Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 8D37D1D90 for ; Fri, 22 Mar 2019 21:11:09 +0000 (UTC) X-Greylist: delayed 00:06:12 by SQLgrey-1.7.6 Received: from bitcoin.jonasschnelli.ch (bitcoinsrv.jonasschnelli.ch [138.201.55.219]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id CA43919B for ; Fri, 22 Mar 2019 21:11:05 +0000 (UTC) Received: by bitcoin.jonasschnelli.ch (Postfix, from userid 1002) id E13A415E4FD4; Fri, 22 Mar 2019 22:04:51 +0100 (CET) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,HTML_MESSAGE, MIME_QP_LONG_LINE autolearn=ham version=3.3.1 Received: from [192.168.0.3] (cable-static-236-151.teleport.ch [213.188.236.151]) by bitcoin.jonasschnelli.ch (Postfix) with ESMTPSA id 8381A15E4721 for ; Fri, 22 Mar 2019 22:04:50 +0100 (CET) From: Jonas Schnelli Content-Type: multipart/signed; boundary="Apple-Mail=_D4FB7183-E1A8-4BFC-AF55-2484312B4577"; protocol="application/pgp-signature"; micalg=pgp-sha256 Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\)) Message-Id: <26A4BEC6-403C-4534-8A2D-57C71D1736FB@jonasschnelli.ch> Date: Fri, 22 Mar 2019 22:04:46 +0100 To: Bitcoin Protocol Discussion X-Mailer: Apple Mail (2.3445.102.3) X-Virus-Scanned: clamav-milter 0.100.2 at bitcoinsrv.jonasschnelli.ch X-Virus-Status: Clean X-Mailman-Approved-At: Fri, 22 Mar 2019 23:16:11 +0000 Subject: [bitcoin-dev] New BIP - v2 peer-to-peer message transport protocol (former BIP151) X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 22 Mar 2019 21:11:09 -0000 --Apple-Mail=_D4FB7183-E1A8-4BFC-AF55-2484312B4577 Content-Type: multipart/alternative; boundary="Apple-Mail=_8E38DED6-E4A9-4675-B6EB-ADCB2DFFEBD1" --Apple-Mail=_8E38DED6-E4A9-4675-B6EB-ADCB2DFFEBD1 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Hi The overhauled version of the former BIP151 has fundamental differences = and deserves (requires?) a new BIP. Calling it =E2=80=9Ev2 peer-to-peer message transport protocol=E2=80=9C = is more accurate since it is no longer only about encryption. The formatted draft proposal can be found here: = https://gist.github.com/jonasschnelli/c530ea8421b8d0e80c51486325587c52 Significant changes compared to the current available BIP151 * A optimised AEAD construct is now proposed (ChaCha20Poly1305@Bitcoin), = reducing the required ChaCha20 rounds (compared to the openSSH version). * introduce NODE_P2P_V2 * 32bytes-per-side =E2=80=9Epseudorandom" key exchange * the multi message envelope has been removed * the length of a packet uses now a 3-byte integer with 23 available = bits * introduction of short-command-ID (ex.: uint8_t 13 =3D=3D INV, etc.) = which result in some v2 messages require less bandwidth then v1 * the key derivation and what communication direction uses what key is = now more specific First benchmarks of the used primitives https://github.com/bitcoin/bitcoin/pull/15519#issuecomment-469705289 = Benchmark of the AEAD compared to the HASH (double SHA256) (Indicates that v2 messages may be more performant): https://github.com/bitcoin/bitcoin/pull/15649#issuecomment-475782376 = Proposal: 
  BIP: ???
  Layer: Peer Services
  Title: Version 2 Peer-to-Peer Message Transport Protocol
  Author: Jonas Schnelli 
  Status: Draft
  Type: Standards Track
  Created: 2019-03-08
  License: PD
=3D=3D Abstract =3D=3D This BIP describes a new Bitcoin peer to peer transport protocol with opportunistic encryption. =3D=3D Motivation =3D=3D The current peer-to-peer protocol is partially inefficient and in = plaintext. With the current unencrypted message transport, BGP hijack, block delay = attacks and message tempering are inexpensive and can be executed in a covert = way (undetectable MITM)[https://btc-hijack.ethz.ch/files/btc_hijack.pdf Hijacking Bitcoin: Routing Attacks on Cryptocurrencies - M. Apostolaki, = A. Zohar, L.Vanbever]. Adding opportunistic encryption introduces a high risk for attackers of = being detected. Peer operators can compare encryption session IDs or use other = form of authentication schemes [https://github.com/bitcoin/bips/blob/master/bip-0150.medi= awiki BIP150] to identify an attack. Each current version 1 Bitcoin peer-to-peer message uses a double-SHA256 checksum truncated to 4 bytes. Roughly the same amount of computation = power would be required for encrypting and authenticating a peer-to-peer = message with ChaCha20 & Poly1305. Additionally, this BIP describes a way how data manipulation (blocking = or tempering commands by an intercepting TCP/IP node) would be identifiable = by the communicating peers. Encrypting traffic between peers is already possible with VPN, tor, = stunnel, curveCP or any other encryption mechanism on a deeper OSI level, = however, most of those solutions require significant knowhow in how to setup such a = secure channel and are therefore not widely deployed. =3D=3D Specification =3D=3D
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", = "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are = to be interpreted as described in RFC = 2119[https://tools.ietf.org/html/rfc2119 RFC 2119].
A peer that supports the message transport protocol as defined in this = proposal MUST accept encryption requests from all peers. Both communication direction share the same shared-secret but have = different symmetric cipher keys. The encryption handshake MUST happen before sending any other messages = to the responding peer. If the responding peer closes the connection after sending the handshake request, the initiating peer MAY try to connect again with the v1 = peer-to-peer transport protocol. Such reconnects allow an attacker to "downgrade" the encryption to plaintext communication and thus, accepting v1 connections = MUST not be done when the Bitcoin peer-to-peer network uses almost only v2 communication. =3D=3D=3D NODE_P2P_V2 =3D=3D=3D Peers supporting the transport protocol after this proposal MUST signal NODE_P2P_V2 
NODE_P2P_V2 =3D (1 << 11)
A peer usually learns an address along with the expected service flags = which MAY be used to filter possible outbound peers. A peer signaling NODE_P2P_V2 MUST accept encrypted = communication specified in this proposal. Peers MAY only make outbound connections to peers supporting NODE_P2P_V2. =3D=3D=3D Handshake =3D=3D=3D 
 =
--------------------------------------------------------------------------=
--------------
 | Initiator                             Responder                       =
               |
 |                                                                       =
               |
 | x, X         :=3D SECP256k1_KEYGEN()                                  =
                 |
 | CLIENT_HDATA :=3D X                                                   =
                 |
 |                                                                       =
               |
 |               --- CLIENT_HDATA --->                                   =
               |
 |                                                                       =
               |
 |                                       y, Y           :=3D =
SECP256k1_KEYGEN()           |
 |                                       ECDH_KEY       :=3D =
SECP256k1_ECDH(X,y)          |
 |                                       SERVER_HDATA   :=3D Y           =
                 |
 |                                                                       =
               |
 |               <-- SERVER_HDATA ----                                   =
               |
 |                                                                       =
               |
 | ECDH_KEY     :=3D SECP256k1_ECDH(x,Y)                                 =
                 |
 =
--------------------------------------------------------------------------=
--------------
To request encrypted communication (only possible if yet no other = messages have been sent or received), the initiating peer generates an EC secp256k1 = ephemeral key and sends the corresponding 32-byte public key to the responding = peer and waits for the remote 32-byte public key from the counterparty. ODD secp256k1 public keys MUST be used (public keys starting with 0x02). = If the public key from the generated ephemeral key is an EVEN public key = (starting with 0x03), negating the key and recalculating its public key SHOULD be = done. Only using ODD public makes it more complex to identify the handshake = based on analyzing the traffic. The handshake request and response message are raw 32byte payloads = containing no header, length or checksum (the pure 32byte payload) and MUST be sent = before anything else. Public keys starting with the 4-byte network magic are forbidden and = MUST lead to locally re-generate an ephemeral-key. Pseudocode for the ephemeral-key generation 
do {
    ecdh_key.MakeNewKey();
    if (ecdh_key.GetPubKey()[0] =3D=3D 3) {
        ecdh_key.Negate();
    }
} while (m_ecdh_key.GetPubKey()[0..3] =3D=3D NETWORK_MAGIC);
Once a peer has received the public key from its counterparty, the = shared secret MUST be calculated by using secp256k1 ECDH. Private keys will never be transmitted. The shared secret can only be calculated if an attacker knows at least one private key and the = counterparties public key. This key-exchange is based on the discrete log problem and = thus not sufficiently strong against known forms of possible quantum computer algorithms. Adding an additional quantum resistant key exchange like = NewHope is possible but out of scope for this proposal. After a successful handshake, the messages format MUST use the "v2 = messages structure". Non-encrypted v1 messages from the initiating peer MUST lead = to an immediate connection termination. After a successful handshake, both peers MUST cleanse the = ephemeral-session-key from memory and/or persistence storage. A peer not supporting this proposal will not perform the described = handshake and thus send a v1 version message. Peers supporting this BIP MAY optionally allow unencrypted v1 = communication by detecting a v1 version message by the initial 11-byte sequence of = 4byte net magic || "version". =3D=3D=3D Symmetric Encryption Cipher Keys =3D=3D=3D Once the ECDH secret (ECDH_KEY) is calculated on each side, = the symmetric encryption cipher keys MUST be derived with HKDF [https://tools.ietf.org/html/rfc5869 HKDF (RFC 5869)] after = the following specification: 1. HKDF extraction PRK =3D HKDF_EXTRACT(hash=3DSHA256, = salt=3D"BitcoinSharedSecret||INITIATOR_32BYTES_PUBKEY||RESPONDER_32BYTES_P= UBKEY", ikm=3DECDH_KEY). 2. Derive Key_1_A (K_1 communication direction A) K1A =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_1_A",= L=3D32) 2. Derive Key_2_A (K_2 communication direction A) K1B =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_2_A",= L=3D32) 3. Derive Key_1_B (K_1 communication direction B) K2 =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_1_B", = L=3D32) 3. Derive Key_2_B (K_2 communication direction B) K2 =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_2_B", = L=3D32) =3D=3D=3D Session ID =3D=3D=3D Both parties MUST also calculate the 256bit session-id using SID =3D= HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinSessionID", = L=3D32). The session-id can be used for authenticating the encryption-session = (identity check). The session-id MUST be presented to the user on request. =3D=3D=3D ChaCha20-Poly1305@Bitcoin Cipher Suite =3D=3D=3D =3D=3D=3D=3D Background =3D=3D=3D=3D ChaCha20 is a stream cipher designed by Daniel Bernstein and described = in [http://cr.yp.to/chacha/chacha-20080128.pdf ChaCha20]. It = operates by permuting 128 fixed bits, 128 or 256 bits of key, a 64 bit nonce and = a 64 bit counter into 64 bytes of output. This output is used as a keystream, = with any unused bytes simply discarded. Poly1305 [http://cr.yp.to/mac/poly1305-20050329.pdf = Poly1305], also by Daniel Bernstein, is a one-time Carter-Wegman MAC that computes a 128 = bit integrity tag given a message and a single-use 256 bit secret key. The chacha20-poly1305@bitcoin combines these two primitives into an authenticated encryption mode. The construction used is based on that = proposed for TLS by Adam Langley in [http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03 = "ChaCha20 and Poly1305 based Cipher Suites for TLS", Adam Langley], but = differs in the layout of data passed to the MAC and in the addition of encryption = of the packet lengths. =3D=3D=3D=3D Detailed Construction =3D=3D=3D=3D The chacha20-poly1305@bitcoin cipher requires two 256 bits of key = material as output from the key exchange. Each key (K_1 and K_2) are used by two = separate instances of chacha20. The instance keyed by K_1 is a stream cipher that is used only to = encrypt the 3 byte packet length field and has its own sequence number. The second = instance, keyed by K_2, is used in conjunction with poly1305 to build an AEAD (Authenticated Encryption with Associated Data) that is used to encrypt = and authenticate the entire packet. Two separate cipher instances are used here so as to keep the packet = lengths confidential but not create an oracle for the packet payload cipher by decrypting and using the packet length prior to checking the MAC. By = using an independently-keyed cipher instance to encrypt the length, an active = attacker seeking to exploit the packet input handling as a decryption oracle can = learn nothing about the payload contents or its MAC (assuming key derivation, ChaCha20 and Poly1305 are secure). The AEAD is constructed as follows: for each packet, generate a Poly1305 = key by taking the first 256 bits of ChaCha20 stream output generated using K_2, = an IV consisting of the packet sequence number encoded as an LE uint64 and a = ChaCha20 block counter of zero. The K_2 ChaCha20 block counter is then set to the little-endian encoding of 1 (i.e. {1, 0, 0, 0, 0, 0, 0, 0}) and this = instance is used for encryption of the packet payload. =3D=3D=3D=3D Packet Handling =3D=3D=3D=3D When receiving a packet, the length must be decrypted first. When 3 = bytes of ciphertext length have been received, they may be decrypted. A ChaCha20 round always calculates 64bytes which is sufficient to crypt = 21 times a 3 bytes length field (21*3 =3D 63). The length field sequence = number can thus be used 21 times (keystream caching). The length field must be enc-/decrypted with the ChaCha20 keystream = keyed with K_1 defined by block counter 0, the length field sequence number in = little endian and a keystream position from 0 to 60. Pseudo code example: 
// init
sequence_nr_payload =3D 0; //payload sequence number
sequence_nr_length_field =3D 0; //length field sequence number (will be =
reused)
aad_length_field_pos =3D 0; //position in the length field cipher =
instance keystream chunk

...

// actual encryption
if cache_length_field_sequence_number !=3D sequence_nr_length_field {
  cache_keystream_64_bytes =3D ChaCha20(key=3DK_1, =
iv=3Dlittle_endian(sequence_nr_length_field), counter=3D0);
  cache_length_field_sequence_number =3D sequence_nr_length_field
}
packet_length =3D =
XOR_TO_LE(cache_length_field_sequence_number[aad_length_field_pos - =
aad_length_field_pos+3], ciphertext[0-3])

sequence_nr_payload++;
aad_length_field_pos +=3D 3; //skip 3 bytes in keystream
if (aad_length_field_pos + 3 > 64) { //if we are outside of the 64byte =
keystream...
  aad_length_field_pos =3D 0; // reset at position 0
  sequence_nr_length_field++; // increase length field sequence number
}
Once the entire packet has been received, the MAC MUST be checked before decryption. A per-packet Poly1305 key is generated as described above = and the MAC tag calculated using Poly1305 with this key over the ciphertext of = the packet length and the payload together. The calculated MAC is then = compared in constant time with the one appended to the packet and the packet = decrypted using ChaCha20 as described above (with K_2, the packet sequence number = as nonce and a starting block counter of 1). Detection of an invalid MAC MUST lead to immediate connection = termination. To send a packet, first encode the 3 byte length and encrypt it using = K_1 as described above. Encrypt the packet payload (using K_2) and append it to = the encrypted length. Finally, calculate a MAC tag and append it. The initiating peer MUST use K_1_A, K_2_A to encrypt = messages on the send channel, K_1_B, K_2_B MUST be used to decrypt = messages on the receive channel. The responding peer MUST use K_1_A, K_2_A to decrypt = messages on the receive channel, K_1_B, K_2_B MUST be used to encrypt = messages on the send channel. Optimized implementations of ChaCha20-Poly1305@bitcoin are relatively = fast in general, therefore it is very likely that encrypted messages require not = more CPU cycles per bytes then the current unencrypted p2p message format (ChaCha20/Poly1305 versus double SHA256). The initial packet sequence numbers are 0. K_2 ChaCha20 cipher instance (payload) must never reuse a {key, nonce} = for encryption nor may it be used to encrypt more than 2^70 bytes under the = same {key, nonce}. K_1 ChaCha20 cipher instance (length field/AAD) must never reuse a {key, = nonce, position-in-keystream} for encryption nor may it be used to encrypt more = than 2^70 bytes under the same {key, nonce}. We use message sequence numbers for both communication directions. 
 =
--------------------------------------------------------------------------=
----------------
 | Initiator                          Responder                          =
                 |
 |                                                                       =
                 |
 | AEAD() =3D ChaCha20Poly1305Bitcoin()                                  =
                   |
 | MSG_A_CIPH =3D AEAD(k=3DK_1_A, K_2_A, payload_nonce=3D0, aad_nonce=3D0,=
 aad_pos=3D0, msg)        |
 |                                                                       =
                 |
 |                         --- MSG_CIPH --->                             =
                 |
 |                                                                       =
                 |
 |                                    msg   :=3D AEAD(k=3DK_1_A,K_2_A, =
n=3D0, ..., MSG_A_CIPH)  |
 |                                                                       =
                 |
 =
--------------------------------------------------------------------------=
----------------
=3D=3D=3D=3D Test Vectors =3D=3D=3D=3D 
message   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00
k1 (DATA) 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00
k2 (AAD)  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00

AAD keystream
76 b8 e0 ad a0 f1 3d 90 40 5d 6a e5 53 86 bd 28 bd d2 19 b8 a0 8d ed 1a =
a8 36 ef cc 8b 77 0d c7 da 41 59 7c 51 57 48 8d 77 24 e0 3f b8 d8 4a 37 =
6a 43 b8 f4 15 18 a1 1c c3 87 b6 69 b2 ee 65 86

ciphertext
76 b8 e0 9f 07 e7 be 55 51 38 7a 98 ba 97 7c 73 2d 08 0d cb 0f 29 a0 48 =
e3 65 69 12 c6 53 3e 32

MAC
d2 fc 11 82 9c 1b 6c 1d f1 f5 51 cd 61 31 ff 08

message   01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00
k1 (DATA) 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00
k2 (AAD)  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00 00 00 00 00 00 00 00 00 00 00

AAD keystream
76 b8 e0 ad a0 f1 3d 90 40 5d 6a e5 53 86 bd 28 bd d2 19 b8 a0 8d ed 1a =
a8 36 ef cc 8b 77 0d c7 da 41 59 7c 51 57 48 8d 77 24 e0 3f b8 d8 4a 37 =
6a 43 b8 f4 15 18 a1 1c c3 87 b6 69 b2 ee 65 86

ciphertext
77 b8 e0 9f 07 e7 be 55 51 38 7a 98 ba 97 7c 73 2d 08 0d cb 0f 29 a0 48 =
e3 65 69 12 c6 53 3e 32

MAC
ba f0 c8 5b 6d ff 86 02 b0 6c f5 2a 6a ef c6 2e

message
ff 00 00 f1 95 e6 69 82 10 5f fb 64 0b b7 75 7f 57 9d a3 16 02 fc 93 ec =
01 ac 56 f8 5a c3 c1 34 a4 54 7b 73 3b 46 41 30 42 c9 44 00 49 17 69 05 =
d3 be 59 ea 1c 53 f1 59 16 15 5c 2b e8 24 1a 38 00 8b 9a 26 bc 35 94 1e =
24 44 17 7c 8a de 66 89 de 95 26 49 86 d9 58 89 fb 60 e8 46 29 c9 bd 9a =
5a cb 1c c1 18 be 56 3e b9 b3 a4 a4 72 f8 2e 09 a7 e7 78 49 2b 56 2e f7 =
13 0e 88 df e0 31 c7 9d b9 d4 f7 c7 a8 99 15 1b 9a 47 50 32 b6 3f c3 85 =
24 5f e0 54 e3 dd 5a 97 a5 f5 76 fe 06 40 25 d3 ce 04 2c 56 6a b2 c5 07 =
b1 38 db 85 3e 3d 69 59 66 09 96 54 6c c9 c4 a6 ea fd c7 77 c0 40 d7 0e =
af 46 f7 6d ad 39 79 e5 c5 36 0c 33 17 16 6a 1c 89 4c 94 a3 71 87 6a 94 =
df 76 28 fe 4e aa f2 cc b2 7d 5a aa e0 ad 7a d0 f9 d4 b6 ad 3b 54 09 87 =
46 d4 52 4d 38 40 7a 6d eb 3a b7 8f ab 78 c9

k1 (DATA) 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
k2 (AAD)  ff 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

AAD keystream
c6 40 c1 71 1e 3e e9 04 ac 35 c5 7a b9 79 1c 8a 1c 40 86 03 a9 0b 77 a8 =
3b 54 f6 c8 44 cb 4b 06 d9 4e 7f c6 c8 00 e1 65 ac d6 61 47 e8 0e c4 5a =
56 7f 6c e6 6d 05 ec 0c ae 67 9d ce eb 89 00 17

ciphertext
39 40 c1 e9 2d a4 58 2f f6 f9 2a 77 6a eb 14 d0 14 d3 84 ee b3 0f 66 0d =
ac f7 0a 14 a2 3f d3 1e 91 21 27 01 33 4e 2c e1 ac f5 19 9d c8 4f 4d 61 =
dd be 65 71 bc a5 af 87 4b 4c 92 26 c2 6e 65 09 95 d1 57 64 4e 18 48 b9 =
6e d6 c2 10 2d 54 89 a0 50 e7 1d 29 a5 a6 6e ce 11 de 5f b5 c9 55 8d 54 =
da 28 fe 45 b0 bc 4d b4 e5 b8 80 30 bf c4 a3 52 b4 b7 06 8e cc f6 56 ba =
e7 ad 6a 35 61 53 15 fc 7c 49 d4 20 03 88 d5 ec a6 7c 2e 82 2e 06 93 36 =
c6 9b 40 db 67 e0 f3 c8 12 09 c5 0f 32 16 a4 b8 9f b3 ae 1b 98 4b 78 51 =
a2 ec 6f 68 ab 12 b1 01 ab 12 0e 1e a7 31 3b b9 3b 5a 0f 71 18 5c 7f ea =
01 7d db 92 76 98 61 c2 9d ba 4f bc 43 22 80 d5 df f2 1b 36 d1 c4 c7 90 =
12 8b 22 69 99 50 bb 18 bf 74 c4 48 cd fe 54 7d 8e d4 f6 57 d8 00 5f dc =
0c d7 a0 50 c2 d4 60 50 a4 4c 43 76 35 58 58

MAC
98 1f be 8b 18 42 88 27 6e 7a 93 ea bc 89 9c 4a
=3D=3D=3D v2 Messages Structure =3D=3D=3D {|class=3D"wikitable" ! Field Size !! Description !! Data type !! Comments |- | 3 || length & flag || 23 + 1 bits || Encrypted length of ciphertext = payload (not counting the MAC tag) in number of bytes (only 2^23 is = usable, most significant bit is the rekey-flag) |- | 1-13 || encrypted command || variable || ASCII command (or one byte = short command ID) |- | ? || encrypted payload || ? || The actual data |- | 16 || MAC tag || ? || 128bit MAC-tag |} Encrypted messages do not have the 4byte network magic. The maximum message size is 2^23 (8=E2=80=99388=E2=80=99608) bytes. = Future communication MAY exceed this limit and thus MUST be split into different messages. Decrypting and processing the message before the authentication succeeds = (MAC verified) MUST not be done. The 4byte sha256 checksum is no longer required because the AEAD (MAC). Both peers MUST keep track of the message sequence number (uint32) of = sent and received messages for building a 64-bit symmetric cipher IV. The command field MUST start with a byte that defines the length of the = ASCII command string up to 12 chars (1 to 12) or a short command ID (see = below). =3D=3D=3D=3D Short Command ID =3D=3D=3D=3D To save valuable bandwidth, the v2 message format supports message = command short IDs for message types with high frequency. The ID/string mapping = is a peer to peer arrangement and MAY be negotiated between the initiating = and responding peer. A peer conforming to this proposal MUST support short = IDs based on the table below and SHOULD use short command IDs for outgoing = messages. {|class=3D"wikitable" ! Number !! Command |- | 13 || INV |- | 14 || HEADERS |- | 15 || PING |- | 16 || PONG |- |} =3D=3D=3D=3D Length comparisons between v1 and v2 messages =3D=3D=3D=3D 
v1 in: 4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+36(Payload) =3D=3D =
60
v2 inv: 3(MessageSize&Flag)+1(Command)+36(Payload)+16(MAC) =3D=3D 56
(93.33%)

v1 ping: 4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+8(Payload) =3D=3D=
 32
v2 pong: 3(MessageSize&Flag)+1(Command)+8(Payload)+16(MAC) =3D=3D 28
(87.5%)

v1 block: =
4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+1=E2=80=99048=E2=80=99576(=
Payload) =3D 1=E2=80=99048=E2=80=99600
v2 block: 3(MessageSize&Flag)+6(CommandStr)+8(Payload)+16(MAC) =3D=3D 28 =
=3D 1=E2=80=99048=E2=80=99601
(100.000095%)
=3D=3D=3D Re-Keying =3D=3D=3D Re-keying can be signaled by setting the most significant bit in the = length field before encryption. A peer signaling a rekey MUST use the next key = for encryption messages AFTER the message where the signaling has been done. A peer identifying a rekey by checking the most significant bit in the = envelope length must use the next key for decrypt messages AFTER the message = where the signaling has been detected. The next symmetric cipher key MUST be calculated by = SHA256(SHA256(session ID || old_symmetric_cipher_key)) and the packet sequence number = of the according encryption direction must be set to 0. Re-Keying interval is a peer policy with a minimum timespan of 10 = seconds. The Re-Keying must be done after every 1GB of data sent (recommended by = RFC4253 SSH Transport) or if the last rekey was more than an hour ago. Peers calculate the counterparty limits and MUST disconnect immediately = if a violation of the limits has been detected. =3D=3D=3D Risks =3D=3D=3D The encryption does not include an authentication scheme. This BIP does = not cover a proposal to avoid MITM attacks during the encryption = initialization. However, peers MUST show the session-id to the user on request which = allows to identify a MITM by a manual verification on a secure channel. Optional authentication schemes may be covered by other proposals [https://github.com/bitcoin/bips/blob/master/bip-0150.medi= awiki BIP150]. An attacker could delay or halt v2 protocol enforcement by providing a reasonable amount of peers not supporting the v2 protocol. =3D=3D Compatibility =3D=3D This proposal is backward compatible (as long as not enforced). = Non-supporting peers can still use unencrypted communications. =3D=3D Reference implementation =3D=3D * Complete Bitcoin Core implementation: = https://github.com/bitcoin/bitcoin/pull/14032 * Reference implementation of the AEAD in C: = https://github.com/jonasschnelli/chacha20poly1305 =3D=3D References =3D=3D =3D=3D Acknowledgements =3D=3D * Pieter Wuille and Gregory Maxwell for most of the ideas in this BIP. * Tim Ruffing for the review and the hint for the enhancement of the = symmetric key derivation =3D=3D Copyright =3D=3D This work is placed in the public domain. --Apple-Mail=_8E38DED6-E4A9-4675-B6EB-ADCB2DFFEBD1 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
Hi

The overhauled version of the former BIP151 has fundamental = differences and deserves (requires?) a new BIP.
Calling it =E2=80=9Ev2 peer-to-peer = message transport protocol=E2=80=9C is more accurate since it is no = longer only about encryption.

The formatted draft proposal can be found here: https://gist.github.com/jonasschnelli/c530ea8421b8d0e80c5148632= 5587c52

Significant changes compared to = the current available BIP151
* A optimised AEAD construct = is now proposed (ChaCha20Poly1305@Bitcoin), reducing the required = ChaCha20 rounds (compared to the openSSH version).
* = introduce NODE_P2P_V2
* 32bytes-per-side =E2=80=9Epseudorand= om" key exchange
* the multi message envelope has been = removed
* the length of a packet uses now a 3-byte integer = with 23 available bits
* introduction of short-command-ID = (ex.: uint8_t 13 =3D=3D INV, etc.) which result in
 some v2 messages require less bandwidth then v1
* the key derivation and what communication direction = uses what key is now more
 specific

First benchmarks of the used = primitives
https://github.com/bitcoin/bitcoin/pull/15519#issuecomment-4697= 05289

Benchmark of the AEAD compared to the HASH (double = SHA256)
(Indicates that v2 messages may be more = performant):
https://github.com/bitcoin/bitcoin/pull/15649#issuecomment-4757= 82376


Proposal:

<pre>
  BIP: ???
  Layer: Peer = Services
  Title: Version 2 Peer-to-Peer = Message Transport Protocol
  Author: Jonas = Schnelli <dev@jonasschnelli.ch>
  = Status: Draft
  Type: Standards = Track
  Created: 2019-03-08
  License: PD
</pre>

=3D=3D Abstract = =3D=3D

This = BIP describes a new Bitcoin peer to peer transport protocol = with 
opportunistic encryption.

=3D=3D Motivation = =3D=3D

The = current peer-to-peer protocol is partially inefficient and in = plaintext.

With = the current unencrypted message transport, BGP hijack, block delay = attacks 
and message tempering are inexpensive = and can be executed in a covert way 
(undetectable = MITM)<ref>[https://btc-hijack.ethz.ch/files/btc_hijack.pdf 
Hijacking Bitcoin: Routing Attacks on Cryptocurrencies = - M. Apostolaki, A. 
Zohar, = L.Vanbever]</ref>.

Adding opportunistic encryption introduces a high risk for = attackers of being 
detected. Peer operators = can compare encryption session IDs or use other form 
of authentication schemes <ref 
name=3D"bip150">[https://github.com/bitcoin/bips/blob/master= /bip-0150.mediawiki 
BIP150]</ref> to = identify an attack.

Each current version 1 Bitcoin peer-to-peer message uses a = double-SHA256 
checksum truncated to 4 bytes. = Roughly the same amount of computation power 
would be required for encrypting and authenticating a = peer-to-peer message with 
ChaCha20 & = Poly1305.

Additionally, this BIP describes a way how data manipulation = (blocking or 
tempering commands by an = intercepting TCP/IP node) would be identifiable by the 
communicating peers.

Encrypting traffic between peers is = already possible with VPN, tor, stunnel, 
curveCP or any other encryption mechanism on a deeper OSI = level, however, most 
of those solutions = require significant knowhow in how to setup such a = secure 
channel and are therefore not widely = deployed.

=3D=3D= Specification =3D=3D

<blockquote>
The key words "MUST", = "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in = this document are to be
interpreted as described in = RFC 2119<ref>[https://tools.ietf.org/html/rfc2119 
RFC 2119]</ref>.
</blockquote>

A peer that supports the message = transport protocol as defined in this proposal 
MUST accept encryption requests from all peers.

Both communication = direction share the same shared-secret but have = different 
symmetric cipher keys.

The encryption handshake = MUST happen before sending any other messages to the 
responding peer.

If the responding peer closes the connection after sending = the handshake 
request, the initiating peer = MAY try to connect again with the v1 peer-to-peer 
transport protocol. Such reconnects allow an attacker to = "downgrade" the 
encryption to plaintext = communication and thus, accepting v1 connections MUST 
not be done when the Bitcoin peer-to-peer network uses almost = only v2 
communication.

=3D= =3D=3D NODE_P2P_V2 =3D=3D=3D

Peers supporting the transport protocol = after this proposal MUST signal 
<code>NODE_P2P_V2</code>
<pre>
NODE_P2P_V2 =3D (1 << = 11)
</pre>

A peer usually learns an address along = with the expected service flags which 
MAY be = used to filter possible outbound peers.

A peer signaling = <code>NODE_P2P_V2</code> MUST accept encrypted = communication 
specified in this = proposal.

Peers = MAY only make outbound connections to peers supporting 
<code>NODE_P2P_V2</code>.

=3D=3D=3D Handshake =3D=3D=3D

<pre>
 ---------------------------------------------------------= -------------------------------
 | Initiator =                     =         Responder           =                     =        |
 |     =                     =                     =                     =                     =  |
 | x, X         :=3D= SECP256k1_KEYGEN()               =                     =                 |
 | CLIENT_HDATA :=3D X         =                     =                     =                   =  |
 |           =                     =                     =                     =                |
 |               --- = CLIENT_HDATA --->               =                     =                |
 |               =                     =                     =                     =            |
 | =                     =                   y, Y =           :=3D SECP256k1_KEYGEN()     =       |
 |       =                     =             ECDH_KEY       = :=3D SECP256k1_ECDH(X,y)          |
 |               =                     =     SERVER_HDATA   :=3D Y         =                   =  |
 |           =                     =                     =                     =                |
 |               = <-- SERVER_HDATA ----             =                     =                 =  |
 |           =                     =                     =                     =                |
 | ECDH_KEY     :=3D SECP256k1_ECDH(x,Y) =                     =                     =          |
 ---------------------------------------------------------= -------------------------------
</pre>

To request encrypted communication (only possible if yet no = other messages have 
been sent or received), = the initiating peer generates an EC secp256k1 ephemeral 
key and sends the corresponding 32-byte public key to the = responding peer and 
waits for the remote = 32-byte public key from the counterparty.

ODD secp256k1 public keys MUST be used = (public keys starting with 0x02). If the 
public= key from the generated ephemeral key is an EVEN public key = (starting 
with 0x03), negating the key and = recalculating its public key SHOULD be done.
Only = using ODD public makes it more complex to identify the handshake based = on 
analyzing the traffic.

The handshake request = and response message are raw 32byte payloads containing 
no header, length or checksum (the pure 32byte payload) and = MUST be sent before 
anything else.

Public keys starting = with the 4-byte network magic are forbidden and MUST = lead 
to locally re-generate an = ephemeral-key.

Pseudocode for the ephemeral-key generation
<pre>
do {
    ecdh_key.MakeNewKey();
    if (ecdh_key.GetPubKey()[0] =3D=3D 3) = {
        = ecdh_key.Negate();
    }
} while (m_ecdh_key.GetPubKey()[0..3] =3D=3D = NETWORK_MAGIC);
</pre>
Once a peer has received the public = key from its counterparty, the shared 
secret = MUST be calculated by using secp256k1 ECDH.

Private keys will never be transmitted. = The shared secret can only be 
calculated if = an attacker knows at least one private key and the = counterparties 
public key. This key-exchange = is based on the discrete log problem and thus not 
sufficiently strong against known forms of possible quantum = computer 
algorithms. Adding an additional = quantum resistant key exchange like NewHope is 
possible but out of scope for this proposal.

After a successful = handshake, the messages format MUST use the "v2 messages 
structure". Non-encrypted v1 messages from the initiating = peer MUST lead to an 
immediate connection = termination.

After a successful handshake, both peers MUST cleanse the = ephemeral-session-key 
from memory and/or = persistence storage.

A peer not supporting this proposal will not perform the = described handshake 
and thus send a v1 = version message.
Peers supporting this BIP MAY = optionally allow unencrypted v1 communication by 
detecting a v1 version message by the initial 11-byte = sequence of <code>4byte 
net magic || = "version"</code>.

=3D=3D=3D Symmetric Encryption Cipher Keys =3D=3D=3D

Once the ECDH secret = (<code>ECDH_KEY</code>) is calculated on each side, = the 
symmetric encryption cipher keys MUST be = derived with HKDF 
<ref>[https://tools.ietf.org/html/rfc5869 HKDF (RFC = 5869)]</ref> after the 
following = specification:

1. HKDF extraction
<code>PRK =3D = HKDF_EXTRACT(hash=3DSHA256, = salt=3D"BitcoinSharedSecret||INITIATOR_32BYTES_PUBKEY||RESPONDER_32BYTES_P= UBKEY", ikm=3DECDH_KEY)</code>.

2. Derive Key_1_A (K_1 communication = direction A)
<code>K1A =3D = HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_1_A", = L=3D32)</code>

2. Derive Key_2_A (K_2 communication direction A)
<code>K1B =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, = info=3D"BitcoinK_2_A", L=3D32)</code>

3. Derive Key_1_B (K_1 communication = direction B)
<code>K2 =3D = HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, info=3D"BitcoinK_1_B", = L=3D32)</code>

3. Derive Key_2_B (K_2 communication direction B)
<code>K2 =3D HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, = info=3D"BitcoinK_2_B", L=3D32)</code>

=3D=3D=3D Session ID =3D=3D=3D

Both parties MUST also = calculate the 256bit session-id using <code>SID =3D 
HKDF_EXPAND(prk=3DPRK, hash=3DSHA256, = info=3D"BitcoinSessionID", L=3D32)</code>. The 
session-id can be used for authenticating the = encryption-session (identity 
check).

The session-id MUST be = presented to the user on request.

=3D=3D=3D ChaCha20-Poly1305@Bitcoin = Cipher Suite =3D=3D=3D

=3D=3D=3D=3D Background =3D=3D=3D=3D

ChaCha20 is a stream cipher designed by = Daniel Bernstein and described in 
<ref>[http://cr.yp.to/chacha/chacha-20080128.pdf = ChaCha20]</ref>. It operates 
by = permuting 128 fixed bits, 128 or 256 bits of key, a 64 bit nonce and a = 64 
bit counter into 64 bytes of output. This = output is used as a keystream, with 
any = unused bytes simply discarded.

Poly1305 = <ref>[http://cr.yp.to/mac/poly1305-20050329.pdf = Poly1305]</ref>, also 
by Daniel = Bernstein, is a one-time Carter-Wegman MAC that computes a 128 = bit 
integrity tag given a message and a = single-use 256 bit secret key.

The chacha20-poly1305@bitcoin combines = these two primitives into an 
authenticated = encryption mode. The construction used is based on that = proposed 
for TLS by Adam Langley = in 
<ref>[http://tools.ietf.org/html/draft-agl-tls-chacha20po= ly1305-03 "ChaCha20 
and Poly1305 based Cipher = Suites for TLS", Adam Langley]</ref>, but differs = in 
the layout of data passed to the MAC and = in the addition of encryption of the 
packet = lengths.

=3D=3D=3D= =3D Detailed Construction =3D=3D=3D=3D

The chacha20-poly1305@bitcoin cipher = requires two 256 bits of key material as 
output= from the key exchange. Each key (K_1 and K_2) are used by two = separate 
instances of chacha20.

The instance keyed by = K_1 is a stream cipher that is used only to encrypt the = 3 
byte packet length field and has its own = sequence number. The second instance, 
keyed = by K_2, is used in conjunction with poly1305 to build an = AEAD 
(Authenticated Encryption with = Associated Data) that is used to encrypt and 
authenticate the entire packet.

Two separate cipher instances are used = here so as to keep the packet lengths 
confidential but not create an oracle for the packet payload = cipher by 
decrypting and using the packet = length prior to checking the MAC. By using an 
independently-keyed cipher instance to encrypt the length, an = active attacker 
seeking to exploit the packet = input handling as a decryption oracle can learn 
nothing about the payload contents or its MAC (assuming key = derivation, 
ChaCha20 and Poly1305 are = secure).

The = AEAD is constructed as follows: for each packet, generate a Poly1305 key = by 
taking the first 256 bits of ChaCha20 = stream output generated using K_2, an IV 
consisting of the packet sequence number encoded as an LE = uint64 and a ChaCha20 
block counter of zero. = The K_2 ChaCha20 block counter is then set to the 
little-endian encoding of 1 (i.e. {1, 0, 0, 0, 0, 0, 0, 0}) = and this instance 
is used for encryption of = the packet payload.

=3D=3D=3D=3D Packet Handling =3D=3D=3D=3D

When receiving a packet, = the length must be decrypted first. When 3 bytes of 
ciphertext length have been received, they may be = decrypted.

A = ChaCha20 round always calculates 64bytes which is sufficient to crypt = 21 
times a 3 bytes length field (21*3 =3D = 63). The length field sequence number can 
thus = be used 21 times (keystream caching).

The length field must be enc-/decrypted = with the ChaCha20 keystream keyed with 
K_1 = defined by block counter 0, the length field sequence number in = little 
endian and a keystream position from 0 = to 60.

Pseudo = code example:
<pre>
// = init
sequence_nr_payload =3D 0; //payload sequence = number
sequence_nr_length_field =3D 0; //length = field sequence number (will be reused)
aad_length_field_pos =3D 0; //position in the length field = cipher instance keystream chunk

...

// actual encryption
if cache_length_field_sequence_number !=3D = sequence_nr_length_field {
  = cache_keystream_64_bytes =3D ChaCha20(key=3DK_1, = iv=3Dlittle_endian(sequence_nr_length_field), counter=3D0);
  cache_length_field_sequence_number =3D = sequence_nr_length_field
}
packet_length =3D = XOR_TO_LE(cache_length_field_sequence_number[aad_length_field_pos - = aad_length_field_pos+3], ciphertext[0-3])

sequence_nr_payload++;
aad_length_field_pos +=3D 3; //skip 3 bytes in = keystream
if (aad_length_field_pos + 3 > 64) { = //if we are outside of the 64byte keystream...
 = aad_length_field_pos =3D 0; // reset at position 0
  sequence_nr_length_field++; // increase length field = sequence number
}
</pre>

Once the entire packet has been received, the MAC MUST be = checked before 
decryption. A per-packet = Poly1305 key is generated as described above and the 
MAC tag calculated using Poly1305 with this key over the = ciphertext of the 
packet length and the = payload together. The calculated MAC is then compared in 
constant time with the one appended to the packet and the = packet decrypted 
using ChaCha20 as described = above (with K_2, the packet sequence number as 
nonce and a starting block counter of 1).

Detection of an invalid = MAC MUST lead to immediate connection termination.

To send a packet, first = encode the 3 byte length and encrypt it using K_1 as 
described above. Encrypt the packet payload (using K_2) and = append it to the 
encrypted length. Finally, = calculate a MAC tag and append it.

The initiating peer MUST use = <code>K_1_A, K_2_A</code> to encrypt messages = on 
the send channel, <code>K_1_B, = K_2_B</code> MUST be used to decrypt messages on 
the receive channel.

The responding peer MUST use = <code>K_1_A, K_2_A</code> to decrypt messages = on 
the receive channel, <code>K_1_B, = K_2_B</code> MUST be used to encrypt messages 
on the send channel.

Optimized implementations of = ChaCha20-Poly1305@bitcoin are relatively fast in 
general, therefore it is very likely that encrypted messages = require not more 
CPU cycles per bytes then = the current unencrypted p2p message format 
(ChaCha20/Poly1305 versus double SHA256).

The initial packet = sequence numbers are 0.

K_2 ChaCha20 cipher instance (payload) must never reuse a = {key, nonce} for 
encryption nor may it be = used to encrypt more than 2^70 bytes under the same 
{key, nonce}.

K_1 ChaCha20 cipher instance (length field/AAD) must never = reuse a {key, nonce, 
position-in-keystream} = for encryption nor may it be used to encrypt more than 
2^70 bytes under the same {key, nonce}.

We use message sequence = numbers for both communication directions.

<pre>
 ---------------------------------------------------------= ---------------------------------
 | Initiator =                     =      Responder             =                     =           |
 |   =                     =                     =                     =                     =      |
 | AEAD() =3D = ChaCha20Poly1305Bitcoin()             =                     =                     = |
 | MSG_A_CIPH =3D AEAD(k=3DK_1_A, K_2_A, = payload_nonce=3D0, aad_nonce=3D0, aad_pos=3D0, msg)       =  |
 |           =                     =                     =                     =                 =  |
 |           =               --- MSG_CIPH ---> =                     =                     =      |
 |       =                     =                     =                     =                     =  |
 |           =                     =      msg   :=3D AEAD(k=3DK_1_A,K_2_A, n=3D0, ..., = MSG_A_CIPH)  |
 |       =                     =                     =                     =                     =  |
 ---------------------------------------------------------= ---------------------------------
</pre>

=3D=3D=3D=3D Test Vectors =3D=3D=3D=3D
<pre>
message=   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00
k1 (DATA) 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 = 00 00 00 00 00
k2 (AAD)  00 00 00 00 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 = 00

AAD = keystream
76 b8 e0 ad a0 f1 3d 90 40 5d 6a e5 53 86 = bd 28 bd d2 19 b8 a0 8d ed 1a a8 36 ef cc 8b 77 0d c7 da 41 59 7c 51 57 = 48 8d 77 24 e0 3f b8 d8 4a 37 6a 43 b8 f4 15 18 a1 1c c3 87 b6 69 b2 ee = 65 86

ciphertext
76 b8 e0 9f 07 e7 be 55 51 38 = 7a 98 ba 97 7c 73 2d 08 0d cb 0f 29 a0 48 e3 65 69 12 c6 53 3e = 32

MAC
d2 fc 11 82 9c 1b 6c 1d f1 f5 51 cd 61 31 ff 08
</pre>

<pre>
message   01 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 = 00 00 00 00
k1 (DATA) 00 00 00 00 00 00 00 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 = 00
k2 (AAD)  00 00 00 00 00 00 00 00 00 00 00 = 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

AAD keystream
76 b8 e0 ad a0 f1 3d 90 40 5d 6a e5 53 86 bd 28 bd d2 19 b8 = a0 8d ed 1a a8 36 ef cc 8b 77 0d c7 da 41 59 7c 51 57 48 8d 77 24 e0 3f = b8 d8 4a 37 6a 43 b8 f4 15 18 a1 1c c3 87 b6 69 b2 ee 65 86

ciphertext
77 b8 e0 9f 07 e7 be 55 51 38 7a 98 ba 97 7c 73 2d 08 0d cb = 0f 29 a0 48 e3 65 69 12 c6 53 3e 32

MAC
ba f0 c8 5b 6d = ff 86 02 b0 6c f5 2a 6a ef c6 2e
</pre>

<pre>
message
ff 00 00 f1 95 e6 69 82 10 5f fb 64 0b b7 75 7f 57 9d a3 16 = 02 fc 93 ec 01 ac 56 f8 5a c3 c1 34 a4 54 7b 73 3b 46 41 30 42 c9 44 00 = 49 17 69 05 d3 be 59 ea 1c 53 f1 59 16 15 5c 2b e8 24 1a 38 00 8b 9a 26 = bc 35 94 1e 24 44 17 7c 8a de 66 89 de 95 26 49 86 d9 58 89 fb 60 e8 46 = 29 c9 bd 9a 5a cb 1c c1 18 be 56 3e b9 b3 a4 a4 72 f8 2e 09 a7 e7 78 49 = 2b 56 2e f7 13 0e 88 df e0 31 c7 9d b9 d4 f7 c7 a8 99 15 1b 9a 47 50 32 = b6 3f c3 85 24 5f e0 54 e3 dd 5a 97 a5 f5 76 fe 06 40 25 d3 ce 04 2c 56 = 6a b2 c5 07 b1 38 db 85 3e 3d 69 59 66 09 96 54 6c c9 c4 a6 ea fd c7 77 = c0 40 d7 0e af 46 f7 6d ad 39 79 e5 c5 36 0c 33 17 16 6a 1c 89 4c 94 a3 = 71 87 6a 94 df 76 28 fe 4e aa f2 cc b2 7d 5a aa e0 ad 7a d0 f9 d4 b6 ad = 3b 54 09 87 46 d4 52 4d 38 40 7a 6d eb 3a b7 8f ab 78 c9

k1 (DATA) 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
k2 (AAD)  ff 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

AAD = keystream
c6 40 c1 71 1e 3e e9 04 ac 35 c5 7a b9 79 = 1c 8a 1c 40 86 03 a9 0b 77 a8 3b 54 f6 c8 44 cb 4b 06 d9 4e 7f c6 c8 00 = e1 65 ac d6 61 47 e8 0e c4 5a 56 7f 6c e6 6d 05 ec 0c ae 67 9d ce eb 89 = 00 17

ciphertext
39 40 c1 e9 2d a4 58 2f f6 f9 = 2a 77 6a eb 14 d0 14 d3 84 ee b3 0f 66 0d ac f7 0a 14 a2 3f d3 1e 91 21 = 27 01 33 4e 2c e1 ac f5 19 9d c8 4f 4d 61 dd be 65 71 bc a5 af 87 4b 4c = 92 26 c2 6e 65 09 95 d1 57 64 4e 18 48 b9 6e d6 c2 10 2d 54 89 a0 50 e7 = 1d 29 a5 a6 6e ce 11 de 5f b5 c9 55 8d 54 da 28 fe 45 b0 bc 4d b4 e5 b8 = 80 30 bf c4 a3 52 b4 b7 06 8e cc f6 56 ba e7 ad 6a 35 61 53 15 fc 7c 49 = d4 20 03 88 d5 ec a6 7c 2e 82 2e 06 93 36 c6 9b 40 db 67 e0 f3 c8 12 09 = c5 0f 32 16 a4 b8 9f b3 ae 1b 98 4b 78 51 a2 ec 6f 68 ab 12 b1 01 ab 12 = 0e 1e a7 31 3b b9 3b 5a 0f 71 18 5c 7f ea 01 7d db 92 76 98 61 c2 9d ba = 4f bc 43 22 80 d5 df f2 1b 36 d1 c4 c7 90 12 8b 22 69 99 50 bb 18 bf 74 = c4 48 cd fe 54 7d 8e d4 f6 57 d8 00 5f dc 0c d7 a0 50 c2 d4 60 50 a4 4c = 43 76 35 58 58 

MAC
98 1f be 8b 18 42 88 27 6e 7a 93 ea = bc 89 9c 4a
</pre>


=3D=3D= =3D v2 Messages Structure =3D=3D=3D

{|class=3D"wikitable"
! Field Size !! Description !! Data type !! = Comments
|-
| 3 || length = & flag || 23 + 1 bits || Encrypted length of ciphertext payload (not = counting the MAC tag) in number of bytes (only 2^23 is usable, most = significant bit is the rekey-flag)
|-
| 1-13 || encrypted command || variable || ASCII command (or = one byte short command ID)
|-
| = ? || encrypted payload || ? || The actual data
|-
| 16 || MAC tag || ? || 128bit = MAC-tag
|}

Encrypted messages do not have the = 4byte network magic.

The maximum message size is 2^23 (8=E2=80=99388=E2=80=99608) = bytes. Future communication MAY 
exceed this = limit and thus MUST be split into different messages.

Decrypting and = processing the message before the authentication succeeds = (MAC 
verified) MUST not be done.

The 4byte sha256 = checksum is no longer required because the AEAD (MAC).

Both peers MUST keep = track of the message sequence number (uint32) of sent = and 
received messages for building a 64-bit = symmetric cipher IV.

The command field MUST start with a byte that defines the = length of the ASCII 
command string up to 12 = chars (1 to 12) or a short command ID (see below).

=3D=3D=3D=3D Short = Command ID =3D=3D=3D=3D

To save valuable bandwidth, the v2 message format supports = message command 
short IDs for message types = with high frequency. The ID/string mapping is a 
peer to peer arrangement and MAY be negotiated between the = initiating and 
responding peer. A peer = conforming to this proposal MUST support short IDs 
based on the table below and SHOULD use short command IDs for = outgoing messages.

{|class=3D"wikitable"
! Number !! = Command
|-
| 13 || = INV
|-
| 14 || = HEADERS
|-
| 15 || = PING
|-
| 16 || PONG
|-
|}

=3D=3D=3D=3D Length comparisons between = v1 and v2 messages =3D=3D=3D=3D

<pre>
v1 in: = 4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+36(Payload) =3D=3D = 60
v2 inv: = 3(MessageSize&Flag)+1(Command)+36(Payload)+16(MAC) =3D=3D = 56
(93.33%)
</pre>

<pre>
v1 ping: = 4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+8(Payload) =3D=3D = 32
v2 pong: = 3(MessageSize&Flag)+1(Command)+8(Payload)+16(MAC) =3D=3D = 28
(87.5%)
</pre>

<pre>
v1 block: = 4(Magic)+12(Command)+4(MessageSize)+4(Checksum)+1=E2=80=99048=E2=80=99576(= Payload) =3D 1=E2=80=99048=E2=80=99600
v2 block: = 3(MessageSize&Flag)+6(CommandStr)+8(Payload)+16(MAC) =3D=3D 28 =3D = 1=E2=80=99048=E2=80=99601
(100.000095%)
</pre>

=3D=3D=3D Re-Keying =3D=3D=3D

Re-keying can be signaled by setting = the most significant bit in the length 
field = before encryption. A peer signaling a rekey MUST use the next key = for 
encryption messages AFTER the message = where the signaling has been done.

A peer identifying a rekey by checking = the most significant bit in the envelope 
length= must use the next key for decrypt messages AFTER the message where = the 
signaling has been detected.

The next symmetric = cipher key MUST be calculated by = <code>SHA256(SHA256(session 
ID || = old_symmetric_cipher_key))</code> and the packet sequence number = of the 
according encryption direction must be = set to 0.

Re-Keying interval is a peer policy with a minimum timespan = of 10 seconds.

The Re-Keying must be done after every 1GB of data sent = (recommended by RFC4253 
SSH Transport) or if = the last rekey was more than an hour ago.

Peers calculate the counterparty limits = and MUST disconnect immediately if a 
violation = of the limits has been detected.


=3D=3D= =3D Risks =3D=3D=3D

The encryption does not include an authentication scheme. = This BIP does not 
cover a proposal to avoid = MITM attacks during the encryption initialization. 
However, peers MUST show the session-id to the user on = request which allows to 
identify a MITM by a = manual verification on a secure channel.

Optional authentication schemes may be = covered by other proposals <ref 
name=3D"bip150">[https://github.com/bitcoin/bips/blob/master= /bip-0150.mediawiki 
BIP150]</ref>.

An attacker could delay or halt v2 = protocol enforcement by providing a 
reasonable = amount of peers not supporting the v2 protocol.

=3D=3D Compatibility =3D=3D

This proposal is = backward compatible (as long as not enforced). = Non-supporting 
peers can still use = unencrypted communications.

=3D=3D Reference implementation =3D=3D
* = Complete Bitcoin Core implementation: = https://github.com/bitcoin/bitcoin/pull/14032
* = Reference implementation of the AEAD in C: = https://github.com/jonasschnelli/chacha20poly1305
=3D=3D References =3D=3D

<references/>

=3D=3D Acknowledgements =3D=3D
* Pieter Wuille and Gregory Maxwell for most of the ideas in = this BIP.
* Tim Ruffing for the review and the hint = for the enhancement of the symmetric 
key = derivation


=3D=3D Copyright =3D=3D
This work is placed in the public domain.

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