Security of Digital Enhanced Cordless Telecommunication

122 Pages·2009·1.59 MB·English

Fachbereich Informatik
Theoretische Informatik – Kryptographie und Computeralgebra
Herr Prof. Dr. rer. nat. Johannes Buchmann

Security
of
Digital Enhanced Cordless
Telecommunication
(DECT)
devices for residential use

Diplomarbeit
Betreuer: Erik Tews
[email protected]

Alexandra Mengele
[email protected]

Darmstadt, 09.04.2009
- I -

Ehrenwörtliche Erklärung

Hiermit versichere ich, dass ich die vorliegende Diplomarbeit ohne Hilfe
Dritter und nur mit den angegebenen Quellen und Hilfsmitteln angefertigt
habe. Ich habe alle Stellen, die ich aus den Quellen wörtlich oder inhaltlich
entnommen habe, als solche kenntlich gemacht. Diese Arbeit hat in gleicher
oder ähnlicher Form noch keiner Prüfungsbehörde vorgelegen.

Darmstadt, am 09. April 2009
Abstract

The Digital Enhanced Cordless Telecommunication (DECT) standard pro-
vides voice, data and networking applications; currently there are about 31.5
million DECT devices only in Germany. Attacks and new analysis methods
were published on www.dedected.org in 2008. In this thesis DECT devices of
different manufacturers were analysed with the help of the named methods;
due to that it was firstly possible to deliver insight into the current security
status of DECT devices for residential use. The amount of implemented secu-
rity mechanisms as recommended by the European Telecommunication
Standard Institute (ETSI) is revealed through these examinations. Finally this
thesis arrives to the conclusion that none of the tested devices provides a
global protection of authenticity and privacy.

Zusammenfassung

Der Digital Enhanced Cordless Telecommunication (DECT) Standard ist ein
Standard für Schnurlostelefone und kabellose Datenübertragung; allein in
Deutschland werden zum jetzigen Zeitpunkt schätzungsweise 31.5 Millio-
nen Geräten betrieben. 2008 wurden neue Angriffsszenarien und Analyse-
möglichkeiten auf www.dedected.org veröffentlicht. Um erstmals einen Ein-
blick in den aktuellen Sicherheitsstatus der zurzeit auf dem Markt befindli-
chen Geräte geben zu können, wurden in dieser Arbeit Geräte verschiedener
Hersteller mit den genannten Analysemethoden untersucht. Die Untersu-
chungen legen offen, inwieweit die vom European Telecommunication Stan-
dard Institute ETSI empfohlenen Sicherheitsmechanismen implementiert
sind. Letztendlich kann als Ergebnis der Arbeit festgehalten werden, dass
keines der untersuchten Geräte einen ganzheitlichen Schutz der Sicherheits-
ziele Authentizität und Privatheit bietet.

Table of Figures
Table of Figures

Figure 1: A DECT Card of type 2 from DOSCH+AMAND................................5

Figure 2: Hohl, 471 residents according to [10].....................................................6

Figure 3: Survey of the DECT security architecture.............................................8

Figure 4: Key allocation..........................................................................................11

Figure 5: authentication of a PT............................................................................12

Figure 6: authentication of a FT............................................................................14

Figure 7: DSAA overview according to [6]..........................................................20

Figure 8: The four DSAA algorithms according to [6].......................................20

Figure 9: Structure of the cassable block cipher according to [6].....................22

Figure 10: PT initiated outgoing call....................................................................27

Figure 11: Scan for active calls in the reachable environment..........................28

Figure 12: Synchronisation with a FP and generation of a dump file.............29

Figure 13: Playback of the voice communication data recorded via ppscan..31

Figure 14: Patching the driver of the DECT card with a choiced RFPI...........41

Figure 15: Patching with a chosen IPUI...............................................................41

Figure 16: Successful Impersonation attack........................................................42
Table Directory
Table Directory

Table 1: Number of inhabitants per base station..................................................6

Table 2: Cryptographic parameters........................................................................9

Table 3: Cryptographic keys....................................................................................9

Table 4: Recorded data...........................................................................................29

Table 5: Overview of ciphering status..................................................................31

Table 6: Called phone number sent in plain text................................................33

Table 7: Calling phone number sent in plain text...............................................33

Table 8: Test results: Signalling data sent over the C channel..........................34

Table 9: Test results: Authentication of a PT.......................................................35

Table 10: Test results: PRNG.................................................................................37

Table 11: Random numbers recorded during the key allocation.....................38

Table 12: Random numbers generated by portable part...................................39

Tabelle 13: Overview about the checked DECT devices...................................40

Table 14: Level of security......................................................................................43

Table 15: CC message summary according to [2]..........................................LXIV

Table 16: CISS message summary according to [2]........................................LXV

Table 17: COMS message summary according to [2].....................................LXV

Table 18: CLMS message summary according to [2].....................................LXV

Table 19: MM message summary according to [2]........................................LXVI

Table 20: LCE message summary according to [2]......................................LXVII

Table 21: {CC-Setup} according to [2]...........................................................LXVIII

Table 22: {CC-INFO} according to [2]..............................................................LXIX

Table 23: {CC-CONNECT} according to [2]....................................................LXX

Table 24: {CC-RELEASE} according to [2].......................................................LXX

Table 25: {CC-RELEASE-COM} according to [2]...........................................LXXI

Table 26: {IWU-INFO} according to [2]...........................................................LXXI

Table 27: {AUTHENTICATION-REJECT} according to [2]........................LXXII

Table 28: {AUTHENTICATION-REQUEST} according to [2]....................LXXII
Table Directory

Table 29: {AUTHENTICATION-REPLY} according to [2]........................LXXIII

Table 30: {CIPHER-REJECT} according to [2].............................................LXXIII

Table 31: {CIPHER-REQUEST} according to [2].........................................LXXIII

Table 32: {CIPHER-SUGGEST} according to [2].........................................LXXIV

Table 33: {KEY-ALLOCATE} according to [2]............................................LXXIV

Table 34: {LOCATE-REQUEST} according to [2]........................................LXXIV

Table 35: {TEMPORARY-IDENTITY-ASSIGN-ACK} according to [2]....LXXV
Table of Contents
Table of Contents

Ehrenwörtliche Erklärung........................................................................................I

Abstract......................................................................................................................II

Zusammenfassung...................................................................................................II

Table of Figures.......................................................................................................IV

Table Directory.........................................................................................................V

Table of Contents....................................................................................................VII

Table of Abbreviations........................................................................................VIII

1 Preliminary note................................................................................................1

1.1 Subject of this thesis...............................................................................1

1.2 Proceeding...............................................................................................2

2 The DECT standard..........................................................................................3

3 DECT security architecture..............................................................................8

4 Security threats................................................................................................17

4.1 Security threat analysis by ETSI.........................................................17

4.2 Security analysis of the authentication algorithm DSAA...............19

4.2.1 Structure DSAA...............................................................................19

4.2.2 Security analysis of DSAA.............................................................23

4.3 Pseudo random number generator....................................................25

5 Measurements..................................................................................................27

5.1 Eavesdropping of active calls.............................................................28

5.1.1 Procedure..........................................................................................28

5.1.2 Results...............................................................................................30

5.2 Impersonation of the base station......................................................40

5.3 Recapitulation.......................................................................................43

6 Conclusion........................................................................................................46

LIST OF LITERATURE............................................................................................X

APPENDIX...............................................................................................................XI
Table of Abbreviations
Table of Abbreviations

A11, A12 Authentication Processes
A21, A22 Authentication Processes
AC Authentication Code
B1, B2 Authentication Key Stream Processes
CK Cipher Key
DCK Derived Cipher Key
DECT Digital Enhanced Cordless Telecommunication™
DECT card COM-ON-AIR PCMICA Card type 2 from,
DOSCH+AMAND
ETSI European Telecommunications Standard Institute
FP Fixed Part
FritzBox FRITZ!Box Fon WLAN 7270
FT Fixed Radio Termination
IV Initialization value obtained from frame counter
K Authentication Key
KS Session Authentication
KS’ Reverse Authentication Key
KSG Key Stream Generator
MC Multi Carrier
PABX Private Automatic Branch Exchange
PP Portable Part
PT Portable Radio Termination
RAND_F Value generated and transmitted by the PP
RAND_P Value generated and transmitted by the FP
RES1 Value computed and transmitted by PP
RES2 Value computed and transmitted by FP
RF Radio Frequency
-IX-
RFP Radio Fixed Part
RFPI RFP Identity
RS Value transmitted by FP in authentication protocol
RSSI Radio Signal Strength Indicator
PRNG Pseudo Random Number Generator
SCK Static Cipher Key
TDD Time Division Duplex
TDMA Time Division Multiple Access
UAK User Authentication Key
UPI User Personal Identity