Base58.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.codec.binary;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.function.BiConsumer;
/**
* Provides Base58 encoding and decoding as commonly used in cryptocurrency and blockchain applications.
* <p>
* 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
* commonly used in Bitcoin and other blockchain systems.
* </p>
* <p>
* Encoding and decoding produce results when EOF is signaled.
* </p>
* <p>
* Decoding rejects input longer than a configurable maximum ({@link #DEFAULT_MAX_DECODE_LENGTH} encoded bytes by default, see
* {@link Builder#setMaxDecodeLength(int)}). Encoding rejects binary input longer than {@link #DEFAULT_MAX_ENCODE_LENGTH} bytes by default; configure it with
* {@link Builder#setMaxEncodeLength(int)}. These limits apply to the total input across all chunks in an operation. Memory usage is proportional to the
* accumulated input and conversion output. Encoded output can exceed the decode limit; configure both limits appropriately for larger trusted values.
* </p>
* <p>
* This class is thread-safe for read operations but the Context object used during encoding/decoding should not be shared between threads.
* </p>
* <p>
* The Base58 alphabet is:
* </p>
*
* <pre>
* 123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
* </pre>
* <p>
* This excludes: {@code 0}, {@code I}, {@code O}, and {@code l}.
* </p>
*
* @see Base58InputStream
* @see Base58OutputStream
* @see <a href="https://datatracker.ietf.org/doc/html/draft-msporny-base58-03">The Base58 Encoding Scheme draft-msporny-base58-03</a>
* @since 1.22.0
*/
public class Base58 extends BaseNCodec {
/**
* Builds {@link Base58} instances with custom configuration.
*/
public static class Builder extends AbstractBuilder<Base58, Builder> {
private int maxDecodeLength = DEFAULT_MAX_DECODE_LENGTH;
private int maxEncodeLength = DEFAULT_MAX_ENCODE_LENGTH;
/**
* Constructs a new Base58 builder.
*/
public Builder() {
super(ENCODE_TABLE);
setDecodeTable(DECODE_TABLE);
}
/**
* Gets a new Base58 instance with the configured settings.
*
* @return A new Base58 codec.
*/
@Override
public Base58 get() {
return new Base58(this);
}
int getMaxDecodeLength() {
return maxDecodeLength;
}
int getMaxEncodeLength() {
return maxEncodeLength;
}
/**
* Sets the encode table and derives the matching decode table.
*
* @param encodeTable The encode table with exactly 58 unique entries, null resets to the default.
* @return {@code this} instance.
* @throws IllegalArgumentException Thrown if the encode table does not contain exactly 58 unique entries.
*/
@Override
public Base58.Builder setEncodeTable(final byte... encodeTable) {
super.setDecodeTableRaw(toDecodeTable(encodeTable));
return super.setEncodeTable(encodeTable);
}
/**
* Sets the line length to zero.
* <p>
* Base58 does not support line chunking. Zero or a negative value selects unchunked output.
* </p>
*
* @param lineLength The line length; must not be positive.
* @return {@code this} instance.
* @throws IllegalArgumentException Thrown if lineLength is positive.
* @since 1.23.0
*/
@Override
public Builder setLineLength(final int lineLength) {
if (lineLength > 0) {
throw new IllegalArgumentException("Base58 does not support line chunking.");
}
return super.setLineLength(lineLength);
}
/**
* Sets the maximum number of encoded bytes accepted by a single decode operation.
* <p>
* Defaults to {@link Base58#DEFAULT_MAX_DECODE_LENGTH}. Pass {@link Integer#MAX_VALUE} to effectively disable the limit for trusted input.
* </p>
*
* @param maxDecodeLength The maximum accepted encoded input length; must be positive.
* @return {@code this} instance.
* @throws IllegalArgumentException Thrown if maxDecodeLength is not positive.
* @since 1.23.0
*/
public Builder setMaxDecodeLength(final int maxDecodeLength) {
if (maxDecodeLength <= 0) {
throw new IllegalArgumentException("maxDecodeLength must be positive.");
}
this.maxDecodeLength = maxDecodeLength;
return this;
}
/**
* Sets the maximum number of binary bytes accepted by a single encode operation.
* <p>
* Defaults to {@link Base58#DEFAULT_MAX_ENCODE_LENGTH}. Pass {@link Integer#MAX_VALUE} to effectively disable the limit for trusted input.
* </p>
*
* @param maxEncodeLength The maximum accepted binary input length; must be positive.
* @return {@code this} instance.
* @throws IllegalArgumentException Thrown if maxEncodeLength is not positive.
* @since 1.23.0
*/
public Builder setMaxEncodeLength(final int maxEncodeLength) {
if (maxEncodeLength <= 0) {
throw new IllegalArgumentException("maxEncodeLength must be positive.");
}
this.maxEncodeLength = maxEncodeLength;
return this;
}
}
private static final BigInteger BASE = BigInteger.valueOf(58);
private static final int DECODING_TABLE_LENGTH = 256;
private static final int ENCODING_TABLE_LENGTH = 58;
/**
* The default maximum number of encoded bytes accepted by a single decode operation: {@value}.
* <p>
* Use {@link Builder#setMaxDecodeLength(int)} to raise (or effectively disable) the limit for trusted input.
* </p>
*
* @since 1.23.0
*/
public static final int DEFAULT_MAX_DECODE_LENGTH = 8192;
/**
* The default maximum number of binary bytes accepted by a single encode operation: {@value}.
* <p>
* Use {@link Builder#setMaxEncodeLength(int)} to raise (or effectively disable) the limit for trusted input.
* </p>
*
* @since 1.23.0
*/
public static final int DEFAULT_MAX_ENCODE_LENGTH = 8192;
/**
* Base58 alphabet: 123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
* (excludes: 0, I, O, l).
*/
private static final byte[] ENCODE_TABLE = {
'1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a',
'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'm', 'n', 'o', 'p', 'q', 'r', 's',
't', 'u', 'v', 'w', 'x', 'y', 'z'
};
/**
* This array is a lookup table that translates Unicode characters drawn from the "Base58 Alphabet"
* into their numeric equivalents (0-57). Characters that are not in the Base58 alphabet are marked
* with -1.
*/
// @formatter:off
private static final byte[] DECODE_TABLE = {
// 0 1 2 3 4 5 6 7 8 9 A B C D E F
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, -1, -1, -1, -1, -1, -1, // 30-3f '1'-'9' -> 0-8
-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')
22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, // 50-5a 'P'-'Z'
-1, -1, -1, -1, -1, // 5b-5f
-1, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, -1, 44, 45, 46, // 60-6f 'a'-'k', 'm'-'o' (skip 'l')
47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, // 70-7a 'p'-'z'
};
// @formatter:on
/**
* Creates a new Builder.
*
* <p>
* To configure a new instance, use a {@link Builder}. For example:
* </p>
*
* <pre>
* Base58 base58 = Base58.builder()
* .setMaxEncodeLength(4096)
* .get()
* </pre>
*
* @return A new Builder.
*/
public static Builder builder() {
return new Builder();
}
/**
* Calculates a decode table for a given encode table.
*
* @param encodeTable that is used to determine decode lookup table.
* @return A new decode table.
* @throws IllegalArgumentException Thrown if the encode table does not contain exactly 58 unique entries.
*/
private static byte[] calculateDecodeTable(final byte[] encodeTable) {
if (encodeTable.length != ENCODING_TABLE_LENGTH) {
throw new IllegalArgumentException("encodeTable must have exactly 58 entries.");
}
final byte[] decodeTable = new byte[DECODING_TABLE_LENGTH];
Arrays.fill(decodeTable, (byte) -1);
for (int i = 0; i < encodeTable.length; i++) {
final int encodedByte = encodeTable[i] & 0xff;
if (decodeTable[encodedByte] != -1) {
throw new IllegalArgumentException("encodeTable must not contain duplicate entries.");
}
decodeTable[encodedByte] = (byte) i;
}
return decodeTable;
}
/**
* Gets the decode table that matches the given encode table.
*
* @param encodeTable that is used to determine decode lookup table.
* @return The matching decode table.
*/
private static byte[] toDecodeTable(final byte[] encodeTable) {
final byte[] table = encodeTable != null ? encodeTable : ENCODE_TABLE;
if (Arrays.equals(table, ENCODE_TABLE)) {
return DECODE_TABLE;
}
return calculateDecodeTable(table);
}
/**
* The maximum number of encoded bytes accepted by a single decode operation.
*/
private final int maxDecodeLength;
/**
* The maximum number of binary bytes accepted by a single encode operation.
*/
private final int maxEncodeLength;
/**
* Constructs a Base58 codec used for encoding and decoding.
*/
public Base58() {
this(new Builder());
}
/**
* Constructs a Base58 codec used for encoding and decoding with custom configuration.
*
* @param builder The builder with custom configuration.
*/
public Base58(final Builder builder) {
super(builder);
this.maxDecodeLength = builder.getMaxDecodeLength();
this.maxEncodeLength = builder.getMaxEncodeLength();
}
private void checkLength(final int length, final int accumulatedLength, final int maximum, final String operation) {
if (length > maximum - accumulatedLength) {
throw new IllegalArgumentException("Base58 input exceeds the maximum " + operation + " length of " + maximum + " bytes.");
}
}
private void code(final byte[] array, final int offset, final int length, final Context context, final int maximum, final String operation,
final BiConsumer<byte[], Context> consumer) {
if (context.eof) {
return;
}
// Base58 needs the complete input before it can convert, so input is accumulated in context.buffer. The number of accumulated bytes
// is tracked in context.ibitWorkArea (otherwise unused by this codec) so the buffer can grow geometrically; reallocating an
// exact-size buffer per chunk would copy the whole accumulation on every chunk, making streaming quadratic in the input length.
if (length < 0) {
context.eof = true;
final byte[] accumulate = context.buffer = context.buffer == null ? EMPTY_BYTE_ARRAY :
context.buffer.length == context.ibitWorkArea ? context.buffer : Arrays.copyOf(context.buffer, context.ibitWorkArea);
if (accumulate.length > 0) {
consumer.accept(accumulate, context);
}
return;
}
final int accumulated = context.ibitWorkArea;
checkLength(length, accumulated, maximum, operation);
if (length > Integer.MAX_VALUE - 8 - accumulated) {
throw new IllegalArgumentException("Base58 input too large to accumulate: " + ((long) accumulated + length) + " bytes.");
}
final int required = accumulated + length;
byte[] buffer = context.buffer != null ? context.buffer : EMPTY_BYTE_ARRAY;
if (required > buffer.length) {
// Grow geometrically to amortize copying across chunks.
buffer = Arrays.copyOf(buffer, (int) Math.min(Math.max((long) buffer.length * 2, required), Math.min(maximum, Integer.MAX_VALUE - 8L)));
}
System.arraycopy(array, offset, buffer, accumulated, length);
context.buffer = buffer;
context.ibitWorkArea = required;
}
/**
* Converts Base58 encoded data to binary.
* <p>
* Uses 32-bit word arithmetic ({@code int[]} with {@code long} carry) to convert the Base58 string to binary data, avoiding {@link BigInteger} and its
* per-digit object allocation. Each Base58 digit is processed left-to-right using Horner's scheme: {@code value = value * 58 + digit}. An
* {@code wordsStart} cursor tracks the leftmost word that contains data, so the inner loop only touches the active portion of the work buffer. The active
* range grows linearly with the number of digits, so total conversion work is quadratic in the input length.
* </p>
* <p>
* At each word position the carry satisfies {@code carry ≤ 57 + 58 × (2³²−1) < 2⁴⁰}, which fits in a Java {@code long}.
* </p>
* <p>
* Leading characters that match the first Base58 alphabet entry each represent a leading zero byte in the output.
* </p>
*
* @param base58 The Base58 encoded data.
* @param context The context for this decoding operation.
* @throws IllegalArgumentException Thrown if the Base58 data contains invalid characters or is longer than the configured maximum decode length.
*/
private void convertFromBase58(final byte[] base58, final Context context) {
checkLength(base58.length, 0, maxDecodeLength, "decode");
final int zero = encodeTable[0] & 0xff;
// Count leading Base58 "zero" characters; each represents a leading zero byte in the output.
int leadingZeros = 0;
for (final byte b : base58) {
if ((b & 0xff) != zero) {
break;
}
leadingZeros++;
}
// Horner's scheme uses 32-bit words and a long carry, avoiding per-digit BigInteger allocation.
// wordsStart tracks the active word range, which grows linearly with the number of digits.
// Traversing this range for each digit makes conversion quadratic in the input length.
// At each word, carry <= 57 + 58 * (2^32 - 1) < 2^40, which fits in a long.
//
// Work buffer of 32-bit words, big-endian, right-aligned.
// Upper bound on decoded bytes is base58.length, so (base58.length+3)/4 words suffice.
final int numWords = base58.length + 3 >>> 2;
final int[] words = new int[numWords];
int wordsStart = numWords; // grows leftward as the value increases
for (int i = leadingZeros; i < base58.length; i++) {
final int b = base58[i] & 0xff;
final int digit = b < decodeTable.length ? decodeTable[b] : -1;
if (digit < 0) {
throw new IllegalArgumentException(String.format("Invalid character in Base58 string: 0x%02x", b));
}
// value = value * 58 + digit (Horner's scheme over 32-bit words)
long carry = digit;
for (int j = numWords - 1; j >= wordsStart; j--) {
carry += 58L * (words[j] & 0xFFFFFFFFL);
words[j] = (int) carry;
carry >>>= 32;
}
while (carry != 0) {
words[--wordsStart] = (int) carry;
carry >>>= 32;
}
}
// Expand active words to bytes (big-endian), then skip leading zero bytes.
final int activeWords = numWords - wordsStart;
final byte[] raw = new byte[activeWords * 4];
for (int i = 0; i < activeWords; i++) {
final int w = words[wordsStart + i];
raw[i * 4] = (byte) (w >>> 24);
raw[i * 4 + 1] = (byte) (w >>> 16);
raw[i * 4 + 2] = (byte) (w >>> 8);
raw[i * 4 + 3] = (byte) w;
}
int rawStart = 0;
while (rawStart < raw.length && raw[rawStart] == 0) {
rawStart++;
}
// Assemble result: leadingZeros zero bytes followed by the decoded value.
final int decodedLength = raw.length - rawStart;
final byte[] result = new byte[leadingZeros + decodedLength];
System.arraycopy(raw, rawStart, result, leadingZeros, decodedLength);
final byte[] buffer = ensureBufferSize(result.length, context);
System.arraycopy(result, 0, buffer, context.pos, result.length);
context.pos += result.length;
}
/**
* Converts accumulated binary data to Base58 encoding.
* <p>
* 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
* alphabet.
* </p>
*
* @param accumulate The binary data to encode.
* @param context The context for this encoding operation.
* @return The buffer containing the encoded data.
*/
private byte[] convertToBase58(final byte[] accumulate, final Context context) {
final StringBuilder base58 = getStringBuilder(accumulate);
final byte[] encodedBytes = new byte[base58.length()];
for (int i = 0; i < encodedBytes.length; i++) {
encodedBytes[i] = (byte) base58.charAt(encodedBytes.length - 1 - i);
}
final byte[] buffer = ensureBufferSize(encodedBytes.length, context);
System.arraycopy(encodedBytes, 0, buffer, context.pos, encodedBytes.length);
context.pos += encodedBytes.length;
return buffer;
}
/**
* Decodes the given Base58 encoded data.
* <p>
* This implementation accumulates data internally. When length is less than 0 (EOF), the accumulated data is converted from Base58 to binary.
* </p>
*
* @param array The byte array containing Base58 encoded data.
* @param offset The offset in the array to start from.
* @param length The number of bytes to decode, or negative to signal EOF.
* @param context The context for this decoding operation.
* @throws IllegalArgumentException Thrown when a problem is detected processing data.
*/
@Override
void decode(final byte[] array, final int offset, final int length, final Context context) {
code(array, offset, length, context, maxDecodeLength, "decode", this::convertFromBase58);
}
/**
* Encodes the given binary data as Base58.
* <p>
* This implementation accumulates data internally. When length is less than 0 (EOF), the accumulated data is converted to Base58.
* </p>
*
* @param array The byte array containing binary data to encode.
* @param offset The offset in the array to start from.
* @param length The number of bytes to encode, or negative to signal EOF.
* @param context The context for this encoding operation.
*/
@Override
void encode(final byte[] array, final int offset, final int length, final Context context) {
code(array, offset, length, context, maxEncodeLength, "encode", this::convertToBase58);
}
/**
* Gets the number of Base58 characters needed to encode the supplied array.
* <p>
* The length depends on the input bytes, including leading zeros. This method observes the configured maximum encode length.
* </p>
*
* @param array The binary input to encode.
* @return The number of Base58 characters that encoding the array produces.
* @throws IllegalArgumentException Thrown if the input exceeds the configured maximum encode length.
* @since 1.23.0
*/
@Override
public long getEncodedLength(final byte[] array) {
checkLength(array.length, 0, maxEncodeLength, "encode");
return getStringBuilder(array).length();
}
/**
* Gets the Base58 string representation of the given binary data.
* <p>
* 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
* character in the Base58 alphabet for each leading zero byte.
* </p>
*
* @param accumulate The binary data to convert.
* @return A StringBuilder with the Base58 representation (not yet reversed).
*/
private StringBuilder getStringBuilder(final byte[] accumulate) {
BigInteger value = new BigInteger(1, accumulate);
int leadingZeros = 0;
for (final byte b : accumulate) {
if (b != 0) {
break;
}
leadingZeros++;
}
final StringBuilder base58 = new StringBuilder();
while (value.signum() > 0) {
final BigInteger[] divRem = value.divideAndRemainder(BASE);
base58.append((char) (encodeTable[divRem[1].intValue()] & 0xff));
value = divRem[0];
}
final char zero = (char) (encodeTable[0] & 0xff);
for (int i = 0; i < leadingZeros; i++) {
base58.append(zero);
}
return base58;
}
/**
* Tests whether the {@code octet} is in the Base58 alphabet.
*
* @param value The value to test.
* @return {@code true} if the value is defined in the Base58 alphabet {@code false} otherwise.
*/
@Override
protected boolean isInAlphabet(final byte value) {
final int octet = value & 0xff;
return octet < decodeTable.length && decodeTable[octet] != -1;
}
}