• (NSString)encryptMD5String:(NSString)string {
  return [string md5Encrypt];
  }

• (NSString *)md5Encrypt {

  const char *str = [self UTF8String];
  unsigned char result[CC_MD5_DIGEST_LENGTH];
  CC_MD5(str, strlen(str), result);
  NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];

  for(int i = 0; i<CC_MD5_DIGEST_LENGTH; i++) {
  [ret appendFormat:@"%02x",result[i]]; // X表示全大写，x表示全小写
  }
  return ret;

// const char *cStr = [self UTF8String];
// unsigned char result[16];
// CC_MD5( cStr, 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]
// ];
}