Message Size Overhead of CoAP Security Protocols

To enable comparison, all the overhead calculations in this section use AES-CCM with a tag length of 8 bytes, a plaintext of 6 bytes, and the sequence number ‘05’. This follows the example in , Figure 16.

This section analyzes the overhead of DTLS 1.2 . The nonce follow the strict profiling given in . This example is taken directly from , Figure 16. .

DTLS 1.2 gives 29 bytes overhead.

This section analyzes the overhead of DTLS 1.2 when compressed with . The compression was done with . Note that the compressed overhead is dependent on the parameters epoch, sequence number, and length. The following is only an example. Note that the sequence number ‘01’ used in , 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.

When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters (epoch, sequence number, length) gives 16 bytes overhead.

This section analyzes the overhead of DTLS 1.2 when compressed with . Note that the compressed overhead is dependent on the parameters epoch and sequence number. The following is only an example. Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with raza-6lo-compressed-dtls.

When compressed with raza-6lo-compressed-dtls, DTLS 1.2 with the above parameters (epoch, sequence number) gives 13 bytes overhead.

This section analyzes the overhead of DTLS 1.3 . The only change compared to DTLS 1.2 is that the DTLS 1.3 record layer does not have an explicit nonce.

DTLS 1.3 gives 21 bytes overhead.

This section analyzes the overhead of DTLS 1.3 when compressed with . Note that the overhead is dependent on the parameters epoch, sequence number, and length. The following is only an example. Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters (epoch, sequence number, length) gives 14 bytes overhead.

This section analyzes the overhead of DTLS 1.3 when compressed with . Note that the compressed overhead is dependent on the parameters epoch and sequence number. The following is only an example. Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with raza-6lo-compressed-dtls.

When compressed with raza-6lo-compressed-dtls, DTLS 1.3 with the above parameters (epoch, sequence number) gives 13 bytes overhead.

This section analyzes the overhead of DTLS with 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.

This section analyzes the overhead of DTLS 1.2 with Connection ID . Note that the overhead is dependent on the parameter Connection ID. The following is only an example.

DTLS 1.2 with Connection ID gives 30 bytes overhead.

This section analyzes the overhead of DTLS 1.2 with Connection ID when compressed with . Note that the compressed overhead is dependent on the parameters epoch, sequence number, Connection ID, and length. The following is only an example. Note that the sequence number ‘01’ used in , 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.

When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters (epoch, sequence number, Connection ID, length) gives 17 bytes overhead.

This section analyzes the overhead of DTLS 1.3 with Connection ID . Note that the overhead is dependent on the parameter Connection ID. The following is only an example.

DTLS 1.3 gives 22 bytes overhead.

This section analyzes the overhead of DTLS 1.3 with Connection ID when compressed with . Note that the overhead is dependent on the parameters epoch, sequence number, Connection ID, and length. The following is only an example. Note that this header compression is not available when DTLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters (epoch, sequence number, Connection ID, length) gives 15 bytes overhead.

This section analyzes the overhead of TLS 1.2 . 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 gives 21 bytes overhead.

This section analyzes the overhead of TLS 1.2 when compressed with . Note that the overhead is dependent on the parameters epoch, sequence number, and length. The following is only an example. Note that this header compression is not available when TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

When compressed with 6LoWPAN-GHC, TLS 1.2 with the above parameters (epoch, sequence number, length) gives 17 bytes overhead.

This section analyzes the overhead of TLS 1.3 . The change compared to TLS 1.2 is that the TLS 1.3 record layer uses a different version.

TLS 1.3 gives 21 bytes overhead.

This section analyzes the overhead of TLS 1.3 when compressed with . Note that the overhead is dependent on the parameters epoch, sequence number, and length. The following is only an example. Note that this header compression is not available when TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

When compressed with 6LoWPAN-GHC, TLS 1.3 with the above parameters (epoch, sequence number, length) gives 17 bytes overhead.

This section analyzes the overhead of OSCORE . Note that the overhead is dependent on the included CoAP Option numbers as well as the length of the OSCORE parameters Sender ID and sequence number. 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.

The below calculation Option Delta = ‘9’, Sender ID = ‘42’, and Sequence Number = ‘05’, and is only an example.

The below calculation uses Option Delta = ‘9’ and is only an example.

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.

DTLS 1.2 has quite a large overhead as it uses an explicit sequence number and an explicit nonce. DTLS 1.3, TLS 1.2, and TLS 1.3 have significantly less (but not small) overhead. Both DTLS compression methods provides very good compression. raza-6lo-compressed-dtls achieves slightly better compression but requires state. GHC is stateless but provides slightly worse compression. As DTLS 1.3 uses the same version number as DTLS 1.2, both GHC and raza-6lo-compressed-dtls works well also for DTLS 1.3. The Generic Header Compression (6LoWPAN-GHC) can in addition to DTLS 1.2 handle DTLS 1.3, DTLS with Connection ID, TLS 1.2, and TLS 1.3. 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 is not as good as the compression of DTLS (as the static dictionary is more or less a DTLS record layer). Similar compression levels as for DTLS could be achieved also for TLS, but this would require different static dictionaries for each version of TLS (as TLS 1.2 and TLS 1.3 uses different version numbers). GHC works as good for DTLS 1.3 as for DTLS 1.2 as the version number is the same. raza-6lo-compressed-dtls is not able to handle DTLS with Connection ID or TLS, all extensions requires an updated mechanism. The header compression is not available when (D)TLS is exchanged over transports that do not use 6LoWPAN together with 6LoWPAN-GHC or raza-6lo-compressed-dtls. OSCORE has much lower overhead than DTLS 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. OSCORE is lightweight because it makes use of some excellent features in CoAP, CBOR, and COSE.