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. . Urien Expires March 2021 [Page 1] 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. Urien Expires March 2021 [page 2] 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 Urien Expires March 2021 [Page 3] Secure Element for TLS Version 1.3 September 2020 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 Urien Expires March 2021 [Page 4] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 5] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 6] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 7] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 8] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 9] Secure Element for TLS Version 1.3 September 2020 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. Urien Expires March 2021 [Page 10] Secure Element for TLS Version 1.3 September 2020 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 Urien Expires March 2021 [Page 11] Secure Element for TLS Version 1.3 September 2020 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] Urien Expires March 2021 [Page 12] Secure Element for TLS Version 1.3 September 2020 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] Urien Expires March 2021 [Page 13] Secure Element for TLS Version 1.3 September 2020 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 Urien Expires March 2021 [Page 14]