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The Long Term Stable (LTS) Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains the JCA/JCE provider and low-level API for the BC LTS version 2.73.7 for Java 8 and later.

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package org.bouncycastle.util.io.pem;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List;

import org.bouncycastle.util.encoders.Base64;

/**
 * A generic PEM reader, based on the format outlined in RFC 1421
 */
public class PemReader
    extends BufferedReader
{
    private static final String BEGIN = "-----BEGIN ";
    private static final String END = "-----END ";

    public PemReader(Reader reader)
    {
        super(reader);
    }

    /**
     * Read the next PEM object as a blob of raw data with header information.
     *
     * @return the next object in the stream, null if no objects left.
     * @throws IOException in case of a parse error.
     */
    public PemObject readPemObject()
        throws IOException
    {
        String line = readLine();

        while (line != null && !line.startsWith(BEGIN))
        {
            line = readLine();
        }

        if (line != null)
        {
            line = line.substring(BEGIN.length()).trim();
            int index = line.indexOf('-');

            if (index > 0 && line.endsWith("-----") && (line.length() - index) == 5)
            {
                String type = line.substring(0, index);

                return loadObject(type);
            }
        }

        return null;
    }

    private PemObject loadObject(String type)
        throws IOException
    {
        String          line;
        String          endMarker = END + type + "-----";
        StringBuffer    buf = new StringBuffer();
        List            headers = new ArrayList();

        while ((line = readLine()) != null)
        {
            int index = line.indexOf(':');
            if (index >= 0)
            {
                String hdr = line.substring(0, index);
                String value = line.substring(index + 1).trim();

                headers.add(new PemHeader(hdr, value));

                continue;
            }

            if (line.indexOf(endMarker) == 0)
            {
                break;
            }
            
            buf.append(line.trim());
        }

        if (line == null)
        {
            throw new IOException(endMarker + " not found");
        }

        return new PemObject(type, headers, Base64.decode(buf.toString()));
    }

}