C语言实现 Base64 和 Base32 编解码
# C语言实现 Base64 和 Base32 编解码### Base64 编解码
#### 定义头文件 `base64.h`
```c
#ifndef _BASE64_H
#define _BASE64_H
#include <stdint.h>
static const char BASE64_MAP[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
static const uint8_t BASE64_REVERSE_MAP[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 62, 0, 0, 0, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 0, 0, 0, 0, 0, 0, 26, 27, 28, 29,
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
};
char *base64encode(const char *str, uint64_t len);
char *base64parse(const char *base64Str, uint64_t len);
#endif //_BASE64_H
```
#### 思路
`Base64`编码就是用64个可打印字符表示二进制数据。$$64 = 2^6$$，所以需要`6 Bit`来表示一个base64字符。一个字节`8 Bit`，6和8的最小公倍数是`24`。编码的过程中，以`3`个字节为一组转为`4`个base64字符，不足`3`个字节以`0`代替。为方便转换，以一个无符号32位整数(`uint32_t`)为中间载体。先由高位到低位将这三个字节填充到这个整数中，然后由高位到低位依次读取6位，获取对应数值的字母，共读取4次。如下图所示。解码的过程是上述的逆过程。
#### 实现
```c
#include "base64.h"
#include <stdlib.h>
#ifndef CEIL_POS
// 正数向上取整 CEIL_POS(2.345) => 3
#define CEIL_POS(X) (X > (uint64_t)(X) ? (uint64_t)(X+1) : (uint64_t)(X))
#endif
char *base64encode(const char *str, uint64_t len) {
uint64_t length = CEIL_POS(len * 4 / 3) + 1;
char *base64Chars = (char *) malloc(sizeof(char) * length);
uint64_t idx = 0;
for (uint64_t i = 0; i < len; i += 3) {
uint32_t byte1 = (uint8_t) str;
uint16_t byte2 = (i + 1 < len) ? (uint8_t) str : 0;
uint8_t byte3 = (i + 2 < len) ? (uint8_t) str : 0;
uint32_t triplet = (byte1 << 16) | (byte2 << 8) | byte3;
for (uint64_t j = 0; (j < 4) && (i + j * 0.75 < len); j++) {
base64Chars = BASE64_MAP[(triplet >> (6 * (3 - j))) & 0x3f];
idx++;
}
}
char paddingChar = BASE64_MAP;
if (paddingChar) {
while (idx % 4) {
base64Chars = paddingChar;
idx++;
}
}
base64Chars = 0;
return base64Chars;
}
char *base64parse(const char *base64Str, uint64_t len) {
while (base64Str == BASE64_MAP) {
len--;
}
uint64_t length = CEIL_POS(len * 3 / 4) + 1;
char *str = (char *) malloc(sizeof(char) * length);
uint64_t idx = 0;
for (uint64_t i = 0; i < len; i += 4) {
uint32_t triplet = 0;
for (uint8_t j = 0; j < 4; ++j) {
if (i + j < len) triplet = (triplet << 6) | ((uint8_t) BASE64_REVERSE_MAP] & 0x3f);
else triplet = triplet << 6;
}
for (uint8_t j = 0; (j < 3); ++j) {
str = (triplet >> (8 * (2 - j))) & 0xff;
idx++;
}
}
str = 0;
return str;
}
```
#### 使用
```c
// test_b64.c
#include <stdio.h>
#include <string.h>
#include "base64.h"
int main() {
char str1[] = "Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.";
char *encoded = base64encode(str1, strlen(str1));
puts(encoded);
char str2[] = "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=";
char *decoded = base64parse(str2, strlen(str2));
puts(decoded);
return 0;
}
```
### Base32 编解码
#### 定义头文件 `base32.h`
```c
#ifndef _BASE32_H
#define _BASE32_H
#include <stdint.h>
static const char BASE32_MAP[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=";
static const uint8_t BASE32_REVERSE_MAP[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 26, 27, 28, 29, 30, 31, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
};
char *base32encode(const char *str, uint64_t len);
char *base32parse(const char *base32Str, uint64_t len);
#endif //_BASE32_H
```
#### 思路
`Base32`编码就是用32个可打印字符表示二进制数据。$$32 = 2^5$$，所以需要`5 Bit`来表示一个base32字符。一个字节`8 Bit`，5和8的最小公倍数是`40`。编码的过程中，以`5`个字节为一组转为`8`个base32字符，不足`5`个字节以`0`代替。为方便转换，以一个无符号64位整数(`uint64_t`)为中间载体。先由高位到低位将这5个字节填充到这个整数中，然后由高位到低位依次读取5位，获取对应数值的字母，共读取8次。如下图所示。解码的过程是上述的逆过程。
#### 实现
```c
#include "base32.h"
#include <stdlib.h>
#ifndef CEIL_POS
#define CEIL_POS(X) (X > (uint64_t)(X) ? (uint64_t)(X+1) : (uint64_t)(X))
#endif
char *base32encode(const char *str, uint64_t len) {
uint64_t length = CEIL_POS(len * 8 / 5) + 1;
char *base32Chars = (char *) malloc(sizeof(char) * length);
uint64_t idx = 0;
for (uint64_t i = 0; i < len; i += 5) {
uint64_t byte1 = (uint8_t) str;
uint64_t byte2 = (i + 1 < len) ? (uint8_t) str : 0;
uint32_t byte3 = (i + 2 < len) ? (uint8_t) str : 0;
uint16_t byte4 = (i + 3 < len) ? (uint8_t) str : 0;
uint8_t byte5 = (i + 4 < len) ? (uint8_t) str : 0;
uint64_t quintuple = (byte1 << 32) | (byte2 << 24) | (byte3 << 16) | (byte4 << 8) | byte5;
for (uint64_t j = 0; (j < 8) && (i + j * 0.625 < len); j++) {
base32Chars = BASE32_MAP[(quintuple >> (5 * (7 - j))) & 0x1f];
idx++;
}
}
char paddingChar = BASE32_MAP;
if (paddingChar) {
while (idx % 8) {
base32Chars = paddingChar;
idx++;
}
}
base32Chars = 0;
return base32Chars;
}
char *base32parse(const char *base32Str, uint64_t len) {
while (base32Str == BASE32_MAP) {
len--;
}
uint64_t length = CEIL_POS(len * 5 / 8) + 1;
char *str = (char *) malloc(sizeof(char) * length);
uint64_t idx = 0;
for (uint64_t i = 0; i < len; i += 8) {
uint64_t quintuple = 0;
for (uint8_t j = 0; j < 8; ++j) {
if (i + j < len) quintuple = (quintuple << 5) | ((uint8_t) BASE32_REVERSE_MAP] & 0x1f);
else quintuple = quintuple << 5;
}
for (uint8_t j = 0; (j < 5); ++j) {
str = (quintuple >> (8 * (4 - j))) & 0xff;
idx++;
}
}
str = 0;
return str;
}
```
#### 使用
```c
// test_b32.c
#include <stdio.h>
#include <string.h>
#include "base32.h"
int main() {
char str1[] = "Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.";
char *encoded = base32encode(str1, strlen(str1));
puts(encoded);
char str2[] = "JVQW4IDJOMQGI2LTORUW4Z3VNFZWQZLEFQQG433UEBXW43DZEBRHSIDINFZSA4TFMFZW63RMEBRHK5BAMJ4SA5DINFZSA43JNZTXK3DBOIQHAYLTONUW63RAMZZG63JAN52GQZLSEBQW42LNMFWHGLBAO5UGSY3IEBUXGIDBEBWHK43UEBXWMIDUNBSSA3LJNZSCYIDUNBQXIIDCPEQGCIDQMVZHGZLWMVZGC3TDMUQG6ZRAMRSWY2LHNB2CA2LOEB2GQZJAMNXW45DJNZ2WKZBAMFXGIIDJNZSGKZTBORUWOYLCNRSSAZ3FNZSXEYLUNFXW4IDPMYQGW3TPO5WGKZDHMUWCAZLYMNSWKZDTEB2GQZJAONUG64TUEB3GK2DFNVSW4Y3FEBXWMIDBNZ4SAY3BOJXGC3BAOBWGKYLTOVZGKLQ=";
char *decoded = base32parse(str2, strlen(str2));
puts(decoded);
return 0;
}
``` zhukoov 发表于 2022-11-20 13:47
楼主的代码给了我很大的启发.得知Base64的译码表即破解.那么在传输过程中如何准确识别Base64呢?
这跟破解有什么关系？base64只是一种数据编码方式，不存在加密解密之说，又何来破解可言？就像十六进制和十进制之间的关系，只是一种数据表示形式而已，base64编码后的内容只是对人类来说不可直接看懂罢了。而且Base64码表也有统一的规范和标准，大多数情况用的都是通用的码表。 BrightXu 发表于 2022-11-21 01:20
这跟破解有什么关系？base64只是一种数据编码方式，不存在加密解密之说，又何来破解可言？就像十六进制和 ...
原来如此，谢谢楼主纠正，我还以为它本身是一种加密呢。现在我了解了，非常感谢。 学习了，这就去试一下 这都能行？ 膜拜大佬 感谢楼主！ 有些看不懂，先学习学习！ 学习了。下来找机会练一下手！ 自实现函数，学习学习 感谢楼主~~