Secondary Certificate Authentication in HTTP/2Microsoftmichael.bishop@microsoft.comMozillamartin.thomson@gmail.com
General
HTTPInternet-DraftTLS provides fundamental mutual authentication services for HTTP,
supporting up to one server certificate and up to one client certificate
associated to the session to prove client and server identities as
necessary. This draft provides mechanisms for providing additional such
certificates at the HTTP layer when these constraints are not
sufficient.Many HTTP servers host content from several origins. HTTP/2
permits clients to reuse an existing HTTP connection to a server
provided that the secondary origin is also in the certificate provided
during the TLS handshake.In many cases, servers will wish to maintain separate certificates for
different origins but still desire the benefits of a shared HTTP
connection. Similarly, servers may require clients to present
authentication, but have different requirements based on the content the
client is attempting to access.This document describes a how such certificates can be provided at the
HTTP layer to support both scenarios.HTTP clients need to know that the content they receive on a connection comes from
the origin that they intended to retrieve in from.
The traditional form of server authentication in HTTP has been in the form of
X.509 certificates provided during the TLS RFC5246 handshake.Many existing HTTP servers also have authentication requirements
for the resources they serve. Of the bountiful authentication options
available for authenticating HTTP requests, client certificates present a unique
challenge for resource-specific authentication requirements because of the
interaction with the underlying TLS layer.TLS 1.2 supports one server and one client certificate on a connection.
These certificates may contain multiple identities, but only one certificate may be
provided.Section 9.1.1 of describes how connections may be used to make
requests from multiple origins as long as the server is authoritative
for both. A server is considered authoritative for an origin if DNS
resolves the origin to the IP address of the server and (for TLS) if the
certificate presented by the server contains the origin in the Subject
Alternative Names field. enables a step of abstraction from the DNS
resolution. If both hosts have provided an Alternative Service at
hostnames which resolve to the IP address of the server, they are
considered authoritative just as if DNS resolved the origin itself to
that address. However, the server’s one TLS certificate is still
required to contain the name of each origin in question.Servers which host many origins often would prefer to have separate
certificates for some sets of origins. This may be for ease of
certificate management (the ability to separately revoke or renew them),
due to different sources of certificates (a CDN acting on behalf of
multiple origins), or other factors which might drive this
administrative decision. Clients connecting to such origins cannot
currently reuse connections, even if both client and server would prefer
to do so.Because the TLS SNI extension is exchanged in the clear, clients might
also prefer to retrieve certificates inside the encrypted context. When
this information is sensitive, it might be advantageous to request a
general-purpose certificate or anonymous ciphersuite at the TLS layer,
while acquiring the “real” certificate in HTTP after the connection is
established.For servers that wish to use client certificates to authenticate users,
they might request client authentication during or immediately after the
TLS handshake. However, if not all users or resources need
certificate-based authentication, a request for a certificate has the
unfortunate consequence of triggering the client to seek a certificate,
possibly requiring user interaction, network traffic, or other
time-consuming activities. During this time, the connection is stalled
in many implementations. Such a request can result in a poor experience,
particularly when sent to a client that does not expect the request.The TLS 1.3 CertificateRequest can be used by servers to give clients
hints about which certificate to offer. Servers that rely on
certificate-based authentication might request different certificates
for different resources. Such a server cannot use contextual information
about the resource to construct an appropriate TLS CertificateRequest
message during the initial handshake.Consequently, client certificates are requested at connection
establishment time only in cases where all clients are expected or
required to have a single certificate that is used for all resources.
Many other uses for client certificates are reactive, that is,
certificates are requested in response to the client making a request.In HTTP/1.1, a server that relies on client authentication for a subset of users
or resources does not request a certificate when the connection is established.
Instead, it only requests a client certificate when a request is made to a
resource that requires a certificate. TLS 1.2 accomodates this
by permitting the server to request a new TLS handshake, in which the server
will request the client’s certificate. shows the server initiating a TLS-layer renegotiation in response
to receiving an HTTP/1.1 request to a protected resource.In this example, the server receives a request for a protected resource (at *1
on ). Upon performing an authorization check, the server
determines that the request requires authentication using a client certificate
and that no such certificate has been provided.The server initiates TLS renegotiation by sending a TLS HelloRequest (at *2).
The client then initiates a TLS handshake. Note that some TLS messages are
elided from the figure for the sake of brevity.The critical messages for this example are the server requesting a certificate
with a TLS CertificateRequest (*3); this request might use information about
the request or resource. The client then provides a certificate and proof of
possession of the private key in Certificate and CertificateVerify messages (*4).When the handshake completes, the server performs any authorization checks a
second time. With the client certificate available, it then authorizes the
request and provides a response (*5).TLS 1.3 introduces a new client authentication mechanism
that allows for clients to authenticate after the handshake has been completed.
For the purposes of authenticating an HTTP request, this is functionally
equivalent to renegotiation. shows the simpler exchange this
enables.TLS 1.3 does not support renegotiation, instead supporting direct client
authentication. In contrast to the TLS 1.2 example, in TLS 1.3, a server can
simply request a certificate.An important part of the HTTP/1.1 exchange is that the client is able to easily
identify the request that caused the TLS renegotiation. The client is able to
assume that the next unanswered request on the connection is responsible. The
HTTP stack in the client is then able to direct the certificate request to the
application or component that initiated that request. This ensures that the
application has the right contextual information for processing the request.In HTTP/2, a client can have multiple outstanding requests. Without some sort
of correlation information, a client is unable to identify which request caused
the server to request a certificate.Thus, the minimum necessary mechanism to support reactive certificate
authentication in HTTP/2 is an identifier that can be use to correlate an HTTP
request with a request for a certificate. Since streams are used for individual
requests, correlation with a stream is sufficient. prohibits renegotiation after any application data has been sent. This
completely blocks reactive certificate authentication in HTTP/2 using TLS 1.2.
If this restriction were relaxed by an extension or update to HTTP/2,
such an identifier could be added to TLS 1.2 by means of an extension to TLS.
Unfortunately, many TLS 1.2 implementations do not permit application data to
continue during a renegotiation. This is problematic for a multiplexed
protocol like HTTP/2.This draft proposes bringing the TLS 1.3 CertificateRequest,
Certificate, and CertificateVerify messages into HTTP/2 frames, enabling
certificate-based authentication of both clients and servers independent
of TLS version. This mechanism can be implemented at the HTTP layer
without requiring new TLS stack behavior and without breaking the
existing interface between HTTP and applications above it.This could be done in a naive manner by replicating the messages as
HTTP/2 frames on each stream. However, this would create needless
redundancy between streams and require frequent expensive signing
operations. Instead, this draft lifts the bulky portions of each message
into frames on stream zero and permits the on-stream frames to
incorporate them by reference as needed.Certificate chains, with proof-of-possession of the corresponding
private key, can be supplied into a collection of available
certificates. Likewise, descriptions of desired certificates can be
supplied into these collections. These pre-supplied elements are then
available for automatic use (in some situations) or for reference by
individual streams. describes how the feature is employed, defining means to
detect support in peers (), make certificates and requests
available (), and indicate when streams are blocked
waiting on an appropriate certificate ().
defines the required frame types, which parallel the TLS
1.3 message exchange. Finally, defines new error types which
can be used to notify peers when the exchange has not been successful.RFC 2119 defines the terms “MUST”, “MUST NOT”, “SHOULD” and “MAY”.A certificate chain is sent as a series of CERTIFICATE frames (see
) on stream zero. Proof of possession of the
corresponding private key is sent as a CERTIFICATE_PROOF frame (see
) on stream zero. Once the holder of a certificate
has sent the chain and proof, this certificate chain is cached by the
recipient and available for future use. If the certificate is marked as
AUTOMATIC_USE, the certificate may be used by the recipient to
authorize any current or future request. Otherwise, the recipient
requests the required certificate on each stream, but the
previously-supplied certificates are available for reference without
having to resend them.Likewise, the details of a request are sent on stream zero and stored by
the recipient. These details will be referenced by subsequent
CERTIFICATE_REQUIRED frames.Data sent by each peer is correlated by the ID given in each frame. This
ID is unrelated to values used by the other peer, even if each uses the
same ID in certain cases.Clients and servers that will accept requests for HTTP-layer certificate
authentication indicate this using the HTTP/2 SETTINGS_HTTP_CERT_AUTH
(0xSETTING-TBD) setting.The initial value for the SETTINGS_HTTP_CERT_AUTH setting is 0,
indicating that the peer does not support HTTP-layer certificate authentication.
If a peer does support HTTP-layer certificate authentication, it uses
the setting to communicate its acceptable hash and signature algorithm.The setting value is a pair of bitmaps. In the lower half, each set bit
reflects an acceptable signing algorithm for provided certificates. Each
bit MUST NOT be set if a proof signed in this way would be unacceptable
to the sender.
ECDSA P-256 with SHA-256
ECDSA P-384 with SHA-384
Ed25519
Ed448
RSA-PSS with SHA-256 and MGF1 (minimum of 2048 bits)
Reserved for future useIf no compatible signature algorithms have been proffered in SETTINGS by a peer,
the frames defined in this specification MUST NOT be sent to them, with the
exception of empty USE_CERTIFICATE frames.In the upper half, each set bit reflects an acceptable form of supporting
data to include with the certificate.
Always set. Indicates the ability to interpret requests for certificates.
Indicates support for OCSP supporting data.
Indicates support for Signed Certificate Timestamp supporting data.
Reserved for future useWhen a peer has advertised support for HTTP-layer certificates as in
, either party can supply additional certificates into the
connection at any time. These certificates then become available for the
peer to consider when deciding whether a connection is suitable to
transport a particular request.Available certificates which have the AUTOMATIC_USE flag set MAY be
used by the recipient without further notice. This means that clients or
servers which predict a certificate will be required could pre-supply
the certificate without being asked. Regardless of whether
AUTOMATIC_USE is set, these certificates are available for reference
by future USE_CERTIFICATE frames.Likewise, either party can supply a certificate request that outlines
parameters of a certificate they might request in the future. It
is important to note that this does not currently request such a
certificate, but makes the contents of the request available for
reference by a future CERTIFICATE_REQUIRED frame.Because certificates can be large and each CERTIFICATE_PROOF requires
a signing operation, the server MAY instead send an ORIGIN frame
including origins which are not in its TLS certificate. This represents
an explicit claim by the server to possess the appropriate certificate
– a claim the client MUST verify using the procedures in
before relying on the server’s authority for the
claimed origin.As defined in , when a client finds that a https:// origin (or
Alternative Service ) to which it needs to
make a request has the same IP address as a server to which it is
already connected, it MAY check whether the TLS certificate provided
contains the new origin as well, and if so, reuse the connection.If the TLS certificate does not contain the new origin, but the server
has advertised support for HTTP-layer certificates (see , it
MAY send a CERTIFICATE_REQUIRED frame on the stream it will use to
make the request. (If the request parameters have not already been made
available using a CERTIFICATE_REQUEST frame, the client will need to
send the CERTIFICATE_REQUEST in order to generate the
CERTIFICATE_REQUIRED frame.) The stream represents a pending request
to that origin which is blocked until a valid certificate is processed.The request is blocked until the server has responded with a
USE_CERTIFICATE frame pointing to a certificate for that origin. If
the certificate is already available, the server SHOULD immediately
respond with the appropriate USE_CERTIFICATE frame. (If the
certificate has not already been transmitted, the server will need to
make the certificate available as described in before
completing the exchange.)If the server does not have the desired certificate, it MUST respond
with an empty USE_CERTIFICATE frame. In this case, or if the server
has not advertised support for HTTP-layer certificates, the client MUST
NOT send any requests for resources in that origin on the current
connection and SHOULD send a RST_STREAM on the stream used for the
request.Likewise, on each stream where certificate authentication is required,
the server sends a CERTIFICATE_REQUIRED frame, which the client
answers with a USE_CERTIFICATE frame indicating the certificate to
use. If the request parameters or the responding certificate are not
already available, they will need to be sent as described in
as part of this exchange.A server MAY push resources from an origin for which it is authoritative
but for which the client has not yet received the certificate. In this
case, the client MUST verify the server’s possession of an appropriate
certificate by sending a CERTIFICATE_REQUIRED frame on the pushed
stream to inform the server that progress is blocked until the request
is satisfied. The client MUST NOT use the pushed resource until an
appropriate certificate has been received and validated.The CERTIFICATE_REQUEST and CERTIFICATE_REQUIRED frames are
correlated by their Request-ID field. Subsequent
CERTIFICATE_REQUIRED frames with the same Request-ID value MAY be
sent on other streams where the sender is expecting a certificate with
the same parameters.The CERTIFICATE, CERTIFICATE_PROOF, and USE_CERTIFICATE frames are
correlated by their Cert-ID field. Subsequent USE_CERTIFICATE frames
with the same Cert-ID MAY be sent in response to other
CERTIFICATE_REQUIRED frames and refer to the same certificate.Request-ID and Cert-ID are sender-local, and the use of the same
value by the other peer does not imply any correlation between their frames.The CERTIFICATE_REQUIRED frame (0xFRAME-TBD2) is sent to indicate that
the HTTP request on the current stream is blocked pending certificate
authentication. The frame includes a request identifier which can be
used to correlate the stream with a previous CERTIFICATE_REQUEST frame
sent on stream zero. The CERTIFICATE_REQUEST describes the certificate
the sender requires to make progress on the stream in question.The CERTIFICATE_REQUIRED frame contains 1 octet, which is the
authentication request identifier, Request-ID. A peer that receives a
CERTIFICATE_REQUIRED of any other length MUST treat this as a stream
error of type PROTOCOL_ERROR. Frames with identical request
identifiers refer to the same CERTIFICATE_REQUEST.A server MAY send multiple CERTIFICATE_REQUIRED frames on the same
stream. If a server requires that a client provide multiple certificates
before authorizing a single request, each required certificate MUST be
indicated with a separate CERTIFICATE_REQUIRED frame, each of which
MUST have a different request identifier (referencing different
CERTIFICATE_REQUEST frames describing each required certificate). To
reduce the risk of client confusion, servers SHOULD NOT have multiple
outstanding CERTIFICATE_REQUIRED frames on the same stream at any
given time.Clients MUST NOT send multiple CERTIFICATE_REQUIRED frames
on the same stream.The CERTIFICATE_REQUIRED frame SHOULD NOT be sent to a peer which has
not advertised support for HTTP-layer certificate authentication.The CERTIFICATE_REQUIRED frame MUST NOT be sent on stream zero, and
MUST NOT be sent on a stream in the “half-open (remote)” state. A client
that receives a CERTIFICATE_REQUIRED frame on a stream which is not in
a valid state SHOULD treat this as a stream error of type
PROTOCOL_ERROR.The USE_CERTIFICATE frame (0xFRAME-TBD5) is sent in response to a
CERTIFICATE_REQUIRED frame to indicate which certificate is being used
to satisfy the requirement.A USE_CERTIFICATE frame with no payload refers to the certificate
provided at the TLS layer, if any. If no certificate was provided at the
TLS layer, the stream should be processed with no authentication, likely
returning an authentication-related error at the HTTP level (e.g. 403)
for servers or routing the request to a new connection for clients.Otherwise, the USE_CERTIFICATE frame contains the Cert-ID of the
certificate the sender wishes to use. This MUST be the ID of a
certificate previously presented in one or more CERTIFICATE frames,
and for which proof of possession has been presented in a
CERTIFICATE_PROOF frame. Recipients of a USE_CERTIFICATE frame of
any other length MUST treat this as a stream error of type
PROTOCOL_ERROR. Frames with identical certificate identifiers refer to
the same certificate chain.The USE_CERTIFICATE frame MUST NOT be sent on stream zero or a stream
on which a CERTIFICATE_REQUIRED frame has not been received. Receipt
of a USE_CERTIFICATE frame in these circmustances SHOULD be treated as
a stream error of type PROTOCOL_ERROR.The referenced certificate chain MUST conform to the requirements
expressed in the CERTIFICATE_REQUEST to the best of the sender’s
ability. Specifically:If the CERTIFICATE_REQUEST contained a non-empty Certificate-Authorities
element, one of the certificates in the chain SHOULD be signed by one of the
listed CAs.If the CERTIFICATE_REQUEST contained a non-empty Cert-Extensions element,
the first certificate MUST match with regard to the extension OIDs recognized
by the sender.Each certificate that is not self-signed MUST be signed using a
hash/signature algorithm listed in the Algorithms element. [[TODO: No
longer exists; does SETTINGS give enough info?]]If these requirements are not satisfied, the recipient MAY at its
discretion either return an error at the HTTP semantic layer, or respond
with a stream error on any stream where the certificate is
used. defines certificate-related error codes which might be
applicable.TLS 1.3 defines the CertificateRequest message, which prompts the client to
provide a certificate which conforms to certain properties specified by the
server. This draft defines the CERTIFICATE_REQUEST frame (0xFRAME-TBD1), which
contains the same contents as a TLS 1.3 CertificateRequest message, but can
be sent over any TLS version.The CERTIFICATE_REQUEST frame SHOULD NOT be sent to a peer which has
not advertised support for HTTP-layer certificate authentication.The CERTIFICATE_REQUEST frame MUST be sent on stream zero. A CERTIFICATE_REQUEST
frame received on any other stream MUST be rejected with a stream error of type
PROTOCOL_ERROR.The frame contains the following fields:Request-ID is an 8-bit opaque identifier used to correlate
subsequent certificate-related frames with this request. The identifier
MUST be unique in the session for the sender.Certificate-Authorities is a series of distinguished names of
acceptable certificate authorities, represented in DER-encoded format.
These distinguished names may specify a desired distinguished name for a root
CA or for a subordinate CA; thus, this message can be used to describe known
roots as well as a desired authorization space. The number of such structures
is given by the 16-bit CA-Count field, which MAY be zero. If the CA-Count
field is zero, then the recipient MAY send any certificate that meets the rest
of the selection criteria in the CERTIFICATE_REQUEST, unless there is some
external arrangement to the contrary.
A list of certificate extension OIDs with their allowed
values, represented in a series of CertificateExtension structures
(see section 6.3.5). The list of OIDs MUST be used
in certificate selection as described in . The
number of Cert-Extension structures is given by the 16-bit
Cert-Extension-Count field, which MAY be zero.Some certificate extension OIDs allow multiple values (e.g. Extended Key
Usage). If the sender has included a non-empty Cert-Extensions
list, the certificate MUST contain all of the specified extension OIDs
that the recipient recognizes. For each extension OID recognized by the
recipient, all of the specified values MUST be present in the
certificate (but the certificate MAY have other values as well).
However, the recipient MUST ignore and skip any unrecognized certificate
extension OIDs.Servers MUST be able to recognize the “subjectAltName” extension
( section 4.2.1.7) at a minimum. Clients MUST always
specify the desired origin using this extension, though other
extensions MAY also be included.PKIX RFCs define a variety of certificate extension OIDs and their
corresponding value types. Depending on the type, matching certificate
extension values are not necessarily bitwise-equal. It is expected that
implementations will rely on their PKI libraries to perform certificate
selection using these certificate extension OIDs.A certificate chain is transferred as a series of CERTIFICATE frames
(0xFRAME-TBD3) with the same Cert-ID, each containing a single
certificate in the chain. The end certificate of the chain can be used
as authentication for previous or subsequent requests.The CERTIFICATE frame defines no flags.While unlikely, it is possible that an exceptionally large certificate
might be too large to fit in a single HTTP/2 frame (see
section 4.2). Senders unable to transfer a requested certificate due to
the recipient’s SETTINGS_MAX_FRAME_SIZE value SHOULD terminate
affected streams with CERTIFICATE_TOO_LARGE.The CERTIFICATE frame MUST be sent on stream zero. A CERTIFICATE
frame received on any other stream MUST be rejected with a stream error
of type PROTOCOL_ERROR.The fields defined by the CERTIFICATE frame are:
The sender-assigned ID of the certificate chain.
An array of Supplemental-Data objects (see
), with the number given by SData-Count,
which MAY be zero. Each Supplemental-Data object contains information
about the certificate.
An X.509v3 certificate in the sender’s certificate chain.The first or only CERTIFICATE frame with a given Cert-ID MUST
contain the sender’s certificate. Each subsequent certificate SHOULD
directly certify the certificate immediately preceding it. A certificate
which specifies a trust anchor MAY be omitted, provided that the
recipient is known to already possess the relevant certificate. (For
example, because it was included in a CERTIFICATE_REQUEST’s
Certificate-Authorities list.)Supplemental data helps a client to validate a certificate, but is
not essential to doing so. Peers SHOULD NOT include supplemental data
which the recipient is known not to support, but MAY offer supplemental
data prior to learning which types the recipient supports.Each supplemental data object has the following format:The Type field indicates which type of supplemental data is being offered:
Data contains an OCSP record supporting this certificate.
Data contains a Signed Certificate Timestamp supporting this
certificate.
Reserved for future use.The CERTIFICATE_PROOF frame proves possession of the private key corresponding
to an end certificate previously shown in a CERTIFICATE frame.The CERTIFICATE_PROOF frame defines one flag:
Indicates that the certificate can be used automatically on future
requests.The CERTIFICATE_PROOF frame (0xFRAME-TBD4) contains an Algorithm
field (a SignatureAndHashAlgorithm, from section
6.3.2.1), describing the hash/signature algorithm pair being used.
[[TODO: Sixteen bits because it is in TLS 1.3; if we’re using a
bitmask to express allowed values, we’re down to ~5 bits needed to
contain all permitted algorithms. Shrink?]]The signature is performed as described in , with
the following values being used:The context string for the signature is “HTTP/2 CERTIFICATE_PROOF”The “specified content” is an exported value, with the following parameters:
Disambiguating label string: “EXPORTER HTTP/2 CERTIFICATE_PROOF”Length: 64 bytesBecause the exported value can be independently calculated by both sides of the
TLS connection, the value to be signed is not sent on the wire at any time.
The same signed value is used for all CERTIFICATE_PROOF frames in a single
HTTP/2 connection.A CERTIFICATE_PROOF frame MUST be sent only after all CERTIFICATE
frames with the same Cert-ID have been sent, and MUST correspond
to the first certificate presented in the first CERTIFICATE frame with
that Cert-ID. Receipt of multiple CERTIFICATE_PROOF frames for
the same Cert-ID, receipt of a CERTIFICATE_PROOF frame
without a corresponding CERTIFICATE frame, or receipt of a CERTIFICATE
frame after a corresponding CERTIFICATE_PROOF MUST be treated as a session
error of type PROTOCOL_ERROR.If the AUTOMATIC_USE flag is set, the recipient MAY omit sending
CERTIFICATE_REQUIRED frames on future streams which would require a
similar certificate and use the referenced certificate for
authentication without further notice to the holder. This behavior is
optional, and receipt of a CERTIFICATE_REQUIRED frame does not imply
that previously-presented certificates were unacceptable, even if
AUTOMATIC_USE was set. Servers MUST set the AUTOMATIC_USE flag when
sending a CERTIFICATE_PROOF frame. A server MUST NOT send certificates
for origins which it is not prepared to service on the current
connection.Because this draft permits certificates to be exchanged at the HTTP
framing layer instead of the TLS layer, several certificate-related
errors which are defined at the TLS layer might now occur at the HTTP
framing layer. In this section, those errors are restated and added to
the HTTP/2 error code registry.
A certificate was corrupt, contained signatures
that did not verify correctly, etc.
A certificate was of an unsupported type or did not contain required
extensions
A certificate was revoked by its signer
A certificate has expired or is not currently valid
The digital signature provided did not match the claimed public key
The certificate cannot be transferred due to the recipient’s
SETTINGS_MAX_FRAME_SIZE
Any other certificate-related errorAs described in , implementations MAY choose to treat a stream
error as a connection error at any time. Of particular note, a stream
error cannot occur on stream 0, which means that implementations cannot
send non-session errors in response to CERTIFICATE_REQUEST,
CERTIFICATE, and CERTIFICATE_PROOF frames. Implementations which do
not wish to terminate the connection MAY either send relevant errors on
any stream which references the failing certificate in question or
process the requests as unauthenticated and provide error information at
the HTTP semantic layer.This mechanism defines an alternate way to obtain server and client
certificates other than the TLS handshake. While the signature of
exporter values is expected to be equally secure, it is important to
recognize that a vulnerability in this code path is at least equal to a
vulnerability in the TLS handshake.This could also increase the impact of a key compromise. Rather than
needing to subvert DNS or IP routing in order to use a compromised
certificate, a malicious server now only needs a client to connect to
some HTTPS site under its control. Clients SHOULD continue to validate
that destination IP addresses are valid for the origin either by direct
DNS resolution or resolution of a validated Alternative Service. (Future
work could include a mechanism for a server to offer proofs.)This draft defines a mechanism which could be used to probe servers for
origins they support, but opens no new attack versus making repeat TLS
connections with different SNI values. Servers SHOULD impose similar
denial-of-service mitigations (e.g. request rate limits) to
CERTIFICATE_REQUEST frames as to new TLS connections.While the CERTIFICATE_REQUEST frame permits the sender to enumerate
the acceptable Certificate Authorities for the requested certificate, it
might not be prudent (either for security or data consumption) to
include the full list of trusted Certificate Authorities in every
request. Senders, particularly clients, are advised to send an empty
Certificate-Authorities element unless they are expecting a
certificate to be signed by a particular CA or small set of CAs.Failure to provide a certificate on a stream after receiving
CERTIFICATE_REQUIRED blocks processing, and SHOULD be subject
to standard timeouts used to guard against unresponsive peers.In order to protect the privacy of the connection against
triple-handshake attacks, this feature of HTTP/2 MUST be used only over
TLS 1.3 or greater, or over TLS 1.2 in combination with the Extended
Master Secret extension defined in .Client implementations need to carefully consider the impact of setting
the AUTOMATIC_USE flag. This flag is a performance optimization,
permitting the client to avoid a round-trip on each request where the
server checks for certificate authentication. However, once this flag
has been sent, the client has zero knowledge about whether the server
will use the referenced cert for any future request, or even for an
existing request which has not yet completed. Clients MUST NOT set this
flag on any certificate which is not appropriate for currently-in-flight
requests, and MUST NOT make any future requests on the same connection
which they are not willing to have associated with the provided
certificate.Implementations need to be aware of the potential for confusion about
the state of a connection. The presence or absence of a validated
certificate can change during the processing of a request, potentially
multiple times, as USE_CERTIFICATE frames are received. A server that
uses certificate authentication needs to be prepared to reevaluate the
authorization state of a request as the set of certificates changes.Finally, validating a multitude of signatures can be computationally
expensive, while generating an invalid signature is computationally
cheap. Implementations will require checks against attacks from this
direction. Signature proofs SHOULD NOT be validated until a stream
requires the certificate to make progress. A signature which is not
valid based on the asserted public key SHOULD be treated as a session
error, to avoid further attacks from the peer, though an implementation
MAY instead disable HTTP-layer certificates for the current connection
instead.This draft establishes two new registries, and adds entries in three others.Acceptable signature methods are registered in . Acceptable
forms of supplemental data are registered in .The HTTP/2 SETTINGS_HTTP_CERT_AUTH setting is registered in .
Five frame types are registered in . Six error codes are registered
in .This document establishes a registry for signature methods acceptable for
use with this extension. The “HTTP-Layer Certificate Signature Method”
registry manages a space of sixteen values. The “HTTP-Layer Certificate Signature Method”
operates under either the “RFC Required” or “IESG Approval” policy.New entries in this registry require the following information:
A name or label for the signature method
A single-bit value from 0x0000 to 0x8000
A document which describes how the signature may be performedThe entries in the following table are registered by this document.This document establishes a registry for supplemental data types acceptable for
use with this extension. The “HTTP-Layer Certificate Supplemental Data”
registry manages a space of sixteen values. The “HTTP-Layer Certificate Supplemental Data”
operates under either the “RFC Required” or “IESG Approval” policy.New entries in this registry require the following information:
A name or label for the supplemental data type
A single-bit value from 0x0000 to 0x8000
A value in the range 0x00 to 0xFF; one type
MAY reserve multiple values
A document which describes how the supplemental data may be interpretedThe entries in the following table are registered by this document.The SETTINGS_HTTP_CERT_AUTH setting is registered in the “HTTP/2 Settings”
registry established in .
SETTINGS_HTTP_CERT_AUTH
0xSETTING-TBD
0
This document.Four new frame types are registered in the “HTTP/2 Frame Types”
registry established in .
CERTIFICATE_REQUIRED
0xFRAME-TBD1
This document.
CERTIFICATE_REQUEST
0xFRAME-TBD2
This document.
CERTIFICATE
0xFRAME-TBD3
This document.
CERTIFICATE_PROOF
0xFRAME-TBD4
This document.
USE_CERTIFICATE
0xFRAME-TBD5
This document.Five new error codes are registered in the “HTTP/2 Error Code”
registry established in .
BAD_CERTIFICATE
0xERROR-TBD1
This document.
UNSUPPORTED_CERTIFICATE
0xERROR-TBD2
This document.
CERTIFICATE_REVOKED
0xERROR-TBD3
This document.
CERTIFICATE_EXPIRED
0xERROR-TBD4
This document.
BAD_SIGNATURE
0xERROR-TBD5
This document.
CERTIFICATE_GENERAL
0xERROR-TBD6
This document.Eric Rescorla pointed out several failings in an earlier revision.
Andrei Popov contributed to the TLS considerations.Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Internet X.509 Public Key Infrastructure Certificate and CRL ProfileThis memo profiles the X.509 v3 certificate and X.509 v2 CRL for use in the Internet. [STANDARDS-TRACK]Keying Material Exporters for Transport Layer Security (TLS)A number of protocols wish to leverage Transport Layer Security (TLS) to perform key establishment but then use some of the keying material for their own purposes. This document describes a general mechanism for allowing that. [STANDARDS-TRACK]The Transport Layer Security (TLS) Protocol Version 1.2This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) ProfileThis memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and RoutingThe Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.Hypertext Transfer Protocol Version 2 (HTTP/2)This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges on the same connection. It also introduces unsolicited push of representations from servers to clients.This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged.Transport Layer Security (TLS) Session Hash and Extended Master Secret ExtensionThe Transport Layer Security (TLS) master secret is not cryptographically bound to important session parameters such as the server certificate. Consequently, it is possible for an active attacker to set up two sessions, one with a client and another with a server, such that the master secrets on the two sessions are the same. Thereafter, any mechanism that relies on the master secret for authentication, including session resumption, becomes vulnerable to a man-in-the-middle attack, where the attacker can simply forward messages back and forth between the client and server. This specification defines a TLS extension that contextually binds the master secret to a log of the full handshake that computes it, thus preventing such attacks.Information technology - ASN.1 encoding Rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)ITU-TThe Transport Layer Security (TLS) Protocol Version 1.3This document specifies Version 1.3 of the Transport Layer Security (TLS) protocol. The TLS protocol allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.The ORIGIN HTTP/2 FrameThis document specifies the ORIGIN frame for HTTP/2, to indicate what origins are available on a given connection.HTTP Alternative ServicesThis document specifies "Alternative Services" for HTTP, which allow an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol configuration.X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSPThis document specifies a protocol useful in determining the current status of a digital certificate without requiring CRLs. [STANDARDS-TRACK]Certificate TransparencyThis document describes an experimental protocol for publicly logging the existence of Transport Layer Security (TLS) certificates as they are issued or observed, in a manner that allows anyone to audit certificate authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs.Logs are network services that implement the protocol operations for submissions and queries that are defined in this document.Digital Signature Standard (DSS)National Institute of Standards and TechnologyEdDSA and Ed25519The elliptic curve signature scheme EdDSA and one instance of it called Ed25519 is described. An example implementation and test vectors are provided.RSA Encryption Standard, Version 1.1RSA Laboratories