Internet Engineering Task Force IETF MSEC
Internet Draft Perrig, Canetti, Song, Tygar, Briscoe
draft-ietf-msec-tesla-intro-03.txt CMU / IBM / CMU / UC Berkeley / BT
August 2004
Expires: 1 February 2005
TESLA: Multicast Source Authentication Transform Introduction
STATUS OF THIS MEMO
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Abstract
Data authentication is an important component for many broadcast
applications, for example audio and video Internet broadcasts, or
data distribution by satellite. This document introduces TESLA,
short for Timed Efficient Stream Loss-tolerant Authentication, a
secure source authentication mechanism for multicast or broadcast
data streams. This document provides an algorithmic description of
TESLA for informational purposes, and in particular, is intended to
assist in writing standardizable and secure specifications for
protocols based on TESLA in different contexts.
The main deterrents so far for a data authentication mechanism for
multicast were the seemingly conflicting requirements: loss
tolerance, efficiency, and no per-receiver state at the sender. The
problem is particularly hard in settings with high packet loss
rates and where lost packets are not retransmitted, and where the
receivers want to authenticate each packet they do receive.
TESLA provides authentication of individual data packets,
regardless of loss rate. In addition, TESLA features low overhead
for both sender and receiver, and does not require per-receiver
state at the sender. TESLA is secure as long as the sender and
receiver are loosely time synchronized.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Functionality . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Threat Model and Security Guarantee . . . . . . . . . . . 4
2.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 5
3 The Basic TESLA Protocol . . . . . . . . . . . . . . . . 5
3.1 Protocol sketch . . . . . . . . . . . . . . . . . . . . . 6
3.2 Sender Setup . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Bootstrapping Receivers . . . . . . . . . . . . . . . . . 7
3.3.1 Time Synchronization. . . . . . . . . . . . . . . . . . . 8
3.4 Broadcasting Authenticated Messages . . . . . . . . . . . 8
3.5 Authentication at Receiver . . . . . . . . . . . . . . . 8
3.6 Determining the Key Disclosure Delay . . . . . . . . . . 9
3.7 An alternative delay description method . . . . . . . . . 10
3.8 Some extensions . . . . . . . . . . . . . . . . . . . . . 11
4 Layer placement . . . . . . . . . . . . . . . . . . . . . 11
5 Security considerations . . . . . . . . . . . . . . . . . 11
6 IP statement . . . . . . . . . . . . . . . . . . . . . . .12
7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . 12
8 References . . . . . . . . . . . . . . . . . . . . . . . 12
A Author Contact Information . . . . . . . . . . . . . . . 13
B Full Copyright Statement . . . . . . . . . . . . . . . . 14
1 Introduction
In multicast, a single packet can reach millions of receivers. This
unfortunately also introduces the danger that an attacker can
potentially also reach millions of receivers with a malicious
packet. Through source authentication, receivers can ensure that a
received multicast packet originates from the correct source.
In unicast communication, we can achieve data authentication
through a simple mechanism: the sender and the receiver share a
secret key to compute a message authentication code (MAC) of all
communicated data. When a message with a correct MAC arrives, the
receiver is assured that the sender generated that message.
Standard mechanisms achieve unicast authentication this way, for
example TLS or IPsec [1,2].
The symmetric MAC authentication is not secure in a broadcast
setting. Consider a sender that broadcasts authentic data to mutually
untrusting receivers. The symmetric MAC is not secure: every receiver
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knows the MAC key, and hence could impersonate the sender and forge
messages to other receivers. Intuitively, we need an asymmetric
mechanism to achieve authenticated broadcast, such that every receiver
can verify the authenticity of messages it receives, without being
able to generate authentic messages. Achieving this in an efficient
way is a challenging problem [3].
The standard approach to achieve such asymmetry for authentication
is to use asymmetric cryptography, e.g., a digital signature.
Digital signatures have the required asymmetric property: the
sender generates the signature with its private key, and all
receivers can verify the signature with the sender's public key,
but a receiver with the public key alone cannot generate a digital
signature for a new message. A digital signature provides
non-repudiation, a stronger property than authentication. However,
digital signatures have a high cost: they have a high computation
overhead for both the sender and the receiver, and most signatures
also have a high bandwidth overhead. Since we assume broadcast
settings where the sender does not retransmit lost packets, and the
receiver still wants to immediately authenticate each packet it
receives, we would need to attach a digital signature to each
message. Because of the high overhead of asymmetric cryptography,
this approach would restrict us to low-rate streams, and to senders
and receivers with powerful workstations. We can try to amortize one
digital signature over multiple messages. However, such an
approach is still expensive in contrast to symmetric cryptography,
since symmetric cryptography is in general 3 to 5 orders of
magnitude more efficient than asymmetric cryptography. In addition,
the straight-forward amortization of one digital signature over
multiple packets requires reliability, as the receiver needs to
receive all packets to verify the signature. A number of schemes
that follow this approach are [4,5,6,7,8]. See [9] for more
details.
This document presents the Timed Efficient Stream Loss-tolerant
Authentication protocol (TESLA). TESLA uses mainly symmetric
cryptography, and uses time delayed key disclosure to achieve the
required asymmetry property. However, TESLA requires loosely
synchronized clocks between the sender and the receivers. See more
details in Section 4. Other schemes that follow a similar approach
to TESLA are [10,11,12].
1.1 Notation
To denote the subscript or an index of a variable, we use the
underscore between the variable name and the index, e.g., the key K
with index i is K_i, the key K with index i+d is K_{i+d}. To write
a superscript we use the caret, e.g., function F with the argument
x executed i times is F^i(x).
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2 Functionality
TESLA provides delayed per-packet data authentication. The key idea
to providing both efficiency and security is a delayed disclosure of
keys. The delayed key disclosure results in an authentication delay.
In practice, the delay is on the order of one RTT (round-trip-time).
TESLA has the following properties:
o Low computation overhead for generation and verification of
authentication information
o Low communication overhead
o Limited buffering required for the sender and the receiver, hence
timely authentication for each individual packet
o Strong robustness to packet loss
o Scales to a large number of receivers
o Security is guaranteed as long as the sender and recipients are
loosely time synchronized, where synchronization can take place
at session set-up.
TESLA can be used either in the network layer, or in the transport
layer, or in the application layer. The delayed authentication,
however, requires buffering of packets until authentication is
completed. Certain applications intolerant of delay may be willing to
process packets in parallel to being buffered awaiting authentication,
as long as roll-back is possible if packets are later found to be
unauthenticated. For instance, an interactive video may play-out
packets still awaiting authentication, but if they are later found to
be unauthenticated, it could stop further play-out and warn the viewer
that the last x msec were unauthenticated and should be ignored.
However, in the remainder of this document, for brevity, we will
assume packets are not processed in parallel to buffering.
2.1 Threat Model and Security Guarantee
We design TESLA to be secure against a powerful adversary with the
following capabilities:
o Full control over the network. The adversary can eavesdrop,
capture, drop, resend, delay, and alter packets.
o Access to a fast network with negligible delay.
o The adversary's computational resources may be very large, but
not unbounded. In particular, this means that the adversary can
perform efficient computations, such as computing a reasonable
number of pseudo-random function applications and MACs with
negligible delay. Nonetheless, the adversary cannot find the key
of a pseudorandom function (or distinguish it from a random
function) with non-negligible probability.
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The security property of TESLA guarantees that the receiver never
accepts M_i as an authentic message unless the sender really sent
M_i. A scheme that provides this guarantee is called a secure
broadcast authentication scheme.
Since TESLA expects the receiver to buffer packets before
authentication, the receiver needs to protect itself from a
potential denial-of-service (DOS) attack due to a flood of bogus
packets.
2.2 Assumptions
TESLA makes the following assumptions in order to provide security:
1. The sender and the receiver must be be able to loosely
synchronize. Specifically, each receiver must be able to
compute an upper bound on the lag of the receiver clock
relative to the sender clock. We denote this quantity by D_t.
(That is, D_t = sender time - receiver time). We note that
an upper bound on D_t can be easily obtained via a simple
two-message exchange. (Such an exchange can be piggybacked on
any secure session initiation protocol. Alternatively, standard
protocols such as as NTP [16] can be used.
2. TESLA MUST be bootstrapped at session set-up through a
regular data authentication system. We recommend to use a
digital signature algorithm for this purpose, in which case
the receiver is required to have an authentic copy of either
the sender's public key certificate or a root key certificate
in case of a PKI (public-key infrastructure). Alternatively,
this initialization step can be done using any secure session
initiation protocol.
3. TESLA uses cryptographic MAC and PRF (pseudo-random functions).
These MUST be cryptographically secure. Further details on
the instantiation of the MAC and PRF are in Section 4.2.
4. We would like to emphasize that the security of TESLA does NOT
rely on any assumptions on network propagation delay.
3 The Basic TESLA Protocol
TESLA is described in several academic publications: A book on
broadcast security [13], a journal paper [14], and two conference
papers [8,15]. Please refer to these publications for an in-depth
treatment.
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3.1 Protocol sketch
We first outline the main ideas behind TESLA.
As we argue in the introduction, broadcast authentication requires
a source of asymmetry. TESLA uses time for asymmetry. We first make
sure that the sender and receivers are loosely time synchronized as
described above. Next, the sender forms a one-way chain of keys,
where each key in chain is associated with a time interval (say, a
second). Here is the basic approach:
o The sender attaches a MAC to each packet. The MAC is computed
over the contents of the packet. For each packet, the sender
uses the current key from the one-way chain as a cryptographic
key to compute the MAC.
o The sender discloses a key from the one-way chain after some
pre-defined time delay. (e.g., the key used in time interval i
is disclosed at time interval i+3.)
o Each receiver receives the packet. Each receiver knows the
schedule for disclosing keys and, since it has an upper bound
on the local time at the sender, it can check that the key used
to compute the MAC was not yet disclosed by the sender. If so,
then the receiver buffers the packet. Otherwise the packet is
dropped due to inability to authenticate. Note that we do not
know for sure whether a "late packet" is a bogus one or simply
a delayed packet. We drop the packet since we are unable to
authenticate it. (Ofcourse, an implementation may choose to
not drop packets and use them unauthenticated.)
o Each receiver checks that the disclosed key belongs to the
hash-chain (by checking against previously released keys in the
chain) and then checks the correctness of the MAC. If the MAC
is correct, the receiver accepts the packet.
Note that one-way chains have the property that if intermediate
values of the one-way chain are lost, they can be recomputed using
subsequent values in the chain . So, even if some key disclosures
are lost, a receiver can recover the corresponding keys and check
the correctness of earlier packets.
We now describe the stages of the basic TESLA protocol in this
order: sender setup, receiver bootstrap, sender transmission of
authenticated broadcast messages, and receiver authentication of
broadcast messages.
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3.2 Sender Setup
The sender divides the time into uniform intervals of duration T_int.
The sender assigns one key from the one-way chain to each time
interval in sequence.
The sender determines the length N of the one-way chain K_0, K_1,
..., K_N, and this length limits the maximum transmission duration
before a new one-way chain must be created. The sender picks a
random value for K_N. Using a pseudo-random function (PRF) f, the
sender constructs the one-way function F: F(k) = f_k(0). The rest
of the chain is computed recursively using K_i = F(K_{i+1}). Note
that this gives us K_i = F^{N-i}(K_N), so the receiver can compute
any value in the key chain from K_N even if is does not have
intermediate values. The key K_i will be used to authenticate
packets sent in time interval i.
Jakobsson [21], and Coppersmith and Jakobsson [22] present a storage
and computation efficient mechanism for one-way chains. For a chain
of length N, storage is about log(N) elements, and the computation
overhead to reconstruct each element is also about log(N).
The sender determines the duration of a time interval, T_int, and the
key disclodure delay, d. (T_int is measured in time units, say
millieconds, and d is measured in number of time intervals. That is,
a key that is used for time interval i will be desclosed in time
interval i+d.) It is stressed that the scheme remains secure for any
values of T_int and d. Still, correct choice of T_int and d is
crucial for the usability of the scheme. The choice is influenced by
the estimated network delay, the length of the transmission, and the
tolerable delay at the receiver. T_int that is too short will cause
the keys to run out too soon. T_int that is too long will cause
excessive delay in authentication for some of the packets (those that
were sent at the beginning of a time period). Delay d that is too
short will cause to many packets to be unverifiable by the receiver.
Delay d that is too long will cause excessive delay in authentication.
If the sender estimates that the average network delay is m
milliseconds, and the sender expects to send a packet every n
milliseconds, then a reasonable value for T_int is max(n,m) and
a reasonable value for d is ceil(2m/T_int). If the application can
tolerate higher authentication delay then T_int can be made
appropriately larger.
Finally, the sender needs to allow each receiver to synchronize
its time with the sender. See more details on how this can be done in
section 3.3. (It is stressed that estimating the network delay is a
separate task than the time synchronization between the sender and
the receivers.)
3.3 Bootstrapping Receivers
Before a receiver can authenticate messages with TESLA, it needs to
have:
o An upper bound D_t on the lag of its own clock with respect to
the clock of the sender. (That is, if the local time reading is
t, the current time reading at the sender is at most t+D_t.).
o One authenticated key of the one-way key chain. (Typically,
this will be the last key in the chain, i.e. K_0, this key will
be signed by the sender, and all receivers will verify the
signature against the public key of the signer.
o The disclosure schedule of keys:
- T_int, the interval duration.
- T_0, the start time of interval 1.
- N, the length of the one-way key chain.
- d, the key disclosure delay d (in number of intervals).
The receiver can perform the time synchronization and getting the
authenticated TESLA parameters in a two-round message exchange,
as described below. We stress again that time synchronization can
be performed as part of the registration protocol between the receiver
and sender, or between the receiver and a group controller.
3.3.1 Time Synchronization
Various approaches exist for time synchronization [16,17,18,19].
TESLA only requires the receiver to know an upper bound on the
delay of its local clock with respect to the sender's clock, so a
simple algorithm is sufficient. TESLA can be used with direct,
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indirect, and delayed synchronization as three default options.
The specific synchronization method will be part of each
instantiation of TESLA.
For completeness, we sketch a simple method for direct
synchronization between the sender and a receiver:
o The receiver sends a (sync t_r) message to the sender and
records its local time t_r.
o Upon receipt of the (sync t_r) message, the sender records its
local time t_s and sends (synch, t_r,t_s) to the receiver.
o Upon receiving (synch,t_r,t_s), the receiver sets D_t = t_s -
t_r + S, where S is an estimated bound on the clock drift
throughout the duration of the session.
Note:
o Assuming that the messages are authentic (i.e., the message
received the receiver was actually sent by the sender), and
assuming that the clock drift is at most S, then at any point
throughout the session we have that T_s < T_r + D_t, where T_s
is the current time at the sender and T_r is the current time
at the receiver.
o The exchange of sync messages needs to be authenticated. This
can be done in a number of ways, for instance a secure NTP
protocol, or in conjunction with a session set-up protocol.
For indirect time synchronization (eg, synchronization via a group
controller), the sender and the controller engage in a protocol for
finding the value D^0_t between the sender and the controller. Next,
each receiver R interacts with the group controller (say, when
registering to the group) and finds the value D^R_t between the group
controller and R. The overall value of D_t within R is set to the sum
D_t = D^R_t + D^0_t.
3.4 Broadcasting Authenticated Messages
Each key in the one-way key chain corresponds to a time interval.
Every time a sender broadcasts a message, it appends a MAC to the
message, using the key corresponding to the current time interval.
The key remains secret for the next d-1 intervals, so messages a
sender broadcasts in interval j effectively disclose key K_j-d. We
call d the key disclosure delay.
We do not want to use the same key multiple times in different
cryptographic operations, that is, to use key K_j to derive the
previous key of the one-way key chain K_{j-1}, and to use the same
key K_j as the key to compute the MACs in time interval j may
potentially lead to a cryptographic weakness. Using a pseudo-random
function (PRF) f', we construct the one-way function F': F'(k) =
f'_k(1). We use F' to derive the key to compute the MAC of messages
in each interval. The sender derives the MAC key as follows: K'_i
= F'(K_i). Figure 1 depicts the one-way key chain construction and
MAC key derivation. To broadcast message M_j in interval i the
sender constructs the packet
P_j = {M_j || i || MAC(K'_i,M_j) || K_{i-d}}
where || denotes concatenation.
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F(K_i) F(K_{i+1}) F(K_{i+2})
K_{i-1} <------- K_i <--------- Ki+1 <------- Ki+2
| | |
| F'(K_{i-1}) | F'(K_i) | F'(K_{i+1})
| | |
V V V
K'_{i-1} K'_i K'_{i+1}
Figure 1: At the top of the figure, we see the one-way key chain
(derived using the one-way function F), and the derived MAC keys
(derived using the one-way function F').
3.5 Authentication at Receiver
Once a sender discloses a key, we must assume that all parties might
have access to that key. An adversary could create a bogus message
and forge a MAC using the disclosed key. So whenever a packet
arrives, the receiver must verify that the MAC is based on a safe
key; a safe key is one that is still secret (only known by the
sender). We define a safe packet or safe message to be one with a MAC
that is computed with a safe key.
If the packet is not safe, the receiver must discard that packet,
because the authenticity is not assured any more.
We now explain the TESLA authentication in more detail. When the
receiver receives packet P_j which carries an interval index i, the
receiver first records local time T in which the packet arrived. It
then computes an upper bound t_j on the sender's clock at the time
where the packet arrived: t_j = T + D_t. To test whether the packet
is safe, the receiver then computes the highest interval x the
sender could possibly be in, namely x = floor((t_j - T_0) / T_int).
The receiver verifies that x < i + d (where i is the interval index),
which implies that the sender is not yet in the interval during which
it discloses the key K_i. If the condition fails then the receiver
considers the packet unauthenticated.
The receiver cannot yet verify the authenticity of packets sent in
interval i without key K_i. Instead, it adds the triplet ( i, M_j,
MAC( K'_i, M_j) ) to a buffer, and verifies the authenticity after it
learns K'_i.
What does a receiver do when it receives the disclosed key K_i?
First, it checks whether it already knows K_i or a later key K_j
with j>i. Then the receiver checks the legitimacy of K_i by verifying,
for some earlier key K_v (v<i) that K_v = F^{i-v}(K_i). The receiver
then computes K'_i = F'(K_i) and verifies the authenticity of packets
of interval i.
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Using a disclosed key, we can calculate all previous disclosed keys,
so even if packets are lost, we will still be able to verify
buffered, safe packets from earlier time intervals. Thus, if i-v>1,
the receiver can also verify the authenticity of the stored packets
of intervals v+1 ... i-1.
3.6 Determining the Key Disclosure Delay
An important TESLA parameter is the key disclosure delay d. Although
the choice of the disclosure delay does not affect the security of
the system, it is an important performance factor. A short disclosure
delay will cause packets to lose their safety property, so receivers
will discard them; but a long disclosure delay leads to a long
authentication delay for receivers. We recommend determining the
disclosure delay as follows: in direct time synchronization let
the RTT be a reasonable upper bound on the round trip time between the
sender and the receiver; then choose d = ceil( RTT / T_int) + 1. Note
that rounding up the quotient ensures that d >= 2. Also note that a
disclosure delay of one time interval (d=1) does not work. Consider
packets sent close to the boundary of the time interval: after the
network propagation delay and the receiver time synchronization
error, a receiver will need to discard the packet, because the sender
will already be in the next time interval, when it discloses the
corresponding key.
We stress that the security of TESLA does not rely on any assumptions on
network propagation delay: If the delay is longer than expected then
authentic packets may be considered unauthenticated. Still,
no unauthentic packet will be accepted as authentic.
3.7 An alternative delay description method
The above description instructs the sender to include the time interval
i in each packet. The receiver then uses i to determine the time at which
the key authenticating the packet is disclosed. This method limits the
the sender to a pre-determined schedule of disclosing keys.
Alternatively, the sender may directly include in each packet the time t_p
at which it is going to disclose the key for this packet. This way, the
receiver does not need to know the duration of intervals or the delay
factor d. All the receiver needs to know is the bound D_t on the clock
skew and T_0, the sender's local time at the initiation of the session.
Then the receiver records the local time T when the packet has arrived,
and verifies that
T <= T_0 + D_t + t_p.
Else the packet is considered aunauthenticated.
Another advantage of this method is that the sender is able to
change the duration of intervals and the key disclosure delay
dynamically throughout the session. It is stressed, however, that the
interval index i must still be included in the packet, to allow the
receiver to know which key K_i should be used to verify the packet.
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3.8 Some extensions
Let us mention two salient extensions of the basic TESLA scheme. A
first extension allows having multiple TESLA authentication chains
for a single stream, where each chain uses a different delay for
disclosing the keys. This extension is typically used to deal with
heterogeneous network delays within a single multicast
transmission. A second extension allows having most of the
buffering of packets at the sender side (rather than at the
receiver side). Both extensions are described in [15].
The requirement in TESLA to receive a key in a later packet for
authentication prevents a receiver from authenticating the last
part of a message. Thus, to enable authentication of the last part
of a message or of the last message before a transmission
suspension, the sender needs to send an empty message with the key
to enable authentication.
4 Layer placement
The TESLA authentication can be performed at any layer in the
networking stack. Three natural places are in the network, transport,
or the application layer. We list some considerations regarding the
choice of layer:
o Performing TESLA in the network layer has the advantage that the
transport or application layer only receives authenticated data,
potentially aiding a reliability protocol and preventing denial
of service attacks. (Indeed, reliable multicast tools based on
forward error correction are highly susceptible to denial of
service due to bogus packets.)
o Performing TESLA in either the transport or the application layer
has the advantage that the network layer remains unchanged; but it
has the drawback that packets are obtained by the application layer
only after being processed by the transport layer. Consequently,
if TCP is used then this may introduce additional and unpredictable
delays on top of the unavoidable network delays. (However, if UDP
is used then this is not a problem.)
o It should be kept in mind that, since TESLA relies upon timing
of packets, deploying TESLA on top of a protocol or layer which
aggressively buffers packets and hides the true packet arrival
time (e.g., TCP) will significantly reduce the perormance of TESLA.
5. Security Considerations
See the academic publications on TESLA [8,14,20] for several
security analyses. Regarding the security of implementations, by
far the most delicate point is the verification of the timing
conditions. Care should be taken to to make sure that: (a) the
value bound D_t on the clock skew is calculated according to the
spec at session set-up; (b) the receiver records the arrival time
of the packet as soon as possible after the packet's arrival, and
computes the safety condition correctly.
It is important to note that, unless appropriate measures are taken,
TESLA increases the susceptibility of receivers to denial of service
(DoS) attacks. Specifically, an attacker can flood a victim receiver
with bogus packets that need to be buffered for delayed authentication.
There are several measures against such attacks. Here we mention
some of the known mechanisms to reduce this susceptibility:
o Limit the size of buffers at the receiver side.
o Add an external MAC that is computed using either (a) a key that
is constant for the session and known to all receivers, or (b)
the key that is disclosed in the current packet. Both mechanisms
prevent simple flooding attacks but are still susceptible to
more sophisticated attacks that have some "inside" information
on the session.
o Move the buffering of packets to the sender side, and allow
receivers to authenticate packets immediately upon receipt.
This method is described in [14].
Finally, in common with all authentication schemes, if verification
is located separately from the ultimate destination application (e.g.
an IPSec tunnel end point), a trusted channel must be present between
verification and the application. For instance, the interface between
the verifier and the application might simply assume that packets
received by the application must have been verified by the verifier
(because otherwise they would have been dropped). The application is
then vulnerable to reception of packets that have managed to bypass
the verifier.
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6 IP Statement
The authors are not aware of any patents that encumber the free
use of TESLA.
7 Acknowledgments
We would like to thank Mike Luby for his feedback and support.
8 References
All references are informative.
[1] T. Dierks and C. Allen, "The TLS protocol version 1.0." Internet
Request for Comments RFC 2246, January 1999. Proposed standard.
[2] IPsec, "IP Security Protocol, IETF working group."
http://www.ietf.org/html.charters/ipsec-charter.html.
[3] D. Boneh, G. Durfee, and M. Franklin, "Lower bounds for multicast
message authentication," in Advances in Cryptology -- EUROCRYPT '2001
(B. Pfitzmann, ed.), vol. 2045 of Lecture Notes in Computer Science ,
(Innsbruck, Austria), pp. 434--450, Springer-Verlag, Berlin Germany,
2001.
[4] R. Gennaro and P. Rohatgi, "How to Sign Digital Streams," tech.
rep., IBM T.J.Watson Research Center, 1997.
[5] P. Rohatgi, "A compact and fast hybrid signature scheme for mul-
ticast packet authentication," in 6th ACM Conference on Computer and
Communications Security , November 1999.
[6] P. Rohatgi, "A hybrid signature scheme for multicast source
authentication," Internet Draft, Internet Engineering Task Force,
June 1999. Work in progress.
[7] C. K. Wong and S. S. Lam, "Digital signatures for flows and mul-
ticasts," in Proc. IEEE ICNP `98 , 1998.
[8] A. Perrig, R. Canetti, J. Tygar, and D. X. Song, "Efficient
authentication and signing of multicast streams over lossy channels,"
in IEEE Symposium on Security and Privacy , May 2000.
[9] R. Canetti, J. Garay, G. Itkis, D. Micciancio, M. Naor, and B.
Pinkas, "Multicast security: A taxonomy and some efficient construc-
tions," in Infocom '99 , 1999.
[10] S. Cheung, "An efficient message authentication scheme for link
state routing," in 13th Annual Computer Security Applications Confer-
ence , 1997.
Perrig, Canetti, Song, Tygar, Briscoe [Page 12]
Internet Draft draft-ietf-msec-tesla-intro-03 August 2004
[11] F. Bergadano, D. Cavagnino, and B. Crispo, "Chained stream
authentication," in Selected Areas in Cryptography 2000 , (Waterloo,
Canada), August 2000. A talk describing this scheme was given at IBM
Watson in August 1998.
[12] F. Bergadano, D. Cavalino, and B. Crispo, "Individual single
source authentication on the mbone," in ICME 2000 , Aug 2000. A talk
containing this work was given at IBM Watson, August 1998.
[13] A. Perrig and J. D. Tygar, Secure Broadcast Communication in
Wired and Wireless Networks Kluwer Academic Publishers, Oct. 2002.
ISBN 0792376501.
[14] A. Perrig, R. Canetti, J. D. Tygar, and D. Song, "The tesla
broadcast authentication protocol," RSA CryptoBytes , vol. 5, no.
Summer, 2002.
[15] A. Perrig, R. Canetti, D. Song, and J. D. Tygar, "Efficient and
secure source authentication for multicast," in Network and Dis-
tributed System Security Symposium, NDSS '01 , pp. 35--46, February
2001.
[16] D. L. Mills, "Network Time Protocol (Version 3) Specification,
Implementation and Analysis." Internet Request for Comments, March
1992. RFC 1305.
[17] B. Simons, J. Lundelius-Welch, and N. Lynch, "An overview of
clock synchronization," in Fault-Tolerant Distributed Computing (B.
Simons and A. Spector, eds.), no. 448 in LNCS, pp. 84--96, Springer-
Verlag, Berlin Germany, 1990.
[18] D. Mills, "Improved algorithms for synchronizing computer net-
work clocks," in Proceedings of the conference on Communications
architectures, protocols and applications, SIGCOMM 94 , (London,
England), pp. 317--327, 1994.
[19] L. Lamport and P. Melliar-Smith, "Synchronizing clocks in the
presence of faults," J. ACM , vol. 32, no. 1, pp. 52--78, 1985.
[20] Philippa Broadfoot and Gavin Lowe, "Analysing a Stream
Authentication Protocol using Model Checking. In Proceedings of the
7th European Symposium on Research in Computer Security (ESORICS),
2002.
[21] M. Jakobsson, "Fractal hash sequence representation and traver¡
sal." Cryptology ePrint Archive, http://eprint.iacr.org/2002/001/,
Jan. 2002.
[22] D. Coppersmith and M. Jakobsson, "Almost optimal hash sequence
traversal," in Proceedings of the Sixth International Financial Cryp¡
tography Conference (FC '02) , March 2002.
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A Author Contact Information
Adrian Perrig
ECE Department
Carnegie Mellon University
Pittsburgh, PA 15218
US
perrig@cmu.edu
Ran Canetti
IBM Research
30 Saw Mill River Rd
Hawthorne, NY 10532
US
canetti@watson.ibm.com
Dawn Song
ECE Department
Carnegie Mellon University
Pittsburgh, PA 15218
US
dawnsong@cmu.edu
Doug Tygar
UC Berkeley
102 South Hall, 4600
Berkeley, CA 94720-4600
US
tygar@cs.berkeley.edu
Bob Briscoe
BT Research
B54/77, BT Labs
Martlesham Heath
Ipswich, IP5 3RE
UK
bob.briscoe@bt.com
Perrig, Canetti, Song, Tygar, Briscoe [Page 12]
Internet Draft draft-ietf-msec-tesla-intro-03 August 2004
B Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this doc-
ument itself may not be modified in any way, such as by removing the
copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of develop-
ing Internet standards in which case the procedures for copyrights
defined in the Internet languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER-
CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Perrig, Canetti, Song, Tygar, Briscoe [Page 13]
