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1、-通信类英文文献及翻译-第 9 页姓名：刘峻霖 班级：通信143班学号：2014101108附 录一、英文原文：Detecting Anomaly Trafc using Flow Data in the real VoIP networkI. INTRODUCTIONRecently, many SIP3/RTP4-based VoIP applications and services have appeared and their penetration ratio is gradually increasing due to the free or cheap call charge
2、and the easy subscription method. Thus, some of the subscribers to the PSTN service tend to change their home telephone services to VoIP products. For example, companies in Korea such as LG Dacom, Samsung Net- works, and KT have begun to deploy SIP/RTP-based VoIP services. It is reported that more t
3、han ve million users have subscribed the commercial VoIP services and 50% of all the users are joined in 2009 in Korea 1. According to IDC, it is expected that the number of VoIP users in US will increase to 27 millions in 2009 2. Hence, as the VoIP service becomes popular, it is not surprising that
4、 a lot of VoIP anomaly trafc has been already known 5. So, Most commercial service such as VoIP services should provide essential security functions regarding privacy, authentication, integrity and non-repudiation for preventing malicious trafc. Particu- larly, most of current SIP/RTP-based VoIP ser
5、vices supply the minimal security function related with authentication. Though secure transport-layer protocols such as Transport Layer Security (TLS) 6 or Secure RTP (SRTP) 7 have been standardized, they have not been fully implemented and deployed in current VoIP applications because of the overhe
6、ads of implementation and performance. Thus, un-encrypted VoIP packets could be easily sniffed and forged, especially in wireless LANs. In spite of authentication,the authentication keys such as MD5 in the SIP header could be maliciously exploited, because SIP is a text-based protocol and unencrypte
7、d SIP packets are easily decoded. Therefore, VoIP services are very vulnerable to attacks exploiting SIP and RTP. We aim at proposing a VoIP anomaly trafc detection method using the ow-based trafc measurement archi-tecture. We consider three representative VoIP anomalies called CANCEL, BYE Denial of
8、 Service (DoS) and RTP ooding attacks in this paper, because we found that malicious users in wireless LAN could easily perform these attacks in the real VoIP network. For monitoring VoIP packets, we employ the IETF IP Flow Information eXport (IPFIX) 9 standard that is based on NetFlow v9. This traf
9、c measurement method provides a exible and extensible template structure for various protocols, which is useful for observing SIP/RTP ows 10. In order to capture and export VoIP packets into IPFIX ows, we dene two additional IPFIX templates for SIP and RTP ows. Furthermore, we add four IPFIX elds to
10、 observe 802.11 packets which are necessary to detect VoIP source spoong attacks in WLANs.II. RELATED WORK8 proposed a ooding detection method by the Hellinger Distance (HD) concept. In 8, they have pre- sented INVITE, SYN and RTP ooding detection meth-ods. The HD is the difference value between a t
11、raining data set and a testing data set. The training data set collected trafc over n sampling period of duration t.The testing data set collected trafc next the training data set in the same period. If the HD is close to 1, this testing data set is regarded as anomaly trafc. For using this method,
12、they assumed that initial training data set did not have any anomaly trafc. Since this method was based on packet counts, it might not easily extended to detect other anomaly trafc except ooding. On the other hand, 11 has proposed a VoIP anomaly trafc detection method using Extended Finite State Mac
13、hine (EFSM). 11 has suggested INVITE ooding, BYE DoS anomaly trafc and media spamming detection methods. However, the state machine required more memory because it had to maintain each ow. 13 has presented NetFlow-based VoIP anomaly detection methods for INVITE, REGIS-TER, RTP ooding, and REGISTER/I
14、NVITE scan. How-ever, the VoIP DoS attacks considered in this paper were not considered. In 14, an IDS approach to detect SIP anomalies was developed, but only simulation results are presented. For monitoring VoIP trafc, SIPFIX 10 has been proposed as an IPFIX extension. The key ideas of the SIPFIX
15、are application-layer inspection and SDP analysis for carrying media session information. Yet, this paper presents only the possibility of applying SIPFIX to DoS anomaly trafc detection and prevention. We described the preliminary idea of detecting VoIP anomaly trafc in 15. This paper elaborates BYE
16、 DoS anomaly trafc and RTP ooding anomaly trafc detec-tion method based on IPFIX. Based on 15, we have considered SIP and RTP anomaly trafc generated in wireless LAN. In this case, it is possible to generate the similiar anomaly trafc with normal VoIP trafc, because attackers can easily extract norm
17、al user information from unencrypted VoIP packets. In this paper, we have extended the idea with additional SIP detection methods using information of wireless LAN packets. Furthermore, we have shown the real experiment results at the commercial VoIP network.III. THE VOIP ANOMALY TRAFFIC DETECTION M
18、ETHODA. CANCEL DoS Anomaly Trafc Detection As the SIP INVITE message is not usually encrypted, attackers could extract elds necessary to reproduce the forged SIP CANCEL message by snifng SIP INVITE packets, especially in wireless LANs. Thus, we cannot tell the difference between the normal SIP CANCE
19、L message and the replicated one, because the faked CANCEL packet includes the normal elds inferred from the SIP INVITE message. The attacker will perform the SIP CANCEL DoS attack at the same wireless LAN, because the purpose of the SIP CANCEL attack is to prevent the normal call estab-lishment whe
20、n a victim is waiting for calls. Therefore, as soon as the attacker catches a call invitation message for a victim, it will send a SIP CANCEL message, which makes the call establishment failed. We have generated faked SIP CANCEL message using sniffed a SIP INVITE message.Fields in SIP header of this
21、 CANCEL message is the same as normal SIP CANCEL message, because the attacker can obtain the SIP header eld from unencrypted normal SIP message in wireless LAN environment. Therefore it is impossible to detect the CANCEL DoS anomaly trafc using SIP headers, we use the different values of the wirele
22、ss LAN frame. That is, the sequence number in the 802.11 frame will tell the difference between a victim host and an attacker. We look into source MAC address and sequence number in the 802.11 MAC frame including a SIP CANCEL message as shown in Algorithm 1. We compare the source MAC address of SIP
23、CANCEL packets with that of the previously saved SIP INVITE ow. If the source MAC address of a SIP CANCEL ow is changed, it will be highly probable that the CANCEL packet is generated by a unknown user. However, the source MAC address could be spoofed. Regarding 802.11 source spoong detection, we em
24、ploy the method in 12 that uses sequence numbers of 802.11 frames. We calculate the gap between n-th and (n-1)-th 802.11 frames. As the sequence number eld in a 802.11 MAC header uses 12 bits, it varies from 0 to 4095. When we nd that the sequence number gap between a single SIP ow is greater than t
25、he threshold value of N that will be set from the experiments, we determine that the SIP host address as been spoofed for the anomaly trafc.B. BYE DoS Anomaly Trafc DetectionIn commercial VoIP applications, SIP BYE messages use the same authentication eld is included in the SIP IN-VITE message for s
26、ecurity and accounting purposes. How-ever, attackers can reproduce BYE DoS packets through snifng normal SIP INVITE packets in wireless LANs.The faked SIP BYE message is same with the normal SIP BYE. Therefore, it is difcult to detect the BYE DoS anomaly trafc using only SIP header information.After
27、 snifng SIP INVITE message, the attacker at the same or different subnets could terminate the normal in- progress call, because it could succeed in generating a BYE message to the SIP proxy server. In the SIP BYE attack, it is difcult to distinguish from the normal call termination procedure. That i
28、s, we apply the timestamp of RTP trafc for detecting the SIP BYE attack. Generally, after normal call termination, the bi-directional RTP ow is terminated in a bref space of time. However, if the call termination procedure is anomaly, we can observe that a directional RTP media ow is still ongoing,
29、whereas an attacked directional RTP ow is broken. Therefore, in order to detect the SIP BYE attack, we decide that we watch a directional RTP ow for a long time threshold of N sec after SIP BYE message. The threshold of N is also set from the experiments.Algorithm 2 explains the procedure to detect
30、BYE DoS anomal trafc using captured timestamp of the RTP packet. We maintain SIP session information between clients with INVITE and OK messages including the same Call-ID and 4-tuple (source/destination IP Address and port number) of the BYE packet. We set a time threshold value by adding Nsec to t
31、he timestamp value of the BYE message. The reason why we use the captured timestamp is that a few RTP packets are observed under 0.5 second. If RTP trafc is observed after the time threshold, this will be considered as a BYE DoS attack, because the VoIP session will be terminated with normal BYE mes
32、sages. C. RTP Anomaly Trafc Detection Algorithm 3 describes an RTP ooding detection method that uses SSRC and sequence numbers of the RTP header. During a single RTP session, typically, the same SSRC value is maintained. If SSRC is changed, it is highly probable that anomaly has occurred. In additio
33、n, if there is a big sequence number gap between RTP packets, we determine that anomaly RTP trafc has happened. As inspecting every sequence number for a packet is difcult, we calculate the sequence number gap using the rst, last, maximum and minimum sequence numbers. In the RTP header, the sequence
34、 number eld uses 16 bits from 0 to 65535. When we observe a wide sequence number gap in our algorithm, we consider it as an RTP ooding attack.IV. PERFORMANCE EVALUATIONA. Experiment EnvironmentIn order to detect VoIP anomaly trafc, we established an experimental environment as gure 1. In this envi-r
35、onment, we employed two VoIP phones with wireless LANs, one attacker, a wireless access router and an IPFIX ow collector. For the realistic performance evaluation, we directly used one of the working VoIP networks deployed in Korea where an 11-digit telephone number (070-XXXX-XXXX) has been assigned
36、 to a SIP phone.With wireless SIP phones supporting 802.11, we could make calls to/from the PSTN or cellular phones. In the wireless access router, we used two wireless LAN cards- one is to support the AP service, and the other is to monitor 802.11 packets. Moreover, in order to observe VoIP packets
37、 in the wireless access router, we modied nProbe 16, that is an open IPFIX ow generator, to create and export IPFIX ows related with SIP, RTP, and 802.11 information. As the IPFIX collector, we have modied libipx so that it could provide the IPFIX ow decoding function for SIP, RTP, and 802.11 templa
38、tes. We used MySQL for the ow DB.B. Experimental ResultsIn order to evaluate our proposed algorithms, we gen-erated 1,946 VoIP calls with two commercial SIP phones and a VoIP anomaly trafc generator. Table I shows our experimental results with precision, recall, and F-score that is the harmonic mean
39、 of precision and recall. In CANCEL DoS anomaly trafc detection, our algorithm represented a few false negative cases, which was related with the gap threshold of the sequence number in 802.11 MAC header. The average of the F-score value for detecting the SIP CANCEL anomaly is 97.69%.For BYE anomaly
40、 tests, we generated 755 BYE mes-sages including 118 BYE DoS anomalies in the exper-iment. The proposed BYE DoS anomaly trafc detec-tion algorithm found 112 anomalies with the F-score of 96.13%. If an RTP ow is terminated before the threshold, we regard the anomaly ow as a normal one. In this algori
41、thm, we extract RTP session information from INVITE and OK or session description messages using the same Call-ID of BYE message. It is possible not to capture those packet, resulting in a few false-negative cases. The RTP ooding anomaly trafc detection experiment for 810 RTP sessions resulted in th
42、e F score of 98%.The reason of false-positive cases was related with the sequence number in RTP header. If the sequence number of anomaly trafc is overlapped with the range of the normal trafc, our algorithm will consider it as normal trafc.V. CONCLUSIONSWe have proposed a ow-based anomaly trafc det
43、ec-tion method against SIP and RTP-based anomaly trafc in this paper. We presented VoIP anomaly trafc detection methods with ow data on the wireless access router. We used the IETF IPFIX standard to monitor SIP/RTP ows passing through wireless access routers, because its template architecture is eas
44、ily extensible to several protocols. For this purpose, we dened two new IPFIX templates for SIP and RTP trafc and four new IPFIX elds for 802.11 trafc. Using these IPFIX ow templates,we proposed CANCEL/BYE DoS and RTP ooding trafc detection algorithms. From experimental results on the working VoIP n
45、etwork in Korea, we showed that our method is able to detect three representative VoIP attacks on SIP phones. In CANCEL/BYE DoS anomaly trafcdetection method, we employed threshold values about time and sequence number gap for classcation of normal and abnormal VoIP packets. This paper has not been
46、mentioned the test result about suitable threshold values. For the future work, we will show the experimental result about evaluation of the threshold values for our detection method.二、英文翻译：交通流数据检测异常在真实的世界中使用的VoIP网络一 .介绍最近,许多SIP3,4基于服务器的VoIP应用和服务出现了,并逐渐增加他们的穿透比及由于自由和廉价的通话费且极易订阅的方法。因此,一些用户服务倾向于改变他们PS
47、TN家里电话服务VoIP产品。例如,公司在韩国LG、三星等Dacom网-作品、KT已经开始部署SIP / RTP-based VoIP服务。据报道,超过5百万的用户已订阅商业VoIP服务和50%的所有的用户都参加了2009年在韩国1。据IDC,预期该用户的数量将增加在我们的VoIP 2009年到27百万2。因此,随着VoIP服务变得很受欢迎,这是一点也不意外,很多人对VoIP异常交通已经知道5。所以,大多数商业服务如VoIP服务应该提供必要的安全功能对于隐私、认证、完整性和不可否认对于防止恶意的交通。Particu - larly,大多数的电流SIP / RTP-based VoIP服务提供最
48、小安全功能相关的认证。虽然安全transport-layer一类协议传输层安全(TLS)6或安全服务器(SRTP)7已经被修正,它们并没有被完全实施和部署在当前的VoIP应用的实施,因为过顶球和性能。因此,un-encrypted VoIP包可以轻易地嗅和伪造的,特别是在无线局域网。尽管的认证, 认证键,如MD5在SIP头可以狠的剥削,因为SIP是基于文本的协议和未加密的SIP包都很容易地被解码。因此,VoIP服务很容易被攻击开发SIP和服务器。我们的目标是在提出一个VoIP异常交通检测方法archi-tecture使用流转交通测量。我们认为有代表性的VoIP异常称为取消,再见拒绝服务(DoS)和快速的洪水袭击在本文中,因为我们发现恶意的用户在无线局域网可以很容易地履行这些袭击的真正的VoIP网络。VoIP包监测,利用IETF出口(IPFIX IP流信息)9标准的基础上,对NetFlow 9节。这一交通测量方法的研究提供了一个灵活的、可扩展的模板结构为各种各样的协议,有利于对观察SIP /服务器流10。摘要为获取和出口VoIP包成IPFIX流中,我们定义两个额外的IPFIX模板为SIP和快速流动。此外,我们加上四个IPFIX领域观察802.11包所必需的欺骗攻击的检测在WLANs VoIP来源。二.相关工作8提出了一种检测方法Hellinger洪水的距离