ios自带的md5,sha1

相信很多在做校验的相关功能中，会用到md5,跟sha1的相关字符串校验，IOS中自带此功能，具体代码如下：

#include "CommonCrypto/CommonDigest.h"// 双引号替换成<>
static inline char hexChar(unsigned char c) {
    return c < 10 ? '0' + c : 'a' + c - 10;
}

static inline void hexString(unsigned char *from, char *to, NSUInteger length) {
    for (NSUInteger i = 0; i < length; ++i) {
        unsigned char c = from[i];
        unsigned char cHigh = c >> 4;
        unsigned char cLow = c & 0xf;
        to[2 * i] = hexChar(cHigh);
        to[2 * i + 1] = hexChar(cLow);
    }
    to[2 * length] = '