Base58.java

import java.math.BigInteger;
import java.util.Arrays;

/**
 * @Author:yong.huang
 * @Date:2020-08-09 15:48
 */
public class Base58 {

    private static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
    private static int[] INDEXS = new int[128];

    static {
        Arrays.fill(INDEXS, -1);
        for (int i = 0; i < ALPHABET.length; i++) {
            INDEXS[ALPHABET[i]] = i;
        }
    }

    /**
     * 辗转相除
     *
     * @param input
     * @return
     */
    public static String encode(byte[] input) {
        char[] encoded = new char[input.length * 2];
        BigInteger x = new BigInteger(input);
        BigInteger base = BigInteger.valueOf(ALPHABET.length);
        BigInteger mod;

        int index = 0;
        while (x.compareTo(BigInteger.ZERO) > 0) {
            mod = x.mod(base);
            x = x.divide(base);
            encoded[index++] = ALPHABET[mod.intValue()];
        }

        // https://en.bitcoin.it/wiki/Base58Check_encoding#Version_bytes
        if (input[0] == 0x00) {
            encoded[index++] = ALPHABET[0];
        }

        // reverse
        for (int i = 0; i < index / 2; i++) {
            char tmp = encoded[i];
            encoded[i] = encoded[index - 1 - i];
            encoded[index - 1 - i] = tmp;
        }

        return new String(encoded, 0, index);
    }

    public static byte[] decode(String message) {
        BigInteger x = BigInteger.ZERO;
        BigInteger base = BigInteger.valueOf(ALPHABET.length);
        for (int i = 0; i < message.length(); i++) {
            char c = message.charAt(i);
            int digit = INDEXS[c];
            x = x.multiply(base).add(BigInteger.valueOf(digit));
        }
        byte[] out = x.toByteArray();

        if (message.charAt(0) == ALPHABET[0]) {
            byte[] tmp = new byte[out.length + 1];
            tmp[0] = 0x00;
            System.arraycopy(out, 0, tmp, 1, out.length);
            out = tmp;
        }

        return out;
    }

    public static void main(String[] args) {
        String address = "1CtymYoZEknYgehNT4vdDXedPY3GfPR5by";
        byte[] decode = decode(address);
        String encode = encode(decode);
        System.out.println(encode);
    }
}

base58

辗转相除；余数做下标到ALPHABET表中取对应的字母；

不使用数字 "0"，字母大写"O"，字母大写 "I"，和字母小写 "l"，以及 "+" 和 "/" 符号