base64.java

另一个使用java编写的加密通用算法包

// $Id: Base64.java,v 1.1.1.1 1997/12/22 03:28:42 hopwood Exp $
//
// $Log: Base64.java,v $
// Revision 1.1.1.1  1997/12/22 03:28:42  hopwood
// + Imported to CVS (tagged as 'start').
//
// Revision 0.1.0  1997/12/20  hopwood
// + Original version (based on cryptix.mime.Base64).
// + Deprecated methods removed.
// + Uses of LegacyString class changed to ISOLatin1.
// + Added MIMEFormatException.
// + Changed to extend TransferEncoding (methods are now non-static).
//
// $Endlog$
/*
 * Copyright (c) 1995-1997 Systemics Ltd
 * on behalf of the Cryptix Development Team.  All rights reserved.
 */

package cryptix.util.mime;
 
/**
 * This class provides methods for encoding and decoding data in MIME base64
 * format.
 * <p>
 * The input to the <code>encode</code> methods is always a byte array.
 * Strictly speaking the output represents a sequence of characters, but
 * since these characters are from a subset of both the Unicode and ASCII
 * character repertoires, it is possible to express the output either as
 * a String or as a byte array.
 * <p>
 * <b>References:</b>
 * <ol>
 *   <li> RFC 2045, <cite>Multipurpose Internet Mail Extensions (MIME) Part One,
 *        Format of Internet Message Bodies</cite>,
 *        "Section 6.8 Base64 Content-Transfer-Encoding,"
 *        <a href="http://www.imc.org/rfc2045">http://www.imc.org/rfc2045</a>
 * </ol>
 * <p>
 * <b>Copyright</b> &copy; 1995-1997
 * <a href="http://www.systemics.com/">Systemics Ltd</a> on behalf of the
 * <a href="http://www.systemics.com/docs/cryptix/">Cryptix Development Team</a>.
 * <br>All rights reserved.
 * <p>
 * <b>$Revision: 1.1.1.1 $</b>
 * @author  Jill Baker
 * @author  David Hopwood
 * @since   Cryptix 3.0.2
 */
public class Base64
{
    /**
     * This is the maximum number of input bytes represented on each line
     * (<em>not</em> the number of output characters).
     */
    private static final int LINEBREAK_LENGTH = 48;

    /**
     * A static array that maps 6-bit integers to a specific char.
     */
    protected final static char[] enc_table =
    {
    //   0   1   2   3   4   5   6   7
        'A','B','C','D','E','F','G','H', // 0 
        'I','J','K','L','M','N','O','P', // 1 
        'Q','R','S','T','U','V','W','X', // 2 
        'Y','Z','a','b','c','d','e','f', // 3 
        'g','h','i','j','k','l','m','n', // 4 
        'o','p','q','r','s','t','u','v', // 5 
        'w','x','y','z','0','1','2','3', // 6 
        '4','5','6','7','8','9','+','/'  // 7 
    };

    /**
     * A static array that maps ASCII code points to a 6-bit integer,
     * or -1 for an invalid code point.
     */
    protected final static byte[] dec_table = 
    { 
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
        -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
        15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
        -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
        41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };
 
    /**
     * Creates a Base64 transfer-encoding object.
     */
    public Base64() {}

    /**
     * Encodes <i>data</i> as a String using base64 encoding. Line breaks
     * in the output are represented as CR LF.
     *
     * @return the encoded string.
     */
    public String encode(byte[] data)
    {
        return ISOLatin1.toString(encodeAsByteArray(data));
    }

    /**
     * Encodes <i>data</i> as a byte array using base64 encoding. The characters
     * 'A'-'Z', 'a'-'z', '0'-'9', '+', '/', and '=' in the output are mapped to
     * their ASCII code points. Line breaks in the output are represented as
     * CR LF (codes 13 and 10).
     *
     * @return the encoded byte array.
     * @since Cryptix 2.2.2
     */
    public byte[] encodeAsByteArray(byte[] data)
    {
        int i = 0, j = 0;
        int len = data.length;
        int delta = len % 3;
        int outlen = ((len+LINEBREAK_LENGTH-1)/LINEBREAK_LENGTH)*2 +
            ((len+2)/3)*4 + (len == 0 ? 2 : 0);
        byte[] output = new byte[outlen];

        byte a, b, c;
        for (int count = len / 3; count > 0; count--)
        {
            a = data[i++];
            b = data[i++];
            c = data[i++];
            output[j++] = (byte) (enc_table[(a >>> 2) & 0x3F]); 
            output[j++] = (byte) (enc_table[((a << 4) & 0x30) + ((b >>> 4) & 0x0F)]); 
            output[j++] = (byte) (enc_table[((b << 2) & 0x3C) + ((c >>> 6) & 0x03)]); 
            output[j++] = (byte) (enc_table[c & 0x3F]); 

            if (i % LINEBREAK_LENGTH == 0) {
                output[j++] = (byte) '\r';
                output[j++] = (byte) '\n';
            }
        }

        if (delta == 1)
        {
            a = data[i++];
            output[j++] = (byte) (enc_table[(a >>> 2) & 0x3F]); 
            output[j++] = (byte) (enc_table[((a << 4) & 0x30)]); 
            output[j++] = (byte) '='; 
            output[j++] = (byte) '='; 
        }
        else if (delta == 2)
        {
            a = data[i++];
            b = data[i++];
            output[j++] = (byte) (enc_table[(a >>> 2) & 0x3F]); 
            output[j++] = (byte) (enc_table[((a << 4) & 0x30) + ((b >>> 4) & 0x0F)]); 
            output[j++] = (byte) (enc_table[((b << 2) & 0x3C)]); 
            output[j++] = (byte) '='; 
        }
        if (i == 0 || i % LINEBREAK_LENGTH != 0) {
            output[j++] = (byte) '\r';
            output[j++] = (byte) '\n';
        }

        if (j != outlen)
            throw new InternalError("Bug in Base64.java: incorrect length calculated for base64 output");

        return output;
    }

    /**
     * Decodes a byte array containing base64-encoded ASCII. Characters with
     * ASCII code points <= 32 (this includes whitespace and newlines) are
     * ignored.
     *
     * @return the decoded data.
     * @exception IllegalArgumentException if data contains invalid characters,
     *          i.e. not codes 0-32, 'A'-'Z', 'a'-'z', '+', '/'. or '=', or is
     *          incorrectly padded.
     */
    public byte[] decode(byte[] data) 
    {
        int padCount = 0;
        int i, len = data.length;
        int real_len = 0;

        for (i=len-1; i >= 0; --i)
        {
            if (data[i] > ' ')
                real_len++;

            if (data[i] == 0x3D) // ASCII '='
                padCount++;
        }

        if (real_len % 4 != 0)
            throw new IllegalArgumentException("Length not a multiple of 4");

        int ret_len = (real_len/4)*3 - padCount;
        byte[] ret = new byte[ret_len];

        i = 0;
        byte[] t = new byte[4];
        int output_index = 0;
        int j = 0;
        t[0] = t[1] = t[2] = t[3] = 0x3D; // ASCII '='
        while (i < len)
        {
            byte c = data[i++];
            if (c > ' ')
                t[j++] = c;

            if (j == 4)
            {
                output_index += decode(ret, output_index, t[0], t[1], t[2], t[3]);
                j = 0;
                t[0] = t[1] = t[2] = t[3] = 0x3D; // ASCII '='
            }
        }
        if (j > 0)
            decode(ret, output_index, t[0], t[1], t[2], t[3]);

        return ret;
    }

    /**
     * Decodes a base64-encoded String. Characters with ASCII code points <= 32
     * (this includes whitespace and newlines) are ignored.
     *
     * @return the decoded data.
     * @exception IllegalArgumentException if data contains invalid characters,
     *          i.e. not codes 0-32, 'A'-'Z', 'a'-'z', '+', '/'. or '=', or is
     *          incorrectly padded.
     */
    public byte[] decode(String msg) throws IllegalArgumentException
    {
        return decode(ISOLatin1.toByteArrayLossless(msg));
    }

    /**
     * Given a block of 4 encoded bytes <code>{ a, b, c, d }</code>, this method
     * decodes up to 3 bytes of output, and stores them starting at
     * <code>ret[ret_offset]</code>.
     *
     * @return the number of bytes converted.
     * @exception IllegalArgumentException if a, b, c or d contain invalid
     *          characters, or are incorrectly padded.
     */
    private int decode(byte[] ret, int ret_off, byte a, byte b, byte c, byte d)
    {
        byte da = dec_table[a];
        byte db = dec_table[b];
        byte dc = dec_table[c];
        byte dd = dec_table[d];

        if (da == -1 || db == -1 || (dc == -1 && c != 0x3D) || (dd == -1 && d != 0x3D))
            throw new IllegalArgumentException("Invalid character [" +
                (a & 0xFF) + ", " + (b & 0xFF) + ", " + (c & 0xFF) + ", " + (d & 0xFF) + "]");

        ret[ret_off++] = (byte) (da << 2 | db >>> 4);
        if (c == 0x3D) // ASCII '='
            return 1;
        ret[ret_off++] = (byte) (db << 4 | dc >>> 2);
        if (d == 0x3D) // ASCII '='
            return 2;
        ret[ret_off++] = (byte) (dc << 6 | dd);
        return 3;
    }
}