LWIG Working Group J. Mattsson Internet-Draft F. Palombini Intended status: Informational Ericsson AB Expires: September 12, 2019 March 11, 2019 Comparison of CoAP Security Protocols draft-ietf-lwig-security-protocol-comparison-03 Abstract This document analyzes and compares the sizes of key exchange flights and the per-packet message size overheads when using different security protocols to secure CoAP. The analyzed security protocols are DTLS 1.2, DTLS 1.3, TLS 1.2, TLS 1.3, EDHOC, OSCORE, and Group OSCORE. The DTLS and TLS record layers are analyzed with and without 6LoWPAN-GHC compression. DTLS is analyzed with and without Connection ID. 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 September 12, 2019. 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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Mattsson & Palombini Expires September 12, 2019 [Page 1]
Internet-Draft Comparison of CoAP Security Protocols March 2019 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overhead of Key Exchange Protocols . . . . . . . . . . . . . 3 2.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.1. Message Sizes RPK + ECDHE . . . . . . . . . . . . . . 5 2.2.2. Message Sizes PSK + ECDHE . . . . . . . . . . . . . . 10 2.2.3. Message Sizes PSK . . . . . . . . . . . . . . . . . . 11 2.2.4. Cached Information . . . . . . . . . . . . . . . . . 12 2.2.5. Resumption . . . . . . . . . . . . . . . . . . . . . 13 2.2.6. Without Connection ID . . . . . . . . . . . . . . . . 14 2.2.7. DTLS Raw Public Keys . . . . . . . . . . . . . . . . 15 2.3. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3.1. Message Sizes RPK + ECDHE . . . . . . . . . . . . . . 16 2.3.2. Message Sizes PSK + ECDHE . . . . . . . . . . . . . . 22 2.3.3. Message Sizes PSK . . . . . . . . . . . . . . . . . . 23 2.4. EDHOC . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.4.1. Message Sizes RPK . . . . . . . . . . . . . . . . . . 24 2.4.2. Message Sizes Certificates . . . . . . . . . . . . . 26 2.4.3. Message Sizes PSK . . . . . . . . . . . . . . . . . . 26 2.4.4. message_1 . . . . . . . . . . . . . . . . . . . . . . 26 2.4.5. message_2 . . . . . . . . . . . . . . . . . . . . . . 26 2.4.6. message_3 . . . . . . . . . . . . . . . . . . . . . . 27 2.4.7. Summary . . . . . . . . . . . . . . . . . . . . . . . 27 2.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . 27 3. Overhead for Protection of Application Data . . . . . . . . . 28 3.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.2. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . 30 3.2.1. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . 30 3.2.2. DTLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 30 3.2.3. DTLS 1.2 with Connection ID . . . . . . . . . . . . . 31 3.2.4. DTLS 1.2 with Connection ID and 6LoWPAN-GHC . . . . . 32 3.3. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . 32 3.3.1. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . 32 3.3.2. DTLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 33 3.3.3. DTLS 1.3 with Connection ID . . . . . . . . . . . . . 33 3.3.4. DTLS 1.3 with Connection ID and 6LoWPAN-GHC . . . . . 34 3.4. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.4.1. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . 34 3.4.2. TLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 35 3.5. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.5.1. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . 35 3.5.2. TLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 36 3.6. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 36 Mattsson & Palombini Expires September 12, 2019 [Page 2]
Internet-Draft Comparison of CoAP Security Protocols March 2019 3.7. Group OSCORE . . . . . . . . . . . . . . . . . . . . . . 38 3.8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . 38 4. Security Considerations . . . . . . . . . . . . . . . . . . . 39 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 6. Informative References . . . . . . . . . . . . . . . . . . . 39 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 1. Introduction This document analyzes and compares the sizes of key exchange flights and the per-packet message size overheads when using different security protocols to secure CoAP over UPD [RFC7252] and TCP [RFC8323]. The analyzed security protocols are DTLS 1.2 [RFC6347], DTLS 1.3 [I-D.ietf-tls-dtls13], TLS 1.2 [RFC5246], TLS 1.3 [RFC8446], EDHOC [I-D.selander-ace-cose-ecdhe], OSCORE [I-D.ietf-core-object-security], and Group OSCORE [I-D.ietf-core-oscore-groupcomm]. The DTLS and TLS record layers are analyzed with and without 6LoWPAN- GHC compression. DTLS is anlyzed with and without Connection ID [I-D.ietf-tls-dtls-connection-id]. Readers are expected to be familiar with some of the terms described in RFC 7925 [RFC7925], such as ICV. Section 2 compares the overhead of key exchange, while Section 3 covers the overhead for protection of application data. 2. Overhead of Key Exchange Protocols This section analyzes and compares the sizes of key exchange flights for different protocols. To enable a fair comparison between protocols, the following assumptions are made: o All the overhead calculations in this section use AES-CCM with a tag length of 8 bytes (e.g. AES_128_CCM_8 or AES-CCM-16-64-128). o A minimum number of algorithms and cipher suites is offered. The algorithm used/offered are Curve25519, ECDSA with P-256, AES- CCM_8, SHA-256. o The length of key identifiers are 1 byte. o The length of connection identifiers are 1 byte. o DTLS RPK makes use of point compression, which saves 32 bytes. o DTLS handshake message fragmentation is not considered. Mattsson & Palombini Expires September 12, 2019 [Page 3]
Internet-Draft Comparison of CoAP Security Protocols March 2019 o Only the DTLS mandatory extensions are considered, except for Connection ID. Section 2.1 gives a short summary of the message overhead based on different parameters and some assumptions. The following sections detail the assumptions and the calculations. 2.1. Summary The DTLS overhead is dependent on the parameter Connection ID. The following overheads apply for all Connection IDs of the same length, when Connection ID is used. The EDHOC overhead is dependent on the key identifiers included. The following overheads apply for Sender IDs of the same length. All the overhead are dependent on the tag length. The following overheads apply for tags of the same length. Figure 1 compares the message sizes of EDHOC [I-D.selander-ace-cose-ecdhe] with the DTLS 1.3 [I-D.ietf-tls-dtls13] and TLS 1.3 [RFC8446] handshakes with connection ID. ===================================================================== Flight #1 #2 #3 Total --------------------------------------------------------------------- DTLS 1.3 RPK + ECDHE 150 373 213 736 DTLS 1.3 Cached X.509/RPK + ECDHE 182 347 213 742 DTLS 1.3 PSK + ECDHE 184 190 57 431 DTLS 1.3 PSK 134 150 57 341 --------------------------------------------------------------------- EDHOC RPK + ECDHE 39 114 80 233 EDHOC PSK + ECDHE 41 45 11 97 ===================================================================== Figure 1: Comparison of message sizes in bytes with Connection ID Figure 2 compares of message sizes of DTLS 1.3 [I-D.ietf-tls-dtls13] and TLS 1.3 [RFC8446] handshakes without connection ID. Mattsson & Palombini Expires September 12, 2019 [Page 4]
Internet-Draft Comparison of CoAP Security Protocols March 2019 ===================================================================== Flight #1 #2 #3 Total --------------------------------------------------------------------- DTLS 1.3 RPK + ECDHE 144 364 212 722 DTLS 1.3 PSK + ECDHE 178 183 56 417 DTLS 1.3 PSK 128 143 56 327 --------------------------------------------------------------------- TLS 1.3 RPK + ECDHE 129 322 194 645 TLS 1.3 PSK + ECDHE 163 157 50 370 TLS 1.3 PSK 113 117 50 280 ===================================================================== Figure 2: Comparison of message sizes in bytes without Connection ID The details of the message size calculations are given in the following sections. 2.2. DTLS 1.3 This section gives an estimate of the message sizes of DTLS 1.3 with different authentication methods. Note that the examples in this section are not test vectors, the cryptographic parts are just replaced with byte strings of the same length, while other fixed length fields are replace with arbitrary strings or omitted, in which case their length is indicated. Values that are not arbitrary are given in hexadecimal. 2.2.1. Message Sizes RPK + ECDHE In this section, a Connection ID of 1 byte is used. 2.2.1.1. flight_1 Record Header - DTLSPlaintext (13 bytes): 16 fe fd EE EE SS SS SS SS SS SS LL LL Handshake Header - Client Hello (10 bytes): 01 LL LL LL SS SS 00 00 00 LL LL LL Legacy Version (2 bytes): fe fd Client Random (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Legacy Session ID (1 bytes): 00 Mattsson & Palombini Expires September 12, 2019 [Page 5]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Legacy Cookie (1 bytes): 00 Cipher Suites (TLS_AES_128_CCM_8_SHA256) (4 bytes): 00 02 13 05 Compression Methods (null) (2 bytes): 01 00 Extensions Length (2 bytes): LL LL Extension - Supported Groups (x25519) (8 bytes): 00 0a 00 04 00 02 00 1d Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes): 00 0d 00 04 00 02 08 07 Extension - Key Share (42 bytes): 00 33 00 26 00 24 00 1d 00 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Extension - Supported Versions (1.3) (7 bytes): 00 2b 00 03 02 03 04 Extension - Client Certificate Type (Raw Public Key) (6 bytes): 00 13 00 01 01 02 Extension - Server Certificate Type (Raw Public Key) (6 bytes): 00 14 00 01 01 02 Extension - Connection Identifier (43) (6 bytes): XX XX 00 02 01 42 13 + 10 + 2 + 32 + 1 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 + 6 = 150 bytes DTLS 1.3 RPK + ECDHE flight_1 gives 150 bytes of overhead. 2.2.1.2. flight_2 Record Header - DTLSPlaintext (13 bytes): 16 fe fd EE EE SS SS SS SS SS SS LL LL Handshake Header - Server Hello (10 bytes): 02 LL LL LL SS SS 00 00 00 LL LL LL Mattsson & Palombini Expires September 12, 2019 [Page 6]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Legacy Version (2 bytes): fe fd Server Random (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Legacy Session ID (1 bytes): 00 Cipher Suite (TLS_AES_128_CCM_8_SHA256) (2 bytes): 13 05 Compression Method (null) (1 bytes): 00 Extensions Length (2 bytes): LL LL Extension - Key Share (40 bytes): 00 33 00 24 00 1d 00 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Extension - Supported Versions (1.3) (6 bytes): 00 2b 00 02 03 04 Extension - Connection Identifier (43) (6 bytes): XX XX 00 02 01 43 Record Header - DTLSCiphertext, Full (6 bytes): HH ES SS 43 LL LL Handshake Header - Encrypted Extensions (10 bytes): 08 LL LL LL SS SS 00 00 00 LL LL LL Extensions Length (2 bytes): LL LL Extension - Client Certificate Type (Raw Public Key) (6 bytes): 00 13 00 01 01 02 Extension - Server Certificate Type (Raw Public Key) (6 bytes): 00 14 00 01 01 02 Handshake Header - Certificate Request (10 bytes): 0d LL LL LL SS SS 00 00 00 LL LL LL Mattsson & Palombini Expires September 12, 2019 [Page 7]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Request Context (1 bytes): 00 Extensions Length (2 bytes): LL LL Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes): 00 0d 00 04 00 02 08 07 Handshake Header - Certificate (10 bytes): 0b LL LL LL SS SS 00 00 00 LL LL LL Request Context (1 bytes): 00 Certificate List Length (3 bytes): LL LL LL Certificate Length (3 bytes): LL LL LL Certificate (59 bytes) // Point compression .... Certificate Extensions (2 bytes): 00 00 Handshake Header - Certificate Verify (10 bytes): 0f LL LL LL SS SS 00 00 00 LL LL LL Signature (68 bytes): ZZ ZZ 00 40 .... Handshake Header - Finished (10 bytes): 14 LL LL LL SS SS 00 00 00 LL LL LL Verify Data (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Record Type (1 byte): 16 Auth Tag (8 bytes): e0 8b 0e 45 5a 35 0a e5 13 + 102 + 6 + 24 + 21 + 78 + 78 + 42 + 1 + 8 = 373 bytes Mattsson & Palombini Expires September 12, 2019 [Page 8]
Internet-Draft Comparison of CoAP Security Protocols March 2019 DTLS 1.3 RPK + ECDHE flight_2 gives 373 bytes of overhead. 2.2.1.3. flight_3 Record Header (6 bytes) // DTLSCiphertext, Full: ZZ ES SS 42 LL LL Handshake Header - Certificate (10 bytes): 0b LL LL LL SS SS XX XX XX LL LL LL Request Context (1 bytes): 00 Certificate List Length (3 bytes): LL LL LL Certificate Length (3 bytes): LL LL LL Certificate (59 bytes) // Point compression .... Certificate Extensions (2 bytes): 00 00 Handshake Header - Certificate Verify (10 bytes): 0f LL LL LL SS SS 00 00 00 LL LL LL Signature (68 bytes): 04 03 LL LL //ecdsa_secp256r1_sha256 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Handshake Header - Finished (10 bytes): 14 LL LL LL SS SS 00 00 00 LL LL LL Verify Data (32 bytes) // SHA-256: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Record Type (1 byte): 16 Auth Tag (8 bytes) // AES-CCM_8: 00 01 02 03 04 05 06 07 6 + 78 + 78 + 42 + 1 + 8 = 213 bytes Mattsson & Palombini Expires September 12, 2019 [Page 9]
Internet-Draft Comparison of CoAP Security Protocols March 2019 DTLS 1.3 RPK + ECDHE flight_2 gives 213 bytes of overhead. 2.2.2. Message Sizes PSK + ECDHE 2.2.2.1. flight_1 The differences in overhead compared to Section 2.2.1.1 are: The following is added: + Extension - PSK Key Exchange Modes (6 bytes): 00 2d 00 02 01 01 + Extension - Pre Shared Key (48 bytes): 00 29 00 2F 00 0a 00 01 ID 00 00 00 00 00 21 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f The following is removed: - Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes) - Extension - Client Certificate Type (Raw Public Key) (6 bytes) - Extension - Server Certificate Type (Raw Public Key) (6 bytes) In total: 150 + 6 + 48 - 8 - 6 - 6 = 184 bytes DTLS 1.3 PSK + ECDHE flight_1 gives 184 bytes of overhead. 2.2.2.2. flight_2 The differences in overhead compared to Section 2.2.1.2 are: The following is added: + Extension - Pre Shared Key (6 bytes) 00 29 00 02 00 00 The following is removed: Mattsson & Palombini Expires September 12, 2019 [Page 10]
Internet-Draft Comparison of CoAP Security Protocols March 2019 - Handshake Message Certificate (78 bytes) - Handshake Message CertificateVerify (78 bytes) - Handshake Message CertificateRequest (21 bytes) - Extension - Client Certificate Type (Raw Public Key) (6 bytes) - Extension - Server Certificate Type (Raw Public Key) (6 bytes) In total: 373 - 78 - 78 - 21 - 6 - 6 + 6 = 190 bytes DTLS 1.3 PSK + ECDHE flight_2 gives 190 bytes of overhead. 2.2.2.3. flight_3 The differences in overhead compared to Section 2.2.1.3 are: The following is removed: - Handshake Message Certificate (78 bytes) - Handshake Message Certificate Verify (78 bytes) In total: 213 - 78 - 78 = 57 bytes DTLS 1.3 PSK + ECDHE flight_3 gives 57 bytes of overhead. 2.2.3. Message Sizes PSK 2.2.3.1. flight_1 The differences in overhead compared to Section 2.2.2.1 are: The following is removed: - Extension - Supported Groups (x25519) (8 bytes) - Extension - Key Share (42 bytes) In total: 184 - 8 - 42 = 134 bytes Mattsson & Palombini Expires September 12, 2019 [Page 11]
Internet-Draft Comparison of CoAP Security Protocols March 2019 DTLS 1.3 PSK flight_1 gives 134 bytes of overhead. 2.2.3.2. flight_2 The differences in overhead compared to Section 2.2.2.2 are: The following is removed: - Extension - Key Share (40 bytes) In total: 190 - 40 = 150 bytes DTLS 1.3 PSK flight_2 gives 150 bytes of overhead. 2.2.3.3. flight_3 There are no differences in overhead compared to Section 2.2.2.3. DTLS 1.3 PSK flight_3 gives 57 bytes of overhead. 2.2.4. Cached Information In this section, we consider the effect of [RFC7924] on the message size overhead. Cached information together with server X.509 can be used to move bytes from flight #2 to flight #1 (cached RPK increases the number of bytes compared to cached X.509). The differences compared to Section 2.2.1 are the following. For the flight #1, the following is added: + Extension - Client Cashed Information (39 bytes): 00 19 LL LL LL LL 01 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f And the following is removed: - Extension - Server Certificate Type (Raw Public Key) (6 bytes) Giving a total of: 150 + 33 = 183 bytes Mattsson & Palombini Expires September 12, 2019 [Page 12]
Internet-Draft Comparison of CoAP Security Protocols March 2019 For the flight #2, the following is added: + Extension - Server Cashed Information (7 bytes): 00 19 LL LL LL LL 01 And the following is removed: - Extension - Server Certificate Type (Raw Public Key) (6 bytes) - Server Certificate (59 bytes -> 32 bytes) Giving a total of: 373 - 26 = 347 bytes A summary of the calculation is given in Figure 3. ====================================================================== Flight #1 #2 #3 Total ---------------------------------------------------------------------- DTLS 1.3 Cached X.509/RPK + ECDHE 183 347 213 743 DTLS 1.3 RPK + ECDHE 150 373 213 736 ======================================================================= Figure 3: Comparison of message sizes in bytes for DTLS 1.3 RPK + ECDH with and without cached X.509 2.2.5. Resumption To enable resumption, a 4th flight (New Session Ticket) is added to the PSK handshake. Mattsson & Palombini Expires September 12, 2019 [Page 13]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Record Header - DTLSCiphertext, Full (6 bytes): HH ES SS 43 LL LL Handshake Header - New Session Ticket (10 bytes): 04 LL LL LL SS SS 00 00 00 LL LL LL Ticket Lifetime (4 bytes): 00 01 02 03 Ticket Age Add (4 bytes): 00 01 02 03 Ticket Nonce (2 bytes): 01 00 Ticket (6 bytes): 00 04 ID ID ID ID Extensions (2 bytes): 00 00 Auth Tag (8 bytes) // AES-CCM_8: 00 01 02 03 04 05 06 07 6 + 10 + 4 + 4 + 2 + 6 + 2 + 8 = 42 bytes The initial handshake when resumption is enabled is just a PSK handshake with 134 + 150 + 57 + 42 = 383 bytes. 2.2.6. Without Connection ID Without a Connection ID the DTLS 1.3 flight sizes changes as follows. DTLS 1.3 Flight #1: -6 bytes DTLS 1.3 Flight #2: -7 bytes DTLS 1.3 Flight #3: -1 byte ======================================================================= Flight #1 #2 #3 Total ----------------------------------------------------------------------- DTLS 1.3 RPK + ECDHE (no cid) 144 364 212 722 DTLS 1.3 PSK + ECDHE (no cid) 178 183 56 417 DTLS 1.3 PSK (no cid) 128 143 56 327 ======================================================================= Figure 4: Comparison of message sizes in bytes for DTLS 1.3 without Connection ID Mattsson & Palombini Expires September 12, 2019 [Page 14]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.2.7. DTLS Raw Public Keys TODO 2.2.7.1. SubjectPublicKeyInfo without point compression 0x30 // Sequence 0x59 // Size 89 0x30 // Sequence 0x13 // Size 19 0x06 0x07 0x2A 0x86 0x48 0xCE 0x3D 0x02 0x01 // OID 1.2.840.10045.2.1 (ecPublicKey) 0x06 0x08 0x2A 0x86 0x48 0xCE 0x3D 0x03 0x01 0x07 // OID 1.2.840.10045.3.1.7 (secp256r1) 0x03 // Bit string 0x42 // Size 66 0x00 // Unused bits 0 0x04 // Uncompressed ...... 64 bytes X and Y Total of 91 bytes 2.2.7.2. SubjectPublicKeyInfo with point compression 0x30 // Sequence 0x59 // Size 89 0x30 // Sequence 0x13 // Size 19 0x06 0x07 0x2A 0x86 0x48 0xCE 0x3D 0x02 0x01 // OID 1.2.840.10045.2.1 (ecPublicKey) 0x06 0x08 0x2A 0x86 0x48 0xCE 0x3D 0x03 0x01 0x07 // OID 1.2.840.10045.3.1.7 (secp256r1) 0x03 // Bit string 0x42 // Size 66 0x00 // Unused bits 0 0x03 // Compressed ...... 32 bytes X Total of 59 bytes Mattsson & Palombini Expires September 12, 2019 [Page 15]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.3. TLS 1.3 In this section, the message sizes are calculated for TLS 1.3. The major changes compared to DTLS 1.3 are that the record header is smaller, the handshake headers is smaller, and that Connection ID is not supported. Recently, additional work has taken shape with the goal to further reduce overhead for TLS 1.3 (see [I-D.schaad-ace-tls-cbor-handshake] ). TLS Assumptions: o Minimum number of algorithms and cipher suites offered o Curve25519, ECDSA with P-256, AES-CCM_8, SHA-256 o Length of key identifiers: 1 bytes o TLS RPK with point compression (saves 32 bytes) o Only mandatory TLS extensions For the PSK calculations, [Ulfheim-TLS13] was a useful resource, while for RPK calculations we followed the work of [IoT-Cert]. 2.3.1. Message Sizes RPK + ECDHE 2.3.1.1. flight_1 Mattsson & Palombini Expires September 12, 2019 [Page 16]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Record Header - TLSPlaintext (5 bytes): 16 03 03 LL LL Handshake Header - Client Hello (4 bytes): 01 LL LL LL Legacy Version (2 bytes): 03 03 Client Random (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Legacy Session ID (1 bytes): 00 Cipher Suites (TLS_AES_128_CCM_8_SHA256) (4 bytes): 00 02 13 05 Compression Methods (null) (2 bytes): 01 00 Extensions Length (2 bytes): LL LL Extension - Supported Groups (x25519) (8 bytes): 00 0a 00 04 00 02 00 1d Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes): 00 0d 00 04 00 02 08 07 Extension - Key Share (42 bytes): 00 33 00 26 00 24 00 1d 00 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Extension - Supported Versions (1.3) (7 bytes): 00 2b 00 03 02 03 04 Extension - Client Certificate Type (Raw Public Key) (6 bytes): 00 13 00 01 01 02 Extension - Server Certificate Type (Raw Public Key) (6 bytes): 00 14 00 01 01 02 5 + 4 + 2 + 32 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 = 129 bytes TLS 1.3 RPK + ECDHE flight_1 gives 129 bytes of overhead. Mattsson & Palombini Expires September 12, 2019 [Page 17]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.3.1.2. flight_2 Record Header - TLSPlaintext (5 bytes): 16 03 03 LL LL Handshake Header - Server Hello (4 bytes): 02 LL LL LL Legacy Version (2 bytes): fe fd Server Random (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Legacy Session ID (1 bytes): 00 Cipher Suite (TLS_AES_128_CCM_8_SHA256) (2 bytes): 13 05 Compression Method (null) (1 bytes): 00 Extensions Length (2 bytes): LL LL Extension - Key Share (40 bytes): 00 33 00 24 00 1d 00 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Extension - Supported Versions (1.3) (6 bytes): 00 2b 00 02 03 04 Record Header - TLSCiphertext (5 bytes): 17 03 03 LL LL Handshake Header - Encrypted Extensions (4 bytes): 08 LL LL LL Extensions Length (2 bytes): LL LL Extension - Client Certificate Type (Raw Public Key) (6 bytes): 00 13 00 01 01 02 Extension - Server Certificate Type (Raw Public Key) (6 bytes): Mattsson & Palombini Expires September 12, 2019 [Page 18]
Internet-Draft Comparison of CoAP Security Protocols March 2019 00 14 00 01 01 02 Handshake Header - Certificate Request (4 bytes): 0d LL LL LL Request Context (1 bytes): 00 Extensions Length (2 bytes): LL LL Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes): 00 0d 00 04 00 02 08 07 Handshake Header - Certificate (4 bytes): 0b LL LL LL Request Context (1 bytes): 00 Certificate List Length (3 bytes): LL LL LL Certificate Length (3 bytes): LL LL LL Certificate (59 bytes) // Point compression .... Certificate Extensions (2 bytes): 00 00 Handshake Header - Certificate Verify (4 bytes): 0f LL LL LL Signature (68 bytes): ZZ ZZ 00 40 .... Handshake Header - Finished (4 bytes): 14 LL LL LL Verify Data (32 bytes): 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Record Type (1 byte): 16 Mattsson & Palombini Expires September 12, 2019 [Page 19]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Auth Tag (8 bytes): e0 8b 0e 45 5a 35 0a e5 5 + 90 + 5 + 18 + 15 + 72 + 72 + 36 + 1 + 8 = 322 bytes TLS 1.3 RPK + ECDHE flight_2 gives 322 bytes of overhead. 2.3.1.3. flight_3 Mattsson & Palombini Expires September 12, 2019 [Page 20]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Record Header - TLSCiphertext (5 bytes): 17 03 03 LL LL Handshake Header - Certificate (4 bytes): 0b LL LL LL Request Context (1 bytes): 00 Certificate List Length (3 bytes): LL LL LL Certificate Length (3 bytes): LL LL LL Certificate (59 bytes) // Point compression .... Certificate Extensions (2 bytes): 00 00 Handshake Header - Certificate Verify (4 bytes): 0f LL LL LL Signature (68 bytes): 04 03 LL LL //ecdsa_secp256r1_sha256 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Handshake Header - Finished (4 bytes): 14 LL LL LL Verify Data (32 bytes) // SHA-256: 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f Record Type (1 byte) 16 Auth Tag (8 bytes) // AES-CCM_8: 00 01 02 03 04 05 06 07 5 + 72 + 72 + 36 + 1 + 8 = 194 bytes TLS 1.3 RPK + ECDHE flight_3 gives 194 bytes of overhead. Mattsson & Palombini Expires September 12, 2019 [Page 21]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.3.2. Message Sizes PSK + ECDHE 2.3.2.1. flight_1 The differences in overhead compared to Section 2.3.1.3 are: The following is added: + Extension - PSK Key Exchange Modes (6 bytes): 00 2d 00 02 01 01 + Extension - Pre Shared Key (48 bytes): 00 29 00 2F 00 0a 00 01 ID 00 00 00 00 00 21 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f The following is removed: - Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes) - Extension - Client Certificate Type (Raw Public Key) (6 bytes) - Extension - Server Certificate Type (Raw Public Key) (6 bytes) In total: 129 + 6 + 48 - 8 - 6 - 6 = 163 bytes TLS 1.3 PSK + ECDHE flight_1 gives 166 bytes of overhead. 2.3.2.2. flight_2 The differences in overhead compared to Section 2.3.1.2 are: The following is added: + Extension - Pre Shared Key (6 bytes) 00 29 00 02 00 00 The following is removed: Mattsson & Palombini Expires September 12, 2019 [Page 22]
Internet-Draft Comparison of CoAP Security Protocols March 2019 - Handshake Message Certificate (72 bytes) - Handshake Message CertificateVerify (72 bytes) - Handshake Message CertificateRequest (15 bytes) - Extension - Client Certificate Type (Raw Public Key) (6 bytes) - Extension - Server Certificate Type (Raw Public Key) (6 bytes) In total: 322 - 72 - 72 - 15 - 6 - 6 + 6 = 157 bytes TLS 1.3 PSK + ECDHE flight_2 gives 157 bytes of overhead. 2.3.2.3. flight_3 The differences in overhead compared to Section 2.3.1.3 are: The following is removed: - Handshake Message Certificate (72 bytes) - Handshake Message Certificate Verify (72 bytes) In total: 194 - 72 - 72 = 50 bytes TLS 1.3 PSK + ECDHE flight_3 gives 50 bytes of overhead. 2.3.3. Message Sizes PSK 2.3.3.1. flight_1 The differences in overhead compared to Section 2.3.2.1 are: The following is removed: - Extension - Supported Groups (x25519) (8 bytes) - Extension - Key Share (42 bytes) In total: 163 - 8 - 42 = 113 bytes Mattsson & Palombini Expires September 12, 2019 [Page 23]
Internet-Draft Comparison of CoAP Security Protocols March 2019 TLS 1.3 PSK flight_1 gives 116 bytes of overhead. 2.3.3.2. flight_2 The differences in overhead compared to Section 2.3.2.2 are: The following is removed: - Extension - Key Share (40 bytes) In total: 157 - 40 = 117 bytes TLS 1.3 PSK flight_2 gives 117 bytes of overhead. 2.3.3.3. flight_3 There are no differences in overhead compared to Section 2.3.2.3. TLS 1.3 PSK flight_3 gives 57 bytes of overhead. 2.4. EDHOC This section gives an estimate of the message sizes of EDHOC with different authentication methods. Note that the examples in this section are not test vectors, the cryptographic parts are just replaced with byte strings of the same length. All examples are given in CBOR diagnostic notation and hexadecimal. 2.4.1. Message Sizes RPK 2.4.1.1. message_1 message_1 = ( 1, 0, h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f', h'c3' ) message_1 (38 bytes): 01 00 58 20 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 41 C3 Mattsson & Palombini Expires September 12, 2019 [Page 24]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.4.1.2. message_2 plaintext = << h'a1', h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b 3c3d3e3f' >> The header map { 4 : h'a1' } is encoded as the two bytes h'a1'. The length of plaintext is 68 bytes so assuming a 64-bit MAC value the length of ciphertext is 76 bytes. message_2 = ( h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f', h'c4', h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b 3c3d3e3f404142434445464748494a4b' ) message_2 (114 bytes): 58 20 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 41 C4 58 51 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B 2.4.1.3. message_3 The plaintext and ciphertext in message_3 are assumed to be of equal sizes as in message_2. message_3 = ( h'c4', h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b 3c3d3e3f404142434445464748494a4b' ) message_3 (80 bytes): 41 C4 58 51 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B Mattsson & Palombini Expires September 12, 2019 [Page 25]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.4.2. Message Sizes Certificates When the certificates are distributed out-of-band and identified with the x5t header parameter and a SHA256/64 hash value, the header map will be 13 bytes (assuming labels in the range -24...23). { TDB1 : [ TDB6, h'0001020304050607' ] } When the certificates are identified with the x5chain header parameter, the message sizes depends on the size of the (truncated) certificate chains. The header map will be 3 bytes + the size of the certificate chain (assuming a label in the range -24...23). { TDB3 : h'0001020304050607...' } 2.4.3. Message Sizes PSK 2.4.4. message_1 message_1 = ( 4, 0, h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f', h'c3', h'a2' ) message_1 (40 bytes): 04 00 58 20 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 41 C3 41 A2 2.4.5. message_2 Assuming a 0 byte plaintext and a 64-bit MAC value the ciphertext is 8 bytes message_2 = ( h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d 1e1f', h'c4', h'0001020304050607' ) message_2 (45 bytes): 58 20 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 41 C4 48 61 62 63 64 65 66 67 68 Mattsson & Palombini Expires September 12, 2019 [Page 26]
Internet-Draft Comparison of CoAP Security Protocols March 2019 2.4.6. message_3 The plaintext and ciphertext in message_3 are assumed to be of equal sizes as in message_2. message_3 = ( h'c4', h'0001020304050607' ) message_3 (11 bytes): 41 C4 48 00 01 02 03 04 05 06 07 2.4.7. Summary The previous examples of typical message sizes are summarized in Figure 5. ===================================================================== PSK RPK x5t x5chain --------------------------------------------------------------------- message_1 40 38 38 38 message_2 45 114 126 116 + Certificate chain message_3 11 80 91 81 + Certificate chain --------------------------------------------------------------------- Total 96 232 255 235 + Certificate chains ===================================================================== Figure 5: Typical message sizes in bytes 2.5. Conclusion To do a fair comparison, one has to choose a specific deployment and look at the topology, the whole protocol stack, frame sizes (e.g. 51 or 128 bytes), how and where in the protocol stack fragmentation is done, and the expected packet loss. Note that the number of byte in each frame that is available for the key exchange protocol may depend on the underlying protocol layers as well as the number of hops in multi-hop networks. The packet loss depends may depend on how many other devices that are transmitting at the same time, and may increase during network formation. The total overhead will be larger due to mechanisms for fragmentation, retransmission, and packet ordering. The overhead of fragmentation is roughly proportional to the number of fragments, while the expected overhead due to retransmission in noisy environments is a superlinear function of the flight sizes. Mattsson & Palombini Expires September 12, 2019 [Page 27]
Internet-Draft Comparison of CoAP Security Protocols March 2019 3. Overhead for Protection of Application Data To enable comparison, all the overhead calculations in this section use AES-CCM with a tag length of 8 bytes (e.g. AES_128_CCM_8 or AES- CCM-16-64), a plaintext of 6 bytes, and the sequence number '05'. This follows the example in [RFC7400], Figure 16. Note that the compressed overhead calculations for DLTS 1.2, DTLS 1.3, TLS 1.2 and TLS 1.3 are dependent on the parameters epoch, sequence number, and length, and all the overhead calculations are dependent on the parameter Connection ID when used. Note that the OSCORE overhead calculations are dependent on the CoAP option numbers, as well as the length of the OSCORE parameters Sender ID and Sequence Number. The following calculations are only examples. Section 3.1 gives a short summary of the message overhead based on different parameters and some assumptions. The following sections detail the assumptions and the calculations. 3.1. Summary The DTLS overhead is dependent on the parameter Connection ID. The following overheads apply for all Connection IDs with the same length. The compression overhead (GHC) is dependent on the parameters epoch, sequence number, Connection ID, and length (where applicable). The following overheads should be representative for sequence numbers and Connection IDs with the same length. The OSCORE overhead is dependent on the included CoAP Option numbers as well as the length of the OSCORE parameters Sender ID and sequence number. The following overheads apply for all sequence numbers and Sender IDs with the same length. Mattsson & Palombini Expires September 12, 2019 [Page 28]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Sequence Number '05' '1005' '100005' ------------------------------------------------------------- DTLS 1.2 29 29 29 DTLS 1.3 11 12 12 ------------------------------------------------------------- DTLS 1.2 (GHC) 16 16 16 DTLS 1.3 (GHC) 12 13 13 ------------------------------------------------------------- TLS 1.2 21 21 21 TLS 1.3 14 14 14 ------------------------------------------------------------- TLS 1.2 (GHC) 17 18 19 TLS 1.3 (GHC) 15 16 17 ------------------------------------------------------------- OSCORE request 13 14 15 OSCORE response 11 11 11 Figure 6: Overhead in bytes as a function of sequence number (Connection/Sender ID = '') Connection/Sender ID '' '42' '4002' ------------------------------------------------------------- DTLS 1.2 29 30 31 DTLS 1.3 11 12 13 ------------------------------------------------------------- DTLS 1.2 (GHC) 16 17 18 DTLS 1.3 (GHC) 12 13 14 ------------------------------------------------------------- OSCORE request 13 14 15 OSCORE response 11 11 11 Figure 7: Overhead in bytes as a function of Connection/Sender ID (Sequence Number = '05') Protocol Overhead Overhead (GHC) ------------------------------------------------------------- DTLS 1.2 21 8 DTLS 1.3 3 4 ------------------------------------------------------------- TLS 1.2 13 9 TLS 1.3 6 7 ------------------------------------------------------------- OSCORE request 5 OSCORE response 3 Figure 8: Overhead (excluding ICV) in bytes (Connection/Sender ID = '', Sequence Number = '05') Mattsson & Palombini Expires September 12, 2019 [Page 29]
Internet-Draft Comparison of CoAP Security Protocols March 2019 3.2. DTLS 1.2 3.2.1. DTLS 1.2 This section analyzes the overhead of DTLS 1.2 [RFC6347]. The nonce follow the strict profiling given in [RFC7925]. This example is taken directly from [RFC7400], Figure 16. DTLS 1.2 record layer (35 bytes, 29 bytes overhead): 17 fe fd 00 01 00 00 00 00 00 05 00 16 00 01 00 00 00 00 00 05 ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Version: fe fd Epoch: 00 01 Sequence number: 00 00 00 00 00 05 Length: 00 16 Nonce: 00 01 00 00 00 00 00 05 Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.2 gives 29 bytes overhead. 3.2.2. DTLS 1.2 with 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.2 [RFC6347] when compressed with 6LoWPAN-GHC [RFC7400]. The compression was done with [OlegHahm-ghc]. Note that the sequence number '01' used in [RFC7400], Figure 15 gives an exceptionally small overhead that is not representative. Note that this header compression is not available when DTLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Mattsson & Palombini Expires September 12, 2019 [Page 30]
Internet-Draft Comparison of CoAP Security Protocols March 2019 Compressed DTLS 1.2 record layer (22 bytes, 16 bytes overhead): b0 c3 03 05 00 16 f2 0e ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.2 record layer header and nonce: b0 c3 03 05 00 16 f2 0e Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters (epoch, sequence number, length) gives 16 bytes overhead. 3.2.3. DTLS 1.2 with Connection ID This section analyzes the overhead of DTLS 1.2 [RFC6347] with Connection ID [I-D.ietf-tls-dtls-connection-id]. The overhead calculations in this section uses Connection ID = '42'. DTLS recored layer with a Connection ID = '' (the empty string) is equal to DTLS without Connection ID. DTLS 1.2 record layer (36 bytes, 30 bytes overhead): 17 fe fd 00 01 00 00 00 00 00 05 42 00 16 00 01 00 00 00 00 00 05 ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Version: fe fd Epoch: 00 01 Sequence number: 00 00 00 00 00 05 Connection ID: 42 Length: 00 16 Nonce: 00 01 00 00 00 00 00 05 Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.2 with Connection ID gives 30 bytes overhead. Mattsson & Palombini Expires September 12, 2019 [Page 31]
Internet-Draft Comparison of CoAP Security Protocols March 2019 3.2.4. DTLS 1.2 with Connection ID and 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.2 [RFC6347] with Connection ID [I-D.ietf-tls-dtls-connection-id] when compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc]. Note that the sequence number '01' used in [RFC7400], Figure 15 gives an exceptionally small overhead that is not representative. Note that this header compression is not available when DTLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed DTLS 1.2 record layer (23 bytes, 17 bytes overhead): b0 c3 04 05 42 00 16 f2 0e ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.2 record layer header and nonce: b0 c3 04 05 42 00 16 f2 0e Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters (epoch, sequence number, Connection ID, length) gives 17 bytes overhead. 3.3. DTLS 1.3 3.3.1. DTLS 1.3 This section analyzes the overhead of DTLS 1.3 [I-D.ietf-tls-dtls13]. The changes compared to DTLS 1.2 are: omission of version number, merging of epoch into the first byte containing signalling bits, optional omission of length, reduction of sequence number into a 1 or 2-bytes field. Only the minimal header format for DTLS 1.3 is analyzed (see Figure 4 of [I-D.ietf-tls-dtls13]). The minimal header formal omit the length field and only a 1-byte field is used to carry the 8 low order bits of the sequence number Mattsson & Palombini Expires September 12, 2019 [Page 32]
Internet-Draft Comparison of CoAP Security Protocols March 2019 DTLS 1.3 record layer (17 bytes, 11 bytes overhead): 21 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 First byte (including epoch): 21 Sequence number: 05 Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 gives 11 bytes overhead. 3.3.2. DTLS 1.3 with 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.3 [I-D.ietf-tls-dtls13] when compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when DTLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed DTLS 1.3 record layer (18 bytes, 12 bytes overhead): 11 21 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 record layer header and nonce: 11 21 05 Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters (epoch, sequence number, no length) gives 12 bytes overhead. 3.3.3. DTLS 1.3 with Connection ID This section analyzes the overhead of DTLS 1.3 [I-D.ietf-tls-dtls13] with Connection ID [I-D.ietf-tls-dtls-connection-id]. In this example, the length field is omitted, and the 1-byte field is used for the sequence number. The minimal DTLSCiphertext structure is used (see Figure 4 of [I-D.ietf-tls-dtls13]), with the addition of the Connection ID field. Mattsson & Palombini Expires September 12, 2019 [Page 33]
Internet-Draft Comparison of CoAP Security Protocols March 2019 DTLS 1.3 record layer (18 bytes, 12 bytes overhead): 31 42 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 First byte (including epoch): 31 Connection ID: 42 Sequence number: 05 Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 with Connection ID gives 12 bytes overhead. 3.3.4. DTLS 1.3 with Connection ID and 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.3 [I-D.ietf-tls-dtls13] with Connection ID [I-D.ietf-tls-dtls-connection-id] when compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when DTLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed DTLS 1.3 record layer (19 bytes, 13 bytes overhead): 12 31 05 42 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 record layer header and nonce: 12 31 05 42 Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters (epoch, sequence number, Connection ID, no length) gives 13 bytes overhead. 3.4. TLS 1.2 3.4.1. TLS 1.2 This section analyzes the overhead of TLS 1.2 [RFC5246]. The changes compared to DTLS 1.2 is that the TLS 1.2 record layer does not have epoch and sequence number, and that the version is different. Mattsson & Palombini Expires September 12, 2019 [Page 34]
Internet-Draft Comparison of CoAP Security Protocols March 2019 TLS 1.2 Record Layer (27 bytes, 21 bytes overhead): 17 03 03 00 16 00 00 00 00 00 00 00 05 ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Version: 03 03 Length: 00 16 Nonce: 00 00 00 00 00 00 00 05 Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 TLS 1.2 gives 21 bytes overhead. 3.4.2. TLS 1.2 with 6LoWPAN-GHC This section analyzes the overhead of TLS 1.2 [RFC5246] when compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when TLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed TLS 1.2 record layer (23 bytes, 17 bytes overhead): 05 17 03 03 00 16 85 0f 05 ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 Compressed TLS 1.2 record layer header and nonce: 05 17 03 03 00 16 85 0f 05 Ciphertext: ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, TLS 1.2 with the above parameters (epoch, sequence number, length) gives 17 bytes overhead. 3.5. TLS 1.3 3.5.1. TLS 1.3 This section analyzes the overhead of TLS 1.3 [RFC8446]. The change compared to TLS 1.2 is that the TLS 1.3 record layer uses a different version. Mattsson & Palombini Expires September 12, 2019 [Page 35]
Internet-Draft Comparison of CoAP Security Protocols March 2019 TLS 1.3 Record Layer (20 bytes, 14 bytes overhead): 17 03 03 00 16 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Legacy version: 03 03 Length: 00 0f Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 TLS 1.3 gives 14 bytes overhead. 3.5.2. TLS 1.3 with 6LoWPAN-GHC This section analyzes the overhead of TLS 1.3 [RFC8446] when compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when TLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed TLS 1.3 record layer (21 bytes, 15 bytes overhead): 14 17 03 03 00 0f ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed TLS 1.3 record layer header and nonce: 14 17 03 03 00 0f Ciphertext (including encrypted content type): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 When compressed with 6LoWPAN-GHC, TLS 1.3 with the above parameters (epoch, sequence number, length) gives 15 bytes overhead. 3.6. OSCORE This section analyzes the overhead of OSCORE [I-D.ietf-core-object-security]. The below calculation Option Delta = '9', Sender ID = '' (empty string), and Sequence Number = '05', and is only an example. Note that Sender ID = '' (empty string) can only be used by one client per server. Mattsson & Palombini Expires September 12, 2019 [Page 36]
Internet-Draft Comparison of CoAP Security Protocols March 2019 OSCORE request (19 bytes, 13 bytes overhead): 92 09 05 ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 CoAP option delta and length: 92 Option value (flag byte and sequence number): 09 05 Payload marker: ff Ciphertext (including encrypted code): ec ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 The below calculation Option Delta = '9', Sender ID = '42', and Sequence Number = '05', and is only an example. OSCORE request (20 bytes, 14 bytes overhead): 93 09 05 42 ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 CoAP option delta and length: 93 Option Value (flag byte, sequence number, and Sender ID): 09 05 42 Payload marker: ff Ciphertext (including encrypted code): ec ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 The below calculation uses Option Delta = '9'. Mattsson & Palombini Expires September 12, 2019 [Page 37]
Internet-Draft Comparison of CoAP Security Protocols March 2019 OSCORE response (17 bytes, 11 bytes overhead): 90 ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 CoAP delta and option length: 90 Option value: - Payload marker: ff Ciphertext (including encrypted code): ec ae a0 15 56 67 92 ICV: 4d ff 8a 24 e4 cb 35 b9 OSCORE with the above parameters gives 13-14 bytes overhead for requests and 11 bytes overhead for responses. Unlike DTLS and TLS, OSCORE has much smaller overhead for responses than requests. 3.7. Group OSCORE This section analyzes the overhead of Group OSCORE [I-D.ietf-core-oscore-groupcomm]. TODO 3.8. Conclusion DTLS 1.2 has quite a large overhead as it uses an explicit sequence number and an explicit nonce. TLS 1.2 has significantly less (but not small) overhead. TLS 1.3 has quite a small overhead. OSCORE and DTLS 1.3 (using the minimal structure) format have very small overhead. The Generic Header Compression (6LoWPAN-GHC) can in addition to DTLS 1.2 handle TLS 1.2, and DTLS 1.2 with Connection ID. The Generic Header Compression (6LoWPAN-GHC) works very well for Connection ID and the overhead seems to increase exactly with the length of the Connection ID (which is optimal). The compression of TLS 1.2 is not as good as the compression of DTLS 1.2 (as the static dictionary only contains the DTLS 1.2 version number). Similar compression levels as for DTLS could be achieved also for TLS 1.2, but this would require different static dictionaries. For TLS 1.3 and DTLS 1.3, GHC increases the overhead. The 6LoWPAN-GHC header compression is not available when (D)TLS is used over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Mattsson & Palombini Expires September 12, 2019 [Page 38]
Internet-Draft Comparison of CoAP Security Protocols March 2019 New security protocols like OSCORE, TLS 1.3, and DTLS 1.3 have much lower overhead than DTLS 1.2 and TLS 1.2. The overhead is even smaller than DTLS 1.2 and TLS 1.2 over 6LoWPAN with compression, and therefore the small overhead is achieved even on deployments without 6LoWPAN or 6LoWPAN without compression. OSCORE is lightweight because it makes use of CoAP, CBOR, and COSE, which were designed to have as low overhead as possible. Note that the compared protocols have slightly different use cases. TLS and DTLS are designed for the transport layer and are terminated in CoAP proxies. OSCORE is designed for the application layer and protects information end-to-end between the CoAP client and the CoAP server. Group OSCORE is designed for group communication and protects information between a CoAP client and any number of CoAP servers. 4. Security Considerations This document is purely informational. 5. IANA Considerations This document has no actions for IANA. 6. Informative References [I-D.ietf-core-object-security] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", draft-ietf-core-object-security-15 (work in progress), August 2018. [I-D.ietf-core-oscore-groupcomm] Tiloca, M., Selander, G., Palombini, F., and J. Park, "Group OSCORE - Secure Group Communication for CoAP", draft-ietf-core-oscore-groupcomm-03 (work in progress), October 2018. [I-D.ietf-tls-dtls-connection-id] Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom, "Connection Identifiers for DTLS 1.2", draft-ietf-tls- dtls-connection-id-02 (work in progress), October 2018. [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-ietf-tls-dtls13-30 (work in progress), November 2018. Mattsson & Palombini Expires September 12, 2019 [Page 39]
Internet-Draft Comparison of CoAP Security Protocols March 2019 [I-D.schaad-ace-tls-cbor-handshake] Schaad, J., "TLS Handshake in CBOR", draft-schaad-ace-tls- cbor-handshake-00 (work in progress), March 2019. [I-D.selander-ace-cose-ecdhe] Selander, G., Mattsson, J., and F. Palombini, "Ephemeral Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace- cose-ecdhe-12 (work in progress), February 2019. [IoT-Cert] Forsby, F., "Digital Certificates for the Internet of Things", June 2017, <https://kth.diva- portal.org/smash/get/diva2:1153958/FULLTEXT01.pdf>. [OlegHahm-ghc] Hahm, O., "Generic Header Compression", July 2016, <https://github.com/OlegHahm/ghc>. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <https://www.rfc-editor.org/info/rfc5246>. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <https://www.rfc-editor.org/info/rfc6347>. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <https://www.rfc-editor.org/info/rfc7252>. [RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November 2014, <https://www.rfc-editor.org/info/rfc7400>. [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security (TLS) Cached Information Extension", RFC 7924, DOI 10.17487/RFC7924, July 2016, <https://www.rfc-editor.org/info/rfc7924>. [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer Security (TLS) / Datagram Transport Layer Security (DTLS) Profiles for the Internet of Things", RFC 7925, DOI 10.17487/RFC7925, July 2016, <https://www.rfc-editor.org/info/rfc7925>. Mattsson & Palombini Expires September 12, 2019 [Page 40]
Internet-Draft Comparison of CoAP Security Protocols March 2019 [RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets", RFC 8323, DOI 10.17487/RFC8323, February 2018, <https://www.rfc-editor.org/info/rfc8323>. [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>. [Ulfheim-TLS13] Driscoll, M., "Every Byte Explained The Illustrated TLS 1.3 Connection", March 2018, <https://tls13.ulfheim.net>. Acknowledgments The authors want to thank Ari Keraenen, Carsten Bormann, Goeran Selander, and Hannes Tschofenig for comments and suggestions on previous versions of the draft. All 6LoWPAN-GHC compression was done with [OlegHahm-ghc]. Authors' Addresses John Mattsson Ericsson AB Email: john.mattsson@ericsson.com Francesca Palombini Ericsson AB Email: francesca.palombini@ericsson.com Mattsson & Palombini Expires September 12, 2019 [Page 41]