Source code
Description: source: package: org.apache.commons.codec.binary, class: Base58

    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.codec.binary;
    019
    020import java.math.BigInteger;
    021import java.util.Arrays;
    022import java.util.function.BiConsumer;
    023
    024/**
    025 * Provides Base58 encoding and decoding as commonly used in cryptocurrency and blockchain applications.
    026 * <p>
    027 * Base58 is a binary-to-text encoding scheme that uses a 58-character alphabet to encode data. It avoids characters that can be confused (0/O, I/l, +/) and is
    028 * commonly used in Bitcoin and other blockchain systems.
    029 * </p>
    030 * <p>
    031 * This implementation accumulates data internally until EOF is signaled, at which point the entire input is converted using BigInteger arithmetic. This is
    032 * necessary because Base58 encoding/decoding requires access to the complete data to properly handle leading zeros.
    033 * </p>
    034 * <p>
    035 * This class is thread-safe for read operations but the Context object used during encoding/decoding should not be shared between threads.
    036 * </p>
    037 * <p>
    038 * The Base58 alphabet is:
    039 * </p>
    040 *
    041 * <pre>
    042 * 123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
    043 * </pre>
    044 * <p>
    045 * This excludes: {@code 0}, {@code I}, {@code O}, and {@code l}.
    046 * </p>
    047 *
    048 * @see Base58InputStream
    049 * @see Base58OutputStream
    050 * @see <a href="https://datatracker.ietf.org/doc/html/draft-msporny-base58-03">The Base58 Encoding Scheme draft-msporny-base58-03</a>
    051 * @since 1.22.0
    052 */
    053public class Base58 extends BaseNCodec {
    054
    055    /**
    056     * Builds {@link Base58} instances with custom configuration.
    057     */
    058    public static class Builder extends AbstractBuilder<Base58, Builder> {
    059
    060        /**
    061         * Constructs a new Base58 builder.
    062         */
    063        public Builder() {
    064            super(ENCODE_TABLE);
    065            setDecodeTable(DECODE_TABLE);
    066        }
    067
    068        /**
    069         * Builds a new Base58 instance with the configured settings.
    070         *
    071         * @return A new Base58 codec.
    072         */
    073        @Override
    074        public Base58 get() {
    075            return new Base58(this);
    076        }
    077
    078        /**
    079         * Sets the encode table and derives the matching decode table.
    080         *
    081         * @param encodeTable The encode table with exactly 58 unique entries, null resets to the default.
    082         * @return {@code this} instance.
    083         * @throws IllegalArgumentException if the encode table does not contain exactly 58 unique entries.
    084         */
    085        @Override
    086        public Base58.Builder setEncodeTable(final byte... encodeTable) {
    087            super.setDecodeTableRaw(toDecodeTable(encodeTable));
    088            return super.setEncodeTable(encodeTable);
    089        }
    090    }
    091    private static final BigInteger BASE = BigInteger.valueOf(58);
    092
    093    private static final int DECODING_TABLE_LENGTH = 256;
    094    private static final int ENCODING_TABLE_LENGTH = 58;
    095
    096    /**
    097     * Base58 alphabet: 123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
    098     * (excludes: 0, I, O, l).
    099     */
    100    private static final byte[] ENCODE_TABLE = {
    101            '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
    102            'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a',
    103            'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'm', 'n', 'o', 'p', 'q', 'r', 's',
    104            't', 'u', 'v', 'w', 'x', 'y', 'z'
    105    };
    106    /**
    107     * This array is a lookup table that translates Unicode characters drawn from the "Base58 Alphabet"
    108     * into their numeric equivalents (0-57). Characters that are not in the Base58 alphabet are marked
    109     * with -1.
    110     */
    111    // @formatter:off
    112    private static final byte[] DECODE_TABLE = {
    113         //  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    114            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
    115            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
    116            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
    117            -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, -1, -1, -1, -1, -1, -1,          // 30-3f '1'-'9' -> 0-8
    118            -1, 9, 10, 11, 12, 13, 14, 15, 16, -1, 17, 18, 19, 20, 21, -1,  // 40-4f 'A'-'N', 'P'-'Z' (skip 'I' and 'O')
    119            22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,                     // 50-5a 'P'-'Z'
    120            -1, -1, -1, -1, -1,                                             // 5b-5f
    121            -1, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, -1, 44, 45, 46, // 60-6f 'a'-'k', 'm'-'o' (skip 'l')
    122            47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57,                     // 70-7a 'p'-'z'
    123    };
    124    // @formatter:on
    125
    126    /**
    127     * Creates a new Builder.
    128     *
    129     * <p>
    130     * To configure a new instance, use a {@link Builder}. For example:
    131     * </p>
    132     *
    133     * <pre>
    134     * Base58 base58 = Base58.builder()
    135     *   .setEncode(true)
    136     *   .get()
    137     * </pre>
    138     *
    139     * @return A new Builder.
    140     */
    141    public static Builder builder() {
    142        return new Builder();
    143    }
    144
    145    /**
    146     * Calculates a decode table for a given encode table.
    147     *
    148     * @param encodeTable that is used to determine decode lookup table.
    149     * @return A new decode table.
    150     * @throws IllegalArgumentException if the encode table does not contain exactly 58 unique entries.
    151     */
    152    private static byte[] calculateDecodeTable(final byte[] encodeTable) {
    153        if (encodeTable.length != ENCODING_TABLE_LENGTH) {
    154            throw new IllegalArgumentException("encodeTable must have exactly 58 entries.");
    155        }
    156        final byte[] decodeTable = new byte[DECODING_TABLE_LENGTH];
    157        Arrays.fill(decodeTable, (byte) -1);
    158        for (int i = 0; i < encodeTable.length; i++) {
    159            final int encodedByte = encodeTable[i] & 0xff;
    160            if (decodeTable[encodedByte] != -1) {
    161                throw new IllegalArgumentException("encodeTable must not contain duplicate entries.");
    162            }
    163            decodeTable[encodedByte] = (byte) i;
    164        }
    165        return decodeTable;
    166    }
    167
    168    /**
    169     * Gets the decode table that matches the given encode table.
    170     *
    171     * @param encodeTable that is used to determine decode lookup table.
    172     * @return The matching decode table.
    173     */
    174    private static byte[] toDecodeTable(final byte[] encodeTable) {
    175        final byte[] table = encodeTable != null ? encodeTable : ENCODE_TABLE;
    176        if (Arrays.equals(table, ENCODE_TABLE)) {
    177            return DECODE_TABLE;
    178        }
    179        return calculateDecodeTable(table);
    180    }
    181
    182    /**
    183     * Constructs a Base58 codec used for encoding and decoding.
    184     */
    185    public Base58() {
    186        this(new Builder());
    187    }
    188
    189    /**
    190     * Constructs a Base58 codec used for encoding and decoding with custom configuration.
    191     *
    192     * @param builder The builder with custom configuration.
    193     */
    194    public Base58(final Builder builder) {
    195        super(builder);
    196    }
    197
    198    private void code(final byte[] array, final int offset, final int length, final Context context, final BiConsumer<byte[], Context> consumer) {
    199        if (context.eof) {
    200            return;
    201        }
    202        if (length < 0) {
    203            context.eof = true;
    204            final byte[] accumulate = context.buffer = context.buffer != null ? context.buffer : EMPTY_BYTE_ARRAY;
    205            if (accumulate.length > 0) {
    206                consumer.accept(accumulate, context);
    207            }
    208            return;
    209        }
    210        final byte[] accumulate = context.buffer = context.buffer != null ? context.buffer : EMPTY_BYTE_ARRAY;
    211        final byte[] newAccumulated = new byte[accumulate.length + length];
    212        if (accumulate.length > 0) {
    213            System.arraycopy(accumulate, 0, newAccumulated, 0, accumulate.length);
    214        }
    215        System.arraycopy(array, offset, newAccumulated, accumulate.length, length);
    216        context.buffer = newAccumulated;
    217    }
    218
    219    /**
    220     * Converts Base58 encoded data to binary.
    221     * <p>
    222     * Uses BigInteger arithmetic to convert the Base58 string to binary data. Leading characters that match the first Base58 alphabet entry represent leading
    223     * zero bytes in the binary data.
    224     * </p>
    225     *
    226     * @param base58 The Base58 encoded data.
    227     * @param context    The context for this decoding operation.
    228     * @throws IllegalArgumentException if the Base58 data contains invalid characters.
    229     */
    230    private void convertFromBase58(final byte[] base58, final Context context) {
    231        BigInteger value = BigInteger.ZERO;
    232        int leadingZeros = 0;
    233        final int zero = encodeTable[0] & 0xff;
    234        for (final byte b : base58) {
    235            if ((b & 0xff) != zero) {
    236                break;
    237            }
    238            leadingZeros++;
    239        }
    240        BigInteger power = BigInteger.ONE;
    241        for (int i = base58.length - 1; i >= leadingZeros; i--) {
    242            final int b = base58[i] & 0xff;
    243            final int digit = b < decodeTable.length ? decodeTable[b] : -1;
    244            if (digit < 0) {
    245                throw new IllegalArgumentException(String.format("Invalid character in Base58 string: 0x%02x", b));
    246            }
    247            value = value.add(BigInteger.valueOf(digit).multiply(power));
    248            power = power.multiply(BASE);
    249        }
    250        final byte[] decoded = toUnsignedBytes(value);
    251        final byte[] result = new byte[leadingZeros + decoded.length];
    252        System.arraycopy(decoded, 0, result, leadingZeros, decoded.length);
    253        final byte[] buffer = ensureBufferSize(result.length, context);
    254        System.arraycopy(result, 0, buffer, context.pos, result.length);
    255        context.pos += result.length;
    256    }
    257
    258    /**
    259     * Converts accumulated binary data to Base58 encoding.
    260     * <p>
    261     * Uses BigInteger arithmetic to convert the binary data to Base58. Leading zeros in the binary data are represented as the first character in the Base58
    262     * alphabet.
    263     * </p>
    264     *
    265     * @param accumulate The binary data to encode.
    266     * @param context    The context for this encoding operation.
    267     * @return The buffer containing the encoded data.
    268     */
    269    private byte[] convertToBase58(final byte[] accumulate, final Context context) {
    270        final StringBuilder base58 = getStringBuilder(accumulate);
    271        final byte[] encodedBytes = new byte[base58.length()];
    272        for (int i = 0; i < encodedBytes.length; i++) {
    273            encodedBytes[i] = (byte) base58.charAt(encodedBytes.length - 1 - i);
    274        }
    275        final byte[] buffer = ensureBufferSize(encodedBytes.length, context);
    276        System.arraycopy(encodedBytes, 0, buffer, context.pos, encodedBytes.length);
    277        context.pos += encodedBytes.length;
    278        return buffer;
    279    }
    280
    281    /**
    282     * Decodes the given Base58 encoded data.
    283     * <p>
    284     * This implementation accumulates data internally. When length is less than 0 (EOF), the accumulated data is converted from Base58 to binary.
    285     * </p>
    286     *
    287     * @param array   The byte array containing Base58 encoded data.
    288     * @param offset  The offset in the array to start from.
    289     * @param length  The number of bytes to decode, or negative to signal EOF.
    290     * @param context The context for this decoding operation.
    291     */
    292    @Override
    293    void decode(final byte[] array, final int offset, final int length, final Context context) {
    294        code(array, offset, length, context, this::convertFromBase58);
    295    }
    296
    297    /**
    298     * Encodes the given binary data as Base58.
    299     * <p>
    300     * This implementation accumulates data internally. When length is less than 0 (EOF), the accumulated data is converted to Base58.
    301     * </p>
    302     *
    303     * @param array   The byte array containing binary data to encode.
    304     * @param offset  The offset in the array to start from.
    305     * @param length  The number of bytes to encode, or negative to signal EOF.
    306     * @param context The context for this encoding operation.
    307     */
    308    @Override
    309    void encode(final byte[] array, final int offset, final int length, final Context context) {
    310        code(array, offset, length, context, this::convertToBase58);
    311    }
    312
    313    /**
    314     * Builds the Base58 string representation of the given binary data.
    315     * <p>
    316     * Converts binary data to a BigInteger and divides by 58 repeatedly to get the Base58 digits. Handles leading zeros by counting them and appending the first
    317     * character in the Base58 alphabet for each leading zero byte.
    318     * </p>
    319     *
    320     * @param accumulate The binary data to convert.
    321     * @return A StringBuilder with the Base58 representation (not yet reversed).
    322     */
    323    private StringBuilder getStringBuilder(final byte[] accumulate) {
    324        BigInteger value = new BigInteger(1, accumulate);
    325        int leadingZeros = 0;
    326        for (final byte b : accumulate) {
    327            if (b != 0) {
    328                break;
    329            }
    330            leadingZeros++;
    331        }
    332        final StringBuilder base58 = new StringBuilder();
    333        while (value.signum() > 0) {
    334            final BigInteger[] divRem = value.divideAndRemainder(BASE);
    335            base58.append((char) (encodeTable[divRem[1].intValue()] & 0xff));
    336            value = divRem[0];
    337        }
    338        final char zero = (char) (encodeTable[0] & 0xff);
    339        for (int i = 0; i < leadingZeros; i++) {
    340            base58.append(zero);
    341        }
    342        return base58;
    343    }
    344
    345    /**
    346     * Returns whether or not the {@code octet} is in the Base58 alphabet.
    347     *
    348     * @param value The value to test.
    349     * @return {@code true} if the value is defined in the Base58 alphabet {@code false} otherwise.
    350     */
    351    @Override
    352    protected boolean isInAlphabet(final byte value) {
    353        final int octet = value & 0xff;
    354        return octet < decodeTable.length && decodeTable[octet] != -1;
    355    }
    356}