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TLS Working Group P. Urien
Internet Draft Telecom Paris
Intended status: Experimental
September 15 2020
Expires: March 2020
Secure Element for TLS Version 1.3
draft-urien-tls-se-00.txt
Abstract
This draft presents ISO7816 interface for TLS1.3 stack running in
secure element. It presents supported cipher suites and key exchange
modes, and describes embedded software architecture. TLS 1.3 is the
de facto security stack for emerging Internet of Things (IoT)
devices. Some of them are constraint nodes, with limited computing
resources. Furthermore cheap System on Chip (SoC) components don't
usually provide tamper resistant features, so private or pre shared
keys are exposed to hacking. According to the technology state of
art, some ISO7816 secure elements are able to process TLS 1.3, but
with a limited set of cipher suites. There are two benefits for TLS-
SE; first fully tamper resistant processing of TLS protocol, which
increases the security level insurance; second embedded software
component ready for use, which relieves the software of the burden
of cryptographic libraries and associated attacks.
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 March 2021.
.
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Copyright Notice
Copyright (c) 2020 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
(http://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 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.
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Secure Element for TLS Version 1.3 September 2020
Table of Contents
Abstract........................................................... 1
Requirements Language.............................................. 1
Status of this Memo................................................ 1
Copyright Notice................................................... 2
1 Overview......................................................... 4
2 About Secure Elements............................................ 4
3 Software components for TLS-SE................................... 5
3.1 Cryptographic resources..................................... 5
3.2 Data exchange............................................... 6
3.2.1 Receiving Record Packet .............................. 6
3.2.2 Sending Record Packet ................................ 7
3.2.4 RECV and SEND procedure for open application AEAD .... 8
3.3 TLS state machine........................................... 9
3.4 TLS library................................................ 10
4 ISO7816 interface............................................... 11
5 ISO 7816 Use Case............................................... 12
5 IANA Considerations............................................. 14
6 Security Considerations......................................... 14
7 References...................................................... 14
7.1 Normative References....................................... 14
7.2 Informative References..................................... 14
8 Authors' Addresses.............................................. 14
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1 Overview
This draft presents ISO7816 interface for TLS1.3 stack running in
secure element, it presents supported cipher suites and key exchange
modes, and describes embedded software architecture. TLS 1.3
[RFC8446] is the de facto security stack for emerging Internet of
Things (IoT) devices. Some of them are constraint nodes, with
limited computing resources. Furthermore cheap System on Chip (SOC)
components don't usually provide tamper resistant features, so
private or pre shared keys are exposed to hacking. The identity
module (im) detailed in [IM] protects identity credentials. The TLS
identity module [IM] MAY be based on secure element [ISO7816].
According to the technology state of art, some secure elements are
able to process TLS 1.3, but with a limited set of cipher suites.
There are two benefits for TLS-SE; first fully tamper resistant
processing of TLS protocol, which increases the security level
insurance; second embedded software component ready for use, which
relieves the software of the burden of cryptographic libraries and
associated attacks.
+-----------+ recv +------------+ RECV +-----------+
| IP + ---> | TCP/IP | ---> | TLS 1.3 |
| Network +------+ Constraint +------+ Secure |
| | <--- | Node | <--- | Element |
+-----------+ send +------------+ SEND +-----------+
| |
Network Interface ISO7816 interface
Figure 1. TLS 1.3 Secure Element (TLS-SE)
2 About Secure Elements
Secure elements are defined according to [ISO7816] standards. They
support hash functions (sha256, sha384, sha512) and associated HMAC
procedures. They also provide signatures and DH procedures in Z/pZ*
groups, or elliptic curves (for example secp256r1). Open software
can be released thanks to Javacard standards, such as JC3.04, or
JC3.05. Most of secure elements use 8 bits Micro Controller Unit
(MCU) and embedded cryptographic accelerator. Non volatile memory
size is up to 100KB, and RAM size is up to 10KB.
Below is an illustration of binary encoding rules for secure element
according to the T=0 ISO7816 protocol.
An ISO7816 request 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 optional payload, or number of expected bytes
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The response comprises an optional payload (up to 256 bytes) and a
two bytes status word (SW1, SW2), SW1=90, SW2=00 (SW=9000) meaning
successful operation.
The ISO7816 defines two main classes for data exchange (called
transport protocol), T=0, and T=1.
The T=0 transport protocol is a byte stream; a payload can be
included in request or response, but not in both.
The T=1 transport protocol is a frame stream; payload can be
included both in request and response.
3 Software components for TLS-SE
+--------+
| Crypto +----------------+
RECV +----------+ | Lib | |
---> | Data | +--------+ +----------+----------+
<--- | Exchange | +---------+ TLS Lib |
SEND +----+-----+ | | Make Record Packet |
| +-----+-----+ | Check Record Packet |
| | TLS State | +---------------------+
+--------+ Machine |
+-----------+
Figure 2. Software Components for TLS-SE
3.1 Cryptographic resources
Many secure elements support hash functions sha256, sha384 and
sha512 used by TLS1.3. Associated HMAC, HKDF-Extract and Derive-
Secret, MUST be implemented by a dedicated cryptographic library.
Many secure elements support the secp256r1 elliptic curve. Diffie-
Hellman (DH )calculation are performed according to [IEEE1363] using
the ECKAS-DH1 scheme with the identity map as the key derivation
function, (KDF), so that the shared secret is the x-coordinate of
the ECDH shared secret elliptic curve point represented as an octet
string. ECDSA signature is also available for 256,384 and 512 hash
size.
AES-128 is usually implemented, by not AES-CCM. So this AEAD
algorithm SHOULD be implemented by a dedicated cryptographic
library.
In summary, according to the state of art TLS-SE supports the
secp256r1 ec group, associated ECDSA signature computing and
checking, and ECDHE key establishment. It also implements the AES-
128-CCM-SHA256 cipher suite.
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3.2 Data exchange
TLS record layer packets are received and sent from/to TCP/IP
networks thanks to well known socket procedures. The TLS-SE
processes these packets according to a state machine.
3.2.1 Receiving Record Packet
Dedicated ISO7816 requests (named RECV) push incoming record
messages in secure element. A fragmentation mechanism splits the
record packet in one a several ISO7816 requests, whose payload size
is less than 255 bytes. A 2 bits fragmentation-flag field indicates
the fragment status; bit F-First notifies the first fragment, and
bit F-Last notifies the last fragment.
The ISO7816 RECV request COULD be encoded as
CLA=00, INS=D8, P1=0, P2=fragmentation-flag, P3=fragment-length
F-First=b01, F-Last=b10, F-More=b00
When application AEAD is opened a two bits flag (F-Encrypt, F-
Decrypt) indicates the cryptographic operation:
- P2=b01= F-Decrypt, decryption
- P2=b10= F-Encrypt, encryption
If F-Last is not set, the ISO7816 response is always 9000 when no
error occurs. For the last fragment five cases may occur:
- sw-ok: no error, no record message returned, response = 9000.
- sw-open, no error, no record message returned, TLS application
AEAD is opened, for example response =9001.
- sw-close: no error, , no record message returned, TLS application
AEAD is closed, for example response =9002
- sw-error: error, no record message returned.
- sw-more(size): no error, a message or message fragment is ready.
For example sw-more(size)= 61xy, in which xy is the size of the
first fragment.
TCP/IP Node Secure Element
| |
|-RECV(F-First, Frag#1)-------->|
|<-------------------sw-ok 9000-|
|-RECV(F-More, Frag#i)-------->|
|<------------------sw-ok= 9000-|
|-RECV(F-Last, Frag#n)-------->|
|<------------------sw-ok= 9000-|
|<----------------sw-open= 9001-|
|<---------------sw-close= 9002-|
|<----------sw-more(size)= 61xy-|
Figure 3. Receiving record packet, segmentation mechanism.
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3.2.2 Sending Record Packet
A sending procedure starts by the reception of a sw-more(size)
status, ending a response. This event may occur at the end of RECV
procedure (see figure 5) or after TLS state machine reset (see
figure 4).
A RECV(F-First, No-Frag) request resets the TLS state machine. For
TLS client a sw-more(size) status is returned. For TLS server the
sw-ok status is returned.
TCP/IP Node Secure Element
| |
|-RECV(F-First, No-Frag)------->|=> Reset State Machine
|<------------------sw-ok= 9000-| Server
|<----------sw-more(size)= 61xy-| Client
Figure 4. Starting the SEND procedure after RESET request.
TCP/IP Node Secure Element
| |
|-RECV(F-Last, Last-Fragment)-->| => End of Message
|<----------sw-more(size)= 61xy-| Client
Figure 5. Starting SEND procedure after the end of RECV procedure.
The SEND(size) reads a record fragment, whose length is equal to
size. It MAY be necessary to adjust the SEND size (see figure 6).
Typically at the end of RECV procedure, the size indicated by the
sw-more(size) status is an expected fragment length. In that case
the status sw-retry status (for example 6Cxy) indicates the fragment
size.
TCP/IP Node Secure Element
| |
|-RECV(F-Last, Last-Frag)------>| => End of Message
|<----------sw-more(size)= 61xy-|
| SEND(size)------------------->|
| <------- sw-retry(size')=6Czt-|
| SEND(size')------------------>|
Figure 6. Adjusting SEND size.
The SEND(size) request is encoded as :
CLA=0, INS=C0, P1=0, P2=0, P3=size
The SEND procedure (see Figure 7) is a set of SEND requests, which
read record packet fragments.
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TCP/IP Node Secure Element
| |
|<--------------- ---sw-more(size#1)= 61xy-|
|-SEND(size#1)---------------------------->|
|<---------------Frag#1 || sw-more(size#2)-|
|-SEND(size#i)---------------------------->|
|<-----------Frag#i || sw-more(size#[i+1])-|
|-SEND(size#n)---------------------------->|
|<------------------------Frag#n || sw-ok)-|=> SEND End
|<------------Frag#n || sw-more(next-size)-|=> SEND Continue
|<----------------------Frag#n || sw-open)-|=> Open
|<----------------------Frag#n || sw-close-|=> Close
Figure 7. The SEND procedure
At the end of SEND procedure four events MAY occur:
- End of SEND procedure (status = sw-ok). No more record packets are
available.
- SEND procedure to be continued (status = sw-more(size)). Another
record packet is available.
- End of SEND procedure, application AEAD is ready for use (status =
sw-open)
- End of SEND procedure, application AEAD is closed (status = sw-
close)
3.2.4 RECV and SEND procedure for open application AEAD
When the application AEAD is opened RECV performs decryption and
encryption operations (see figure 8).
For decryption operation (RECV(F-Decrypt)) the RECV procedure pushes
the incoming record packet. The returned payload by the SEND
procedure is the decrypted message ended by the protocol byte.
For encryption operation (RECV(F-Encrypt)) the RECV procedure pushes
the content to encrypt ended by the associated protocol byte. The
returned payload by the SEND procedure is a record packet, including
the encrypted content.
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TCP/IP Node Secure Element
| |
|-RECV(F-First, Frag#1)-------------------------->|
|<------------------------------------sw-ok= 9000-|
|-RECV(F-More, Frag#i)-------------------------->|
|<------------------------------------sw-ok= 9000-|
|-RECV(F-Decrypt/F-Encrypt, F-Last, Frag#n)------>|
|<--------------------------sw-more(size#1)= 61xy-|
|-SEND(size#1)----------------------------------->|
|<----------------------Frag#1 || sw-more(size#2)-|
|-SEND(size#i)----------------------------------->|
|<------------------Frag#i || sw-more(size#[i+1])-|
|-SEND(size#n)----------------------------------->|
|<-------------------------------Frag#n || sw-ok)-|=> SEND End
|<-----------------------------Frag#n || sw-close-|=> Close
Figure 8. Decryption/Encryption operations.
3.3 TLS state machine
The state machine manages TLS flights, it determines the next record
packet to be received & checked, and the next record packet to be
built and sent. The number of states and their order is dependent on
the TLS-SE role (client or server), and on the supported working
mode (pre shared key, server with certificate, server and client
with certificate). Figure 9 details an example of state machine for
TLS-SE server, using pre-shared key. The ordered list of states
comprises: S-Ready, S-Extensions, S-SFinished, S-ClientCCS, S-
CFinished and S-Open.
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TCP/IP Node Secure Element
| |
|-RESET------------------------>|
|<------------------------sw-ok-| state = S-Ready
Client |-RECV(F-First,Frag#1)--------->|
Hello |<------------------------sw-ok-|
|-RECV(F-Last,Frag#2)---------->|
| | Check-ClientHello
| | Make-ServerHello
|<----------------sw-more(size)-| state= S-Extensions
|-SEND(size)------------------->|
Server |<--------Packet||sw-more(size)-|
Hello | |
|-SEND(size)------------------->| Make-Extensions
Server |<--------Packet||sw-more(size)-| state= S-SFinished
Encrypted | |
Extension |-SEND(size)------------------->|
| | Make-ServerFinished
Server |<----------------Packet||sw-ok-| state= S-ClientCCS
Finished | |
| |
ClientCCS |-RECV(F-First,F-Last,Packet)-->| Check-Client, Check CCS
|<------------------------sw-ok-| state= S-CFinished
| |
| |
Client |-RECV(F-First,F-Last,Packet)->-| Check-CFinished
Finished |<----------------------sw-open-| state= S-Open
| |
Packet |-RECV(F-Decrypt,Packet)------->| Decrypt Packet
|<----------------sw-more(size)-| Clear Form Message
|-SEND(size)------------------->|
|<------ -Message||ptcol||sw-ok-|
| |
Message |-RECV(F-Encrypt,Message)------>| Encrypt
|<----------------sw-more(size)-| Record Packet
|-SEND(size)------------------->|
|<------ -Record Packet ||sw-ok-|
| |
Figure 9. TLS-SE server with pre-share key state machine
3.4 TLS library
The TLS-SE library is a set of procedures that check, according to
the state machine, incoming record packets and build outgoing record
packets. In figure 9 the TLS library comprises the following
elements: Check-ClientHello, Check-ClientCCS, Check-ClientFinished,
Make-ServerHello, Make-EncryptedExensions, and MakeServerFinished.
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4 ISO7816 interface
The RECV and SEND binary encoding is shown by figure 10
+------+-----+-----+-------------+-----------+----------+---------+
+ name | CLA | INS | P1 | P2 | P3 | Payload |
+------+-----+-----+-------------+-----------+----------+---------+
| RECV | 00 | D8 | 01= Decrypt | 01= First | Fragment | |
| | | 02= Encrypt | 02= Last | Length | Yes |
| | | | | | 0= RESET | |
+------+-----+-----+-------------+-----------+----------+---------+
| SEND | 00 | C0 | 00 | 00 | Incoming | No |
| | | | | | Length | |
+------+-----+-----+-------------+-----------+----------+---------+
Figure 10. RECV and SEND ISO7816 requests binary encoding
The status word binary encoding is shown by figure 11. Two binary
encoding of sw-more MUST be supported. In the T=0 context, SE
operating system returns the 61xy status when a request including a
payload, induces a response with a payload. The status 9Fxy is
managed by the application in order to notify response size to be
returned. The TLS-SE application MAY use 61xy status, but this could
induce interoperability issues.
+----------------+-----+------+
| name | SW1 | SW2 |
+----------------+-----+------+
| sw-ok | 90 | 00 |
+----------------+-----+------+
| sw-more(size) | 61 | size |
| | 9F | size |
+----------------+-----+------+
| sw-retry(size) | 6C + size |
+----------------+-----+------+
| sw-open | 90 | 01 |
+----------------+-----+------+
| sw-close | 90 | 02 |
+----------------+-----+------+
| sw-error | 6D |error |
| | 6F |number|
+----------------+-----+------+
Figure 11. ISO7816 status word binary encoding
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5 ISO 7816 Use Case
Below is an illustration of TLS-SE server, using a pre-shared key
(PSK) with DHE over the secp256r1 curve, and the cipher suite AES-
128-CCM-SHA256. The time consumed by handshake is about 1.4s.
PSK=
0102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20
DHE=
037E6E633541EC03DB700A28E7DABB74F8E84D4A28E5F024B46F468A7821305D
RECV(Client Hello)
Tx: 00 D8 00 01 F0 16 03 03 00 F2 01 00 00 EE 03 03
4E 65 53 05 52 AB 3E 83 14 0B 2F 9C 2F D7 BC 16
F9 F5 C4 A9 86 CA 3F C8 8C 6E 8C D1 10 BB B1 57
00 00 02 13 04 01 00 00 C3 00 2D 00 03 02 00 01
00 2B 00 03 02 03 04 00 0D 00 1E 00 1C 06 03 05
03 04 03 02 03 08 06 08 0B 08 05 08 0A 08 04 08
09 06 01 05 01 04 01 02 01 00 33 00 47 00 45 00
17 00 41 04 9A 1E 0A D8 40 88 D4 21 D1 55 D7 F2
8F 78 4C 28 75 F5 19 CA 12 71 96 92 C4 07 8F B4
35 42 57 E7 64 24 C1 BC 5D 89 0E F4 08 FD 25 8D
24 F4 64 BB C3 F4 80 D3 BF 2C 23 A0 F9 2D A7 88
0C 5B 44 53 00 0A 00 06 00 04 00 18 00 17 00 29
00 3A 00 15 00 0F 43 6C 69 65 6E 74 5F 69 64 65
6E 74 69 74 79 00 00 00 00 00 21 20 CC 05 4A 9F
DE 70 E9 96 D6 01 69 61 F5 9A 78 20 D9 FC 6D ED
4C C6 0A 7B 0D
Rx: 90 00 [47 ms]
Tx: 00 D8 00 02 07 4B 68 8F 4E B9 B2 CA
Rx: 61 86 [879 ms]
SEND(Server Hello)
Tx: 00 C0 00 00 86
Rx: 16 03 03 00 81 02 00 00 7D 03 03 5C 78 A4 E1 93
34 D7 D9 64 B2 85 64 1B E4 76 63 94 39 1F 4A 15
27 0A A4 C6 A0 C6 93 D9 E2 16 4D 00 13 04 00 00
55 00 29 00 02 00 00 00 33 00 45 00 17 00 41 04
25 C9 16 94 8B 39 51 D2 8E 88 70 F7 F5 4E 6C 31
62 93 B1 65 55 2C 30 B2 5E 75 6C D8 FE AF DA A7
67 D8 AD A7 BE 68 54 EA 3E A0 0B 4D CC 62 93 96
38 07 68 29 3E D5 E6 0C 25 4A EA 12 C9 F8 99 7F
00 2B 00 02 03 04 9F 1C [32 ms]
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SEND(Server Encrypted Extensions)
Tx: 00 C0 00 00 1C
Rx: 17 03 03 00 17 E6 04 4A 52 1A 50 B5 54 D8 73 5E
00 F4 FD 66 BB B3 74 50 99 36 C8 08 9F 3A [78 ms]
SEND(Server Encrypted Finished)
Tx: 00 C0 00 00 3A
Rx: 17 03 03 00 35 CB CA 03 3E E4 34 7E D2 0C 7C 24
C1 8F 39 A2 74 39 24 47 78 BE 94 95 7A 31 EC 03
D5 0C A8 1C 46 04 05 F2 83 3E 99 0D AD D6 66 63
60 23 F8 5D 7B 77 0F 95 18 35 90 00 [185 ms]
RECV(Client Encrypted Finished)
Tx: 00 D8 00 03 3A 17 03 03 00 35 BC 29 18 D1 B8 4B
C0 3F 6F 81 79 D9 7E FD 58 E3 76 EA 61 13 9C 3E
40 0F 34 CD 94 CE C1 44 CB 76 70 7D DA 8A 54 69
41 D9 80 CD 5D 52 8F E5 38 D8 52 92 20 54 5E
Rx: 90 01 [389 ms]
TLS13 session is open
Decryption of incoming Record Packet
RECV(Decrypt, Packet)
Tx: 00 D8 01 03 24 17 03 03 00 1F 56 E2 D5 B5 C4 A6
E2 3E 54 56 5A C4 2D E9 99 F3 58 22 34 15 15 A7
96 FD 0E B0 61 60 4C 52 87
Rx: 61 0F [78 ms]
SEND(Message)
Tx: 00 C0 00 00 0F
Rx: 68 65 6C 6C 6F 20 77 6F 72 6C 64 21 0D 0A 17 90
00 [15 ms]
Rx: hello world! ptcol=17
Encryption of message
RECV(Encrypt,Message)
Tx: 00 D8 02 03 0F 68 65 6C 6C 6F 20 77 6F 72 6C 64
21 0D 0A 17
Rx: 61 24 [79 ms]
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SEND(Record Packet)
Tx: 00 C0 00 00 24
Rx: 17 03 03 00 1F 6F 78 FF 68 0F CA 9E 31 53 2C 96
B3 FA D7 B0 51 1B 92 81 35 3D DB FE E9 18 A7 DF
36 2F A5 27 90 00 [16 ms]
5 IANA Considerations
TODO
6 Security Considerations
TODO
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.
[ISO7816] ISO 7816, "Cards Identification - Integrated Circuit Cards
with Contacts", The International Organization for Standardization
(ISO).
[IEEE1363] IEEE, "IEEE Standard Specifications for Public Key
Cryptography", IEEE Std. 1363-2000, DOI 10.1109/IEEESTD.2000.92292.
7.2 Informative References
[IM] Urien, P., "Identity Module for TLS Version 1.3", draft-urien-
tls-im-03.txt, July 2020.
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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