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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 and up.
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package org.bouncycastle.asn1;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Vector;

/**
 * ASN.1 OctetStrings, with indefinite length rules, and constructed form support.
 * 
 * The Basic Encoding Rules (BER) format allows encoding using so called "constructed form",
 * which DER and CER formats forbid allowing only "primitive form".
 * 

 * This class always produces the constructed form with underlying segments
 * in an indefinite length array.  If the input wasn't the same, then this output
 * is not faithful reproduction.
 * 
 * 
 * See {@link ASN1OctetString} for X.690 encoding rules of OCTET-STRING objects.
 * 
 */
public class BEROctetString
    extends ASN1OctetString
{
    private static final int DEFAULT_CHUNK_SIZE = 1000;

    private final int chunkSize;
    private final ASN1OctetString[] octs;

    /**
     * Convert a vector of octet strings into a single byte string
     */
    static private byte[] toBytes(
        ASN1OctetString[]  octs)
    {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();

        for (int i = 0; i != octs.length; i++)
        {
            try
            {
                DEROctetString o = (DEROctetString)octs[i];

                bOut.write(o.getOctets());
            }
            catch (ClassCastException e)
            {
                throw new IllegalArgumentException(octs[i].getClass().getName() + " found in input should only contain DEROctetString");
            }
            catch (IOException e)
            {
                throw new IllegalArgumentException("exception converting octets " + e.toString());
            }
        }

        return bOut.toByteArray();
    }

    /**
     * Create an OCTET-STRING object from a byte[]
     * @param string the octets making up the octet string.
     */
    public BEROctetString(
        byte[] string)
    {
        this(string, DEFAULT_CHUNK_SIZE);
    }

    /**
     * Multiple {@link ASN1OctetString} data blocks are input,
     * the result is constructed form.
     *
     * @param octs an array of OCTET STRING to construct the BER OCTET STRING from.
     */
    public BEROctetString(
        ASN1OctetString[] octs)
    {
        this(octs, DEFAULT_CHUNK_SIZE);
    }

    /**
     * Create an OCTET-STRING object from a byte[]
     * @param string the octets making up the octet string.
     * @param chunkSize the number of octets stored in each DER encoded component OCTET STRING.
     */
    public BEROctetString(
        byte[] string,
        int    chunkSize)
    {
        this(string, null, chunkSize);
    }

    /**
     * Multiple {@link ASN1OctetString} data blocks are input,
     * the result is constructed form.
     *
     * @param octs an array of OCTET STRING to construct the BER OCTET STRING from.
     * @param chunkSize the number of octets stored in each DER encoded component OCTET STRING.
     */
    public BEROctetString(
        ASN1OctetString[] octs,
        int chunkSize)
    {
        this(toBytes(octs), octs, chunkSize);
    }

    private BEROctetString(byte[] string, ASN1OctetString[] octs, int chunkSize)
    {
        super(string);
        this.octs = octs;
        this.chunkSize = chunkSize;
    }

    /**
     * Return a concatenated byte array of all the octets making up the constructed OCTET STRING
     * @return the full OCTET STRING.
     */
//    public byte[] getOctets()
//    {
//        return string;
//    }

    /**
     * Return the OCTET STRINGs that make up this string.
     *
     * @return an Enumeration of the component OCTET STRINGs.
     */
    public Enumeration getObjects()
    {
        if (octs == null)
        {
            return generateOcts().elements();
        }

        return new Enumeration()
        {
            int counter = 0;

            public boolean hasMoreElements()
            {
                return counter < octs.length;
            }

            public Object nextElement()
            {
                return octs[counter++];
            }
        };
    }

    private Vector generateOcts()
    { 
        Vector vec = new Vector();
        for (int i = 0; i < string.length; i += chunkSize)
        { 
            int end = Math.min(string.length, i + chunkSize); 

            byte[] nStr = new byte[end - i]; 

            System.arraycopy(string, i, nStr, 0, nStr.length);

            vec.addElement(new DEROctetString(nStr));
         } 
        
         return vec; 
    }

    boolean isConstructed()
    {
        return true;
    }

    int encodedLength()
        throws IOException
    {
        int length = 0;
        for (Enumeration e = getObjects(); e.hasMoreElements();)
        {
            length += ((ASN1Encodable)e.nextElement()).toASN1Primitive().encodedLength();
        }

        return 2 + length + 2;
    }

    /**
     * @deprecated
     */
    public void encode(ASN1OutputStream out)
        throws IOException
    {
        out.writeObject(this);
    }

    void encode(ASN1OutputStream out, boolean withTag) throws IOException
    {
        out.writeEncodedIndef(withTag, BERTags.CONSTRUCTED | BERTags.OCTET_STRING,  getObjects());
    }

    static BEROctetString fromSequence(ASN1Sequence seq)
    {
        int count = seq.size();
        ASN1OctetString[] v = new ASN1OctetString[count];
        for (int i = 0; i < count; ++i)
        {
            v[i] = ASN1OctetString.getInstance(seq.getObjectAt(i));
        }
        return new BEROctetString(v);
    }
}