C语言：从证书字符串中，解析出公钥

Question

最近遇到个需求，需要从证书字符串（不是文件，是一串字符串），解析出公钥(rsa_st格式)

即，我已经从证书中提取到公钥，只不过这个公钥是unsigned char *p_key格式的

不能进行后续的处理

我在调查时，发现有一位老哥用GO语言做出来了，但是分析了一下，似乎无法借鉴到C语言工程中
链接：https://blog.csdn.net/FFDreamer/article/details/122165634

所以想问问各位老哥，有没有知道相应的接口，或者处理方法
谢谢。

Answer 1

仅供参考：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define BASE64_VALUE_SZ 256
int     base64_value[BASE64_VALUE_SZ];
const unsigned char alphabet[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
class Base64Utility {
public:
    Base64Utility();
    int base64_encode(char *src, int srclen, char *dst, int tail);
    int base64_decode(char *src, int srclen, char *dst);
private:
    void base_64_init(void);
};
Base64Utility::Base64Utility() {
    base_64_init();
}
void Base64Utility::base_64_init(void) {
    int i;

    for (i = 0; i < BASE64_VALUE_SZ; i++) base64_value[i] = -1;
    for (i = 0; i < 64; i++) base64_value[(int) alphabet[i]] = i;
    base64_value['='] = 0;
}
int Base64Utility::base64_encode(char *src, int srclen, char *dst, int tail) {
    int     bits, char_count, len;
    char    *o_char, *lim, *o_lim;
    unsigned char   c;

    if ( !src || !dst) return 0;
    len = srclen;
    lim = src + len;
    o_char = dst;
    o_lim  = dst + (len*4)/3 + 1;
    char_count = 0;
    bits = 0;
    while ( (src < lim) && (o_char < o_lim)) {
        c = *(src++);
        bits += c;
        char_count++;
        if (char_count == 3) {
            *(o_char++) = alphabet[bits >> 18];
            *(o_char++) = alphabet[(bits >> 12) & 0x3f];
            *(o_char++) = alphabet[(bits >> 6) & 0x3f];
            *(o_char++) = alphabet[bits & 0x3f];
            bits = 0;
            char_count = 0;
        } else {
            bits <<= 8;
        }
    }
    if (char_count != 0) {
        bits <<= 16 - (8 * char_count);
        *(o_char++) = alphabet[bits >> 18];
        *(o_char++) = alphabet[(bits >> 12) & 0x3f];
        if (char_count == 1) {
            if (tail) {
                *(o_char++) = '=';
                *(o_char++) = '=';
            }
        } else {
            *(o_char++) = alphabet[(bits >> 6) & 0x3f];
            if (tail) {
                *(o_char++) = '=';
            }
        }
    }
    *(o_char) = 0;
    return strlen(dst);
}
int Base64Utility::base64_decode(char *src, int srclen, char *dst) {
    int j;
    unsigned int k;
    int c, base_result_sz;
    long val;

    if (!src || !dst) return 0;
    base_result_sz = srclen;
    val = c = 0;
    for (j = 0; *src; src++) {
        k = (int) *src % BASE64_VALUE_SZ;
        if (base64_value[k] < 0) continue;
        val <<= 6;
        val += base64_value[k];
        if (++c < 4) continue;
        dst[j++] = (char) (val >> 16);
        dst[j++] = (val >> 8) & 0xff;
        dst[j++] = val & 0xff;
        val = c = 0;
    }
    switch (c) {
        case 2://xxxxxx xx0000
            dst[j++] = (val >> 4) & 0xff;
        break;
        case 3://XXXXXX XXxxxx xxxx00
            dst[j++] = (char) (val >> 10);
            dst[j++] = (val >> 2) & 0xff;
        break;
    }
    return j;
}
Base64Utility b64u;
#define MAXLENS 1048576
#define MAXLEND 1405092 //1048576*1.34
char bufd[MAXLEND];
char bufs[MAXLENS];
FILE *fs,*fd;
int fsize;
int main(int argc,char *argv[]) {
    if (argc<4) {
    USE:
        printf("%s <-e|-E|-d> srcfile desfile\n",argv[0]);
        return 1;
    }
    if (stricmp(argv[1],"-e") && stricmp(argv[1],"-d")) goto USE;
    if (0==stricmp(argv[1],"-e")) {
        fs=fopen(argv[2],"rb");
        if (NULL==fs) {
            printf("Can not open file %s!\n",argv[2]);
            return 2;
        }
        fsize=fread(bufs,1,MAXLENS,fs);
        if (fsize<=0) {
            fclose(fs);
            printf("Can not read file %s!\n",argv[2]);
            return 3;
        }
        if (MAXLENS==fsize) printf("Warning: Up to %d bytes.\n",MAXLENS);
        fclose(fs);
        b64u.base64_encode(bufs,fsize,bufd,('E'==argv[2][1]));
        fd=fopen(argv[3],"w");
        if (NULL==fd) {
            printf("Can not create file %s!\n",argv[3]);
            return 4;
        }
        fprintf(fd,"%s",bufd);
        fclose(fd);
    } else {//0==stricmp(argv[1],"-d")
        fd=fopen(argv[2],"rb");
        if (NULL==fd) {
            printf("Can not open file %s!\n",argv[2]);
            return 2;
        }
        fsize=fread(bufd,1,MAXLEND,fd);
        if (fsize<=0) {
            fclose(fd);
            printf("Can not read file %s!\n",argv[2]);
            return 3;
        }
        if (MAXLEND==fsize) printf("Warning: Up to %d bytes.\n",MAXLEND);
        fclose(fd);
        fsize=b64u.base64_decode(bufd,fsize,bufs);
        fs=fopen(argv[3],"wb");
        if (NULL==fs) {
            printf("Can not create file %s!\n",argv[3]);
            return 4;
        }
        if (fsize!=(int)fwrite(bufs,1,fsize,fs)) {
            printf("Write %s error!\n",argv[3]);
            fclose(fs);
            return 5;
        }
        fclose(fs);
    }
    return 0;
}