c++ - 将 base64 解码后的字符串转换为 unsigned char[32]

Question

我正在使用 ed25519-donna进行数字签名。

key 是unsigned char[32]，签名是unsigned char[64]。

我找到了 this base64 encoding , 但它只解码为 string.

我发现并尝试了很多技巧，但仍然不确定如何转换。

如何将 base64 解码的 string 转换为 unsigned char[32]？

Answer 1

格拉克斯:

在这里。享受吧!

#include <iostream>
#include <string>

struct BASE64_DEC_TABLE {
    signed char n[256];

    BASE64_DEC_TABLE() {
        for(int i=0; i<256; ++i)    n[i] = -1;
        for(unsigned char i='0'; i<='9'; ++i) n[i] = 52+i-'0';
        for(unsigned char i='A'; i<='Z'; ++i) n[i] = i-'A';
        for(unsigned char i='a'; i<='z'; ++i) n[i] = 26+i-'a';
        n['+'] = 62;
        n['/'] = 63;
    }
    int operator [] (unsigned char i) const { return n[i]; }
};

size_t Base64Decode(const std::string& source, void* pdest, size_t dest_size) {
    static const BASE64_DEC_TABLE b64table;
    if(!dest_size) return 0;
    const size_t len = source.length();
    int bc=0, a=0;
    char* const pstart = static_cast<char*>(pdest);
    char* pd = pstart;
    char* const pend = pd + dest_size;
    for(size_t i=0; i<len; ++i) {
        const int n = b64table[source[i]];
        if(n == -1) continue;
        a |= (n & 63) << (18 - bc);
        if((bc += 6) > 18) {
            *pd = a >> 16; if(++pd >= pend) return pd - pstart;
            *pd = a >> 8;  if(++pd >= pend) return pd - pstart;
            *pd = a;       if(++pd >= pend) return pd - pstart;
            bc = a = 0;
    }    }
    if(bc >= 8) {
        *pd = a >> 16; if(++pd >= pend) return pd - pstart;
        if(bc >= 16) *(pd++) = a >> 8;
    }
    return pd - pstart;
}

int main() {
    std::string base64_string = "AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8=";
    unsigned char decoded_data[32] = {0};

    Base64Decode(base64_string, decoded_data, sizeof(decoded_data));

    for(auto b : decoded_data) {
        std::cout << static_cast<unsigned>(b) << ' ';
    }
    std::cout << std::endl;
    return 0;
}