Hash String via SHA-256 in Java

问题

By looking around here as well as the internet in general, I have found Bouncy Castle. I want to use Bouncy Castle (or some other freely available utility) to generate a SHA-256 Hash of a String in Java. Looking at their documentation I can't seem to find any good examples of what I want to do. Can anybody here help me out?

回答1:

To hash a string, use the built-in MessageDigest class:

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.nio.charset.StandardCharsets;
import java.math.BigInteger;

public class CryptoHash {
  public static void main(String[] args) throws NoSuchAlgorithmException {
    MessageDigest md = MessageDigest.getInstance("SHA-256");
    String text = "Text to hash, cryptographically.";

    // Change this to UTF-16 if needed
    md.update(text.getBytes(StandardCharsets.UTF_8));
    byte[] digest = md.digest();

    String hex = String.format("%064x", new BigInteger(1, digest));
    System.out.println(hex);
  }
}

In the snippet above, digest contains the hashed string and hex contains a hexadecimal ASCII string with left zero padding.

回答2:

This is already implemented in the runtime libs.

public static String calc(InputStream is) {
    String output;
    int read;
    byte[] buffer = new byte[8192];

    try {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        while ((read = is.read(buffer)) > 0) {
            digest.update(buffer, 0, read);
        }
        byte[] hash = digest.digest();
        BigInteger bigInt = new BigInteger(1, hash);
        output = bigInt.toString(16);
        while ( output.length() < 32 ) {
            output = "0"+output;
        }
    } 
    catch (Exception e) {
        e.printStackTrace(System.err);
        return null;
    }

    return output;
}

In a JEE6+ environment one could also use JAXB DataTypeConverter:

import javax.xml.bind.DatatypeConverter;

String hash = DatatypeConverter.printHexBinary( 
           MessageDigest.getInstance("MD5").digest("SOMESTRING".getBytes("UTF-8")));

回答3:

You don't necessarily need the BouncyCastle library. The following code shows how to do so using the Integer.toHexString function

public static String sha256(String base) {
    try{
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] hash = digest.digest(base.getBytes("UTF-8"));
        StringBuffer hexString = new StringBuffer();

        for (int i = 0; i < hash.length; i++) {
            String hex = Integer.toHexString(0xff & hash[i]);
            if(hex.length() == 1) hexString.append('0');
            hexString.append(hex);
        }

        return hexString.toString();
    } catch(Exception ex){
       throw new RuntimeException(ex);
    }
}

Special thanks to user1452273 from this post: How to hash some string with sha256 in Java?

Keep up the good work !

回答4:

When using hashcodes with any jce provider you first try to get an instance of the algorithm, then update it with the data you want to be hashed and when you are finished you call digest to get the hash value.

MessageDigest sha = MessageDigest.getInstance("SHA-256");
sha.update(in.getBytes());
byte[] digest = sha.digest();

you can use the digest to get a base64 or hex encoded version according to your needs

回答5:

Java 8: Base64 available:

    MessageDigest md = MessageDigest.getInstance( "SHA-512" );
    md.update( inbytes );
    byte[] aMessageDigest = md.digest();

    String outEncoded = Base64.getEncoder().encodeToString( aMessageDigest );
    return( outEncoded );

回答6:

I suppose you are using a relatively old Java Version without SHA-256. So you must add the BouncyCastle Provider to the already provided 'Security Providers' in your java version.

    // NEEDED if you are using a Java version without SHA-256    
    Security.addProvider(new BouncyCastleProvider());

    // then go as usual 
    MessageDigest md = MessageDigest.getInstance("SHA-256");
    String text = "my string...";
    md.update(text.getBytes("UTF-8")); // or UTF-16 if needed
    byte[] digest = md.digest();