HTTP Working Group R. Polli
Internet-Draft Team Digitale, Italian Government
Obsoletes: 3230 (if approved) L. Pardue
Intended status: Standards Track Cloudflare
Expires: November 26, 2022 May 25, 2022
Digest Fields
draft-ietf-httpbis-digest-headers-09
Abstract
This document defines HTTP fields that support integrity digests.
The Content-Digest field can be used for the integrity of HTTP
message content. The Repr-Digest field can be used for the integrity
of HTTP representations. Want-Content-Digest and Want-Repr-Digest
can be used to indicate a sender's interest and preferences for
receiving the respective Integrity fields.
This document obsoletes RFC 3230 and the Digest and Want-Digest HTTP
fields.
About This Document
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Structure . . . . . . . . . . . . . . . . . . . 4
1.2. Concept Overview . . . . . . . . . . . . . . . . . . . . 4
1.3. Obsoleting RFC 3230 . . . . . . . . . . . . . . . . . . . 5
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 6
2. The Content-Digest Field . . . . . . . . . . . . . . . . . . 7
3. The Repr-Digest Field . . . . . . . . . . . . . . . . . . . . 8
3.1. Using Repr-Digest in State-Changing Requests . . . . . . 9
3.2. Repr-Digest and Content-Location in Responses . . . . . . 10
4. Integrity preference fields . . . . . . . . . . . . . . . . . 10
5. Hash Algorithms for HTTP Digest Fields Registry . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6.1. HTTP Messages Are Not Protected In Full . . . . . . . . . 12
6.2. End-to-End Integrity . . . . . . . . . . . . . . . . . . 13
6.3. Usage in Signatures . . . . . . . . . . . . . . . . . . . 13
6.4. Usage in Trailer Fields . . . . . . . . . . . . . . . . . 14
6.5. Usage with Encryption . . . . . . . . . . . . . . . . . . 14
6.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 14
6.7. Resource exhaustion . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7.1. HTTP Field Name Registration . . . . . . . . . . . . . . 15
7.2. Establish the Hash Algorithms for HTTP Digest Fields
Registry . . . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
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8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 17
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Appendix A. Resource Representation and Representation Data . . 19
Appendix B. Examples of Unsolicited Digest . . . . . . . . . . . 21
B.1. Server Returns Full Representation Data . . . . . . . . . 21
B.2. Server Returns No Representation Data . . . . . . . . . . 22
B.3. Server Returns Partial Representation Data . . . . . . . 22
B.4. Client and Server Provide Full Representation Data . . . 23
B.5. Client Provides Full Representation Data, Server Provides
No Representation Data . . . . . . . . . . . . . . . . . 24
B.6. Client and Server Provide Full Representation Data . . . 25
B.7. POST Response does not Reference the Request URI . . . . 25
B.8. POST Response Describes the Request Status . . . . . . . 26
B.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 27
B.10. Error responses . . . . . . . . . . . . . . . . . . . . . 28
B.11. Use with Trailer Fields and Transfer Coding . . . . . . . 29
Appendix C. Examples of Want-Repr-Digest Solicited Digest . . . 29
C.1. Server Selects Client's Least Preferred Algorithm . . . . 30
C.2. Server Selects Algorithm Unsupported by Client . . . . . 30
C.3. Server Does Not Support Client Algorithm and Returns an
Error . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Appendix D. Migrating from RFC 3230 . . . . . . . . . . . . . . 31
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 32
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
G.1. Since draft-ietf-httpbis-digest-headers-08 . . . . . . . 34
G.2. Since draft-ietf-httpbis-digest-headers-07 . . . . . . . 34
G.3. Since draft-ietf-httpbis-digest-headers-06 . . . . . . . 34
G.4. Since draft-ietf-httpbis-digest-headers-05 . . . . . . . 34
G.5. Since draft-ietf-httpbis-digest-headers-04 . . . . . . . 34
G.6. Since draft-ietf-httpbis-digest-headers-03 . . . . . . . 35
G.7. Since draft-ietf-httpbis-digest-headers-02 . . . . . . . 35
G.8. Since draft-ietf-httpbis-digest-headers-01 . . . . . . . 35
G.9. Since draft-ietf-httpbis-digest-headers-00 . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
HTTP does not define the means to protect the data integrity of
content or representations. When HTTP messages are transferred
between endpoints, lower layer features or properties such as TCP
checksums or TLS records [RFC2818] can provide some integrity
protection. However, transport-oriented integrity provides a limited
utility because it is opaque to the application layer and only covers
the extent of a single connection. HTTP messages often travel over a
chain of separate connections, in between connections there is a
possibility for unintended or malicious data corruption. An HTTP
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integrity mechanism can provide the means for endpoints, or
applications using HTTP, to detect data corruption and make a choice
about how to act on it. An example use case is to aid fault
detection and diagnosis across system boundaries.
This document defines two digest integrity mechanisms for HTTP.
First, content integrity, which acts on conveyed content (Section 6.4
of [SEMANTICS]). Second, representation data integrity, which acts
on representation data (Section 3.2 of [SEMANTICS]). This supports
advanced use cases such as validating the integrity of a resource
that was reconstructed from parts retrieved using multiple requests
or connections.
This document obsoletes RFC 3230 and therefore the Digest and Want-
Digest HTTP fields; see Section 1.3.
1.1. Document Structure
This document is structured as follows:
o Section 2 defines the Content-Digest request and response header
and trailer field,
o Section 3 defines the Repr-Digest request and response header and
trailer field,
o Section 4 defines the Want-Repr-Digest and Want-Content-Digest
request and response header and trailer field,
o Section 5 describes algorithms and their relation to the fields
defined in this document,
o Section 3.1 details computing representation digests,
o Appendix B and Appendix C provide examples of using Repr-Digest
and Want-Repr-Digest.
1.2. Concept Overview
The HTTP fields defined in this document can be used for HTTP
integrity. Senders choose a hashing algorithm and calculate a digest
from an input related to the HTTP message, the algorithm identifier
and digest are transmitted in an HTTP field. Receivers can validate
the digest for integrity purposes. Hashing algorithms are registered
in the "Hash Algorithms for HTTP Digest Fields" (see Section 5).
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Selecting the data on which digests are calculated depends on the use
case of HTTP messages. This document provides different headers for
HTTP representation data and HTTP content.
There are use-cases where a simple digest of the HTTP content bytes
is required. The "Content-Digest" request and response header and
trailer field is defined to support digests of content (Section 3.2
of [SEMANTICS]); see Section 2.
For more advanced use-cases, the "Repr-Digest" request and response
header and trailer field (Section 3) is defined. It contains a
digest value computed by applying a hashing algorithm to selected
representation data (Section 3.2 of [SEMANTICS]). Basing "Repr-
Digest" on the selected representation makes it straightforward to
apply it to use-cases where the transferred data requires some sort
of manipulation to be considered a representation or conveys a
partial representation of a resource, such as Range Requests (see
Section 14.2 of [SEMANTICS]).
"Content-Digest" and "Repr-Digest" support hashing algorithm agility.
The "Want-Content-Digest" and "Want-Repr-Digest" fields allow
endpoints to express interest in "Content-Digest" and "Repr-Digest"
respectively, and preference of algorithms in either.
"Content-Digest" and "Repr-Digest" are collectively termed Integrity
fields. "Want-Content-Digest" and "Want-Repr-Digest" are
collectively termed Integrity preference fields.
Integrity fields are tied to the "Content-Encoding" and "Content-
Type" header fields. Therefore, a given resource may have multiple
different digest values when transferred with HTTP.
Integrity fields do not provide integrity for HTTP messages or
fields. However, they can be combined with other mechanisms that
protect metadata, such as digital signatures, in order to protect the
phases of an HTTP exchange in whole or in part. For example, HTTP
Message Signatures [SIGNATURES] could be used to sign Integrity
fields, thus providing coverage for HTTP content or representation
data.
This specification does not define means for authentication,
authorization or privacy.
1.3. Obsoleting RFC 3230
[RFC3230] defined the "Digest" and "Want-Digest" HTTP fields for HTTP
integrity. It also coined the term "instance" and "instance
manipulation" in order to explain concepts that are now more
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universally defined, and implemented, as HTTP semantics such as
selected representation data (Section 3.2 of [SEMANTICS]).
Experience has shown that implementations of [RFC3230] have
interpreted the meaning of "instance" inconsistently, leading to
interoperability issues. The most common mistake being the
calculation of the digest using (what we now call) message content,
rather than using (what we now call) representation data as was
originally intended. Interestingly, time has also shown that a
digest of message content can be beneficial for some use cases. So
it is difficult to detect if non-conformance to [RFC3230] is
intentional or unintentional.
In order to address potential inconsistencies and ambiguity across
implementations of "Digest" and "Want-Digest", this document
obsoletes [RFC3230]. The Integrity fields (Section 3 and Section 2)
and Integrity preference fields (Section 4) defined in this document
are better aligned with current HTTP semantics and have names that
more clearly articulate the intended usages.
1.4. Notational Conventions
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the Augmented BNF defined in [RFC5234] and updated
by [RFC7405].
This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Boolean, Byte
Sequence, Dictionary, Integer, and List.
The definitions "representation", "selected representation",
"representation data", "representation metadata", "user agent" and
"content" in this document are to be interpreted as described in
[SEMANTICS].
Hashing algorithm names respect the casing used in their definition
document (e.g. SHA-1, CRC32c) whereas hashing algorithm keys are
quoted (e.g. "sha", "crc32c").
The term "checksum" describes the output of the application of an
algorithm to a sequence of bytes, whereas "digest" is only used in
relation to the value contained in the fields.
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Integrity fields: collective term for "Content-Digest" and "Repr-
Digest"
Integrity preference fields: collective term for "Want-Repr-Digest"
and "Want-Content-Digest"
2. The Content-Digest Field
The "Content-Digest" HTTP field can be used in requests and responses
to communicate digests that are calculated using a hashing algorithm
applied to the actual message content (see Section 6.4 of
[SEMANTICS]). It is a "Dictionary" (see Section 3.2 of
[STRUCTURED-FIELDS]) where each:
o key conveys the hashing algorithm (see Section 5) used to compute
the digest;
o value is a "Byte Sequence" (Section 3.3.5 of [STRUCTURED-FIELDS]),
that contains the output of the digest calculation.
For example:
NOTE: '\' line wrapping per RFC 8792
Content-Digest: \
sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrI\
iYllu7BNNyealdVLvRwEmTHWXvJwew==:
The "Dictionary" type can be used, for example, to attach multiple
digests calculated using different hashing algorithms in order to
support a population of endpoints with different or evolving
capabilities. Such an approach could support transitions away from
weaker algorithms (see Section 6.6).
NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \
sha-256=:4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=:,\
sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrI\
iYllu7BNNyealdVLvRwEmTHWXvJwew==:
A recipient MAY ignore any or all digests. This allows the recipient
to choose which hashing algorithm(s) to use for validation instead of
verifying every digest.
A sender MAY send a digest without knowing whether the recipient
supports a given hashing algorithm, or even knowing that the
recipient will ignore it.
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"Content-Digest" can be sent in a trailer section. In this case,
"Content-Digest" MAY be merged into the header section; see
Section 6.5.1 of [SEMANTICS].
3. The Repr-Digest Field
The "Repr-Digest" HTTP field can be used in requests and responses to
communicate digests that are calculated using a hashing algorithm
applied to the entire selected representation data (see Section 8.1
of [SEMANTICS]).
Representations take into account the effect of the HTTP semantics on
messages. For example, the content can be affected by Range Requests
or methods such as HEAD, while the way the content is transferred "on
the wire" is dependent on other transformations (e.g. transfer
codings for HTTP/1.1 - see Section 6.1 of [HTTP11]). To help
illustrate HTTP representation concepts, several examples are
provided in Appendix A.
When a message has no representation data it is still possible to
assert that no representation data was sent by computing the digest
on an empty string (see Section 6.3).
"Repr-Digest" is a "Dictionary" (see Section 3.2 of
[STRUCTURED-FIELDS]) where each:
o key conveys the hashing algorithm (see Section 5) used to compute
the digest;
o value is a "Byte Sequence" that contains the output of the digest
calculation.
For example:
NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \
sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrI\
iYllu7BNNyealdVLvRwEmTHWXvJwew==:
The "Dictionary" type can be used, for example, to attach multiple
digests calculated using different hashing algorithms in order to
support a population of endpoints with different or evolving
capabilities. Such an approach could support transitions away from
weaker algorithms (see Section 6.6).
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NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \
sha-256=:4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=:,\
sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrI\
iYllu7BNNyealdVLvRwEmTHWXvJwew==:
A recipient MAY ignore any or all digests. This allows the recipient
to choose which hashing algorithm(s) to use for validation instead of
verifying every digest.
A sender MAY send a digest without knowing whether the recipient
supports a given hashing algorithm, or even knowing that the
recipient will ignore it.
"Repr-Digest" can be sent in a trailer section. In this case, "Repr-
Digest" MAY be merged into the header section; see Section 6.5.1 of
[SEMANTICS].
3.1. Using Repr-Digest in State-Changing Requests
When the representation enclosed in a state-changing request does not
describe the target resource, the representation digest MUST be
computed on the representation data. This is the only possible
choice because representation digest requires complete representation
metadata (see Section 3).
In responses,
o if the representation describes the status of the request, "Repr-
Digest" MUST be computed on the enclosed representation (see
Appendix B.8 );
o if there is a referenced resource "Repr-Digest" MUST be computed
on the selected representation of the referenced resource even if
that is different from the target resource. That might or might
not result in computing "Repr-Digest" on the enclosed
representation.
The latter case is done according to the HTTP semantics of the given
method, for example using the "Content-Location" header field (see
Section 8.7 of [SEMANTICS]). In contrast, the "Location" header
field does not affect "Repr-Digest" because it is not representation
metadata.
For example, in "PATCH" requests, the representation digest will be
computed on the patch document because the representation metadata
refers to the patch document and not to the target resource (see
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Section 2 of [PATCH]). In responses, instead, the representation
digest will be computed on the selected representation of the patched
resource.
3.2. Repr-Digest and Content-Location in Responses
When a state-changing method returns the "Content-Location" header
field, the enclosed representation refers to the resource identified
by its value and "Repr-Digest" is computed accordingly. An example
is given in Appendix B.7.
4. Integrity preference fields
Senders can indicate their interest in Integrity fields and hashing
algorithm preferences using the "Want-Content-Digest" or "Want-Repr-
Digest" fields. These can be used in both requests and responses.
"Want-Content-Digest" indicates that the sender would like to receive
a content digest on messages associated with the request URI and
representation metadata, using the "Content-Digest" field.
"Want-Repr-Digest" indicates that the sender would like to receive a
representation digest on messages associated with the request URI and
representation metadata, using the "Repr-Digest" field.
If "Want-Content-Digest" or "Want-Repr-Digest" are used in a
response, it indicates that the server would like the client to
provide the respective Integrity field on future requests.
"Want-Content-Digest" and "Want-Repr-Digest" are of type "Dictionary"
where each:
o key conveys the hashing algorithm (see Section 5);
o value is an "Integer" (Section 3.3.1 of [STRUCTURED-FIELDS]) that
conveys an ascending, relative, weighted preference. It must be
in the range 0 to 10 inclusive. 1 is the least preferred, 10 is
the most preferred, and a value of 0 means "not acceptable".
Examples:
Want-Repr-Digest: sha-256=1
Want-Repr-Digest: sha-512=3, sha-256=10, unixsum=0
Want-Content-Digest: sha-256=1
Want-Content-Digest: sha-512=3, sha-256=10, unixsum=0
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5. Hash Algorithms for HTTP Digest Fields Registry
The "Hash Algorithms for HTTP Digest Fields", maintained by IANA at
https://www.iana.org/assignments/http-dig-alg/ [1], registers
algorithms for use with the Integrity and Integrity preference fields
defined in this document.
This registry uses the Specification Required policy (Section 4.6 of
[RFC8126]).
Registrations MUST include the following fields:
o Algorithm Key: the Structured Fields key value used in "Content-
Digest", "Repr-Digest", "Want-Content-Digest", or "Want-Repr-
Digest" field Dictionary member keys
o Status: the status of the algorithm. Use "standard" for
standardized algorithms without known problems; "experimental" or
some other appropriate value
* e.g. according to the type and status of the primary document
in which the algorithm is defined; "insecure" when the
algorithm is insecure; "reserved" when the algorithm references
a reserved token value
o Description: a short description of the algorithm
o Reference(s): a set of pointers to the primary documents defining
the algorithm and key
Insecure hashing algorithms MAY be used to preserve integrity against
corruption, but MUST NOT be used in a potentially adversarial
setting; for example, when signing Integrity fields' values for
authenticity.
The entries in Table 1 are registered by this document.
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+-----------+----------+--------------------------+-----------------+
| Algorithm | Status | Description | Reference(s) |
| Key | | | |
+-----------+----------+--------------------------+-----------------+
| sha-512 | standard | The SHA-512 algorithm. | [RFC6234], |
| | | | [RFC4648], this |
| | | | document. |
| sha-256 | standard | The SHA-256 algorithm. | [RFC6234], |
| | | | [RFC4648], this |
| | | | document. |
| md5 | insecure | The MD5 algorithm. It is | [RFC1321], |
| | | vulnerable to collision | [RFC4648], this |
| | | attacks; see [NO-MD5] | document. |
| | | and [CMU-836068] | |
| sha | insecure | The SHA-1 algorithm. It | [RFC3174], |
| | | is vulnerable to | [RFC4648], |
| | | collision attacks; see | [RFC6234] this |
| | | [NO-SHA] and | document. |
| | | [IACR-2020-014] | |
| unixsum | insecure | The algorithm used by | [RFC4648], |
| | | the UNIX "sum" command. | [RFC6234], |
| | | | [UNIX], this |
| | | | document. |
| unixcksum | insecure | The algorithm used by | [RFC4648], |
| | | the UNIX "cksum" | [RFC6234], |
| | | command. | [UNIX], this |
| | | | document. |
| adler | insecure | The ADLER32 algorithm. | [RFC1950], this |
| | | | document. |
| crc32c | insecure | The CRC32c algorithm. | [RFC4960] |
| | | | appendix B, |
| | | | this document. |
+-----------+----------+--------------------------+-----------------+
Table 1: Initial Hash Algorithms
6. Security Considerations
6.1. HTTP Messages Are Not Protected In Full
This document specifies a data integrity mechanism that protects HTTP
representation data or content, but not HTTP header and trailer
fields, from certain kinds of corruption.
Integrity fields are not intended to be a general protection against
malicious tampering with HTTP messages. This can be achieved by
combining it with other approaches such as transport-layer security
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or digital signatures (for example, HTTP Message Signatures
[SIGNATURES]).
6.2. End-to-End Integrity
Integrity fields can help detect representation data or content
modification due to implementation errors, undesired "transforming
proxies" (see Section 7.7 of [SEMANTICS]) or other actions as the
data passes across multiple hops or system boundaries. Even a simple
mechanism for end-to-end representation data integrity is valuable
because a user agent can validate that resource retrieval succeeded
before handing off to a HTML parser, video player etc. for parsing.
Note that using these mechanisms alone does not provide end-to-end
integrity of HTTP messages over multiple hops, since metadata could
be manipulated at any stage. Methods to protect metadata are
discussed in Section 6.3.
6.3. Usage in Signatures
Digital signatures are widely used together with checksums to provide
the certain identification of the origin of a message [NIST800-32].
Such signatures can protect one or more HTTP fields and there are
additional considerations when Integrity fields are included in this
set.
There are no restrictions placed on the type or format of digitial
signature that Integrity fields can be used with. One possible
approach is to combine them with HTTP Message Signatures
[SIGNATURES].
Digests explicitly depend on the "representation metadata" (e.g. the
values of "Content-Type", "Content-Encoding" etc). A signature that
protects Integrity fields but not other "representation metadata" can
expose the communication to tampering. For example, an actor could
manipulate the "Content-Type" field-value and cause a digest
validation failure at the recipient, preventing the application from
accessing the representation. Such an attack consumes the resources
of both endpoints. See also Section 3.2.
Signatures are likely to be deemed an adversarial setting when
applying Integrity fields; see Section 5. Using signatures to
protect the checksum of an empty representation allows receiving
endpoints to detect if an eventual payload has been stripped or
added.
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Any mangling of Integrity fields, including digests' de-duplication
or combining different field values (see Section 5.2 of [SEMANTICS])
might affect signature validation.
6.4. Usage in Trailer Fields
Before sending Integrity fields in a trailer section, the sender
should consider that intermediaries are explicitly allowed to drop
any trailer (see Section 6.5.2 of [SEMANTICS]).
When Integrity fields are used in a trailer section, the field-values
are received after the content. Eager processing of content before
the trailer section prevents digest validation, possibly leading to
processing of invalid data.
Not every hashing algorithm is suitable for use in the trailer
section, some may require to pre-process the whole payload before
sending a message (e.g. see [I-D.thomson-http-mice]).
6.5. Usage with Encryption
The checksum of an encrypted payload can change between different
messages depending on the encryption algorithm used; in those cases
its value could not be used to provide a proof of integrity "at rest"
unless the whole (e.g. encoded) content is persisted.
6.6. Algorithm Agility
The security properties of hashing algorithms are not fixed.
Algorithm Agility (see [RFC7696]) is achieved by providing
implementations with flexibility to choose hashing algorithms from
the IANA Hash Algorithms for HTTP Digest Fields registry; see
Section 7.2.
The "standard" algorithms listed in this document are suitable for
many purposes, including adversarial situations where hash functions
might need to provide resistance to collision, first-preimage and
second-preimage attacks. Algorithms listed as "insecure" either
provide none of these properties, or are known to be weak (see
[NO-MD5] and [NO-SHA]).
For adversarial situations, which of the "standard" algorithms are
acceptable will depend on the level of protection the circumstances
demand. As there is no negotiation, endpoints that depend on a
digest for security will be vulnerable to attacks on the weakest
algorithm they are willing to accept.
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Transition from weak algorithms is supported by negotiation of
hashing algorithm using "Want-Content-Digest" or "Want-Repr-Digest"
(see Section 4) or by sending multiple digests from which the
receiver chooses. Endpoints are advised that sending multiple values
consumes resources, which may be wasted if the receiver ignores them
(see Section 3).
While algorithm agility allows the migration to stronger algorithms
it does not prevent the use of weaker algorithms. Integrity fields
do not provide any mitigiations for downgrade or substitution attacks
(see Section 1 of [RFC6211]) of the hashing algorithm. To protect
against such attacks, endpoints could restrict their set of supported
algorithms to stronger ones and protect the fields value by using TLS
and/or digital signatures.
6.7. Resource exhaustion
Integrity fields validation consumes computational resources. In
order to avoid resource exhaustion, implementations can restrict
validation of the algorithm types, number of validations, or the size
of content.
7. IANA Considerations
7.1. HTTP Field Name Registration
IANA is asked to update the "Hypertext Transfer Protocol (HTTP) Field
Name Registry" registry ([SEMANTICS]) according to the table below:
+---------------------+-----------+---------------------------------+
| Field Name | Status | Reference |
+---------------------+-----------+---------------------------------+
| Content-Digest | permanent | Section 2 of this document |
| Repr-Digest | permanent | Section 3 of this document |
| Want-Content-Digest | permanent | Section 4 of this document |
| Want-Repr-Digest | permanent | Section 4 of this document |
| Digest | obsoleted | [RFC3230], Section 1.3 of this |
| | | document |
| Want-Digest | obsoleted | [RFC3230], Section 1.3 of this |
| | | document |
+---------------------+-----------+---------------------------------+
7.2. Establish the Hash Algorithms for HTTP Digest Fields Registry
This memo sets this specification to be the establishing document for
the Hash Algorithms for HTTP Digest Fields [2] registry defined in
Section 5.
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IANA is asked to initialize the registry with the entries in Table 1.
8. References
8.1. Normative References
[CMU-836068]
Carnagie Mellon University, Software Engineering
Institute, "MD5 Vulnerable to collision attacks", December
2008, .
[IACR-2020-014]
Leurent, G. and T. Peyrin, "SHA-1 is a Shambles", January
2020, .
[NIST800-32]
National Institute of Standards and Technology, U.S.
Department of Commerce, "Introduction to Public Key
Technology and the Federal PKI Infrastructure", February
2001, .
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
.
[RFC1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
.
[RFC3230] Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
RFC 3230, DOI 10.17487/RFC3230, January 2002,
.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
.
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[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014,
.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[SEMANTICS]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", draft-ietf-httpbis-semantics-19 (work in
progress), September 2021.
[STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
.
[UNIX] The Open Group, "The Single UNIX Specification, Version 2
- 6 Vol Set for UNIX 98", February 1997.
8.2. Informative References
[HTTP11] Fielding, R. T., Nottingham, M., and J. Reschke,
"HTTP/1.1", draft-ietf-httpbis-messaging-19 (work in
progress), September 2021.
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[I-D.thomson-http-mice]
Thomson, M. and J. Yasskin, "Merkle Integrity Content
Encoding", draft-thomson-http-mice-03 (work in progress),
August 2018.
[NO-MD5] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011,
.
[NO-SHA] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
.
[PATCH] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, DOI 10.17487/RFC5789, March 2010,
.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
.
[RFC6211] Schaad, J., "Cryptographic Message Syntax (CMS) Algorithm
Identifier Protection Attribute", RFC 6211,
DOI 10.17487/RFC6211, April 2011,
.
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
.
[SIGNATURES]
Backman, A., Richer, J., and M. Sporny, "HTTP Message
Signatures", draft-ietf-httpbis-message-signatures-09
(work in progress), March 2022.
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8.3. URIs
[1] https://www.iana.org/assignments/http-dig-alg/
[2] https://www.iana.org/assignments/http-structured-dig-alg/
Appendix A. Resource Representation and Representation Data
The following examples show how representation metadata, payload
transformations and method impacts on the message and content. When
the content contains non-printable characters (e.g. when it is
compressed) it is shown as a Base64-encoded string.
PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json
{"hello": "world"}
Request containing a JSON object without any content coding
PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json
Content-Encoding: gzip
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
Request containing a gzip-encoded JSON object
Now the same content conveys a malformed JSON object, because the
request does not indicate a content coding.
PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
Request containing malformed JSON
A Range-Request alters the content, conveying a partial
representation.
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GET /entries/1234 HTTP/1.1
Host: foo.example
Range: bytes=1-7
Request for partial content
HTTP/1.1 206 Partial Content
Content-Encoding: gzip
Content-Type: application/json
Content-Range: bytes 1-7/18
iwgAla3RXA==
Partial response from a gzip-encoded representation
The method can also alter the content. For example, the response to
a HEAD request does not carry content.
HEAD /entries/1234 HTTP/1.1
Host: foo.example
Accept: application/json
Accept-Encoding: gzip
HEAD request
HTTP/1.1 200 OK
Content-Type: application/json
Content-Encoding: gzip
Response to HEAD request (empty content)
Finally, the semantics of an HTTP response might decouple the
effective request URI from the enclosed representation. In the
example response below, the "Content-Location" header field indicates
that the enclosed representation refers to the resource available at
"/authors/123", even though the request is directed to "/authors/".
POST /authors/ HTTP/1.1
Host: foo.example
Accept: application/json
Content-Type: application/json
{"author": "Camilleri"}
POST request
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HTTP/1.1 201 Created
Content-Type: application/json
Content-Location: /authors/123
Location: /authors/123
{"id": "123", "author": "Camilleri"}
Response with Content-Location header
Appendix B. Examples of Unsolicited Digest
The following examples demonstrate interactions where a server
responds with a "Content-Digest" or "Repr-Digest" fields even though
the client did not solicit one using "Want-Content-Digest" or "Want-
Repr-Digest".
Some examples include JSON objects in the content. For presentation
purposes, objects that fit completely within the line-length limits
are presented on a single line using compact notation with no leading
space. Objects that would exceed line-length limits are presented
across multiple lines (one line per key-value pair) with 2 spaced of
leading indentation.
Checksum mechanisms defined in this document are media-type agnostic
and do not provide canonicalization algorithms for specific formats.
Examples are calculated inclusive of any space. While examples can
include both fields, "Content-Digest" and "Repr-Digest" can be
returned independently.
B.1. Server Returns Full Representation Data
In this example, the message content conveys complete representation
data. This means that in the response, "Content-Digest" and "Repr-
Digest" are both computed over the JSON object "{"hello": "world"}",
and thus have the same value.
GET /items/123 HTTP/1.1
Host: foo.example
GET request for an item
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NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Content-Digest: \
sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
Repr-Digest: \
sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
{"hello": "world"}
Response with identical Repr-Digest and Content-Digest
B.2. Server Returns No Representation Data
In this example, a HEAD request is used to retrieve the checksum of a
resource.
The response "Content-Digest" field-value is computed on empty
content. "Repr-Digest" is calculated over the JSON object "{"hello":
"world"}", which is not shown because there is no payload data.
HEAD /items/123 HTTP/1.1
Host: foo.example
HEAD request for an item
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Content-Digest: \
sha-256=:47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=:
Repr-Digest: \
sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
Response with both Content-Digest and Digest; empty content
B.3. Server Returns Partial Representation Data
In this example, the client makes a range request and the server
responds with partial content.
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GET /items/123 HTTP/1.1
Host: foo.example
Range: bytes=1-7
Request for partial content
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 206 Partial Content
Content-Type: application/json
Content-Range: bytes 1-7/18
Content-Digest: \
sha-256=:Wqdirjg/u3J688ejbUlApbjECpiUUtIwT8lY/z81Tno=:
Repr-Digest: \
sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
"hello"
Partial response with both Content-Digest and Repr-Digest
In the response message above, note that the "Repr-Digest" and
"Content-Digests" are different. The "Repr-Digest" field-value is
calculated across the entire JSON object "{"hello": "world"}", and
the field is
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
However, since the message content is constrained to bytes 1-7, the
"Content-Digest" field-value is calculated over the byte sequence
""hello"", thus resulting in
NOTE: '\' line wrapping per RFC 8792
Content-Digest: \
sha-256=:Wqdirjg/u3J688ejbUlApbjECpiUUtIwT8lY/z81Tno=:
B.4. Client and Server Provide Full Representation Data
The request contains a "Repr-Digest" field-value calculated on the
enclosed representation. It also includes an "Accept-Encoding: br"
header field that advertises the client supports Brotli encoding.
The response includes a "Content-Encoding: br" that indicates the
selected representation is Brotli-encoded. The "Repr-Digest" field-
value is therefore different compared to the request.
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For presentation purposes, the response body is displayed as a
Base64-encoded string because it contains non-printable characters.
PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept-Encoding: br
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
{"hello": "world"}
PUT Request with Digest
HTTP/1.1 200 OK
Content-Type: application/json
Content-Location: /items/123
Content-Encoding: br
Content-Length: 22
Repr-Digest: sha-256=:4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=:
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
Response with Digest of encoded response
B.5. Client Provides Full Representation Data, Server Provides No
Representation Data
The request "Repr-Digest" field-value is calculated on the enclosed
payload.
The response "Repr-Digest" field-value depends on the representation
metadata header fields, including "Content-Encoding: br" even when
the response does not contain content.
PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Content-Length: 18
Accept-Encoding: br
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
{"hello": "world"}
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HTTP/1.1 204 No Content
Content-Type: application/json
Content-Encoding: br
Repr-Digest: sha-256=:4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=:
Empty response with Digest
B.6. Client and Server Provide Full Representation Data
The response contains two digest values using different algorithms.
As the response body contains non-printable characters, it is
displayed as a base64-encoded string.
PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept-Encoding: br
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
{"hello": "world"}
PUT Request with Digest
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Content-Encoding: br
Content-Location: /items/123
Repr-Digest: \
sha-256=:4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=:,\
sha-512=:pxo7aYzcGI88pnDnoSmAnaOEVys0MABhgvHY9+VI+ElE60jBCwnMPyA/\
s3NF3ZO5oIWA7lf8ukk+5KJzm3p5og==:
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
Response with Digest of Encoded Content
B.7. POST Response does not Reference the Request URI
The request "Repr-Digest" field-value is computed on the enclosed
representation (see Section 3.1).
The representation enclosed in the response refers to the resource
identified by "Content-Location" (see Section 6.4.2 of [SEMANTICS]).
"Repr-Digest" is thus computed on the enclosed representation.
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POST /books HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept: application/json
Accept-Encoding: identity
Repr-Digest: sha-256=:bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=:
{"title": "New Title"}
POST Request with Digest
HTTP/1.1 201 Created
Content-Type: application/json
Content-Location: /books/123
Location: /books/123
Repr-Digest: sha-256=:yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=:
{
"id": "123",
"title": "New Title"
}
Response with Digest of Resource
Note that a "204 No Content" response without content but with the
same "Repr-Digest" field-value would have been legitimate too. In
that case, "Content-Digest" would have been computed on an empty
content.
B.8. POST Response Describes the Request Status
The request "Repr-Digest" field-value is computed on the enclosed
representation (see Section 3.1).
The representation enclosed in the response describes the status of
the request, so "Repr-Digest" is computed on that enclosed
representation.
Response "Repr-Digest" has no explicit relation with the resource
referenced by "Location".
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POST /books HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept: application/json
Accept-Encoding: identity
Repr-Digest: sha-256=:bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=:
{"title": "New Title"}
POST Request with Digest
HTTP/1.1 201 Created
Content-Type: application/json
Repr-Digest: sha-256=:2LBp5RKZGpsSNf8BPXlXrX4Td4Tf5R5bZ9z7kdi5VvY=:
Location: /books/123
{
"status": "created",
"id": "123",
"ts": 1569327729,
"instance": "/books/123"
}
Response with Digest of Representation
B.9. Digest with PATCH
This case is analogous to a POST request where the target resource
reflects the effective request URI.
The PATCH request uses the "application/merge-patch+json" media type
defined in [RFC7396].
"Repr-Digest" is calculated on the enclosed payload, which
corresponds to the patch document.
The response "Repr-Digest" field-value is computed on the complete
representation of the patched resource.
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PATCH /books/123 HTTP/1.1
Host: foo.example
Content-Type: application/merge-patch+json
Accept: application/json
Accept-Encoding: identity
Repr-Digest: sha-256=:bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=:
{"title": "New Title"}
Figure 1: PATCH Request with Digest
HTTP/1.1 200 OK
Content-Type: application/json
Repr-Digest: sha-256=:yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=:
{
"id": "123",
"title": "New Title"
}
Response with Digest of Representation
Note that a "204 No Content" response without content but with the
same "Repr-Digest" field-value would have been legitimate too.
B.10. Error responses
In error responses, the representation data does not necessarily
refer to the target resource. Instead, it refers to the
representation of the error.
In the following example, a client sends the same request from
Figure 1 to patch the resource located at /books/123. However, the
resource does not exist and the server generates a 404 response with
a body that describes the error in accordance with [RFC7807].
The response "Repr-Digest" field-value is computed on this enclosed
representation.
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HTTP/1.1 404 Not Found
Content-Type: application/problem+json
Repr-Digest: sha-256=:KPqhVXAT25LLitV1w0O167unHmVQusu+fpxm65zAsvk=:
{
"title": "Not Found",
"detail": "Cannot PATCH a non-existent resource",
"status": 404
}
Response with Digest of Error Representation
B.11. Use with Trailer Fields and Transfer Coding
An origin server sends "Repr-Digest" as trailer field, so it can
calculate digest-value while streaming content and thus mitigate
resource consumption. The "Repr-Digest" field-value is the same as
in Appendix B.1 because "Repr-Digest" is designed to be independent
from the use of one or more transfer codings (see Section 3).
GET /items/123 HTTP/1.1
Host: foo.example
GET Request
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
Trailer: Digest
8\r\n
{"hello"\r\n
8
: "world\r\n
2\r\n
"}\r\n
0\r\n
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
Chunked Response with Digest
Appendix C. Examples of Want-Repr-Digest Solicited Digest
The following examples demonstrate interactions where a client
solicits a "Repr-Digest" using "Want-Repr-Digest". The behavior of
"Content-Digest" and "Want-Content-Digest" is identical.
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Some examples include JSON objects in the content. For presentation
purposes, objects that fit completely within the line-length limits
are presented on a single line using compact notation with no leading
space. Objects that would exceed line-length limits are presented
across multiple lines (one line per key-value pair) with 2 spaced of
leading indentation.
Checksum mechanisms described in this document are media-type
agnostic and do not provide canonicalization algorithms for specific
formats. Examples are calculated inclusive of any space.
C.1. Server Selects Client's Least Preferred Algorithm
The client requests a digest, preferring "sha". The server is free
to reply with "sha-256" anyway.
GET /items/123 HTTP/1.1
Host: foo.example
Want-Repr-Digest: sha-256=3, sha=10
GET Request with Want-Repr-Digest
HTTP/1.1 200 OK
Content-Type: application/json
Repr-Digest: sha-256=:X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=:
{"hello": "world"}
Response with Different Algorithm
C.2. Server Selects Algorithm Unsupported by Client
The client requests a "sha" digest because that is the only algorithm
it supports. The server is not obliged to produce a response
containing a "sha" digest, it instead uses a different algorithm.
GET /items/123 HTTP/1.1
Host: foo.example
Want-Repr-Digest: sha=10
GET Request with Want-Repr-Digest
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NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Repr-Digest: \
sha-512=:WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrI\
iYllu7BNNyealdVLvRwEmTHWXvJwew==:
{"hello": "world"}
Response with Unsupported Algorithm
C.3. Server Does Not Support Client Algorithm and Returns an Error
Appendix C.2 is an example where a server ignores the client's
preferred digest algorithm. Alternatively a server can also reject
the request and return an error.
In this example, the client requests a "sha" "Repr-Digest", and the
server returns an error with problem details [RFC7807] contained in
the content. The problem details contain a list of the hashing
algorithms that the server supports. This is purely an example, this
specification does not define any format or requirements for such
content.
GET /items/123 HTTP/1.1
Host: foo.example
Want-Repr-Digest: sha=10
GET Request with Want-Repr-Digest
HTTP/1.1 400 Bad Request
Content-Type: application/problem+json
{
"title": "Bad Request",
"detail": "Supported hashing algorithms: sha-256, sha-512",
"status": 400
}
Response advertising the supported algorithms
Appendix D. Migrating from RFC 3230
HTTP digests are computed by applying a hashing algorithm to input
data. RFC 3230 defined the input data as an "instance", a term it
also defined. The concept of instance has since been superseded by
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the HTTP semantic term "representation". It is understood that some
implementations of RFC 3230 mistook "instance" to mean HTTP content.
Using content for the Digest field is an error that leads to
interoperability problems between peers that implement RFC 3230.
For the uncertainty of doubt, RFC 3230 was only ever intended to use
what HTTP now defines as selected representation data. The semantic
concept of digest and representation are explained alongside the
definition of Representation-Digest Section 3.
While the syntax of Digest and Repr-Digest are different, the
considerations and examples this document gives to Repr-Digest apply
equally to Digest because they operate on the same input data. See
Section 3.1, Section 6 and Section 6.3.
RFC 3230 could never communicate the digest of HTTP message content
in the Digest field; Content-Digest now provides that capability.
Acknowledgements
This document is based on ideas from [RFC3230], so thanks to J.
Mogul and A. Van Hoff for their great work. The original idea of
refreshing RFC3230 arose from an interesting discussion with M.
Nottingham, J. Yasskin and M. Thomson when reviewing the MICE
content coding.
Thanks to Julian Reschke for his valuable contributions to this
document, and to the following contributors that have helped improve
this specification by reporting bugs, asking smart questions,
drafting or reviewing text, and evaluating open issues: Mike Bishop,
Brian Campbell, Matthew Kerwin, James Manger, Tommy Pauly, Sean
Turner, Justin Richer, and Erik Wilde.
Code Samples
_RFC Editor: Please remove this section before publication._
How can I generate and validate the "Repr-Digest" values shown in the
examples throughout this document?
The following python3 code can be used to generate digests for JSON
objects using SHA algorithms for a range of encodings. Note that
these are formatted as base64. This function could be adapted to
other algorithms and should take into account their specific
formatting rules.
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import base64, json, hashlib, brotli, logging
log = logging.getLogger()
def encode_item(item, encoding=lambda x: x):
indent = 2 if isinstance(item, dict) and len(item) > 1 else None
json_bytes = json.dumps(item, indent=indent).encode()
return encoding(json_bytes)
def digest_bytes(bytes_, algorithm=hashlib.sha256):
checksum_bytes = algorithm(bytes_).digest()
log.warning("Log bytes: \n[%r]", bytes_)
return base64.encodebytes(checksum_bytes).strip()
def digest(item, encoding=lambda x: x, algorithm=hashlib.sha256):
content_encoded = encode_item(item, encoding)
return digest_bytes(content_encoded, algorithm)
item = {"hello": "world"}
print("Encoding | hashing algorithm | digest-value")
print("Identity | sha256 |", digest(item))
# Encoding | hashing algorithm | digest-value
# Identity | sha256 | X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
print("Encoding | hashing algorithm | digest-value")
print("Brotli | sha256 |", digest(item, encoding=brotli.compress))
# Encoding | hashing algorithm | digest-value
# Brotli | sha256 | 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
print("Encoding | hashing algorithm | digest-value")
print("Identity | sha512 |", digest(item, algorithm=hashlib.sha512))
print("Brotli | sha512 |", digest(item, algorithm=hashlib.sha512,
encoding=brotli.compress))
# Encoding | hashing algorithm | digest-value
# Identity | sha512 |b'WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm'
# '+AbwAgBWnrIiYllu7BNNyealdVLvRwEmTHWXvJwew=='
# Brotli | sha512 | b'pxo7aYzcGI88pnDnoSmAnaOEVys0MABhgvHY9+VI+ElE6'
# '0jBCwnMPyA/s3NF3ZO5oIWA7lf8ukk+5KJzm3p5og=='
Changes
_RFC Editor: Please remove this section before publication._
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G.1. Since draft-ietf-httpbis-digest-headers-08
o Add note about migrating from RFC 3230. #1968, #1971
o Clarify what Want-* means in responses. #2097
o Editorial changes to structure and to align to HTTP style guide.
G.2. Since draft-ietf-httpbis-digest-headers-07
o Introduced Repr-Digest and Want-Repr-Digest, and deprecated Digest
and Want-Digest. Use of Structured Fields. #1993, #1919
o IANA refactoring. #1983
o No normative text in security considerations. #1972
G.3. Since draft-ietf-httpbis-digest-headers-06
o Remove id-sha-256 and id-sha-512 from the list of supported
algorithms #855
G.4. Since draft-ietf-httpbis-digest-headers-05
o Reboot digest-algorithm values registry #1567
o Add Content-Digest #1542
o Remove SRI section #1478
G.5. Since draft-ietf-httpbis-digest-headers-04
o Improve SRI section #1354
o About duplicate digest-algorithms #1221
o Improve security considerations #852
o md5 and sha deprecation references #1392
o Obsolete 3230 #1395
o Editorial #1362
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G.6. Since draft-ietf-httpbis-digest-headers-03
o Reference semantics-12
o Detail encryption quirks
o Details on Algorithm agility #1250
o Obsolete parameters #850
G.7. Since draft-ietf-httpbis-digest-headers-02
o Deprecate SHA-1 #1154
o Avoid id-* with encrypted content
o Digest is independent from MESSAGING and HTTP/1.1 is not normative
#1215
o Identity is not a valid field value for content-encoding #1223
o Mention trailers #1157
o Reference httpbis-semantics #1156
o Add contentMD5 as an obsoleted digest-algorithm #1249
o Use lowercase digest-algorithms names in the doc and in the
digest-algorithm IANA table.
G.8. Since draft-ietf-httpbis-digest-headers-01
o Digest of error responses is computed on the error representation-
data #1004
o Effect of HTTP semantics on payload and message body moved to
appendix #1122
o Editorial refactoring, moving headers sections up. #1109-#1112,
#1116, #1117, #1122-#1124
G.9. Since draft-ietf-httpbis-digest-headers-00
o Align title with document name
o Add id-sha-* algorithm examples #880
o Reference [RFC6234] and [RFC3174] instead of FIPS-1
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o Deprecate MD5
o Obsolete ADLER-32 but don't forbid it #828
o Update CRC32C value in IANA table #828
o Use when acting on resources (POST, PATCH) #853
o Added Relationship with SRI, draft Use Cases #868, #971
o Warn about the implications of "Content-Location"
Authors' Addresses
Roberto Polli
Team Digitale, Italian Government
Italy
Email: robipolli@gmail.com
Lucas Pardue
Cloudflare
Email: lucaspardue.24.7@gmail.com
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