draft-ietf-httpbis-encryption-encoding-00.txt   draft-ietf-httpbis-encryption-encoding-01.txt 
Network Working Group M. Thomson HTTP Working Group M. Thomson
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Standards Track December 22, 2015 Intended status: Standards Track March 20, 2016
Expires: June 24, 2016 Expires: September 21, 2016
Encrypted Content-Encoding for HTTP Encrypted Content-Encoding for HTTP
draft-ietf-httpbis-encryption-encoding-00 draft-ietf-httpbis-encryption-encoding-01
Abstract Abstract
This memo introduces a content-coding for HTTP that allows message This memo introduces a content-coding for HTTP that allows message
payloads to be encrypted. payloads to be encrypted.
Note to Readers
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/ .
Working Group information can be found at http://httpwg.github.io/ ;
source code and issues list for this draft can be found at
https://github.com/httpwg/http-extensions/labels/encryption .
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 24, 2016. This Internet-Draft will expire on September 21, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The "aesgcm128" HTTP Content Encoding . . . . . . . . . . . . 3 2. The "aesgcm" HTTP Content Encoding . . . . . . . . . . . . . 4
3. The Encryption HTTP Header Field . . . . . . . . . . . . . . 5 3. The Encryption HTTP Header Field . . . . . . . . . . . . . . 5
3.1. Encryption Header Field Parameters . . . . . . . . . . . 6 3.1. Encryption Header Field Parameters . . . . . . . . . . . 6
3.2. Content Encryption Key Derivation . . . . . . . . . . . . 6 3.2. Content Encryption Key Derivation . . . . . . . . . . . . 7
3.3. Nonce Derivation . . . . . . . . . . . . . . . . . . . . 7 3.3. Nonce Derivation . . . . . . . . . . . . . . . . . . . . 7
4. Crypto-Key Header Field . . . . . . . . . . . . . . . . . . . 8 4. Crypto-Key Header Field . . . . . . . . . . . . . . . . . . . 8
4.1. Explicit Key . . . . . . . . . . . . . . . . . . . . . . 8 4.1. Explicit Key . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Diffie-Hellman . . . . . . . . . . . . . . . . . . . . . 9 4.2. Diffie-Hellman . . . . . . . . . . . . . . . . . . . . . 9
4.3. Pre-shared Authentication Secrets . . . . . . . . . . . . 10 4.3. Pre-shared Authentication Secrets . . . . . . . . . . . . 10
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Successful GET Response . . . . . . . . . . . . . . . . . 11 5.1. Successful GET Response . . . . . . . . . . . . . . . . . 11
5.2. Encryption and Compression . . . . . . . . . . . . . . . 11 5.2. Encryption and Compression . . . . . . . . . . . . . . . 12
5.3. Encryption with More Than One Key . . . . . . . . . . . . 11 5.3. Encryption with More Than One Key . . . . . . . . . . . . 12
5.4. Encryption with Explicit Key . . . . . . . . . . . . . . 12 5.4. Encryption with Explicit Key . . . . . . . . . . . . . . 12
5.5. Diffie-Hellman Encryption . . . . . . . . . . . . . . . . 12 5.5. Encryption with Multiple Records . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 5.6. Diffie-Hellman Encryption . . . . . . . . . . . . . . . . 13
6.1. Key and Nonce Reuse . . . . . . . . . . . . . . . . . . . 13 5.7. Diffie-Hellman with Authentication Secret . . . . . . . . 14
6.2. Content Integrity . . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6.3. Leaking Information in Headers . . . . . . . . . . . . . 14 6.1. Key and Nonce Reuse . . . . . . . . . . . . . . . . . . . 15
6.4. Poisoning Storage . . . . . . . . . . . . . . . . . . . . 14 6.2. Content Integrity . . . . . . . . . . . . . . . . . . . . 15
6.5. Sizing and Timing Attacks . . . . . . . . . . . . . . . . 15 6.3. Leaking Information in Headers . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6.4. Poisoning Storage . . . . . . . . . . . . . . . . . . . . 16
7.1. The "aesgcm128" HTTP Content Encoding . . . . . . . . . . 15 6.5. Sizing and Timing Attacks . . . . . . . . . . . . . . . . 16
7.2. Encryption Header Fields . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.3. The HTTP Encryption Parameter Registry . . . . . . . . . 16 7.1. The "aesgcm" HTTP Content Encoding . . . . . . . . . . . 16
7.3.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 16 7.2. Encryption Header Fields . . . . . . . . . . . . . . . . 17
7.3.2. salt . . . . . . . . . . . . . . . . . . . . . . . . 16 7.3. The HTTP Encryption Parameter Registry . . . . . . . . . 17
7.3.3. rs . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.3.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4. The HTTP Crypto-Key Parameter Registry . . . . . . . . . 17 7.3.2. salt . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 17 7.3.3. rs . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4.2. aesgcm128 . . . . . . . . . . . . . . . . . . . . . . 17 7.4. The HTTP Crypto-Key Parameter Registry . . . . . . . . . 18
7.4.3. dh . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.4.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.4.2. aesgcm . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . 18 7.4.3. dh . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . 19 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
Appendix A. JWE Mapping . . . . . . . . . . . . . . . . . . . . 20 8.1. Normative References . . . . . . . . . . . . . . . . . . 19
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 21 8.2. Informative References . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21 Appendix A. JWE Mapping . . . . . . . . . . . . . . . . . . . . 21
Appendix B. Intermediate Values for Encryption . . . . . . . . . 22
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
It is sometimes desirable to encrypt the contents of a HTTP message It is sometimes desirable to encrypt the contents of a HTTP message
(request or response) so that when the payload is stored (e.g., with (request or response) so that when the payload is stored (e.g., with
a HTTP PUT), only someone with the appropriate key can read it. a HTTP PUT), only someone with the appropriate key can read it.
For example, it might be necessary to store a file on a server For example, it might be necessary to store a file on a server
without exposing its contents to that server. Furthermore, that same without exposing its contents to that server. Furthermore, that same
file could be replicated to other servers (to make it more resistant file could be replicated to other servers (to make it more resistant
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identify keys will depend on the use case. Though a complete key identify keys will depend on the use case. Though a complete key
management system is not described, this document defines an Crypto- management system is not described, this document defines an Crypto-
Key header field that can be used to convey keying material. Key header field that can be used to convey keying material.
1.1. Notational Conventions 1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. The "aesgcm128" HTTP Content Encoding Base64url encoding is defined in Section 2 of [RFC7515].
The "aesgcm128" HTTP content-coding indicates that a payload has been 2. The "aesgcm" HTTP Content Encoding
The "aesgcm" HTTP content-coding indicates that a payload has been
encrypted using Advanced Encryption Standard (AES) in Galois/Counter encrypted using Advanced Encryption Standard (AES) in Galois/Counter
Mode (GCM) as identified as AEAD_AES_128_GCM in [RFC5116], Mode (GCM) as identified as AEAD_AES_128_GCM in [RFC5116],
Section 5.1. The AEAD_AES_128_GCM algorithm uses a 128 bit content Section 5.1. The AEAD_AES_128_GCM algorithm uses a 128 bit content
encryption key. encryption key.
When this content-coding is in use, the Encryption header field When this content-coding is in use, the Encryption header field
(Section 3) describes how encryption has been applied. The Crypto- (Section 3) describes how encryption has been applied. The Crypto-
Key header field (Section 4) can be included to describe how the Key header field (Section 4) can be included to describe how the
content encryption key is derived or retrieved. content encryption key is derived or retrieved.
The "aesgcm128" content-coding uses a single fixed set of encryption The "aesgcm" content-coding uses a single fixed set of encryption
primitives. Cipher suite agility is achieved by defining a new primitives. Cipher suite agility is achieved by defining a new
content-coding scheme. This ensures that only the HTTP Accept- content-coding scheme. This ensures that only the HTTP Accept-
Encoding header field is necessary to negotiate the use of Encoding header field is necessary to negotiate the use of
encryption. encryption.
The "aesgcm128" content-coding uses a fixed record size. The The "aesgcm" content-coding uses a fixed record size. The resulting
resulting encoding is a series of fixed-size records, with a final encoding is a series of fixed-size records, with a final record that
record that is one or more octets shorter than a fixed sized record. is one or more octets shorter than a fixed sized record.
+------+ input of between rs-256 +------+ input of between rs-65537
| data | and rs-1 octets | data | and rs-2 octets
+------+ (one fewer for the last record) +------+ (one fewer for the last record)
| |
v v
+-----+-----------+ +-----+-----------+
| pad | data | add padding to form plaintext | pad | data | add padding to form plaintext
+-----+-----------+ +-----+-----------+
| |
v v
+--------------------+ +--------------------+
| ciphertext | encrypt with AEAD_AES_128_GCM | ciphertext | encrypt with AEAD_AES_128_GCM
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field. field.
AEAD_AES_128_GCM expands ciphertext to be 16 octets longer than its AEAD_AES_128_GCM expands ciphertext to be 16 octets longer than its
input plaintext. Therefore, the length of each enciphered record input plaintext. Therefore, the length of each enciphered record
other than the last is equal to the value of the "rs" parameter plus other than the last is equal to the value of the "rs" parameter plus
16 octets. A receiver MUST fail to decrypt if the final record 16 octets. A receiver MUST fail to decrypt if the final record
ciphertext is 16 octets or less in size. Valid records always ciphertext is 16 octets or less in size. Valid records always
contain at least one byte of padding and a 16 octet authentication contain at least one byte of padding and a 16 octet authentication
tag. tag.
Each record contains between 1 and 256 octets of padding, inserted Each record contains between 2 and 65537 octets of padding, inserted
into a record before the enciphered content. Padding consists of a into a record before the enciphered content. Padding consists of a
length byte, followed that number of zero-valued octets. A receiver two octet unsigned integer in network byte order, followed that
MUST fail to decrypt if any padding octet other than the first is number of zero-valued octets. A receiver MUST fail to decrypt if any
non-zero, or a record has more padding than the record size can padding octet other than the first two are non-zero, or a record has
accommodate. more padding than the record size can accommodate.
The nonce for each record is a 96-bit value constructed from the The nonce for each record is a 96-bit value constructed from the
record sequence number and the input keying material. Nonce record sequence number and the input keying material. Nonce
derivation is covered in Section 3.3. derivation is covered in Section 3.3.
The additional data passed to each invocation of AEAD_AES_128_GCM is The additional data passed to each invocation of AEAD_AES_128_GCM is
a zero-length octet sequence. a zero-length octet sequence.
A sequence of full-sized records can be truncated to produce a A sequence of full-sized records can be truncated to produce a
shorter sequence of records with valid authentication tags. To shorter sequence of records with valid authentication tags. To
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The following parameters are used in determining the content The following parameters are used in determining the content
encryption key that is used for encryption: encryption key that is used for encryption:
keyid: The "keyid" parameter contains a string that identifies the keyid: The "keyid" parameter contains a string that identifies the
keying material that is used. The "keyid" parameter SHOULD be keying material that is used. The "keyid" parameter SHOULD be
included, unless key identification is guaranteed by other means. included, unless key identification is guaranteed by other means.
The "keyid" parameter MUST be used if keying material included in The "keyid" parameter MUST be used if keying material included in
an Crypto-Key header field is needed to derive the content an Crypto-Key header field is needed to derive the content
encryption key. encryption key.
salt: The "salt" parameter contains a base64 URL-encoded octets that salt: The "salt" parameter contains a base64url-encoded octets
is used as salt in deriving a unique content encryption key (see [RFC7515] that is used as salt in deriving a unique content
Section 3.2). The "salt" parameter MUST be present, and MUST be encryption key (see Section 3.2). The "salt" parameter MUST be
exactly 16 octets long when decoded. The "salt" parameter MUST present, and MUST be exactly 16 octets long when decoded. The
NOT be reused for two different payload bodies that have the same "salt" parameter MUST NOT be reused for two different payload
input keying material; generating a random salt for every bodies that have the same input keying material; generating a
application of the content encoding ensures that content random salt for every application of the content encoding ensures
encryption key reuse is highly unlikely. that content encryption key reuse is highly unlikely.
rs: The "rs" parameter contains a positive decimal integer that rs: The "rs" parameter contains a positive decimal integer that
describes the record size in octets. This value MUST be greater describes the record size in octets. This value MUST be greater
than 1. If the "rs" parameter is absent, the record size defaults than 1. If the "rs" parameter is absent, the record size defaults
to 4096 octets. to 4096 octets.
3.2. Content Encryption Key Derivation 3.2. Content Encryption Key Derivation
In order to allow the reuse of keying material for multiple different In order to allow the reuse of keying material for multiple different
HTTP messages, a content encryption key is derived for each message. HTTP messages, a content encryption key is derived for each message.
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The decoded value of the "salt" parameter is the salt input to HKDF The decoded value of the "salt" parameter is the salt input to HKDF
function. The keying material identified by the "keyid" parameter is function. The keying material identified by the "keyid" parameter is
the input keying material (IKM) to HKDF. Input keying material can the input keying material (IKM) to HKDF. Input keying material can
either be prearranged, or can be described using the Crypto-Key either be prearranged, or can be described using the Crypto-Key
header field (Section 4). The first step of HKDF is therefore: header field (Section 4). The first step of HKDF is therefore:
PRK = HMAC-SHA-256(salt, IKM) PRK = HMAC-SHA-256(salt, IKM)
The info parameter to HKDF is set to the ASCII-encoded string The info parameter to HKDF is set to the ASCII-encoded string
"Content-Encoding: aesgcm128", a single zero octet and an optional "Content-Encoding: aesgcm", a single zero octet and an optional
context string: context string:
cek_info = "Content-Encoding: aesgcm128" || 0x00 || context cek_info = "Content-Encoding: aesgcm" || 0x00 || context
Unless otherwise specified, the context is a zero length octet Unless otherwise specified, the context is a zero length octet
sequence. Specifications that use this content encoding MAY specify sequence. Specifications that use this content encoding MAY specify
the use of an expanded context to cover additional inputs in the key the use of an expanded context to cover additional inputs in the key
derivation. derivation.
AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption
key, so the length (L) parameter to HKDF is 16. The second step of key, so the length (L) parameter to HKDF is 16. The second step of
HKDF can therefore be simplified to the first 16 octets of a single HKDF can therefore be simplified to the first 16 octets of a single
HMAC: HMAC:
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The Crypto-Key header field uses the extended ABNF syntax defined in The Crypto-Key header field uses the extended ABNF syntax defined in
Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231]. Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231].
Crypto-Key = #crypto_key_params Crypto-Key = #crypto_key_params
crypto_key_params = [ parameter *( ";" parameter ) ] crypto_key_params = [ parameter *( ";" parameter ) ]
keyid: The "keyid" parameter corresponds to the "keyid" parameter in keyid: The "keyid" parameter corresponds to the "keyid" parameter in
the Encryption header field. the Encryption header field.
aesgcm128: The "aesgcm128" parameter contains the URL-safe base64 aesgcm: The "aesgcm" parameter contains the base64url-encoded octets
[RFC4648] octets of the input keying material. [RFC7515] of the input keying material.
dh: The "dh" parameter contains an ephemeral Diffie-Hellman share. dh: The "dh" parameter contains an ephemeral Diffie-Hellman share.
This form of the header field can be used to encrypt content for a This form of the header field can be used to encrypt content for a
specific recipient. specific recipient.
Crypto-Key header field values with multiple instances of the same Crypto-Key header field values with multiple instances of the same
parameter name are invalid. parameter name are invalid.
The input keying material used by the key derivation (see The input keying material used by the key derivation (see
Section 3.2) can be determined based on the information in the Section 3.2) can be determined based on the information in the
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Note that different methods for determining input keying material Note that different methods for determining input keying material
will produce different amounts of data. The HKDF process ensures will produce different amounts of data. The HKDF process ensures
that the final content encryption key is the necessary size. that the final content encryption key is the necessary size.
Alternative methods for determining input keying material MAY be Alternative methods for determining input keying material MAY be
defined by specifications that use this content-encoding. defined by specifications that use this content-encoding.
4.1. Explicit Key 4.1. Explicit Key
The "aesgcm128" parameter is decoded and used as the input keying The "aesgcm" parameter is decoded and used as the input keying
material for the "aesgcm128" content encoding. The "aesgcm128" material for the "aesgcm" content encoding. The "aesgcm" parameter
parameter MUST decode to at least 16 octets in order to be used as MUST decode to at least 16 octets in order to be used as input keying
input keying material for "aesgcm128" content encoding. material for "aesgcm" content encoding.
Other key determination parameters can be ignored if the "aesgcm128" Other key determination parameters can be ignored if the "aesgcm"
parameter is present. parameter is present.
4.2. Diffie-Hellman 4.2. Diffie-Hellman
The "dh" parameter is included to describe a Diffie-Hellman share, The "dh" parameter is included to describe a Diffie-Hellman share,
either modp (or finite field) Diffie-Hellman [DH] or elliptic curve either modp (or finite field) Diffie-Hellman [DH] or elliptic curve
Diffie-Hellman (ECDH) [RFC4492]. Diffie-Hellman (ECDH) [RFC4492].
This share is combined with other information at the recipient to This share is combined with other information at the recipient to
determine the HKDF input keying material. In order for the exchange determine the HKDF input keying material. In order for the exchange
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context = label || 0x00 || context = label || 0x00 ||
length(recipient_public) || recipient_public || length(recipient_public) || recipient_public ||
length(sender_public) || sender_public length(sender_public) || sender_public
The two length fields are encoded as a two octet unsigned integer in The two length fields are encoded as a two octet unsigned integer in
network byte order. network byte order.
Specifications that rely on an Diffie-Hellman exchange for Specifications that rely on an Diffie-Hellman exchange for
determining input keying material MUST either specify the parameters determining input keying material MUST either specify the parameters
for Diffie-Hellman (group parameters, or curves and point format) for Diffie-Hellman (label, group parameters, or curves and point
that are used, or describe how those parameters are negotiated format) that are used, or describe how those parameters are
between sender and receiver. negotiated between sender and receiver.
4.3. Pre-shared Authentication Secrets 4.3. Pre-shared Authentication Secrets
Key derivation MAY be extended to include an additional Key derivation MAY be extended to include an additional
authentication secret. Such a secret is shared between the sender authentication secret. Such a secret is shared between the sender
and receiver of a message using other means. and receiver of a message using other means.
A pre-shared authentication secret is not explicitly signaled in A pre-shared authentication secret is not explicitly signaled in
either the Encryption or Crypto-Key header fields. Use of this either the Encryption or Crypto-Key header fields. Use of this
additional step depends on prior agreement. additional step depends on prior agreement.
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provided to the final key derivation stages. Alternatively, this provided to the final key derivation stages. Alternatively, this
phase can be viewed as always having a zero-length context. phase can be viewed as always having a zero-length context.
Note that in the absence of an authentication secret, the input Note that in the absence of an authentication secret, the input
keying material is simply the raw keying material: keying material is simply the raw keying material:
IKM = raw_key IKM = raw_key
5. Examples 5. Examples
This section shows a few examples of the content encoding.
Note: All binary values in the examples in this section use the URL
and filename safe variant of base64 [RFC4648]. This includes the
bodies of requests. Whitespace in these values is added to fit
formatting constraints.
5.1. Successful GET Response 5.1. Successful GET Response
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/octet-stream Content-Type: application/octet-stream
Content-Encoding: aesgcm128 Content-Encoding: aesgcm
Connection: close Connection: close
Encryption: keyid="http://example.org/bob/keys/123"; Encryption: keyid="http://example.org/bob/keys/123";
salt="XZwpw6o37R-6qoZjw6KwAw" salt="XZwpw6o37R-6qoZjw6KwAw"
[encrypted payload] [encrypted payload]
Here, a successful HTTP GET response has been encrypted using input Here, a successful HTTP GET response has been encrypted using input
keying material that is identified by a URI. keying material that is identified by a URI.
Note that the media type has been changed to "application/octet- Note that the media type has been changed to "application/octet-
stream" to avoid exposing information about the content. stream" to avoid exposing information about the content.
5.2. Encryption and Compression 5.2. Encryption and Compression
In this example, a response is first compressed, then encrypted.
Note that this particular encoding might compromise confidentiality
if the contents of the response could be influenced by an attacker.
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: text/html Content-Type: text/html
Content-Encoding: aesgcm128, gzip Content-Encoding: gzip, aesgcm
Transfer-Encoding: chunked Transfer-Encoding: chunked
Encryption: keyid="mailto:me@example.com"; Encryption: keyid="mailto:me@example.com";
salt="m2hJ_NttRtFyUiMRPwfpHA" salt="m2hJ_NttRtFyUiMRPwfpHA"
[encrypted payload] [encrypted payload]
5.3. Encryption with More Than One Key 5.3. Encryption with More Than One Key
Here, a PUT request has been encrypted twice with different input
keying material; decrypting twice is necessary to read the content.
The outer layer of encryption uses a 1200 octet record size.
PUT /thing HTTP/1.1 PUT /thing HTTP/1.1
Host: storage.example.com Host: storage.example.com
Content-Type: application/http Content-Type: application/http
Content-Encoding: aesgcm128, aesgcm128 Content-Encoding: aesgcm, aesgcm
Content-Length: 1234 Content-Length: 1235
Encryption: keyid="mailto:me@example.com"; Encryption: keyid="mailto:me@example.com";
salt="NfzOeuV5USPRA-n_9s1Lag", salt="NfzOeuV5USPRA-n_9s1Lag",
keyid="http://example.org/bob/keys/123"; keyid="http://example.org/bob/keys/123";
salt="bDMSGoc2uobK_IhavSHsHA"; rs=1200 salt="bDMSGoc2uobK_IhavSHsHA"; rs=1200
[encrypted payload] [encrypted payload]
Here, a PUT request has been encrypted twice with different input
keying material; decrypting twice is necessary to read the content.
The outer layer of encryption uses a 1200 octet record size.
5.4. Encryption with Explicit Key 5.4. Encryption with Explicit Key
This example shows the UTF-8 encoded string "I am the walrus"
encrypted using an directly provided value for the input keying
material. The content body contains a single record only and is
shown here using base64url encoding for presentation reasons.
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Length: 32 Content-Length: 33
Content-Encoding: aesgcm128 Content-Encoding: aesgcm
Encryption: keyid="a1"; salt="vr0o6Uq3w_KDWeatc27mUg" Encryption: keyid="a1"; salt="vr0o6Uq3w_KDWeatc27mUg"
Crypto-Key: keyid="a1"; aesgcm128="csPJEXBYA5U-Tal9EdJi-w" Crypto-Key: keyid="a1"; aesgcm="csPJEXBYA5U-Tal9EdJi-w"
fuag8ThIRIazSHKUqJ5OduR75UgEUuM76J8UFwadEvg VDeU0XxaJkOJDAxPl7h9JD5V8N43RorP7PfpPdZZQuwF
This example shows the string "I am the walrus" encrypted using an 5.5. Encryption with Multiple Records
directly provided value for the input keying material. The content
body contains a single record only and is shown here encoded in URL-
safe base64 for presentation reasons only.
5.5. Diffie-Hellman Encryption This example shows the same encrypted message, but split into records
of 10 octets each. The first record includes a single additional
octet of padding, which causes the end of the content to align with a
record boundary, forcing the creation of a third record that contains
only padding.
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Length: 32 Content-Length: 70
Content-Encoding: aesgcm128 Content-Encoding: aesgcm
Encryption: keyid="a1"; salt="4pdat984KmT9BWsU3np0nw"; rs=10
Crypto-Key: keyid="a1"; aesgcm="BO3ZVPxUlnLORbVGMpbT1Q"
uzLfrZ4cbMTC6hlUqHz4NvWZshFlTN3o2RLr6FrIuOKEfl2VrM_jYgoiIyEo
Zvc-ZGwV-RMJejG4M6ZfGysBAdhpPqrLzw
5.6. Diffie-Hellman Encryption
HTTP/1.1 200 OK
Content-Length: 33
Content-Encoding: aesgcm
Encryption: keyid="dhkey"; salt="Qg61ZJRva_XBE9IEUelU3A" Encryption: keyid="dhkey"; salt="Qg61ZJRva_XBE9IEUelU3A"
Crypto-Key: keyid="dhkey"; Crypto-Key: keyid="dhkey";
dh="BDgpRKok2GZZDmS4r63vbJSUtcQx4Fq1V58-6-3NbZzS dh="BDgpRKok2GZZDmS4r63vbJSUtcQx4Fq1V58-6-3NbZzS
TlZsQiCEDTQy3CZ0ZMsqeqsEb7qW2blQHA4S48fynTk" TlZsQiCEDTQy3CZ0ZMsqeqsEb7qW2blQHA4S48fynTk"
G6j_sfKg0qebO62yXpTCayN2KV24QitNiTvLgcFiEj0 yqD2bapcx14XxUbtwjiGx69eHE3Yd6AqXcwBpT2Kd1uy
This example shows the same string, "I am the walrus", encrypted This example shows the same string, "I am the walrus", encrypted
using ECDH over the P-256 curve [FIPS186], which is identified with using ECDH over the P-256 curve [FIPS186], which is identified with
the label "P-256" encoded in ASCII. The content body is shown here the label "P-256" encoded in ASCII. The content body is shown here
encoded in URL-safe base64 for presentation reasons only. encoded in URL-safe base64url for presentation reasons only.
The receiver (in this case, the HTTP client) uses a key pair that is The receiver (in this case, the HTTP client) uses a key pair that is
identified by the string "dhkey" and the sender (the server) uses a identified by the string "dhkey" and the sender (the server) uses a
key pair for which the public share is included in the "dh" parameter key pair for which the public share is included in the "dh" parameter
above. The keys shown below use uncompressed points [X9.62] encoded above. The keys shown below use uncompressed points [X9.62] encoded
using URL-safe base64. Line wrapping is added for presentation using base64url. Line wrapping is added for presentation purposes
purposes only. only.
Receiver: Receiver:
private key: 9FWl15_QUQAWDaD3k3l50ZBZQJ4au27F1V4F0uLSD_M private key: 9FWl15_QUQAWDaD3k3l50ZBZQJ4au27F1V4F0uLSD_M
public key: BCEkBjzL8Z3C-oi2Q7oE5t2Np-p7osjGLg93qUP0wvqR public key: BCEkBjzL8Z3C-oi2Q7oE5t2Np-p7osjGLg93qUP0wvqR
T21EEWyf0cQDQcakQMqz4hQKYOQ3il2nNZct4HgAUQU T21EEWyf0cQDQcakQMqz4hQKYOQ3il2nNZct4HgAUQU
Sender: Sender:
private key: vG7TmzUX9NfVR4XUGBkLAFu8iDyQe-q_165JkkN0Vlw private key: vG7TmzUX9NfVR4XUGBkLAFu8iDyQe-q_165JkkN0Vlw
public key: <the value of the "dh" parameter> public key: <the value of the "dh" parameter>
5.7. Diffie-Hellman with Authentication Secret
This example shows the same receiver key pair from Section 5.6, but
with a shared authentication secret of "R29vIGdvbyBnJyBqb29iIQ".
HTTP/1.1 200 OK
Content-Length: 33
Content-Encoding: aesgcm
Encryption: keyid="dhkey"; salt="lngarbyKfMoi9Z75xYXmkg"
Crypto-Key: keyid="dhkey";
dh="BNoRDbb84JGm8g5Z5CFxurSqsXWJ11ItfXEWYVLE85Y7
CYkDjXsIEc4aqxYaQ1G8BqkXCJ6DPpDrWtdWj_mugHU"
6nqAQUME8hNqw5J3kl8cpVVJylXKYqZOeseZG8UueKpA
The sender's private key used in this example is "nCScek-QpEjmOOlT-
rQ38nZzvdPlqa00Zy0i6m2OJvY". Intermediate values for this example
are included in Appendix B.
6. Security Considerations 6. Security Considerations
This mechanism assumes the presence of a key management framework This mechanism assumes the presence of a key management framework
that is used to manage the distribution of keys between valid senders that is used to manage the distribution of keys between valid senders
and receivers. Defining key management is part of composing this and receivers. Defining key management is part of composing this
mechanism into a larger application, protocol, or framework. mechanism into a larger application, protocol, or framework.
Implementation of cryptography - and key management in particular - Implementation of cryptography - and key management in particular -
can be difficult. For instance, implementations need to account for can be difficult. For instance, implementations need to account for
the potential for exposing keying material on side channels, such as the potential for exposing keying material on side channels, such as
skipping to change at page 15, line 23 skipping to change at page 16, line 46
so on, may leak sensitive information. so on, may leak sensitive information.
This risk can be mitigated through the use of the padding that this This risk can be mitigated through the use of the padding that this
mechanism provides. Alternatively, splitting up content into mechanism provides. Alternatively, splitting up content into
segments and storing the separately might reduce exposure. HTTP/2 segments and storing the separately might reduce exposure. HTTP/2
[RFC7540] combined with TLS [RFC5246] might be used to hide the size [RFC7540] combined with TLS [RFC5246] might be used to hide the size
of individual messages. of individual messages.
7. IANA Considerations 7. IANA Considerations
7.1. The "aesgcm128" HTTP Content Encoding 7.1. The "aesgcm" HTTP Content Encoding
This memo registers the "encrypted" HTTP content-coding in the HTTP This memo registers the "encrypted" HTTP content-coding in the HTTP
Content Codings Registry, as detailed in Section 2. Content Codings Registry, as detailed in Section 2.
o Name: aesgcm128 o Name: aesgcm
o Description: AES-GCM encryption with a 128-bit content encryption o Description: AES-GCM encryption with a 128-bit content encryption
key key
o Reference: this specification o Reference: this specification
7.2. Encryption Header Fields 7.2. Encryption Header Fields
This memo registers the "Encryption" HTTP header field in the This memo registers the "Encryption" HTTP header field in the
Permanent Message Header Registry, as detailed in Section 3. Permanent Message Header Registry, as detailed in Section 3.
skipping to change at page 17, line 18 skipping to change at page 18, line 40
o Purpose: The size of the encrypted records. o Purpose: The size of the encrypted records.
o Reference: this document o Reference: this document
7.4. The HTTP Crypto-Key Parameter Registry 7.4. The HTTP Crypto-Key Parameter Registry
This memo establishes a registry for parameters used by the "Crypto- This memo establishes a registry for parameters used by the "Crypto-
Key" header field under the "Hypertext Transfer Protocol (HTTP) Key" header field under the "Hypertext Transfer Protocol (HTTP)
Parameters" grouping. The "Hypertext Transfer Protocol (HTTP) Parameters" grouping. The "Hypertext Transfer Protocol (HTTP)
Encryption Parameters" operates under an "Specification Required" Crypto-Key Parameters" operates under an "Specification Required"
policy [RFC5226]. policy [RFC5226].
Entries in this registry are expected to include the following Entries in this registry are expected to include the following
information: information:
o Parameter Name: The name of the parameter. o Parameter Name: The name of the parameter.
o Purpose: A brief description of the purpose of the parameter. o Purpose: A brief description of the purpose of the parameter.
o Reference: A reference to a specification that defines the o Reference: A reference to a specification that defines the
skipping to change at page 17, line 41 skipping to change at page 19, line 15
The initial contents of this registry are: The initial contents of this registry are:
7.4.1. keyid 7.4.1. keyid
o Parameter Name: keyid o Parameter Name: keyid
o Purpose: Identify the key that is in use. o Purpose: Identify the key that is in use.
o Reference: this document o Reference: this document
7.4.2. aesgcm128 7.4.2. aesgcm
o Parameter Name: aesgcm128 o Parameter Name: aesgcm
o Purpose: Provide an explicit input keying material value for the o Purpose: Provide an explicit input keying material value for the
aesgcm128 content encoding. aesgcm content encoding.
o Reference: this document o Reference: this document
7.4.3. dh 7.4.3. dh
o Parameter Name: dh o Parameter Name: dh
o Purpose: Carry a modp or elliptic curve Diffie-Hellman share used o Purpose: Carry a modp or elliptic curve Diffie-Hellman share used
to derive input keying material. to derive input keying material.
skipping to change at page 18, line 39 skipping to change at page 20, line 11
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, for Transport Layer Security (TLS)", RFC 4492,
DOI 10.17487/RFC4492, May 2006, DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>. <http://www.rfc-editor.org/info/rfc4492>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>. <http://www.rfc-editor.org/info/rfc5116>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010, DOI 10.17487/RFC5869, May 2010,
<http://www.rfc-editor.org/info/rfc5869>. <http://www.rfc-editor.org/info/rfc5869>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>. <http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>. <http://www.rfc-editor.org/info/rfc7231>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <http://www.rfc-editor.org/info/rfc7515>.
8.2. Informative References 8.2. Informative References
[FIPS186] National Institute of Standards and Technology (NIST), [FIPS186] National Institute of Standards and Technology (NIST),
"Digital Signature Standard (DSS)", NIST PUB 186-4 , July "Digital Signature Standard (DSS)", NIST PUB 186-4 , July
2013. 2013.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R. [RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880, Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC4880, November 2007, DOI 10.17487/RFC4880, November 2007,
<http://www.rfc-editor.org/info/rfc4880>. <http://www.rfc-editor.org/info/rfc4880>.
skipping to change at page 20, line 20 skipping to change at page 21, line 43
[X9.62] ANSI, "Public Key Cryptography For The Financial Services [X9.62] ANSI, "Public Key Cryptography For The Financial Services
Industry: The Elliptic Curve Digital Signature Algorithm Industry: The Elliptic Curve Digital Signature Algorithm
(ECDSA)", ANSI X9.62 , 1998. (ECDSA)", ANSI X9.62 , 1998.
[XMLENC] Eastlake, D., Reagle, J., Imamura, T., Dillaway, B., and [XMLENC] Eastlake, D., Reagle, J., Imamura, T., Dillaway, B., and
E. Simon, "XML Encryption Syntax and Processing", W3C E. Simon, "XML Encryption Syntax and Processing", W3C
REC , December 2002, <http://www.w3.org/TR/xmlenc-core/>. REC , December 2002, <http://www.w3.org/TR/xmlenc-core/>.
Appendix A. JWE Mapping Appendix A. JWE Mapping
The "aesgcm128" content encoding can be considered as a sequence of The "aesgcm" content encoding can be considered as a sequence of JSON
JSON Web Encryption (JWE) objects [RFC7516], each corresponding to a Web Encryption (JWE) objects [RFC7516], each corresponding to a
single fixed size record. The following transformations are applied single fixed size record that includes leading padding. The
to a JWE object that might be expressed using the JWE Compact following transformations are applied to a JWE object that might be
Serialization: expressed using the JWE Compact Serialization:
o The JWE Protected Header is fixed to a value { "alg": "dir", o The JWE Protected Header is fixed to a value { "alg": "dir",
"enc": "A128GCM" }, describing direct encryption using AES-GCM "enc": "A128GCM" }, describing direct encryption using AES-GCM
with a 128-bit content encryption key. This header is not with a 128-bit content encryption key. This header is not
transmitted, it is instead implied by the value of the Content- transmitted, it is instead implied by the value of the Content-
Encoding header field. Encoding header field.
o The JWE Encrypted Key is empty, as stipulated by the direct o The JWE Encrypted Key is empty, as stipulated by the direct
encryption algorithm. encryption algorithm.
skipping to change at page 20, line 48 skipping to change at page 22, line 23
Section 3.3). This value is also not transmitted. Section 3.3). This value is also not transmitted.
o The final value is the concatenated JWE Ciphertext and the JWE o The final value is the concatenated JWE Ciphertext and the JWE
Authentication Tag, both expressed without URL-safe Base 64 Authentication Tag, both expressed without URL-safe Base 64
encoding. The "." separator is omitted, since the length of these encoding. The "." separator is omitted, since the length of these
fields is known. fields is known.
Thus, the example in Section 5.4 can be rendered using the JWE Thus, the example in Section 5.4 can be rendered using the JWE
Compact Serialization as: Compact Serialization as:
eyAiYWxnIjogImRpciIsICJlbmMiOiAiQTEyOEdDTSIgfQ..AAAAAAAAAAAAAAAA. eyAiYWxnIjogImRpciIsICJlbmMiOiAiQTEyOEdDTSIgfQ..31iQYc1v4a36EgyJ.
LwTC-fwdKh8de0smD2jfzA.eh1vURhu65M2lxhctbbntA VDeU0XxaJkOJDAxPl7h9JD4.VfDeN0aKz-z36T3WWULsBQ
Where the first line represents the fixed JWE Protected Header, JWE
Encrypted Key, and JWE Initialization Vector, all of which are
determined algorithmically. The second line contains the encoded
body, split into JWE Ciphertext and JWE Authentication Tag.
Appendix B. Acknowledgements Where the first line represents the fixed JWE Protected Header, an
empty JWE Encrypted Key, and the algorithmically-determined JWE
Initialization Vector. The second line contains the encoded body,
split into JWE Ciphertext and JWE Authentication Tag.
Appendix B. Intermediate Values for Encryption
The intermediate values calculated for the example in Section 5.7 are
shown here. The following are inputs to the calculation:
Plaintext: SSBhbSB0aGUgd2FscnVz
Sender public key: BNoRDbb84JGm8g5Z5CFxurSqsXWJ11ItfXEWYVLE85Y7
CYkDjXsIEc4aqxYaQ1G8BqkXCJ6DPpDrWtdWj_mugHU
Sender private key: nCScek-QpEjmOOlT-rQ38nZzvdPlqa00Zy0i6m2OJvY
Receiver public key: BCEkBjzL8Z3C-oi2Q7oE5t2Np-p7osjGLg93qUP0wvqR
T21EEWyf0cQDQcakQMqz4hQKYOQ3il2nNZct4HgAUQU
Receiver private key: 9FWl15_QUQAWDaD3k3l50ZBZQJ4au27F1V4F0uLSD_M
Salt: lngarbyKfMoi9Z75xYXmkg
Note that knowledge of just one of the private keys is necessary.
The sender randomly generates the salt value, whereas salt is input
to the receiver.
This produces the following intermediate values:
Shared secret (raw_key): RNjC-NVW4BGJbxWPW7G2mowsLeDa53LYKYm4-NOQ6Y
Input keying material (IKM): EhpZec37Ptm4IRD5-jtZ0q6r1iK5vYmY1tZwtN8
fbZY
Context for content encryption key derivation:
Q29udGVudC1FbmNvZGluZzogYWVzZ2NtAFAtMjU2AABB BCEkBjzL8Z3C-
oi2Q7oE5t2Np-p7osjGLg93qUP0wvqR
T21EEWyf0cQDQcakQMqz4hQKYOQ3il2nNZct4HgAUQUA
QQTaEQ22_OCRpvIOWeQhcbq0qrF1iddSLX1xFmFSxPOW
OwmJA417CBHOGqsWGkNRvAapFwiegz6Q61rXVo_5roB1
Content encryption key (CEK): AN2-xhvFWeYh5z0fcDu0Ww
Context for nonce derivation: Q29udGVudC1FbmNvZGluZzogbm9uY2UAUC0yNT
YAAEEE ISQGPMvxncL6iLZDugTm3Y2n6nuiyMYuD3epQ_TC-pFP
bUQRbJ_RxANBxqRAyrPiFApg5DeKXac1ly3geABRBQBB
BNoRDbb84JGm8g5Z5CFxurSqsXWJ11ItfXEWYVLE85Y7
CYkDjXsIEc4aqxYaQ1G8BqkXCJ6DPpDrWtdWj_mugHU
Base nonce: JY1Okw5rw1Drkg9J
When the CEK and nonce are used with AES GCM and the padded plaintext
of AABJIGFtIHRoZSB3YWxydXM, the final ciphertext is
6nqAQUME8hNqw5J3kl8cpVVJylXKYqZOeseZG8UueKpA, as shown in the
example.
Appendix C. Acknowledgements
Mark Nottingham was an original author of this document. Mark Nottingham was an original author of this document.
The following people provided valuable input: Richard Barnes, David The following people provided valuable input: Richard Barnes, David
Benjamin, Peter Beverloo, Mike Jones, Stephen Farrell, Adam Langley, Benjamin, Peter Beverloo, Mike Jones, Stephen Farrell, Adam Langley,
John Mattsson, Eric Rescorla, and Jim Schaad. John Mattsson, Eric Rescorla, and Jim Schaad.
Author's Address Author's Address
Martin Thomson Martin Thomson
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