TLS Working Group P. Urien
Internet Draft Telecom Paris
Intended status: Experimental
July 5 2020
Expires: January 2020
Identity Module for TLS Version 1.3
draft-urien-tls-im-01.txt
Abstract
TLS 1.3 will be deployed in the Internet of Things ecosystem. In
many IoT frameworks, TLS or DTLS protocols, based on pre-shared key
(PSK), are used for device authentication. So PSK tamper resistance,
is a critical market request, in order to prevent hijacking issues.
If DH exchange is used with certificate bound to DH ephemeral public
key, there is also a benefit to protect its signature procedure. The
TLS identity module (im) MAY be based on secure element; it realizes
some HKDF operations bound to PSK, and cryptographic signature if
certificates are used. Secure Element form factor could be
standalone chip, or embedded in SOC like eSIM.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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 http://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 2020.
.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Identity Module for TLS Version 1.3 July 2020
Table of Contents
Abstract........................................................... 1
Requirements Language.............................................. 1
Status of this Memo................................................ 1
Copyright Notice................................................... 2
1 Overview......................................................... 4
2 Protecting the Key Schedule for PSK.............................. 4
2.1 Context..................................................... 4
2.2 Identity Module Procedures.................................. 5
2.3 KSGS: Keys Secure Generation and Storage.................... 5
2.4 Identity Module Key Procedures (IMKP)....................... 5
2.4.1 CETS: Client Early Traffic Secret .................... 5
2.4.2 EEMS: Early Exporter Master Secret ................... 6
2.4.3 HEDSK: HKDF-Extract from Derived Secret Key .......... 6
2.4.4 HBSK: HMAC from Binder Key Secret .................... 6
3. Asymmetric Signature............................................ 6
3.1 GENKEY...................................................... 6
3.2 GETPUB...................................................... 7
3.3 SIGN........................................................ 7
4. Secure Element as Identity Module............................... 8
4.1 Administrative mode......................................... 8
4.2 User Mode................................................... 8
4.3 KSGS: Keys Secure Generation and Storage.................... 8
4.3.1 Example .............................................. 9
4.4 CETS: Client Early Traffic Secret........................... 9
4.4.1 Example .............................................. 9
4.5 EEMS: Early Exporter Master Secret.......................... 9
4.5.1 Example ............................................. 10
4.6 HEDSK: HKDF-Extract from Derived Secret Key................ 10
4.6.1 Example ............................................. 10
4.7 HBSK: HMAC from Binder Key Secret.......................... 10
4.7.1 Example ............................................. 10
5 IANA Considerations............................................. 10
6 Security Considerations......................................... 10
7 References...................................................... 11
7.1 Normative References....................................... 11
7.2 Informative References..................................... 11
8 Authors' Addresses.............................................. 11
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Identity Module for TLS Version 1.3 July 2020
1 Overview
TLS 1.3 [RFC8446] will be deployed in the Internet of Things
ecosystem. In many IoT frameworks, TLS or DTLS protocols, based on
pre-shared key (PSK), are used for device authentication. So PSK
tamper resistance, is a critical market request, in order to prevent
hijacking issues. If DH exchange is used with certificate bound to
DH ephemeral public key, there is also a benefit to protect its
signature procedure. The TLS identity module (im) MAY be based on
secure element [ISO7816]; it realizes some HKDF [RFC5869] operations
bound to PSK, and cryptographic signature if certificates are used.
Secure Element form factor could be standalone chip or embedded in
SOC like eSIM.
+-----------+ +----------+
| Processor | | Identity |
| TLS 1.3 +------+ Module |
| | | im |
+-----------+ +----------+
Figure 1. TLS 1.3 Identity Module (im)
2 Protecting the Key Schedule for PSK
2.1 Context
According to [RFC8446] external PSKs MAY be provisioned outside of
TLS.
The Early Secret (ESK) is computed according to relation:
ESK =HKDF-Extract(salt=0s,PSK) = HMAC(salt=0s,PSK)
The Binder Key (BSK) for outside provisioning is computed according
to the relation:
BSK = Derive-Secret(ESK, "ext binder", "")
The Derived Secret (DSK) is computed according to the relation:
DSK= Derive-Secret(ESK, "derived", "")
The Finished External Key (FEK) is computed according to the
relation:
FEK = KDF-Expand-Label(BSK, "finished", "", Hash.length)
For Derive-Secret procedures, "" is equivalent to the value
hash(empty), whose size is hash-length
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2.2 Identity Module Procedures
The identity module MUST provide a KSGS (Keys Secure Generation and
Storage) procedure, which computes and securely stores ESK, BSK and
FEK keys.
This procedure MUST require administrative rights.
A set IMKP (Identity Module Key Procedures) of four procedures is
required, in order to protect from public exposure ESK, BSK, and
FSK:
- CETS: Client Early Traffic Secret
- EEMS: Early Exporter Master Secret
- HEDSK: HKDF-Extract from Derived Secret Key
- HBSK: HMAC from Binder Key Secret
These procedures MAY require user rights.
2.3 KSGS: Keys Secure Generation and Storage
The Identity module MUST provide a KSGS procedure, requiring
administrative rights, which computes and securely stores ESK, BSK,
DSK, FSK
Input: salt and PSK
Output: Success or Failure
ESK, DSK, and BSK secret values are stored in the identity module
HL16 : hash Length, 16 bits
HL8: hash length, 8 bits
H0 : hash(empty)
ESK= HMAC(salt=0s,PSK)
DSK= HMAC(ESK,HL16||0d746c7331332064657269766564||HL8||H0||01)
BSK= HMAC(ESK,HL16||10746c733133206578742062696e646572||HL8||H0||01)
FSK= HMAC(BSK,HL16||0E746C7331332066696E69736865640001)
2.4 Identity Module Key Procedures (IMKP)
2.4.1 CETS: Client Early Traffic Secret
Input: Length, Message
Output: Client Early Traffic Secret or Failure
CETS(ClientHello) = Derive-Secret(ESK, "c e traffic", Message)
= HMAC(ESK, Length || 11746c733133206320652074726166666963 ||
Message || 01)
Message is a hash value.
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2.4.2 EEMS: Early Exporter Master Secret
Input: Length, Message
Output: Early Exporter Master Secret or Failure
EEMS(ClientHello) = Derive-Secret(ESK, "e exp master", Message)
= HMAC(ESK, Length || 12746c733133206520657870206d6173746572 ||
Message || 01)
Message is a hash value
2.4.3 HEDSK: HKDF-Extract from Derived Secret Key
Input: DHE
Output: Handshake Secret or Failure
EDSK(DHE)= HKDF-Extract(salt=DSK,DHE) = HMAC(DSK, DHE)
2.4.4 HBSK: HMAC from Binder Key Secret
Input: data
Output: HMAC(BSK, data) or Failure
HBSK(data) = HMAC(FSK, data)
Data is a hash value
3. Asymmetric Signature
The identity module MUST provide a GENKEY (GENKEY: Generate Key)
procedure, in order to store or generate private asymmetric key and
associated public key.
This procedure MUST require administrative rights.
The procedure GETPUB (GETPUB: Get Public Key) is required in order
to read the public key value.
This procedure MAY require user rights.
The procedure SIGN (SIGN: Signature) is required in order to perform
a raw signature for a digest value, computed from certificate.
This procedure MAY require user rights.
3.1 GENKEY
Input: None
Output: Success or Failure
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A private key is generated and store in the identity module. A
public key is computed from the private key.
3.2 GETPUB
Input: None
Output: Public Key Value or Failure
3.3 SIGN
Input: DigestValue
Output: Signature Value or Failure
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4. Secure Element as Identity Module
Secure elements are defined according to [ISO7816] standards. They
support hash functions (sha256, sha384, sha512) and associated HMAC
procedures. They also provide DH procedures in Z/pZ* groups, and
elliptic curves. Open software can be released thanks to the
Javacard standards, such as JC3.04, JC3.05.
Below is an illustration of binary encoding rules for secure element
according to the T=1 ISO7816 protocol.
An ISO7816 command (TAPDU) is a set of bytes comprising a five byte
header and an optional payload (up to 255 bytes)
The header comprises the following five bytes
- CLA, Class
- INS, Instruction code
- P1, P1 byte
- P2, P2 byte
- P3, length of the payload, or number of expected bytes
The response comprises a payload (up to 256 bytes) and a two bytes
status word (SW1, SW2), 9000 meaning successful operation.
4.1 Administrative mode
The [ISO7816] command VERIFY (INS=0x20) SHOULD be used to enter the
administrative mode
Tx: CLA=00 INS=20 P1=00 P2=Adm P3=PIN-Length [PIN-Value]
Rx: 9000
4.2 User Mode
The [ISO7816] command VERIFY SHOULD be used to enter the user mode
Tx: CLA=00 INS=20 P1=00 P2=User P3=PIN-Length [PIN-Value]
Rx: 9000
4.3 KSGS: Keys Secure Generation and Storage
Length= 2 + Salt-Length + PSK-Length
Tx: CLA=00 INS=TLS13 P1=0 P2=KSGS P3=Length Salt-Length [Salt-Value]
PSK-Length [PSK-Value]
Rx: 9000
This procedure computes and stores ESK, BSK DSK and FSK.
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4.3.1 Example
PSK=0102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20
Tx: CLA=00 INS=85 P1=00 P2=0A P3=23 01 00 20
0102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20
Rx:9000
sha56(empty) =
E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855
ESK= HMAC-SHA256(0,PSK)
ESK=
23499E7EDF0FBE6BAA137DF0F23BECAEFA722AD19FC262855409DE8CD8B3C897
DSK= HMAC-SHA256(ESK,0020 0d746c7331332064657269766564 20
E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855 01)
DSK=
E8E7AC087158FC8440E41A12989F9194783764CD5FC36564028037F2C8206E96
BSK = HMAC-SHA256(ESK,0020 10746c733133206578742062696e646572 20
E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855 01)
BSK=
4351F8A53AA85AC394AB04C516464CAB96E9340C269632D09899537887EE651F
FSK= HMAC-256(BSK, 0020 0E746C7331332066696E6973686564 00 01)
4.4 CETS: Client Early Traffic Secret
Length = 2 + Messages-Length
Hash-Length: the hash length (2 bytes)
Tx: CLA INS=TLS13 P1=CETS P2=ESK P3=Length Hash-Length Messages-
Length [Messages]
Rx:[Client Early Traffic Secret] 9000
4.4.1 Example
Tx: CLA=00 INS=85 P1=00 P2=0B P3=03 0020 00
Rx: 0738A2B6F6FAA2AF5CDD9B6F0F2B232F19B3256A5926EAC600B911F91E98D2D4
9000
Message= NULL = 0s
[Client Early Traffic Secret] =
HMAC-SHA256(ESK, 0020 11746c733133206320652074726166666963 00 01)
4.5 EEMS: Early Exporter Master Secret
Length = 2 + Messages-Length
Hash-Length: the hash length (2 bytes)
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Tx: CLA INS=TLS13 P1=EEMS P2=ESK P3=Length Hash-Length Messages-
Length [Messages]
Rx: [Early Exporter Master Secret] 9000
4.5.1 Example
Tx: CLA=00 INS=85 P1=01 P2=0B P3=03 0020 00
Rx: 9B7FC6A8F854C16A301DFC566859931DB5EE9A22793142A0C67159C445E7BEAB
9000
Message= NULL = 0s
[Early Exporter Master Secret] =
HMAC-SHA256(ESK, 0020 12746c733133206520657870206d6173746572 00 01)
4.6 HEDSK: HKDF-Extract from Derived Secret Key
Tx: CLA INS=TLS13 P1=0 P2=HEDSK P3=Data-Length [Data]
Rx: [HMAC(Data,DSK)] 9000
4.6.1 Example
Tx: CLA=00 INS=85 P1=00 P2=0E P3=01 00
Rx: 7092C2117D67E6AEB5C5FDF5E6D9C70FBDC69B374E914C26AB08A122483D0E73
DHE=NULL=0s
HMAC-256(DSK,DHE)= HMAC-256(DSK,0s)
4.7 HBSK: HMAC from Binder Key Secret
Tx: CLA INS=TLS13 P1=0 P2=HBSK P3=Data-Length [Data]
Rx: [HMAC(FSK,data)] 9000
4.7.1 Example
Tx: CLA=00 INS=85 P1=00 P2=0C P3=01 00
Rx: 3E015D850B89C2470D4C49D4BD8E7C76F2B74175DDD85F393569315DA15480A4
Data=NULL=0s
HMAC-256(FSK,Data)= HMAC-256(DSK,0s)
5 IANA Considerations
TODO
6 Security Considerations
TODO
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7 References
7.1 Normative References
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
https://www.rfc-editor.org/info/rfc8446.
[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>.
[ISO7816] ISO 7816, "Cards Identification - Integrated Circuit Cards
with Contacts", The International Organization for Standardization
(ISO).
7.2 Informative References
8 Authors' Addresses
Pascal Urien
Telecom Paris
19 place Marguerite Perey
91120 Palaiseau Phone: NA
France Email: Pascal.Urien@telecom-paris.fr
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