| Internet-Draft | Signing HTTP Messages | April 2020 |
| Backman, et al. | Expires 12 October 2020 | [Page] |
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.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
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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:¶
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.¶
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:¶
Connection header field ([HTTP], Section 6.1).¶
Via ([HTTP], Section 5.7.1) and Forwarded ([RFC7239], Section 4).¶
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:¶
obs-folds.¶
Additionally, all changes to content not covered by the signature are considered safe.¶
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:¶
"." 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. ]]¶
"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. ]]¶
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.¶
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.¶
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:¶
"," and space " " between each item. The resulting string is the canonicalized value.¶
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.
|
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].¶
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].¶
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:¶
" ".¶
:path pseudo-header in [HTTP2], Section 8.1.2.3. The resulting string is the canonicalized value.¶
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 *
|
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.¶
HTTP Message Signatures have metadata properties that provide information regarding the signature's generation and/or verification. The following metadata properties are defined:¶
The key material required to verify the signature.¶
In order to create a signature, a signer completes the following process:¶
The following sections describe each of these steps in detail.¶
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 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". |
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.
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==
In order to verify a signature, a verifier MUST:¶
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.¶
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:¶
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.¶
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.¶
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:¶
algorithmRECOMMENDED. 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".¶
createdcreated 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.¶
expiresexpires 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.¶
headersheaders 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)".¶
keyIdkeyId 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.¶
signaturesignature parameter contains the signature value, as described in Section 3.2.3.¶
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=="¶
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.¶
"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.¶
[[ 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
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.¶
"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.¶
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¶ |
[[ 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].¶
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.¶
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-----¶
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. |
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"}¶
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=="¶
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=="¶
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¶
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¶
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¶
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.¶
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.¶
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.¶
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.¶
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.¶
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].¶
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".¶
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.¶
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.¶
The Covered Content list should be part of the Signature Input, to protect against malicious changes.¶
The Algorithm should be part of the Signature Input, to protect against malicious changes.¶
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.¶
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).¶
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).¶
The processing instructions for Creation Time and Expiration Time imply that verifiers are not permitted to account for clock skew during signature verification.¶
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.¶
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?¶
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.¶
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."¶
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.¶
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.¶
Add more examples showing different cases e.g, where created or expires are not present.¶
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.¶
It should be possible to independently include the following content and metadata properties in Covered Content:¶
[[ 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:¶
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.¶
[[ 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.¶
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.¶
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.)¶
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 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¶
This section is to be removed before publishing as an RFC.¶
draft-ietf-httpbis-message-signatures¶
draft-richanna-http-message-signatures¶
-00¶
Signature auth-scheme definition and related content.¶
algorithm parameter. Now MUST NOT be relied upon.¶
algorithm and expires parameters.¶