Hi all,
Inspired by the discussion in this thread, I did more detailed calculations of
the number of bytes when DTLS 1.3 is used for typical IoT use cases (PSK, RPK,
Connection ID). The plan is to add this information to
draft-ietf-lwig-security-protocol-comparison as this has been requested by
several people. I think some bytes were missing in the earlier estimates for
TLS 1.3, and as Ben commented, DTLS 1.3 adds some bytes compared to TLS 1.3.
==============================================================================
Flight #1 #2 #3 Total
------------------------------------------------------------------------------
DTLS 1.3 RPK + ECDHE 149 373 213 735
DTLS 1.3 PSK + ECDHE 186 190 57 433
DTLS 1.3 PSK 136 150 57 343
------------------------------------------------------------------------------
EDHOC RPK + ECDHE 38 121 86 245
EDHOC PSK + ECDHE 43 47 12 102
==============================================================================
Number of bytes
Assumptions:
- Minimum number of algorithms and cipher suites offered
- Curve25519, ECDSA with P-256, AES-CCM_8, SHA-256
- Length of key identifiers: 4 bytes
- Connection identifiers: 1 byte
- The DTLS RPKs use point compression (saves 32 bytes)
- No DTLS handshake message fragmentation
- Only mandatory DTLS extentions, except for connection ID
- Version 30 https://tools.ietf.org/html/draft-ietf-tls-dtls13-30
(EDHOC numbers are for the soon to be published -11 version with cipher suites)
I hope this information is useful for people. Please comment if I missed
something or if you have any suggestion of things to add or how to present
things. I do not know currently how these numbers compare to DTLS 1.2.
Below is detailed information about where the byte in different flights as well
as the RPKs (SubjectPublicKeyInfo). Most of the bytes should have the correct
value, but most of the length fields are just written as LL LL LL. Below is
also information about how resumption, cached information [RFC 7924], and not
using Connection ID affects the number of bytes.
======================================================
DTLS 1.3 Flight #1 RPK + ECDHE
======================================================
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
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 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 + 6 = 149 bytes
------------------------------------------------------
DTLS 1.3 Flight #1 PSK + ECDHE
------------------------------------------------------
Differences compared to RPK + ECDHE
+ Extension - PSK Key Exchange Modes (6 bytes)
00 2d 00 02 01 01
+ Extension - Pre Shared Key (51 bytes)
00 29 00 2F
00 0a 00 04 ID ID ID 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
- 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)
149 + 6 + 51 - 8 - 6 - 6 = 186 bytes
------------------------------------------------------
DTLS 1.3 Flight #1 PSK
------------------------------------------------------
Differences compared to PSK + ECDHE
- Extension - Supported Groups (x25519) (8 bytes)
- Extension - Key Share (42 bytes)
186 - 8 - 42 = 136 bytes
======================================================
DTLS 1.3 Flight #2 RPK + ECDHE
======================================================
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
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
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
------------------------------------------------------
DTLS 1.3 Flight #2 PSK + ECDHE
------------------------------------------------------
Differences compared to RPK + ECDHE
- 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)
+ Extension - Pre Shared Key (6 bytes)
00 29 00 02 00 00
373 - 78 - 78 - 21 - 6 - 6 + 6 = 190 bytes
------------------------------------------------------
DTLS 1.3 Flight #2 PSK
------------------------------------------------------
Differences compared to PSK + ECDHE
- Extension - Key Share (40 bytes)
190 - 40 = 150 bytes
======================================================
DTLS 1.3 Flight #3 RPK + ECDHE
======================================================
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
------------------------------------------------------
DTLS 1.3 Flight #3 PSK + ECDHE
-----------------------------------------------------
Differences compared to RPK + ECDHE
- Handshake Message Certificate (78 bytes)
- Handshake Message Certificate Verify (78 bytes)
213 - 78 - 78 = 57 bytes
------------------------------------------------------
DTLS 1.3 Flight #3 PSK
-----------------------------------------------------
Differences compared to PSK + ECDHE
None
57 bytes
======================================================
DTLS 1.3 - Cached information [RFC 7924]
======================================================
- 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)
Differences compared to RPK + ECDHE
Flight #1
- Extension - Server Certificate Type (Raw Public Key) (6 bytes)
+ 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
149 + 33 = 182 bytes
Flight #2
- Extension - Server Certificate Type (Raw Public Key) (6 bytes)
+ Extension - Server Cashed Information (7 bytes)
00 19 LL LL LL LL 01
- Server Certificate (59 bytes -> 32 bytes)
373 - 26 = 347 bytes
==============================================================================
Flight #1 #2 #3 Total
------------------------------------------------------------------------------
DTLS 1.3 Cached X.509/RPK + ECDHE 182 347 213 742
DTLS 1.3 RPK + ECDHE 149 373 213 735
==============================================================================
======================================================
DTLS 1.3 - Resumption
======================================================
To enable resumption, a 4th flight (New Session Ticket) is added
Flight #4 - New Session Ticket
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 resumption handshake is just a PSK handshake with 136 + 150 + 57 = 343 bytes
==============================================================================
Flight #1 #2 #3 #4 Total
------------------------------------------------------------------------------
DTLS 1.3 RPK + ECDHE + NewSessionTicket 149 373 213 42 777
DTLS 1.3 PSK (resumption) 136 150 57 343
==============================================================================
======================================================
DTLS 1.3 - 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) 143 364 212 721
DTLS 1.3 PSK + ECDHE (no cid) 180 183 56 419
DTLS 1.3 PSK (no cid) 130 143 56 329
==============================================================================
======================================================
DTLS Raw Public Keys
======================================================
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
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
======================================================
Helpful Sources of Information
======================================================
In addition to relevant RFCs and the estimates done by Jim, the following
references were helpful:
Every Byte Explained: The Illustrated TLS 1.3 Connection
https://tls13.ulfheim.net/
Digital Certificates for the Internet of Things
https://kth.diva-portal.org/smash/get/diva2:1153958/FULLTEXT01.pdf
/John
-----Original Message-----
From: Benjamin Kaduk <[email protected]>
Date: Saturday, 3 November 2018 at 15:59
To: John Mattsson <[email protected]>
Cc: "[email protected]" <[email protected]>, "[email protected]" <[email protected]>
Subject: Re: [Ace] EDHOC standardization
On Fri, Nov 02, 2018 at 02:55:54PM +0000, John Mattsson wrote:
> Hi Benjamin, Salvador
>
> While DTLS 1.3 have done a very good job of lowering the overhead of the
> record layer when application data is sent (see e.g.
> https://tools.ietf.org/html/draft-ietf-lwig-security-protocol-comparison-01
> for a comparison between different protocols), I do not think the handshake
> protocol is much leaner (is it leaner at all?).
(There are some handshake messages that are removed entirely.)
> We tried to make an fair comparison between EDHOC and TLS 1.3 in the
> presentation at IETF 101 (see
> https://datatracker.ietf.org/meeting/101/materials/slides-101-ace-key-exchange-w-oscore-00).
> Since then, we have significantly optimized the encoding in EDHOC and the
> upcoming version (-11) is expected to have the following message sizes.
>
> Auth. PSK RPK x5t x5chain
> --------------------------------------------------------------------
> EDHOC message_1 43 38 38 38
> EDHOC message_2 47 121 127 117 + Certificate chain
> EDHOC message_3 12 86 92 82 + Certificate chain
> --------------------------------------------------------------------
> Total 102 245 257 237 + Certificate chains
>
> As Salvador writes, the handshakes in TLS 1.3 and DTLS 1.3 are basically the
> same, so the numbers presented at IETF 101 should be a good estimate also for
> DTLS 1.3.
>
> Auth. PSK RPK
> --------------------------------------------------------------------
> (D)TLS message_1 142 107
> (D)TLS message_2 135 264
> (D)TLS message_3 51 167
> --------------------------------------------------------------------
> Total 328 538
Thanks for the numbers!
> The numbers above include ECDHE. For handshake messages, my understanding is
> that the DTLS 1.3 and TLS 1.3 record layer have exactly the same size.
The DTLS 1.3 ones will be worse, due to the epoch and sequence number
fields.
-Ben
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