项目中需要用到3DES加密，进行与后台的接口数据交互。因为加密传参的过程是，先将字典类型的参数转换为JSONstring，所以将3DES加密扩展到string类型里面，调用的时候方便

extension String{
    //3des加解密
    func threeDESEncryptOrDecrypt(op: Int) -> String? {
        //op传1位加密，0为解密
        //CCOperation（kCCEncrypt）加密 1
        //CCOperation（kCCDecrypt) 解密 0

        var ccop = CCOperation()
        let key = "跟后台同志商量好的加密串"
        let iv = "偏移量"
        // Key
        let keyData: NSData = (key as NSString).data(using: String.Encoding.utf8.rawValue) as NSData!
        let keyBytes         = UnsafeRawPointer(keyData.bytes)
        
        // 加密或解密的内容
        var data: NSData = NSData()
        if op == 1 {
            ccop = CCOperation(kCCEncrypt)
            data  = (self as NSString).data(using: String.Encoding.utf8.rawValue) as NSData!
        }
        else {
            ccop = CCOperation(kCCDecrypt)
            data = NSData(base64Encoded: self, options: NSData.Base64DecodingOptions.ignoreUnknownCharacters)!
        }
        
        let dataLength    = size_t(data.length)
        let dataBytes     = UnsafeRawPointer(data.bytes)
        
        // 返回数据
        let cryptData    = NSMutableData(length: Int(dataLength) + kCCBlockSize3DES)
        let cryptPointer = UnsafeMutableRawPointer(cryptData!.mutableBytes)
        let cryptLength  = size_t(cryptData!.length)
        
        //  可选 的初始化向量
        let viData :NSData = (iv as NSString).data(using: String.Encoding.utf8.rawValue) as NSData!
        let viDataBytes    = UnsafeRawPointer(viData.bytes)
        
        // 特定的几个参数
        let keyLength              = size_t(kCCKeySize3DES)
        let operation: CCOperation = UInt32(ccop)
        let algoritm:  CCAlgorithm = UInt32(kCCAlgorithm3DES)
        let options:   CCOptions   = UInt32(kCCOptionPKCS7Padding)
        
        var numBytesCrypted :size_t = 0
        
        let cryptStatus = CCCrypt(operation, // 加密还是解密
            algoritm, // 算法类型
            options,  // 密码块的设置选项
            keyBytes, // 秘钥的字节
            keyLength, // 秘钥的长度
            viDataBytes, // 可选初始化向量的字节
            dataBytes, // 加解密内容的字节
            dataLength, // 加解密内容的长度
            cryptPointer, // output data buffer
            cryptLength,  // output data length available
            &numBytesCrypted) // real output data length
       
        if UInt32(cryptStatus) == UInt32(kCCSuccess) {
            cryptData!.length = Int(numBytesCrypted)
            if op == 1  {
                let base64cryptString = cryptData!.base64EncodedString(options: .lineLength64Characters)
                //返回加密的数据
                return base64cryptString
            }
            else {
                let base64cryptString = NSString(data: cryptData! as Data,  encoding: String.Encoding.utf8.rawValue) as String?
                //返回解密的数据
                return base64cryptString
            }
        } else {
            print("Error: \(cryptStatus)")
        }
        return nil
    }
}

//字典转换为jsonString
func getJsonStringFromDictionary(dictionary:NSDictionary) -> String {
    if (!JSONSerialization.isValidJSONObject(dictionary)) {
        print("无法解析出JSONString")
        return ""
    }
    let data : NSData! = try? JSONSerialization.data(withJSONObject: dictionary, options: []) as NSData!
    let JSONString = String(data: data as Data, encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue))
    return JSONString!
}

在开始调用之前有一点需要跟大家交代一下，转为3DES加密串之后传给后台或者接口后台返回参数的时候是base64位的，base64进行http请求的时候不能识别"/"、"+"、"="等特殊字符，需要转换一下

extension String{
//向后台传值的时候
func urlBase64EncodedString() -> String {
      let first = self.replacingOccurrences(of: "/", with: "_")
      let second = first.replacingOccurrences(of: "+", with: "-")
      let third = second.replacingOccurrences(of: "=", with: "")
      return third
}
//接收后台返回的值的时候
func urlBase64DecodedString() -> String {
      let first = NSMutableString(string: self)
      let mod4:Int = first.length % 4
      print(first.length)
      if(mod4>0){
          var str = "===="
          let start1 = str.index(str.startIndex, offsetBy: 0)
          str = str.substring(from: start1)
          let end1 = str.index(str.startIndex, offsetBy: 4-mod4)
          let sub5 = str.substring(to: end1)
          first.append(sub5)
      }
      let second = first.replacingOccurrences(of: "_", with: "/")
      let third = second.replacingOccurrences(of: "-", with: "+")
      return third
  }
}

最后调用后台接口传参的时候只需要将参数字典转化为jsonString,然后调用加密方法，赋值给后台规定的加密参数就可以了

var params:[String:Any] = [:]
let paramsString = getJsonStringFromDictionary(dictionary: paramsDic as NSDictionary)
params["parameter"] = paramsString.threeDESEncryptOrDecrypt(op: 1)!.urlBase64EncodedString() 

解密后台接口返回的数据并转为字典类型

extension String{
//解密加转换字典
  func toDecryptJsonDic() -> [String:Any]{
    let decryptJsonString = self.urlBase64DecodedString().threeDESEncryptOrDecrypt(op: 0)
    let decryptJsonDic = decryptJsonString?.toDictionary()
    if decryptJsonDic != nil {
        return decryptJsonDic!
    }
    return [String:Any].init()
  }
}
使用方式
返回值(jsonString). toDecryptJsonDic()