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Author Topic: base58 for private key  (Read 1005 times)
redPanda
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March 17, 2015, 06:23:55 PM
 #1

I would like to generate a WIF private key from a random 256 bit private key.
I use the private key given in "mastering Bitcoin" :
http://chimera.labs.oreilly.com/books/1234000001802/ch04.html#_implementing_keys_and_addresses_in_python
Example 4-4.
Code:
print "Private Key (hex) is: ", private_key
print "Private Key (decimal) is: ", decoded_private_key
# Convert private key to WIF format
wif_encoded_private_key = bitcoin.encode_privkey(decoded_private_key, 'wif')
print "Private Key (WIF) is: ", wif_encoded_private_key
the output is:
Code:
Private Key (hex) is:       3aba4162c7251c891207b747840551a71939b0de081f85c4e44cf7c13e41daa6
Private Key (decimal) is:  26563230048437957592232553826663696440606756685920117476832299673293013768870
Private Key (WIF) is:       5JG9hT3beGTJuUAmCQEmNaxAuMacCTfXuw1R3FCXig23RQHMr4K
Here is my code (with GMP: GNU Multiple Precision Arithmetic Library):
Code:
#include <iostream>
#include <string>
#include <algorithm>
#include <gmpxx.h>
using namespace std;

mpz_class base58ToBigNum (const string);
string bigNum2base58 (mpz_class);
int main (void)
{
    mpz_class bigNumber = 0;

    string privKeyHexa("3aba4162c7251c891207b747840551a71939b0de081f85c4e44cf7c13e41daa6");

    cout << endl << "privKeyHexa:" << privKeyHexa << endl;
    bigNumber = hexaToBigNum(privKeyHexa);
    cout << endl << "bigNumber: " << bigNumber << endl;

    string strBase58WIF = bigNum2base58(bigNumber);
    cout << "strBase58WIF : " << strBase58WIF << endl << endl;
   
    return 0;
}


// ex: A259BD07F
// = 10 * 16^8 + 2 * 16^7 + 5 * 16^6 + 9 * 16^5 + 11 * 16^4 + 13 * 16^3 + 0 * 16^2 + 7 * 16^1 + 15 * 16^0
// = 43580641407
mpz_class hexaToBigNum (const string myString)
{
    string hexa_digits = "0123456789ABCDEF";

    int index;
    mpz_class m = 0;
       
    for( size_t i = 0; i < myString.size(); i++ ) {
        m *= 16;
        index = hexa_digits.find(toupper(myString[i]));
        m += index;
    }
   
    return m;
}


string bigNum2base58 (mpz_class bigNumber)
{
    string b58_digits = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

    string base58string;
    string mycharString;

    mpz_class divisor(58), quotient, remainder;
    mpz_class x = bigNumber;
   
    while (x > 0) {
    mpz_fdiv_qr(quotient.get_mpz_t(), remainder.get_mpz_t(), x.get_mpz_t(), divisor.get_mpz_t());
    mycharString = string(1, b58_digits[mpz_get_ui(remainder.get_mpz_t())]);
    base58string.insert(0, mycharString);
    x = quotient;
    }
   
    return base58string;
}
The while loop in pseudocode is simply:
Code:
   while(x > 0)
       {
           (x, remainder) = divide(x, 58)
           output_string.append(b58_digits[remainder])
       }
and my output is
Code:
privKeyHexa:  3aba4162c7251c891207b747840551a71939b0de081f85c4e44cf7c13e41daa6
bigNumber:    26563230048437957592232553826663696440606756685920117476832299673293013768870
base58 :      4xFNZQXb9uCKNsupB4AsWmiyd1N7Rk1ibQ42GbytvTed
The base58 string (WIF) should start with 5.
Questions:
according to: mastering Bitcoin Table 4-1.
I have to add a version prefix of 0x80, but where ?
I have the same bigNumber than Example 4-4.
if I add 0x80 to privKeyHexa : 803aba4162c7251c89....
I have a different big number and a wrong result: f6Lnp6NkNmwag....
So where do I add this prefix ?
And do I have to do a checksum somewhere ?


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redPanda
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March 17, 2015, 07:34:09 PM
 #2

I found this tuto : https://en.bitcoin.it/wiki/Wallet_import_format
All the steps are well explained. I checked my code and my functions are right
except the output of the SHA256. So my question is now:
Are there different implementations of SHA256 ?
(see https://bitcointalk.org/index.php?topic=994088.0)
cr1776
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March 18, 2015, 12:12:32 AM
 #3

I found this tuto : https://en.bitcoin.it/wiki/Wallet_import_format
All the steps are well explained. I checked my code and my functions are right
except the output of the SHA256. So my question is now:
Are there different implementations of SHA256 ?
(see https://bitcointalk.org/index.php?topic=994088.0)

I answered you in the other thread, but the values you have for the SHA-256, are hashing the string (ASCII representation of the hex number) instead of the hex number itself.  Like hashing the number 120 vs the ASCII representation of "120", you'll get much different values.

If you do the hash on the number instead of the ASCII string, I suspect that things may fall into place quite quickly.  ;-)

Does that help?

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March 18, 2015, 03:38:26 PM
 #4

Yes, perfect
Thanks
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