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The Bouncy Castle Java API for handling the OpenPGP protocol. This jar contains the OpenPGP API for JDK 1.4. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.

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package org.bouncycastle.bcpg;

import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import org.bouncycastle.util.StringList;
import org.bouncycastle.util.Strings;

/**
 * reader for Base64 armored objects - read the headers and then start returning
 * bytes when the data is reached. An IOException is thrown if the CRC check
 * is detected and fails.
 * 
 * By default a missing CRC will not cause an exception. To force CRC detection use:
 *  
 *     ArmoredInputStream aIn = []
 *
 *     aIn.setDetectMissingCRC(true);
 *


 * 
 */
public class ArmoredInputStream
    extends InputStream
{
    /*
     * set up the decoding table.
     */
    private static final byte[] decodingTable;

    static
    {
        decodingTable = new byte[128];

        for (int i = 0; i < decodingTable.length; i++)
        {
            decodingTable[i] = (byte)0xff;
        }

        for (int i = 'A'; i <= 'Z'; i++)
        {
            decodingTable[i] = (byte)(i - 'A');
        }

        for (int i = 'a'; i <= 'z'; i++)
        {
            decodingTable[i] = (byte)(i - 'a' + 26);
        }

        for (int i = '0'; i <= '9'; i++)
        {
            decodingTable[i] = (byte)(i - '0' + 52);
        }

        decodingTable['+'] = 62;
        decodingTable['/'] = 63;
    }

    /**
     * decode the base 64 encoded input data.
     *
     * @return the offset the data starts in out.
     */
    private static int decode(int in0, int in1, int in2, int in3, byte[] out)
        throws IOException
    {
        int b1, b2, b3, b4;

        if (in3 < 0)
        {
            throw new EOFException("unexpected end of file in armored stream.");
        }

        if (in2 == '=')
        {
            b1 = decodingTable[in0] &0xff;
            b2 = decodingTable[in1] & 0xff;

            if ((b1 | b2) < 0)
            {
                throw new ArmoredInputException("invalid armor");
            }

            out[2] = (byte)((b1 << 2) | (b2 >> 4));

            return 2;
        }
        else if (in3 == '=')
        {
            b1 = decodingTable[in0];
            b2 = decodingTable[in1];
            b3 = decodingTable[in2];

            if ((b1 | b2 | b3) < 0)
            {
                throw new ArmoredInputException("invalid armor");
            }

            out[1] = (byte)((b1 << 2) | (b2 >> 4));
            out[2] = (byte)((b2 << 4) | (b3 >> 2));

            return 1;
        }
        else
        {
            b1 = decodingTable[in0];
            b2 = decodingTable[in1];
            b3 = decodingTable[in2];
            b4 = decodingTable[in3];

            if ((b1 | b2 | b3 | b4) < 0)
            {
                throw new ArmoredInputException("invalid armor");
            }

            out[0] = (byte)((b1 << 2) | (b2 >> 4));
            out[1] = (byte)((b2 << 4) | (b3 >> 2));
            out[2] = (byte)((b3 << 6) | b4);

            return 0;
        }
    }

    /*
     * Ignore missing CRC checksums.
     * https://tests.sequoia-pgp.org/#ASCII_Armor suggests that missing CRC sums do not invalidate the message.
     */
    private boolean detectMissingChecksum = false;

    InputStream    in;
    boolean        start = true;
    byte[]         outBuf = new byte[3];
    int            bufPtr = 3;
    CRC24          crc = new FastCRC24();
    boolean        crcFound = false;
    boolean        hasHeaders = true;
    String         header = null;
    boolean        newLineFound = false;
    boolean        clearText = false;
    boolean        restart = false;
    StringList     headerList= Strings.newList();
    int            lastC = 0;
    boolean        isEndOfStream;
    
    /**
     * Create a stream for reading a PGP armoured message, parsing up to a header 
     * and then reading the data that follows.
     * 
     * @param in
     */
    public ArmoredInputStream(
        InputStream    in) 
        throws IOException
    {
        this(in, true);
    }

    /**
     * Create an armoured input stream which will assume the data starts
     * straight away, or parse for headers first depending on the value of 
     * hasHeaders.
     * 
     * @param in
     * @param hasHeaders true if headers are to be looked for, false otherwise.
     */
    public ArmoredInputStream(
        InputStream    in,
        boolean        hasHeaders) 
        throws IOException
    {
        this.in = in;
        this.hasHeaders = hasHeaders;
        
        if (hasHeaders)
        {
            parseHeaders();
        }

        start = false;
    }
    
    public int available()
        throws IOException
    {
        return in.available();
    }
    
    private boolean parseHeaders()
        throws IOException
    {
        header = null;
        
        int        c;
        int        last = 0;
        boolean    headerFound = false;
        
        headerList = Strings.newList();
        
        //
        // if restart we already have a header
        //
        if (restart)
        {
            headerFound = true;
        }
        else
        {
            while ((c = in.read()) >= 0)
            {
                if (c == '-' && (last == 0 || last == '\n' || last == '\r'))
                {
                    headerFound = true;
                    break;
                }
    
                last = c;
            }
        }

        if (headerFound)
        {
            boolean         eolReached = false;
            boolean         crLf = false;

            ByteArrayOutputStream buf = new ByteArrayOutputStream();
            buf.write('-');

            if (restart)    // we've had to look ahead two '-'
            {
                buf.write('-');
            }
            
            while ((c = in.read()) >= 0)
            {
                if (last == '\r' && c == '\n')
                {
                    crLf = true;
                }
                if (eolReached && (last != '\r' && c == '\n'))
                {
                    break;
                }
                if (eolReached && c == '\r')
                {
                    break;
                }
                if (c == '\r' || (last != '\r' && c == '\n'))
                {
                    String line = Strings.fromUTF8ByteArray(buf.toByteArray());
                    if (line.trim().length() == 0)
                    {
                        break;
                    }
                    if (headerList.size() != 0 && line.indexOf(':') < 0)
                    {
                        throw new ArmoredInputException("invalid armor header");
                    }
                    headerList.add(line);
                    buf.reset();
                }

                if (c != '\n' && c != '\r')
                {
                    buf.write(c);
                    eolReached = false;
                }
                else
                {
                    if (c == '\r' || (last != '\r' && c == '\n'))
                    {
                        eolReached = true;
                    }
                }
                
                last = c;
            }
            
            if (crLf)
            {
                int nl = in.read(); // skip last \n
                if (nl != '\n')
                {
                    throw new ArmoredInputException("inconsistent line endings in headers");
                }
            }
        }
        
        if (headerList.size() > 0)
        {
            header = headerList.get(0);
        }
        
        clearText = "-----BEGIN PGP SIGNED MESSAGE-----".equals(header);
        newLineFound = true;

        return headerFound;
    }

    /**
     * @return true if we are inside the clear text section of a PGP
     * signed message.
     */
    public boolean isClearText()
    {
        return clearText;
    }

    /**
     * @return true if the stream is actually at end of file.
     */
    public boolean isEndOfStream()
    {
        return isEndOfStream;
    }

    /**
     * Return the armor header line (if there is one)
     * @return the armor header line, null if none present.
     */
    public String    getArmorHeaderLine()
    {
        return header;
    }
    
    /**
     * Return the armor headers (the lines after the armor header line),
     * @return an array of armor headers, null if there aren't any.
     */
    public String[] getArmorHeaders()
    {
        if (headerList.size() <= 1)
        {
            return null;
        }

        return headerList.toStringArray(1, headerList.size());
    }
    
    private int readIgnoreSpace() 
        throws IOException
    {
        int    c = in.read();
        
        while (c == ' ' || c == '\t' || c == '\f' || c == '\u000B') // \u000B ~ \v
        {
            c = in.read();
        }

        if (c >= 128)
        {
            throw new ArmoredInputException("invalid armor");
        }

        return c;
    }
    
    public int read()
        throws IOException
    {
        int    c;

        if (start)
        {
            if (hasHeaders)
            {
                parseHeaders();
            }

            crc.reset();
            start = false;
        }
        
        if (clearText)
        {
            c = in.read();

            if (c == '\r' || (c == '\n' && lastC != '\r'))
            {
                newLineFound = true;
            }
            else if (newLineFound && c == '-')
            {
                c = in.read();
                if (c == '-')            // a header, not dash escaped
                {
                    clearText = false;
                    start = true;
                    restart = true;
                }
                else                   // a space - must be a dash escape
                {
                    c = in.read();
                }
                newLineFound = false;
            }
            else
            {
                if (c != '\n' && lastC != '\r')
                {
                    newLineFound = false;
                }
            }
            
            lastC = c;

            if (c < 0)
            {
                isEndOfStream = true;
            }
            
            return c;
        }

        if (bufPtr > 2 || crcFound)
        {
            c = readIgnoreSpace();
            
            if (c == '\r' || c == '\n')
            {
                c = readIgnoreSpace();
                
                while (c == '\n' || c == '\r')
                {
                    c = readIgnoreSpace();
                }

                if (c == '=')            // crc reached
                {
                    bufPtr = decode(readIgnoreSpace(), readIgnoreSpace(), readIgnoreSpace(), readIgnoreSpace(), outBuf);
                    if (bufPtr != 0)
                    {
                        throw new ArmoredInputException("malformed crc in armored message");
                    }

                    crcFound = true;

                    int i = ((outBuf[0] & 0xff) << 16)
                          | ((outBuf[1] & 0xff) << 8)
                          | (outBuf[2] & 0xff);
                    if (i != crc.getValue())
                    {
                        throw new ArmoredInputException("crc check failed in armored message");
                    }

                    return read();
                }

                if (c == '-')        // end of record reached
                {
                    while ((c = in.read()) >= 0)
                    {
                        if (c == '\n' || c == '\r')
                        {
                            break;
                        }
                    }

                    if (!crcFound && detectMissingChecksum)
                    {
                        throw new ArmoredInputException("crc check not found");
                    }

                    crcFound = false;
                    start = true;
                    bufPtr = 3;

                    if (c < 0)
                    {
                        isEndOfStream = true;
                    }

                    return -1;
                }
            }

            if (c < 0)
            {
                isEndOfStream = true;
                return -1;
            }

            bufPtr = decode(c, readIgnoreSpace(), readIgnoreSpace(), readIgnoreSpace(), outBuf);

            if (bufPtr == 0)
            {
                crc.update3(outBuf, 0);
            }
            else
            {
                for (int i = bufPtr; i < 3; ++i)
                {
                    crc.update(outBuf[i] & 0xFF);
                }
            }
        }

        return outBuf[bufPtr++] & 0xFF;
    }

    /**
     * Reads up to  len

bytes of data from the input stream into * an array of bytes. An attempt is made to read as many as * len bytes, but a smaller number may be read. * The number of bytes actually read is returned as an integer. * * The first byte read is stored into element b[off], the * next one into b[off+1], and so on. The number of bytes read * is, at most, equal to len. * * NOTE: We need to override the custom behavior of Java's {@link InputStream#read(byte[], int, int)}, * as the upstream method silently swallows {@link IOException IOExceptions}. * This would cause CRC checksum errors to go unnoticed. * * @see Related BC bug report * @param b byte array * @param off offset at which we start writing data to the array * @param len number of bytes we write into the array * @return total number of bytes read into the buffer * * @throws IOException if an exception happens AT ANY POINT */ public int read(byte[] b, int off, int len) throws IOException { checkIndexSize(b.length, off, len); if (len == 0) { return 0; } int c = read(); if (c == -1) { return -1; } b[off] = (byte)c; int i = 1; for (; i < len ; i++) { c = read(); if (c == -1) { break; } b[off + i] = (byte)c; } return i; } private void checkIndexSize(int size, int off, int len) { if (off < 0 || len < 0) { throw new IndexOutOfBoundsException("Offset and length cannot be negative."); } if (off > size - len) { throw new IndexOutOfBoundsException("Invalid offset and length."); } } public void close() throws IOException { in.close(); } /** * Change how the stream should react if it encounters missing CRC checksum. * The default value is false (ignore missing CRC checksums). If the behavior is set to true, * an {@link IOException} will be thrown if a missing CRC checksum is encountered. * * @param detectMissing ignore missing CRC sums */ public void setDetectMissingCRC(boolean detectMissing) { this.detectMissingChecksum = detectMissing; } }