| I2NSF Working Group | J. Yang |
| Internet-Draft | J. Jeong |
| Intended status: Standards Track | J. Kim |
| Expires: April 25, 2019 | Sungkyunkwan University |
| October 22, 2018 |
Security Policy Translation in Interface to Network Security Functions
draft-yang-i2nsf-security-policy-translation-02
This document proposes a scheme of security policy translation (i.e., Security Policy Translator) in Interface to Network Security Functions (I2NSF) Framework. When I2NSF User delivers a high-level security policy for a security service, Security Policy Translator in Security Controller translates it into a low-level security policy for Network Security Functions (NSFs).
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This document defines a scheme of a security policy translation in Interface to Network Security Functions (I2NSF) Framework [RFC8329]. First of all, this document explains the necessity of a security policy translator (shortly called policy translator) in the I2NSF framework.
The policy translator resides in Security Controller in the I2NSF framework and translates a high-level security policy to a low-level security policy for Network Security Functions (NSFs). A high-level policy is specified by I2NSF User in the I2NSF framework and is delivered to Security Controller via Consumer-Facing Interface [consumer-facing-inf]. It is translated into a low-level policy by Policy Translator in Security Controller and is delivered to NSFs to execute the rules corresponding to the low-level policy via NSF-Facing Interface [nsf-facing-inf].
This document uses the terminology specified in [i2nsf-terminology] [RFC8329].
Security Controller acts as a coordinator between I2NSF User and NSFs. Also, Security Controller has capability information of NSFs that are registered via Registration Interface [registration-inf] by Developer's Management System [RFC8329]. As a coordinator, Security Controller needs to generate a low-level policy in the form of security rules intended by the high-level policy, which can be understood by the corresponding NSFs.
A high-level security policy is specified by RESTCONF/YANG [RFC8040][RFC6020], and a low-level security policy is specified by NETCONF/YANG [RFC6241][RFC6020]. The translation from a high-level security policy to the corresponding low-level security policy will be able to rapidly elevate I2NSF in real-world deployment. A rule in a high-level policy can include a broad target object, such as employees in a company for a security service (e.g., firewall and web filter). Such employees may be from human resource (HR) department, software engineering department, and advertisement department. A keyword of employee needs to be mapped to these employees from various departments. This mapping needs to be handled by a policy translator in a flexible way while understanding the intention of a policy specification. Let us consider the following two policies:
The above two sentences are examples of policies for blocking malicious websites. Both policies are for the same operation. However, NSF cannot understand the first policy, because the policy does not have any specified information for NSF. To set up the policy at an NSF, the NSF MUST receive at least the source IP address and website address for an operation. It means that the first sentence is NOT compatible for an NSF policy. Conversely, when I2NSF users request a security policy to the system, they never make a security policy like the second example. For generating a security policy like the second sentence, the user MUST know that the NSF needs to receive the specified information, source IP address and website address. It means that the user understands the NSF professionally, but there are not many professional users in a small size of company or at a residential area. In conclusion, the I2NSF user prefers to issue a security policy in the first sentence, but an NSF will require the same policy as the second sentence with specific information. Therefore, an advanced translation scheme of security policy is REQUIRED in I2NSF.
This document proposes an approach using Automata theory [Automata] for the policy tranlation, such as Deterministic Finite Automaton (DFA) and Context-Free Grammar (CFG). Note that Automata theory is the foundation of programming language and compiler. Thus, with this approach, I2NSF User can easily specify a high-level security policy that will be enforced into the corresponding NSFs with a compatibly low-level security policy with the help of Policy Translator. Also, for easy management, a modularized translator structure is proposed.
Common security policies are created by Extensible Markup Language (XML) [XML] files. A popular way to change the format of an XML file is to use an Extensible Stylesheet Language Transformation (XSLT) [XSLT] document. XSLT is an XML-based language to transform an input XML file into another output XML file. However, the use of XSLT makes it difficult to manage the policy translator and to handle the registration of new capabilities of NSFs. With the necessity for a policy translator, this document describes a policy translator based on Automata theory [Automata].
High-Level Policy
Security |
Controller V Consumer-Facing Interface
+------------------------+-------------------------+
| Policy | |
| Translator | |
| +---------------------+----------------------+ |
| | | | |
| | +-------+--------+ | |
| | | DFA-based | | |
| | | Data Extractor | | |
| | +-------+--------+ | |
| | | Extracted Data from | |
| | V High-Level Policy | |
| | +-----+-----+ +--------+ | |
| | | Data | <-> | NSF DB | | |
| | | Converter | +--------+ | |
| | +-----+-----+ | |
| | | Required Data for | |
| | V Target NSFs | |
| | +--------+---------+ | |
| | | CFG-based | | |
| | | Policy Generator | | |
| | +--------+---------+ | |
| | | | |
| +---------------------+----------------------+ |
| | |
+------------------------+-------------------------+
| NSF-Facing Interface
V
Low-Level Policy
Figure 1: The Overall Design of Policy Translator
Figure 1 shows the overall design for Policy Translator in Security Controller. There are three main components for Policy Translator: Data Extractor, Data Converter, and Policy Generator.
Extractor is a DFA-based module for extracting data from a high-level policy which I2NSF User delivered via Consumer-Facing Interface. Data Converter converts the extracted data to the capabilities of target NSFs for a low-level policy. It refers to NSF Database (DB) in order to convert an abstract subject or object into the corresponding concrete subject or object (e.g., IP address and website URL). Policy Generator generates a low-level policy which will execute the NSF capabilities from Converter.
+----------+
| accepter |
+----------+
| ^
<tag 1>| |</tag 1>
v |
+------------------------------------------------------+
| middle 1 |
+------------------------------------------------------+
| ^ | ^ | ^
<tag 2>| |</tag 2> <tag 3>| |</tag 3> ... <tag n>| |</tag n>
v | v | v |
... ... ...
+-------------+ +-------------+ +-------------+
| extractor 1 | | extractor 2 | ... | extractor m |
+-------------+ +-------------+ +-------------+
data:1 data:2 data:m
Figure 2: DFA Architecture of Data Extractor
Figure 2 shows a design for Data Extractor in the policy translator. If a high-level policy contains data along the hierarchical structure of the standard Consumer-Facing Interface YANG data model [consumer-facing-inf], data can be easily extracted using the state transition machine, such as DFA. The extracted data can be processed and used by an NSF to understand it. Extractor can be constructed by designing a DFA with the same hierarchical structure as a YANG data model.
After constructing a DFA, Data Extractor can extract all of data in the enterred high-level policy by using state transitions. Also, the DFA can easily detect the grammar errors of the high-level policy. The extracting algorithm of Data Extractor is as follows:
<I2NSF>
<name>block_web</name>
<cond>
<src>Son's_PC</src>
<dest>malicious</dest>
</cond>
<action>block<action>
</I2NSF>
Figure 3: The Example of High-level Policy
+----------+
| accepter |
+----------+
| ^
<I2NSF>| |</I2NSF>
v |
+------------------------------------------------------+
| middle 1 |
+------------------------------------------------------+
| ^ | ^ | ^
<name>| |</name> <cond>| |</cond> <action>| |</action>
v | v | v |
+-------------+ +----------------------+ +-------------+
| extractor 1 | | middle 2 | | extractor 4 |
+-------------+ +----------------------+ +-------------+
block_web | ^ | ^ block
<src>| |</src> <dest>| |</dest>
v | v |
+-------------+ +-------------+
| extractor 2 | | extractor 3 |
+-------------+ +-------------+
Son's_PC malicious
Figure 4: The Example of Data Extractor
To explain the Data Extractor process by referring to an example scenario, assume that Security Controller received a high-level policy for a web-filtering as shown in Figure 3. Then we can construct DFA-based Data Extractor by using the design as shown in Figure 2. Figure 4 shows the architecture of Data Extractor that is based on the architection in Figure 2 along with the input high-level policy in Figure 3. Data Extractor can automatically extract all of data in the high-level policy according to the following process: Figure 3, 'block_web', 'Son's_PC', 'malicious', and 'block'.
The above process is constructed by an extracting algorithm. After finishing all the steps of the above process, Data Extractor can extract all of data in
Since the translator is modularized into a DFA structure, a visual understanding is feasible. Also, The performance of Data Extractor is excellent compared to one-to-one searching of data for a particular field. In addition, the management is efficient because the DFA completely follows the hierarchy of Consumer-Facing Interface. If I2NSF User wants to modify the data model of a high-level policy, it only needs to change the connection of the relevant DFA node.
Every NSF has its own unique capabilities. The capabilities of an NSF are registered into Security Controller by a Developer's Management System, which manages the NSF, via Registration Interface. Therefore, Security Controller already has all information about the capabilities of NSFs. This means that Security Controller can find target NSFs with only the data (e.g., subject and object for a security policy) of the high-level policy by comparing the extracted data with all capabilities of each NSF. This search process for appropriate NSFs is called by policy provisioning, and it eliminates the need for I2NSF User to specify the target NSFs explicitly in a high-level security policy.
Data Converter selects target NSFs and converts the extracted data into the capabilities of selected NSFs. If Security Controller uses this data convertor, it can provide the policy provisioning function to the I2NSF User automatically. Thus, the translator design provides big benefits to the I2NSF Framework.
High-level Low-level
Policy Data Policy Data
+---------------+ +------------------------------+
| Rule Name | | Rule Name |
| +-----------+ | The Same value | +-------------------------+ |
| | block_web |-|------------------->|->| block_web | |
| +-----------+ | | +-------------------------+ |
| | | |
| Source | Conversion into | Source IPv4 |
| +-----------+ | User's IP address | +-------------------------+ |
| | Son's_PC |-|------------------->|->| [10.0.0.1, 10.0.0.3] | |
| +-----------+ | | +-------------------------+ |
| | | |
| Destination | Conversion into | URL Category |
| +-----------+ | malicious websites | +-------------------------+ |
| | malicious |-|------------------->|->| [harm.com, illegal.com] | |
| +-----------+ | | +-------------------------+ |
| | | |
| Action | Conversion into | Log Action Drop Action |
| +-----------+ | NSF Capability | +----------+ +----------+ |
| | block |-|------------------->|->| True | | True | |
| +-----------+ | | +----------+ +----------+ |
+---------------+ +------------------------------+
Figure 5: Example of Data Conversion
Figure 5 shows an example for describing a data conversion in Data Converter. High-level policy data MUST be converted into low-level policy data which are compatible with NSFs. If a ystem administrator attaches a database to Data Converter, it can convert contents by referring to the database with SQL queries. Data conversion in Figure 5 is based on the following list:
Log-keeper Low-level Web-filter
NSF Policy Data NSF
+-------------------+ +--------------------+ +-------------------+
| Rule Name | | Rule Name | | Rule Name |
| +--------------+ | | +--------------+ | | +--------------+ |
| | block_web |<-|<-|<-| block_web |->|->|->| block_web | |
| +--------------+ | | +--------------+ | | +--------------+ |
| | | | | |
| Source IPv4 | | Source IPv4 | | Source IPv4 |
| +--------------+ | | +--------------+ | | +--------------+ |
| | [10.0.0.1, |<-|<-|<-| [10.0.0.1, |->|->|->| [10.0.0.1, | |
| | 10.0.0.3] | | | | 10.0.0.3] | | | | 10.0.0.3] | |
| +--------------+ | | +--------------+ | | +--------------+ |
| | | | | |
| | | URL Category | | URL Category |
| | | +--------------+ | | +--------------+ |
| | | | [harm.com, |->|->|->| [harm.com, | |
| | | | illegal.com] | | | | illegal.com] | |
| | | +--------------+ | | +--------------+ |
| | | | | |
| Log Action | | Log Action | | |
| +--------------+ | | +--------------+ | | |
| | True |<-|<-|<-| True | | | |
| +--------------+ | | +--------------+ | | |
+-------------------+ | | | |
| Drop Action | | Drop Action |
| +--------------+ | | +--------------+ |
| | True |->|->|->| True | |
| +--------------+ | | +--------------+ |
+--------------------+ +-------------------+
Figure 6: Example of Policy Provisioning
Generator searches for proper NSFs which can cover all of capabilities in the high-level policy. Generator searches for target NSFs by comparing only NSF capabilities which is registered by Vendor Management System. This process is called by "policy provisioning" because Generator finds proper NSFs by using only the policy. If target NSFs are found by using other data which is not included in a user's policy, it means that the user already knows the specific knowledge of an NSF in the I2NSF Framework. Figure 6 shows an example of policy provisioning. In this example, log-keeper NSF and web-filter NSF are selected for covering capabilities in the security policy. All of capabilities can be covered by two selected NSFs.
Generator makes low-level security policies for each target NSF with the extracted data. We constructed Generator by using a Context-Free Grammar called CFG. CFG is a set of production rules which can describe all possible strings in a given formal language(e.g., programming language). The low-level policy also has its own language based on a YANG data model of NSF-Facing Interface. Thus, we can construct the productions based on the YANG data model. The productions that makes up the low-level security policy are categorized into two types, 'Content Production' and 'Structure Production'.
Content Production is for injecting data into low-level policies to be generated. A security manager(i.e., a person (or software) to make productions for security policies) can construct Content Productions in the form of an expression as the following productions:
Square brackets mean non-terminal state. If there are no non-terminal states, it means that the string is completely generated. When the duplication of content tag is allowed, the security manager adds the first production for a rule. If there is no need to allow duplication, the first production can be skipped because it is an optional production.
The second production is the main production for Content Production because it generates the tag which contains data for low-level policy. Last, the third production is for injecting data into a tag which is generated by the second production. If data is changed for an NSF, the security manager needs to change "only the third production" for data mapping in each NSF.
For example, if the security manager wants to express a low-level policy for source IP address, Content Production can be constructed in the following productions:
Structure Production is for grouping other tags into a hierarchy. The security manager can construct Structure Production in the form of an expression as the following production:
Structure Production can be expressed as a single production. The above production means to group other tags by the name of a tag which is called by 'struct_tag'. [prod_x] is a state for generating a tag which wants to be grouped by Structure Production. [prod_x] can be both Content Production and Structure Production. For example, if the security manager wants to express the low-level policy for the I2NSF tag, which is grouping 'name' and 'rules', Structure Production can be constructed as the following production where [cont_name] is the state for Content Production and [struct_rule] is the state for Structure Production.
The security manager can build a generator by combining the two productions which are described in Section 4.4.1 and Section 4.4.2. Figure 7 shows the CFG-based Generator construction of the web-filter NSF. It is constructed based on the NSF-Facing Interface Data Model in [nsf-facing-inf]. According to Figure 7, the security manager can express productions for each clause as in following CFG: Figure 8 shows the generated low-level policy where tab characters and newline characters are added.
Then, Generator generates a low-level policy by using the above CFG. The low-level policy is generated by the following process:
The last production has no non-terminal state, and the low-level policy is completely generated.
+-----------------------------------------------------+
| +----------+ +----------+ +----------+ +----------+ |
Content | | Rule | | Source | | URL | | Drop | |
Production | | Name | | IPv4 | | Category | | Action | |
| +-----+----+ +-----+----+ +----+-----+ +----+-----+ |
| | | | | |
+--------------------+-----------+--------------------+
| | | |
V V V V
+-------+------------+-----------+------------+-------+
| | | | | |
| | V V | |
| | +----------+ +----------+ | |
| | | Packet | | Payload | | |
| | | Clause | | Clause | | |
| | +-----+----+ +----+-----+ | |
| | | | | |
| | V V | |
| | +---------------+ | |
| | | Condition | | |
Structure | | | Clause | | |
Production | | +-------+-------+ | |
| | | | |
| | V V |
| | +----------------------+ |
| | | Rule Clause | |
| | +-----------+----------+ |
| | | |
| V V |
| +-----------------------------------------+ |
| | I2NSF Clause | |
| +--------------------+--------------------+ |
| | |
+--------------------------+--------------------------+
|
V
Low-Level Policy
Figure 7: Generator Construction for Web-Filter NSF
<I2NSF>
<rule-name>block_web</rule-name>
<rules>
<condition>
<packet>
<ipv4>10.0.0.1</ipv4>
<ipv4>10.0.0.3</ipv4>
</packet>
<payload>
<url>harm.com</url>
<url>illegal.com</url>
</payload>
</condition>
<action>drop</action>
</rules>
</I2NSF>
Figure 8: Example of Low-Level Policy
First, by showing a visualized translator structure, the security manager can handle various policy changes. Translator can be shown by visualizing DFA and Context-Free Grammar so that the manager can easily understand the structure of Policy Translator.
Second, if I2NSF User only keeps the hierarchy of the data model, I2NSF User can freely create high-level policies. In the case of DFA, data extraction can be performed in the same way even if the order of input is changed. The design of the policy translator is more flexible than the existing method that works by keeping the tag 's position and order exactly.
Third, the structure of Policy Translator can be updated even while Policy Translator is operating. Because Policy Translator is modularized, the translator can adapt to changes in the NSF capability while the I2NSF framework is running. The function of changing the translator's structure can be provided through Registration Interface.
There is no security concern in a security policy translator proposed in this document as long as the I2NSF interfaces (i.e., Consumer-Facing Interface, NSF-Facing Interface, and Registration Interface) are protected by secure communication channels.
This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea MSIT (Ministry of Science and ICT) (R-20160222-002755, Cloud based Security Intelligence Technology Development for the Customized Security Service Provisioning).
This work was supported in part by the MSIT under the ITRC (Information Technology Research Center) support program (IITP-2018-2017-0-01633) supervised by the IITP.
| [Automata] | Peter, L., "Formal Languages and Automata, 6th Edition", January 2016. |
| [RFC6020] | Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, October 2010. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. |
| [RFC8040] | Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", RFC 8040, January 2017. |
| [RFC8329] | Lopez, D., Lopez, E., Dunbar, L., Strassner, J. and R. Kumar, "Framework for Interface to Network Security Functions", RFC 8329, February 2018. |
| [XML] | W3C, "On Views and XML (Extensible Markup Language)", June 1999. |
| [consumer-facing-inf] | Jeong, J., Kim, E., Ahn, T., Kumar, R. and S. Hares, "I2NSF Consumer-Facing Interface YANG Data Model", Internet-Draft draft-ietf-i2nsf-consumer-facing-interface-dm-01, July 2018. |
| [i2nsf-terminology] | Hares, S., Strassner, J., Lopez, D., Xia, L. and H. Birkholz, "Interface to Network Security Functions (I2NSF) Terminology", Internet-Draft draft-ietf-i2nsf-terminology-06, July 2018. |
| [nsf-facing-inf] | Kim, J., Jeong, J., Park, J., Hares, S. and Q. Lin, "I2NSF Network Security Function-Facing Interface YANG Data Model", Internet-Draft draft-ietf-i2nsf-nsf-facing-interface-data-model-01, July 2018. |
| [registration-inf] | Hyun, S., Jeong, J., Roh, T., Wi, S. and J. Park, "I2NSF Registration Interface YANG Data Model", Internet-Draft draft-ietf-i2nsf-registration-dm-00, October 2018. |
| [XSLT] | W3C, "Extensible Stylesheet Language Transformations (XSLT) Version 1.0", November 1999. |
The following changes are made from draft-yang-i2nsf-security-policy-translation-01: