draft-ietf-httpbis-encryption-encoding-08.txt   draft-ietf-httpbis-encryption-encoding-09.txt 
HTTP Working Group M. Thomson HTTP Working Group M. Thomson
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Standards Track March 2, 2017 Intended status: Standards Track April 18, 2017
Expires: September 3, 2017 Expires: October 20, 2017
Encrypted Content-Encoding for HTTP Encrypted Content-Encoding for HTTP
draft-ietf-httpbis-encryption-encoding-08 draft-ietf-httpbis-encryption-encoding-09
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 Note to Readers
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
skipping to change at page 1, line 41 skipping to change at page 1, line 41
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 September 3, 2017. This Internet-Draft will expire on October 20, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 24 skipping to change at page 2, line 24
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The "aes128gcm" HTTP Content Coding . . . . . . . . . . . . . 3 2. The "aes128gcm" HTTP Content Coding . . . . . . . . . . . . . 3
2.1. Encryption Content Coding Header . . . . . . . . . . . . 5 2.1. Encryption Content Coding Header . . . . . . . . . . . . 5
2.2. Content Encryption Key Derivation . . . . . . . . . . . . 6 2.2. Content Encryption Key Derivation . . . . . . . . . . . . 6
2.3. Nonce Derivation . . . . . . . . . . . . . . . . . . . . 6 2.3. Nonce Derivation . . . . . . . . . . . . . . . . . . . . 6
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Encryption of a Response . . . . . . . . . . . . . . . . 7 3.1. Encryption of a Response . . . . . . . . . . . . . . . . 7
3.2. Encryption with Multiple Records . . . . . . . . . . . . 8 3.2. Encryption with Multiple Records . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
4.1. Message Truncation . . . . . . . . . . . . . . . . . . . 9 4.1. Automatic Decryption . . . . . . . . . . . . . . . . . . 9
4.2. Key and Nonce Reuse . . . . . . . . . . . . . . . . . . . 9 4.2. Message Truncation . . . . . . . . . . . . . . . . . . . 9
4.3. Data Encryption Limits . . . . . . . . . . . . . . . . . 10 4.3. Key and Nonce Reuse . . . . . . . . . . . . . . . . . . . 9
4.4. Content Integrity . . . . . . . . . . . . . . . . . . . . 10 4.4. Data Encryption Limits . . . . . . . . . . . . . . . . . 9
4.5. Leaking Information in Header Fields . . . . . . . . . . 10 4.5. Content Integrity . . . . . . . . . . . . . . . . . . . . 10
4.6. Poisoning Storage . . . . . . . . . . . . . . . . . . . . 11 4.6. Leaking Information in Header Fields . . . . . . . . . . 10
4.7. Sizing and Timing Attacks . . . . . . . . . . . . . . . . 11 4.7. Poisoning Storage . . . . . . . . . . . . . . . . . . . . 11
4.8. Sizing and Timing Attacks . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. The "aes128gcm" HTTP Content Coding . . . . . . . . . . . 12 5.1. The "aes128gcm" HTTP Content Coding . . . . . . . . . . . 12
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . 12 6.1. Normative References . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . 13 6.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. JWE Mapping . . . . . . . . . . . . . . . . . . . . 14 Appendix A. JWE Mapping . . . . . . . . . . . . . . . . . . . . 14
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 15 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
skipping to change at page 3, line 35 skipping to change at page 3, line 35
uses content encryption. How clients and servers acquire and uses content encryption. How clients and servers acquire and
identify keys will depend on the use case. In particular, a key identify keys will depend on the use case. In particular, a key
management system is not described. management system is not described.
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].
Base64url encoding is defined in Section 2 of [RFC7515].
2. The "aes128gcm" HTTP Content Coding 2. The "aes128gcm" HTTP Content Coding
The "aes128gcm" HTTP content coding indicates that a payload has been The "aes128gcm" 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.
Using this content coding requires knowledge of a key. How this key Using this content coding requires knowledge of a key. How this key
is acquired is not defined in this document. is acquired is not defined in this document.
skipping to change at page 5, line 47 skipping to change at page 5, line 47
have the same input keying material; generating a random salt for have the same input keying material; generating a random salt for
every application of the content coding ensures that content every application of the content coding ensures that content
encryption key reuse is highly unlikely. encryption key reuse is highly unlikely.
rs: The "rs" or record size parameter contains an unsigned 32-bit rs: The "rs" or record size parameter contains an unsigned 32-bit
integer in network byte order that describes the record size in integer in network byte order that describes the record size in
octets. Note that it is therefore impossible to exceed the octets. Note that it is therefore impossible to exceed the
2^36-31 limit on plaintext input to AEAD_AES_128_GCM. Values 2^36-31 limit on plaintext input to AEAD_AES_128_GCM. Values
smaller than 18 are invalid. smaller than 18 are invalid.
keyid: The "keyid" parameter can be used to identify the keying idlen: The "idlen" parameter is an unsigned 8-bit integer that
material that is used. Recipients that receive a message are defines the length of the "keyid" parameter.
expected to know how to retrieve keys; the "keyid" parameter might
be input to that process. A "keyid" parameter SHOULD be a UTF-8
[RFC3629] encoded string, particularly where the identifier might keyid: The "keyid" parameter can be used to identify the keying
need to appear in a textual form. material that is used. This field is the length determined by the
"idlen" parameter. Recipients that receive a message are expected
to know how to retrieve keys; the "keyid" parameter might be input
to that process. A "keyid" parameter SHOULD be a UTF-8 [RFC3629]
encoded string, particularly where the identifier might need to be
rendered in a textual form.
2.2. Content Encryption Key Derivation 2.2. 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.
The content encryption key is derived from the "salt" parameter using The content encryption key is derived from the "salt" parameter using
the HMAC-based key derivation function (HKDF) described in [RFC5869] the HMAC-based key derivation function (HKDF) described in [RFC5869]
using the SHA-256 hash algorithm [FIPS180-4]. using the SHA-256 hash algorithm [FIPS180-4].
The value of the "salt" parameter is the salt input to HKDF function. The value of the "salt" parameter is the salt input to HKDF function.
skipping to change at page 6, line 29 skipping to change at page 6, line 30
be provided to recipients separately. The extract phase of HKDF be provided to recipients separately. The extract phase of HKDF
therefore produces a pseudorandom key (PRK) as follows: therefore produces a pseudorandom key (PRK) as follows:
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: aes128gcm" and a single zero octet: "Content-Encoding: aes128gcm" and a single zero octet:
cek_info = "Content-Encoding: aes128gcm" || 0x00 cek_info = "Content-Encoding: aes128gcm" || 0x00
Note: Concatenation of octet sequences is represented by the "||" Note(1): Concatenation of octet sequences is represented by the "||"
operator. operator.
Note(2): The strings used here and in Section 2.3 do not include a
terminating 0x00 octet, as is used in some programming languages.
AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption key AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption key
(CEK), so the length (L) parameter to HKDF is 16. The second step of (CEK), 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:
CEK = HMAC-SHA-256(PRK, cek_info || 0x01) CEK = HMAC-SHA-256(PRK, cek_info || 0x01)
2.3. Nonce Derivation 2.3. Nonce Derivation
The nonce input to AEAD_AES_128_GCM is constructed for each record. The nonce input to AEAD_AES_128_GCM is constructed for each record.
skipping to change at page 7, line 21 skipping to change at page 7, line 21
The result is combined with the record sequence number - using The result is combined with the record sequence number - using
exclusive or - to produce the nonce. The record sequence number exclusive or - to produce the nonce. The record sequence number
(SEQ) is a 96-bit unsigned integer in network byte order that starts (SEQ) is a 96-bit unsigned integer in network byte order that starts
at zero. at zero.
Thus, the final nonce for each record is a 12 octet value: Thus, the final nonce for each record is a 12 octet value:
NONCE = HMAC-SHA-256(PRK, nonce_info || 0x01) XOR SEQ NONCE = HMAC-SHA-256(PRK, nonce_info || 0x01) XOR SEQ
This nonce construction prevents removal or reordering of records. This nonce construction prevents removal or reordering of records.
However, it permits truncation of the tail of the sequence (see
Section 2 for how this is avoided).
3. Examples 3. Examples
This section shows a few examples of the encrypted content coding. This section shows a few examples of the encrypted content coding.
Note: All binary values in the examples in this section use base64url Note: All binary values in the examples in this section use Base 64
encoding [RFC7515]. This includes the bodies of requests. Encoding with URL and Filename Safe Alphabet [RFC4648]. This
Whitespace and line wrapping is added to fit formatting constraints. includes the bodies of requests. Whitespace and line wrapping is
added to fit formatting constraints.
3.1. Encryption of a Response 3.1. Encryption of a Response
Here, a successful HTTP GET response has been encrypted. This uses a Here, a successful HTTP GET response has been encrypted. This uses a
record size of 4096 and no padding (just the single octet padding record size of 4096 and no padding (just the single octet padding
delimiter), so only a partial record is present. The input keying delimiter), so only a partial record is present. The input keying
material is identified by an empty string (that is, the "keyid" field material is identified by an empty string (that is, the "keyid" field
in the header is zero octets in length). in the header is zero octets in length).
The encrypted data in this example is the UTF-8 encoded string "I am The encrypted data in this example is the UTF-8 encoded string "I am
skipping to change at page 8, line 24 skipping to change at page 8, line 15
stream" to avoid exposing information about the content. stream" to avoid exposing information about the content.
Alternatively (and equivalently), the Content-Type header field can Alternatively (and equivalently), the Content-Type header field can
be omitted. be omitted.
Intermediate values for this example (all shown using base64url): Intermediate values for this example (all shown using base64url):
salt (from header) = I1BsxtFttlv3u_Oo94xnmw salt (from header) = I1BsxtFttlv3u_Oo94xnmw
PRK = zyeH5phsIsgUyd4oiSEIy35x-gIi4aM7y0hCF8mwn9g PRK = zyeH5phsIsgUyd4oiSEIy35x-gIi4aM7y0hCF8mwn9g
CEK = _wniytB-ofscZDh4tbSjHw CEK = _wniytB-ofscZDh4tbSjHw
NONCE = Bcs8gkIRKLI8GeI8 NONCE = Bcs8gkIRKLI8GeI8
plaintext = SSBhbSB0aGUgd2FscnVzAg unencrypted data = SSBhbSB0aGUgd2FscnVzAg
3.2. Encryption with Multiple Records 3.2. Encryption with Multiple Records
This example shows the same message with input keying material of This example shows the same message with input keying material of
"BO3ZVPxUlnLORbVGMpbT1Q". In this example, the plaintext is split "BO3ZVPxUlnLORbVGMpbT1Q". In this example, the plaintext is split
into records of 25 octets each (that is, the "rs" field in the header into records of 25 octets each (that is, the "rs" field in the header
is 25). The first record includes one 0x00 padding octet. This is 25). The first record includes one 0x00 padding octet. This
means that there are 7 octets of message in the first record, and 8 means that there are 7 octets of message in the first record, and 8
in the second. A key identifier of the UTF-8 encoded string "a1" is in the second. A key identifier of the UTF-8 encoded string "a1" is
also included in the header. also included in the header.
skipping to change at page 9, line 12 skipping to change at page 9, line 5
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
might be exposed by the time it takes to perform a given operation. might be exposed by the time it takes to perform a given operation.
The requirements for a good implementation of cryptographic The requirements for a good implementation of cryptographic
algorithms can change over time. algorithms can change over time.
As a content coding, presence of the "aes128gcm" coding might be 4.1. Automatic Decryption
transparent to a consumer of a message. Recipients that depend on
content origin authentication using this mechanism MUST reject
messages that don't include the "aes128gcm" content coding.
4.1. Message Truncation As a content coding, a "aes128gcm" content coding might be
automatically removed by a receiver in way that is not obvious to the
ultimate consumer of a message. Recipients that depend on content
origin authentication using this mechanism MUST reject messages that
don't include the "aes128gcm" content coding.
4.2. Message Truncation
This content encoding is designed to permit the incremental This content encoding is designed to permit the incremental
processing of large messages. It also permits random access to processing of large messages. It also permits random access to
plaintext in a limited fashion. The content encoding permits a plaintext in a limited fashion. The content encoding permits a
receiver to detect when a message is truncated. receiver to detect when a message is truncated.
A partially delivered message MUST NOT be processed as though the A partially delivered message MUST NOT be processed as though the
entire message was successfully delivered. For instance, a partially entire message was successfully delivered. For instance, a partially
delivered message cannot be cached as though it were complete. delivered message cannot be cached as though it were complete.
An attacker might exploit willingness to process partial messages to An attacker might exploit willingness to process partial messages to
cause a receiver to remain in a specific intermediate state. cause a receiver to remain in a specific intermediate state.
Implementations performing processing on partial messages need to Implementations performing processing on partial messages need to
ensure that any intermediate processing states don't advantage an ensure that any intermediate processing states don't advantage an
attacker. attacker.
4.2. Key and Nonce Reuse 4.3. Key and Nonce Reuse
Encrypting different plaintext with the same content encryption key Encrypting different plaintext with the same content encryption key
and nonce in AES-GCM is not safe [RFC5116]. The scheme defined here and nonce in AES-GCM is not safe [RFC5116]. The scheme defined here
uses a fixed progression of nonce values. Thus, a new content uses a fixed progression of nonce values. Thus, a new content
encryption key is needed for every application of the content coding. encryption key is needed for every application of the content coding.
Since input keying material can be reused, a unique "salt" parameter Since input keying material can be reused, a unique "salt" parameter
is needed to ensure a content encryption key is not reused. is needed to ensure a content encryption key is not reused.
If a content encryption key is reused - that is, if input keying If a content encryption key is reused - that is, if input keying
material and salt are reused - this could expose the plaintext and material and salt are reused - this could expose the plaintext and
the authentication key, nullifying the protection offered by the authentication key, nullifying the protection offered by
encryption. Thus, if the same input keying material is reused, then encryption. Thus, if the same input keying material is reused, then
the salt parameter MUST be unique each time. This ensures that the the salt parameter MUST be unique each time. This ensures that the
content encryption key is not reused. An implementation SHOULD content encryption key is not reused. An implementation SHOULD
generate a random salt parameter for every message; a counter could generate a random salt parameter for every message.
achieve the same result.
4.3. Data Encryption Limits 4.4. Data Encryption Limits
There are limits to the data that AEAD_AES_128_GCM can encipher. The There are limits to the data that AEAD_AES_128_GCM can encipher. The
maximum value for the record size is limited by the size of the "rs" maximum value for the record size is limited by the size of the "rs"
field in the header (see Section 2.1), which ensures that the 2^36-31 field in the header (see Section 2.1), which ensures that the 2^36-31
limit for a single application of AEAD_AES_128_GCM is not reached limit for a single application of AEAD_AES_128_GCM is not reached
[RFC5116]. In order to preserve a 2^-40 probability of [RFC5116]. In order to preserve a 2^-40 probability of
indistinguishability under chosen plaintext attack (IND-CPA), the indistinguishability under chosen plaintext attack (IND-CPA), the
total amount of plaintext that can be enciphered with the key derived total amount of plaintext that can be enciphered with the key derived
from the same input keying material and salt MUST be less than 2^44.5 from the same input keying material and salt MUST be less than 2^44.5
blocks of 16 octets [AEBounds]. blocks of 16 octets [AEBounds].
If the record size is a multiple of 16 octets, this means 398 If the record size is a multiple of 16 octets, this means 398
terabytes can be encrypted safely, including padding and overhead. terabytes can be encrypted safely, including padding and overhead.
However, if the record size is not a multiple of 16 octets, the total However, if the record size is not a multiple of 16 octets, the total
amount of data that can be safely encrypted is reduced because amount of data that can be safely encrypted is reduced because
skipping to change at page 10, line 25 skipping to change at page 10, line 19
blocks of 16 octets [AEBounds]. blocks of 16 octets [AEBounds].
If the record size is a multiple of 16 octets, this means 398 If the record size is a multiple of 16 octets, this means 398
terabytes can be encrypted safely, including padding and overhead. terabytes can be encrypted safely, including padding and overhead.
However, if the record size is not a multiple of 16 octets, the total However, if the record size is not a multiple of 16 octets, the total
amount of data that can be safely encrypted is reduced because amount of data that can be safely encrypted is reduced because
partial AES blocks are encrypted. The worst case is a record size of partial AES blocks are encrypted. The worst case is a record size of
18 octets, for which at most 74 terabytes of plaintext can be 18 octets, for which at most 74 terabytes of plaintext can be
encrypted, of which at least half is padding. encrypted, of which at least half is padding.
4.4. Content Integrity 4.5. Content Integrity
This mechanism only provides content origin authentication. The This mechanism only provides content origin authentication. The
authentication tag only ensures that an entity with access to the authentication tag only ensures that an entity with access to the
content encryption key produced the encrypted data. content encryption key produced the encrypted data.
Any entity with the content encryption key can therefore produce Any entity with the content encryption key can therefore produce
content that will be accepted as valid. This includes all recipients content that will be accepted as valid. This includes all recipients
of the same HTTP message. of the same HTTP message.
Furthermore, any entity that is able to modify both the Content- Furthermore, any entity that is able to modify both the Content-
Encoding header field and the HTTP message body can replace the Encoding header field and the HTTP message body can replace the
contents. Without the content encryption key or the input keying contents. Without the content encryption key or the input keying
material, modifications to or replacement of parts of a payload body material, modifications to or replacement of parts of a payload body
are not possible. are not possible.
4.5. Leaking Information in Header Fields 4.6. Leaking Information in Header Fields
Because only the payload body is encrypted, information exposed in Because only the payload body is encrypted, information exposed in
header fields is visible to anyone who can read the HTTP message. header fields is visible to anyone who can read the HTTP message.
This could expose side-channel information. This could expose side-channel information.
For example, the Content-Type header field can leak information about For example, the Content-Type header field can leak information about
the payload body. the payload body.
There are a number of strategies available to mitigate this threat, There are a number of strategies available to mitigate this threat,
depending upon the application's threat model and the users' depending upon the application's threat model and the users'
skipping to change at page 11, line 22 skipping to change at page 11, line 17
in other representations, etc.), omit the relevant headers, and/ in other representations, etc.), omit the relevant headers, and/
or normalize them. In the case of Content-Type, this could be or normalize them. In the case of Content-Type, this could be
accomplished by always sending Content-Type: application/octet- accomplished by always sending Content-Type: application/octet-
stream (the most generic media type), or no Content-Type at all. stream (the most generic media type), or no Content-Type at all.
3. If it is considered sensitive information and it is not possible 3. If it is considered sensitive information and it is not possible
to convey it elsewhere, encapsulate the HTTP message using the to convey it elsewhere, encapsulate the HTTP message using the
application/http media type (Section 8.3.2 of [RFC7230]), application/http media type (Section 8.3.2 of [RFC7230]),
encrypting that as the payload of the "outer" message. encrypting that as the payload of the "outer" message.
4.6. Poisoning Storage 4.7. Poisoning Storage
This mechanism only offers encryption of content; it does not perform This mechanism only offers data origin authentication; it does not
authentication or authorization, which still needs to be performed perform authentication or authorization of the message creator, which
(e.g., by HTTP authentication [RFC7235]). could still need to be performed (e.g., by HTTP authentication
[RFC7235]).
This is especially relevant when a HTTP PUT request is accepted by a This is especially relevant when a HTTP PUT request is accepted by a
server; if the request is unauthenticated, it becomes possible for a server without decrypting the payload; if the request is
third party to deny service and/or poison the store. unauthenticated, it becomes possible for a third party to deny
service and/or poison the store.
4.7. Sizing and Timing Attacks 4.8. Sizing and Timing Attacks
Applications using this mechanism need to be aware that the size of Applications using this mechanism need to be aware that the size of
encrypted messages, as well as their timing, HTTP methods, URIs and encrypted messages, as well as their timing, HTTP methods, URIs and
so on, may leak sensitive information. so on, may leak sensitive information. See for example [NETFLIX] or
[CLINIC].
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 them separately might reduce exposure. HTTP/2 segments and storing them 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.
Developing a padding strategy is difficult. A good padding strategy Developing a padding strategy is difficult. A good padding strategy
can depend on context. Common strategies include padding to a small can depend on context. Common strategies include padding to a small
set of fixed lengths, padding to multiples of a value, or padding to set of fixed lengths, padding to multiples of a value, or padding to
powers of 2. Even a good strategy can still cause size information powers of 2. Even a good strategy can still cause size information
to leak if processing activity of a recipient can be observed. This to leak if processing activity of a recipient can be observed. This
is especially true if the trailing records of a message contain only is especially true if the trailing records of a message contain only
padding. Distributing non-padding data is recommended to avoid padding. Distributing non-padding data across records is recommended
leaking size information. to avoid leaking size information.
5. IANA Considerations 5. IANA Considerations
5.1. The "aes128gcm" HTTP Content Coding 5.1. The "aes128gcm" HTTP Content Coding
This memo registers the "aes128gcm" HTTP content coding in the HTTP This memo registers the "aes128gcm" HTTP content coding in the HTTP
Content Codings Registry, as detailed in Section 2. Content Codings Registry, as detailed in Section 2.
o Name: aes128gcm o Name: aes128gcm
skipping to change at page 13, line 10 skipping to change at page 13, line 10
[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>.
6.2. Informative References 6.2. Informative References
[AEBounds] [AEBounds]
Luykx, A. and K. Paterson, "Limits on Authenticated Luykx, A. and K. Paterson, "Limits on Authenticated
Encryption Use in TLS", March 2016, Encryption Use in TLS", March 2016,
<http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>. <http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>.
[CLINIC] Miller, B., Huang, L., Joseph, A., and J. Tygar, "I Know
Why You Went to the Clinic: Risks and Realization of HTTPS
Traffic Analysis", March 2014, <https://arxiv.org/
abs/1403.0297>.
[NETFLIX] Reed, A. and M. Kranch, "Identifying HTTPS-Protected
Netflix Videos in Real-Time", Proceedings of the Seventh
ACM on Conference on Data and Application Security and
Privacy - CODASPY '17 , DOI 10.1145/3029806.3029821, 2017.
[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>.
[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>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
 End of changes. 28 change blocks. 
51 lines changed or deleted 71 lines changed or added

This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/