MD5算法，代码示例如下：
导入头文件：
#import <CommonCrypto/CommonDigest.h>
+ (NSString *)md5:(NSString *)inputString{
const char *cStr = [inputString UTF8String];
unsigned char result[CC_MD5_DIGEST_LENGTH];
CC_MD5(cStr, (unsigned int)strlen(cStr), result);
return [[NSString stringWithFormat:@"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
result[0], result[1], result[2], result[3],
result[4], result[5], result[6], result[7],
result[8], result[9], result[10], result[11],
result[12], result[13], result[14], result[15]
] lowercaseString];
}
