How to hash some string with sha256 in Java?

How can I hash some string with sha256 in Java?

SHA-256 isn't an "encoding" - it's a one-way hash.

You'd basically convert the string into bytes (e.g. using text.getBytes(StandardCharsets.UTF_8)) and then hash the bytes. Note that the result of the hash would also be arbitrary binary data, and if you want to represent that in a string, you should use base64 or hex... don't try to use the String(byte[], String) constructor.

e.g.

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(text.getBytes(StandardCharsets.UTF_8));

I think that the easiest solution is to use Apache Common Codec:

String sha256hex = org.apache.commons.codec.digest.DigestUtils.sha256Hex(stringText);	

Another alternative is Guava which has an easy-to-use suite of Hashing utilities. For example, to hash a string using SHA256 as a hex-string you would simply do:

final String hashed = Hashing.sha256()
        .hashString("your input", StandardCharsets.UTF_8)
        .toString();

Full example hash to string as another string.

public static String sha256(final String base) {
	try{
		final MessageDigest digest = MessageDigest.getInstance("SHA-256");
		final byte[] hash = digest.digest(base.getBytes("UTF-8"));
		final StringBuilder hexString = new StringBuilder();
		for (int i = 0; i < hash.length; i++) {
			final 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);
	}
}

If you are using Java 8 you can encode the byte[] by doing

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(text.getBytes(StandardCharsets.UTF_8));
String encoded = Base64.getEncoder().encodeToString(hash);

import java.security.MessageDigest;

public class CodeSnippets {

 public static String getSha256(String value) {
    try{
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(value.getBytes());
        return bytesToHex(md.digest());
    } catch(Exception ex){
        throw new RuntimeException(ex);
    }
 }
 private static String bytesToHex(byte[] bytes) {
    StringBuffer result = new StringBuffer();
    for (byte b : bytes) result.append(Integer.toString((b & 0xff) + 0x100, 16).substring(1));
    return result.toString();
 }
}

String hashWith256(String textToHash) {
    MessageDigest digest = MessageDigest.getInstance("SHA-256");
    byte[] byteOfTextToHash = textToHash.getBytes(StandardCharsets.UTF_8);
    byte[] hashedByetArray = digest.digest(byteOfTextToHash);
    String encoded = Base64.getEncoder().encodeToString(hashedByetArray);
    return encoded;
}

I traced the Apache code through DigestUtils and sha256 seems to default back to java.security.MessageDigest for calculation. Apache does not implement an independent sha256 solution. I was looking for an independent implementation to compare against the java.security library. FYI only.

This was my approach using Kotlin:

private fun getHashFromEmailString(email : String) : String{
    val charset = Charsets.UTF_8
    val byteArray = email.toByteArray(charset)
    val digest = MessageDigest.getInstance("SHA-256")
    val hash = digest.digest(byteArray)
    
    return hash.fold("", { str, it -> str + "%02x".format(it)})
}

In Java 8

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Scanner;
import javax.xml.bind.DatatypeConverter;


Scanner scanner = new Scanner(System.in);
String password = scanner.nextLine();
scanner.close();

MessageDigest digest = null;
try {
	digest = MessageDigest.getInstance("SHA-256");
} catch (NoSuchAlgorithmException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
}
byte[] hash = digest.digest(password.getBytes(StandardCharsets.UTF_8));
String encoded = DatatypeConverter.printHexBinary(hash);        
System.out.println(encoded.toLowerCase());

   

Here is a slightly more performant way to turn the digest into a hex string:

private static final char[] hexArray = "0123456789abcdef".toCharArray();

public static String getSHA256(String data) {
    StringBuilder sb = new StringBuilder();
    try {
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(data.getBytes());
        byte[] byteData = md.digest();
        sb.append(bytesToHex(byteData);
    } catch(Exception e) {
        e.printStackTrace();
    }
    return sb.toString();
}

private static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    for ( int j = 0; j < bytes.length; j++ ) {
        int v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return String.valueOf(hexChars);
}

Does anyone know of a faster way in Java?

You can use MessageDigest in the following way:

public static String getSHA256(String data){
	StringBuffer sb = new StringBuffer();
	try{
		MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(data.getBytes());
        byte byteData[] = md.digest();

        for (int i = 0; i < byteData.length; i++) {
         sb.append(Integer.toString((byteData[i] & 0xff) + 0x100, 16).substring(1));
        }
	} catch(Exception e){
		e.printStackTrace();
	}
    return sb.toString();
}

This is what i have been used for hashing:

String pass = "password";

MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
byte hashBytes[] = messageDigest.digest(pass.getBytes(StandardCharsets.UTF_8));
BigInteger noHash = new BigInteger(1, hashBytes);
String hashStr = noHash.toString(16);

Output: 5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8

In Java, MessageDigest class is used to calculate cryptographic hashing value. This class provides cryptographic hash function ( MD5, SHA-1 and SHA-256) to find hash value of text.

Code example for using SHA-256 algorithm.

public void printHash(String str) throws NoSuchAlgorithmException {

MessageDigest md=MessageDigest.getInstance("SHA-256");

byte[] sha256=md.digest(str.getBytes(StandardCharsets.UTF_8));

   for(byte b : sha256){

      System.out.printf("%02x",b);

  }
}

Here's a method which returns a String:

public static String sha256(final String data) {
    try {
        final byte[] hash = MessageDigest.getInstance("SHA-256").digest(data.getBytes(StandardCharsets.UTF_8));
        final StringBuilder hashStr = new StringBuilder(hash.length);

        for (byte hashByte : hash)
            hashStr.append(Integer.toHexString(255 & hashByte));

        return hashStr.toString();
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
        return null;
    }
}

private static String getMessageDigest(String message, String algorithm) {
 MessageDigest digest;
 try {
  digest = MessageDigest.getInstance(algorithm);
  byte data[] = digest.digest(message.getBytes("UTF-8"));
  return convertByteArrayToHexString(data);
 } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
 return null;
}

You can call above method with different algorithms like below.

getMessageDigest(message, "MD5");
getMessageDigest(message, "SHA-256");
getMessageDigest(message, "SHA-1");

You can refer this link for complete application.