Can you explain to me what's the meaning of the algorithm of SHA-1?


package Finals;


public class SHA { 
    private static String convertToHex(byte[] data) { 
        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < data.length; i++) { 
            int halfbyte = (data[i] >>> 4) & 0x0F;
            int two_halfs = 0;
            do { 
                if ((0 <= halfbyte) && (halfbyte <= 9)) 
                    buf.append((char) ('0' + halfbyte));
                    buf.append((char) ('a' + (halfbyte - 10)));
                halfbyte = data[i] & 0x0F;
            } while(two_halfs++ < 1);
        return buf.toString();
    public static String SHA1(String text) 
    throws NoSuchAlgorithmException, UnsupportedEncodingException  { 
    MessageDigest md;
    md = MessageDigest.getInstance("SHA-1");
    byte[] sha1hash = new byte[40];
    md.update(text.getBytes("iso-8859-1"), 0, text.length());
    sha1hash = md.digest();
    return convertToHex(sha1hash);
Attachments 365px-SHA-1.svg_.png 14.57 KB

Generally, hashes are used to verify that the contents of a message has not been changed. There is no known way to "carefully" change the message so that the resulting hash of the message will remain unchanged.

(This is not a property of CRCs, which are used primarily for random error detection: It's easy to manipulate the last few bytes of a message to get a desired CRC value. That's a desirable feature in some applications.)

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