Internet Architecture Board (IAB)                         D. Thaler, Ed.
Request for Comments: 6943                                     Microsoft
Category: Informational                                         May 2013
ISSN: 2070-1721
Internet Architecture Board (IAB)                         D. Thaler, Ed.
Request for Comments: 6943                                     Microsoft
Category: Informational                                         May 2013
ISSN: 2070-1721

Issues in Identifier Comparison for Security Purposes




Identifiers such as hostnames, URIs, IP addresses, and email addresses are often used in security contexts to identify security principals and resources. In such contexts, an identifier presented via some protocol is often compared using some policy to make security decisions such as whether the security principal may access the resource, what level of authentication or encryption is required, etc. If the parties involved in a security decision use different algorithms to compare identifiers, then failure scenarios ranging from denial of service to elevation of privilege can result. This document provides a discussion of these issues that designers should consider when defining identifiers and protocols, and when constructing architectures that use multiple protocols.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


This document is a product of the Internet Architecture Board (IAB) and represents information that the IAB has deemed valuable to provide for permanent record. It represents the consensus of the Internet Architecture Board (IAB). Documents approved for publication by the IAB are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

本文件是互联网体系结构委员会(IAB)的产品,代表IAB认为有价值提供永久记录的信息。它代表了互联网体系结构委员会(IAB)的共识。IAB批准发布的文件不适用于任何级别的互联网标准;见RFC 5741第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2013 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。

Table of Contents


   1. Introduction ....................................................3
      1.1. Classes of Identifiers .....................................5
      1.2. Canonicalization ...........................................5
   2. Identifier Use in Security Policies and Decisions ...............6
      2.1. False Positives and Negatives ..............................7
      2.2. Hypothetical Example .......................................8
   3. Comparison Issues with Common Identifiers .......................9
      3.1. Hostnames ..................................................9
           3.1.1. IPv4 Literals ......................................11
           3.1.2. IPv6 Literals ......................................12
           3.1.3. Internationalization ...............................13
           3.1.4. Resolution for Comparison ..........................14
      3.2. Port Numbers and Service Names ............................14
      3.3. URIs ......................................................15
           3.3.1. Scheme Component ...................................16
           3.3.2. Authority Component ................................16
           3.3.3. Path Component .....................................17
           3.3.4. Query Component ....................................17
           3.3.5. Fragment Component .................................17
           3.3.6. Resolution for Comparison ..........................18
      3.4. Email Address-Like Identifiers ............................18
   4. General Issues .................................................19
      4.1. Conflation ................................................19
      4.2. Internationalization ......................................20
      4.3. Scope .....................................................21
      4.4. Temporality ...............................................21
   5. Security Considerations ........................................22
   6. Acknowledgements ...............................................22
   7. IAB Members at the Time of Approval ............................23
   8. Informative References .........................................23
   1. Introduction ....................................................3
      1.1. Classes of Identifiers .....................................5
      1.2. Canonicalization ...........................................5
   2. Identifier Use in Security Policies and Decisions ...............6
      2.1. False Positives and Negatives ..............................7
      2.2. Hypothetical Example .......................................8
   3. Comparison Issues with Common Identifiers .......................9
      3.1. Hostnames ..................................................9
           3.1.1. IPv4 Literals ......................................11
           3.1.2. IPv6 Literals ......................................12
           3.1.3. Internationalization ...............................13
           3.1.4. Resolution for Comparison ..........................14
      3.2. Port Numbers and Service Names ............................14
      3.3. URIs ......................................................15
           3.3.1. Scheme Component ...................................16
           3.3.2. Authority Component ................................16
           3.3.3. Path Component .....................................17
           3.3.4. Query Component ....................................17
           3.3.5. Fragment Component .................................17
           3.3.6. Resolution for Comparison ..........................18
      3.4. Email Address-Like Identifiers ............................18
   4. General Issues .................................................19
      4.1. Conflation ................................................19
      4.2. Internationalization ......................................20
      4.3. Scope .....................................................21
      4.4. Temporality ...............................................21
   5. Security Considerations ........................................22
   6. Acknowledgements ...............................................22
   7. IAB Members at the Time of Approval ............................23
   8. Informative References .........................................23
1. Introduction
1. 介绍

In computing and the Internet, various types of "identifiers" are used to identify humans, devices, content, etc. This document provides a discussion of some security issues that designers should consider when defining identifiers and protocols, and when constructing architectures that use multiple protocols. Before discussing these security issues, we first give some background on some typical processes involving identifiers. Terms such as "identifier", "identity", and "principal" are used as defined in [RFC4949].


As depicted in Figure 1, there are multiple processes relevant to our discussion.


1. An identifier is first generated. If the identifier is intended to be unique, the generation process must include some mechanism, such as allocation by a central authority or verification among the members of a distributed authority, to help ensure uniqueness. However, the notion of "unique" involves determining whether a putative identifier matches any other identifier that has already been allocated. As we will see, for many types of identifiers, this is not simply an exact binary match.

1. 首先生成一个标识符。如果标识符是唯一的,那么生成过程必须包括一些机制,例如中央机构的分配或分布式机构成员之间的验证,以帮助确保唯一性。然而,“唯一”的概念涉及确定假定标识符是否与已分配的任何其他标识符匹配。正如我们将看到的,对于许多类型的标识符,这不仅仅是一个精确的二进制匹配。

After generating the identifier, it is often stored in two locations: with the requester or "holder" of the identifier, and with some repository of identifiers (e.g., DNS). For example, if the identifier was allocated by a central authority, the repository might be that authority. If the identifier identifies a device or content on a device, the repository might be that device.


2. The identifier is distributed, either by the holder of the identifier or by a repository of identifiers, to others who could use the identifier. This distribution might be electronic, but sometimes it is via other channels such as voice, business card, billboard, or other form of advertisement. The identifier itself might be distributed directly, or it might be used to generate a portion of another type of identifier that is then distributed. For example, a URI or email address might include a server name, and hence distributing the URI or email address also inherently distributes the server name.

2. 标识符由标识符持有者或标识符存储库分发给可以使用该标识符的其他人。这种分发可能是电子的,但有时是通过其他渠道,如语音、名片、广告牌或其他形式的广告。标识符本身可以直接分发,也可以用来生成另一种类型的标识符的一部分,然后再分发。例如,URI或电子邮件地址可能包含服务器名称,因此分发URI或电子邮件地址也会固有地分发服务器名称。

3. The identifier is used by some party. Generally, the user supplies the identifier, which is (directly or indirectly) sent to the repository of identifiers. The repository of identifiers must then attempt to match the user-supplied identifier with an identifier in its repository.

3. 该标识符由某一方使用。通常,用户提供标识符,该标识符(直接或间接)发送到标识符存储库。然后,标识符存储库必须尝试将用户提供的标识符与其存储库中的标识符相匹配。

For example, using an email address to send email to the holder of an identifier may result in the email arriving at the holder's email server, which has access to the mail stores.


                          |  Holder of |     1. Generation
                          | identifier +<---------+
                          +----+-------+          |
                               |                  | Match
                               |                  v/
                               |          +-------+-------+
                               +----------+ Repository of |
                               |          |  identifiers  |
                               |          +-------+-------+
               2. Distribution |                  ^\
                               |                  | Match
                               v                  |
                     +---------+-------+          |
                     |      User of    |          |
                     |    identifier   +----------+
                     +-----------------+    3. Use
                          |  Holder of |     1. Generation
                          | identifier +<---------+
                          +----+-------+          |
                               |                  | Match
                               |                  v/
                               |          +-------+-------+
                               +----------+ Repository of |
                               |          |  identifiers  |
                               |          +-------+-------+
               2. Distribution |                  ^\
                               |                  | Match
                               v                  |
                     +---------+-------+          |
                     |      User of    |          |
                     |    identifier   +----------+
                     +-----------------+    3. Use

Figure 1: Typical Identifier Processes


Another variation is where a user is given the identifier of a resource (e.g., a web site) to access securely, sometimes known as a "reference identifier" [RFC6125], and the server hosting the resource then presents its identity at the time of use. In this case, the user application attempts to match the presented identity against the reference identifier.


One key aspect is that the identifier values passed in generation, distribution, and use may all be in different forms. For example, an identifier might be exchanged in printed form at generation time, distributed to a user via voice, and then used electronically. As such, the match process can be complicated.


Furthermore, in many cases, the relationship between holder, repositories, and users may be more involved. For example, when a hierarchy of web caches exists, each cache is itself a repository of a sort, and the match process is usually intended to be the same as on the origin server.


Another aspect to keep in mind is that there can be multiple identifiers that refer to the same object (i.e., resource, human, device, etc.). For example, a human might have a passport number and a drivers license number, and an RFC might be available at multiple locations ( and In this document, we focus


on comparing two identifiers to see whether they are the same identifier, rather than comparing two different identifiers to see whether they refer to the same entity (although a few issues with the latter are touched on in several places, such as Sections 3.1.4 and 3.3.6).


1.1. Classes of Identifiers
1.1. 标识符类别

In this document, we will refer to the following classes of identifiers:


o Absolute: identifiers that can be compared byte-by-byte for equality. Two identifiers that have different bytes are defined to be different. For example, binary IP addresses are in this class.

o 绝对值:可以逐字节比较以获得相等值的标识符。具有不同字节的两个标识符被定义为不同的。例如,二进制IP地址在这个类中。

o Definite: identifiers that have a single well-defined comparison algorithm. For example, URI scheme names are required to be US-ASCII [USASCII] and are defined to match in a case-insensitive way; the comparison is thus definite, since there is a well-specified algorithm (Section 9.2.1 of [RFC4790]) on how to do a case-insensitive match among ASCII strings.

o 明确的:具有单个明确定义的比较算法的标识符。例如,URI方案名称必须是US-ASCII[USASCII],并且定义为以不区分大小写的方式匹配;因此,比较是确定的,因为有一个明确的算法(RFC4790的第9.2.1节)来说明如何在ASCII字符串之间进行不区分大小写的匹配。

o Indefinite: identifiers that have no single well-defined comparison algorithm. For example, human names are in this class. Everyone might want the comparison to be tailored for their locale, for some definition of "locale". In some cases, there may be limited subsets of parties that might be able to agree (e.g., ASCII users might all agree on a common comparison algorithm, whereas users of other Roman-derived scripts, such as Turkish, may not), but identifiers often tend to leak out of such limited environments.

o 不确定:没有单一明确定义的比较算法的标识符。例如,人名在这个类中。每个人都可能希望根据自己的语言环境,根据“语言环境”的某些定义进行比较。在某些情况下,可能会有有限的各方子集能够达成一致(例如,ASCII用户可能都同意一个通用的比较算法,而其他罗马衍生脚本(如土耳其)的用户可能不同意),但标识符往往会从这种有限的环境中泄漏出来。

1.2. Canonicalization
1.2. 规范化

Perhaps the most common algorithm for comparison involves first converting each identifier to a canonical form (a process known as "canonicalization" or "normalization") and then testing the resulting canonical representations for bitwise equality. In so doing, it is thus critical that all entities involved agree on the same canonical form and use the same canonicalization algorithm so that the overall comparison process is also the same.


Note that in some contexts, such as in internationalization, the terms "canonicalization" and "normalization" have a precise meaning. In this document, however, we use these terms synonymously in their more generic form, to mean conversion to some standard form.


While the most common method of comparison includes canonicalization, comparison can also be done by defining an equivalence algorithm, where no single form is canonical. However, in most cases, a canonical form is useful for other purposes, such as output, and so in such cases defining a canonical form suffices to define a comparison method.


2. Identifier Use in Security Policies and Decisions
2. 安全策略和决策中的标识符使用

Identifiers such as hostnames, URIs, and email addresses are used in security contexts to identify security principals (i.e., entities that can be authenticated) and resources as well as other security parameters such as types and values of claims. Those identifiers are then used to make security decisions based on an identifier presented via some protocol. For example:


o Authentication: a protocol might match a security principal's identifier to look up expected keying material and then match keying material.

o 身份验证:协议可能匹配安全主体的标识符以查找预期的密钥材料,然后匹配密钥材料。

o Authorization: a protocol might match a resource name against some policy. For example, it might look up an access control list (ACL) and then look up the security principal's identifier (or a surrogate for it) in that ACL.

o 授权:协议可能会根据某些策略匹配资源名称。例如,它可能会查找访问控制列表(ACL),然后在该ACL中查找安全主体的标识符(或其代理)。

o Accounting: a system might create an accounting record for a security principal's identifier or resource name, and then might later need to match a presented identifier to (for example) add new filtering rules based on the records in order to stop an attack.

o 记帐:系统可能会为安全主体的标识符或资源名称创建记帐记录,然后稍后可能需要匹配显示的标识符(例如)根据记录添加新的筛选规则以阻止攻击。

If the parties involved in a security decision use different matching algorithms for the same identifiers, then failure scenarios ranging from denial of service to elevation of privilege can result, as we will see.


This is especially complicated in cases involving multiple parties and multiple protocols. For example, there are many scenarios where some form of "security token service" is used to grant to a requester permission to access a resource, where the resource is held by a third party that relies on the security token service (see Figure 2). The protocol used to request permission (e.g., Kerberos or OAuth) may be different from the protocol used to access the resource (e.g., HTTP). Opportunities for security problems arise when two protocols define different comparison algorithms for the same type of identifier, or when a protocol is ambiguously specified and two endpoints (e.g., a security token service and a resource holder) implement different algorithms within the same protocol.


         | security |
         |  token   |
         | service  |
              | 1. supply credentials and
              |    get token for resource
              |                                             +--------+
         +----------+  2. supply token and access resource  |resource|
         |requester |=------------------------------------->| holder |
         +----------+                                       +--------+
         | security |
         |  token   |
         | service  |
              | 1. supply credentials and
              |    get token for resource
              |                                             +--------+
         +----------+  2. supply token and access resource  |resource|
         |requester |=------------------------------------->| holder |
         +----------+                                       +--------+

Figure 2: Simple Security Exchange


In many cases, the situation is more complex. With X.509 Public Key Infrastructure (PKIX) certificates [RFC6125], for example, the name in a certificate gets compared against names in ACLs or other things. In the case of web site security, the name in the certificate gets compared to a portion of the URI that a user may have typed into a browser. The fact that many different people are doing the typing, on many different types of systems, complicates the problem.


Add to this the certificate enrollment step, and the certificate issuance step, and two more parties have an opportunity to adjust the encoding, or worse, the software that supports them might make changes that the parties are unaware are happening.


2.1. False Positives and Negatives
2.1. 假阳性和假阴性

It is first worth discussing in more detail the effects of errors in the comparison algorithm. A "false positive" results when two identifiers compare as if they were equal but in reality refer to two different objects (e.g., security principals or resources). When privilege is granted on a match, a false positive thus results in an elevation of privilege -- for example, allowing execution of an operation that should not have been permitted otherwise. When privilege is denied on a match (e.g., matching an entry in a block/deny list or a revocation list), a permissible operation is denied. At best, this can cause worse performance (e.g., a cache miss or forcing redundant authentication) and at worst can result in a denial of service.


A "false negative" results when two identifiers that in reality refer to the same thing compare as if they were different, and the effects are the reverse of those for false positives. That is, when privilege is granted on a match, the result is at best worse performance and at worst a denial of service; when privilege is denied on a match, elevation of privilege results.


Figure 3 summarizes these effects.


                      | "Grant on match"       | "Deny on match"
       False positive | Elevation of privilege | Denial of service
       False negative | Denial of service      | Elevation of privilege
                      | "Grant on match"       | "Deny on match"
       False positive | Elevation of privilege | Denial of service
       False negative | Denial of service      | Elevation of privilege

Figure 3: Worst Effects of False Positives/Negatives


When designing a comparison algorithm, one can typically modify it to increase the likelihood of false positives and decrease the likelihood of false negatives, or vice versa. Which outcome is better depends on the context.


Elevation of privilege is almost always seen as far worse than denial of service. Hence, for URIs, for example, Section 6.1 of [RFC3986] states that "comparison methods are designed to minimize false negatives while strictly avoiding false positives".


Thus, URIs were defined with a "grant privilege on match" paradigm in mind, where it is critical to prevent elevation of privilege while minimizing denial of service. Using URIs in a "deny privilege on match" system can thus be problematic.


2.2. Hypothetical Example
2.2. 假设例子
   In this example, both security principals and resources are
   identified using URIs.  Foo Corp has paid for access to
   the Stuff service.  Foo Corp allows its employees to create accounts
   on the Stuff service.  Alice gets the account
   "" and Bob gets
   "".  It turns out, however, that
   Foo Corp's URI canonicalizer includes URI fragment components in
   comparisons whereas's does not, and Foo Corp does not
   disallow the # character in the account name.  So Chuck, who is a
   malicious employee of Foo Corp, asks to create an account at with the name alice#stuff.  Foo Corp's URI logic checks
   its records for accounts it has created with stuff and sees that
   there is no account with the name alice#stuff.  Hence, in its
   In this example, both security principals and resources are
   identified using URIs.  Foo Corp has paid for access to
   the Stuff service.  Foo Corp allows its employees to create accounts
   on the Stuff service.  Alice gets the account
   "" and Bob gets
   "".  It turns out, however, that
   Foo Corp's URI canonicalizer includes URI fragment components in
   comparisons whereas's does not, and Foo Corp does not
   disallow the # character in the account name.  So Chuck, who is a
   malicious employee of Foo Corp, asks to create an account at with the name alice#stuff.  Foo Corp's URI logic checks
   its records for accounts it has created with stuff and sees that
   there is no account with the name alice#stuff.  Hence, in its

records, it associates the account alice#stuff with Chuck and will only issue tokens good for use with "" to Chuck.


Chuck, the attacker, goes to a security token service at Foo Corp and asks for a security token good for "". Foo Corp issues the token, since Chuck is the legitimate owner (in Foo Corp's view) of the alice#stuff account. Chuck then submits the security token in a request to "".

攻击者Chuck前往Foo Corp的安全令牌服务,要求提供一个安全令牌,用于“". Foo Corp发行代币,因为Chuck是alice#stuff账户的合法所有者(在Foo Corp看来)。Chuck然后在请求中将安全令牌提交给“".

But uses a URI canonicalizer that, for the purposes of checking equality, ignores fragments. So when looks in the security token to see if the requester has permission from Foo Corp to access the given account, it successfully matches the URI in the security token, "", with the requested resource name "".

但是example.com使用一个URI规范化程序,为了检查相等性,它会忽略片段。因此,当example.com查找安全令牌以查看请求者是否具有Foo Corp访问给定帐户的权限时,它会成功匹配安全令牌中的URI,”,具有请求的资源名称".

Leveraging the inconsistencies in the canonicalizers used by Foo Corp and, Chuck is able to successfully launch an elevation-of-privilege attack and access Alice's resource.

Chuck利用Foo Corp和example.com使用的规范化程序中的不一致性,成功发起提升权限攻击并访问Alice的资源。

Furthermore, consider an attacker using a similar corporation, such as "foocorp" (or any variation containing a non-ASCII character that some humans might expect to represent the same corporation). If the resource holder treats them as different but the security token service treats them as the same, then elevation of privilege can occur in this scenario as well.


3. Comparison Issues with Common Identifiers
3. 与公共标识符的比较问题

In this section, we walk through a number of common types of identifiers and discuss various issues related to comparison that may affect security whenever they are used to identify security principals or resources. These examples illustrate common patterns that may arise with other types of identifiers.


3.1. Hostnames
3.1. 主机名

Hostnames (composed of dot-separated labels) are commonly used either directly as identifiers, or as components in identifiers such as in URIs and email addresses. Another example is in Sections 7.2 and 7.3 of [RFC5280] (and updated in Section 3 of [RFC6818]), which specify use in PKIX certificates.


In this section, we discuss a number of issues in comparing strings that appear to be some form of hostname.


It is first worth pointing out that the term "hostname" itself is often ambiguous, and hence it is important that any use clarify which definition is intended. Some examples of definitions include:


a. A Fully Qualified Domain Name (FQDN),

a. 完全限定域名(FQDN),

b. An FQDN that is associated with address records in the DNS,

b. 与DNS中的地址记录关联的FQDN,

c. The leftmost label in an FQDN, or

c. FQDN中最左边的标签,或

d. The leftmost label in an FQDN that is associated with address records.

d. FQDN中与地址记录关联的最左侧标签。

The use of different definitions in different places results in questions such as whether "example" and "" are considered equal or not, and hence it is important when writing new specifications to be clear about which definition is meant.


Section 3 of [RFC6055] discusses the differences between a "hostname" and a "DNS name", where the former is a subset of the latter by using a restricted set of characters (letters, digits, and hyphens). If one canonicalizer uses the "DNS name" definition whereas another uses a "hostname" definition, a name might be valid in the former but invalid in the latter. As long as invalid identifiers are denied privilege, this difference will not result in elevation of privilege.


Section 3.1 of [RFC1034] discusses the difference between a "complete" domain name, which ends with a dot (such as ""), and a multi-label relative name such as "" that assumes the root (".") is in the suffix search list. In most contexts, these are considered equal, but there may be issues if different entities in a security architecture have different interpretations of a relative domain name.


[IAB1123] briefly discusses issues with the ambiguity around whether a label will be "alphabetic" -- including, among other issues, how "alphabetic" should be interpreted in an internationalized environment -- and whether a hostname can be interpreted as an IP address. We explore this last issue in more detail below.


3.1.1. IPv4 Literals
3.1.1. IPv4文本

Section 2.1 of [RFC1123] states:


Whenever a user inputs the identity of an Internet host, it SHOULD be possible to enter either (1) a host domain name or (2) an IP address in dotted-decimal ("#.#.#.#") form. The host SHOULD check the string syntactically for a dotted-decimal number before looking it up in the Domain Name System.



This last requirement is not intended to specify the complete syntactic form for entering a dotted-decimal host number; that is considered to be a user-interface issue.


In specifying the inet_addr() API, the Portable Operating System Interface (POSIX) standard [IEEE-1003.1] defines "IPv4 dotted decimal notation" as allowing not only strings of the form "" but also allowing octal and hexadecimal, and addresses with less than four parts. For example, "10.0.258", "0xA000102", and "012.0x102" all represent the same IPv4 address in standard "IPv4 dotted decimal" notation. We will refer to this as the "loose" syntax of an IPv4 address literal.


In Section 6.1 of [RFC3493], getaddrinfo() is defined to support the same (loose) syntax as inet_addr():


If the specified address family is AF_INET or AF_UNSPEC, address strings using Internet standard dot notation as specified in inet_addr() are valid.


In contrast, Section 6.3 of the same RFC states, specifying inet_pton():


If the af argument of inet_pton() is AF_INET, the src string shall be in the standard IPv4 dotted-decimal form:




where "ddd" is a one to three digit decimal number between 0 and 255. The inet_pton() function does not accept other formats (such as the octal numbers, hexadecimal numbers, and fewer than four numbers that inet_addr() accepts).


As shown above, inet_pton() uses what we will refer to as the "strict" form of an IPv4 address literal. Some platforms also use the strict form with getaddrinfo() when the AI_NUMERICHOST flag is passed to it.


Both the strict and loose forms are standard forms, and hence a protocol specification is still ambiguous if it simply defines a string to be in the "standard IPv4 dotted decimal form". And, as a result of these differences, names such as "10.11.12" are ambiguous as to whether they are an IP address or a hostname, and even "" can be ambiguous because of the "SHOULD" in the above text from RFC 1123, making it optional whether to treat it as an address or a DNS name.

严格形式和松散形式都是标准形式,因此,如果协议规范只是将字符串定义为“标准十进制形式”,那么它仍然是不明确的。而且,由于这些差异,诸如“10.11.12”之类的名称在它们是IP地址还是主机名方面模棱两可,甚至“”也可能模棱两可,因为RFC 1123的上述文本中有“应该”,这使得将其视为地址还是DNS名称是可选的。

Protocols and data formats that can use addresses in string form for security purposes need to resolve these ambiguities. For example, for the host component of URIs, Section 3.2.2 of [RFC3986] resolves the first ambiguity by only allowing the strict form and resolves the second ambiguity by specifying that it is considered an IPv4 address literal. New protocols and data formats should similarly consider using the strict form rather than the loose form in order to better match user expectations.


A string might be valid under the "loose" definition but invalid under the "strict" definition. As long as invalid identifiers are denied privilege, this difference will not result in elevation of privilege. Some protocols, however, use strings that can be either an IP address literal or a hostname. Such strings are at best Definite identifiers, and often turn out to be Indefinite identifiers. (See Section 4.1 for more discussion.)


3.1.2. IPv6 Literals
3.1.2. IPv6文本

IPv6 addresses similarly have a wide variety of alternate but semantically identical string representations, as defined in Section 2.2 of [RFC4291] and Section 2 of [RFC6874]. As discussed in Section 3.2.5 of [RFC5952], this fact causes problems in security contexts if comparison (such as in PKIX certificates) is done between strings rather than between the binary representations of addresses.


[RFC5952] specified a recommended canonical string format as an attempt to solve this problem, but it may not be ubiquitously supported at present. And, when strings can contain non-ASCII characters, the same issues (and more, since hexadecimal and colons are allowed) arise as with IPv4 literals.


Whereas (binary) IPv6 addresses are Absolute identifiers, IPv6 address literals are Definite identifiers, since string-to-address conversion for IPv6 address literals is unambiguous.


3.1.3. Internationalization
3.1.3. 国际化

The IETF policy on character sets and languages [RFC2277] requires support for UTF-8 in protocols, and as a result many protocols now do support non-ASCII characters. When a hostname is sent in a UTF-8 field, there are a number of ways it may be encoded. For example, hostname labels might be encoded directly in UTF-8, or they might first be Punycode-encoded [RFC3492] or even percent-encoded from UTF-8.


For example, in URIs, Section 3.2.2 of [RFC3986] specifically allows for the use of percent-encoded UTF-8 characters in the hostname as well as the use of Internationalized Domain Names in Applications (IDNA) encoding [RFC3490] using the Punycode algorithm.


Percent-encoding is unambiguous for hostnames, since the percent character cannot appear in the strict definition of a "hostname", though it can appear in a DNS name.


Punycode-encoded labels (or "A-labels"), on the other hand, can be ambiguous if hosts are actually allowed to be named with a name starting with "xn--", and false positives can result. While this may be extremely unlikely for normal scenarios, it nevertheless provides a possible vector for an attacker.


A hostname comparator thus needs to decide whether a Punycode-encoded label should or should not be considered a valid hostname label, and if so, then whether it should match a label encoded in some other form such as a percent-encoded Unicode label (U-label).


For example, Section 3 of "Transport Layer Security (TLS) Extensions: Extension Definitions" [RFC6066] states:


"HostName" contains the fully qualified DNS hostname of the server, as understood by the client. The hostname is represented as a byte string using ASCII encoding without a trailing dot. This allows the support of internationalized domain names through the use of A-labels defined in [RFC5890]. DNS hostnames are case-insensitive. The algorithm to compare hostnames is described in [RFC5890], Section


For some additional discussion of security issues that arise with internationalization, see Section 4.2 and [TR36].


3.1.4. Resolution for Comparison
3.1.4. 用于比较的分辨率

Some systems (specifically Java URLs [JAVAURL]) use the rule that if two hostnames resolve to the same IP address(es) then the hostnames are considered equal. That is, the canonicalization algorithm involves name resolution with an IP address being the canonical form.


For example, if resolution was done via DNS, and DNS contained:

例如,如果通过DNS进行解析,并且DNS包含: IN A CNAME IN A。在10.0.0.6示例.net中。CNAME。。在10.0.0.6中

then the algorithm might treat all three names as equal, even though the third name might refer to a different entity.


With the introduction of dynamic IP addresses; private IP addresses; multiple IP addresses per name; multiple address families (e.g., IPv4 vs. IPv6); devices that roam to new locations; commonly deployed DNS tricks that result in the answer depending on factors such as the requester's location and the load on the server whose address is returned; etc., this method of comparison cannot be relied upon. There is no guarantee that two names for the same host will resolve the name to the same IP addresses; nor that the addresses resolved refer to the same entity, such as when the names resolve to private IP addresses; nor even that the system has connectivity (and the willingness to wait for the delay) to resolve names at the time the answer is needed. The lifetime of the identifier, and of any cached state from a previous resolution, also affects security (see Section 4.4).


In addition, a comparison mechanism that relies on the ability to resolve identifiers such as hostnames to other identifiers such as IP addresses leaks information about security decisions to outsiders if these queries are publicly observable. (See [PRIVACY-CONS] for a deeper discussion of information disclosure.)


Finally, it is worth noting that resolving two identifiers to determine if they refer to the same entity can be thought of as a use of such identifiers, as opposed to actually comparing the identifiers themselves, which is the focus of this document.


3.2. Port Numbers and Service Names
3.2. 端口号和服务名称

Port numbers and service names are discussed in depth in [RFC6335]. Historically, there were port numbers, service names used in SRV records, and mnemonic identifiers for assigned port numbers (known as port "keywords" at [IANA-PORT]). The latter two are now unified, and


various protocols use one or more of these types in strings. For example, the common syntax used by many URI schemes allows port numbers but not service names. Some implementations of the getaddrinfo() API support strings that can be either port numbers or port keywords (but not service names).


For protocols that use service names that must be resolved, the issues are the same as those for resolution of addresses in Section 3.1.4. In addition, Section 5.1 of [RFC6335] clarifies that service names/port keywords must contain at least one letter. This prevents confusion with port numbers in strings where both are allowed.


3.3. URIs
3.3. URI

This section looks at issues related to using URIs for security purposes. For example, Section 7.4 of [RFC5280] specifies comparison of URIs in certificates. Examples of URIs in security-token-based access control systems include WS-*, SAML 2.0 [OASIS-SAMLv2-CORE], and OAuth Web Resource Authorization Profiles (WRAP) [OAuth-WRAP]. In such systems, a variety of participants in the security infrastructure are identified by URIs. For example, requesters of security tokens are sometimes identified with URIs. The issuers of security tokens and the relying parties who are intended to consume security tokens are frequently identified by URIs. Claims in security tokens often have their types defined using URIs, and the values of the claims can also be URIs.

本节讨论与出于安全目的使用URI相关的问题。例如,[RFC5280]的第7.4节规定了证书中URI的比较。基于安全令牌的访问控制系统中的URI示例包括WS-*、SAML 2.0[OASIS-SAMLv2-CORE]和OAuth Web资源授权配置文件(WRAP)[OAuth WRAP]。在这样的系统中,uri标识了安全基础设施中的各种参与者。例如,安全令牌的请求者有时用URI标识。安全令牌的发行人和打算使用安全令牌的依赖方通常由URI标识。安全令牌中的声明通常使用URI定义其类型,声明的值也可以是URI。

URIs are defined with multiple components, each of which has its own rules. We cover each in turn below. However, it is also important to note that there exist multiple comparison algorithms. Section 6.2 of [RFC3986] states:


A variety of methods are used in practice to test URI equivalence. These methods fall into a range, distinguished by the amount of processing required and the degree to which the probability of false negatives is reduced. As noted above, false negatives cannot be eliminated. In practice, their probability can be reduced, but this reduction requires more processing and is not cost-effective for all applications.


If this range of comparison practices is considered as a ladder, the following discussion will climb the ladder, starting with practices that are cheap but have a relatively higher chance of producing false negatives, and proceeding to those that have higher computational cost and lower risk of false negatives.


The ladder approach has both pros and cons. On the pro side, it allows some uses to optimize for security, and other uses to optimize for cost, thus allowing URIs to be applicable to a wide range of uses. A disadvantage is that when different approaches are taken by different components in the same system using the same identifiers, the inconsistencies can result in security issues.


3.3.1. Scheme Component
3.3.1. 方案组成部分

[RFC3986] defines URI schemes as being case-insensitive US-ASCII and in Section specifies that scheme names should be normalized to lowercase characters.


New schemes can be defined over time. In general, however, two URIs with an unrecognized scheme cannot be safely compared. This is because the canonicalization and comparison rules for the other components may vary by scheme. For example, a new URI scheme might have a default port of X, and without that knowledge, a comparison algorithm cannot know whether "" and "" should be considered to match in the authority component. Hence, for security purposes, it is safest for unrecognized schemes to be treated as invalid identifiers. However, if the URIs are only used with a "grant access on match" paradigm, then unrecognized schemes can be supported by doing a generic case-sensitive comparison, at the expense of some false negatives.


3.3.2. Authority Component
3.3.2. 权限组件

The authority component is scheme-specific, but many schemes follow a common syntax that allows for userinfo, host, and port.

authority组件是特定于方案的,但许多方案遵循一种通用语法,允许用户信息、主机和端口。 Host 主办

Section 3.1 discusses issues with hostnames in general. In addition, Section 3.2.2 of [RFC3986] allows future changes using the IPvFuture production. As with IPv4 and IPv6 literals, IPvFuture formats may have issues with multiple semantically identical string representations and may also be semantically identical to an IPv4 or IPv6 address. As such, false negatives may be common if IPvFuture is used.

第3.1节讨论了主机名的一般问题。此外,[RFC3986]第3.2.2节允许将来使用IPV产品进行更改。与IPv4和IPv6文本一样,IPvFuture格式可能存在多个语义相同的字符串表示的问题,并且可能与IPv4或IPv6地址的语义相同。因此,如果使用IPvFuture,假阴性可能很常见。 Port 港口城市

See discussion in Section 3.2.

见第3.2节中的讨论。 Userinfo 用户信息

[RFC3986] defines the userinfo production that allows arbitrary data about the user of the URI to be placed before '@' signs in URIs. For example, "" has the value "alice:bob" as its userinfo. When comparing URIs in a security context, one must decide whether to treat the userinfo as being significant or not. Some URI comparison services, for example, treat "" and "" as being equal.


When the userinfo is treated as being significant, it has additional considerations (e.g., whether or not it is case sensitive), which we cover in Section 3.4.


3.3.3. Path Component
3.3.3. 路径组件

[RFC3986] supports the use of path segment values such as "./" or "../" for relative URIs. As discussed in Section of [RFC3986], they are intended only for use within a reference relative to some other base URI, but Section 5.2.4 of [RFC3986] nevertheless defines an algorithm to remove them as part of URI normalization.


Unless a scheme states otherwise, the path component is defined to be case sensitive. However, if the resource is stored and accessed using a filesystem using case-insensitive paths, there will be many paths that refer to the same resource. As such, false negatives can be common in this case.


3.3.4. Query Component
3.3.4. 查询组件

There is the question as to whether "", "", and "" are each considered equal or different.

有一个问题是“是否”", "“、和”“每个都被认为是平等的或不同的。

Similarly, it is unspecified whether the order of values matters. For example, should "" be considered equal to ""? And if a domain name is permitted to appear in a query component (e.g., in a reference to another URI), the same issues in Section 3.1 apply.

同样,价值顺序是否重要也未明确。例如,“应该”“被认为等于”"? 如果允许域名出现在查询组件中(例如,在对另一个URI的引用中),则第3.1节中的相同问题也适用。

3.3.5. Fragment Component
3.3.5. 片段成分

Some URI formats include fragment identifiers. These are typically handles to locations within a resource and are used for local reference. A classic example is the use of fragments in HTTP URIs where a URI of the form "" means retrieve the resource "" and, once it has arrived locally, find the HTML anchor named "ick" and display that.

一些URI格式包括片段标识符。这些通常是资源中位置的句柄,用于本地引用。一个典型的例子是在HTTP URI中使用片段,其中URI的形式为““表示检索资源”并且,一旦它到达本地,找到名为“ick”的HTML锚并显示它。

So, for example, when a user clicks on the link "", a browser will check its cache by doing a URI comparison for "" and, if the resource is present in the cache, a match is declared.


Hence, comparisons for security purposes typically ignore the fragment component and treat all fragments as equal to the full resource. However, if one were actually trying to compare the piece of a resource that was identified by the fragment identifier, ignoring it would result in potential false positives.


3.3.6. Resolution for Comparison
3.3.6. 用于比较的分辨率

It may be tempting to define a URI comparison algorithm based on whether URIs resolve to the same content, along the lines of resolving hostnames as described in Section 3.1.4. However, such an algorithm would result in similar problems, including content that dynamically changes over time or that is based on factors such as the requester's location, potential lack of external connectivity at the time or place that comparison is done, introduction of potentially undesirable delay, etc.


In addition, as noted in Section 3.1.4, resolution leaks information about security decisions to outsiders if the queries are publicly observable.


3.4. Email Address-Like Identifiers
3.4. 类似电子邮件地址的标识符

Section 3.4.1 of [RFC5322] defines the syntax of an email address-like identifier, and Section 3.2 of [RFC6532] updates it to support internationalization. Section 7.5 of [RFC5280] further discusses the use of internationalized email addresses in certificates.


Regarding the security impact of internationalized email headers, [RFC6532] points to Section 14 of [RFC6530], which contains a discussion of many issues resulting from internationalization.


Email address-like identifiers have a local part and a domain part. The issues with the domain part are essentially the same as with hostnames, as covered earlier in Section 3.1.


The local part is left for each domain to define. People quite commonly use email addresses as usernames with web sites such as banks or shopping sites, but the site doesn't know whether is the same person as Thus, email address-like identifiers are typically Indefinite identifiers.

本地部分留给每个域定义。人们通常在银行或购物网站等网站上使用电子邮件地址作为用户名,但该网站不知道foo@example.com是同一个人吗 因此,类似电子邮件地址的标识符通常是不确定的标识符。

To avoid false positives, some security mechanisms (such as those described in [RFC5280]) compare the local part using an exact match. Hence, like URIs, email address-like identifiers are designed for use in grant-on-match security schemes, not in deny-on-match schemes.


Furthermore, when such identifiers are actually used as email addresses, Section 2.4 of [RFC5321] states that the local part of a mailbox must be treated as case sensitive, but if a mailbox is stored and accessed using a filesystem using case-insensitive paths, there may be many paths that refer to the same mailbox. As such, false negatives can be common in this case.


4. General Issues
4. 一般问题
4.1. Conflation
4.1. 合并

There are a number of examples (some in the preceding sections) of strings that conflate two types of identifiers, using some heuristic to try to determine which type of identifier is given. Similarly, two ways of encoding the same type of identifier might be conflated within the same string.


Some examples include:


1. A string that might be an IPv4 address literal or an IPv6 address literal

1. 可能是IPv4地址文字或IPv6地址文字的字符串

2. A string that might be an IP address literal or a hostname

2. 可能是IP地址文字或主机名的字符串

3. A string that might be a port number or a service name

3. 可能是端口号或服务名称的字符串

4. A DNS label that might be literal or be Punycode-encoded

4. 一个DNS标签,可以是文字的,也可以是Punycode编码的

Strings that allow such conflation can only be considered Definite if there exists a well-defined rule to determine which identifier type is meant. One way to do so is to ensure that the valid syntax for the two is disjoint (e.g., distinguishing IPv4 vs. IPv6 address literals by the use of colons in the latter). A second way to do so is to define a precedence rule that results in some identifiers being inaccessible via a conflated string (e.g., a host literally named "xn--de-jg4avhby1noc0d" may be inaccessible due to the "xn--" prefix denoting the use of Punycode encoding). In some cases, such inaccessible space may be reserved so that the actual set of identifiers in use is unambiguous. For example, Section of [RFC4291] defines a range of the IPv6 address space for representing IPv4 addresses.


4.2. Internationalization
4.2. 国际化

In addition to the issues with hostnames discussed in Section 3.1.3, there are a number of internationalization issues that apply to many types of Definite and Indefinite identifiers.


First, there is no DNS mechanism for identifying whether non-identical strings would be seen by a human as being equivalent. There are problematic examples even with US-ASCII (Basic Latin) strings, including regional spelling variations such as "color" and "colour", and with many non-English cases, including partially numeric strings in Arabic script contexts, Chinese strings in Simplified and Traditional forms, and so on. Attempts to produce such alternate forms algorithmically could produce false positives and hence have an adverse effect on security.


Second, some strings are visually confusable with others, and hence if a security decision is made by a user based on visual inspection, many opportunities for false positives exist. As such, using visual inspection for security is unreliable. In addition to the security issues, visual confusability also adversely affects the usability of identifiers distributed via visual media. Similar issues can arise with audible confusability when using audio (e.g., for radio distribution, accessibility to the blind, etc.) in place of a visual medium. Furthermore, when strings conflate two types of identifiers as discussed in Section 4.1, allowing non-ASCII characters can cause one type of identifier to appear to a human as another type of identifier. For example, characters that may look like digits and dots may appear to be an IPv4 literal to a human (especially to one who might expect digits to appear in his or her native script). Hence, conflation often increases the chance of confusability.


Determining whether a string is a valid identifier should typically be done after, or as part of, canonicalization. Otherwise, an attacker might use the canonicalization algorithm to inject (e.g., via percent encoding, Normalization Form KC (NFKC), or non-shortest-form UTF-8) delimiters such as '@' in an email address-like identifier, or a '.' in a hostname.


Any case-insensitive comparisons need to define how comparison is done, since such comparisons may vary by the locale of the endpoint. As such, using case-insensitive comparisons in general often results in identifiers being either Indefinite or, if the legal character set is restricted (e.g., to US-ASCII), Definite.


See also [WEBER] for a more visual discussion of many of these issues.


Finally, the set of permitted characters and the canonical form of the characters (and hence the canonicalization algorithm) sometimes vary by protocol today, even when the intent is to use the same identifier, such as when one protocol passes identifiers to the other. See [RFC6885] for further discussion.


4.3. Scope
4.3. 范围

Another issue arises when an identifier (e.g., "localhost", "", etc.) is not globally unique. Section 1.1 of [RFC3986] states:


URIs have a global scope and are interpreted consistently regardless of context, though the result of that interpretation may be in relation to the end-user's context. For example, "http://localhost/" has the same interpretation for every user of that reference, even though the network interface corresponding to "localhost" may be different for each end-user: interpretation is independent of access.


Whenever an identifier that is not globally unique is passed to another entity outside of the scope of uniqueness, it will refer to a different resource and can result in a false positive. This problem is often addressed by using the identifier together with some other unique identifier of the context. For example, "alice" may uniquely identify a user within a system but must be used with "" (as in "") to uniquely identify the context outside of that system.


It is also worth noting that IPv6 addresses that are not globally scoped can be written with, or otherwise associated with, a "zone ID" to identify the context (see [RFC4007] for more information). However, zone IDs are only unique within a host, so they typically narrow, rather than expand, the scope of uniqueness of the resulting identifier.


4.4. Temporality
4.4. 暂时性

Often, identifiers are not unique across all time but have some lifetime associated with them after which they may be reassigned to another entity. For example, might be assigned to an employee of the Example company, but if he leaves and another Bob is later hired, the same identifier might be reused. As another example, IP address might be assigned to one subscriber and then later reassigned to another subscriber. Security issues can arise if updates are not made in all entities that store the identifier (e.g., in an access control list as discussed in Section 2, or in a resolution cache as discussed in Section 3.1.4).


This issue is similar to the issue of scope discussed in Section 4.3, except that the scope of uniqueness is temporal rather than topological.


5. Security Considerations
5. 安全考虑

This entire document is about security considerations.


To minimize issues related to elevation of privilege, any system that requires the ability to use both deny and allow operations within the same identifier space should avoid the use of Indefinite identifiers in security comparisons.


To minimize future security risks, any new identifiers being designed should specify an Absolute or Definite comparison algorithm, and if extensibility is allowed (e.g., as new schemes in URIs allow), then the comparison algorithm should remain invariant so that unrecognized extensions can be compared. That is, security risks can be reduced by specifying the comparison algorithm, making sure to resolve any ambiguities pointed out in this document (e.g., "standard dotted decimal").


Some issues (such as unrecognized extensions) can be mitigated by treating such identifiers as invalid. Validity checking of identifiers is further discussed in [RFC3696].


Perhaps the hardest issues arise when multiple protocols are used together, such as in Figure 2, where the two protocols are defined or implemented using different comparison algorithms. When constructing an architecture that uses multiple such protocols, designers should pay attention to any differences in comparison algorithms among the protocols in order to fully understand the security risks. How to deal with such security risks in current systems is an area for future work.


6. Acknowledgements
6. 致谢

Yaron Goland contributed to the discussion on URIs. Patrik Faltstrom contributed to the background on identifiers. John Klensin contributed text in a number of different sections. Additional helpful feedback and suggestions came from Bernard Aboba, Fred Baker, Leslie Daigle, Mark Davis, Jeff Hodges, Bjoern Hoehrmann, Russ Housley, Christian Huitema, Magnus Nystrom, Tom Petch, and Chris Weber.

Yaron Goland对URI的讨论做出了贡献。Patrik Faltstrom对标识符的背景知识做出了贡献。约翰·克莱辛在许多不同的章节中贡献了这篇文章。其他有用的反馈和建议来自伯纳德·阿博巴、弗雷德·贝克、莱斯利·戴格尔、马克·戴维斯、杰夫·霍奇斯、比约恩·霍尔曼、罗斯·霍斯利、克里斯蒂安·惠特马、马格纳斯·奈斯特罗姆、汤姆·佩奇和克里斯·韦伯。

7. IAB Members at the Time of Approval
7. 批准时的IAB成员

Bernard Aboba Jari Arkko Marc Blanchet Ross Callon Alissa Cooper Spencer Dawkins Joel Halpern Russ Housley David Kessens Danny McPherson Jon Peterson Dave Thaler Hannes Tschofenig


8. Informative References
8. 资料性引用

[IAB1123] Internet Architecture Board, "IAB Statement: 'The interpretation of rules in the ICANN gTLD Applicant Guidebook'", February 2012, < correspondence-reports-documents/2012-2/iab-statement-the-interpretation-of-rules-in-the-icann-gtld-applicant-guidebook>.

[IAB1123]互联网架构委员会,“IAB声明:ICANN gTLD申请人指南中的规则解释”,2012年2月< 通信报告文件/2012-2/iab声明icann gtld申请人指南>中规则的解释。

[IANA-PORT] IANA, "Service Name and Transport Protocol Port Number Registry", March 2013, <>.


[IEEE-1003.1] IEEE and The Open Group, "The Open Group Base Specifications, Issue 6, IEEE Std 1003.1, 2004 Edition", IEEE Std 1003.1, 2004.

[IEEE-1003.1]IEEE和开放组,“开放组基本规范,第6期,IEEE Std 1003.12004版”,IEEE Std 1003.12004。

[JAVAURL] Oracle, "Class URL", Java(TM) Platform Standard Ed. 7, 2013, < URL.html>.

[JAVAURL]Oracle,“类URL”,Java(TM)平台标准版,2013年第7版< URL.html>。

[OASIS-SAMLv2-CORE] Cantor, S., Ed., Kemp, J., Ed., Philpott, R., Ed., and E. Maler, Ed., "Assertions and Protocols for the OASIS Security Assertion Markup Language (SAML) V2.0", OASIS Standard saml-core-2.0-os, March 2005, < saml-core-2.0-os.pdf>.

[OASIS-SAMLv2-CORE]Cantor,S.,Ed.,Kemp,J.,Ed.,Philpott,R.,Ed.,和E.Maler,Ed.,“OASIS安全断言标记语言(SAML)V2.0的断言和协议”,OASIS标准SAML-CORE-2.0-os,2005年3月< saml-core-2.0-os.pdf>。

[OAuth-WRAP] Hardt, D., Ed., Tom, A., Eaton, B., and Y. Goland, "OAuth Web Resource Authorization Profiles", Work in Progress, January 2010.

[OAuth WRAP]Hardt,D.,Ed.,Tom,A.,Eaton,B.,和Y.Goland,“OAuth Web资源授权配置文件”,正在进行的工作,2010年1月。

[PRIVACY-CONS] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", Work in Progress, April 2013.


[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.

[RFC1034]Mockapetris,P.,“域名-概念和设施”,STD 13,RFC 1034,1987年11月。

[RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989.

[RFC1123]Braden,R.,“互联网主机的要求-应用和支持”,STD 3,RFC 1123,1989年10月。

[RFC2277] Alvestrand, H.T., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998.

[RFC2277]Alvestrand,H.T.,“IETF字符集和语言政策”,BCP 18,RFC 2277,1998年1月。

[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003.

[RFC3490]Faltstrom,P.,Hoffman,P.,和A.Costello,“应用程序中的域名国际化(IDNA)”,RFC 34902003年3月。

[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)", RFC 3492, March 2003.

[RFC3492]Costello,A.,“Punycode:应用程序中国际化域名的Unicode引导字符串编码(IDNA)”,RFC 3492,2003年3月。

[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, February 2003.

[RFC3493]Gilligan,R.,Thomson,S.,Bound,J.,McCann,J.,和W.Stevens,“IPv6的基本套接字接口扩展”,RFC 3493,2003年2月。

[RFC3696] Klensin, J., "Application Techniques for Checking and Transformation of Names", RFC 3696, February 2004.

[RFC3696]Klensin,J.,“名称检查和转换的应用技术”,RFC 36962004年2月。

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.

[RFC3986]Berners Lee,T.,Fielding,R.,和L.Masinter,“统一资源标识符(URI):通用语法”,STD 66,RFC 3986,2005年1月。

[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and B. Zill, "IPv6 Scoped Address Architecture", RFC 4007, March 2005.

[RFC4007]Deering,S.,Haberman,B.,Jinmei,T.,Nordmark,E.,和B.Zill,“IPv6作用域地址体系结构”,RFC 4007,2005年3月。

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.

[RFC4291]Hinden,R.和S.Deering,“IP版本6寻址体系结构”,RFC 42912006年2月。

[RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet Application Protocol Collation Registry", RFC 4790, March 2007.

[RFC4790]Newman,C.,Duerst,M.,和A.Gulbrandsen,“互联网应用协议整理注册表”,RFC 47902007年3月。

[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC 4949, August 2007.

[RFC4949]Shirey,R.,“互联网安全术语表,第2版”,RFC 49492007年8月。

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008.

[RFC5280]Cooper,D.,Santesson,S.,Farrell,S.,Boeyen,S.,Housley,R.,和W.Polk,“Internet X.509公钥基础设施证书和证书撤销列表(CRL)配置文件”,RFC 52802008年5月。

[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, October 2008.

[RFC5321]Klensin,J.,“简单邮件传输协议”,RFC 53212008年10月。

[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, October 2008.


[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010.

[RFC5952]Kawamura,S.和M.Kawashima,“IPv6地址文本表示的建议”,RFC 59522010年8月。

[RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on Encodings for Internationalized Domain Names", RFC 6055, February 2011.

[RFC6055]Thaler,D.,Klensin,J.,和S.Cheshire,“IAB对国际化域名编码的思考”,RFC 60552011年2月。

[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, January 2011.


[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, March 2011.

[RFC6125]Saint Andre,P.和J.Hodges,“在传输层安全(TLS)环境下使用X.509(PKIX)证书在互联网公钥基础设施中表示和验证基于域的应用程序服务标识”,RFC 61252011年3月。

[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, August 2011.

[RFC6335]Cotton,M.,Eggert,L.,Touch,J.,Westerlund,M.,和S.Cheshire,“互联网分配号码管理局(IANA)服务名称和传输协议端口号注册管理程序”,BCP 165,RFC 63352011年8月。

[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 6530, February 2012.


[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized Email Headers", RFC 6532, February 2012.

[RFC6532]Yang,A.,Steele,S.,和N.Freed,“国际化电子邮件标题”,RFC 6532,2012年2月。

[RFC6818] Yee, P., "Updates to the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 6818, January 2013.

[RFC6818]Yee,P.,“互联网X.509公钥基础设施证书和证书撤销列表(CRL)配置文件的更新”,RFC 6818,2013年1月。

[RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing IPv6 Zone Identifiers in Address Literals and Uniform Resource Identifiers", RFC 6874, February 2013.

[RFC6874]Carpenter,B.,Cheshire,S.和R.Hinden,“以地址文本和统一资源标识符表示IPv6区域标识符”,RFC 6874,2013年2月。

[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and Problem Statement for the Preparation and Comparison of Internationalized Strings (PRECIS)", RFC 6885, March 2013.

[RFC6885]Blanchet,M.和A.Sullivan,“编制和比较国际化字符串(PRECIS)的Stringprep修订和问题声明”,RFC 68852013年3月。

[TR36] Unicode Consortium, "Unicode Security Considerations", Unicode Technical Report #36, Revision 11, July 2012, <>.


[USASCII] American National Standards Institute, "Coded Character Sets -- 7-bit American Standard Code for Information Interchange (7-bit ASCII)", ANSI X3.4, 1986.

[USASCII]美国国家标准协会,“编码字符集——信息交换用7位美国标准代码(7位ASCII)”,ANSI X3.41986。

[WEBER] Weber, C., "Attacking Software Globalization", March 2010, < Chris_Weber_Character%20Transformations%20v1.7_IUC33.pdf>.

[WEBER]WEBER,C.,“攻击软件全球化”,2010年3月< Chris_Weber_字符%20v1.7\u IUC33.pdf>。

Author's Address


Dave Thaler (editor) Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA

Dave Thaler(编辑)微软公司美国华盛顿州雷德蒙微软大道一号,邮编:98052

   Phone: +1 425 703 8835
   Phone: +1 425 703 8835