Hybrid Public Key Encryption
draft-irtf-cfrg-hpke-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9180.
|
|
|---|---|---|---|
| Authors | Richard Barnes , Karthikeyan Bhargavan | ||
| Last updated | 2019-07-21 (Latest revision 2019-07-04) | ||
| Replaces | draft-barnes-cfrg-hpke | ||
| RFC stream | Internet Research Task Force (IRTF) | ||
| Formats | |||
| IETF conflict review | conflict-review-irtf-cfrg-hpke, conflict-review-irtf-cfrg-hpke, conflict-review-irtf-cfrg-hpke, conflict-review-irtf-cfrg-hpke, conflict-review-irtf-cfrg-hpke, conflict-review-irtf-cfrg-hpke | ||
| Additional resources | Mailing list discussion | ||
| Stream | IRTF state | (None) | |
| Consensus boilerplate | Unknown | ||
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 9180 (Informational) | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-irtf-cfrg-hpke-00
Network Working Group R. Barnes
Internet-Draft Cisco
Intended status: Informational K. Bhargavan
Expires: January 4, 2020 Inria
July 03, 2019
Hybrid Public Key Encryption
draft-irtf-cfrg-hpke-00
Abstract
This document describes a scheme for hybrid public-key encryption
(HPKE). This scheme provides authenticated public key encryption of
arbitrary-sized plaintexts for a recipient public key. HPKE works
for any combination of an asymmetric key encapsulation mechanism
(KEM), key derivation function (KDF), and authenticated encryption
with additional data (AEAD) encryption function. We provide
instantiations of the scheme using widely-used and efficient
primitives.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Security Properties . . . . . . . . . . . . . . . . . . . . . 3
4. Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Cryptographic Dependencies . . . . . . . . . . . . . . . . . 4
5.1. DH-Based KEM . . . . . . . . . . . . . . . . . . . . . . 5
6. Hybrid Public Key Encryption . . . . . . . . . . . . . . . . 6
6.1. Creating an Encryption Context . . . . . . . . . . . . . 7
6.2. Encryption to a Public Key . . . . . . . . . . . . . . . 10
6.3. Authentication using a Pre-Shared Key . . . . . . . . . . 10
6.4. Authentication using an Asymmetric Key . . . . . . . . . 11
6.5. Authentication using both a PSK and an Asymmetric Key . . 12
6.6. Encryption and Decryption . . . . . . . . . . . . . . . . 12
7. Algorithm Identifiers . . . . . . . . . . . . . . . . . . . . 13
7.1. Key Encapsulation Mechanisms (KEMs) . . . . . . . . . . . 13
7.2. Key Derivation Functions (KDFs) . . . . . . . . . . . . . 14
7.3. Authentication Encryption with Associated Data (AEAD)
Functions . . . . . . . . . . . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Possible TODOs . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
"Hybrid" public-key encryption schemes (HPKE) that combine asymmetric
and symmetric algorithms are a substantially more efficient solution
than traditional public key encryption techniques such as those based
on RSA or ElGamal. Encrypted messages convey a single ciphertext and
authentication tag alongside a short public key, which may be further
compressed. The key size and computational complexity of elliptic
curve cryptographic primitives for authenticated encryption therefore
make it compelling for a variety of use cases. This type of public
key encryption has many applications in practice, for example:
o PGP [RFC6637]
o Messaging Layer Security [I-D.ietf-mls-protocol]
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o Encrypted Server Name Indication [I-D.ietf-tls-esni]
o Protection of 5G subscriber identities [fiveG]
Currently, there are numerous competing and non-interoperable
standards and variants for hybrid encryption, including ANSI X9.63
[ANSI], IEEE 1363a [IEEE], ISO/IEC 18033-2 [ISO], and SECG SEC 1
[SECG]. All of these existing schemes have problems, e.g., because
they rely on outdated primitives, lack proofs of IND-CCA2 security,
or fail to provide test vectors.
This document defines an HPKE scheme that provides a subset of the
functions provided by the collection of schemes above, but specified
with sufficient clarity that they can be interoperably implemented
and formally verified.
2. Requirements Notation
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
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Security Properties
As a hybrid authentication encryption algorithm, we desire security
against (adaptive) chosen ciphertext attacks (IND-CCA2 secure). The
HPKE variants described in this document achieve this property under
the Random Oracle model assuming the gap Computational Diffie Hellman
(CDH) problem is hard [S01].
[[ TODO - Provide citations to these proofs once they exist ]]
4. Notation
The following terms are used throughout this document to describe the
operations, roles, and behaviors of HPKE:
o Initiator (I): Sender of an encrypted message.
o Responder (R): Receiver of an encrypted message.
o Ephemeral (E): A fresh random value meant for one-time use.
o "(skX, pkX)": A KEM key pair used in role X; "skX" is the private
key and "pkX" is the public key
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o "pk(skX)": The public key corresponding to private key "skX"
o "len(x)": The length of the octet string "x", expressed as a two-
octet unsigned integer in network (big-endian) byte order
o "encode_big_endian(x, n)": An octet string encoding the integer
value "x" as an n-byte big-endian value
o "concat(x0, ..., xN)": Concatenation of octet strings.
"concat(0x01, 0x0203, 0x040506) = 0x010203040506"
o "zero(n)": An all-zero octet string of length "n". "zero(4) =
0x00000000"
o "xor(a,b)": XOR of octet strings; "xor(0xF0F0, 0x1234) = 0xE2C4".
It is an error to call this function with two arguments of unequal
length.
5. Cryptographic Dependencies
HPKE variants rely on the following primitives:
o A Key Encapsulation Mechanism (KEM):
* GenerateKeyPair(): Generate a key pair (sk, pk)
* Marshal(pk): Produce a fixed-length octet string encoding the
public key "pk"
* Unmarshal(enc): Parse a fixed-length octet string to recover a
public key
* Encap(pk): Generate an ephemeral symmetric key and a fixed-
length encapsulation of that key that can be decapsulated by
the holder of the private key corresponding to pk
* Decap(enc, sk): Use the private key "sk" to recover the
ephemeral symmetric key from its encapsulated representation
"enc"
* AuthEncap(pkR, skI) (optional): Same as Encap(), but the
outputs encode an assurance that the ephemeral shared key is
known only to the holder of the private key "skI"
* AuthDecap(skR, pkI) (optional): Same as Decap(), but the holder
of the private key "skR" is assured that the ephemeral shared
key is known only to the holder of the private key
corresponding to "pkI"
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* Nenc: The length in octets of an encapsulated key from this KEM
* Npk: The length in octets of a public key for this KEM
o A Key Derivation Function:
* Extract(salt, IKM): Extract a pseudorandom key of fixed length
from input keying material "IKM" and an optional octet string
"salt"
* Expand(PRK, info, L): Expand a pseudorandom key "PRK" using
optional string "info" into "L" bytes of output keying material
* Nh: The output size of the Extract function
o An AEAD encryption algorithm [RFC5116]:
* Seal(key, nonce, aad, pt): Encrypt and authenticate plaintext
"pt" with associated data "aad" using secret key "key" and
nonce "nonce", yielding ciphertext and tag "ct"
* Open(key, nonce, aad, ct): Decrypt ciphertext "ct" using
associated data "aad" with secret key "key" and nonce "nonce",
returning plaintext message "pt" or the error value "OpenError"
* Nk: The length in octets of a key for this algorithm
* Nn: The length in octets of a nonce for this algorithm
A set of algorithm identifiers for concrete instantiations of these
primitives is provided in Section 7. Algorithm identifier values are
two octets long.
5.1. DH-Based KEM
Suppose we are given a Diffie-Hellman group that provides the
following operations:
o GenerateKeyPair(): Generate an ephemeral key pair "(sk, pk)" for
the DH group in use
o DH(sk, pk): Perform a non-interactive DH exchange using the
private key sk and public key pk to produce a fixed-length shared
secret
o Marshal(pk): Produce a fixed-length octet string encoding the
public key "pk"
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o Unmarshal(enc): Parse a fixed-length octet string to recover a
public key
Then we can construct a KEM (which we'll call "DHKEM") in the
following way:
def Encap(pkR):
skE, pkE = GenerateKeyPair()
zz = DH(skE, pkR)
enc = Marshal(pkE)
return zz, enc
def Decap(enc, skR):
pkE = Unmarshal(enc)
return DH(skR, pkE)
def AuthEncap(pkR, skI):
skE, pkE = GenerateKeyPair()
zz = concat(DH(skE, pkR), DH(skI, pkR))
enc = Marshal(pkE)
return zz, enc
def AuthDecap(enc, skR, pkI):
pkE = Unmarshal(enc)
return concat(DH(skR, pkE), DH(skR, pkI))
The GenerateKeyPair, Marshal, and Unmarshal functions are the same as
for the underlying DH group. The Marshal functions for the curves
referenced in {#ciphersuites} are as follows:
o P-256: The X-coordinate of the point, encoded as a 32-octet big-
endian integer
o P-521: The X-coordinate of the point, encoded as a 66-octet big-
endian integer
o Curve25519: The standard 32-octet representation of the public key
o Curve448: The standard 56-octet representation of the public key
6. Hybrid Public Key Encryption
In this section, we define a few HPKE variants. All variants take a
recipient public key and a sequence of plaintexts "pt", and produce
an encapsulated key "enc" and a sequence of ciphertexts "ct". These
outputs are constructed so that only the holder of the private key
corresponding to "pkR" can decapsulate the key from "enc" and decrypt
the ciphertexts. All of the algorithms also take an "info" parameter
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that can be used to influence the generation of keys (e.g., to fold
in identity information) and an "aad" parameter that provides
Additional Authenticated Data to the AEAD algorithm in use.
In addition to the base case of encrypting to a public key, we
include two authenticated variants, one of which authenticates
possession of a pre-shared key, and one of which authenticates
possession of a KEM private key. The following one-octet values will
be used to distinguish between modes:
+---------------+-------+
| Mode | Value |
+---------------+-------+
| mode_base | 0x00 |
| | |
| mode_psk | 0x01 |
| | |
| mode_auth | 0x02 |
| | |
| mode_psk_auth | 0x03 |
+---------------+-------+
All of these cases follow the same basic two-step pattern:
1. Set up an encryption context that is shared between the sender
and the recipient
2. Use that context to encrypt or decrypt content
A "context" encodes the AEAD algorithm and key in use, and manages
the nonces used so that the same nonce is not used with multiple
plaintexts.
The procedures described in this session are laid out in a Python-
like pseudocode. The algorithms in use are left implicit.
6.1. Creating an Encryption Context
The variants of HPKE defined in this document share a common
mechanism for translating the protocol inputs into an encryption
context. The key schedule inputs are as follows:
o "pkR" - The receiver's public key
o "zz" - A shared secret generated via the KEM for this transaction
o "enc" - An encapsulated key produced by the KEM for the receiver
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o "info" - Application-supplied information (optional; default value
"")
o "psk" - A pre-shared secret held by both the initiator and the
receiver (optional; default value "zero(Nh)").
o "pskID" - An identifier for the PSK (optional; default value """ =
zero(0)"
o "pkI" - The initiator's public key (optional; default value
"zero(Npk)")
The "psk" and "pskID" fields MUST appear together or not at all.
That is, if a non-default value is provided for one of them, then the
other MUST be set to a non-default value.
The key and nonce computed by this algorithm have the property that
they are only known to the holder of the receipient private key, and
the party that ran the KEM to generate "zz" and "enc". If the "psk"
and "pskID" arguments are provided, then the recipient is assured
that the initiator held the PSK. If the "pkIm" argument is provided,
then the recipient is assued that the initator held the corresponding
private key (assuming that "zz" and "enc" were generated using the
AuthEncap / AuthDecap methods; see below).
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default_pkIm = zero(Npk)
default_psk = zero(Nh)
default_pskId = zero(0)
def VerifyMode(mode, psk, pskID, pkIm):
got_psk = (psk != default_psk and pskID != default_pskID)
no_psk = (psk == default_psk and pskID == default_pskID)
got_pkIm = (pkIm != default_pkIm)
no_pkIm = (pkIm == default_pkIm)
if mode == mode_base and (got_psk or got_pkIm):
raise Exception("Invalid configuration for mode_base")
if mode == mode_psk and (no_psk or got_pkIm):
raise Exception("Invalid configuration for mode_psk")
if mode == mode_auth and (got_psk or no_pkIm):
raise Exception("Invalid configuration for mode_auth")
if mode == mode_psk_auth and (no_psk or no_pkIm):
raise Exception("Invalid configuration for mode_psk_auth")
def EncryptionContext(mode, pkRm, zz, enc, info, psk, pskID, pkIm):
VerifyMode(mode, psk, pskID, pkI)
pkRm = Marshal(pkR)
context = concat(mode, ciphersuite, enc, pkRm, pkIm,
len(pskID), pskID, len(info), info)
secret = Extract(psk, zz)
key = Expand(secret, concat("hpke key", context), Nk)
nonce = Expand(secret, concat("hpke nonce", context), Nn)
return Context(key, nonce)
Note that the context construction in the KeySchedule procedure is
equivalent to serializing a structure of the following form in the
TLS presentation syntax:
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struct {
// Mode and algorithms
uint8 mode;
uint16 ciphersuite;
// Public inputs to this key exchange
opaque enc[Nenc];
opaque pkR[Npk];
opaque pkI[Npk];
opaque pskID<0..2^16-1>;
// Application-supplied info
opaque info<0..2^16-1>;
} HPKEContext;
6.2. Encryption to a Public Key
The most basic function of an HPKE scheme is to enable encryption for
the holder of a given KEM private key. The "SetupBaseI()" and
"SetupBaseR()" procedures establish contexts that can be used to
encrypt and decrypt, respectively, for a given private key.
The the shared secret produced by the KEM is combined via the KDF
with information describing the key exchange, as well as the explicit
"info" parameter provided by the caller.
def SetupBaseI(pkR, info):
zz, enc = Encap(pkR)
return enc, KeySchedule(mode_base, pkR, zz, enc, info,
default_psk, default_pskID, default_pkIm)
def SetupBaseR(enc, skR, info):
zz = Decap(enc, skR)
return KeySchedule(mode_base, pk(skR), zz, enc, info,
default_psk, default_pskID, default_pkIm)
6.3. Authentication using a Pre-Shared Key
This variant extends the base mechansism by allowing the recipient to
authenticate that the sender possessed a given pre-shared key (PSK).
We assume that both parties have been provisioned with both the PSK
value "psk" and another octet string "pskID" that is used to identify
which PSK should be used.
The primary differences from the base case are:
o The PSK is used as the "salt" input to the KDF (instead of 0)
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o The PSK ID is added to the context string used as the "info" input
to the KDF
This mechanism is not suitable for use with a low-entropy password as
the PSK. A malicious recipient that does not possess the PSK can use
decryption of a plaintext as an oracle for performing offline
dictionary attacks.
def SetupPSKI(pkR, psk, pskID, info):
zz, enc = Encap(pkR)
return enc, KeySchedule(pkR, zz, enc, info,
psk, pskId, default_pkIm)
def SetupPSKR(enc, skR, psk, pskID, info):
zz = Decap(enc, skR)
return KeySchedule(pk(skR), zz, enc, info,
psk, pskId, default_pkIm)
6.4. Authentication using an Asymmetric Key
This variant extends the base mechansism by allowing the recipient to
authenticate that the sender possessed a given KEM private key. This
assurance is based on the assumption that "AuthDecap(enc, skR, pkI)"
produces the correct shared secret only if the encapsulated value
"enc" was produced by "AuthEncap(pkR, skI)", where "skI" is the
private key corresponding to "pkI". In other words, only two people
could have produced this secret, so if the recipient is one, then the
sender must be the other.
The primary differences from the base case are:
o The calls to "Encap" and "Decap" are replaced with calls to
"AuthEncap" and "AuthDecap".
o The initiator public key is added to the context string
Obviously, this variant can only be used with a KEM that provides
"AuthEncap()" and "AuthDecap()" procuedures.
This mechanism authenticates only the key pair of the initiator, not
any other identity. If an application wishes to authenticate some
other identity for the sender (e.g., an email address or domain
name), then this identity should be included in the "info" parameter
to avoid unknown key share attacks.
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def SetupAuthI(pkR, skI, info):
zz, enc = AuthEncap(pkR, skI)
pkIm = Marshal(pk(skI))
return enc, KeySchedule(pkR, zz, enc, info,
default_psk, default_pskID, pkIm)
def SetupAuthR(enc, skR, pkI, info):
zz = AuthDecap(enc, skR, pkI)
pkIm = Marshal(pkI)
return KeySchedule(pk(skR), zz, enc, info,
default_psk, default_pskID, pkIm)
6.5. Authentication using both a PSK and an Asymmetric Key
This mode is a straightforward combination of the PSK and
authenticated modes. The PSK is passed through to the key schedule
as in the former, and as in the latter, we use the authenticated KEM
variants.
def SetupAuthI(pkR, psk, pskID, skI, info):
zz, enc = AuthEncap(pkR, skI)
pkIm = Marshal(pk(skI))
return enc, KeySchedule(pkR, zz, enc, info, psk, pskID, pkIm)
def SetupAuthR(enc, skR, psk, pskID, pkI, info):
zz = AuthDecap(enc, skR, pkI)
pkIm = Marshal(pkI)
return KeySchedule(pk(skR), zz, enc, info, psk, pskID, pkIm)
6.6. Encryption and Decryption
HPKE allows multiple encryption operations to be done based on a
given setup transaction. Since the public-key operations involved in
setup are typically more expensive than symmetric encryption or
decryption, this allows applications to "amortize" the cost of the
public-key operations, reducing the overall overhead.
In order to avoid nonce reuse, however, this decryption must be
stateful. Each of the setup procedures above produces a context
object that stores the required state:
o The AEAD algorithm in use
o The key to be used with the AEAD algorithm
o A base nonce value
o A sequence number (initially 0)
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All of these fields except the sequence number are constant. The
sequence number is used to provide nonce uniqueness: The nonce used
for each encryption or decryption operation is the result of XORing
the base nonce with the current sequence number, encoded as a big-
endian integer of the same length as the nonce. Implementations MAY
use a sequence number that is shorter than the nonce (padding on the
left with zero), but MUST return an error if the sequence number
overflows.
Each encryption or decryption operation increments the sequence
number for the context in use. A given context SHOULD be used either
only for encryption or only for decryption.
It is up to the application to ensure that encryptions and
decryptions are done in the proper sequence, so that the nonce values
used for encryption and decryption line up.
[[ TODO: Check for overflow, a la TLS ]]
def Context.Nonce(seq):
encSeq = encode_big_endian(seq, len(self.nonce))
return xor(self.nonce, encSeq)
def Context.Seal(aad, pt):
ct = Seal(self.key, self.Nonce(self.seq), aad, pt)
self.seq += 1
return ct
def Context.Open(aad, ct):
pt = Open(self.key, self.Nonce(self.seq), aad, ct)
if pt == OpenError:
return OpenError
self.seq += 1
return pt
7. Algorithm Identifiers
7.1. Key Encapsulation Mechanisms (KEMs)
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+--------+-------------------+------+-----+--------------+
| Value | KEM | Nenc | Npk | Reference |
+--------+-------------------+------+-----+--------------+
| 0x0000 | (reserved) | N/A | N/A | N/A |
| | | | | |
| 0x0001 | DHKEM(P-256) | 32 | 32 | [NISTCurves] |
| | | | | |
| 0x0002 | DHKEM(Curve25519) | 32 | 32 | [RFC7748] |
| | | | | |
| 0x0003 | DHKEM(P-521) | 65 | 65 | [NISTCurves] |
| | | | | |
| 0x0004 | DHKEM(Curve448) | 56 | 56 | [RFC7748] |
+--------+-------------------+------+-----+--------------+
For the NIST curves P-256 and P-521, the Marshal function of the DH
scheme produces the normal (non-compressed) representation of the
public key, according to [SECG]. When these curves are used, the
recipient of an HPKE ciphertext MUST validate that the ephemeral
public key "pkE" is on the curve. The relevant validation procedures
are defined in [keyagreement]
For the CFRG curves Curve25519 and Curve448, the Marshal function is
the identity function, since these curves already use fixed-length
octet strings for public keys.
7.2. Key Derivation Functions (KDFs)
+--------+-------------+-----+-----------+
| Value | KDF | Nh | Reference |
+--------+-------------+-----+-----------+
| 0x0000 | (reserved) | N/A | N/A |
| | | | |
| 0x0001 | HKDF-SHA256 | 32 | [RFC5869] |
| | | | |
| 0x0002 | HKDF-SHA512 | 64 | [RFC5869] |
+--------+-------------+-----+-----------+
7.3. Authentication Encryption with Associated Data (AEAD) Functions
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+--------+------------------+-----+-----+-----------+
| Value | AEAD | Nk | Nn | Reference |
+--------+------------------+-----+-----+-----------+
| 0x0000 | (reserved) | N/A | N/A | N/A |
| | | | | |
| 0x0001 | AES-GCM-128 | 16 | 12 | [GCM] |
| | | | | |
| 0x0002 | AES-GCM-256 | 32 | 12 | [GCM] |
| | | | | |
| 0x0003 | ChaCha20Poly1305 | 32 | 12 | [RFC8439] |
+--------+------------------+-----+-----+-----------+
8. Security Considerations
[[ TODO ]]
9. IANA Considerations
[[ TODO: Make IANA registries for the above ]]
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[ANSI] "Public Key Cryptography for the Financial Services
Industry -- Key Agreement and Key Transport Using Elliptic
Curve Cryptography", n.d..
[fiveG] "Security architecture and procedures for 5G System",
n.d.,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3169>.
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[GCM] Dworkin, M., "Recommendation for block cipher modes of
operation :", National Institute of Standards and
Technology report, DOI 10.6028/nist.sp.800-38d, 2007.
[I-D.ietf-mls-protocol]
Barnes, R., Millican, J., Omara, E., Cohn-Gordon, K., and
R. Robert, "The Messaging Layer Security (MLS) Protocol",
draft-ietf-mls-protocol-06 (work in progress), May 2019.
[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. Wood,
"Encrypted Server Name Indication for TLS 1.3", draft-
ietf-tls-esni-03 (work in progress), March 2019.
[IEEE] "IEEE 1363a, Standard Specifications for Public Key
Cryptography - Amendment 1 -- Additional Techniques",
n.d..
[ISO] "ISO/IEC 18033-2, Information Technology - Security
Techniques - Encryption Algorithms - Part 2 -- Asymmetric
Ciphers", n.d..
[keyagreement]
Barker, E., Chen, L., Roginsky, A., and M. Smid,
"Recommendation for Pair-Wise Key Establishment Schemes
Using Discrete Logarithm Cryptography", National Institute
of Standards and Technology report,
DOI 10.6028/nist.sp.800-56ar2, May 2013.
[MAEA10] "A Comparison of the Standardized Versions of ECIES",
n.d., <http://sceweb.sce.uhcl.edu/yang/teaching/
csci5234WebSecurityFall2011/Chaum-blind-signatures.PDF>.
[NISTCurves]
"Digital Signature Standard (DSS)", National Institute of
Standards and Technology report,
DOI 10.6028/nist.fips.186-4, July 2013.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC6637] Jivsov, A., "Elliptic Curve Cryptography (ECC) in
OpenPGP", RFC 6637, DOI 10.17487/RFC6637, June 2012,
<https://www.rfc-editor.org/info/rfc6637>.
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[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC8439] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
<https://www.rfc-editor.org/info/rfc8439>.
[S01] "A Proposal for an ISO Standard for Public Key Encryption
(verison 2.1)", n.d.,
<http://www.shoup.net/papers/iso-2_1.pdf>.
[SECG] "Elliptic Curve Cryptography, Standards for Efficient
Cryptography Group, ver. 2", n.d.,
<http://www.secg.org/download/aid-780/sec1-v2.pdf>.
Appendix A. Possible TODOs
The following extensions might be worth specifying:
o Multiple recipients - It might be possible to add some
simplifications / assurances for the case where the same value is
being encrypted to multiple recipients.
o Test vectors - Obviously, we can provide decryption test vectors
in this document. In order to provide known-answer tests, we
would have to introduce a non-secure deterministic mode where the
ephemeral key pair is derived from the inputs. And to do that
safely, we would need to augment the decrypt function to detect
the deterministic mode and fail.
o A reference implementation in hacspec or similar
Authors' Addresses
Richard L. Barnes
Cisco
Email: rlb@ipv.sx
Karthik Bhargavan
Inria
Email: karthikeyan.bhargavan@inria.fr
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