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针对sm2和sm4两种加密算法的java实现
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package com.bouncycastle.asn1;

import java.io.IOException;

/**
 * DER NumericString object - this is an ascii string of characters {0,1,2,3,4,5,6,7,8,9, }.
 */
public class DERNumericString
    extends ASN1Object
    implements DERString
{
    String  string;

    /**
     * return a Numeric string from the passed in object
     *
     * @exception IllegalArgumentException if the object cannot be converted.
     */
    public static DERNumericString getInstance(
        Object  obj)
    {
        if (obj == null || obj instanceof DERNumericString)
        {
            return (DERNumericString)obj;
        }

        throw new IllegalArgumentException("illegal object in getInstance: " + obj.getClass().getName());
    }

    /**
     * return an Numeric String from a tagged object.
     *
     * @param obj the tagged object holding the object we want
     * @param explicit true if the object is meant to be explicitly
     *              tagged false otherwise.
     * @exception IllegalArgumentException if the tagged object cannot
     *               be converted.
     */
    public static DERNumericString getInstance(
        ASN1TaggedObject obj,
        boolean          explicit)
    {
        DERObject o = obj.getObject();

        if (explicit || o instanceof DERNumericString)
        {
            return getInstance(o);
        }
        else
        {
            return new DERNumericString(ASN1OctetString.getInstance(o).getOctets());
        }
    }

    /**
     * basic constructor - with bytes.
     */
    public DERNumericString(
        byte[]   string)
    {
        char[]  cs = new char[string.length];

        for (int i = 0; i != cs.length; i++)
        {
            cs[i] = (char)(string[i] & 0xff);
        }

        this.string = new String(cs);
    }

    /**
     * basic constructor -  without validation..
     */
    public DERNumericString(
        String   string)
    {
        this(string, false);
    }

    /**
     * Constructor with optional validation.
     *
     * @param string the base string to wrap.
     * @param validate whether or not to check the string.
     * @throws IllegalArgumentException if validate is true and the string
     * contains characters that should not be in a NumericString.
     */
    public DERNumericString(
        String   string,
        boolean  validate)
    {
        if (validate && !isNumericString(string))
        {
            throw new IllegalArgumentException("string contains illegal characters");
        }

        this.string = string;
    }

    public String getString()
    {
        return string;
    }

    public String toString()
    {
        return string;
    }

    public byte[] getOctets()
    {
        char[]  cs = string.toCharArray();
        byte[]  bs = new byte[cs.length];

        for (int i = 0; i != cs.length; i++)
        {
            bs[i] = (byte)cs[i];
        }

        return bs; 
    }

    void encode(
        DEROutputStream  out)
        throws IOException
    {
        out.writeEncoded(NUMERIC_STRING, this.getOctets());
    }

    public int hashCode()
    {
        return this.getString().hashCode();
    }

    boolean asn1Equals(
        DERObject  o)
    {
        if (!(o instanceof DERNumericString))
        {
            return false;
        }

        DERNumericString  s = (DERNumericString)o;

        return this.getString().equals(s.getString());
    }

    /**
     * Return true if the string can be represented as a NumericString ('0'..'9', ' ')
     *
     * @param str string to validate.
     * @return true if numeric, fale otherwise.
     */
    public static boolean isNumericString(
        String  str)
    {
        for (int i = str.length() - 1; i >= 0; i--)
        {
            char    ch = str.charAt(i);

            if (ch > 0x007f)
            {
                return false;
            }

            if (('0' <= ch && ch <= '9') || ch == ' ')
            {
                continue;
            }

            return false;
        }

        return true;
    }
}