One document matched: draft-hallambaker-httpsession-02.xml
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<rfc category="std" docName="draft-hallambaker-httpsession-02" ipr="trust200902">
<front>
<title abbrev="HTTP Session Management">HTTP Session Management</title>
<author fullname="Phillip Hallam-Baker" initials="P. M." surname="Hallam-Baker">
<organization>Comodo Group Inc.</organization>
<address>
<email>philliph@comodo.com</email>
</address>
</author>
<date day="21" month="January" year="2014" />
<area>General</area>
<workgroup>Internet Engineering Task Force</workgroup>
<abstract>
<t>
The HTTP Session Management Mechanism provides a mean of securely establishing
a persistent authentication session between a HTTP client and server that does not
rely on the presentation of a confidential bearer token. The Session
Management Mechanism is intended to provide a replacement for the existing
HTTP State Management Mechanism (Cookies) for this purpose.
</t>
<t>
This document defines the HTTP Accept-Session, Set-Session and Session
headers
and specifies their use to establish symmetric authentication keys and their use to
authenticate and verify specific parts of an HTTP message.
Other means by which keys used to authenticate the messages
are established are outside the scope of this document.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
The HTTP State Management Mechanism 'Cookies'<xref target="RFC6265"/>
was intended to allow HTTP <xref target="RFC2616"/> servers
to let servers maintain a stateful session over the mostly stateless HTTP protocol.
While the exchange of static tokens is an acceptable mechanism for maintaining state,
use of static tokens as bearer tokens for authentication is not. Such
tokens are not bound to any part of the message they purport to authenticate and
may be disclosed to intermediaries including HTTP proxies and caches.
</t>
<t>
While use of TLS transport provides a confidentiality enhancement for HTTP content,
recent research <xref target="CRIME" />, <xref target="BEAST" /> demonstrates that relying on a transport or network
layer to protect the confidentiality of a bearer authentication token is fundamentaly
unsound. The interaction of HTTP header compression mechanisms and a Turing complete
active code mechanism under control of the attacker produces a threat model in which
the capabilities afforded the attacker far exceed the capabilities that it is sensible
to expect a protocol design to resist.
</t>
<t>
The HTTP Accept-Session, Set-Session and Session headers provide a simple and effective means
of maintaining a HTTP authentication session without passing static authentication
data in either direction after the authentication session has been established.
The design of the Set-Session and Session headers permit them to be used as a
replacement for the Set-Cookie and Cookie headers in situations where they are
supported by both the client and the server and ensure correct behavior by
intermediaries conformant to the HTTP specification.
</t>
<t>
A HTTP authentication session MAY be established inband by means of the Set-Session
header. The Set-Session header specifies a unique identifier for the session and
determines the session parameters including the cryptographic algorithm and shared
key.
</t>
<t>
Applications SHOULD make use of cryptographic enhancements to protect the
confidentiality of a session context established using the Set-Session header.
</t>
<t>
Clients and Servers MAY support other means of establishing a HTTP authentication
session. For example in a federated authentication scheme such as SAML, Kerberos
or OpenID, the authentication session might be provided by a third party.
</t>
<t>
Once the HTTP authentication session is established, a Session header is added to
HTTP requests and/or responses as directed by the session context.
The session header specifies the session identifier and an authentication value
calculated over portions of the HTTP message and other attributes to which it is
bound as directed by
the corresponding session context. The bound attributes and portions of the HTTP
message cannot then
be changed without invalidating the authentication value.
</t>
<t>
The use of bound attributes permits protection against TLS channel rebinding and/or
HTTP message replay attacks.
</t>
<t>
The portions of a HTTP message to which it is desirable to bind an authentication
session depend on the situation. Binding the authentication session to the message
content prevents modification of the content but imposes more constraints on
implementations than binding to the message start line. Interactions with
intermediaries and in particular intermediarries that are not fully compliant with
the HTTP specification also raise concerns Web browsers are typically coded to be
tollerant of such implementation defects and operate despite unauthorized modification
of content by caches and other intermediaries. The prefered behavior of a Web
Service client in such situations is likely to be to abort the transaction rather than
risk continuing with corrupted data.
</t>
<section title="Relationship to Other Authentication Technologies">
<t>
The term 'user authentication' is commonly used in three separate contexts;
credential management, credential presentation and
session continuation:
</t>
<t>
<list>
<t>
Credential Management describes the means by which credentials are created,
issued and revoked.
</t>
<t>
Credential Presentation describes the means by which a party demonstrates
holdership of a credential to establish an authentication session.
</t>
<t>
Session Continuation describes the means by which a party demonstrates
that a particular transaction is taking place within the context of a
particular authentication session.
</t>
</list>
</t>
<t>
The HTTP Session Management Mechanism is designed to support only Session Continuation and
to compliment existing and future mechanisms for Credential management and Credential Presentation.
While a session continuation
mechanism is not in itself a solution to the problem of user authentication,
the provision of a robust session continuation mechanism that does not
depend on a bearer token addresses the
most challenging problem
facing the designers of SAML, OpenID and OAUTH.
</t>
</section>
<section title="Example: Web Browser User Authentication">
<t>
The principal mechanism for user authentication in use today is to present
a HTML form in which the user enters their username and password.
</t>
<t>
This approach has many
known defects that are outside the scope of this document. These include the risk of
impersonation of the Web site causing the user
to enter their username and password into a form controlled by the attack and the strong
likelihood that the user will use the same password across multiple sites.
</t>
<t>
The client indicates that it supports the session header by including one or
more Accept-Session headers in the request transfering the username and password
values. The Accept-Session header specifies the scope and replay binding options
that the client offers to support.
</t>
<t>[NB: These examples are not yet generated from running code and are for illustrative purposes only]</t>
<figure>
<artwork>
<![CDATA[POST /login.php HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: application/x-www-form-urlencoded
Content-Length: 29
Accept-Session: Start=required Request=required Content=optional Time=required
username=skroob&password=1234]]>
</artwork>
</figure>
<t>
If the browser does not specify a Accept-Session header the server MAY reject the
connection request entirely or fallback to the traditional Cookie mechanism as
determined by site policy.
</t>
<t>
If the service accepts the offer of session management support, it includes
a Set-session Header in the response specifying the session context:
</t>
<figure>
<artwork>
<![CDATA[HTTP/1.1 201 OK
Content-Length: 35
Set-Session:
Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
Key=7eb219188339135ba51e8715f3900bfb974995e145d6e490e4addbbdb26f4bb4
Alg=HMAC-SHA256 Start=True Request=True Time=True Now=745531 Domain=example.com
Max-Age=31536000
<html><h1>Authenticated</h1></html>]]>
</artwork>
</figure>
<t>
In this case the server avoids the need to track per client state by using
a time based mechanism to avoid replay attacks and storing the state associated
with the client session as encrypted data within the session identifier. The
scope of the content binding is limited to the start line and the timer to be used
for replay attack prevention has an offset 745531 seconds in the past.
</t>
<t>
Once the session has been established, the client MUST include a Session header
in subsequent HTTP requests made to the specified DNS domains.
</t>
<figure>
<artwork>
<![CDATA[GET /status.php HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: application/x-www-form-urlencoded
Content-Length: 29
Session: Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
Value=cjkMkfnnYP8JYWZAbRLvtpqImmOK3rsrOT1XcvAgHDk=;
Now=745533
]]>
</artwork>
</figure>
<t>
In this case the session scope does not specify responses and so the response does
not require an Session header but a server MAY provide one so as to specify updated values
for the replay attack prevention attributes Now and/or Count. Whenever a Session
header is present the Id and Value attributes MUST be specified and correct:
</t>
<figure>
<artwork>
<![CDATA[HTTP/1.1 201 OK
Content-Length: 35
Session:
Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
Value=cjkMkfnnYP8JYWZAbRLvtpqImmOK3rsrOT1XcvAgHDk=;
Now=745532
<html><h1>Shield is Closed</h1></html>]]>
</artwork>
</figure>
<t>
In this particular instance the clock at the server is running behind that of the
client requiring the timer offset value to be decreased by one second. To ensure that
the replay attack protection values only increase or stay the same, the client uses the
last value of the old time offset until the new time offset value has superceded it.
</t>
<t>
The Web Browser MAY terminate the session by simply deleting the session context information
from its store preventing reuse. A client MAY inform the server that the session context is
about to be deleted by including a Session header with the Deleted attribute:
</t>
<figure>
<artwork>
<![CDATA[HEAD /status.php HTTP/1.1
Host: example.com
Session: Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
Value=cjkMkfnnYP8JYWZAbRLvtpqImmOK3rsrOT1XcvAgHDk=;
Deleted
]]>
</artwork>
</figure>
<t>
A server may inform the client that the session has been terminated by including a Session
header with the Deleted attribute in the response.
</t>
</section>
<section title="Use in Web Services">
<t>
Use of HTTP Session Managment simplifies implemenatation of
Web Services. Using the SOAP [TBS] approach a Web Service message is encoded in XML [TBS], wrapped in
a SOAP envelope and a WS-Security [TBS] header with an XML Signature [TBS] attached. The whole
package is then attached to a HTTP message as a content payload.
</t>
<t>
This approach involves a considerable degree of complexity and in most cases does
nothing more than attach authentication data to a message. Carrying the authentication value as a HTTP
header typically eliminates the need for the SOAP and WS-Security layers entirely.
</t>
<t>
Use of session management in Web Services presents different requirements and constraints.
In the case of an entirely new Web Service with no deployment history, there is no need to
consider support for legacy code at all, eliminating one of the principal constraints
governing use of new HTTP protocol features in Web Browsers.
</t>
<t>
A single HTTP message MAY have multiple Session headers. This facilitates support
for multi-party transactions in which A submits a transaction to B who countersigns it
and passes it to C who is required to chek that she has proof of agreement by both
A and B.
</t>
<t>
Use of the Session header permits the developer to isolate integrity and
authentication checks to a single point of control, as is advised by best security
practice. The security monitor examines a HTTP message, verifies that the
required integrity data is present and correct and only passes the payload on for
processing by the Web Service itself if and only if the verification checks have
been passed.
</t>
</section>
</section>
<section title="Session Context">
<t>
The processing of the Session header is determined by the session context which consists of
a set of fixed attributes that remain constant for the lifetime of the session and
state attributes that are updated as Session headers are generated and verified.
</t>
<section title="Fixed Session Context">
<t>
The fixed session context elements are set when the session is established and remain
constant for the lifetime of the session. The values specified can only be changed by
establishing a new session which MUST have a different session identifier.
</t>
<section title="Id: Identifier">
<t>
The session identifier is a statistically unique sequence of binary data which SHOULD be unique,
MUST be statistically unique, SHOULD be less than 512 octets in length and MUST
NOT be longer than 4096 octets in length.
</t>
<t>
Servers MAY avoid the need to maintain per-session server side state by encoding the
some or all of the fixed session context parameters in to the identifier. Servers
MUST ensure that appropriate cryptographic enhancements are employed to authenticate the
sessikon context and protect the
confidentiality of the authentication key. The scheme used to construct the session
identifiers used in the examples is described in <xref target="session_id"/>
</t>
</section>
<section title="MAC: Message Authentication Code Algorithm">
<t>
The message authentication algorithm to be used to calculate the authentication value.
</t>
<t>
HMAC construction <xref target="RFC2104"/>
</t>
<t>
<list style="hanging">
<t hangText="HMAC-SHA256-128">
HMAC using the SHA-1 algorithm with the output truncated to the first
64 bits.
</t>
<t hangText="HMAC-SHA512-256">
HMAC using the SHA-1 algorithm with the output truncated to the first
256 bits.
</t>
<t hangText="HMAC-SHA2-256-128">
HMAC using the SHA-2 algorithm with the output truncated to the first
128 bits.
</t>
<t hangText="HMAC-SHA2-512-256">
HMAC using the SHA-2 algorithm with the output truncated to the first
256 bits.
</t>
</list>
</t>
<t>
CMAC Construction <xref target="RFC4493"/>
</t>
<t>
<list style="hanging">
<t hangText="CMAC-AES128-64">
The AES algorithm employed in CMAC mode with a 128 bit key and the output truncated to the
first 64 bits.
</t>
<t hangText="CMAC-AES128">
The AES algorithm employed in CMAC mode with a 128 bit key and the entire output.
</t>
<!-- <t hangText="CMAC-AES256">
The AES algorithm employed in CMAC mode with a 256 bit key and the entire output. NB: RFC
4493 only specifies CMAC for 128 bit keys so this would need an extension.
</t> -->
</list>
</t>
</section>
<section title="Key: Authentication Key">
<t>
The cryptographic key to be used to calculate the authentication value.
</t>
</section>
<section title="Scope Attributes">
<t>
The scope attributes specify which parts of the message are authenticated.
</t>
<!-- <t>
[Separating the scope attribute from the authentication context so that it is specified in
each Session header would permit the scope of the
authentication check to be declared to intermediaries and allows the same authentication
context to be used to authenticate different portions of the HTTP message separately.
I do not see the need to do this however and doing this would likely lead to implementations
that are vulnerable to downgrade attacks by scope stripping.]
</t> -->
<t>
The scope is specified by the start, header and content attributes. The order in which the
scope attributes are specified in the HTTP Set-Session header is immaterial. The scope is
always constructed in the same order as the elements occur in a HTTP message, i.e. start,
dummy headers and content.
</t>
<t>
<list style="hanging">
<t hangText="Content: Boolean">
If set true, the specified scope includes the message body. The content transfer encoding
(e.g. chunked) is ignored for the purpose of determining the content.
</t>
<t hangText="ContentDigest: Label">
If a message digest algorithm is specified the authentication scope MAY be
calculated indirectly by first calculating a Message Digest value over the content
and using the resulting value in place of the actual content value to
calculate the Message Authentication Code value.
</t>
<t hangText="Start: Boolean">
If set true, the specified scope includes the message start line. This being the request Line in
the case of a request and the status line in the case of a response.
</t>
</list>
</t>
<!--<t>
[The inclusion of HTTP headers in the authentication scope was considered but
rejected as unnecessarily complex. At the very least headers would have to
be duplicated. This does however have the unfortunate side effect of leaving the content
meta-data outside the authentication scope. Perhaps there is a way that this
could be finessed. For example a content-metadata option?]
</t> -->
</section>
<section title="Replay Attacks">
<t>
Preventing replay attacks in HTTP requests and responses poses
considerably different challenges. Since a HTTP response is always
immediately preceded by a request,
return of a request nonce is sufficient to prevent a response
replay attack. This approach is stateless and does not require
client or server to store state information.
</t>
<t>
Since the HTTP protocol requires that certain methods be idempotent,
the HTTP protocol does not lend itself to preventing request
replay attacks in the same fashion. Request replay MAY be
prevented by use of counter techniques or mitigated by limiting
request replay to a particular time window.
</t>
<section title="Request Replay Attack">
<t>
Two mechanisms for preventing or mitigating request replay attacks
are specified:
</t>
<t>
<list style="hanging">
<t hangText="Counter: Boolean">
Counter based mechanisms are supported by the count attribute.
The value of a counter MUST increase
for successive transactions within the same transaction stream. Concurrency
MAY be supported by specifying multiple streams but this requires a separate
counter state to be maintained for each transaction stream.
</t>
<t hangText="Time: Boolean">
Time based approaches are supported by the time attribute. If the value of the
time attribute falls within the permitted acceptance window, the message
MAY be accepted. Otherwise the message MUST be rejected.
</t>
<t>
Using a time based approach avoids the need to maintain state at either the
client or server. The principal disadvantage of this approach being that the
mechanism only protects against a replay attack within a specific time.
</t>
<t>
Another disadvantage to the time based approach is that it relies on the
sender and receiver maintaining a tollerably close time synchronization
over the duration of the transaction and for the latency introduced by the
communication path being tollerably small.
</t>
</list>
</t>
<t>
Neither method is entirely satisfactory. The counter mechanism requires that
the client and server both maintain state and the time based mechanism only
prevents request replay attack outside a specified time interval.
</t>
<t>
For Web Services that require a stronger assurance that request replay
attack cannot succeed (e.g. payment transactions) without maintaining
server side state, such controls should be provided by the Web Service
protocol rather than relying on the HTTP session continuation mechanism.
For example, the Web Services protocol might define a two phase interaction
in which the client requested a server nonce in the first phase
to be returned in the second phase.
</t>
</section>
<section title="Response Replay Attack">
<t>
If a HTTP Session header in a request specifies a nonce value, the
corresponding Session header in the response (if present) MUST specify
the same nonce value.
</t>
</section>
</section>
<section title="Direction">
<t>
A session MAY be defined to apply to requests only, responses only or to both
requests and responses.
</t>
<t>
<list style="hanging">
<t hangText="Request: Boolean">
This session context applies to requests.
</t>
<t hangText="Response: Boolean">
This session context applies to responses.
</t>
</list>
</t>
</section>
<section title="TLS Binding (Fixed)">
<t>
The TLS binding attribute specifies whether TLS channel binding is to be used.
</t>
</section>
<section title="Domain: String">
<t>
The DNS Domain(s) to which the session context applies. The syntax and semantics of
the Domain attribute are identical to those of the Domain attribute of the Cookie
header defined in [].
</t>
</section>
</section>
<section title="Session Context State Attributes">
<section title="Expiry time: Max-Age">
<t>
The time at which the session expires. To avoid the need for the client or server to have
access to a realtime clock, Set-Session and Session headers specify the expiry time as the
remaining lifetime of the session from the instant the header is generated in seconds.
</t>
<t>
A server MAY update the value Max-Age value to extend the lifetime of the session
before expiry by specifying a new value for Max-Age in the Session header.
</t>
</section>
<section title="Now: Time Offset (Time)">
<t>
The Time Offset value is used to calculate the value of the Now attribute in the
session header and is only required when the Time replay protection mechanism is in use.
</t>
<t>
To avoid the need for clients or servers to have access to a reference time source,
time values used to protect against replay attack are specified relative to an arbitrary
epoch start time specified by the server. The Time Offset value is the difference
between the time epoch specified by the server and the local time according to the machine.
A server MAY use the same epoch start time
for all clients or use a different epoch for each one.
</t>
<section title="Now: Last Now (Time)">
<t>
If the local clock at the client runs faster or slower than that of the server, a timing
discrepancy emerges over time. A client SHOULD and a server MAY correct for such inaccuracies by
noting the value of the now attribute specified by the other party and adjusting the local
time offset value accordingly provided that the mechanism employed to do so ensures that
the values of the now attribute in a HTTP message is never less than the value specified
in a previous header.
</t>
<t>
Recording the value of the last value of Now specified in a header permits this condition
to be met.
</t>
</section>
</section>
<section title="Count: Last Count (Count)">
<t>
If counter based replay attack prevention is in use the client and server MUST maintain a
record of the last value of the counter for each concurrent stream active within the
session.
</t>
</section>
<section title="Nonce: Last Nonce (Nonce)">
<t>
If nonce based replay attack prevention is in use, the parties MUST maintain a record
of the last nonce value so as to be able to return it when necessary.
</t>
<t>
In most circumstances the nonce value is used immediately and need not be stored.
</t>
</section>
</section>
</section>
<section title="Syntax">
<t>The Accept-Session, Set-Session and Session headers use the
following common syntax elements</t>
<t>
<list style="hanging">
<t hangText="Label"> [ alpha (alpha | '-')* ]</t>
<t hangText="Binary"> [Base 64 encoding of a binary value] </t>
<t hangText="Offer"> [ "Optional" | "Required" | "Refused" ] </t>
<t hangText="DTime"> [Decimal time value from current time] </t>
<t hangText="Decimal"> [Decimal numeric value] </t>
</list>
</t>
<section title="Accept-Session Header">
<t>
The Accept-Session header is used to negotiate the establishment of an authentication
context. When used in a request the Accept-Session header specifies a set of
acceptable parameters for the session context.
</t>
<t>
<list style="hanging">
<t hangText="MAC=[Label(,Label)*]">
The message authentication algorithms the client is willing to support.
</t>
<t hangText="Content=[Offer]">
Offers or requires the inclusion of the message content in the authentication scope.
</t>
<t hangText="ContentDigest=[Offer]">
Offers or requires the inclusion of the message content by means of a content digest
in the authentication scope.
</t>
<t hangText="Start=[Offer]">
Offers or requires the inclusion of the message start line
in the authentication scope.
</t>
<t hangText="Request=[Offer]">
Offers or requires the use of a Session header in a request message.
</t>
<t hangText="Response=[Offer]">
Offers or requires the use of a Session header in a response message.
</t>
<t hangText="TLSU=[Offer]">
Offers or requires the use of tls-unique TLS chanel binding as
specified in <xref target="RFC5929"/>.
</t>
<t hangText="TLSE=[Offer]">
Offers or requires the use of tls-server-end-point TLS chanel binding as specified in
<xref target="RFC5929"/>.
</t>
<t hangText="Nonce=[Offer]">
Offers or requires the use of the nonce response replay attack prevention mechanism.
</t>
<t hangText="Counter=[Offer]">
Offers or requires the use of the counter request replay attack prevention mechanism.
</t>
<t hangText="Time=[Optional | Required]">
Offers or requires the use of the time request replay attack prevention mechanism.
</t>
</list>
</t>
<t>
When used by the client to offer the use of an authentication session, all header
attributes are optional. Note however that even though it is permissable for a client
to offer an empty Accept-Session header, doing so does not allow a valid session context
to be established as the server is required to specify at least an authentication
scope and MAC algorithm from amongst those offered by the client.
</t>
</section>
<section title="Set-Session Header">
<t>
The Set-Session Header is specified in a response to accept an offer
of using the session continuation mechanism made by specifing
accept-session in the corresponding request.
</t>
<t>
The features specified in the Set-Session header MUST
be consistent with the features offered in the corresponding request.
</t>
<t>
<list style="hanging">
<t hangText="Id=[Binary]">
The session context identifier in base64 encoding.
</t>
<t hangText="Key=[Binary]">
The cryptographic key to be used to calculate the authentication value in base64 encoding.
</t>
<t hangText="MAC=[Label]">
The message authentication algorithm to be used to calculate the authentication value
as defined in <xref target="RFC5698"/> .
</t>
<t hangText="Content">
Specifies the inclusion of the message content in the authentication scope.
</t>
<t hangText="ContentDigest">
Specifies the inclusion of the message content by means of a content digest
in the authentication scope.
</t>
<t hangText="Start">
Specifies the inclusion of the message start line
in the authentication scope.
</t>
<t hangText="Request">
Specifies the use of a Session header in a request message.
</t>
<t hangText="Response">
Specifies the use of a Session header in a response message.
</t>
<t hangText="TLSBinging">
Specifies the use of TLS Binding [Need to think this through further]
</t>
<t hangText="Counter=[Decimal]">
Specifies the use of the counter replay attack prevention mechanism.
The value of the attribute specifies the maximum number of permitted
streams.
</t>
<t hangText="Time=[NTime]">
Specifies the use of the time replay attack prevention mechanism and
the current value of the time value in seconds.
</t>
<t>
Servers SHOULD NOT use a time offset from a fixed epoch (e.g. 32 bit
UNIX epoch).
</t>
<t hangText="Max-Age=[NTime]">
Specifies the number of seconds in which the session parameters expire
measured from the time at which the request was issued.
</t>
</list>
</t>
<t>
A Set-Session header MUST contain the following elements:
</t>
<t>
<list>
<t>
Id
</t>
<t>
Key
</t>
<t>MAC</t>
<t>At least one Scope attribute offered by the client</t>
<t>At least one direction attribute</t>
<t>A Max-Age value</t>
</list>
</t>
</section>
<section title="Session Header">
<t>
The Session header has the tag 'Session' and takes a sequence of attribute values
as follows:
</t>
<t>
[Insert ABNF here]
</t>
<t hangText="Id=[Binary] (required)">
The session context identifier as in base64 encoding.
</t>
<section title="Value=[Binary] (required)">
<t>
The value attribute specifies the value resulting from applying the authentication context
and nonce (if present) to
the specified scope.
</t>
</section>
<section title="Nonce=[Binary]">
<t>
The nonce attribute MAY be specified in a request. If a request specifies a
nonce attribute, the corresponding response MUST specify a nonce attribute
with the same value.
</t>
</section>
<section title="Stream=[Decimal]">
<t>
The Stream attribute MUST NOT be specified in a request unless the counter
attribute is specified in the session context and the value of the stream
count is less than the number of permitted streams.
</t>
<section title="Count=[Decimal]">
<t>
The Count attribute MUST NOT be specified in a request unless the counter
attribute is specified in the session context. The value of the count
attribute MUST be greater than the value of the count attribute
in all previous requests under the specified session with the same stream
attribute.
</t>
</section>
<section title="Time=[NTime]">
<t>
Specifies a time value to be used in combination with the specified authentication context.
The format of the time value is determined by the authentication context.
</t>
</section>
<section title="Attribute tlsu=[value]">
<t>
Specifies the TLS unique channel binding as specified in <xref target="RFC5929"/>.
</t>
</section>
<section title="Attribute tlss=[value]">
<t>
Specifies the TLS server end point channel binding as specified in <xref target="RFC5929"/>.
</t>
</section>
</section>
<section title="Preparing the Input to the Authentication Algorithm">
<t>
[Should specify how the content scope is assembles and how the replay attack
attributes are included within it.]
</t>
</section>
</section>
</section>
<section title="Processing">
<section title="Calculating the Authentication Value">
<t>
The input to the MAC algorithm is the concatenation of the following values.
</t>
<t>
<list style="hanging">
<t hangText="The Start Line">Is included if and only if the value of the start attribute of the session context is true.</t>
<t hangText="The Canonical HTTP Headers">Are always included.</t>
<t hangText="The Message Content">Is included if and only if the value of the content attribute of the session context is true.</t>
</list>
</t>
<section title="Start line">
<t>
The Start line is the HTTP start line including the final CRLF.
</t>
<t>
Example:
</t>
</section>
<section title="Canonical Headers">
<t>
The canonical form of the header(s) specified for inclusion in the authentication scope by the session context sorted into alphabetical
order. At present only the Session header is specified and MUST always be included.
</t>
<t>
The canonical Session header contains all the attributes of the Session header to be added to the HTTP message with the
exception of the Value attribute. Attributes MUST be specified in alphabetical order.
</t>
<t>
Example:
</t>
</section>
<section title="Message Content">
<t>
If the Content-Digest parameter of the session context is empty the Message content value is the actual value of the message content
ignoring any transfer encoding but after any content-encoding has taken place.
</t>
<t>
If the Content-Digest parameter of the session context specifies at least one Message Digest algorithm, the sender MAY chose to calculate
the authentication value over the actual value of the content as specified above or first apply one of the specified message digest algorithms
to the actual value of the message content as specified above and then calculate the authentication value over the resulting digest value.
</t>
<t>
Example:
</t>
</section>
</section>
<section title="Generating a Session Header">
<t>
Generating a Session Header requires the following steps to be performed:
</t>
<t>
<list>
<t>The Session header parameters are calculated according to the session context.</t>
<t>If necessary, the session context is updated to reflect new values of relevant replay attack prevention
attributes.</t>
<t>The authentication value is calculated over the specified scope.</t>
<t>The Session header is added to the HTTP headers.</t>
</list>
</t>
<t>
</t>
</section>
<section title="Verifying a HTTP Message under a Session Context">
<t>
Verifying messages follows the same approach as generation. The verifier calculates the authentication
value over the input values as specified in the session context. If the resulting authentication value
matches that specified by the sender, the authentication succeeds and fails otherwise.
</t>
</section>
</section>
<section title="Security Considerations">
<section title="Data outside the specified scope is not authenticated">
<t>
The integrity check only extends to the portions of the message that
are within the specified scope.
</t>
</section>
<section title="Truncated Hash Algorithms">
<t>
If the authentication context permits the use of a truncated MAC, it
MUST specify the minimum length of the MAC after truncation and
verifiers MUST reject MAC values shorter than that length as invalid.
</t>
</section>
<section title="Randomness of Secret Keys and nonces">
<t>
The security of any cryptographic protocol relies on the difficulty
of guessing secret keys. Secret keys and nonces SHOULD be generated
using a mechanism that ensures that the range of possible values
is sufficiently large to prevent 'brute force' guessing attacks.
For more information see <xref target="RFC4086"/>.
</t>
</section>
<section title="Weak Ciphers">
<t>
Specification of the cryptographic algorithms used to construct the
Integrity header value is implicit in the authentication context identifier
and thus outside the scope of this specification.
</t>
</section>
</section>
<section title="IANA Considerations">
<t>
Add the 'Accept-Session', 'Set-Session' and 'Session' headers to the list of provisional HTTP headers.
</t>
<t>
Add the HMAC algorithm entries to the RFC 5698 regitry http://www.iana.org/assignments/dssc/dssc.xml
</t>
<t>
[Upgrade if/when this becomes an RFC]
</t>
<t>
Create a registry for Session Header attributes. The initial contents of
the registry to be:
</t>
<t>
[Stuff from rest of document.]
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2104;
&RFC2119;
&RFC2616;
&RFC2965;
&RFC5246;
&RFC5698;
&RFC5929;
&RFC4086;
&RFC4493;
</references>
<references title="Non Normative References">
<reference anchor="CRIME" target="CRIME">
<front>
<title>TBS</title>
<author initials="" surname="" fullname="">
<organization />
</author>
<date month="" year="" />
</front>
<seriesInfo name="" value="" />
</reference>
<reference anchor="BEAST" target="BEAST">
<front>
<title>TBS</title>
<author initials="" surname="" fullname="">
<organization />
</author>
<date month="" year="" />
</front>
<seriesInfo name="" value="" />
</reference>
&RFC5652;
&RFC3275;
&RFC4120;
&RFC6265;
</references>
<section title="Session Identifier Encoding" anchor="session_id"></section>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-23 02:45:42 |