DUNDi!"# $. %!%&" ' &" 2008

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DUNDi

!"# $. %

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.

, : 10/06/2008 ! "# $ "# " " "# %&' (' ! "# $ "# " " "# %&' (' ! "# $ "# " " "# %&' ('

)

2008

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' *& '%! " + & , %& (, ' - .+ & ' ' &$( / " 0 ' ".' ' ' % ' ". % Distributed Universal Number Discovery (DUNDi). #' .' ' ' & + + &' ' ! + Voice over Internet Protocol (VoIP) " 1#/ " &' & "( '." % ! & * ' & + ' " ' -* ' ! &'# ' % VoIP.

' .' ' % " %1 , %& (, ' ' & "( ! "' &' "( ' / '$. / Asterisk, . / & " / ' / 0 .' ' / " ' . / ' + ' +" '(&' & " ' & ' /. & /, &' 0 .' ' + ($ '

& " " '( + % ! & '$. Asterisk " ' . / '

+ ' .

' &% ! , %& (, ' & "./ ' . / ' % + / ' % ' ". % DUNDi. %' ".' , + ($ ' + " ' + ' , ' & / &! 0 " & / " & " / &% + / % "' * ' &' '." . ' &% ! ,

'*&& ' 1 0 ' / / ' ' ' '." '& #&' ! % '%! " ' -* 0* ". % ' ' , % .

' . .' ' , + ($ ' ! ' "' " ' % 0 "'* % '

! & 1 " + ' "' & ' ' "# ' & . .+ ' & /, " " / " " /, ! % & ' " / $ / + ' .0 & ' % ' ". % DUNDi. 2'& , %& (, ' ' ' "( 0 0 ' " ' + (3 " 1 0 + ( %& / ' %/. & /, ! ' & ' " "

' " ( %& ' &' ' &' "# ' & (' " 1#/ " ' & "( &% (& ' ' ' %' .' ' '*&& % , ' ' &$( / " - &' / & &! & ' .+ '." . - '(, ' 0 0 , ' ' &' %' ".' ' /, " .' ' / " &' & / ' %'.' ' / &' '." DUNDi. / &%, ' * ' 0* . '

& "( ' - &' / % ! % " ' + $ ! & &' '." DUNDi.

.

! "# $ "# " " "# %&' (' - 2008

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ABSTRACT

In this dissertation is presented the evaluation of security parameters and the efficiency of the protocol Distributed Universal Number Discovery (DUNDi). The first section is an introduction in the Voice over Internet Protocol (VoIP) technology and to the basic VoIP protocols that are being used for the communication of VoIP entities.

In the following section, are presented the main attributes of the Asterisk PBX and the way that it is installed and configured. Furthermore, we outline the basic directories that are being used after the Asterisk activation.

In the next section, we focus on the protocol DUNDi. There is an analytical examination on the way that the DUNDi protocol, dynamically discover how to reach users throughout the VoIP network Moreover, there is an extended description on the configuration of DUNDi files and the process that is used for the communication of two DUNDi `s entities. In the following section, we set out the architecture of the network that was used for the research. The network was relatively small but we got very important results for the efficiency of the DUNDi protocol. In this section are presented the results of the research and the methodology that was used for analyzing them. Furthermore, is given a quantitative and a qualitative analysis of the statistical results and finally the main conclusions.

The final section is focused on security and reliability issues of the DUNDi protocol. There is an examination about the issues deal with the confidentiality, the integrity and the authentication services of the DUNDi protocol. Finally are presented some reliability problems that are committed to date, about the DUNDi protocol.

PETROS G. PISSAS

Information and Communication Systems Engineering UNIVERSITY OF THE AEGEAN - 2008

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-

" & ' / 0 ' " / % + & / & ' 0 ' " ' ' / ' '%! "# % & %0# . %' &' + , ' ( " '( + %! &' & ( . . %/ ' %/ + / %, " # + , + ' &' - & . %/ ' %/ ' / % % ! . %'( ' ! . . 4 & / %! &' & ' 0 $. % ' , % " 1 0 + & &' / 0*&" / &' + / '

'%! "# % & %0# " 1 & %& &' "( &' " #& %'. ' &'.! . # $ & - . %' ' & 0 . %/ ' %/ $ %/ % " &' ( " 1 & + ' "( &' #& %'( ' ! . % , & &'

&. 5 / ' %/ $ 1 / 0 1 ! $'(& ! 0#.

6'( ' / . / &' " *$ & ' '%! "# % & %0# , #1 ' (+" %! &' & ' ". % (" + ' " 1 0 + & % % ! &' 0*&" + ' / 0 ' " /. + + ./ .' . ' " ' ! (&' " ' & / " ,

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# ' /, %' ' 0*&" 0 % ' (, + ' . &'(0 ' & %0# %, 1 1 %! &' & . ' 0 0 "' ". & ". ' % ' ' / ' ! "# $ "# " " "# %&' (' + ' + #& % % ' 0 & . (& / % ! ( "( % #1 &!% . &' ' + &' ". ( % , * . %' 0* +(, . %'( ' 0*&"

( " 0 ' "( ! . % , & , & /.

0 ' " + & $ # ' &' 0 $. % ' , + ' & ' "( & ' ' 0 ' % ' & " 0 1 & 0 % &' / . $ / ( " &' / 0*&" / / % 1 " %1 & % .

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1.VoIP... 1

1.1 & + + &' VoIP... 1

1.2 '." VoIP... 3 1.2.1 .323... 3 1.2.2 SIP... 5 1.2.3 IAX2... 8 2. Asterisk... 10 2.1 Asterisk Installation... 11 2.1.1 ' & / %&' ' /... 11 2.1.2 +" '(&' & ' ' ' " ' ... 12

2.2 +" '(&' & Asterisk... 12

2.2.1 +" '(&' & & Ubuntu 6.x... 12

2.2.2 +" '(&' & & Fedora Core... 15

2.3 '( + % ! & * ' . ' Asterisk... 19 2.4 "" & ' % Asterisk... 23 3. DUNDi ... 26 3.1 & + + ' DUNDi ... 26 3.2 ' % + % ' ". %... 28 3.3 % + / % ' ". % DUNDi... 29 3.3.1 " /... 30 3.3.2 ++ $ – ! " & ... 30 3.3.3 "( %3 ! 0 & /... 30

3.3.4 ' ' EID (Entity IDentifier)... 32

3.3.5 0 + ' # % +# ... 32 3.4 " ' ... 34 3.5 . $ & % ' ". % DUNDi... 35 3.5.1 ! dundi.conf ... 35 3.5.2 ! iax.conf ... 41 3.5.3 . $ & ' % ! % extensions.conf... 41 3.6 " .' . ... 44 4. _!" _{# $"... 56} 4.1 . $ & "'* %... 56 4.2 "' & ' & ... 61 4.3 * / ' & ... 62

4.4 ' & / – ( %& ' & (' ... 66

4.4.1 * % ' ... 67

5. %$ & ! " ! '! ! ( "... 75

5.1 7 ' ' &$( /... 75

5.1.1 General Peer Agreement (GPA)... 76

5.1.2 %1 ' " & " " .' ' ... 79

5.1.2.1 RSA... 79

5.1.2.2 Advanced Encryption Standard (AES)... 81

5.1.2.3 DUNDi, AES " RSA... 84

5.1.3 Peer-to-Peer vs. Clients Server (DNS)... 86

5.2 7 ' ' - &' /... 88

5.2.1 ("' & " & /... 88

5.2.2 '( %& ". ... 89

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1

1. VoIP (Voice over Internet Protocol)

VoIP

.

1.1 VoIP

VoIP [REF.1]

( ) Internet Protocol (IP). !

" # , IP. ! # . $ " , , VoIP " . % VoIP . 1 VoIP VoIP.

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2 1. VoIP VoIP : & ' . . % , ' . VoIP : " IP , VoIP. % VoIP .

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3 ( # " . ( . VoIP " ( . . 100, 166 .). ) VoIP spamming .

1.2 VoIP

1.2.1 .323 H.323 [REF.2] . ITU " IP. % H.323

real-time audio, video, . !

, video

.

H.323 4 H.323

, " H.323 .

, gateways, gatekeepers multipoint control units (MCUs). 2

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4

2. H.323

%

( . . , voice mail, video cameras ). MS

Netmeeting !.323 . % / video . .. gateways " , . ISDN, PSTN H.323 . * gateways . ) gateway SIP H.323. % gatekeepers " !.323 . gatekeepers

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5 +,. ) " gatekeeper ‘Petros’ 192.168.1.2. % gatekeepers , . gatekeeper !.323. , . MCUs " # . H.323 " , ad-hoc.

% back-end server (BES)

" !.323. * BES , , , . gatekeepers gateways. 1.2.2 SIP % SIP [REF.3] IP UDP ( 5060) SIP SIP . SIP video . & " . SIP . video , " . SIP , IP "

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6 PSTN. SIP

. -

,

Proxy Servers User Agents. $ " . - VoIP " , SIP " IP (' ) . SIP " IETF, !.323 " ITU. . " . ! SIP RFC 2543. RFC 3261 . SIP HTTP " . . human readable " – . / , -. % SIP , , !.323. -SIP !.323. 3 " SIP:

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7 3. SIP * SIP , SIP . $ . % DUNDi ENUM SIP . & SIP . & SIP . SIP SIP " Peer-to-Peer (P2P) . SIP.

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8 1.2.3 IAX2

IAX2 [REF.4], Inter Asterisk eXchange,

+$( . - Asterisk, +$( , " +$(, Asterisk. (interfaces) IAX Asterisk. IAX2 , . - UDP ( 4569) . ! in-band ( ‘’ ’’, ), (firewall) .

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9 3. IAX % IAX2 " . * (firewalls). ! # IAX2 UDP . & , .

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10

2. Asterisk

Asterisk [REF.5] , (hardware), (middleware) (software) . -Asterisk , , , . Asterisk “*”, Unix/Linux DOS , , . / , Asterisk , . - , 0 " . / , . Asterisk PBX. - PBX . 1 VoIP . $ Linux. $

OpenBSD, FreeBSD, MacOSX, Sun Solaris

MS-Windows. - , Linux "

.

Asterisk VoIP. $ SIP

!.323 ,

Inter-Asterisk Exchange (IAX) Asterisk,

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11

2.1 Asterisk Installation

" Asterisk . Asterisk Linux.

Asterisk , Ubuntu 6.10 Fedora FC6.

$ Linux, Asterisk. $ Asterisk . & " Asterisk : ‘’- Asterisk; ‘’ : ‘’$ ’’. 2.1.1 ! Asterisk 1.2.13 . " . Asterisk, Zaptel

PRI (libpri). " VoIP

" Asterisk. % Zaptel " # VoIP. ! libpri . .

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12 * asterisk-sounds. - ` Asterisk , . " " , . 2.1.2 - Asterisk gcc ( 3.x ). /

bison ncurses CLI.

! Asterisk OpenSSL " . Zaptel " . / " libpri Asterisk. Zaptel linnewt zttool

usb-uhci ztdummy. / PRI

Zaptel " libpri

.

2.2 Asterisk

,

Asterisk

Ubuntu 6.x Fedora Core.

2.2.1 Ubuntu 6.x

Asterisk

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13 : asterisk-1.2.13.tar.gz , asterisk-addons-1.2.5.tar.gz asterisk-sounds-1.2.1.tar.gz. /usr/src/ . 2 root . # : # cd /usr/src/ # tar zxvf asterisk-1.2.13.tar.gz # tar zxvf asterisk-sounds-1.2.1.tar.gz # tar zxvf asterisk-addons-1.2.5.tar.gz & : /usr/src/asterisk-1.2.13/ /usr/src/asterisk-sounds-1.2.1/ /usr/src/asterisk-addons-1.2.5/ Asterisk . 2 :

# sudo apt-get install gcc build-essential # sudo apt-get install libncurses-dev # sudo apt-get install openssl linssl-dev # sudo apt-get install zlib1g-dev

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14 $ , Asterisk. % : # cd /usr/src/asterisk-1.2.13/ # make clean # make # make install # make samples # make progdocs ! make clean « " » (binaries) . $ . / make samples . ! « » Asterisk . Asterisk. $

/etc/asterisk/, make samples

.old . ) extensions.conf extensions.conf.old. - , , make samples # . samples configs/ Asterisk . ! make progdocs doxygen . / doxygen

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15 . $ 3 , . asterisk-sounds-1.2.1. . - , . / : #cd /usr/asterisk-sounds-1.2.1 #make install asterisk-addons-1.2.1 ,

CDRs (Call Detail Records) MySQL

MP3 . /

Perl " Asterisk .

2.2.2 Fedora Core

) Asterisk Linux fedora core

Ubuntu .

4 libpri Zaptel

.

Asterisk

Meetme mp3 music hold on.

$ (kernel)

. ! :

# uname –a

:

Linux luser 2.6.17-1.2142_EL #1 Wen Aug 15 11:32:12 ED 2007 i686 i686 i368 GNU/Linux.

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16 $ kernel 2.6 2.4. 2.6. . (kernel sources) . ) # rpm -q kernel-devel / kernel sources yum. ) :

# yum install kernel-devel

/ yum install kernel sources . " . $ : # rpm -q bison # rpm -q bison-devel # rpm -q ncurses # rpm -q ncurses-devel # rpm -q zlib # rpm -q zlib-devel # rpm -q openssl # rpm -q openssl-devel # rpm -q gnutls-devel # rpm -q gcc # rpm -q gcc-c++

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17 $

yum :

# yum install bison # yum install bison-devel # yum install ncurses # yum install ncurses-devel # yum install zlib

# yum install zlib-devel # yum install openssl # yum install openssl-devel # yum install gnutls-devel # yum install gcc # yum install gcc-c++ yum " PBone (http://rpm.pbone.net/). $ , : # rpm -i PACKAGE.rpm # rpm -Uvh PACKAGE.rpm

Fedora kernel sources /usr/src/linuc

Makefile Zaptel Asterisk. ) `

/usr/src link " 'linux'

kernel sources (% default /usr/src/kernels).

" "

" :

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18 $ , : Libpri: # cd /path/to/source/libpri # make # make install Zaptel: # cd /usr/src/asterisk/zaptel # make ( 2.4 ) # make linux26 ( 2.6 ) # make install Asterisk: # cd /usr/src/asterisk/asterisk # make mpg123 ! mp3 music on hold. ) Asterisk : # make # make install # make samples ! 1.2.13 Asterisk " Fedora " chan_phone. ) Makefile /asterisk/channels/ chan_phone. chan_phone.c #include compiler.h.

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19

2.3 Asterisk

Asterisk [REF.7]. % asterisk.conf.

. !

" voice mail recordings, (voice promts)

. /etc/asterisk/ Asterisk. /usr/lib/asterisk/modules/ % (modules) Asterisk. / , , Asterisk. / Asterisk . / modules.conf, " Asterisk . Asterisk . /var/lib/asterisk/ $ astdb . astdb Asterisk,

Microsoft Windows. ! Asterisk

v1 Berkeley . %

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20 agi-bin/

$ ,

Asterisk Asterisk

Getway Interface (AGI) .

firmware/ $ - (firmware) Asterisk. / iax/. images/ / " , ’ . " , . 5 , " . keys/ Asterisk / RSA # . $ keys/, " ( IAX2 ). . $ , . .pub .key keys/.

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21 sounds/ 4 Asterisk ’ . , Asterisk, sounds.txt . sounds-extra.txt, ( asterisk-sounds-1.2.1). var/spool/asterisk/ % ,

outgoing/, qcall/, tmp/ voicemail/. Asterisk outgoing qcall . % tmp/ . . " # # . $ " # . 4 (voicemail) voicemail/. var/run/ % process id (pid) , Asterisk ( " asterisk.conf). $ var/run/ ` .

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22 var/log/asterisk/ % Asterisk . & " logger.conf /etc/asterisk " . $ logger.conf: ; Logging Configuration ; ’ . [general] ; ' ; ! ISO 8601 yyyy-mm-dd HH:MM:SS ;dateformat=%F %T ; host . ;appendhostname = yes ; " . ;(! yes). ;queue_log = no ; " ;(! yes). ;event_log = no ;) " . ;) ; Asterisk –v ( ) ; -d ( ). [logfiles] ; ! « »

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23 ;« » : ; debug ; notice ; warning ; error ; verbose ; dtmf ; "console" ;debug => debug console => notice,warning,error messages => notice,warning,error ;full => notice,warning,error,debug,verbose

2.4 Asterisk

! Asterisk /usr/sbin/. &

asterisk (daemon) . ) asterisk –h : #cd /usr/sbin/ #asterisk –h :

-c : (console) / Asterisk CLI.

-v: (verbosity) $

CLI .

-g: (core dump) $ asterisk (crash) ,

core gdb.

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24 -r: (remote) $ Asterisk . -x : (execute) ( –r CLI , CLI . $ . ) Asterisk CLI (verbosity) 3, : #asterisk –cvvv $ Asterisk , : #asterisk –vvvr petros-deskop:~ # asterisk -cvvv

Asterisk already running on /var/run/asterisk.ctl. Use 'asterisk -r' to connect. petros-desktop:~ # asterisk -vvvr

======================================================== Connected to Asterisk 1.2.13 currently running on Petros-desktop (pid = 7450) -- Remote UNIX connection

Verbosity is at least 3 Petros-desktop*CLI>

) CLI

( . . script),

–x –r :

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25

, :

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26

3. !

DUNDi

DUNDi [REF.8] . DUNDi . .

3.1 DUNDi

& DUNDi VoIP

Public Switched Network (PSTN). %

DUNDi (www.dundi.com) : ‘’ DUNDi Peer-to-Peer (P2P) . $ ( ENUM), DUNDi ’’. DUNDi " " . DUNDi . " (SIP, IAX, H.323). . DUNDi "

6 bytes. $ Ethernet MAC

Address.

DUNDi " (dialplans)

-. )

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27

" (context) ‘’private’’.

. %

/.164[REF.9]. ) DUNDi

E.164 General Peering Agreement (GPA) [REF.10]

. ) DUNDi " " . $ . -, . 4 DUNDi , . )

Advanced Encryption Standard (AES) [REF.11] RSA[REF.12]

,

" . /

General Peering Agreement (GPA) [REF.10]

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28

3.2 "

!

$ DUNDi , , [REF.8]. , ( " ) . - DUNDi : 4. # 4 $ B ' 6 $ ). $, 6, ) ' " . $ $ 1234. $ " . " 6 ' "

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29 . $ 6 ' " ( ) $ " . 6 1234 ) . ) $ 1234 . $ " $ ( ) . $ ' ) .

3.3 !

DUNDi

& [REF.8] DUNDi

. & " 16 bit, 1 65535. % . . " . ! ‘’0’’ . . . 1 bit ‘’F’’ (Final) 1 . .

(incoming sequence number) (outgoing sequence number)

8 bit . 0

1 (ACK)

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30 3.3.1 DUNDi 10 . . $ 10 10 . 3.3.2 - DUNDi REGREQ REGRESPONSE. % REGREQ ( ) REGRESPONSE . / EXPIRATION REGRESPONSE. & . 3.3.3 $ % % DPDISCOVER DPRESPONSE # . ! DPDISCOVER . $ ( ) (ACK) DPRESPONSE " . . 4 DPDISCOVER DPRESPONSE milliseconds TTL 200

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31 2000. & DPDISCOVER CANCEL + 200 milliseconds . DPDISCOVER DPRESPONSE DPDISCOVER . / DPDISCOVER DPDISCOVER : 1. 2 TTL 1 DPDISCOVER. TTL 0 . 2. . 3. " DPREQUEST . / DPDISCOVER DPRESPONSE: 1. DPRESPONSE . / .

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32 2. / TTL 1 flag TTLEXPIRED . 3. ! UNAFFECTED 1 DPDISCOVER ( EID_DIRECT). 4. ! DONTASK 1 " " .

3.3.4 EID (Entity IDentifier)

% EIDQUERY EIDRESPONSE . * EIDQUERY . / EIDRESPONSE " bit F 1 . % EID DPDISCOVER DPRESPONSE. 3.3.5 % & ' ' DUNDi. 1 Si , So , Ts , Td F bit. .

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33

% 1: request/response

#

---REGREQ (So=0, Si=0, Ts=1234, Td=0, F=0) ---> <--- REGRESPONSE (So=0, Si=1, Ts=5678, Td=1234, F=1) ---

--- ACK (So=1, Si=1, Ts=1234, Td=5678, F=1) --->

% 2: $ %

#

---DPDISCOVER (So=0, Si=0, Ts=2345, Td=0, F=0) ---> <--- ACK (So=0, Si=1, Ts=6789, Td=2345, F=0) ---

<--- DPRESPONSE (So=0, Si=1, Ts=6789, Td=2345, F=1) --- --- ACK (So=1, Si=1, Ts=2345, Td=6789, F=1) --->

% 3: EID

#

---EIDQUERY (So=0, Si=0, Ts=3456, Td=0, F=0) ---> <--- ACK (So=0, Si=1, Ts=6789, Td=3456, F=0) ---

<--- EIDRESPONSE (So=0, Si=1, Ts=6789, Td=2346, F=1) --- --- ACK (So=1, Si=1, Ts=3456, Td=6789, F=1) --->

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34

3.4 (

!

[REF.8] DUNDi UDP 4520. % 6 bytes . . . & MAC address . ! DUNDi : 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

Source Transaction Destination Transaction

ISeqno OSeqno F R CmdResp CmdFlags

Information Elements Source Transaction: % . Destination Transaction: % . ISeqno: % .

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35 OSeqno: % . F: bit. / 1 . R: bit . / 0 1 . CmdResp: ! . CmdFlags: / – . Information Elements: . .

3.5 (

!

DUNDi

)

DUNDi. $ dundi.conf, extensions.conf iax.conf.

* iax.conf , DUNDi . * sip.conf, h323.conf mgcp.conf. 3.5.1 dundi.conf dundi.conf " . $ " " .

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36

/ ,

" .

- dundi.conf

Asterisk:

; DUNDi configuration file ; ; [general] ; ; "general" ; client server. ; ; ; , ; . ; ;department=Your Department ;organization=Your Company, Inc. ;locality=Your City ;stateprov=ST ;country=US ;email=your@email.com ;phone=+12565551212 ; ; ; IP , ; 4520 ; ;bindaddr=0.0.0.0 ;port=4520 ;

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37 ; ! ( MAC ; . " eth, ; MAC ; !). ; ;entityid=00:07:E9:3B:76:60 ; ; # DUNDi ( ; ). ; ttl=32 ; ; $ ACK DPREQUEST 2000ms, autokill ; yes, ( ; ). ;% & ; ; host . $ «yes» ;«no» ; . autokill=yes ; ;' pbx_dundi «secret», ; ; «secretpath». " ;dundi ( ; dundi/secret); ;secretpath=dundi [mappings] ; ;' «mappings» DUNDi

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38

; ;Asterisk. ;

DUNDi ; DUNDi General Peering Agreement

(GPA). ; ; dundi_context => local_context,weight,tech,dest[,options]] ; ;' dundi_context . ;' local_context ; .

;' tech (IAX, SIP, H323)

;' dest ( ; . ${NUMBER} ; . ;! (options) : ;nounsolicited: # ; . ;nocomunsolicit: # . ;residential: % . ;commercial: % . ;mobile: % . ;nopartial: ) (partial) . ; DUNDi ; , . ; ;e164 =>

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dundi-e164-39 canonical,0,IAX2,dundi:${SECRET}@${IPADDR}/${NUMBER},nounsolicited,no comunsolicit,nopartial ;e164 => dundi-e164-customers,100,IAX2,dundi:${SECRET}@${IPADDR}/${NUMBER},nounsolicited ,nocomunsolicit,nopartial ;e164 => dundi-e164-via-pstn,400,IAX2,dundi:${SECRET}@${IPADDR}/${NUMBER},nounsolicited,noco munsolicit,nopartial ;digexten => default,0,IAX2,guest@lappy/${NUMBER} ;asdf => ; ; ; ' ; . ' name ; ; ; . ;inkey: * . ;outkey: . ;host: host. ;order: (order) . *

;(primary), (secondary), (tertiary)

(quartiary).

;include:

; ( «all»

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40 ;noinclude: )

; ( «all»

host).

;permit: $ & (

DUNDi ; ( «all» host

).

;deny: % & (

DUNDi ; ( «all» host

).

;model: $ (inbound), ( (outbound),

(symmetric) ; ,

.

;! ‘*’

. ;

; Sample Primary e164 DUNDi peer ; [00:50:8B:F3:75:BB] model = symmetric host = 64.215.96.114 inkey = digium outkey = misery include = e164 permit = e164 qualify = yes ;

; Sample Secondary e164 DUNDi peer ;

;[00:A0:C9:96:92:84] ;model = symmetric

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41 ;host = misery.digium.com ;inkey = misery ;outkey = ourkey ;include = e164 ;permit = e164 ;qualify = yes ;order = secondary ;[*] ; 5.2 iax.conf " Asterisk " . [priv] type=user dbsecret=dundi/secret context=dundi-priv-incoming disallow=all allow=ulaw allow=g726 3.5.3 ( extensions.conf extensions.conf " . ; Macro Block [macro-stdexten]

; standard extension macro exten => s,1,Answer

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42 exten => s,2,Dial(SIP/${ARG1},25,t) exten => s,3,Goto(s-${DIALSTATUS},1) exten => s-NOANSWER,1,Voicemail(u${ARG1}) exten => s-NOANSWER,2,Hangup exten => s-BUSY,1,Voicemail(b${ARG1}) exten => s-BUSY,2,Hangup exten => _s.,1,Goto(s-NOANSWER,1) exten => a,1,VoicemailMain(${ARG1}) [macro-dundi-lookup] exten => s,1,Goto(${ARG1},1) include => dundi-priv-lookup

;Directory Service Contexts

[dundi-test-canonical] exten => 19050000000,1,Goto(pstn-in,s,1) exten => 19050000001,1,Goto(pstn2-in,s,1) exten => 14160000000,1,Goto(pstn2-in,s,1) ;$ DUNDi 0. ;% . [dundi-test-local] include => dundi-test-canonical include => dundi-pstn-local ;E ;dundi-test, ( . [dundi-test-lookup] switch => DUNDi/dundi-test ;$ ( , ; . " switch & (

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43

; .

[dundi-pstn-local]

exten => _1416NXXXXXX,1,SetGroup(OUTBOUND) ; increase PSTN-OUTBOUND +1

exten => _1416NXXXXXX,2,CheckGroup(2) ; check if <=1, else n+101 exten => _1416NXXXXXX,3,Dial(${LOCALTRUNK}/${EXTEN:1}) exten => _1416NXXXXXX,103,Wait(1) ; too many callers, drop exten => _1416NXXXXXX,104,Playback(goodbye) exten => _1905NXXXXXX,1,SetGroup(PSTN-OUTBOUND) exten => _1905NXXXXXX,2,CheckGroup(2) exten => _1905NXXXXXX,3,Dial(${LOCALTRUNK}/${EXTEN:1}) exten => _1905NXXXXXX,103,Wait(1) exten => _1905NXXXXXX,104,Playback(goodbye) ;$ 416 905, ; 2. [dundi-priv-local] exten => _1XXX,1,Macro(stdexten,${EXTEN}) ;+ 1000 -> 1999 . [dundi-priv-lookup] switch => DUNDi/priv ;+ ( . , ( ;'priv' dundi. [dundi-priv-incoming] include => dundi-priv-local

(50)

44

;- ,

; .

;Outgoing Calls Contexts

[local] exten => _[1-2]XXX,1,Macro(dundi-lookup,${EXTEN}) ; . 1000 -> 2999 ; dundi-lookup.

3.6 )

#

DUNDi . ! Asterisk DUNDi ` . 2 " 227-303-(((( . . * 7 , DUNDi. [REF.12] +$( ( " DUNDi VoIP). 2 iax.conf DUNDi " .

(51)

45 iax.conf : [priv] type=user dbsecret=dundi/secret context=dundi-priv-local & " priv Asterisk. % priv dundi-priv-local. / " . dbsecret . dundi.conf dundi-priv-local. $ " [mappings] . -. priv=>dundi-priv-canonical,0,IAX2,priv:${SECRET}@{IPADDR} /${NUMBER},nopartial priv => dundi-priv-via-pstn,100,IAX2,priv:${SECRET}@{IPADDR} /${NUMBER},nopartial

priv => dundi-priv- customers,400,IAX2,priv:${SECRET}@{IPADDR} /${NUMBER},nopartial

6 0 , 100 400 . &

" ,

(52)

46 . 0 " . & {IPADDR} 127.0.0.1 . ) ` . extensions.conf " Asterisk. / , " . - extensions.conf DUNDi. $ " . ) " .

;private DUNDi network [dundi-priv-canonical] ;Direct numbers [dundi-priv-customers] ; ; ITSP [dundi-priv-via-pstn] ; ;

(53)

47 [dundi-priv-local] include => dundi-priv-canonical include => dundi-priv-customers include => dundi-priv-via-pstn [dundi-priv-switch] ; # switch => DUNDi/priv [dundi-priv-lookup] include => dundi-priv-local include => dundi-priv-switch [macro-dundi-priv] exten => s,1,Goto(${ARG1},1) include => dundi-priv-lookup [trydundi] exten => _.,1,Macro(dundi-priv,${EXTEN}) exten => _.,2,Congestion " . script

./asterisk-1.2.13/var/lib/asterisk/keys. & astgenkey " hostname

Asterisk . )

hostname . )

, server " box1 domain

domain.com hostname box1.domain.com,

(54)

48 " Asterisk. - " hostname petros1. # cd /var/lib/asterisk/keys # astgenkey –n petros1

This script generates an RSA private and public key pair in PEM format for use by Asterisk. You will be asked to enter a passcode for your key multiple times. Please enter the same code each time. The resulting files will need to be moved to /var/lib/asterisk/keys if you want to use them, and any private keys (.key files) will need to be initialized at runtime either by running Asterisk with the '-i' option, or with the 'init keys' command once Asterisk is running.

Press ENTER to continue or ^C to cancel. Generating SSL key 'petros1':

Generating RSA private key, 1024 bit long modulus

...++++++

e is 65537 (0x10001) writing RSA key

Key creation successful. Public key: petros1.pub Private key: petros1.key petros1:/var/lib/asterisk/keys #

4 script "

(55)

49 petro1.key. $ /var/lib/asterisk/keys. web server " . & text. ! . - " : petros1.pub:

---BEGIN PUBLIC KEY---

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADiQKBgQC45BoYojLegRQOLOunRlX WOiGu O5iMbVhyuDipF/fY+qY9vQDacAT6xBTuIJteJewQ8BclLiRtmJLx+2/ZAXv37pW8 mtqPHO2l69PpRUCkEI52dvylZ11HfsyQl3fPpAhXGUG//oe59RUbCCqI3+NuaCb F qIdzPQ3E1BO7q6YXlQIDAQAB ---END PUBLIC KEY---

petros1.key:

---BEGIN RSA PRIVATE KEY---

MIICXwIBAAKBgQC45BoYojLegRQOLOunRlXWOiGuO5iMbVhyuDipF/fY+qY9vQDa cAT6xBTuIJteJewQ8BclLiRtmJLx+2/ZAXv37pW8mtqPHO2l69PpRUCkEI52dvyl Z11HfsyQl3fPpAhXGUG//oe59RUbCCqI3+NuaCbFqIdzPQ3E1BO7q6YXlQIDAQAB AoGBAJcJd6wB7G5JobmGxqcqVPqhGFx9wLuOo79rcJXpx4VQFLfAi07mTZsQzUxO BL3fWr3nc/Dihc2l4vycex0aEkruR9McTAu2yXjuqTFcEC1MpnDPMhDh6xvrUkEM btDUpL/GfQ8yd+9CL9WC+cNEuZKwfJsTv8dMX1pzhDqy9YehAkEA59B6WulCt4J+ FA/dnFVsB3UVryJ7qr1aAgPvAwiSpVjnZZGL1FQvm6108cLArY6wywrrnSzILC/V pCPrLZWl2QJBAMwuWZkyoZuJlBJ0zqc2xf8lETRnL4v0yj06kZYeS+byKxUyxUr7

(56)

50 +5IYxA90yr4xYLMOOdImohNTj6m+WeAt/h0CQQCSzzx+ENY45AK27+lYldzJyEQI W11Yn3y+ZAFduXMuFmTNtWSJ/xr7i9nRNpbSE9kxbeQT8YWAPncd8cWCZBDZAkEA syqo7MmFDhr3mApvnENwEqfQJQ+2pTU0ke3m+rezGwC91Wgrv9TFuDmLMZTmo2Zo 2DZPfpzv882LbwPdkd5J8QJBAMSQeBIh3IlxoAURsLmISBxC1R9cjCxdcMWpN46l ctE3/+Fv6P6Kr3sTWik3Z6whNCD879FVJSayrMZSn7ymRJE=

---END RSA PRIVATE KEY---

$ CLI Asterisk

show keys :

*CLI> show keys

Key Name Type Status Sum

switch-1.n2net.net PUBLIC [Loaded] 58197ca5bae150876332eef373685197 petros1 PUBLIC [Loaded] 34bae63322c802fcd90fae81218332d9

petros1 PRIVATE [Loaded] 4cc788941a9292468ebeb7213031b17d freeworlddialup PUBLIC [Loaded] 5efd552d73309f29212331a75f3c701e samos PUBLIC [Loaded] f9c6003c32d8969a80a2e234b6374b3c

iaxtel PUBLIC [Loaded] d919b3ef03eb4dc54c8fee86bfeeada1 6 known RSA keys.

/

res_crypto.so pbx_dundi.so Asterisk

dundi.conf

.

*CLI> reload res_crypto.so

-- Reloading module 'res_crypto.so' (Cryptographic Digital Signatures) -- Loaded PRIVATE key 'petros1'

(57)

51 *CLI> reload pbx_dundi.so

-- Reloading module 'pbx_dundi.so' (Distributed Universal Number Discovery (DUNDi))

== Parsing '/etc/asterisk/dundi.conf': Found

$ "

,

. 4

DUNDi MAC

(Media Access Control) "

.

) MAC

Linux:

# ifconfig eth0

eth0 Link encap:Ethernet HWaddr 00:02:AA:12:A2:32

inet addr: 64.215.96.114 Bcast:192.168.98.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100

RX bytes:0 (0.0 b) TX bytes:0 (0.0 b) Interrupt:9 Base address:0x5000

! MAC . )

CLI

Asterisk :

pbx*CLI> dundi show entityid

(58)

52 & MAC , dundi.conf. # . ) hostname petros1.domain.com petros-desktop.domain.com. " , # : petros1.domain.com.key / petros1.domain.com.pub petros-desktop.domain.com.pub / petros-desktop.domain.com.key MAC : petros1.domain.com 00:02:AA:12:A2:32 petros-desktop.domain.com 00:01:A2:6/:92:$6 $ dundi.conf : . petros1.domain.com

; Primary e164 DUNDi peer ; [00:02:AA:12:A2:32] model = symmetric host = 64.215.96.114 inkey = petros-desktop.domain.com.pub outkey = petros1.domain.com.pub include = e164

(59)

53 permit = e164

qualify = yes

. petros-desktop.domain.com

; Primary e164 DUNDi peer ; [00:01:A2:6/:92:$6] model = symmetric host = 64.215.96.115 inkey = petros1.domain.com.pub outkey = petros-desktop.domain.com.pub include = e164 permit = e164 qualify = yes $ dundi.conf Asterisk ‘’ ’’ # . $ CLI Asterisk

dundi show peers :

*CLI> dundi show peers

EID Host Model AvgTime Status

00:01:A2:6/:92:$6 64.215.96.115 (S) Symmetric Unavail OK (273 ms) 1 dundi peers [1 online, 0 offline, 0 unmonitored]

. $

. &

dundi show peer CLI Asterisk

(60)

54 *CLI> dundi show peer 00:01:A2:6/:92:$6

Peer: 00:01:A2:6/:92:$6 Model: Symmetric Host: 64.215.96.115 Dynamic: no KeyPend: no Reg: No In Key: petros1.domain.com.pub

Out Key: petros-desktop.domain.com.pub Include logic: -- include dundi-priv Query logic: -- permit dundi-priv $ extension.conf " . * DUNDi " . , DUNDi. ) " . . ! extensions.conf . ) " # [dundi-priv-customers] . $ " # 2 : exten => _2XXX,1,Goto(ext-local,${EXTEN},1)

(61)

55

&

DUNDi

2100 .

$ dundi lookup CL+ Asterisk.

*CLI> dundi lookup 2100

1. 0 IAX2/dundi: 34bae63322c802fcd90fae81218332d9@ petros1.domain.com /2100

(EXISTS|NOUNSLCTD|NOCOMUNSLTS) from 00:01:A2:6/:92:$6 , expires in 787 s DUNDi lookup completed in 331 ms

"

:

DUNDi lookup returned no results. DUNDi lookup completed in 1006 ms

(62)

56

4. *

%

DUNDi. $ DUNDi. . .

4.1 (

(

) . %

RAM 512 &6, Intel Pentium 2,8 MHz 80 GB.

Linux Ubuntu 6.10 Fedora FC6. % 512 &6 RAM, 1,6 &!z Intel Celeron

60 GB. % RAM 1GB,

Intel Pentium 2,4 &!z 200 GB.

Linux Ubuntu 6.10. Asterisk 1.2.13 ( ./ .3). $ Asterisk. - " . hostname MAC, +, ( ) " .

(63)

57 PC1 hostname: petros-desktop MAC: 00:01:02:DE:27:2E IP: 195.251.166.32 NUMBER: 1000-1999 PC2 hostname: petros1 MAC: 00:0D:9D:D1:5E:92 IP: 195.251.166.81 NUMBER: 2000-2999 PC3 hostname: gkamb1 MAC: 00:16:17:C4:62:44 IP: 195.251.166.165 NUMBER: 9000-9999 PC4 hostname: petros2 MAC: 00:50:04:44:53:96 IP: 195.251.166.23 NUMBER: 3000-3999 PC5 hostname: petros23 MAC: 00:01:02:DE:27:A3 IP : 195.251.166.36 NUMBER: 4000-4999 ) . $

(64)

58

, NFS SMB.

shared-keys :

# sudo mkdir /home/petros/Desktop/shared-keys

$ . $ shared . $ IP . , mount . $ :

# sudo mount 195.251.166.81:/home/petros/Desktop/shared-keys /home/gkamb1/Desktop/shared-keys

$

.

DUNDi

(65)

59

5 DUNDi:

(66)

60 5 " . (PC1, PC2, PC3, PC4, PC5) . & " DUNDi. % . 4 DUNDi . $ . , " . . ( 1000) . ' " VoIP. $ ’ DUNDi . ) 1000:

1. 0 IAX2/dundi: 34bae63322c802fcd90fae81218332d9@karlovasi.gr/1000 (EXISTS|NOUNSLCTD|NOCOMUNSLTS)

from 00:0F:FE:0A:7E:97, expires in 787 s DUNDi lookup completed in 731 ms

(67)

61

4.2 *

[REF.13]. ) ` script, . script ( . . 1 – : result1.txt), . test. $ Linux : $ ./test % script : clear

for ( ( i=100; i<=599 ; i++ ) ) do

asterisk –rx “dundi lookup 1$i@priv” >> resultX done script « " » . for. " $i " # 500. script asterisk –rx CLI asterisk . ! " 1XXX DUNDi priv. % 1((( " . ' " 1100, "

(68)

62 1101 1599. " resultX ( # . & 500 " . % . $

4.3 !

*

# . hops " . % " " . hop. 6 hop . 6. « 1»

(69)

63 hop. 7 hop . 7. « 2» hop. 8 hop . 8. « 3»

(70)

64 hop. 9 hop . 9. « 4» hops. , " . ! " 10. * & & . ' & .

(71)

65

10. « 5»

hop result1. $

. ' , result2, result3, result4 result5

"

DUNDi. !

(72)

66

4.4 *

–

& : / script , . " . ' : script " . ' # : % . $ . . . , ( # ). / , cache . ! / & : % 11 % 2007 ! ( ) . $ : (txt) Excel .

(73)

67 4.4.1 Excel . , , [REF.13]. $ " ) min( ), max(x x * hop . & . $ , Excel, AVERAGE . 1 2 1 ... 1 i i x x x x

x

4 , # . ) . - . & /(() ( . ) VAR Excel

(74)

68 1 1 2 2 2 ) ( 1 1 i i i i x x s . %

STDEV (standard deviation) Excel. 2 s s - . 11-15 . " . 11: ( ' #1

(75)

69

12: ( ' #2

(76)

70

14: ( ' #4

(77)

71 1 . -#1 -#2 -#3 -#4 -#5 / (ms) 32 32 38 34 32 & (ms) 46 56 57 60 62 & 41,1506 43,22807 45,26316 47,15894 46,16291 ' 6,94082 5,754261 4,213565 5,859116 6,371842 $ 2,63454 2,398041 2,052697 2,420561 2,524250 * #1: 1 HOP #2: 2 HOPs #3: 3 HOPs #4: 4 HOPs #5: 4 HOPs . 1:

(78)

72 $ 2 2,6 milliseconds. $ 2 2,6 (milliseconds). . 41,1506 43,22807. * 2,07747 ms. & " 5,17%. 43,22807 45,26316. * 2,03509 ms. $ 4,7%. ) 45,26316 47,15894. * 1,9 ms. & " 4,2%. $ - #1 #2 $ - #2 #3 $ - #3 #4 -& & 5,17% 4,7% 4,7% 2: # . ) #5 " DUNDi

(79)

73 #4. $ DUNDi . * #4 , #5 . & " . : 16: * # . * #5 . & [REF.14] " y(x) = 1.707x + 39.68 y " x hops DUNDi .

(80)

74 ! DUNDi hop . DUNDi 2 millisecond . % . , .

(81)

75

5. +

,

" DUNDi. - " " . , " . * VoIP , ,2, [REF.12] DNS server [REF.13]. DUNDi.

5.1 +

4 , DUNDi " VoIP , ,2,. & , " DNS . DUNDi " , . ' ( . . # , # .). & , . & DUNDi.

(82)

76

! , "

DUNDi, " E.164 [REF.9]

" “e.164”. )

" “e.164”

# General Peer Agreement (GPA) [REF.10], .

GPA. 2 , "

,

GPA, "

,.

5.1.1 General Peer Agreement (GPA)

GPA , " E.164 “e.164”. & " . % . , " . GPA " . . $ " DUNDi , GPA . , " E.164, # . , E.164.

(83)

77 GPA DUNDi VoIP . ) “e.164”, . " “e.164”, , " . * , " " P2P. “e.164”. 26 . -" . ( . .DUNDi, E.164, Peering System, Propagate, Participant, Weight . .). " ,

, " , " . / . & , . # . & . ! GPA. forum ,

(84)

78 , . " . 2 « » , . % . / ,2, , . % , . % GPA . . . % " . . ) DUNDi. 1 , . ! , . % . % . " #

(85)

79 , " " . / " . . & GPA " . # . % .

site DUNDi (http://www.dundi.com). $

# . 5.1.2 - DUNDi , AES RES RSA . 5.1.2.1 RSA % RSA [REF.17] 1978

(Rivest, Shamir, Adleman). $

RSA . RSA " ( - ) . " . %

(86)

80 . . . ) " RSA . " . * f(n)=(p-1)(q-1), p q n . $ Euler n . e, f(n), e f(n) 1. , " d, e modulo f(n), d=e-1 mod f(n). O e d " . 1 $ 6. $ $ 6. $ C=Me mod n C. $ B , &=Cd_{mod n,} . % RSA . ! " , . " , . # .

(87)

81 % " n. ! " . , , " " . - , 2048 bit .

5.1.2.2 Advanced Encryption Standard (AES)

% AES [REF.18]

. &

, 2002 AES

. AES

128 bit, 192 bit

256 bit 128 bit, 192 bit 256 bit.

" , ,

#

. $

«Rijndael key schedule»

-.

. %

: ByteSub, ShiftRow, MixColumn, AddRoundKey.

AES .

(88)

82 % ByteSub bytes [ . 17]. 17: ByteSub ShiftRow byte , [ . 18]. 18: ShiftRow

(89)

83 MixColumn " c(x) [ . 19]. 19: MixColumn AddRoundKey byte " byte XOR ( ) [ . 20]. 20: AddRoundKey

(90)

84

%

(side channel attacks)

AES. 128 bit ,

"

AES .

.

5.1.2.3 DUNDi, AES RSA

4 DUNDi

RSA AES

.

RSA 1024 bit AES 128 bit.

RSA . 6 . AES . $ # DUNDi. , " ( . 3.6). " RSA. ! " RSA # . . DUNDi PKI . ! , web site . DUNDi "

(91)

85 RSA " . $ . DUNDi . DUNDi :

Information Element Notes

EID . KEYCRC32 CRC AES, RSA . SHAREDKEY AES , . ENCDATA AES . 6 , . $ . CRC-32 [REF.19] AES . & " . % SHAREDKEY KEYCRC32. $ " ,

(92)

86 . SHAREDKEY AES . REGREQ " . $ ENCDATA. % REGRESPONSE . # , AES . ! DUNDi , , " .

5.1.3 Peer-to-Peer vs. Client Server (DNS)

VoIP ENUM [REF.23] DUNDi [REF.8],

"

.

ENUM, DUNDi, –

(client - server) [REF.20], Domain Name System (DNS)

[REF.16], "

E.164. ENUM DNS #

E.164 DNS . )

, Nameserver (NS) Naming

Authority Pointer (NAPTR), DNS

. & ENUM

(93)

87 DNS . 4 DNS . & , , . $ , DNS

.. % Denial of Service (DoS) [REF.22]

Pharming [REF.21].

% DoS DNS

. .

, (Distributed DoS [REF.22]),

DNS , , . DNS , . % Pharming . % DNS . , . & # . % Pharming . 4 , DUNDi ENUM " P2P . DUNDi " . ! , GPA DUNDi. * , "

(94)

88 DNS . , DUNDi . $ " DUNDi.

5.2 +

,

DUNDi [REF.25]. 5.2.1 , . DUNDi , . ) " . - , DUNDi " « » ( ) . DUNDi « » , « » . , " " . $ « » DUNDi, . % « » DUNDi " , . ! " 21.

(95)

89 21: ( DUNDi # 5.2.1 $ $ D. ! , 17 13 ( ). , lookup. " . ( ) " . . . 5.2.2 # " . ! " , DUNDi, . / ,

(96)

90 , . $ . ) 16. 1 7 16. 4 . $ 4 – 5, 7 – 8, 2 – 3 5 – 6. 7, 4, 1, 2, 5, 8, 9, 17, 13, 16. . $ , 7 4 1. 5. " 1 2 . ' , 2 3 5 . 5 ( 4). * 7 16 " .

(97)

91 22: % # 5.2.2 4 5 . . # DUNDi. / .

(98)

92

6.

, DUNDi. $ , Asterisk, DUNDi . ! Asterisk , VoIP . DUNDi Asterisk. DUNDi, . ! , DUNDi Asterisk, , . / DUNDi # . $ " " DUNDi " . . $ , , . % DUNDi , . ' , , . / , . $ ( . . . 4), hop 2 ms. - DUNDi ( ) ’ " .

(99)

93 / , " " DUNDi. * , ENUM. . % DNS , P2P DUNDi . & AES RSA , DUNDi . DUNDi , . DUNDi GPA, " . & DUNDi , GPA " . , DUNDi " , " " " . ENUM . $ # . DUNDi , " .

(100)

94

$

[REF.]

1. http://www.voip-info.org/

2. H.323 Protocol Overview: Paul E. Jones (October 2007) 3. SIP Protocol Overview: RADVISION Team

4. IAX: Inter-Asterisk eXchange Version 2: M. Spencer 5. Asterisk: A Non-Technical Overview: Nasser K. Manesh 6. http://www.asterisk.org/

7. Asterisk: The Future of Telephony: Leif Madsen, Jared Smith

8. Distributed Universal Number Discovery (DUNDi)draft-mspencer-dundi-01: M. Spencer Internet-Draft Digium, Inc. October 13, 2004

9. RFC 2916 E.164 number and DNS September 2000

10. DIGIUM GENERAL PEERING AGREEMENT (TM)Version 1.0.0: Sept. 2004

11. $ ' 1 : ) " , .. . ,

' ) "

12. Practical VoIP Security: Thomas Porter, Jan Kanclirz, Andy Zmolek, Antonio Rosela, Michael Cross, Larry Chaffin, Brian Baskin, Choon Shim.

13. & : ) . ' , 6 (. (

14. : . ). '

15. An Overview of Peer-to-Peer: Sami Rollins

16. RFC 883 DOMAIN NAMES - IMPLEMENTATION and SPECIFICATION 17. http://www.rsa.com/

18. ADVANCED ENCRYPTION STANDARD (AES) Federal Information Processing Standards Publication 197

19. http://citeseer.ist.psu.edu

20. The Future of Asterisk: Kevin P. Fleming 21. Routing Security: Steven M. Bellovin

(101)

95 22. Spoof Detection for Preventing DoS Attacks against DNS Servers: Fanglu Guo

Jiawu Chen Tzi-cker Chiueh

23. "Security and Privacy issues towards ENUM", Proceedings of the ISSPIT ‘05 5th IEEE International Symposium on Signal Processing and Information Technology, pp. 478-483, December 2005, Athens, Greece, IEEE Press 24. G. Kambourakis, D. Geneiatakis, S. Gritzalis, T. Dagiuklas, C. Lambrinoudakis. 25. http://www.enum.org/