I've implemented the optional buffering of the attachment streams on
receiving end, and prototyped the following text, I don't have the
experience to drive it further, nor do I expect it to make it to the
draft stage, but I thought I'd type in some prototype.
Thanks, Sergey
Using Json Web Signature (JWS) to sign HTTP Multipart payloads
Abstract.
JSON Web Signature (JWS) represents content secured with digital
signatures or Message Authentication Codes (MACs) using JSON-based
data structures, with the content being optionally detached [RFC7515].
The content can also be secured without it being Base64URL-encoded
[RFC7797].
HTTP Multipart payloads are HTTP messages constructed according to HTTP
multipart
media type rules [RFC1341]. This specification describes how HTTP
multipart payloads
can be signed using JWS With Detached and Unencoded Content mechanism.
Introduction.
HTTP Multipart data structure, in combination with JWS With Detached and
Unencoded Content mechanism,
can provide for the end to end integrity protection of HTTP Multiparts.
The sender of such secured payloads will stream and have no need to
buffer the data while the receiver may optionally continue
streaming the data (see Security Considerations).
Implementation.
Implementations supporting this specification will need to intercept
HTTP Multipart write and read processes.
When request or response attachment parts are about to be submitted to
the HTTP Multipart serialization provider, JWS Multipart Output Filter
initializes a JWS Signature object which can dynamically build up a
signature. Next every parts's output stream is replaced with the
filtering output stream which updates the signature object on every
write operation. Finally this multipart filter adds one more attachment
part to the list of the attachments to be written - this part holds a
reference to JWS Signature. When this last part is written, JWSSignature
produces the signature bytes which are encoded using either JWS Compact
or JWS JSON format, with the detached and unencoded content already
being pushed to the output stream.
When the attachment parts are about to be read by the Multipart
deserialization provider, their signature carried over in the last part
will need to be verified. Just before the parts are about to be read in
order to be made available to the application code, JWS Multipart Input
Filter checks the last part and initializes a JWS Verification Signature
object which can dynamically build up a signature. Next for every
attachment but the last one it replaces the input stream with the
filtering input stream which updates the signature verification object
on every read operation. Once all the data have been read it compares
the calculated signature with the received signature.
Example.
JWS-signed HTTP Multipart payload captured on the wire
Security Considerations.
Using JWS to validate Detached Content implies that the content and the
signature have been obtained
via the different channels with the receiver starting the signature
verification process once both the
data and the signature have been received.
In the case of this specification the references to the attachment data
can become available to the receiving code
before the data have been validated, with the data read process failing
to complete in case of the signature verification failure.
However, if, as part of the read process, the receiver copies the data
to the medium which can pro-actively interpret the copied bytes,
example, the client receiver copies the data to the embedded browser
window, then, in order to avoid the side-effects, the receiver of signed
HTTP multipart payload MUST buffer and validate the multipart data first
before making it available to the application code.
References.
https://tools.ietf.org/html/rfc7515
https://tools.ietf.org/html/rfc7797
http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html
See also:
https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding-09
On 12/05/17 20:14, Sergey Beryozkin wrote:
Hi,
On 12/05/17 17:45, Jim Schaad wrote:
-----Original Message-----
From: jose [mailto:[email protected]] On Behalf Of Sergey Beryozkin
Sent: Friday, May 12, 2017 9:04 AM
To: Ilari Liusvaara <[email protected]>
Cc: [email protected]
Subject: Re: [jose] JWS Signing of HTTP attachments
Thanks for the initial feedback. I'm not following at the moment how
any of
these attacks can affect it. Perhaps I'll need to work on making it more
obvious how it is all implemented.
It is simply a concrete implementation of JWS with Detached Content.
The content is written out and by the time it's finished the JWS payload
will be finished and will accompany this content.
On the receiving end the verification provider will be instantiated (with
the proper care, example, the server will not support the dynamic
verification provider selection process - i.e - will be expected to
process
only RSA or HMAC etc signatures). Once this provider is available it will
then get all the data which is being read passing through the
verification
process and finally compare the signatures
[JLS] To be clear here, the question that is being asked is - are we
going
to show content to the user, and perhaps start executing script,
before we
have finished verifying the signature. This is normal for browsers as
they
do incremental display as things are processed. And then, what
happens to
the display if the signature fails to verify.
Right, I understand what the concern is, thanks.
I believe this is a general security issue to be considered for JWS With
Detached Content - the secured data and their signature have reached the
destinations via the different channels, where the data has already been
obtained (possibly read completely), and now is passed to the JOSE
library to verify the data are still OK.
I guess it should be noted that JWS With Detached Content should be used
with care when it is expected that the data will be made available to
the user's display or similar. Perhaps I'll send another email to keep
the issue tracked ?
For my project I think I'll introduce an optional (possibly enabled by
default) buffering of the attachments on the receiving end - so it will
be 50% (sender-only) streaming friendly in this case :-).
FYI my primary goal has been to ensure the client application, Java
based or browser-based, can post the secured attachments to the HTTP
service - say a service will need to copy InputStream to the disk - in
this case, even though the code will access the stream immediately, the
copy process will fail to complete, etc. I suspect it could be
acceptable in some cases especially if the task is to protect 1MB.etc
attachments.
However I do understand that if such data are started immediately acted
upon before the read process is even complete, either on the server, or
especially on the UI-aware client side then there could be the
side-effects and as I noted I'll optionally support the caching of the
attachment parts before they are submitted to the service code.
Thanks very much, Sergey
Cheers, Sergey
On 12/05/17 16:52, Ilari Liusvaara wrote:
On Fri, May 12, 2017 at 01:59:21PM +0100, Sergey Beryozkin wrote:
Hi All,
I've experimented in our project with having HTTP attachment parts
protected using JWS with Detached Content and Unencoded Payload options
[1].
This approach appears to be quite effective to me. It also appears to
me that the data as shown in the example at [1], can, in principle,
be produced and processed by any HTTP stack that can work with
multiparts, assuming a JOSE library supporting the detached and
unencoded content is also available.
I'd appreciate if the experts could comment on 1) do you see some
weaknesses in the proposed approach and 2) can someone see a point in
drafting some text around it (I can contribute if it is of interest) ?
It look from the text that the implementation can produce output
before the entiere signature (or tag in case of encryption) has been
verified.
This is very dangerous if so.
Then there are the standard attacks against JOSE (the JOSE library
must not be vulernable to these):
- The JWS HMAC versus signature confusion
- The JWE ECDH-ES invalid curve attack.
-Ilari
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