Roughtime
draft-ietf-ntp-roughtime-04
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Aanchal Malhotra , Adam Langley , Watson Ladd , Marcus Dansarie | ||
| Last updated | 2021-02-21 (Latest revision 2020-08-29) | ||
| Replaces | draft-roughtime-aanchal | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-ntp-roughtime-04
Internet Engineering Task Force A. Malhotra
Internet-Draft Boston University
Intended status: Informational A. Langley
Expires: August 25, 2021 Google
W. Ladd
Cloudflare
M. Dansarie
February 21, 2021
Roughtime
draft-ietf-ntp-roughtime-04
Abstract
This document specifies Roughtime - a protocol that aims to achieve
rough time synchronization while detecting servers that provide
inaccurate time and providing cryptographic proof of their
malfeasance.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 25, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Malhotra, et al. Expires August 25, 2021 [Page 1]
Internet-Draft Roughtime February 2021
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4
4. The Guarantee . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Message Format . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Data Types . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.1. int32 . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.2. uint32 . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.3. uint64 . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.4. Tag . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.5. Timestamp . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Header . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Requests . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Responses . . . . . . . . . . . . . . . . . . . . . . . . 9
6.3. The Merkle Tree . . . . . . . . . . . . . . . . . . . . . 11
6.3.1. Root Value Validity Check Algorithm . . . . . . . . . 11
6.4. Validity of Response . . . . . . . . . . . . . . . . . . 12
7. Integration into NTP . . . . . . . . . . . . . . . . . . . . 12
8. Grease . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Roughtime Servers . . . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11.1. Service Name and Transport Protocol Port Number Registry 13
11.2. Roughtime Version Registry . . . . . . . . . . . . . . . 14
11.3. Roughtime Tag Registry . . . . . . . . . . . . . . . . . 14
12. Security Considerations . . . . . . . . . . . . . . . . . . . 15
13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. Normative References . . . . . . . . . . . . . . . . . . 16
14.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Terms and Abbreviations . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Time synchronization is essential to Internet security as many
security protocols and other applications require synchronization
[RFC7384] [MCBG]. Unfortunately widely deployed protocols such as
the Network Time Protocol (NTP) [RFC5905] lack essential security
features, and even newer protocols like Network Time Security (NTS)
[RFC8915] lack mechanisms to ensure that the servers behave
Malhotra, et al. Expires August 25, 2021 [Page 2]
Internet-Draft Roughtime February 2021
correctly. Authenticating time servers prevents network adversaries
from modifying time packets, but an authenticated time server still
has full control over the contents of the time packet and may go
rogue. The Roughtime protocol provides cryptographic proof of
malfeasance, enabling clients to detect and prove to a third party a
server's attempts to influence the time a client computes.
+--------------+----------------------+-----------------------------+
| Protocol | Authenticated Server | Server Malfeasance Evidence |
+--------------+----------------------+-----------------------------+
| NTP, Chronos | N | N |
| NTP-MD5 | Y* | N |
| NTP-Autokey | Y** | N |
| NTS | Y | N |
| Roughtime | Y | Y |
+--------------+----------------------+-----------------------------+
Security Properties of current protocols
Table 1
Y* For security issues with symmetric-key based NTP-MD5
authentication, please refer to RFC 8573 [RFC8573].
Y** For security issues with Autokey Public Key Authentication, refer
to [Autokey].
o If a server's timestamps do not fit into the time context of other
servers' responses, then a Roughtime client can cryptographically
prove this misbehavior to third parties. This helps detect "bad"
servers.
o A Roughtime client can roughly detect (with no absolute guarantee)
a delay attack [DelayAttacks] but can not cryptographically prove
this to a third party. However, the absence of proof of
malfeasance should not be considered a proof of absence of
malfeasance. So Roughtime should not be used as a witness that a
server is overall "good".
o Note that delay attacks cannot be detected/stopped by any
protocol. Delay attacks can not, however, undermine the security
guarantees provided by Roughtime.
o Although delay attacks cannot be prevented, they can be limited to
a predetermined upper bound. This can be done by defining a
maximal tolerable Round Trip Time (RTT) value, MAX-RTT, that a
Roughtime client is willing to accept. A Roughtime client can
measure the RTT of every request-response handshake and compare it
Malhotra, et al. Expires August 25, 2021 [Page 3]
Internet-Draft Roughtime February 2021
to MAX-RTT. If the RTT exceeds MAX-RTT, the corresponding server
is assumed to be a falseticker. When this approach is used the
maximal time error that can be caused by a delay attack is MAX-
RTT/2. It should be noted that this approach assumes that the
nature of the system is known to the client, including reasonable
upper bounds on the RTT value.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Protocol Overview
Roughtime is a protocol for rough time synchronization that enables
clients to provide cryptographic proof of server malfeasance. It
does so by having responses from servers include a signature with a
certificate rooted in a long-term public/private key pair over a
value derived from a nonce provided by the client in its request.
This provides cryptographic proof that the timestamp was issued after
the server received the client's request. The derived value included
in the server's response is the root of a Merkle tree which includes
the hash of the client's nonce as the value of one of its leaf nodes.
This enables the server to amortize the relatively costly signing
operation over a number of client requests.
Single server mode: At its most basic level, Roughtime is a one round
protocol in which a completely fresh client requests the current time
and the server sends a signed response. The response includes a
timestamp and a radius used to indicate the server's certainty about
the reported time. For example, a radius of 1,000,000 microseconds
means the server is absolutely confident that the true time is within
one second of the reported time.
The server proves freshness of its response as follows: The client's
request contains a nonce. The server incorporates the nonce into its
signed response so that the client can verify the server's signatures
covering the nonce issued by the client. Provided that the nonce has
sufficient entropy, this proves that the signed response could only
have been generated after the nonce.
Malhotra, et al. Expires August 25, 2021 [Page 4]
Internet-Draft Roughtime February 2021
4. The Guarantee
A Roughtime server guarantees that a response to a query sent at t_1,
received at t_2, and with timestamp t_3 has been created between the
transmission of the query and its reception. If t_3 is not within
that interval, a server inconsistency may be detected and used to
impeach the server. The propagation of such a guarantee and its use
of type synchronization is discussed in Section 7. No delay attacker
may affect this: they may only expand the interval between t_1 and
t_2, or of course stop the measurement in the first place.
5. Message Format
Roughtime messages are maps consisting of one or more (tag, value)
pairs. They start with a header, which contains the number of pairs,
the tags, and value offsets. The header is followed by a message
values section which contains the values associated with the tags in
the header. Messages MUST be formatted according to Figure 1 as
described in the following sections.
Messages may be recursive, i.e. the value of a tag can itself be a
Roughtime message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of pairs (uint32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. N-1 offsets (uint32) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. N tags (uint32) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Values .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Roughtime Message Format
Malhotra, et al. Expires August 25, 2021 [Page 5]
Internet-Draft Roughtime February 2021
5.1. Data Types
5.1.1. int32
An int32 is a 32 bit signed integer. It is serialized in sign-
magnitude representation with the sign bit in the most significant
bit. It is serialized least significant byte first. The negative
zero value (0x80000000) MUST NOT be used.
5.1.2. uint32
A uint32 is a 32 bit unsigned integer. It is serialized with the
least significant byte first.
5.1.3. uint64
A uint64 is a 64 bit unsigned integer. It is serialized with the
least significant byte first.
5.1.4. Tag
Tags are used to identify values in Roughtime messages. A tag is a
uint32 but may also be listed as a sequence of up to four ASCII
characters [RFC0020]. ASCII strings shorter than four characters can
be unambiguously converted to tags by padding them with zero bytes.
For example, the ASCII string "NONC" would correspond to the tag
0x434e4f4e and "PAD" would correspond to 0x00444150.
5.1.5. Timestamp
A timestamp is a uint64 interpreted in the following way. The most
significant 3 bytes contain the integer part of a Modified Julian
Date (MJD). The least significant 5 bytes is a count of the number
of Coordinated Universal Time (UTC) microseconds [ITU-R_TF.460-6]
since midnight on that day.
The MJD is the number of UTC days since 17 November 1858
[ITU-R_TF.457-2]. It is useful to note that 1 January 1970 is 40,587
days after 17 November 1858.
Note that, unlike NTP, this representation does not use the full
number of bits in the fractional part and that days with leap seconds
will have more or fewer than the nominal 86,400,000,000 microseconds.
Malhotra, et al. Expires August 25, 2021 [Page 6]
Internet-Draft Roughtime February 2021
5.2. Header
All Roughtime messages start with a header. The first four bytes of
the header is the uint32 number of tags N, and hence of (tag, value)
pairs. The following 4*(N-1) bytes are offsets, each a uint32. The
last 4*N bytes in the header are tags.
Offsets refer to the positions of the values in the message values
section. All offsets MUST be multiples of four and placed in
increasing order. The first post-header byte is at offset 0. The
offset array is considered to have a not explicitly encoded value of
0 as its zeroth entry. The value associated with the ith tag begins
at offset[i] and ends at offset[i+1]-1, with the exception of the
last value which ends at the end of the message. Values may have
zero length.
Tags MUST be listed in the same order as the offsets of their values.
A tag MUST NOT appear more than once in a header. Tags MUST also be
sorted in ascending order by numeric value.
6. Protocol
As described in Section 3, clients initiate time synchronization by
sending requests containing a nonce to servers who send signed time
responses in return. Roughtime packets can be sent between clients
and servers either as UDP datagrams or via TCP streams. Servers
SHOULD support the UDP transport mode, while TCP transport is
OPTIONAL.
A Roughtime packet MUST be formatted according to Figure 2 and as
described here. The first field is a uint64 with the value
0x4d49544847554f52 ("ROUGHTIM" in ASCII). The second field is a
uint32 and contains the length of the third field. The third and
last field contains a Roughtime message as specified in Section 5.1.
Malhotra, et al. Expires August 25, 2021 [Page 7]
Internet-Draft Roughtime February 2021
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x4d49544847554f52 (uint64) |
| ("ROUGHTIM") |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message length (uint32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Roughtime message .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Roughtime Packet Format
Roughtime request and response packets MUST be transmitted in a
single datagram when the UDP transport mode is used. Setting the
packet's don't fragment bit [RFC0791] is OPTIONAL in IPv4 networks.
Multiple requests and responses can be exchanged over an established
TCP connection. Clients MAY send multiple requests at once and
servers MAY send responses out of order. The connection SHOULD be
closed by the client when it has no more requests to send and has
received all expected responses. Either side SHOULD close the
connection in response to synchronization, format, implementation-
defined timeouts, or other errors.
All requests and responses MUST contain the VER tag. It contains a
list of one or more uint32 version numbers. The version of Roughtime
specified by this memo has version number 1.
For testing drafts of this memo, a version number of 0x80000000 plus
the draft number is used.
6.1. Requests
A request MUST contain the tags NONC and VER.
The value of the NONC tag is a 64 byte nonce. It SHOULD be generated
in a manner indistinguishable from random.
In a request, the VER tag contains a list of versions. The VER tag
MUST include at least one Roughtime version supported by the client.
The client MUST ensure that the version numbers and tags included in
the request are not incompatible with each other or the packet
contents.
Malhotra, et al. Expires August 25, 2021 [Page 8]
Internet-Draft Roughtime February 2021
Tags other than NONC and VER SHOULD be ignored by the server.
The size of the request message SHOULD be at least 1024 bytes when
the UDP transport mode is used. To attain this size the PAD tag
SHOULD be added to the message. Its value SHOULD be all zeros.
Responding to requests shorter than 1024 bytes is OPTIONAL and
servers MUST NOT send responses larger than the requests they are
replying to.
6.2. Responses
A response MUST contain the tags CERT, INDX, NONC, PATH, SIG, SREP,
and VER.
The SIG tag is a signature over the SREP value using the public key
contained in CERT, as explained below.
The SREP tag contains a time response. Its value is a Roughtime
message with the tags ROOT, MIDP, and RADI. The server MAY include
any of the tags DUT1, DTAI and LEAP in the contents of the SREP tag.
The NONC tag contains the nonce of the message being responded to.
The ROOT tag contains a 32 byte value of a Merkle tree root as
described in Section 6.3.
The MIDP tag value is a timestamp of the moment of processing.
The RADI tag value is a uint32 representing the server's estimate of
the accuracy of MIDP in microseconds. Servers MUST ensure that the
true time is within (MIDP-RADI, MIDP+RADI) at the time they compose
the response message.
The DUT1 tag value is an int32 indicating the predicted difference
between UT1 and UTC (UT1 - UTC) in milliseconds as given by the
International Earth Rotation and Reference Systems Service (IERS).
The DTAI tag value is an int32 indicating the current difference
between International Atomic Time (TAI) and UTC (TAI - UTC) in
milliseconds as published in the International Bureau of Weights and
Measures' (BIPM) Circular T.
The LEAP tag contains zero or more int32 values, each representing a
past or future leap second event. Positive values represent the
addition of a second and negative values represent the removal of a
second. The absolute value represents the MJD of the second after
the leap second event, i.e., the first second with a new UTC - TAI
difference. The leap second events MUST be sorted in reverse
Malhotra, et al. Expires August 25, 2021 [Page 9]
Internet-Draft Roughtime February 2021
chronological order and the first item MUST be the last (past or
future) leap second event that the server knows about. A LEAP tag
with zero int32 values indicates that the server does not hold any
updated leap second information.
The SIG tag value is a 64 byte Ed25519 signature [RFC8032] over a
signature context concatenated with the entire value of a DELE or
SREP tag. Signatures of DELE tags MUST use the ASCII string
"RoughTime v1 delegation signature--" and signatures of SREP tags
MUST use the ASCII string "RoughTime v1 response signature" as
signature context. Both strings MUST include a terminating zero
byte.
The CERT tag contains a public-key certificate signed with the
server's long-term key. Its value is a Roughtime message with the
tags DELE and SIG, where SIG is a signature over the DELE value.
The DELE tag contains a delegated public-key certificate used by the
server to sign the SREP tag. Its value is a Roughtime message with
the tags MINT, MAXT, and PUBK. The purpose of the DELE tag is to
enable separation of a long-term public key from keys on devices
exposed to the public Internet.
The MINT tag is the minimum timestamp for which the key in PUBK is
trusted to sign responses. MIDP MUST be more than or equal to MINT
for a response to be considered valid.
The MAXT tag is the maximum timestamp for which the key in PUBK is
trusted to sign responses. MIDP MUST be less than or equal to MAXT
for a response to be considered valid.
The PUBK tag contains a temporary 32 byte Ed25519 public key which is
used to sign the SREP tag.
The INDX tag value is a uint32 determining the position of NONC in
the Merkle tree used to generate the ROOT value as described in
Section 6.3.
The PATH tag value is a multiple of 32 bytes long and represents a
path of 32 byte hash values in the Merkle tree used to generate the
ROOT value as described in Section 6.3. In the case where a response
is prepared for a single request and the Merkle tree contains only
the root node, the size of PATH is zero.
In a response, the VER tag MUST contain a single version number. It
SHOULD be one of the version numbers supplied by the client in its
request. The server MUST ensure that the version number corresponds
with the rest of the packet contents.
Malhotra, et al. Expires August 25, 2021 [Page 10]
Internet-Draft Roughtime February 2021
6.3. The Merkle Tree
A Merkle tree is a binary tree where the value of each non-leaf node
is a hash value derived from its two children. The root of the tree
is thus dependent on all leaf nodes.
In Roughtime, each leaf node in the Merkle tree represents the nonce
of one request that a response message is sent in reply to. Leaf
nodes are indexed left to right, beginning with zero.
The values of all nodes are calculated from the leaf nodes and up
towards the root node using the first 32 bytes of the output of the
SHA-512 hash algorithm [SHS]. For leaf nodes, the byte 0x00 is
prepended to the nonce before applying the hash function. For all
other nodes, the byte 0x01 is concatenated with first the left and
then the right child node value before applying the hash function.
The value of the Merkle tree's root node is included in the ROOT tag
of the response.
The index of a request's nonce node is included in the INDX tag of
the response.
The values of all sibling nodes in the path between a request's nonce
node and the root node is stored in the PATH tag so that the client
can reconstruct and validate the value in the ROOT tag using its
nonce.
6.3.1. Root Value Validity Check Algorithm
One starts by computing the hash of the NONC value from the request,
with 0x00 prepended. Then one walks from the least significant bit
of INDX to the most significant bit, and also walks towards the end
of PATH.
If PATH ends then the remaining bits of the INDX MUST be all zero.
This indicates the termination of the walk, and the current value
MUST equal ROOT if the response is valid.
If the current bit is 0, one hashes 0x01, the current hash, and the
value from PATH to derive the next current value.
If the current bit is 1 one hashes 0x01, the value from PATH, and the
current hash to derive the next current value.
Malhotra, et al. Expires August 25, 2021 [Page 11]
Internet-Draft Roughtime February 2021
6.4. Validity of Response
A client MUST check the following properties when it receives a
response. We assume the long-term server public key is known to the
client through other means.
o The signature in CERT was made with the long-term key of the
server.
o The DELE timestamps and the MIDP value are consistent.
o The INDX and PATH values prove NONC was included in the Merkle
tree with value ROOT using the algorithm in Section 6.3.1.
o The signature of SREP in SIG validates with the public key in
DELE.
A response that passes these checks is said to be valid. Validity of
a response does not prove the time is correct, but merely that the
server signed it, and thus guarantees that it began to compute the
signature at a time in the interval (MIDP-RADI, MIDP+RADI).
7. Integration into NTP
We assume that there is a bound PHI on the frequency error in the
clock on the machine. Given a measurement taken at a local time t1,
we know the true time is in [ t1-delta-sigma, t1-delta+sigma ].
After d seconds have elapsed we know the true time is within [ t1-
delta-sigma-d*PHI, t1-delta+sigma+d*PHI]. A simple and effective way
to mix with NTP or PTP discipline of the clock is to trim the
observed intervals in NTP to fit entirely within this window or
reject measurements that fall to far outside. This assumes time has
not been stepped. If the NTP process decides to step the time, it
MUST use Roughtime to ensure the new truetime estimate that will be
stepped to is consistent with the true time.
Should this window become too large, another Roughtime measurement is
called for. The definition of "too large" is implementation defined.
Implementations MAY use other, more sophisticated means of adjusting
the clock respecting Roughtime information.
8. Grease
Servers MAY send back a fraction of responses that are syntactically
invalid or contain invalid signatures as well as incorrect times.
Clients MUST properly reject such responses. Servers MUST NOT send
Malhotra, et al. Expires August 25, 2021 [Page 12]
Internet-Draft Roughtime February 2021
back responses with incorrect times and valid signatures. Either
signature MAY be invalid for this application.
9. Roughtime Servers
The below list contains a list of servers with their public keys in
Base64 format. These servers may implement older versions of this
specification.
address: roughtime.cloudflare.com
port: 2002
long-term key: gD63hSj3ScS+wuOeGrubXlq35N1c5Lby/S+T7MNTjxo=
address: roughtime.int08h.com
port: 2002
long-term key: AW5uAoTSTDfG5NfY1bTh08GUnOqlRb+HVhbJ3ODJvsE=
address: roughtime.sandbox.google.com
port: 2002
long-term key: etPaaIxcBMY1oUeGpwvPMCJMwlRVNxv51KK/tktoJTQ=
address: roughtime.se
port: 2002
long-term key: S3AzfZJ5CjSdkJ21ZJGbxqdYP/SoE8fXKY0+aicsehI=
10. Acknowledgements
Thomas Peterson corrected multiple nits. Peter Loethberg (Lothberg),
Tal Mizrahi, Ragnar Sundblad, Kristof Teichel, and the other members
of the NTP working group contributed comments and suggestions.
11. IANA Considerations
11.1. Service Name and Transport Protocol Port Number Registry
IANA is requested to allocate the following entry in the Service Name
and Transport Protocol Port Number Registry [RFC6335]:
Service Name: Roughtime
Transport Protocol: tcp,udp
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: Roughtime time synchronization
Malhotra, et al. Expires August 25, 2021 [Page 13]
Internet-Draft Roughtime February 2021
Reference: [[this memo]]
Port Number: [[TBD1]], selected by IANA from the User Port range
11.2. Roughtime Version Registry
IANA is requested to create a new registry entitled " Roughtime
Version Registry " Entries shall have the following fields:
Version ID (REQUIRED): a 32-bit unsigned integer
Version name (REQUIRED): A short text string naming the version
being identified.
Reference (REQUIRED): A reference to a relevant specification
document.
The policy for allocation of new entries SHOULD be: IETF Review.
The initial contents of this registry shall be as follows:
+-----------------------+------------------------------+------------+
| Version ID | Version name | Reference |
+-----------------------+------------------------------+------------+
| 0x0 | Reserved | [[this |
| | | memo]] |
| 0x1 | Roughtime version 1 | [[this |
| | | memo]] |
| 0x2-0x7fffffff | Unassigned | |
| 0x80000000-0xffffffff | Reserved for Private or | [[this |
| | Experimental use | memo]] |
+-----------------------+------------------------------+------------+
11.3. Roughtime Tag Registry
IANA is requested to create a new registry entitled "Roughtime Tag
Registry". Entries SHALL have the following fields:
Tag (REQUIRED): A 32-bit unsigned integer in hexadecimal format.
ASCII Representation (OPTIONAL): The ASCII representation of the
tag in accordance with Section 5.1.4 of this memo, if applicable.
Reference (REQUIRED): A reference to a relevant specification
document.
The policy for allocation of new entries in this registry SHOULD be:
Specification Required.
Malhotra, et al. Expires August 25, 2021 [Page 14]
Internet-Draft Roughtime February 2021
The initial contents of this registry SHALL be as follows:
+------------+----------------------+---------------+
| Tag | ASCII Representation | Reference |
+------------+----------------------+---------------+
| 0x00444150 | PAD | [[this memo]] |
| 0x00474953 | SIG | [[this memo]] |
| 0x00524556 | VER | [[this memo]] |
| 0x31545544 | DUT1 | [[this memo]] |
| 0x434e4f4e | NONC | [[this memo]] |
| 0x454c4544 | DELE | [[this memo]] |
| 0x48544150 | PATH | [[this memo]] |
| 0x49415444 | DTAI | [[this memo]] |
| 0x49444152 | RADI | [[this memo]] |
| 0x4b425550 | PUBK | [[this memo]] |
| 0x5041454c | LEAP | [[this memo]] |
| 0x5044494d | MIDP | [[this memo]] |
| 0x50455253 | SREP | [[this memo]] |
| 0x544e494d | MINT | [[this memo]] |
| 0x544f4f52 | ROOT | [[this memo]] |
| 0x54524543 | CERT | [[this memo]] |
| 0x5458414d | MAXT | [[this memo]] |
| 0x58444e49 | INDX | [[this memo]] |
+------------+----------------------+---------------+
12. Security Considerations
Since the only supported signature scheme, Ed25519, is not quantum
resistant, the Roughtime version described in this memo will not
survive the advent of quantum computers.
Maintaining a list of trusted servers and adjudicating violations of
the rules by servers is not discussed in this document and is
essential for security. Roughtime clients MUST update their view of
which servers are trustworthy in order to benefit from the detection
of misbehavior.
Validating timestamps made on different dates requires knowledge of
leap seconds in order to calculate time intervals correctly.
Servers carry out a significant amount of computation in response to
clients, and thus may experience vulnerability to denial of service
attacks.
This protocol does not provide any confidentiality, and given the
nature of timestamps such impact is minor.
Malhotra, et al. Expires August 25, 2021 [Page 15]
Internet-Draft Roughtime February 2021
The compromise of a PUBK's private key, even past MAXT, is a problem
as the private key can be used to sign invalid times that are in the
range MINT to MAXT, and thus violate the good behavior guarantee of
the server.
Servers MUST NOT send response packets larger than the request
packets sent by clients, in order to prevent amplification attacks.
13. Privacy Considerations
This protocol is designed to obscure all client identifiers. Servers
necessarily have persistent long-term identities essential to
enforcing correct behavior.
Generating nonces in a nonrandom manner can cause leaks of private
data or enable tracking of clients as they move between networks.
14. References
14.1. Normative References
[ITU-R_TF.457-2]
ITU-R, "Use of the Modified Julian Date by the Standard-
Frequency and Time-Signal Services", ITU-R
Recommendation TF.457-2, October 1997.
[ITU-R_TF.460-6]
ITU-R, "Standard-Frequency and Time-Signal Emissions",
ITU-R Recommendation TF.460-6, February 2002.
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
Malhotra, et al. Expires August 25, 2021 [Page 16]
Internet-Draft Roughtime February 2021
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard", DOI 10.6028/NIST.FIPS.180-4, FIPS 180-4,
August 2015.
14.2. Informative References
[Autokey] Rottger, S., "Analysis of the NTP Autokey Procedures",
2012, <https://zero-entropy.de/autokey_analysis.pdf>.
[DelayAttacks]
Mizrahi, T., "A Game Theoretic Analysis of Delay Attacks
Against Time Synchronization Protocols",
DOI 10.1109/ISPCS.2012.6336612, 2012,
<https://ieeexplore.ieee.org/document/6336612>.
[MCBG] Malhotra, A., Cohen, I., Brakke, E., and S. Goldberg,
"Attacking the Network Time Protocol", 2015,
<https://eprint.iacr.org/2015/1020>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Malhotra, et al. Expires August 25, 2021 [Page 17]
Internet-Draft Roughtime February 2021
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8573] Malhotra, A. and S. Goldberg, "Message Authentication Code
for the Network Time Protocol", RFC 8573,
DOI 10.17487/RFC8573, June 2019,
<https://www.rfc-editor.org/info/rfc8573>.
[RFC8915] Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
Sundblad, "Network Time Security for the Network Time
Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
<https://www.rfc-editor.org/info/rfc8915>.
Appendix A. Terms and Abbreviations
ASCII American Standard Code for Information Interchange
IANA Internet Assigned Numbers Authority
JSON JavaScript Object Notation [RFC8259]
MJD Modified Julian Date
NTP Network Time Protocol [RFC5905]
NTS Network Time Security [RFC8915]
TAI International Atomic Time (Temps Atomique International)
[ITU-R_TF.460-6]
TCP Transmission Control Protocol [RFC0793]
UDP User Datagram Protocol [RFC0768]
UT Universal Time [ITU-R_TF.460-6]
UTC Coordinated Universal Time [ITU-R_TF.460-6]
Malhotra, et al. Expires August 25, 2021 [Page 18]
Internet-Draft Roughtime February 2021
Authors' Addresses
Aanchal Malhotra
Boston University
111 Cummington Mall
Boston 02215
USA
Email: aanchal4@bu.edu
Adam Langley
Google
Email:
agl@google.com
Watson Ladd
Cloudflare
101 Townsend St
San Francisco
USA
Email: watsonbladd@gmail.com
Marcus Dansarie
Sweden
Email: marcus@dansarie.se
URI: https://orcid.org/0000-0001-9246-0263
Malhotra, et al. Expires August 25, 2021 [Page 19]