Network Working Group J. Mattsson Internet-Draft F. Palombini Intended status: Informational Ericsson AB Expires: August 26, 2018 February 22, 2018 Comparison of CoAP Security Protocols draft-mattsson-lwig-security-protocol-comparison-00 Abstract This document analyzes and compares 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, and OSCORE. DTLS and TLS are analyzed with and without 6LoWPAN-GHC compression. DTLS is anlyzed 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/. 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Mattsson & Palombini Expires August 26, 2018 [Page 1] Internet-Draft CoAP Security Overhead February 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Overhead of Security Protocols . . . . . . . . . . . . . . . 3 2.1. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . 3 2.1.2. DTLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 4 2.1.3. DTLS 1.2 with Connection ID . . . . . . . . . . . . . 4 2.1.4. DTLS 1.2 with Connection ID and 6LoWPAN-GHC . . . . . 5 2.2. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2. DTLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 6 2.2.3. DTLS 1.3 with Connection ID . . . . . . . . . . . . . 7 2.2.4. DTLS 1.3 with Connection ID and 6LoWPAN-GHC . . . . . 7 2.2.5. DTLS 1.3 with short header . . . . . . . . . . . . . 8 2.2.6. DTLS 1.3 with short header and 6LoWPAN-GHC . . . . . 8 2.3. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3.1. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . 9 2.3.2. TLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 9 2.4. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4.1. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . 10 2.4.2. TLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 10 2.5. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. Overhead with Different Parameters . . . . . . . . . . . . . 12 4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Informative References . . . . . . . . . . . . . . . . . . . 15 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction This document analyzes and compares 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 [I-D.ietf-tls-tls13], and OSCORE [I-D.ietf-core-object-security]. The DTLS and TLS record layers are analyzed with and without compression. DTLS is anlyzed with and without Connection ID [I-D.ietf-tls-dtls-connection-id] and DTLS 1.3 is analyzed with and without the use of the short header. Readers are expected to be familiar with some of the terms described in RFC 7925 [RFC7925], such as ICV. Mattsson & Palombini Expires August 26, 2018 [Page 2] Internet-Draft CoAP Security Overhead February 2018 2. Overhead of Security Protocols To enable comparison, all the overhead calculations in this section use AES-CCM with a tag length of 8 bytes (AES_128_CCM_8), 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 are only examples. 2.1. DTLS 1.2 2.1.1. 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. Mattsson & Palombini Expires August 26, 2018 [Page 3] Internet-Draft CoAP Security Overhead February 2018 2.1.2. DTLS 1.2 with 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.2 [RFC6347] when compressed with [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 exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. 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. 2.1.3. 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 with a Connection ID = '' (the empty string) is equal to DTLS without Connection ID. Mattsson & Palombini Expires August 26, 2018 [Page 4] Internet-Draft CoAP Security Overhead February 2018 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. 2.1.4. 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 [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 exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Mattsson & Palombini Expires August 26, 2018 [Page 5] Internet-Draft CoAP Security Overhead February 2018 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. 2.2. DTLS 1.3 2.2.1. 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 and sequence number fields (of total 8 bytes) into one 4-bytes-field. DTLS 1.3 Record Layer (22 bytes, 16 bytes overhead): 17 40 00 00 05 00 0f ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Epoch and Sequence: 40 00 00 05 Length: 00 0f Ciphertext (including encrypted ContentType): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 gives 16 bytes overhead. 2.2.2. DTLS 1.3 with 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.3 [I-D.ietf-tls-dtls13] when compressed with [RFC7400] [OlegHahm-ghc]. Mattsson & Palombini Expires August 26, 2018 [Page 6] Internet-Draft CoAP Security Overhead February 2018 Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed DTLS 1.3 Record Layer (23 bytes, 17 bytes overhead): 02 17 40 80 12 05 00 0f ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 Record Layer Header and Nonce: 02 17 40 80 12 05 00 0f Ciphertext (including encrypted ContentType): 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, length) gives 17 bytes overhead. 2.2.3. 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]. DTLS 1.3 Record Layer (23 bytes, 17 bytes overhead): 17 40 00 00 05 42 00 0f ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Content type: 17 Epoch and Sequence: 40 00 00 05 Connection ID: 42 Length: 00 0f Ciphertext (including encrypted ContentType): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 gives 17 bytes overhead. 2.2.4. 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 [RFC7400] [OlegHahm-ghc]. Mattsson & Palombini Expires August 26, 2018 [Page 7] Internet-Draft CoAP Security Overhead February 2018 Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Compressed DTLS 1.3 Record Layer (24 bytes, 18 bytes overhead): 02 17 40 80 13 05 42 00 0f ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 Record Layer Header and Nonce: 02 17 40 80 13 05 42 00 0f Ciphertext (including encrypted ContentType): 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, length) gives 18 bytes overhead. 2.2.5. DTLS 1.3 with short header This section analyzes the overhead of DTLS 1.3 with short header format [I-D.ietf-tls-dtls13]. The short header format for DTLS 1.3 reduces the header of 5 bytes, by omitting the length value and sending 1 lower bit of epoch value instead of 2, and 12 lower bits of sequence number instead of 30. DTLS 1.3 Record Layer (17 bytes, 11 bytes overhead): 30 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 short header: 30 05 Ciphertext (including encrypted ContentType): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 DTLS 1.3 with short header gives 11 bytes overhead. 2.2.6. DTLS 1.3 with short header and 6LoWPAN-GHC This section analyzes the overhead of DTLS 1.3 with short header [I-D.ietf-tls-dtls13] when compressed with [RFC7400] [OlegHahm-ghc]. Mattsson & Palombini Expires August 26, 2018 [Page 8] Internet-Draft CoAP Security Overhead February 2018 Compressed DTLS 1.3 Record Layer (18 bytes, 12 bytes overhead) 11 30 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 short header (including sequence number) 11 30 05 Ciphertext (including encrypted ContentType): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 Compressed DTLS 1.3 with short header gives 12 bytes overhead. 2.3. TLS 1.2 2.3.1. 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. 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. 2.3.2. TLS 1.2 with 6LoWPAN-GHC This section analyzes the overhead of TLS 1.2 [RFC5246] when compressed with [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Mattsson & Palombini Expires August 26, 2018 [Page 9] Internet-Draft CoAP Security Overhead February 2018 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. 2.4. TLS 1.3 2.4.1. TLS 1.3 This section analyzes the overhead of TLS 1.3 [I-D.ietf-tls-tls13]. The change compared to TLS 1.2 is that the TLS 1.3 record layer uses a different version. 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 ContentType): ae a0 15 56 67 92 ec ICV: 4d ff 8a 24 e4 cb 35 b9 TLS 1.3 gives 14 bytes overhead. 2.4.2. TLS 1.3 with 6LoWPAN-GHC This section analyzes the overhead of TLS 1.3 [I-D.ietf-tls-tls13] when compressed with [RFC7400] [OlegHahm-ghc]. Note that this header compression is not available when TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. Mattsson & Palombini Expires August 26, 2018 [Page 10] Internet-Draft CoAP Security Overhead February 2018 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 ContentType): 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. 2.5. OSCORE This section analyzes the overhead of OSCORE [I-D.ietf-core-object-security]. Note that Sender ID = '' (empty string) can only be used by one client per server. The examples below assume that the original messages does not have payload (note that this does not affect the overhead). The below calculation Option Delta = '9', Sender ID = '' (empty string), and Sequence Number = '05', and is only an example. 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. Mattsson & Palombini Expires August 26, 2018 [Page 11] Internet-Draft CoAP Security Overhead February 2018 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'. 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. Overhead with Different Parameters 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. Mattsson & Palombini Expires August 26, 2018 [Page 12] Internet-Draft CoAP Security Overhead February 2018 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. Sequence Number '05' '1005' '100005' ------------------------------------------------------------- DTLS 1.2 29 29 29 DTLS 1.3 16 16 16 DTLS 1.3 (short header) 11 11 11 ------------------------------------------------------------- DTLS 1.2 (GHC) 16 16 16 DTLS 1.3 (GHC) 17 17 17 DTLS 1.3 (short header) (GCH) 12 12 12 ------------------------------------------------------------- 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 1: 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 16 17 18 DTLS 1.3 (short header) 11 12 13 ------------------------------------------------------------- DTLS 1.2 (GHC) 16 17 18 DTLS 1.3 (GHC) 17 18 19 DTLS 1.3 (short header) (GCH) 12 13 14 ------------------------------------------------------------- OSCORE Request 13 14 15 OSCORE Response 11 11 11 Figure 2: Overhead in bytes as a function of Connection/Sender ID (Sequence Number = '05') Mattsson & Palombini Expires August 26, 2018 [Page 13] Internet-Draft CoAP Security Overhead February 2018 Protocol Overhead Overhead (GHC) ------------------------------------------------------------- DTLS 1.2 21 8 DTLS 1.3 8 9 DTLS 1.3 (short header) 3 4 ------------------------------------------------------------- TLS 1.2 13 9 TLS 1.3 6 7 ------------------------------------------------------------- OSCORE Request 5 OSCORE Response 3 Figure 3: Overhead (excluding ICV) in bytes (Connection/Sender ID = '', Sequence Number = '05') 4. Summary 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 and DTLS 1.3 have quite small overhead. DTLS 1.3 with short header format has 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. Note that GHC in some cases might be able to compress the payload and therefore reduce total overhead. The 6LoWPAN-GHC header compression is not available when (D)TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC. The short header format for DTLS 1.3 reduces the header of 5 bytes, by omitting the length value and sending 1 lower bit of epoch value instead of 2, and 12 lower bits of sequence number instead of 30. This may create problems reconstructing the full sequence number, if ~2000 datagrams in sequence are lost. OSCORE has much lower overhead than DTLS (with no short header format) and TLS. The overhead of OSCORE is smaller than DTLS over 6LoWPAN with compression, and this small overhead is achieved even on deployments without 6LoWPAN or 6LoWPAN without DTLS compression. Mattsson & Palombini Expires August 26, 2018 [Page 14] Internet-Draft CoAP Security Overhead February 2018 OSCORE is lightweight because it makes use of some excellent features in CoAP, CBOR, and COSE. 5. Security Considerations This document is purely informational. 6. IANA Considerations This document has no actions for IANA. 7. 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-08 (work in progress), January 2018. [I-D.ietf-tls-dtls-connection-id] Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom, "The Datagram Transport Layer Security (DTLS) Connection Identifier", draft-ietf-tls-dtls-connection-id-00 (work in progress), December 2017. [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-dtls13-22 (work in progress), November 2017. [I-D.ietf-tls-tls13] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", draft-ietf-tls-tls13-23 (work in progress), January 2018. [OlegHahm-ghc] Hahm, O., "Generic Header Compression", July 2016, . [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, . Mattsson & Palombini Expires August 26, 2018 [Page 15] Internet-Draft CoAP Security Overhead February 2018 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [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, . [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, . [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, . 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 August 26, 2018 [Page 16]