How can I calculate the SHA-256 hash of a string with a secret key in Android?

Question

I need to calculate a SHA-256 hash of a string with a secret key. I found this code :

public String computeHash(String input)
    throws NoSuchAlgorithmException, UnsupportedEncodingException
{
    MessageDigest digest = MessageDigest.getInstance("SHA-256");
    digest.reset();

    byte[] byteData = digest.digest(input.getBytes("UTF-8"));
    StringBuffer sb = new StringBuffer();

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

for calculating the hash without the secret key. How can I calculate with a secret key? I searched but I didn't find any solution in Android. Any idea ?

Instinct

do you understand the purpose of an hashing algorithm? – Pristine

@Pristine yes, I do. what is so strange to my question? This is what I must do. I saw that in other programming languages this is possible. – Instinct

can you show me how a key is related to the hashing phase? I never read about this anywhere and i don't even get your point of if this is something that can be real. – Pristine

Take a look here : hash.online-convert.com/sha256-generator – Instinct

which is something about cryptography and not steganography, it's also something much more similar to a protocol rather than an hashing algorithm or an hashing phase. you are talking about 2 different things. the hashing doesn't use a key, never, if you are talking about a particular protocol or solution you have to specify it. – Pristine

So it's about hmac. If so @Chirag answer is correct. – Buckthorn

An explanation of HMAC. – Satisfied

Answer 1

Look at this example.

/**
 * Encryption of a given text using the provided secretKey
 * 
 * @param text
 * @param secretKey
 * @return the encoded string
 * @throws SignatureException
 */
public static String hashMac(String text, String secretKey)
  throws SignatureException {

 try {
  Key sk = new SecretKeySpec(secretKey.getBytes(), HASH_ALGORITHM);
  Mac mac = Mac.getInstance(sk.getAlgorithm());
  mac.init(sk);
  final byte[] hmac = mac.doFinal(text.getBytes());
  return toHexString(hmac);
 } catch (NoSuchAlgorithmException e1) {
  // throw an exception or pick a different encryption method
  throw new SignatureException(
    "error building signature, no such algorithm in device "
      + HASH_ALGORITHM);
 } catch (InvalidKeyException e) {
  throw new SignatureException(
    "error building signature, invalid key " + HASH_ALGORITHM);
 }
}

Where HASH_ALGORITHM is defined as:

private static final String HASH_ALGORITHM = "HmacSHA256";

public static String toHexString(byte[] bytes) {  
    StringBuilder sb = new StringBuilder(bytes.length * 2);  

    Formatter formatter = new Formatter(sb);  
    for (byte b : bytes) {  
        formatter.format("%02x", b);  
    }  

    return sb.toString();  
}  

Tieback

Which is the method toHexString()? – Instinct

Let me know : How can I calculate the SHA-1 hash of a String with a Secret key in android ? – Lullaby

how can i reverse from Hash string to original String ? Any idea thanks – Liqueur

@ShanXeeshi You're out of luck there. A hash is a one-way digest; it cannot be "reversed" to get the original text. Sorry. – Wawro

Answer 2

In kotlin, use below function.

import java.security.MessageDigest
import javax.crypto.Mac
import javax.crypto.spec.SecretKeySpec

fun String.hmacSha256(key: String): String {
    val secretKey = SecretKeySpec(key.toByteArray(Charsets.UTF_8), "HmacSHA256")
    val mac = Mac.getInstance("HmacSHA256")
    mac.init(secretKey)
    val hash = mac.doFinal(this.toByteArray(Charsets.UTF_8))
    return hash.joinToString("") { "%02x".format(it) }
}

Here,

val key = "secret key"
val message = "message to be encrypted"
val encryptedMessage = message.hmacSha256(key) // final result

Ledoux

Answer 3

Use the below code,

/**
 * Returns a hexadecimal encoded SHA-256 hash for the input String.
 * @param data
 * @return
 */
private static String getSHA256Hash(String data) {
    String result = null;
    try {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] hash = digest.digest(data.getBytes("UTF-8"));
        return bytesToHex(hash); // make it printable
    }catch(Exception ex) {
        ex.printStackTrace();
    }
    return result;
}

/**
 * Use javax.xml.bind.DatatypeConverter class in JDK
 * to convert byte array to a hexadecimal string. Note that this generates hexadecimal in upper case.
 * @param hash
 * @return
 */
private static String  bytesToHex(byte[] hash) {
    return DatatypeConverter.printHexBinary(hash);
}

To use DatatypeConverter, download the jar file from the below link.

http://www.java2s.com/Code/Jar/j/Downloadjavaxxmlbindjar.htm

Where

there is no secret key – Mod