Internet DRAFT - draft-richanna-http-jwt-signature
draft-richanna-http-jwt-signature
Network Working Group A. Backman, Ed.
Internet-Draft Amazon
Intended status: Standards Track November 19, 2019
Expires: May 22, 2020
Signing HTTP Requests via JSON Web Signatures
draft-richanna-http-jwt-signature-00
Abstract
This document defines a method for generating and validating a
digital signature or Message Authentication Code (MAC) over a set of
protocol elements within an HTTP Request, using JSON Web Signatures
(JWS).
Status of This Memo
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This Internet-Draft will expire on May 22, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Generating a HTTP Request Signature Using JWS . . . . . . . . 3
3.1. Generating the Payload of the JWS . . . . . . . . . . . . 4
3.2. Calculating the query parameter list and hash . . . . . . 5
3.3. Calculating the header list and hash . . . . . . . . . . 6
4. Validating the HTTP Request Signature . . . . . . . . . . . . 6
4.1. Validating the query parameter list and hash . . . . . . 7
4.2. Validating the header list and hash . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. JSON Web Signature and Encryption Type Values
Registration . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6.1. Offering Confidentiality Protection for Access to
Protected Resources . . . . . . . . . . . . . . . . . . . 8
6.2. Plaintext Storage of Credentials . . . . . . . . . . . . 9
6.3. Entropy of Keys . . . . . . . . . . . . . . . . . . . . . 9
6.4. Denial of Service . . . . . . . . . . . . . . . . . . . . 9
6.5. Validating the integrity of HTTP message . . . . . . . . 9
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Digital signatures and MACs are popular cryptographic tools that can
be used to address a variety of use cases, such as providing message
integrity, or establishing proof of possession of a cryptographic
key. While several digital signature algorithms exist, they
generally share the constraint that any party wishing to validate a
signature must have or be able to produce the exact byte sequence of
the message that was signed. Consequently, it is non-trivial to
create digital signatures over content that may undergo
transformation, such as can occur with HTTP messages as they pass
through proxies and software libraries in use by the sender or
recipient.
This draft describes a method for generating and validating digital
signatures or MACs over a set of protocol elements within an HTTP
Request. This method consists of:
Mechanisms for identifying the protocol elements covered by the
signature.
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Mechanisms for creating canonical representations of protocol
elements for the purpose of signing.
A mechanism creating and encoding a signature over those canonical
representations using JSON Web Signatures (JWS) [RFC7515].
Many HTTP application frameworks reorder or insert extra headers,
query parameters, and otherwise manipulate the HTTP request on its
way from the web server into the application code itself. Such
transformations may be applied by the sender and recipient, as well
as any proxy through which the message passes. It is the goal of
this draft to have a signature protection mechanism that is
sufficiently robust against such deployment constraints while still
providing sufficient security benefits.
This draft is concerned specifically with the generation,
representation, and validation of signatures over elements within an
HTTP request, with the expectation that this draft will be profiled
by later drafts that seek to apply these signatures to address
specific use cases within a larger application context.
Consequently, key distribution, signing algorithm selection, and
determination of which elements must be covered by the signature are
all out of scope of this draft.
2. 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 RFC
2119 [RFC2119].
Other terms such as "client", "server", "HTTP request", and "protocol
element" are inherited from HTTP [RFC7230].
This document uses the term 'sign' (or 'signature') to denote both a
keyed message digest and a digital signature operation.
3. Generating a HTTP Request Signature Using JWS
This specification uses JSON Web Signature [RFC7515] to sign a set of
protocol elements taken from an HTTP Request. When a JWS is created
for this purpose, its ""typ"" header attribute MUST have the value
""http-sig"".
The JWS MUST be signed with a valid algorithm as defined in
[RFC7518]. The "none" algorithm MUST NOT be used.
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3.1. Generating the Payload of the JWS
The JWS Payload is a JSON object containing the data that will be
covered by the signature. In order to include a protocol element
within the covered data, its value must be represented within this
JSON object. Some elements are represented directly, by setting the
value of a member in the object to the element's value in the HTTP
Request. Others are included indirectly, by setting the value of a
member in the object to a cryptographic hash or other value derived
from the element's value in the HTTP Request.
The below list defines the means of inclusion of various protocol
elements, including the JSON object member that MUST be used when
including the element, and how the element's value should be
included. When present, each of these members MUST be a top-level
member of the JSON object.
The JSON object MAY contain other top-level members. The syntax and
semantics of members not listed below are out of scope of this
specification. Implementations SHOULD consider a signature invalid
if the JSON object contains members that the implementation does not
understand.
ts RECOMMENDED. The timestamp. This integer provides replay
protection of the signed JSON object. Its value MUST be a number
containing an integer value representing number of whole integer
seconds from midnight, January 1, 1970 GMT.
m OPTIONAL. The HTTP Method used to make this request. This MUST
be the uppercase HTTP verb as a JSON string.
u OPTIONAL. The HTTP URL host component as a JSON string. This MAY
include the port separated from the host by a colon in host:port
format.
p OPTIONAL. The HTTP URL path component of the request as an HTTP
string.
q OPTIONAL. The hashed HTTP URL query parameter map of the request
as a two-part JSON array. The first part of this array is a JSON
array listing all query parameters that were used in the
calculation of the hash in the order that they were added to the
hashed value as described below. The second part of this array is
a JSON string containing the Base64URL encoded hash itself,
calculated as described below.
h OPTIONAL. The hashed HTTP request headers as a two-part JSON
array. The first part of this array is a JSON array listing all
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headers that were used in the calculation of the hash in the order
that they were added to the hashed value as described below. The
second part of this array is a JSON string containing the
Base64URL encoded hash itself, calculated as described below.
b OPTIONAL. The base64URL encoded hash of the HTTP Request body,
calculated as the SHA256 of the byte array of the body
All hashes SHALL be calculated using the SHA256 algorithm.
3.2. Calculating the query parameter list and hash
To generate the query parameter list and hash, the signer creates two
data objects: an ordered list of strings to hold the query parameter
names and a string buffer to hold the data to be hashed.
The signer iterates through all query parameters in whatever order it
chooses and for each query parameter it does the following:
1. Adds the name of the query parameter to the end of the list.
2. Percent-encodes the name and value of the parameter as specified
in [RFC3986]. Note that if the name and value have already been
percent-encoded for transit, they are not re-encoded for this
step.
3. Encodes the name and value of the query parameter as "name=value"
and appends it to the string buffer separated by the ampersand
"&" character.
Repeated parameter names are processed separately with no special
handling. Parameters MAY be skipped by the client if they are not
required (or desired) to be covered by the signature.
The signer then calculates the hash over the resulting string buffer.
The list and the hash result are added to a list as the value of the
"q" member.
For example, the query parameter set of "b=bar", "a=foo", "c=duck" is
concatenated into the string:
b=bar&a=foo&c=duck
When added to the JSON structure using this process, the results are:
"q": [["b", "a", "c"], "u4LgkGUWhP9MsKrEjA4dizIllDXluDku6ZqCeyuR-JY"]
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3.3. Calculating the header list and hash
To generate the header list and hash, the signer creates two data
objects: an ordered list of strings to hold the header names and a
string buffer to hold the data to be hashed.
The signer iterates through all query parameters in whatever order it
chooses and for each query parameter it does the following:
1. Lowercases the header name.
2. Adds the name of the header to the end of the list.
3. Encodes the name and value of the header as "name: value" and
appends it to the string buffer separated by a newline "\n"
character.
Repeated header names are processed separately with no special
handling. Headers MAY be skipped by the client if they are not
required (or desired) to be covered by the signature.
The signer then calculates the hash over the resulting string buffer.
The list and the hash result are added to a list as the value of the
"h" member.
For example, the headers "Content-Type: application/json" and "Etag:
742-3u8f34-3r2nvv3" are concatenated into the string:
content-type: application/json
etag: 742-3u8f34-3r2nvv3
"h": [["content-type", "etag"],
"bZA981YJBrPlIzOvplbu3e7ueREXXr38vSkxIBYOaxI"]
4. Validating the HTTP Request Signature
Validation of the signature is done using normal JWS validation for
the signature and key type. Additionally, in order to trust any of
the hashed components of the HTTP request, the validator MUST re-
create and verify a hash for each component as described below. This
process is a mirror of the process used to create the hashes in the
first place, with a mind toward the fact that order may have changed
and that elements may have been added or deleted. The protected
resource MUST similarly compare the replicated values included in
various JSON fields with the corresponding actual values from the
request. Failure to do so will allow an attacker to modify the
underlying request while at the same time having the application
layer verify the signature correctly.
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4.1. Validating the query parameter list and hash
The validator has at its disposal a map that indexes the query
parameter names to the values given. The validator creates a string
buffer for calculating the hash. The validator then iterates through
the "list" portion of the "p" parameter. For each item in the list
(in the order of the list) it does the following:
1. Fetch the value of the parameter from the HTTP request query
parameter map. If a parameter is found in the list of signed
parameters but not in the map, the validation fails.
2. Percent-encodes the name and value of the parameter as specified
in [RFC3986]. Note that if the name and value have already been
percent-encoded for transit, they are not re-encoded for this
step.
3. Encode the parameter as "name=value" and concatenate it to the
end of the string buffer, separated by an ampersand character.
The validator calculates the hash of the string buffer and base64url
encodes it. The protected resource compares that string to the
string passed in as the hash. If the two match, the hash validates,
and all named parameters and their values are considered covered by
the signature.
There MAY be additional query parameters that are not listed in the
list and are therefore not covered by the signature. The validator
MUST decide whether or not to accept a request with these uncovered
parameters.
4.2. Validating the header list and hash
The validator has at its disposal a map that indexes the header names
to the values given. The validator creates a string buffer for
calculating the hash. The validator then iterates through the "list"
portion of the "h" parameter. For each item in the list (in the
order of the list) it does the following:
1. Fetch the value of the header from the HTTP request header map.
If a header is found in the list of signed parameters but not in
the map, the validation fails.
2. Encode the parameter as "name: value" and concatenate it to the
end of the string buffer, separated by a newline character.
The validator calculates the hash of the string buffer and base64url
encodes it. The protected resource compares that string to the
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string passed in as the hash. If the two match, the hash validates,
and all named headers and their values are considered covered by the
signature.
There MAY be additional headers that are not listed in the list and
are therefore not covered by the signature. The validator MUST
decide whether or not to accept a request with these uncovered
headers.
5. IANA Considerations
5.1. JSON Web Signature and Encryption Type Values Registration
This specification registers the "http-sig" type value in the IANA
JSON Web Signature and Encryption Type Values registry [RFC7515]:
o "typ" Header Parameter Value: "http-sig"
o Abbreviation for MIME Type: None
o Change Controller: IETF
o Specification Document(s): [[ this document ]]
6. Security Considerations
6.1. Offering Confidentiality Protection for Access to Protected
Resources
This specification can be used with and without Transport Layer
Security (TLS).
Without TLS this protocol provides a mechanism for verifying the
integrity of requests, it provides no confidentiality protection.
Consequently, eavesdroppers will have full access to communication
content and any further messages exchanged between the client and the
server. This could be problematic when data is exchanged that
requires care, such as personal data.
When TLS is used then confidentiality of the transmission can be
ensured between endpoints, including both the request and the
response. The use of TLS in combination with the signed HTTP request
mechanism is highly recommended to ensure the confidentiality of the
data returned from the protected resource.
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6.2. Plaintext Storage of Credentials
The mechanism described in this document works in a similar way to
many three-party authentication and key exchange mechanisms. In
order to compute the signature over the HTTP request, the client must
have access to the decryption key in plaintext form. If an attacker
were to gain access to these stored secrets at the client or (in case
of symmetric keys) at the server they would be able to forge
signatures for any HTTP request they wished, effectively allowing
them to impersonate the client.
It is therefore paramount to the security of the protocol that any
private or symmetric keys used to sign HTTP requests are protected
from unauthorized access.
6.3. Entropy of Keys
Unless TLS is used between the client and the resource server,
eavesdroppers will have full access to requests sent by the client.
They will thus be able to mount off-line brute-force attacks to
attempt recovery of the session key or private key used to compute
the keyed message digest or digital signature, respectively.
Key generation and distribution is out of scope for this document.
It is the responsibility of users of this specification to ensure
that keys are generated with sufficient entropy and rotated at an
appropriate frequency to sufficiently mitigate the risk of such
attacks, as appropriate for their use case.
6.4. Denial of Service
This specification includes a number of features which may make
resource exhaustion attacks against servers possible. For example,
server may need to consult back-end databases or other servers in
order to verify a signature, or the cryptographic overhead may
present a significant burden on the server. An attacker could
leverage this overhead to attempt a denial of service attack by
sending a large number of invalid requests to the server, causing the
server to expend significant resources checking invalid signatures.
This attack vector must be taken into consideration when implementing
or deploying this specification.
6.5. Validating the integrity of HTTP message
This specification provides flexibility for selectively validating
the integrity of the HTTP request, including header fields, query
parameters, and message bodies. Since all components of the HTTP
request are only optionally validated by this method, and even some
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components may be validated only in part (e.g., some headers but not
others) it is up to developers to verify that any vital parameters in
a request are actually covered by the signature. Failure to do so
could allow an attacker to inject vital parameters or headers into
the request, ouside of the protection of the signature.
The application verifying this signature MUST NOT assume that any
particular parameter is appropriately covered by the signature unless
it is included in the signed structure and the hash is verified. Any
applications that are sensitive of header or query parameter order
MUST verify the order of the parameters on their own. The
application MUST also compare the values in the JSON container with
the actual parameters received with the HTTP request (using a direct
comparison or a hash calculation, as appropriate). Failure to make
this comparison will render the signature mechanism useless for
protecting these elements.
The behavior of repeated query parameters or repeated HTTP headers is
undefined by this specification. If a header or query parameter is
repeated on either the outgoing request from the client or the
incoming request to the protected resource, that query parameter or
header name MUST NOT be covered by the hash and signature.
This specification records the order in which query parameters and
headers are hashed, but it does not guarantee that order is preserved
between the client and protected resource. If the order of
parameters or headers are significant to the underlying application,
it MUST confirm their order on its own, apart from the signature and
HTTP message validation.
7. Privacy Considerations
This specification addresses machine to machine communications and
raises no privacy considerations beyond existing HTTP interactions.
8. Acknowledgements
The authors thank the OAuth Working Group for input into this work.
In particular, the authors thank Justin Richer for his work on
[I-D.ietf-oauth-signed-http-request], on which this specification is
based.
9. Normative References
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[I-D.ietf-oauth-signed-http-request]
Richer, J., Bradley, J., and H. Tschofenig, "A Method for
Signing HTTP Requests for OAuth", draft-ietf-oauth-signed-
http-request-03 (work in progress), August 2016.
[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>.
[RFC7230] 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>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.
Author's Address
Annabelle Backman (editor)
Amazon
Email: richanna@amazon.com
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