HashUtil.java

import lombok.NonNull;
import lombok.SneakyThrows;
import org.apache.commons.codec.binary.Base32;
import org.springframework.lang.Nullable;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.Arrays;
import java.util.Locale;
import java.util.regex.Pattern;

public final class HashUtil {
    public static final String HASH_REGEX = "^[a-z0-9]{128}$";
    private static final Pattern HASH_PATTERN = Pattern.compile(HASH_REGEX);

    public static boolean isValidHash(@Nullable String hash) {
        return hash == null || HASH_PATTERN.matcher(hash).matches();
    }

    private HashUtil() {
    }

    public static String createHash(@NonNull String plainText) {
        return createHash(plainText, null);
    }

    /**
     * @param plainText the input text to hash
     * @param salt a salt for the hash
     *
     * @return the encoded value of the hash, containing only lowercase alphanumeric characters
     */
    @SneakyThrows
    public static String createHash(@NonNull String plainText, @Nullable byte[] salt) {
        MessageDigest md = MessageDigest.getInstance("SHA-512");
        if (salt != null && salt.length > 0) {
            // add salt if one is provided
            md.update(salt);
        }

        byte[] hash = md.digest(plainText.getBytes(StandardCharsets.UTF_8));

        // encode with base32 for case-insensitivity
        return new Base32(false)
            // pad the hash before encoding to ensure url safety (no trailing '=' chars)
            .encodeToString(addPadding(hash))
            // use [a-z] instead of [A-Z]
            .toLowerCase(Locale.ROOT);
    }

    public static byte[] addPadding(byte[] input) {
        int res = 16 - input.length % 16;
        byte[] result = new byte[res];
        Arrays.fill(result, (byte) res);
        return merge(input, result);
    }

    private static byte[] merge(byte[] arr1, byte[] arr2) {
        byte[] results = new byte[arr1.length + arr2.length];
        int i = 0;
        for (; i < arr1.length; i += 1) {
            results[i] = arr1[i];
        }
        for (int j = i; j - i < arr2.length; j += 1) {
            results[j] = arr2[j - i];
        }
        return results;
    }
}