Signing HTTP Messages
draft-ietf-httpbis-message-signatures-00
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Annabelle Backman , Justin Richer , Manu Sporny | ||
| Last updated | 2020-10-12 (Latest revision 2020-04-10) | ||
| Replaces | draft-richanna-http-message-signatures, draft-cavage-http-signatures | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-httpbis-message-signatures-00
HTTPbis Working Group A. Backman, Ed.
Internet-Draft Amazon
Intended status: Standards Track J. Richer
Expires: 12 October 2020 Bespoke Engineering
M. Sporny
Digital Bazaar
10 April 2020
Signing HTTP Messages
draft-ietf-httpbis-message-signatures-00
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.
Note
This draft is based on draft-cavage-http-signatures-12. The
community (https://github.com/w3c-dvcg/http-signatures/
issues?page=2&q=is%3Aissue+is%3Aopen) 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
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 October 2020.
Copyright Notice
Copyright (c) 2020 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Discussion . . . . . . . . . . . . . . . . . 4
1.2. HTTP Message Transformations . . . . . . . . . . . . . . 5
1.3. Safe Transformations . . . . . . . . . . . . . . . . . . 5
1.4. Conventions and Terminology . . . . . . . . . . . . . . . 6
2. Identifying and Canonicalizing Content . . . . . . . . . . . 7
2.1. HTTP Header Fields . . . . . . . . . . . . . . . . . . . 7
2.2. Signature Creation Time . . . . . . . . . . . . . . . . . 8
2.3. Signature Expiration Time . . . . . . . . . . . . . . . . 9
2.4. Target Endpoint . . . . . . . . . . . . . . . . . . . . . 9
3. HTTP Message Signatures . . . . . . . . . . . . . . . . . . . 10
3.1. Signature Metadata . . . . . . . . . . . . . . . . . . . 10
3.2. Creating a Signature . . . . . . . . . . . . . . . . . . 11
3.2.1. Choose and Set Signature Metadata Properties . . . . 11
3.2.2. Create the Signature Input . . . . . . . . . . . . . 13
3.2.3. Sign the Signature Input . . . . . . . . . . . . . . 14
3.3. Verifying a Signature . . . . . . . . . . . . . . . . . . 14
3.3.1. Enforcing Application Requirements . . . . . . . . . 15
4. The 'Signature' HTTP Header . . . . . . . . . . . . . . . . . 15
4.1. Signature Header Parameters . . . . . . . . . . . . . . . 16
4.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
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5.1. HTTP Signature Algorithms Registry . . . . . . . . . . . 17
5.1.1. Registration Template . . . . . . . . . . . . . . . . 17
5.1.2. Initial Contents . . . . . . . . . . . . . . . . . . 18
5.2. HTTP Signature Parameters Registry . . . . . . . . . . . 20
5.2.1. Registration Template . . . . . . . . . . . . . . . . 20
5.2.2. Initial Contents . . . . . . . . . . . . . . . . . . 20
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. Normative References . . . . . . . . . . . . . . . . . . 21
7.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 23
A.1. Example Keys . . . . . . . . . . . . . . . . . . . . . . 23
A.1.1. "rsa-test" . . . . . . . . . . . . . . . . . . . . . 23
A.2. Example "keyId" Values . . . . . . . . . . . . . . . . . 24
A.3. Test Cases . . . . . . . . . . . . . . . . . . . . . . . 25
A.3.1. Signature Generation . . . . . . . . . . . . . . . . 25
A.3.2. Signature Verification . . . . . . . . . . . . . . . 27
Appendix B. Topics for Working Group Discussion . . . . . . . . 30
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 36
Document History . . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
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
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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 (https://openjdk.java.net/groups/net/httpclient/
intro.html)). These applications need to be able to generate and
verify signatures despite incomplete knowledge of the HTTP message.
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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)
and "Forwarded" ([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.
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* 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.
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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:
1. 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.
2. Strip leading and trailing whitespace from each item in the list.
3. Concatenate the list items together, with a comma "","" and space
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"" "" 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." |
+---------------------+------------------------------------+
Table 1: Non-normative examples of header field
canonicalization.
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
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(https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
V1_chap04.html#tag_04_16) of [POSIX.1].
| The use of seconds since the Epoch to canonicalize a timestamp
| simplifies processing and avoids timezone management required
| by specifications such as [RFC3339].
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
(https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
V1_chap04.html#tag_04_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:
1. Take the lowercased HTTP method of the message.
2. Append a space "" "".
3. 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.
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+-------------------------+--------------------+
| HTTP Message | "(request-target)" |
+=========================+====================+
| POST /?param=value HTTP/1.1| "post |
| Host: www.example.com | /?param=value" |
+-------------------------+--------------------+
| POST /a/b HTTP/1.1 | "post /a/b" |
| Host: www.example.com | |
+-------------------------+--------------------+
| 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| "connect /" |
| Host: server.example.com| |
+-------------------------+--------------------+
| OPTIONS * HTTP/1.1 | "options *" |
| Host: server.example.com| |
+-------------------------+--------------------+
Table 2: Non-normative examples of "(request-target)"
canonicalization.
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.
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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:
1. Choose key material and algorithm, and set metadata properties
(Section 3.2.1)
2. Create the Signature Input (Section 3.2.2)
3. 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
1. 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.
2. 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.
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3. The signer sets the signature's Creation Time property to the
current time.
4. 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.
5. 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", or "ecdsa", signers SHOULD include "(created)" and
"(request-target)" in the list.
If the signature's Algorithm starts with "rsa", "hmac", or
"ecdsa", signers SHOULD include "date" 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 | "(request-target)", "(created)", "host", "date", |
| Content | "cache-contol", "x-emptyheader", "x-example" |
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+--------------+--------------------------------------------------+
| Creation | Equal to the value specified in the Date header |
| Time | field. |
+--------------+--------------------------------------------------+
| Expiration | Equal to the Creation Time plus five minutes. |
| Time | |
+--------------+--------------------------------------------------+
| Verification | The public key provided in Appendix A.1.1 and |
| Key Material | identified by the "keyId" value "test-key-b". |
+--------------+--------------------------------------------------+
Table 3: Non-normative example metadata values
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:
(request-target): get /foo
(created): 1402170695
host: example.org
date: Tue, 07 Jun 2014 20:51:35 GMT
cache-control: max-age=60, must-revalidate
x-emptyheader:
x-example: Example header with some whitespace.
Figure 1: Non-normative example Signature Input
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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:
T1l3tWH2cSP31nfuvc3nVaHQ6IAu9YLEXg2pCeEOJETXnlWbgKtBTaXV6LNQWtf4O42V2
DZwDZbmVZ8xW3TFW80RrfrY0+fyjD4OLN7/zV6L6d2v7uBpuWZ8QzKuHYFaRNVXgFBXN3
VJnsIOUjv20pqZMKO3phLCKX2/zQzJLCBQvF/5UKtnJiMp1ACNhG8LF0Q0FPWfe86YZBB
xqrQr5WfjMu0LOO52ZAxi9KTWSlceJ2U361gDb7S5Deub8MaDrjUEpluphQeo8xyvHBoN
Xsqeax/WaHyRYOgaW6krxEGVaBQAfA2czYZhEA05Tb38ahq/gwDQ1bagd9rGnCHtAg==
Figure 2: Non-normative example signature value
3.3. Verifying a Signature
In order to verify a signature, a verifier MUST:
1. 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.
2. Use the received HTTP message and the signature's metadata to
recreate the Signature Input, using the process described in
Section 3.2.2.
3. 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.
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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.
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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 the "keyId" parameter
rather than from "algorithm". If "algorithm" is provided and
differs from or is incompatible with the algorithm or key material
identified by "keyId" (for example, "algorithm" has a value of
"rsa-sha256" but "keyId" 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 the "algorithm" 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
the "Date" 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 parameter "MUST"
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
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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's "Verification 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
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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"
Algorithm Name
"hs2019"
Status
active
Description
Derived from metadata associated with "keyId". Recommend support
for:
* RSASSA-PSS [RFC8017] using SHA-512 [RFC6234]
* HMAC [RFC2104] using SHA-512 [RFC6234]
* ECDSA using curve P-256 [DSS] and SHA-512 [RFC6234]
* Ed25519ph, Ed25519ctx, and Ed25519 [RFC8032]
"rsa-sha1"
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Algorithm Name
"rsa-sha1"
Status
Deprecated; SHA-1 not secure.
Description
RSASSA-PKCS1-v1_5 [RFC8017] using SHA-1 [RFC6234]
"rsa-sha256"
Algorithm Name
"rsa-sha256"
Status
Deprecated; specifying signature algorithm enables attack vector.
Description
RSASSA-PKCS1-v1_5 [RFC8017] using SHA-256 [RFC6234]
"hmac-sha256"
Algorithm Name
"hmac-sha256"
Status
Deprecated; specifying signature algorithm enables attack vector.
Description
HMAC [RFC2104] using SHA-256 [RFC6234]
"ecdsa-sha256"
Algorithm Name
"ecdsa-sha256"
Status
Deprecated; specifying signature algorithm enables attack vector.
Description
ECDSA using curve P-256 [DSS] and SHA-256 [RFC6234]
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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.
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+-------------+--------+------------------------------+
| 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 |
+-------------+--------+------------------------------+
Table 4: Initial contents of the HTTP Signature
Parameters Registry.
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, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[DSS] NIST, "Digital Signature Standard (DSS)", FIPS 186-4,
DOI 10.6028/NIST.FIPS.186-4, July 2013,
<https://csrc.nist.gov/publications/detail/fips/186/4/
final>.
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[HTTP] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<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, May 2015,
<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, 2018,
<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, February 1997,
<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, March 1997,
<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, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<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, May 2015,
<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,
May 2017, <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, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.
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[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
RFC 7239, DOI 10.17487/RFC7239, June 2014,
<https://www.rfc-editor.org/info/rfc7239>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<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, November 2016,
<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, January 2017,
<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, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[WP-HTTP-Sig-Audit]
Sporny, M., "Security Considerations for HTTP Signatures",
June 2013, <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:
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-----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-----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-----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.
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+--------------+---------------------------------+-----------------+
| "keyId" | Algorithm | Verification |
| | | Key |
+==============+=================================+=================+
| "test-key-a" | "hs2019", using RSASSA-PSS | The public key |
| | [RFC8017] and SHA-512 [RFC6234] | specified in |
| | | Appendix A.1.1. |
+--------------+---------------------------------+-----------------+
| "test-key-b" | "rsa-256" | The public key |
| | | specified in |
| | | Appendix A.1.1. |
+--------------+---------------------------------+-----------------+
Table 5
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 | "(created) (request-target)" |
| Content | |
+--------------+-----------------------------------+
| Creation | 8:51:35 PM GMT, June 7th, 2014 |
| Time | |
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+--------------+-----------------------------------+
| Expiration | Undefined |
| Time | |
+--------------+-----------------------------------+
| Verification | The public key specified in |
| Key Material | Appendix A.1.1. |
+--------------+-----------------------------------+
Table 6
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 | "(created)", "(request-target)", "host", "date", |
| Content | "content-type", "digest", "content-length" |
+--------------+--------------------------------------------------+
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| Creation | 8:51:35 PM GMT, June 7th, 2014 |
| Time | |
+--------------+--------------------------------------------------+
| Expiration | Undefined |
| Time | |
+--------------+--------------------------------------------------+
| Verification | The public key specified in Appendix A.1.1. |
| Key Material | |
+--------------+--------------------------------------------------+
Table 7
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
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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 | "(created)" |
| Content | |
+--------------+-----------------------------------+
| Creation | 8:51:35 PM GMT, June 7th, 2014 |
| Time | |
+--------------+-----------------------------------+
| Expiration | Undefined |
| Time | |
+--------------+-----------------------------------+
| Verification | The public key specified in |
| Key Material | Appendix A.1.1. |
+--------------+-----------------------------------+
Table 8
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:
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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 | "(created)" |
| Content | |
+--------------+-----------------------------------+
| Creation | 8:51:35 PM GMT, June 7th, 2014 |
| Time | |
+--------------+-----------------------------------+
| Expiration | Undefined |
| Time | |
+--------------+-----------------------------------+
| Verification | The public key specified in |
| Key Material | Appendix A.1.1. |
+--------------+-----------------------------------+
Table 9
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:
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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. |
+---------------------------+--------------------------+
Table 10
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
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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
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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
See: issue #26 (https://github.com/w3c-dvcg/http-signatures/
issues/26)
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.
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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?
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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
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B.2.1. Define more content identifiers
It should be possible to independently include the following content
and metadata properties in Covered Content:
* The signature's Algorithm
* The signature's Covered Content
* The value used for the "keyId" parameter
* Request method
* Individual components of the effective request URI: scheme,
authority, path, query
* Status code
* Request body (currently supported via Digest header)
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.
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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 Böhlmark, Stéphane 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
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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-ietf-httpbis-message-signatures*
- *-00*
o Copied from draft-richanna-http-message-signatures
o Corrected header field content identifiers in Table 1.
* *draft-richanna-http-message-signatures*
- *-00*
o Converted to xml2rfc v3 and reformatted to comply with RFC
style guides.
o Removed "Signature" auth-scheme definition and related
content.
o Removed conflicting normative requirements for use of
"algorithm" parameter. Now MUST NOT be relied upon.
o Removed Extensions appendix.
o Rewrote abstract and introduction to explain context and
need, and challenges inherent in signing HTTP messages.
o Rewrote and heavily expanded algorithm definition, retaining
normative requirements.
o Added definitions for key terms, referenced RFC 7230 for
HTTP terms.
o Added examples for canonicalization and signature generation
steps.
o Rewrote Signature header definition, retaining normative
requirements.
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o Added default values for "algorithm" and "expires"
parameters.
o Rewrote HTTP Signature Algorithms registry definition.
Added change control policy and registry template. Removed
suggested URI.
o Added IANA HTTP Signature Parameter registry.
o Added additional normative and informative references.
o Added Topics for Working Group Discussion section, to be
removed prior to publication as an RFC.
Authors' Addresses
Annabelle Backman (editor)
Amazon
P.O. Box 81226
Seattle, WA 98108-1226
United States of America
Email: richanna@amazon.com
URI: https://www.amazon.com/
Justin Richer
Bespoke Engineering
Email: ietf@justin.richer.org
URI: https://bspk.io/
Manu Sporny
Digital Bazaar
203 Roanoke Street W.
Blacksburg, VA 24060
United States of America
Phone: +1 540 961 4469
Email: msporny@digitalbazaar.com
URI: https://manu.sporny.org/
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