Internet-Draft | Signing HTTP Messages | December 2019 |
Backman, et al. | Expires 14 June 2020 | [Page] |
- Workgroup:
- HTTPbis Working Group
- Internet-Draft:
- draft-richanna-http-message-signatures-00
- Published:
- Intended Status:
- Standards Track
- Expires:
Signing HTTP Messages
Abstract
This document describes a mechanism for creating, encoding, and verifying digital signatures or message authentication codes over content within an HTTP message. This mechanism supports use cases where the full HTTP message may not be known to the signer, and where the message may be transformed (e.g., by intermediaries) before reaching the verifier.¶
This draft is based on draft-cavage-http-signatures-12. The community and the authors have identified several issues with the current text. Additionally, the authors have identified a number of features that are required in order to support additional use cases. In order to preserve continuity with the effort that has been put into draft-cavage-http-signatures-12, this draft maintains normative compatibility with it, and thus does not address these issues or include these features, as doing so requires making backwards-incompatible changes to normative requirements. While such changes are inevitable, the editor recommends that they be driven by working group discussion following adoption of the draft (see Topics for Working Group Discussion). The editor requests that the working group recognize the intent of this initial draft and this recommendation when considering adoption of this draft.¶
This note is to be removed before publishing as an RFC.¶
Status of This Memo
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
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This Internet-Draft will expire on 14 June 2020.¶
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
1. Introduction
Message integrity and authenticity are important security properties that are critical to the secure operation of many [HTTP] applications. Application developers typically rely on the transport layer to provide these properties, by operating their application over TLS [RFC8446]. However, TLS only guarantees these properties over a single TLS connection, and the path between client and application may be composed of multiple independent TLS connections (for example, if the application is hosted behind a TLS-terminating gateway or if the client is behind a TLS Inspection appliance). In such cases, TLS cannot guarantee end-to-end message integrity or authenticity between the client and application. Additionally, some operating environments present obstacles that make it impractical to use TLS, or to use features necessary to provide message authenticity. Furthermore, some applications require the binding of an application-level key to the HTTP message, separate from any TLS certificates in use. Consequently, while TLS can meet message integrity and authenticity needs for many HTTP-based applications, it is not a universal solution.¶
This document defines a mechanism for providing end-to-end integrity and authenticity for content within an HTTP message. The mechanism allows applications to create digital signatures or message authentication codes (MACs) over only that content within the message that is meaningful and appropriate for the application. Strict canonicalization rules ensure that the verifier can verify the signature even if the message has been transformed in any of the many ways permitted by HTTP.¶
The mechanism described in this document consists of three parts:¶
- A common nomenclature and canonicalization rule set for the different protocol elements and other content within HTTP messages.¶
- Algorithms for generating and verifying signatures over HTTP message content using this nomenclature and rule set.¶
- A mechanism for attaching a signature and related metadata to an HTTP message.¶
1.1. Requirements Discussion
HTTP permits and sometimes requires intermediaries to transform messages in a variety of ways. This may result in a recipient receiving a message that is not bitwise equivalent to the message that was oringally sent. In such a case, the recipient will be unable to verify a signature over the raw bytes of the sender's HTTP message, as verifying digital signatures or MACs requires both signer and verifier to have the exact same signed content. Since the raw bytes of the message cannot be relied upon as signed content, the signer and verifier must derive the signed content from their respective versions of the message, via a mechanism that is resilient to safe changes that do not alter the meaning of the message.¶
For a variety of reasons, it is impractical to strictly define what constitutes a safe change versus an unsafe one. Applications use HTTP in a wide variety of ways, and may disagree on whether a particular piece of information in a message (e.g., the body, or the Date header field) is relevant. Thus a general purpose solution must provide signers with some degree of control over which message content is signed.¶
HTTP applications may be running in environments that do not provide complete access to or control over HTTP messages (such as a web browser's JavaScript environment), or may be using libraries that abstract away the details of the protocol (such as the Java HTTPClient library). These applications need to be able to generate and verify signatures despite incomplete knowledge of the HTTP message.¶
1.2. HTTP Message Transformations
As mentioned earlier, HTTP explicitly permits and in some cases requires implementations to transform messages in a variety of ways. Implementations are required to tolerate many of these transformations. What follows is a non-normative and non-exhaustive list of transformations that may occur under HTTP, provided as context:¶
- Re-ordering of header fields with different header field names ([HTTP], Section 3.2.2).¶
- Combination of header fields with the same field name ([HTTP], Section 3.2.2).¶
- Removal of header fields listed in the
Connection
header field ([HTTP], Section 6.1).¶ - Addition of header fields that indicate control options ([HTTP], Section 6.1).¶
- Addition or removal of a transfer coding ([HTTP], Section 5.7.2).¶
- Addition of header fields such as
Via
([HTTP], Section 5.7.1) andForwarded
([RFC7239], Section 4).¶
1.3. Safe Transformations
Based on the definition of HTTP and the requirements described above, we can identify certain types of transformations that should not prevent signature verification, even when performed on content covered by the signature. The following list describes those transformations:¶
- Combination of header fields with the same field name.¶
- Reordering of header fields with different names.¶
- Conversion between HTTP/1.x and HTTP/2, or vice-versa.¶
- Changes in casing (e.g., "Origin" to "origin") of any case-insensitive content such as header field names, request URI scheme, or host.¶
- Addition or removal of leading or trailing whitespace to a header field value.¶
- Addition or removal of
obs-fold
s.¶ - Changes to the request-target and Host header field that when applied together do not result in a change to the message's effective request URI, as defined in Section 5.5 of [HTTP].¶
Additionally, all changes to content not covered by the signature are considered safe.¶
1.4. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The terms "HTTP message", "HTTP method", "HTTP request", "HTTP response", absolute-form
, absolute-path
, "effective request URI", "gateway", "header field", "intermediary", request-target
, "sender", and "recipient" are used as defined in [HTTP].¶
For brevity, the term "signature" on its own is used in this document to refer to both digital signatures and keyed MACs. Similarly, the verb "sign" refers to the generation of either a digital signature or keyed MAC over a given input string. The qualified term "digital signature" refers specifically to the output of an asymmetric cryptographic signing operation.¶
In addition to those listed above, this document uses the following terms:¶
- Decimal String
- An Integer String optionally concatenated with a period
"."
followed by a second Integer String, representing a positive real number expressed in base 10. The first Integer String represents the integral portion of the number, while the optional second Integer String represents the fractional portion of the number. [[ Editor's note: There's got to be a definition for this that we can reference. ]]¶ - Integer String
- A US-ASCII string of one or more digits
"0-9"
, representing a positive integer in base 10. [[ Editor's note: There's got to be a definition for this that we can reference. ]]¶ - Signer
- The entity that is generating or has generated an HTTP Message Signature.¶
- Verifier
- An entity that is verifying or has verified an HTTP Message Signature against an HTTP Message. Note that an HTTP Message Signature may be verified multiple times, potentially by different entities.¶
This document contains non-normative examples of partial and complete HTTP messages. To improve readability, header fields may be split into multiple lines, using the obs-fold
syntax. This syntax is deprecated in [HTTP], and senders MUST NOT generate messages that include it.¶
2. Identifying and Canonicalizing Content
In order to allow signers and verifiers to establish which content is covered by a signature, this document defines content identifiers for signature metadata and discrete pieces of message content that may be covered by an HTTP Message Signature.¶
Some content within HTTP messages may undergo transformations that change the bitwise value without altering meaning of the content (for example, the merging together of header fields with the same name). Message content must therefore be canonicalized before it is signed, to ensure that a signature can be verified despite such innocuous transformations. This document defines rules for each content identifier that transform the identifier's associated content into such a canonical form.¶
The following sections define content identifiers, their associated content, and their canonicalization rules.¶
2.1. HTTP Header Fields
An HTTP header field value is identified by its header field name. While HTTP header field names are case-insensitive, implementations SHOULD use lowercased field names (e.g., content-type
, date
, etag
) when using them as content identifiers.¶
An HTTP header field value is canonicalized as follows:¶
- Create an ordered list of the field values of each instance of the header field in the message, in the order that they occur (or will occur) in the message.¶
- Strip leading and trailing whitespace from each item in the list.¶
- Concatenate the list items together, with a comma
","
and space" "
between each item. The resulting string is the canonicalized value.¶
2.1.1. Canonicalization Examples
This section contains non-normative examples of canonicalized values for header fields, given the following example HTTP message:¶
HTTP/1.1 200 OK Server: www.example.com Date: Tue, 07 Jun 2014 20:51:35 GMT X-OWS-Header: Leading and trailing whitespace. X-Obs-Fold-Header: Obsolete line folding. X-Empty-Header: Cache-Control: max-age=60 Cache-Control: must-revalidate¶
The following table shows example canonicalized values for header fields, given that message:¶
Header Field | Canonicalized Value |
---|---|
(cache-control)
|
max-age=60, must-revalidate
|
(date)
|
Tue, 07 Jun 2014 20:51:35 GMT
|
(server)
|
www.example.com
|
(x-empty-header)
|
|
(x-obs-fold-header)
|
Obsolete line folding.
|
(x-ows-header)
|
Leading and trailing whitespace.
|
2.2. Signature Creation Time
The signature's Creation Time (Section 3.1) is identified by the (created)
identifier.¶
Its canonicalized value is an Integer String containing the signature's Creation Time expressed as the number of seconds since the Epoch, as defined in Section 4.16 of [POSIX.1].¶
2.3. Signature Expiration Time
The signature's Expiration Time (Section 3.1) is identified by the (expired)
identifier.¶
Its canonicalized value is a Decimal String containing the signature's Expiration Time expressed as the number of seconds since the Epoch, as defined in Section 4.16 of [POSIX.1].¶
2.4. Target Endpoint
The request target endpoint, consisting of the request method and the path and query of the effective request URI, is identified by the (request-target)
identifier.¶
Its value is canonicalized as follows:¶
- Take the lowercased HTTP method of the message.¶
- Append a space
" "
.¶ - Append the path and query of the request target of the message, formatted according to the rules defined for the
:path
pseudo-header in [HTTP2], Section 8.1.2.3. The resulting string is the canonicalized value.¶
2.4.1. Canonicalization Examples
The following table contains non-normative example HTTP messages and their canonicalized (request-target)
values.¶
HTTP Message |
(request-target)
|
---|---|
POST /?param=value HTTP/1.1 Host: www.example.com¶ |
post /?param=value
|
POST /a/b HTTP/1.1 Host: www.example.com¶ |
post /a/b
|
GET http://www.example.com/a/ HTTP/1.1¶ |
get /a/
|
GET http://www.example.com HTTP/1.1¶ |
get /
|
CONNECT server.example.com:80 HTTP/1.1 Host: server.example.com¶ |
connect /
|
OPTIONS * HTTP/1.1 Host: server.example.com¶ |
options *
|
3. HTTP Message Signatures
An HTTP Message Signature is a signature over a string generated from a subset of the content in an HTTP message and metadata about the signature itself. When successfully verified against an HTTP message, it provides cryptographic proof that with respect to the subset of content that was signed, the message is semantically equivalent to the message for which the signature was generated.¶
3.1. Signature Metadata
HTTP Message Signatures have metadata properties that provide information regarding the signature's generation and/or verification. The following metadata properties are defined:¶
- Algorithm
- An HTTP Signature Algorithm defined in the HTTP Signature Algorithms Registry defined in this document. It describes the signing and verification algorithms for the signature.¶
- Creation Time
- A timestamp representing the point in time that the signature was generated. Sub-second precision is not supported. A signature's Creation Time MAY be undefined, indicating that it is unknown.¶
- Covered Content
- An ordered list of content identifiers (Section 2) that indicates the metadata and message content that is covered by the signature. The order of identifiers in this list affects signature generation and verification, and therefore MUST be preserved.¶
- Expiration Time
- A timestamp representing the point in time at which the signature expires. An expired signature always fails verification. A signature's Expiration Time MAY be undefined, indicating that the signature does not expire.¶
- Verification Key Material
-
The key material required to verify the signature.¶
3.2. Creating a Signature
In order to create a signature, a signer completes the following process:¶
- Choose key material and algorithm, and set metadata properties (Section 3.2.1)¶
- Create the Signature Input (Section 3.2.2)¶
- Sign the Signature Input (Section 3.2.3)¶
The following sections describe each of these steps in detail.¶
3.2.1. Choose and Set Signature Metadata Properties
- The signer chooses an HTTP Signature Algorithm from those registered in the HTTP Signature Algorithms Registry defined by this document, and sets the signature's Algorithm property to that value. The signer MUST NOT choose an algorithm marked "Deprecated". The mechanism by which the signer chooses an algorithm is out of scope for this document.¶
- The signer chooses key material to use for signing and verification, and sets the signature's Verification Key Material property to the key material required for verification. The signer MUST choose key material that is appropriate for the signature's Algorithm, and that conforms to any requirements defined by the Algorithm, such as key size or format. The mechanism by which the signer chooses key material is out of scope for this document.¶
- The signer sets the signature's Creation Time property to the current time.¶
- The signer sets the signature's Expiration Time property to the time at which the signature is to expire, or to undefined if the signature will not expire.¶
- The signer creates an ordered list of content identifiers representing the message content and signature metadata to be covered by the signature, and assigns this list as the signature's Covered Content. Each identifier MUST be one of those defined in Section 2. This list MUST NOT be empty, as this would result in creating a signature over the empty string. If the signature's Algorithm name does not start with
rsa
,hmac
, orecdsa
, signers SHOULD include(created)
and(request-target)
in the list. If the signature's Algorithm starts withrsa
,hmac
, orecdsa
, signers SHOULD includedate
and(request-target)
in the list. Further guidance on what to include in this list and in what order is out of scope for this document. However, the list order is significant and once established for a given signature it MUST be preserved for that signature.¶
For example, given the following HTTP message:¶
GET /foo HTTP/1.1 Host: example.org Date: Tue, 07 Jun 2014 20:51:35 GMT X-Example: Example header with some whitespace. X-EmptyHeader: Cache-Control: max-age=60 Cache-Control: must-revalidate¶
The following table presents a non-normative example of metadata values that a signer may choose:¶
Property | Value |
---|---|
Algorithm |
rsa-256
|
Covered Content |
(request-target) , (created) , host , date , cache-contol , x-emptyheader , x-example
|
Creation Time | Equal to the value specified in the Date header field. |
Expiration Time | Equal to the Creation Time plus five minutes. |
Verification Key Material | The public key provided in Appendix A.1.1 and identified by the keyId value "test-key-b". |
3.2.2. Create the Signature Input
The Signature Input is a US-ASCII string containing the content that will be signed. To create it, the signer concatenates together entries for each identifier in the signature's Covered Content in the order it occurs in the list, with each entry separated by a newline "\n"
. An identifier's entry is a US-ASCII string consisting of the lowercased identifier followed with a colon ":"
, a space " "
, and the identifier's canonicalized value (described below).¶
If Covered Content contains (created)
and the signature's Creation Time is undefined or the signature's Algorithm name starts with rsa
, hmac
, or ecdsa
an implementation MUST produce an error.¶
If Covered Content contains (expires)
and the signature does not have an Expiration Time or the signature's Algorithm name starts with rsa
, hmac
, or ecdsa
an implementation MUST produce an error.¶
If Covered Content contains an identifier for a header field that is not present or malformed in the message, the implementation MUST produce an error.¶
For the non-normative example Signature metadata in Table 3, the corresponding Signature Input is:¶
3.2.3. Sign the Signature Input
The signer signs the Signature Input using the signing algorithm described by the signature's Algorithm property, and the key material chosen by the signer. The signer then encodes the result of that operation as a base 64-encoded string [RFC4648]. This string is the signature value.¶
For the non-normative example Signature metadata in Section 3.2.1 and Signature Input in Figure 1, the corresponding signature value is:¶
3.3. Verifying a Signature
In order to verify a signature, a verifier MUST:¶
- Examine the signature's metadata to confirm that the signature meets the requirements described in this document, as well as any additional requirements defined by the application such as which header fields or other content are required to be covered by the signature.¶
- Use the received HTTP message and the signature's metadata to recreate the Signature Input, using the process described in Section 3.2.2.¶
- Use the signature's Algorithm and Verification Key Material with the recreated Signing Input to verify the signature value.¶
A signature with a Creation Time that is in the future or an Expiration Time that is in the past MUST NOT be processed.¶
The verifier MUST ensure that a signature's Algorithm is appropriate for the key material the verifier will use to verify the signature. If the Algorithm is not appropriate for the key material (for example, if it is the wrong size, or in the wrong format), the signature MUST NOT be processed.¶
3.3.1. Enforcing Application Requirements
The verification requirements specified in this document are intended as a baseline set of restrictions that are generally applicable to all use cases. Applications using HTTP Message Signatures MAY impose requirements above and beyond those specified by this document, as appropriate for their use case.¶
Some non-normative examples of additional requirements an application might define are:¶
- Requiring a specific set of header fields to be signed (e.g., Authorization, Digest).¶
- Enforcing a maximum signature age.¶
- Prohibiting the use of certain algorithms, or mandating the use of an algorithm.¶
- Requiring keys to be of a certain size (e.g., 2048 bits vs. 1024 bits).¶
Application-specific requirements are expected and encouraged. When an application defines additional requirements, it MUST enforce them during the signature verification process, and signature verification MUST fail if the signature does not conform to the application's requirements.¶
Applications MUST enforce the requirements defined in this document. Regardless of use case, applications MUST NOT accept signatures that do not conform to these requirements.¶
4. The 'Signature' HTTP Header
The "Signature" HTTP header provides a mechanism to attach a signature to the HTTP message from which it was generated. The header field name is "Signature" and its value is a list of parameters and values, formatted according to the signature
syntax defined below, using the extended Augmented Backus-Naur Form (ABNF) notation used in [HTTP].¶
signature = #( sig-param ) sig-param = token BWS "=" BWS ( token / quoted-string )¶
Each sig-param
is the name of a parameter defined in the Section 5.2 defined in this document. The initial contents of this registry are described in Section 4.1.¶
4.1. Signature Header Parameters
The Signature header's parameters contain the signature value itself and the signature metadata properties required to verify the signature. Unless otherwise specified, parameters MUST NOT occur multiple times in one header, whether with the same or different values. The following parameters are defined:¶
algorithm
-
RECOMMENDED. The
algorithm
parameter contains the name of the signature's Algorithm, as registered in the HTTP Signature Algorithms Registry defined by this document. Verifiers MUST determine the signature's Algorithm from thekeyId
parameter rather than fromalgorithm
. Ifalgorithm
is provided and differs from or is incompatible with the algorithm or key material identified bykeyId
(for example,algorithm
has a value ofrsa-sha256
butkeyId
identifies an EdDSA key), then implementations MUST produce an error. Implementers should note that previous versions of this specification determined the signature's Algorithm using thealgorithm
parameter only, and thus could be utilized by attackers to expose security vulnerabilities. The default value for this parameter is "hs2019".¶ created
-
RECOMMENDED. The
created
parameter contains the signature's Creation Time, expressed as the canonicalized value of the(created)
content identifier, as defined in Section 2. If not specified, the signature's Creation Time is undefined. This parameter is useful when signers are not capable of controlling theDate
HTTP Header such as when operating in certain web browser environments.¶ expires
-
OPTIONAL. The
expires
parameter contains the signature's Expiration Time, expressed as the canonicalized value of the(expires)
content identifier, as defined in Section 2. If the signature does not have an Expiration Time, this parameterMUST
be omitted. If not specified, the signature's Expiration Time is undefined.¶ headers
-
OPTIONAL. The
headers
parameter contains the signature's Covered Content, expressed as a string containing a quoted list of the identifiers in the list, in the order they occur in the list, with a space" "
between each identifier. If specified, identifiers for header fields SHOULD be lowercased and all others MUST be lowercased. The default value for this parameter is "(created)".¶ keyId
-
REQUIRED. The
keyId
parameter is a US-ASCII string whose value can be used by a verifier to identify and/or obtain the signature'sVerification Key Material
. The format and semantics of this value are out of scope for this document.¶ signature
-
REQUIRED. The
signature
parameter contains the signature value, as described in Section 3.2.3.¶
4.2. Example
The following is a non-normative example Signature header field representing the signature in Figure 2:¶
Signature: keyId="test-key-b", algorithm="rsa-sha256", created=1402170695, expires=1402170995, headers="(request-target) (created) host date cache-control x-emptyheader x-example", signature="T1l3tWH2cSP31nfuvc3nVaHQ6IAu9YLEXg2pCeEOJETXnlWbgKtBTa XV6LNQWtf4O42V2DZwDZbmVZ8xW3TFW80RrfrY0+fyjD4OLN7/zV6L6d2v7uB puWZ8QzKuHYFaRNVXgFBXN3VJnsIOUjv20pqZMKO3phLCKX2/zQzJLCBQvF/5 UKtnJiMp1ACNhG8LF0Q0FPWfe86YZBBxqrQr5WfjMu0LOO52ZAxi9KTWSlceJ 2U361gDb7S5Deub8MaDrjUEpluphQeo8xyvHBoNXsqeax/WaHyRYOgaW6krxE GVaBQAfA2czYZhEA05Tb38ahq/gwDQ1bagd9rGnCHtAg=="¶
5. IANA Considerations
5.1. HTTP Signature Algorithms Registry
This document defines HTTP Signature Algorithms, for which IANA is asked to create and maintain a new registry titled "HTTP Signature Algorithms". Initial values for this registry are given in Section 5.1.2. Future assignments and modifications to existing assignment are to be made through the Expert Review registration policy [BCP 26] and shall follow the template presented in Section 5.1.1.¶
5.1.1. Registration Template
- Algorithm Name
- An identifier for the HTTP Signature Algorithm. The name MUST be an ASCII string consisting only of lower-case characters (
"a"
-"z"
), digits ("0"
-"9"
), and hyphens ("-"
), and SHOULD NOT exceed 20 characters in length. The identifier MUST be unique within the context of the registry.¶ - Status
- A brief text description of the status of the algorithm. The description MUST begin with one of "Active" or "Deprecated", and MAY provide further context or explanation as to the reason for the status.¶
- Description
- A description of the algorithm used to sign the signing string when generating an HTTP Message Signature, or instructions on how to determine that algorithm. When the description specifies an algorithm, it MUST include a reference to the document or documents that define the algorithm.¶
5.1.2. Initial Contents
[[ MS: The references in this section are problematic as many of the specifications that they refer to are too implementation specific, rather than just pointing to the proper signature and hashing specifications. A better approach might be just specifying the signature and hashing function specifications, leaving implementers to connect the dots (which are not that hard to connect). ]]¶
hs2019
rsa-sha1
rsa-sha256
hmac-sha256
ecdsa-sha256
5.2. HTTP Signature Parameters Registry
This document defines the Signature header field, whose value contains a list of named parameters. IANA is asked to create and maintain a new registry titled "HTTP Signature Parameters" to record and maintain the set of named parameters defined for use within the Signature header field. Initial values for this registry are given in Section 5.2.2. Future assignments and modifications to existing assignment are to be made through the Expert Review registration policy [BCP 26] and shall follow the template presented in Section 5.2.1.¶
5.2.1. Registration Template
- Name
- An identifier for the parameter. The name MUST be an ASCII string consisting only of lower-case characters (
"a"
-"z"
), digits ("0"
-"9"
), and hyphens ("-"
), and SHOULD NOT exceed 20 characters in length. The identifier MUST be unique within the context of the registry.¶ - Status
- A value indicating the status of the parameter definition. Allowed values are "Active" and "Deprecated". Active parameter definitions are available for general use. Deprecated parameter definitions may be in use by existing implementations, but SHOULD NOT be used by new implementations.¶
- Reference(s)
- A reference or list of references to the documents that define the purpose, content, and usage of the parameter. The parameter definition MUST define the format of the parameter's value using the extended ABNF notation used in [HTTP], or by referencing one or more standard formats such as base 64 or URI. The parameter definition MUST also specify the normative requirements for when and how the parameter may be used. Value formats MUST NOT allow values that would break the parameter list syntax used by the Signature header.¶
5.2.2. Initial Contents
The table below contains the initial contents of the HTTP Signature Parameters Registry. Each row in the table represents a distinct entry in the registry.¶
Name | Status | Reference(s) |
---|---|---|
algorithm
|
Active | Section 4.1 of this document |
created
|
Active |
Section 4.1 of this document¶ |
expires
|
Active |
Section 4.1 of this document¶ |
headers
|
Active |
Section 4.1 of this document¶ |
keyId
|
Active |
Section 4.1 of this document¶ |
signature
|
Active |
Section 4.1 of this document¶ |
6. Security Considerations
[[ TODO: need to dive deeper on this section; not sure how much of what's referenced below is actually applicable, or if it covers everything we need to worry about. ]]¶
[[ TODO: Should provide some recommendations on how to determine what content needs to be signed for a given use case. ]]¶
There are a number of security considerations to take into account when implementing or utilizing this specification. A thorough security analysis of this protocol, including its strengths and weaknesses, can be found in Security Considerations for HTTP Signatures [WP-HTTP-Sig-Audit].¶
7. References
7.1. Normative References
- [BCP 26]
- Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, , <https://www.rfc-editor.org/info/rfc8126>.
- [DSS]
- NIST, "Digital Signature Standard (DSS)", FIPS 186-4, DOI 10.6028/NIST.FIPS.186-4, , <https://csrc.nist.gov/publications/detail/fips/186/4/final>.
- [HTTP]
- Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, , <https://www.rfc-editor.org/info/rfc7230>.
- [HTTP2]
- Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, , <https://www.rfc-editor.org/info/rfc7540>.
- [POSIX.1]
- IEEE and The Open Group, "The Open Group Base Specifications Issue 7, 2018 edition", IEEE Std 1003.1-2017, , <https://pubs.opengroup.org/onlinepubs/9699919799/>.
- [RFC2104]
- Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, , <https://www.rfc-editor.org/info/rfc2104>.
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
- [RFC3986]
- Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <https://www.rfc-editor.org/info/rfc3986>.
- [RFC4648]
- Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, , <https://www.rfc-editor.org/info/rfc4648>.
- [RFC7541]
- Peon, R. and H. Ruellan, "HPACK: Header Compression for HTTP/2", RFC 7541, DOI 10.17487/RFC7541, , <https://www.rfc-editor.org/info/rfc7541>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
- [RFC3339]
- Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, , <https://www.rfc-editor.org/info/rfc3339>.
- [RFC6234]
- Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, , <https://www.rfc-editor.org/info/rfc6234>.
- [RFC7239]
- Petersson, A. and M. Nilsson, "Forwarded HTTP Extension", RFC 7239, DOI 10.17487/RFC7239, , <https://www.rfc-editor.org/info/rfc7239>.
- [RFC7518]
- Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, , <https://www.rfc-editor.org/info/rfc7518>.
- [RFC8017]
- Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, , <https://www.rfc-editor.org/info/rfc8017>.
- [RFC8032]
- Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, , <https://www.rfc-editor.org/info/rfc8032>.
- [RFC8446]
- Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/info/rfc8446>.
- [WP-HTTP-Sig-Audit]
- Sporny, M., "Security Considerations for HTTP Signatures", , <https://web-payments.org/specs/source/http-signatures-audit/>.
Appendix A. Examples
A.1. Example Keys
This section provides cryptographic keys that are referenced in example signatures throughout this document. These keys MUST NOT be used for any purpose other than testing.¶
A.1.1. rsa-test
The following key is a 2048-bit RSA public and private key pair:¶
-----BEGIN RSA PUBLIC KEY----- MIIBCgKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsPBRrw WEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsdJKFq MGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75jfZg kne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKIlE0P uKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZSFlQ PSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQAB -----END RSA PUBLIC KEY----- -----BEGIN RSA PRIVATE KEY----- MIIEqAIBAAKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsP BRrwWEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsd JKFqMGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75 jfZgkne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKI lE0PuKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZ SFlQPSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQABAoIBAG/JZuSWdoVHbi56 vjgCgkjg3lkO1KrO3nrdm6nrgA9P9qaPjxuKoWaKO1cBQlE1pSWp/cKncYgD5WxE CpAnRUXG2pG4zdkzCYzAh1i+c34L6oZoHsirK6oNcEnHveydfzJL5934egm6p8DW +m1RQ70yUt4uRc0YSor+q1LGJvGQHReF0WmJBZHrhz5e63Pq7lE0gIwuBqL8SMaA yRXtK+JGxZpImTq+NHvEWWCu09SCq0r838ceQI55SvzmTkwqtC+8AT2zFviMZkKR Qo6SPsrqItxZWRty2izawTF0Bf5S2VAx7O+6t3wBsQ1sLptoSgX3QblELY5asI0J YFz7LJECgYkAsqeUJmqXE3LP8tYoIjMIAKiTm9o6psPlc8CrLI9CH0UbuaA2JCOM cCNq8SyYbTqgnWlB9ZfcAm/cFpA8tYci9m5vYK8HNxQr+8FS3Qo8N9RJ8d0U5Csw DzMYfRghAfUGwmlWj5hp1pQzAuhwbOXFtxKHVsMPhz1IBtF9Y8jvgqgYHLbmyiu1 mwJ5AL0pYF0G7x81prlARURwHo0Yf52kEw1dxpx+JXER7hQRWQki5/NsUEtv+8RT qn2m6qte5DXLyn83b1qRscSdnCCwKtKWUug5q2ZbwVOCJCtmRwmnP131lWRYfj67 B/xJ1ZA6X3GEf4sNReNAtaucPEelgR2nsN0gKQKBiGoqHWbK1qYvBxX2X3kbPDkv 9C+celgZd2PW7aGYLCHq7nPbmfDV0yHcWjOhXZ8jRMjmANVR/eLQ2EfsRLdW69bn f3ZD7JS1fwGnO3exGmHO3HZG+6AvberKYVYNHahNFEw5TsAcQWDLRpkGybBcxqZo 81YCqlqidwfeO5YtlO7etx1xLyqa2NsCeG9A86UjG+aeNnXEIDk1PDK+EuiThIUa /2IxKzJKWl1BKr2d4xAfR0ZnEYuRrbeDQYgTImOlfW6/GuYIxKYgEKCFHFqJATAG IxHrq1PDOiSwXd2GmVVYyEmhZnbcp8CxaEMQoevxAta0ssMK3w6UsDtvUvYvF22m qQKBiD5GwESzsFPy3Ga0MvZpn3D6EJQLgsnrtUPZx+z2Ep2x0xc5orneB5fGyF1P WtP+fG5Q6Dpdz3LRfm+KwBCWFKQjg7uTxcjerhBWEYPmEMKYwTJF5PBG9/ddvHLQ EQeNC8fHGg4UXU8mhHnSBt3EA10qQJfRDs15M38eG2cYwB1PZpDHScDnDA0= -----END RSA PRIVATE KEY-----¶
A.2. Example keyId
Values
The table below maps example keyId
values to associated algorithms and/or keys. These are example mappings that are valid only within the context of examples in examples within this and future documents that reference this section. Unless otherwise specified, within the context of examples it should be assumed that the signer and verifier understand these keyId
mappings. These keyId
values are not reserved, and deployments are free to use them, with these associations or others.¶
keyId
|
Algorithm | Verification Key |
---|---|---|
test-key-a
|
hs2019 , using RSASSA-PSS [RFC8017] and SHA-512 [RFC6234]
|
The public key specified in Appendix A.1.1. |
test-key-b
|
rsa-256
|
The public key specified in Appendix A.1.1. |
A.3. Test Cases
This section provides non-normative examples that may be used as test cases to validate implementation correctness. These examples are based on the following HTTP message:¶
POST /foo?param=value&pet=dog HTTP/1.1 Host: example.com Date: Tue, 07 Jun 2014 20:51:35 GMT Content-Type: application/json Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Content-Length: 18 {"hello": "world"}¶
A.3.1. Signature Generation
A.3.1.1. hs2019
signature over minimal recommended content
This presents metadata for a Signature using hs2019
, over minimum recommended data to sign:¶
Property | Value |
---|---|
Algorithm |
hs2019 , using RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]
|
Covered Content |
(created) (request-target)
|
Creation Time | 8:51:35 PM GMT, June 7th, 2014 |
Expiration Time | Undefined |
Verification Key Material | The public key specified in Appendix A.1.1. |
The Signature Input is:¶
(created): 1402170695 (request-target): post /foo?param=value&pet=dog¶
The signature value is:¶
e3y37nxAoeuXw2KbaIxE2d9jpE7Z9okgizg6QbD2Z7fUVUvog+ZTKKLRBnhNglVIY6fAa YlHwx7ZAXXdBVF8gjWBPL6U9zRrB4PFzjoLSxHaqsvS0ZK9FRxpenptgukaVQ1aeva3PE 1aD6zZ93df2lFIFXGDefYCQ+M/SrDGQOFvaVykEkte5mO6zQZ/HpokjMKvilfSMJS+vbv C1GJItQpjs636Db+7zB2W1BurkGxtQdCLDXuIDg4S8pPSDihkch/dUzL2BpML3PXGKVXw HOUkVG6Q2ge07IYdzya6N1fIVA9eKI1Y47HT35QliVAxZgE0EZLo8mxq19ReIVvuFg==¶
A possible Signature header for this signature is:¶
Signature: keyId="test-key-a", created=1402170695, headers="(created) (request-target)", signature="e3y37nxAoeuXw2KbaIxE2d9jpE7Z9okgizg6QbD2Z7fUVUvog+ZTKK LRBnhNglVIY6fAaYlHwx7ZAXXdBVF8gjWBPL6U9zRrB4PFzjoLSxHaqsvS0ZK 9FRxpenptgukaVQ1aeva3PE1aD6zZ93df2lFIFXGDefYCQ+M/SrDGQOFvaVyk Ekte5mO6zQZ/HpokjMKvilfSMJS+vbvC1GJItQpjs636Db+7zB2W1BurkGxtQ dCLDXuIDg4S8pPSDihkch/dUzL2BpML3PXGKVXwHOUkVG6Q2ge07IYdzya6N1 fIVA9eKI1Y47HT35QliVAxZgE0EZLo8mxq19ReIVvuFg=="¶
A.3.1.2. hs2019
signature covering all header fields
This presents metadata for a Signature using hs2019
that covers all header fields in the request:¶
Property | Value |
---|---|
Algorithm |
hs2019 , using RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]
|
Covered Content |
(created) , (request-target) , host , date , content-type , digest , content-length
|
Creation Time | 8:51:35 PM GMT, June 7th, 2014 |
Expiration Time | Undefined |
Verification Key Material | The public key specified in Appendix A.1.1. |
The Signature Input is:¶
(created): 1402170695 (request-target): post /foo?param=value&pet=dog host: example.com date: Tue, 07 Jun 2014 20:51:35 GMT content-type: application/json digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= content-length: 18¶
The signature value is:¶
KXUj1H3ZOhv3Nk4xlRLTn4bOMlMOmFiud3VXrMa9MaLCxnVmrqOX5BulRvB65YW/wQp0o T/nNQpXgOYeY8ovmHlpkRyz5buNDqoOpRsCpLGxsIJ9cX8XVsM9jy+Q1+RIlD9wfWoPHh qhoXt35ZkasuIDPF/AETuObs9QydlsqONwbK+TdQguDK/8Va1Pocl6wK1uLwqcXlxhPEb 55EmdYB9pddDyHTADING7K4qMwof2mC3t8Pb0yoLZoZX5a4Or4FrCCKK/9BHAhq/RsVk0 dTENMbTB4i7cHvKQu+o9xuYWuxyvBa0Z6NdOb0di70cdrSDEsL5Gz7LBY5J2N9KdGg==¶
A possible Signature header for this signature is:¶
Signature: keyId="test-key-a", algorithm="hs2019", created=1402170695, headers="(request-target) (created) host date content-type digest content-length", signature="KXUj1H3ZOhv3Nk4xlRLTn4bOMlMOmFiud3VXrMa9MaLCxnVmrqOX5B ulRvB65YW/wQp0oT/nNQpXgOYeY8ovmHlpkRyz5buNDqoOpRsCpLGxsIJ9cX8 XVsM9jy+Q1+RIlD9wfWoPHhqhoXt35ZkasuIDPF/AETuObs9QydlsqONwbK+T dQguDK/8Va1Pocl6wK1uLwqcXlxhPEb55EmdYB9pddDyHTADING7K4qMwof2m C3t8Pb0yoLZoZX5a4Or4FrCCKK/9BHAhq/RsVk0dTENMbTB4i7cHvKQu+o9xu YWuxyvBa0Z6NdOb0di70cdrSDEsL5Gz7LBY5J2N9KdGg=="¶
A.3.2. Signature Verification
A.3.2.1. Minimal Required Signature Header
This presents a Signature header containing only the minimal required parameters:¶
Signature: keyId="test-key-a", (created): 1402170695, signature="V3SijFpJOvDUT8t1/EnYli/4TbF2AGqwBGiGUGrgClCkiOAIlOxxY7 2Mr13DccFkYzg3gX1jIOpKXzH70C5bru4b71SBG+ShiJLu34gHCG33iw44NLG UvT5+F+LCKbbHberyk8eyYsZ+TLwtZAYKafxfNOWQXF4o3QaWslDMm8Tcgrd8 onM45ayFyR4nXRlcGad4PISYGz8PmO4Y+K8RYOyDkgsmRxKtftFQUYG41anyE lccNLfEfLBKsyV6kxr36U1Q7FdUopLv8kqluQySrWD6kesvFxNvbEOi+1uZqT uFlK8ZldITQiqtNYaabRjQFZio63gma2y+UAaTGLdM9A=="¶
The corresponding signature metadata derived from this header field is:¶
Property | Value |
---|---|
Algorithm |
hs2019 , using RSASSA-PSS [RFC8017] using SHA-256 [RFC6234]
|
Covered Content |
(created)
|
Creation Time | 8:51:35 PM GMT, June 7th, 2014 |
Expiration Time | Undefined |
Verification Key Material | The public key specified in Appendix A.1.1. |
The corresponding Signature Input is:¶
(created): 1402170695¶
A.3.2.2. Minimal Recommended Signature Header
This presents a Signature header containing only the minimal required and recommended parameters:¶
Signature: algorithm="hs2019", keyId="test-key-a", (created): 1402170695, signature="V3SijFpJOvDUT8t1/EnYli/4TbF2AGqwBGiGUGrgClCkiOAIlOxxY7 2Mr13DccFkYzg3gX1jIOpKXzH70C5bru4b71SBG+ShiJLu34gHCG33iw44NLG UvT5+F+LCKbbHberyk8eyYsZ+TLwtZAYKafxfNOWQXF4o3QaWslDMm8Tcgrd8 onM45ayFyR4nXRlcGad4PISYGz8PmO4Y+K8RYOyDkgsmRxKtftFQUYG41anyE lccNLfEfLBKsyV6kxr36U1Q7FdUopLv8kqluQySrWD6kesvFxNvbEOi+1uZqT uFlK8ZldITQiqtNYaabRjQFZio63gma2y+UAaTGLdM9A=="¶
The corresponding signature metadata derived from this header field is:¶
Property | Value |
---|---|
Algorithm |
hs2019 , using RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]
|
Covered Content |
(created)
|
Creation Time | 8:51:35 PM GMT, June 7th, 2014 |
Expiration Time | Undefined |
Verification Key Material | The public key specified in Appendix A.1.1. |
The corresponding Signature Input is:¶
(created): 1402170695¶
A.3.2.3. Minimal Signature Header using rsa-256
This presents a minimal Signature header for a signature using the rsa-256
algorithm:¶
Signature: algorithm="rsa-256", keyId="test-key-b", headers="date", signature="HtXycCl97RBVkZi66ADKnC9c5eSSlb57GnQ4KFqNZplOpNfxqk62Jz Z484jXgLvoOTRaKfR4hwyxlcyb+BWkVasApQovBSdit9Ml/YmN2IvJDPncrlh PDVDv36Z9/DiSO+RNHD7iLXugdXo1+MGRimW1RmYdenl/ITeb7rjfLZ4b9VNn LFtVWwrjhAiwIqeLjodVImzVc5srrk19HMZNuUejK6I3/MyN3+3U8tIRW4LWz x6ZgGZUaEEP0aBlBkt7Fj0Tt5/P5HNW/Sa/m8smxbOHnwzAJDa10PyjzdIbyw lnWIIWtZKPPsoVoKVopUWEU3TNhpWmaVhFrUL/O6SN3w=="¶
The corresponding signature metadata derived from this header field is:¶
Property | Value |
---|---|
Algorithm |
rsa-256
|
Covered Content |
date
|
Creation Time | Undefined |
Expiration Time | Undefined |
Verification Key Material | The public key specified in Appendix A.1.1. |
The corresponding Signature Input is:¶
date: Tue, 07 Jun 2014 20:51:35 GMT¶
Appendix B. Topics for Working Group Discussion
This section is to be removed before publishing as an RFC.¶
The goal of this draft document is to provide a starting point at feature parity and compatible with the cavage-12 draft. The draft has known issues that will need to be addressed during development, and in the spirit of keeping compatibility, these issues have been enumerated but not addressed in this version. The editor recommends the working group discuss the issues and features described in this section after adoption of the document by the working group. Topics are not listed in any particular order.¶
B.1. Issues
B.1.1. Confusing guidance on algorithm and key identification
The current draft encourages determining the Algorithm metadata property from the keyId
field, both in the guidance for the use of algorithm
and keyId
, and the definition for the hs2019
algorithm and deprecation of the other algorithms in the registry. The current state arose from concern that a malicious party could change the value of the algorithm
parameter, potentially tricking the verifier into accepting a signature that would not have been verified under the actual parameter.¶
Punting algorithm identification into keyId
hurts interoperability, since we aren't defining the syntax or semantics of keyId
. It actually goes against that claim, as we are dictating that the signing algorithm must be specified by keyId
or derivable from it. It also renders the algorithm registry essentially useless. Instead of this approach, we can protect against manipulation of the Signature header field by adding support for (and possibly mandating) including Signature metadata within the Signature Input.¶
B.1.2. Lack of definition of keyId
hurts interoperability
The current text leaves the format and semantics of keyId
completely up to the implementation. This is primarily due to the fact that most implementers of Cavage have extensive investment in key distribution and management, and just need to plug an identifier into the header. We should support those cases, but we also need to provide guidance for the developer that doesn't have that and just wants to know how to identify a key. It may be enough to punt this to profiling specs, but this needs to be explored more.¶
B.1.3. Algorithm Registry duplicates work of JWA
JSON Web Algorithms (JWA) [RFC7518] already defines an IANA registry for cryptographic algorithms. This wasn't used by Cavage out of concerns about complexity of JOSE, and issues with JWE and JWS being too flexible, leading to insecure combinations of options. Using JWA's definitions does not need to mean we're using JOSE, however. We should look at if/how we can leverage JWA's work without introducing too many sharp edges for implementers.¶
In any use of JWS algorithms, this spec would define a way to create the JWS Signing Input string to be applied to the algorithm. It should be noted that this is incompatible with JWS itself, which requires the inclusion of a structured header in the signature input.¶
A possible approach is to incorporate all elements of the JWA signature algorithm registry into this spec using a prefix or other marker, such as jws-RS256
for the RSA 256 JSON Web Signature algorithm.¶
B.1.4. Algorithm Registry should not be initialized with deprecated entries
The initial entries in this document reflect those in Cavage. The ones that are marked deprecated were done so because of the issue explained in Appendix B.1.1, with the possible exception of rsa-sha1
. We should probably just remove that one.¶
B.1.5. No percent-encoding normalization of path/query
The canonicalization rules for (request-target)
do not perform handle minor, semantically meaningless differences in percent-encoding, such that verification could fail if an intermediary normalizes the effective request URI prior to forwarding the message.¶
At a minimum, they should be case and percent-encoding normalized as described in sections 6.2.2.1 and 6.2.2.2 of [RFC3986].¶
B.1.6. Misleading name for headers
parameter
The Covered Content list contains identifiers for more than just headers, so the header
parameter name is no longer appropriate. Some alternatives: "content", "signed-content", "covered-content".¶
B.1.7. Changes to whitespace in header field values break verification
Some header field values contain RWS, OWS, and/or BWS. Since the header field value canonicalization rules do not address whitespace, changes to it (e.g., removing OWS or BWS or replacing strings of RWS with a single space) can cause verification to fail.¶
B.1.8. Multiple Set-Cookie headers are not well supported
The Set-Cookie header can occur multiple times but does not adhere to the list syntax, and thus is not well supported by the header field value concatenation rules.¶
B.1.9. Covered Content list is not signed
The Covered Content list should be part of the Signature Input, to protect against malicious changes.¶
B.1.10. Algorithm is not signed
The Algorithm should be part of the Signature Input, to protect against malicious changes.¶
B.1.11. Verification key identifier is not signed
The Verification key identifier (e.g., the value used for the keyId
parameter) should be part of the Signature Input, to protect against malicious changes.¶
B.1.12. Max values, precision for Integer String and Decimal String not defined
The definitions for Integer String and Decimal String do not specify a maximum value. The definition for Decimal String (used to provide sub-second precision for Expiration Time) does not define minimum or maximum precision requirements. It should set a sane requirement here (e.g., MUST support up to 3 decimal places and no more).¶
B.1.13. keyId
parameter value could break list syntax
The keyId
parameter value needs to be constrained so as to not break list syntax (e.g., by containing a comma).¶
B.1.14. Creation Time and Expiration Time do not allow for clock skew
The processing instructions for Creation Time and Expiration Time imply that verifiers are not permitted to account for clock skew during signature verification.¶
B.1.15. Should require lowercased header field names as identifiers
The current text allows mixed-case header field names when they are being used as content identifiers. This is unnecessary, as header field names are case-insensitive, and creates opportunity for incompatibility. Instead, content identifiers should always be lowercase.¶
B.1.16. Reconcile Date header and Creation Time
The draft is missing guidance on if/how the Date header relates to signature Creation Time. There are cases where they may be different, such as if a signature was pre-created. Should Creation Time default to the value in the Date header if the created
parameter is not specified?¶
B.1.17. Remove algorithm-specific rules for content identifiers
The rules that restrict when the signer can or must include certain identifiers appear to be related to the pseudo-revving of the Cavage draft that happened when the hs2019
algorithm was introduced. We should drop these rules, as it can be expected that anyone implementing this draft will support all content identifiers.¶
B.1.18. Add guidance for signing compressed headers
The draft should provide guidance on how to sign headers when HTTP/2 header compression [RFC7541] is used. This guidance might be as simple as "sign the uncompressed header field value."¶
B.1.19. Transformations to Via header field value break verification
Intermediaries are permitted to strip comments from the Via header field value, and consolidate related sequences of entries. The canonicalization rules do not account for these changes, and thus they cause signature verification to fail if the Via header is signed. At the very least, guidance on signing or not signing Via headers needs to be included.¶
B.1.20. Case changes to case-insensitive header field values break verification
Some header field values are case-insensitive, in whole or in part. The canonicalization rules do not account for this, thus a case change to a covered header field value causes verification to fail.¶
B.1.21. Need more examples for Signature header
Add more examples showing different cases e.g, where created
or expires
are not present.¶
B.1.22. Expiration not needed
In many cases, putting the expiration of the signature into the hands of the signer opens up more options for failures than necessary. Instead of the expires
, any verifier can use the created
field and an internal lifetime or offset to calculate expiration. We should consider dropping the expires
field.¶
B.2. Features
B.2.1. Define more content identifiers
It should be possible to independently include the following content and metadata properties in Covered Content:¶
B.2.2. Multiple signature support
[[ Editor's note: I believe this use case is theoretical. Please let me know if this is a use case you have. ]]¶
There may be scenarios where attaching multiple signatures to a single message is useful:¶
- A gateway attaches a signature over headers it adds (e.g., Forwarded) to messages already signed by the user agent.¶
- A signer attaches two signatures signed by different keys, to be verified by different entities.¶
This could be addressed by changing the Signature header syntax to accept a list of parameter sets for a single signature, e.g., by separating parameters with ";"
instead of ","
. It may also be necessary to include a signature identifier parameter.¶
B.2.3. Support for incremental signing of header field value list items
[[ Editor's note: I believe this use case is theoretical. Please let me know if this is a use case you have. ]]¶
Currently, signing a header field value is all-or-nothing: either the entire value is signed, or none of it is. For header fields that use list syntax, it would be useful to be able to specify which items in the list are signed.¶
A simple approach that allowed the signer to indicate the list size at signing time would allow a signer to sign header fields that are may be appended to by intermediaries as the message makes its way to the recipient. Specifying list size in terms of number of items could introduce risks of list syntax is not strictly adhered to (e.g., a malicious party crafts a value that gets parsed by the application as 5 items, but by the verifier as 4). Specifying list size in number of octets might address this, but more exploration is required.¶
B.2.4. Support expected authority changes
In some cases, the authority of the effective request URI may be expected to change, for example from "public-service-name.example.com" to "service-host-1.public-service-name.example.com". This is commonly the case for services that are hosted behind a load-balancing gateway, where the client sends requests to a publicly known domain name for the service, and these requests are transformed by the gateway into requests to specific hosts in the service fleet.¶
One possible way to handle this would be to special-case the Host header field to allow verifier to substitute a known expected value, or a value provided in another header field (e.g., Via) when generating the Signature Input, provided that the verifier also recognizes the real value in the Host header. Alternatively, this logic could apply to an (audience)
content identifier.¶
B.2.5. Support for signing specific cookies
A signer may only wish to sign one or a few cookies, for example if the website requires its authentication state cookie to be signed, but also sets other cookies (e.g., for analytics, ad tracking, etc.)¶
Acknowledgements
This specification is based on the draft-cavage-http-signatures draft. The editor would like to thank the authors of that draft, Mark Cavage and Manu Sporny, for their work on that draft and their continuing contributions.¶
The editor would also like to thank the following individuals for feedback on and implementations of the draft-cavage-http-signatures draft (in alphabetical order): Mark Adamcin, Mark Allen, Paul Annesley, Karl Boehlmark, Stephane Bortzmeyer, Sarven Capadisli, Liam Dennehy, ductm54, Stephen Farrell, Phillip Hallam-Baker, Eric Holmes, Andrey Kislyuk, Adam Knight, Dave Lehn, Dave Longley, James H. Manger, Ilari Liusvaara, Mark Nottingham, Yoav Nir, Adrian Palmer, Lucas Pardue, Roberto Polli, Julian Reschke, Michael Richardson, Wojciech Rygielski, Adam Scarr, Cory J. Slep, Dirk Stein, Henry Story, Lukasz Szewc, Chris Webber, and Jeffrey Yasskin¶
Document History
This section is to be removed before publishing as an RFC.¶
-
draft-richanna-http-message-signatures¶
-
-00¶
- Converted to xml2rfc v3 and reformatted to comply with RFC style guides.¶
- Removed
Signature
auth-scheme definition and related content.¶ - Removed conflicting normative requirements for use of
algorithm
parameter. Now MUST NOT be relied upon.¶ - Removed Extensions appendix.¶
- Rewrote abstract and introduction to explain context and need, and challenges inherent in signing HTTP messages.¶
- Rewrote and heavily expanded algorithm definition, retaining normative requirements.¶
- Added definitions for key terms, referenced RFC 7230 for HTTP terms.¶
- Added examples for canonicalization and signature generation steps.¶
- Rewrote Signature header definition, retaining normative requirements.¶
- Added default values for
algorithm
andexpires
parameters.¶ - Rewrote HTTP Signature Algorithms registry definition. Added change control policy and registry template. Removed suggested URI.¶
- Added IANA HTTP Signature Parameter registry.¶
- Added additional normative and informative references.¶
- Added Topics for Working Group Discussion section, to be removed prior to publication as an RFC.¶
-