/decipher code with a program to demonstrate the problem. import java.math.BigInteger; public class Main { static BigInteger P = new BigInteger("15893293927989454301918026303382412" + "2586402937727056707057089173871237566896685250125642378268385842" + "6917261652781627945428519810052550093673226849059197769795219973" + "9423619267147615314847625134014485225178547696778149706043781174" + "2873134844164791938367765407368476144402513720666965545242487520" + "288928241768306844169"); static BigInteger G = new BigInteger("33234037774370419907086775226926852" + "1714093595439329931523707339920987838600777935381196897157489391" + "8360683761941170467795379762509619438720072694104701372808513985" + "2267495266642743136795903226571831274837537691982486936010899433" + "1742996138863988537349011363534657200181054004755211807985189183" + "22832092343085067869"); static BigInteger R = new BigInteger("72294619754760174015019300613282868" + "7219874058383991405961870844510501809885568825032608592198728334" + "7842806755320938980653857292210955880919036195738252708294945320" + "3969657021169134916999794791553544054426668823852291733234236693" + "4178738081619274342922698767296233937873073756955509269717272907" + "8566607940937442517"); static BigInteger A = new BigInteger("32189274574111378750865973746687106" + "3695160924347574569923113893643975328118502246784387874381928804" + "6865920942258286938666201264395694101012858796521485171319748255" + "4630425677084511454641229993833255506759834486100188932905136959" + "7287419551379203001848457730376230681693887924162381650252270090" + "28296990388507680954"); public static void main(String[] args) { FewChars(); System.out.println(); ManyChars(); } public static void FewChars() { //ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) BigInteger[] cipherText = ElGamal.ElGamalEncipher("This is a string " + "of 129 characters which works just fine . This is a string " + "of 129 characters which works just fine . This is a s", P, G, R); System.out.println("This is a string of 129 characters which works " + "just fine . This is a string of 129 characters which works " + "just fine . This is a s"); //ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) System.out.println("The decrypted text is: " + ElGamal.ElGamalDecipher(cipherText[0], cipherText[1], A, P)); } public static void ManyChars() { //ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) BigInteger[] cipherText = ElGamal.ElGamalEncipher("This is a string " + "of 130 characters which doesn’t work! This is a string of " + "130 characters which doesn’t work! This is a string of ", P, G, R); System.out.println("This is a string of 130 characters which doesn’t " + "work! This is a string of 130 characters which doesn’t work!" + " This is a string of "); //ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) System.out.println("The decrypted text is: " + ElGamal.ElGamalDecipher(cipherText[0], cipherText[1], A, P)); } } import java.math.BigInteger; import java.security.SecureRandom; public class ElGamal { public static BigInteger[] ElGamalEncipher(String plaintext, BigInteger p, BigInteger g, BigInteger r) { // returns a BigInteger[] cipherText // cipherText[0] is c // cipherText[1] is d SecureRandom sr = new SecureRandom(); BigInteger[] cipherText = new BigInteger[2]; BigInteger pText = new BigInteger(plaintext.getBytes()); // 1: select a random integer k such that 1 <= k <= p-2 BigInteger k = new BigInteger(p.bitLength() - 2, sr); // 2: Compute c = g^k(mod p) BigInteger c = g.modPow(k, p); // 3: Compute d= P*r^k = P(g^a)^k(mod p) BigInteger d = pText.multiply(r.modPow(k, p)).mod(p); // C =(c,d) is the ciphertext cipherText[0] = c; cipherText[1] = d; return cipherText; } public static String ElGamalDecipher(BigInteger c, BigInteger d, BigInteger a, BigInteger p) { //returns the plaintext enciphered as (c,d) // 1: use the private key a to compute the least non-negative residue // of an inverse of (c^a)' (mod p) BigInteger z = c.modPow(a, p).modInverse(p); BigInteger P = z.multiply(d).mod(p); byte[] plainTextArray = P.toByteArray(); return new String(plainTextArray); } }

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  • Can per-user randomized salts be replaced with iterative hashing?

    - by Chas Emerick
    In the process of building what I'd like to hope is a properly-architected authentication mechanism, I've come across a lot of materials that specify that: user passwords must be salted the salt used should be sufficiently random and generated per-user ...therefore, the salt must be stored with the user record in order to support verification of the user password I wholeheartedly agree with the first and second points, but it seems like there's an easy workaround for the latter. Instead of doing the equivalent of (pseudocode here): salt = random(); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword, salt); Why not use the hash of the username as the salt? This yields a domain of salts that is well-distributed, (roughly) random, and each individual salt is as complex as your salt function provides for. Even better, you don't have to store the salt in the database -- just regenerate it at authentication-time. More pseudocode: salt = hash(username); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword); (Of course, hash in the examples above should be something reasonable, like SHA-512, or some other strong hash.) This seems reasonable to me given what (little) I know of crypto, but the fact that it's a simplification over widely-recommended practice makes me wonder whether there's some obvious reason I've gone astray that I'm not aware of.

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  • Hiding a value in an Android application

    - by Ewan
    Hi, I need to hide a value in a mobile (Android OS) application. As far as I can see, encrypting the value is of no use as the key to the encryption mechanism must be available to the program and is thus available to an attacker reverse-engineering the code. So, it seems that the only "solution" is to hide the secret value in the application as well as possible, obviously not ideal. Any comments? Am I missing something? If not, what's the best way to hide the value? Thanks for your ideas! Ewan

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  • Mathematical attack on the Digital Signature Algorithm

    - by drelihan
    Does anybody know the mathematics behind an attack on DSA where modulus p has p-1 made up of only small factors. In reality, this would not happen as the key generator would guarantee that this is not so. There is much information on the web on generating good input paramters for DSA so that it is hard to crack but no information on how you find X if modulus p has p-1 made up of only small factors.

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  • AES Encryption library

    - by Spines
    Is there a library or something that will allow me to simply call a function that will AES encrypt a byte array? I don't want to deal with multiple update blocks/transformFinal/etc, because there is a possibility I will mess up...

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  • Hash 32bit int to 16bit int?

    - by dkamins
    What are some simple ways to hash a 32-bit integer (e.g. IP address, e.g. Unix time_t, etc.) down to a 16-bit integer? E.g. hash_32b_to_16b(0x12345678) might return 0xABCD. Let's start with this as a horrible but functional example solution: function hash_32b_to_16b(val32b) { return val32b % 0xffff; } Question is specifically about JavaScript, but feel free to add any language-neutral solutions, preferably without using library functions. Simple = good. Wacky+obfuscated = amusing.

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  • Handling User Authentication in .NET?

    - by Daniel
    I am new to .NET, and don't have much experience in programming. What is the standard way of handling user authentication in .NET in the following situation? In Process A, User inputs ID/Password Process A sends the ID/Password to Process B over a nonsecure public channel. Process B authenticates the user with the recieved ID/Password what are some of the standard cryptographic algorithms I can use in above model?

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  • RC2 key schedule

    - by calccrypto
    Can someone explain how the RC2 key schedule works (particularly the very beginning of it)? i know it uses little endian, but my implementation is not working for any key except "0000 0000 0000 0000" Test Vector Key = 88bc a90e 9087 5a Plaintext = 0000 0000 0000 0000 Ciphertext = 6ccf 4308 974c 267f im assuming that the first thing to do with the key would be to change it into bc88 0ea9 8790 5a and yes i know RC2 is not even used anymore, but i would still like to know

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  • If attacker has original data and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require storage in the database. I'm leaning towards the the one-way-hash-stored-in-the-db, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • How to store a public key in a machine-level RSA key container

    - by Andrew Kimball
    I'm having a problem using a machine level RSA key container when storing only the public key of a public/private key pair. The following code creates a public/private pair and extracts the public key from that pair. The pair and the public key are stored in separate key containers. The keys are then obtained from those key containers at which point they should be the same as the keys going into the containers. The code works when CspProviderFlags.UseDefaultKeyContainer is specified for CspParameters.Flags (i.e. the key read back out from the PublicKey container is the same), but when CspProviderFlags.UseMachineKeyStore is specified for CspParameters.Flags the key read back from PublicKey is different. Why is the behaviour different, and what do I need to do differently to retrieve the public key from a machine-level RSA key container? var publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true, }; var publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true }; //Export the key. publicRsa.ImportParameters(publicPrivateRsa.ExportParameters(false)); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); //Dispose those two CSPs. using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); } publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); }

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  • Encryption puzzle / How to create a ProxyStub for a Remote Assistance ticket

    - by Jon Clegg
    I am trying to create a ticket for Remote Assistance. Part of that requires creating a PassStub parameter. As of the documenation: http://msdn.microsoft.com/en-us/library/cc240115(PROT.10).aspx PassStub: The encrypted novice computer's password string. When the Remote Assistance Connection String is sent as a file over e-mail, to provide additional security, a password is used.<16 In part 16 they detail how to create as PassStub. In Windows XP and Windows Server 2003, when a password is used, it is encrypted using PROV_RSA_FULL predefined Cryptographic provider with MD5 hashing and CALG_RC4, the RC4 stream encryption algorithm. As PassStub looks like this in the file: PassStub="LK#6Lh*gCmNDpj" If you want to generate one yourself run msra.exe in Vista or run the Remote Assistance tool in WinXP. The documentation says this stub is the result of the function CryptEncrypt with the key derived from the password and encrypted with the session id (Those are also in the ticket file). The problem is that CryptEncrypt produces a binary output way larger then the 15 byte PassStub. Also the PassStub isn't encoding in any way I've seen before. Some interesting things about the PassStub encoding. After doing statistical analysis the 3rd char is always a one of: !#$&()+-=@^. Only symbols seen everywhere are: *_ . Otherwise the valid characters are 0-9 a-z A-Z. There are a total of 75 valid characters and they are always 15 bytes. Running msra.exe with the same password always generates a different PassStub, indicating that it is not a direct hash but includes the rasessionid as they say. Some other ideas I've had is that it is not the direct result of CryptEncrypt, but a result of the rasessionid in the MD5 hash. In MS-RA (http://msdn.microsoft.com/en-us/library/cc240013(PROT.10).aspx). The "PassStub Novice" is simply hex encoded, and looks to be the right length. The problem is I have no idea how to go from any hash to way the ProxyStub looks like.

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  • I'm really offtopic. But I've got a really good reason.

    - by lost
    Is there anyway Encryption on an unidentified file can be broken(file in question: config file and log files from ardamax keylogger). These files date back all the way to 2008. I searched everywhere, nothing on slashdot, nothing on google. Ardamax Keyviewer? Should I just write to Ardamax? I am at a loss of what to do. I feel comprimised. Anyone managed to decrpyt files with Crypto-analysis?

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  • If I write an algorithm to encrypt a file, are their tools available to break the encryption?

    - by Andrew
    I have an idea for encryption that I could program fairly easily to encrypt some local text file. Given that my approach is novel, and does not use any of the industry standard encryption techniques, would I be able to test the strength of my encryption using 'cracker' apps or suchlike? Or do all those tools rely on advanced knowledge of the encryption process (or intercepted 'keys'), meaning I'd have to build my own cracker for testing?

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  • C# Crypto API examples

    - by Gearoid Murphy
    Hello, I'm looking for examples + information on how to extract certificate information from the windows certificate store and perform operations like verifying signatures using the retrieved certificates. The API documentation for C# in this regard is quite poor, with many of the entries in msdn marked with "This language is not supported, or no code example is available.", I'm sorry I can't be more specific, I haven't done any programming using cryptographic api's. The particular certificate will be provided via a USB token. Any help or pointers would be much appreciated, thanks.

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