encode/decode Base-58 C++

I have built a base-58 encoder using this formula: https://www.youtube.com/watch?v=GedV3S9X89c&feature=youtu.be

Is there a smarter way to encode/decode with base-58?

I read somewhere that you need a bignum library which I use Boost for.

My goal is to convert between these two:

008D4D508F5BF2C28B20A3863405F05D3CD374B045E4B316E7
1Dt8ty59tU9LkrXG2ocWeSzKFAY8fu6jga

Which so easily this website do: http://lenschulwitz.com/base58

I know bitcoin source code have a base-58 encoder/decoder, but I do not know how to implement it successfully.

base58

dalslandan200

Posted 2018-06-21T10:42:42.443

Reputation: 45

this may help: https://bitcoin.stackexchange.com/questions/5829/how-do-i-base58-checked-encode-decode-an-address-in-c-what-does-normalize-l

– Zombie – 2018-06-21T11:12:34.107

Answers

I've used Base58 encoding/decoding many times. On the contrary, I hated using a BIGNUM library. So, I used Base-x's base conversion algorithm. (Make sure to respect the MIT license) It should be easy to translate it to any language.

const char * const ALPHABET =
    "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
const char ALPHABET_MAP[128] = {
    -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,  0,  1,  2,  3,  4,  5,  6,  7,  8, -1, -1, -1, -1, -1, -1,
    -1,  9, 10, 11, 12, 13, 14, 15, 16, -1, 17, 18, 19, 20, 21, -1,
    22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, -1, -1, -1, -1, -1,
    -1, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, -1, 44, 45, 46,
    47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, -1, -1, -1, -1, -1
};

// result must be declared: char result[len * 137 / 100];
int EncodeBase58(const unsigned char *bytes, int len, unsigned char result[]) {
    unsigned char digits[len * 137 / 100];
    int digitslen = 1;
    for (int i = 0; i < len; i++) {
        unsigned int carry = (unsigned int) bytes[i];
        for (int j = 0; j < digitslen; j++) {
            carry += (unsigned int) (digits[j]) << 8;
            digits[j] = (unsigned char) (carry % 58);
            carry /= 58;
        }
        while (carry > 0) {
            digits[digitslen++] = (unsigned char) (carry % 58);
            carry /= 58;
        }
    }
    int resultlen = 0;
    // leading zero bytes
    for (; resultlen < len && bytes[resultlen] == 0;)
        result[resultlen++] = '1';
    // reverse
    for (int i = 0; i < digitslen; i++)
        result[resultlen + i] = ALPHABET[digits[digitslen - 1 - i]];
    result[digitslen + resultlen] = 0;
    return digitslen + resultlen;
}

// result must be declared (for the worst case): char result[len * 2];
int DecodeBase58(
    const unsigned char *str, int len, unsigned char *result) {
    result[0] = 0;
    int resultlen = 1;
    for (int i = 0; i < len; i++) {
        unsigned int carry = (unsigned int) ALPHABET_MAP[str[i]];
        for (int j = 0; j < resultlen; j++) {
            carry += (unsigned int) (result[j]) * 58;
            result[j] = (unsigned char) (carry & 0xff);
            carry >>= 8;
        }
        while (carry > 0) {
            result[resultlen++] = (unsigned int) (carry & 0xff);
            carry >>= 8;
        }
    }

    for (int i = 0; i < len && str[i] == '1'; i++)
        result[resultlen++] = 0;

    // Poorly coded, but guaranteed to work.
    for (int i = resultlen - 1, z = (resultlen >> 1) + (resultlen & 1);
        i >= z; i--) {
        int k = result[i];
        result[i] = result[resultlen - i - 1];
        result[resultlen - i - 1] = k;
    }
    return resultlen;
}

MCCCS

Posted 2018-06-21T10:42:42.443

Reputation: 5 827

1Cool. What would be a quick example on how to use this code? – dalslandan200 – 2018-06-21T14:08:10.250

@dalslandan200 https://hastebin.com/ujepeduqus.cpp

– MCCCS – 2018-06-21T14:13:11.020

I used BIGNUM from openssl to encode hex with base58

 #include <string>
 #include <vector>
 #include <openssl/bn.h>

 string b58(const char *priv_hex)
 {
   char 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'};

BIGNUM *base58 = NULL;

BIGNUM *resultExp = BN_new();
BIGNUM *resultAdd = BN_new();
BIGNUM *resultRem = BN_new();
BN_CTX *bn_ctx = BN_CTX_new();

BN_dec2bn(&base58, "58");

string endresult;
vector<int> v;

BN_hex2bn( &resultAdd, priv_hex );

while( !BN_is_zero(resultAdd) ) {
    BN_div(resultAdd, resultRem, resultAdd, base58, bn_ctx);
    char *asdf = BN_bn2dec(resultRem);
    v.push_back(atoi(asdf));
}

for (int i = (int)v.size()-1; i >= 0; i--) {
    endresult = endresult + table[v[i]];
}

BN_free(resultAdd);
BN_free(resultExp);
BN_free(resultRem);
BN_CTX_free(bn_ctx);

return endresult;
}

and then use it like this:

string ttest = "008D4D508F5BF2C28B20A3863405F05D3CD374B045E4B316E7";
const char *phex = ttest.c_str();
string ret = b58(phex);
cout << ret << endl;

"Dt8ty59tU9LkrXG2ocWeSzKFAY8fu6jga"

Markus

Posted 2018-06-21T10:42:42.443

Reputation: 1

I have sill a problem with leading zeros. I try to fix this as well – Markus – 2018-11-18T21:50:14.983