Voice communication security

Voice communication securityPrivacy protection, existing solution and emerging technologies for wiretapping and voice encryption

Crypto Lab (University of Trento)

24 Aug 2010

Fabio Pietrosanti (naif)

Email: [email protected]

Blog: http://infosecurity.ch

mailto:[email protected]

http://infosecurity.ch/

Agenda: Mission

impossible in 2 hours?

• 1 - The need to intercept phone calls

• 2 - Methods to intercept phone calls

• 3 - The risk of eavesdropping

• 4 - Real case, Real world, Real risk scenario

• 5 – Understanding voice encryption

• 6 – Mobile TLC industry standards

• 7 - Government and Military standards

• 8 - Public Safety standards

• 9 - IETF VoIP Security standards

• 10 - Various anti-wiretapping secure phones

• 11 - Conclusion

From this talk you will learn a lot about:

- voice interception techniques and context

- Different requirements among voice encryption technologies

- Major voice encryption standards

Who am iFabio Pietrosanti

• Works in IT Sec till ’98

• Stay in digital underground with nickname “naif” till ’95

• Worked as network security manager for I.NET SpA, Security Advisor Corporate Security Telecom Italia

• Now CTO of KHAMSA ITALIA SPA doing voice encryption stuff http://www.privatewave.com

• Project and engineer strong encryption products and technologies for VOICE

• Technology partnership with Philip Zimmermann

• Participate to underground communities, sikurezza.org, s0ftpj, metro olografix, progetto winston smith, etc

• Being founder and CTO of a company doing voice encryption this presentation follow my view on encryption and security/wiretapping technologies

• My personal and professional feeling are about voice crypto are philosophically near to openness, standardization open-source, open and transparent peer review and i hate every closed and proprietary solution

• This presentation try to be as much as objective as possible

1

The need to intercept phone calls

Once upon a time...

• Communication interception was limited to fixed phone lines

• Few companies, Telco monopoly, was involved

• The interception was limited in providing useful information for investigation and intelligence needs


But now...• Ubiquitous computing is

a reality and mobility is everywhere

• Plenty of different operators

• Plenty of different technologies (voip, virtual operators, etc)

• Cross-border communication services complexity

• More data can be retrieved (ex: Location data, phone call logs, sms messages, etc,)


An appealing business today

•Acquiring access to communications today means acquiring *full* access to a person life

•But who has such need?


Subjects interested in other parties communications

•Law Enforcement Agencies

•National Secret Services

•Foreign Secret services

•Almost all large corporation in international context

•Outsourced intelligence service providers

•Organized crime

•Military organization in battlefield

(those information may require dedicated slides for each subject)


Lawful interception

•Lawful interception

• Action (based on the law) performed by a network operator / access provider / service provider (NWO/AP/SvP), of making available certain information and providing that information to a law enforcement monitoring facility for investigation purposes


Unlawful interception

•Unlawful interception

• Action (against the law) performed by a government agency / network operator / access provider / service provider (NWO/AP/SvP) / Large enterprise / Intelligence Agency / Intelligence professional / disgruntled employee, of making available certain information and providing that information to an interested third party that provided enough budget to proceed to that information collection


Signal Intelligence

•Signal Intelligence

• Military action of espionage and counter espionage performed by military intelligence against foreign forces in the area of battlefield or in a pre-emptive manner near to enemy tactical base. It apply to all kind of communications equipments.


2

Methods to intercept phone calls

(do it by yourself)

Tactical Vs. Non-Tactical Interception

• Tactical interception

• It directly apply to communication lines

• Does not involve the telecommunication operator knowledge

• It can be lawful or unlawful

• Almost most unlawful interception use Tactical methods

2 - Methods to intercept phone calls

Interception targets and approach

• Target Identity

• Target Devices

• Target Communication lines

• Parametric Interception

• Target a perimeter

• Target specific content (keyword, language, stress, mix of all of them)


Practical Approach: Once upon a time...

•Manual switching cable on Telco offices was an easy to do task.


Practical Approach: Mobile interception (1)

• Mobile phones can be intercepted with appropriate equipment (GSM, UMTS)

• Active Method (Risk of detection)

• Passive Method (A5 Cracking)

• Semi-Active Method (100% success)

• Mobile spyware intelligence

• UMTS


Practical Approach: Mobile interception (2)


• Many approach to crack different GSM crypto algorithms:

• A5/0

• A5/1

• A5/2

• A5/3

Practical Approach: GSM Active IMSI-catcher


• Create a fake GSM network with powerful antenna and RX/TX power

• Mobile phones goes to powerful BTS

• Wiretapping trough man in the middle

• Patented by Rohde & Schwarz “Virtual base station”

• Can be easily done with OpenBTS + USRP device

• Dozen of commercial products for intelligence purpose

Practical Approach: GSM A5/1 passive


• Using rainbowtables to cracking A5/1 encryption

• Fully passive encryption cracking

• Based on known plan text of certain GSM messages (SI5, SI6, SI6bis)

• In theory fixed… but upcoming public attack via SMS!

• Available via cheap USRP1 + airprobe + kraken or trough professional products

• http://srlabs.de - http://reflextor.com/a51

http://srlabs.de/

Practical Approach: GSM Semi Active


• 1) Use a Fake BTS that ask for weak A5/2

• 2) Mobile phones roam with A5/2, leaking Kc used on A5/1 real BTS

• 3) Disconnect mobile phone

• 4) Intercept A5/1 with known Kc

• Example: Siacorp Semi-Active GSM monitoring System SCL-5020SE

• Within some months: attacks with OpenBTS + Airprobe

Practical Approach: Mobile spyware


• On device spyware

• Many commercial trojan for Symbian, Blackberry, iPhone, Android

• Tap phone calls by conference calling

• Someone is able to tap silently and send via GPRS

Practical Approach: UMTS?


• Theoretically broken

• No practical implementation around

• All phones are Dual-Mode

• If you can’t crack it, just block it with a Jammer

• Automatic UMTS -> GSM roaming

Practical Approach: GSM towers uplink

•Uplink of operators between towers are usually not encrypted


Practical Approach: ISDN/PSTN Interception

•Simple cable cut give impressive results!

•Budget? Less than 250 USD for a professional equipment transmitting in VHF


Practical approach: Fiber Tapping (voip)

• Less than 300 USD equipment

• Open the bottle, bypass the fiber, get the whole traffic of area


Practical approach: DSL copper tapping

•Tap directly on ADSL copper with Tactical ADSL probe (Trace Span)

•System integrated one with 3500 EUR


Practical Approach: Easy ethernet tapping (voip)

•From 20 to 150 USD budget


Practical Approach: What about CDR?


• Call data records give full mapping of a person social network

• Identify relations strength

• Analysis of CDR always done before wiretapping

• Commercial available software such as verint.com X-Tract

• NSA call database count 1.9 trillion CDRs

Everything else is Military SIGINT


3

The risk of eavesdropping

(for people safety and democracy)

Quis custodiet ipsos custodes?Who will watch the watchman?•The most important sentence.

•Reflect on the impact that eavesdropping have on the democracy

3 - The risk of eavesdropping

The human factor: Can we trust all of them together?


• Law Enforcement Employee

•Telco Employee

•Outsourced interception services employee

•Technical support employee of interception products

•Any party involved in the process...

The human factor: QuizAn employee of a Telco, 1800 USD net salary, working on technical structure

is askedby an unknown person to wiretap a certain line. Is given 20k USD in advance.

What he will do?


a) Refuse the offer and report to the authority the request. He has an ethic!

b) Accept the offer and execute the taping

c) Accept and propose also a list price for phone call logs and details on owners of lines

The technical factor


•Most interception are done by redirecting and/or copying intercepted traffic to a centralized place

•Do you think that the diverted traffic is protected? NO!

• From one place, the LEA office lines, every interception can be intercepted.

•VoIP multiply the risk factor by moving the intercepted traffic over the internet without protection.

The political factor andnew freedom risks


•New parametric interception techniques are able to detect certain kind of pattern in ALL voice flows.

• Language blacklisting, gender detection and blacklisting, keyword matching give too much power in the hands of few persons and there’s no law on how to deal with it.

The political factorin unstable countries


•Unstable countries face the issue of cross-agency interception

•Wiretapping became a strong cause of political instability

The need of perfectly enforceable laws on wiretapping

• Laws and procedures for efficient, controlled and guaranteed wiretapping are required

• Wiretapping of civil, secret and military agencies has to be regulated and the rules has to be subject to public scrutiny


The need of perfectly enforceable laws on wiretapping

• Church Commitee Report (1976)

• The Committee finds that information has been collected and disseminated in order to serve the purely political interests of an intelligence agency or the administration, and to influence social policy and political action. White House officials have requested and obtained politically useful information from the FBI, including information on the activities of political opponents or critics. The FBI has also used intelligence as a vehicle for covert efforts to influence social policy and political action.

• USA: Foreign Intelligence Surveillance Act (1978)

• NSA Warrantless Wiretapping (2005)

• New York Times: Bush Lets U.S. Spy on Callers Without Courts

• “The White House asked The New York Times not to publish this article”


4

Real case, Real world, Real risk scenario

Global interception: Echelon•USA confirmed their global interception program with support of Great Britain and New Zealand

• European Parlament confirmed that Echelon was used to illegally divert airplanes deals to make US company wins respect to EU company

4 - Real case, Real world, Real risk scenario

1994 - France: Political spying by Mitterand cause him to loose election


1996 - Poland: Plenty of requests by citizens to ombudsman that received illegal transcripts of

intercepted phone calls


1999 - Turkey: Continuous interception scandals, blackmailing and transcripts of wiretapping

• Since 1996 in Turkey the political instability has caused a continuous tapping of phone calls of journalists, politicians, military and police representative

• Almost every year a scandals get out


2000 - UK: Incredible increased interception power and revelation of past activities


2001 - Finland: Interception scandals, mobile phones intercepted without warrants

• 3 top official of Finland Security Policy and the head of the security department of Sonera are charged for illegally intercepting user phone calls.

• The recording has been going for nearly a year without any formal authorization nor request


2002 - Netherland: Dutch secret services interception equipment brought from Israel is tapping the

interceptors

• Interception equipment used by Dutch Intelligence agencies was brought from the israel company Verint. That equipment was leaking information on interception to israel.

• Interception technology is intercepting the interceptor! Another fall into the monitoring systems!


2005 - Grece: Interception scandals, a bug has been put in Vodafone ICT infrastructure

• Costas Tsalikidis has been found dead head of Security of the Mobile Telco was found “suicided”

• The prime minister, the chief of secret services, a lot of activists has been intercepted

• No responsability has been found

• All phone calls were diverted to a bunch of prepaid anonymous SIM cards


2006 - Italy: Interception scandals, thousands of persons was profiled, intercepted and someone

blackmailed.

• Adamo Bove, the head of Security of the Mobile Telco TIM was found “suicided”

• The head of secret services was wiretapped

• Thousands of people phone logs was acquired

• A numbers of illegal interception has been done

• http://www.edri.org/edrigram/number4.15/italy


http://www.edri.org/edrigram/number4.15/italy

http://www.edri.org/edrigram/number4.15/italy

2007 - USA: FBI missed to get authorization for interceptions because of too complicated laws


2009 - Colombia: Continue the debate and fight on corrupted officials doing wiretapping paid by drug

traffickers


Conclusion of real world scenariosThe tip of the iceberg.


• It’s a serious problem that affect democracy and freedom even of western “democratic” countries

• It’s a concrete and real problem

• Only few facts reach the public media

5

Overview of voice encryption systems

Communication technologies• Traditional telephony (circuit switched)

• ISDN (fixed)

• PSTN (fixed)

• GSM/CDMA/UMTS (mobile)

• SAT (iridium, turaya, inmarsat, etc)

• VoIP Telephony (packet switched)

• Softphone on PC

• Hardware phones

• Mobile internet (GPRS, EV-DO, EVDO, etc)

• Radio transmission

• HF, UHF, EHF, VLF (air, space, earth, sea)

Understanding voice encryption

Authorities for standards

• ISO

• ITU-T

• GSM Consortium

• 3GPP

• 3GPP2

• NSA

• NATO

• IETF

• Telecom Industry Association (US interim standards)


Result of complexity in technologies and authorities

• NO single standard for telephony

• NO single standard for security (not even enough!)


Digital vs. Analog

• Scrambling Vs. Encryption

• Analog connection Vs. Digital connection

• Creating a digital data path over the media

• And what about the signaling?

• Outband signaling

• Inband signaling

Best review of scrambling technologies with security evaluation: https://upcommons.upc.edu/pfc/bitstream/2099.1/4858/1/MarkusBrandau.pdf


TLC Communication technologies

Data Transmission

Circuit Switched Packet Switched

ISDN, GSM,CDMA,UMTS, PSTN, SAT VoIP

Quality of service GrantedGPRS / EDGE / UMTS

Not Granted

Coverage Full Only Urban Area

BillingPer-second

(sender pay)

Per-packet(sender/receiver

pay)

Signaling Outband In-band (over IP)

• But bear in mind military and public safety requirement: Radio from ELF (3-3000hz) to EHF (30-300ghz)


Different use case and requirements

• Government (embassies and agencies) and Military (battlefield, earth, air, sea)

• Public safety

• Mobile Telecommunication industry

• IETF standards

• Misc use anti-wiretapping secure phone


Different security model

• End-to-end Security

• point-to-point

• point-to-multipoint

• End-to-site

• Mixed setup


Security of crypto operation

• Tamper proof encryption key container (SIM Card)

• Tamper proof enciphering hardware (NSA / NATO Crypto Card)

• Embedded hw/sw encryption along with tlc equipment

• General Trusted operating system

• General operating system

• Embedded custom (firmware) operating system

• False sense of security using old concepts

• Jtag debugging & reversing are currently diffused

• Firmware can be broken if not protected with trusted hardware


Standards vs Proprietary

• Moving from a cold-war to multilateral operations bring to standardization and interoperability requirements

• Proprietary technology

• Require gateway for interoperability breaking end-to-end security

• Increase delay

• High costs

• Single vendor dependency

• Standards and open technologies

• Standards but closed technologies

• Standards but partially closed technologies


NSA Cryptographic Modernization Program

• Moving from proprietary to standard solution

• Interoperate with NATO and coalition

• Replacing 1.3milion encryption units in 10 years

• Avoid dependency on single vendor

• Reduce costs

• Update all equipments to modular crypto systems

• Not anymore single crypto system but modular upgradable systems


The race to standardization

• Mobile TLC industry:

• GSM 2G: A5/1 , A5/2, A5/3

• GPRS 2.5G: GEA1, GEA2, GEA3

• UMTS 3G: UEA1, UEA2

• UMA/GAN: IPSEC with IKEv2 / AES

• LTE 4G: 128-EEA1, 128-EEA2, 128-EEA3

• Government and Military: SCIP / FBNDT

• Public safety: TETRA

• IETF Standard: SIP/RTP (SRTP -> SDES / ZRTP / DTLS)

• Secure Phone: Still plenty of various proprietary solution


Beware of Snake Oil Crypto

• Staying careful about snake oil encryption

• Bruce Schneier and Phil Zimmermann reference

• Snake Oil Encryption is

• Secret Algorithm

• Algorithm without key exchange details

• Security Expert review and useless certificates

• Unbreakable

• Unsubstantiated bit claims

• Not explaining the security model (end-to-end vs end-to-site)

• http://en.wikipedia.org/wiki/Snake_oil_(cryptography)

• http://www.interhack.net/people/cmcurtin/snake-oil-faq.html


http://en.wikipedia.org/wiki/Snake_oil_(cryptography

Mobile TLC Industry

GSMA / 3GPP / LTE

Security by lobbying and patenting

Mobile TLC industry

• TLC industry is represented mainly by large corporation

• Each standard is defined inside defined organization with the direct industry participation

• Standards are specifically defined in a cryptic and complex document formats

• Standards in mobile environment are very often plenty of patented methodologies

• Even if we refer always to “GSM” there are a lot of GSM releases

• Information is fragmented and the “Algorithm” custodian concept prevent immediate use for research

http://gsmworld.com/our-work/programmes-and-initiatives/fraud-and-security/gsm_security_algorithms.htm

2G: GSM encryption

Mobile TLC industry

• Operate at Layer1

• Provide one-way mobile to network authentication

• Provide mobile-to-BTS encryption

• A wide set of algorithms

• A5/0 (no encryption)

• A5/1 (standard encryption)

• A5/2 (export version, weak)

• A5/3 (Use of Kasumi in GSM)

• Given the peculiarity of the overall protocol all GSM communication can be broken, even with an upgrade to A5/3, because interoperability and compatibility has to be kept and most mobile phones cannot be upgraded

2.5G: GPRS/EDGE Encryption

Mobile TLC industry

• Operate at Layer2 (LLC)

• Does not have any relationship with A5/1 or A5/2 of GSM

• Algorithm used:

• GEA0 (no encryption)

• GEA1 (export controlled)

• GEA2 (normal strength)

• GEA3 (GPRS use of Kasumi)

3G: UMTS encryption

Mobile TLC industry

• UMTS use two set of algorithms:

• UEA1 and UIA1, based on Kasumi

• UEA2 and UIA2, based on SNOW 3G

• In UMTS there is a mutual authentication between handset and the network

• In 2005 it has been demonstrated 1st an attack (yet not so practical) against KASUMI

• In 2010 it has been demonstrated the recovery of full key against Kasumi, but still not practical for how it’s used in 3G systems

Have a look at http://eprint.iacr.org/2010/013

4G: LTE multiple encryption

Mobile TLC industry

• LTE is a still a work-in-progress protocol

• It follow a completely different approach respect to 2G and 3G:

• Supporting a multiple set of conceptually different encryption algorithms to be able to resist against a single attack

• 128-EEA1 and 128-EIA1 (identical to UMTS UEA2 and UIA2 based on SNOW)

• 128-EEA2 and 128-EIA2 (based on AES)

• 128-EEA3 and 128-EIA3 (based on ZUC)

• Extend USIM key length up to 256-bit

• Mandatory Backhaul protection (BTS/BSC -> MSC)

• Mandatory TS 33.401 Security Architecture for LTE

UMA / GAN

Mobile TLC industry

• Trough UMA (Unlimited Mobile Access) / GAN (Generic Access Network), roaming between 2G/3G and IP network

• UMA reuse as-is IETF available standards

• IPSEC with IKEv2 key exchange

• 3DES/AES encryption

• NAT-T IPSEC tunneling

• EAP-SIM for authentication with SIM

• EAP-AKA for authentication with USIM

Government and Military

NATO / NSA

Intro

• Government always used to keep encryption algorithm and protocols secrets

• Multiple different communication protocol

• Multiple different security protocols

• Multiple different cryptographic suites

• Multiple different key management system

• Current multilateral context is changing

• Budget reduction and military cooperation lead to interoperability requirements


SIGSALY Secure Voice System

Circa 1943, SIGSALY provided perfect security for secure voice communication among allies. Twelve units were built and deployed in Washington, London, Algiers, Brisbane , Paris …..

Reference: SCIP, Objective, History and Future Development: Veselin Tselkov


76

Sylvania’s ACP-0(Advanced Computational Processor)

Circa 1966, the ACP-0 was the first programmable digital signal processing computer. A 12-bit machine, it was used to program modems, voice and error control coders. One unit was built, leading to the ACP-1, a 16-bit machine.



Sylvania’s PSP(Programmable Signal Processor)

Circa 1970, the PSP was Sylvania’s third generation programmable digital signal processing computer. A 16-bit machine. The PSP led to the STU-I.



STU-I

Circa 1979, the STU-I used the PSP digital signal processing computer. A few hundred units were eventually deployed.



Original STU-II

Circa 1982, the STU-II provided 2400 and 9600 bps secure voice. A few thousand units were eventually deployed.



First interoperability attempt• US STU-II was first device set interoperable with NATO NBSV-II devices

• But in 1985 NSA initiated FSVS (Future Secure Voice System) and created in 1987 STU-III ISDN voice encryption Units

•


German TopSec-703 Selex BRENT

BRENT

And the story repeat again… broken interoperability with European NATO partners!

But again in the ‘90 STE appeared!• A new architecture for secure

telecommunication for multi-media communication lines (Radio, ISDN, Satellite)

• STE works by completely avoiding internal crypto operations with KOV-14 Fortezza Plus Crypto Card


Since 2004 STE are currently the official voice encryption device of US, with firmware upgrade to support SCIP, VoIP and for a variety of new Crypto Card:

• KSV-21 – Type 1 TOP Secret USA

• KSV-40 – NATO TOP Secret

• SSV-50 – Coalition Partners

• KSV-30 – CCEB (Australia, New Zealand, UK, US, Canada)

Finally standard telephony: FNBDT / SCIP

• In 1997 Future Narrow Band Digital Terminal (FNBDT) project is started in the US to create a multiple media and interoperable voice secure communication protocol

• Baton 320-bit NSA secret symmetric crypto algorithm

• Firefly key exchange for EKMS (standardized as Photuris RFC2522)

• In 2003 it has been proposed for use within NATO, with the creation of IICWG interworking group

• In 2004 it has been renamed to Secure Communication Interoperability Protocol (SCIP)

• AES for symmetric encryption

• Extended key exchange with Enhanced Firefly


SCIP: Tech sheet• Application layer secure telephony protocol (L7)

• Works over any media (Radio, GSM, ATM, ISDN, SATCOM)

• Use MELPe codec (600-2400bit/s) or G.729D (5300bit), royalty free only for US Government and NATO

• Allow the implementation of custom proprietary symmetric and asymmetric encryption system while keeping interoperability

• Example multi-vendor interoperable Voice infrastructure


NSA EKMS

• The Electronic Key Management System of NSA has been adopted as a standard for the handling of key distribution and authentication

• EKMS is based on Enhanced Firefly (Photuris RFC specification)

• Periodic Re-keying is required by policy (OTAR)

• EKMS Is tier-based hierarchy… do you remember x509v3 PKI? :-)


SCIP: Where are the specification?• It’s the typical not-so-open but standard technology

• Googling tell you something about what to look for:

• FNBDT-120 – Key Management Plan

• FNBDT-230 Cryptographic Specification

• FNBDT-220 Conditions for interoperability

• SCIP-231 AES Encryption

• But no official public document other than….

• Check http://nc3a.info/MDS/FNBDT/FNBDT_NATO_BriefV9.ppt

• FNBDT Signaling schematics!!!

• Check http://www.dtic.mil/dticasd/sbir/sbir041/srch/sbir147.html

• FNBDT 1999 partial initial specification document!!!!!


http://nc3a.info/MDS/FNBDT/FNBDT_NATO_BriefV9.ppt

http://www.dtic.mil/dticasd/sbir/sbir041/srch/sbir147.html

SCIP protocol stack view


Some SCIP Manufacturer

• US - NSA, General Dynamic, L3 Communications

• UK – QinetiQ, DSTL

• DE – BSI, R&S

• IT – SELEX

• FR – EADS, SAGEM, THALES

• ES – GS, Technobi

• RO – Electromagnetica

• TR – TUBITAK, ASSELSAN

• NATO – NHQC3S, NC3A


Public Safety

European ETSI standard for an interoperable world

From analog scrambler….

• First encrypted radio was using unsecure voice frequency inversion (scrambling)

• RSA and Diffie-Hellman was born trying to create syncronization methods from scramblers

• Scramblers cannot be secure as they don’t do encryption

• Often referred scrambler are digitizer (modem) that over the digital path make encryption

• Scrambler has been cracked in a lot of countries with simple PC software

• Frequency Hopping Radio transmission techniques (TRANSEC) has been added to modern radio security techniques to increase security at layer1

Public Safety

To TETRA (1)

• Designed as ETSI standard Terrestrial Trunked Radio

(but France has it’s own TETRAPOL variant)

• Used in +35 nations (not only europe but also Russia, India, Brazil, Argentina, etc)

• Operate on 400mhz on a different infrastructure

• 0.5s call setup

• Provide IP packet transport over tetra

• Operate without a network with Direct Mode Operations

• Each device is able to works as a independent repeater

Public Safety

To TETRA (2)

• Signaling is encrypted

• Voice and Data are encrypted

• Similar to GSM with Ki private secret residing on SIM or on Trusted Mobile device

• Support for mutual authentication with the network

• Support point-to-point and point-to-multipoint end-to-end encryption

• Release:

• 1994 Formation of Tetra consortium

• 1999 Tetra Release 1

• 2005 Tetra Release 2 (+AMR +CELP +Extended DMO)

Public Safety

TETRA encryption algorithms

• Tetra Authentication Key Management Algorithm: TAA1

• Algorithm for encryption (secret codes):

• TEA1: 1st exportable Tetra algorithm (distributed by ETSI)

• TEA2: 1s strong encryption for schengen countries (distributed by Dutch Police IT Organization)

• TEA3: 2nd strong encryption for schengen countries (distributed by ETSI)

• TEA4: 2nd exportable Tetra algorithm (distributed by ETSI)

• Support end-to-end encryption with IDEA, AES and custom algorithms

http://www.tetramou.com/uploadedFiles/Files/Documents/Overviewofstandardcryptographicalgorithms.pdf

http://www.tetramou.com/uploadedFiles/About_TETRA/TETRA%2520Security%2520pdf.pdf

Public Safety

http://www.tetramou.com/uploadedFiles/Files/Documents/Overviewofstandardcryptographicalgorithms.pdf

TETRA encryption configuration• Clear (no air interface encryption) without End to End Encryption

• TETRA Encryption Algorithm 1 (TEA1) without End to End Encryption



• Clear (no air interface encryption) with End to End Encryption

• TETRA Encryption Algorithm 1 (TEA1) with End to End Encryption



Public Safety

TETRA BOS digital radio (germany)

• Example implementation by BSI of the German TETRA network with smartcard security

• https://www.bsi-fuer-buerger.de/cae/servlet/contentblob/487530/publicationFile/27989/BSI_AnnualReport2005_pdf

Public Safety

IETF VoIP security standards

VoIP basic

• IETF VoIP standard apply to internet and IP based communications

• SIP is used to transport signaling information

• RTP is used to carry media traffic (audio, video)

• Both usually works over UDP protocol

• SIP can works securely across a TLS secured channel


Signaling Encryption: SIP/TLS• Provide a secured and network authenticated channel for

signaling with TLSv1 (much like HTTPS)


Media encryption: SRTP • SRTP describe how to encrypt and guarantee the integrity of RTP

packets

• Encryption has been brought to IETF standard in March 2004 with SRTP (RFC3711)

• Several Key Exchange methods has been standardized

• SRTP support for symmetric encryption

• AES128 Counter mode

• AES128 f8-mode

• SRTP for integrity checking HMAC-SHA1

• 32 bit version

• 80 bit version

• Upcoming internet-draft fo AES-192 and AES-256


Media encryption: SRTP


E2S Key exchange: SDES•SDES is the only widely diffused and implemented key agreement

method

• It’s transported over SIP channel protected with TLS


E2S Key exchange: SDES packet

INVITE sips:*[email protected];user=phone SIP/2.0Via: SIP/2.0/TLS 172.20.25.100:2049;branch=z9hG4bK-s5kcqq8jqjv3;rportFrom: "123" <sips:[email protected]>;tag=mogkxsrhm4To: <sips:*[email protected];user=phone>Call-ID: 3c269247a122-f0ee6wcrvkcq@snom360-000413230A07CSeq: 1 INVITEMax-Forwards: 70Contact: <sip:[email protected]:2049;transport=tls;line=gyhiepdm>;reg-id=1User-Agent: snom360/6.2.2Accept: application/sdpAllow: INVITE, ACK, CANCEL, BYE, REFER, OPTIONS, NOTIFY, SUBSCRIBE, PRACK, MESSAGE, INFOAllow-Events: talk, hold, referSupported: timer, 100rel, replaces, calleridSession-Expires: 3600;refresher=uasMin-SE: 90Content-Type: application/sdpContent-Length: 477

v=0o=root 2071608643 2071608643 IN IP4 172.20.25.100s=callc=IN IP4 172.20.25.100t=0 0m=audio 57676 RTP/AVP 0 8 9 2 3 18 4 101a=crypto:1 AES_CM_128_HMAC_SHA1_32 inline:WbTBosdVUZqEb6Htqhn+m3z7wUh4RJVR8nE15GbNa=rtpmap:0 pcmu/8000a=rtpmap:8 pcma/8000a=rtpmap:9 g722/8000a=rtpmap:2 g726-32/8000a=rtpmap:3 gsm/8000a=rtpmap:18 g729/8000a=rtpmap:4 g723/8000a=rtpmap:101 telephone-event/8000a=fmtp:101 0-16a=ptime:20a=encryption:optionala=sendrecv








E2E/E2S Key exchange: MIKEY

•Mikey has been standardized in 2004 as RFC3830

•Provide a key exchange method for SRTP on the SIP channel via SDP attribute

• It has been updated with RFC4738 to support other exchange method

•Mikey support several key exchange method

•Null

•Pre-shared keys

•Diffie Hellman

•Diffie Hellman HMAC

•RSA

•RSA (reverse mode)

•Given the implementation complexity it never got really deployed


End-to-end encryption key exchange for SRTP

• As a story we all have already seen with OpenPGP/MIME vs. S/MIME there are two competing standards

• A Hierarchical standard to be integrated within PKI infrastructure - DTLS

• A non hierarchical standard with a very high level or paranoid feature - ZRTP


E2E key exchange - DTLS

• In March 2006 DTLS (Datagram Transport Layer Security) has been defined to protect UDP streams much like SSL and the successor TLS used in the web world

• RTP runs over UDP

• In 2008 a method to use DTLS as a key exchange method of SRTP to encipher RTP packets won the standardization path of IETF


E2E Key Exchange: DTLS-SRTP

• Require a PKI to be used

• It completely rely on SIP channel integrity

• In order to keep the SIP channel integrity “Enhanced SIP identity” standard (RFC4475) has to be used .

• Unfortunately MiTM protection cannot be guaranteed when calling a phone number (+4179123456789) and so DTLS-SRTP collapse in providing security

• So the basic concept is that DTLS require a PKI to works, with all the burocracy and complexity around building it

• Most of the vendor that announced to use DTLS-SRTP said that they will provide self-signed certificate


E2E Key exchange: ZRTP (1)

• Mr. Zimmermann did it again and by leveraging the old PGPhone concept of 1995 he designed and proposed for standardization ZRTP VoIP security protocol

• ZRTP does not use SIP but instead use in a clever way the RTP packet to perform in-band (inside RTP) key handshake

• The concept is simple: what we need to protect?

• The media

• So why modify the SIP signaling increasing complexity?

• KISS principle always stay ahead

• Implemented by Philip Zimmermann (zfoneproject.com), Werner Viettmann (gnutelephony.org), MT5 (unknown non-public implementation)



• ZRTP is provided to IETF as a standard (currently in standardization path) as a key initialization method for SRTP

• ZRTP use different key agreements method inside the cryptographic protocol

• ECDH (NSA Suite B)

• DH

• Preshared Key

• ZRTP support PFS (Perfect Forward Secrecy)

• Self-healing key cache (avoid ssh-like attack)

• Can be used over most signaling protocols that use RTP for media transport (SIP, H.323, Jingle, P2P SIP)




ZRTP (4)

• Short Authentication String as a method to detect MiTM wiretapper

• the two users at the endpoints verbally compare a shared value displayed at both end

• If the value don’t match, it indicates the presence of someone doing a man in the middle attack


Comparison of key agreements method of SRTP

Technology SDES SRTP - ZRTP SRTP - MIKEY SRTP - DTLS

Require signaling security

Yes No DependYes (with additional

complexity)

End-to-Site security

Yes No Depend Yes

End-to-End security

No Yes DependYes (it

depends)

Man in the middle

protectionNo Yes Yes

Yes (not always)

Different implementati

on in 2010Yes Yes not widely

diffusedNo


Various anti-wiretapping secure phone

Misc solutions not fitting precisely in any category

(private, business)

Too many technologies


• A lot of technologies

• Extremely fragmented market

• Companies often based on captive customer group

• 90% of case no details on custom crypto: Just trust the company!

• Mainly targeting enterprise and VIP sector

A bit of history: clipper, born to fail

• Clipper Chip was created by White House in 1993 implementing SkipJack algorithm

• In 1994 FIPS 185 Escrowed Encryption Standard has been approved

• AT&T release TD3600E

• 56bit encryption

• 4800bps data path over PSTN• In 1996 the project was considered a complete failure

• In 1998 skipJack has been declassified


A bit of history: PGPhone

• In 1995 mr. Philip Zimmermann (2 ‘n) created PGPhone

• PGPhone was a software for Windows to be used connecting the PC trough a modem an dialing the other party

• Was using ephemeral Diffie-Hellmann protocol

• Was using a short authentication string to detect man in the middle attack

• Unfortunately he was too visionary, in 1996 the internet world was still not ready for such technology

• In 1997 it became abandon-ware


A bit of history: Cryptophone

• In 2001 Cryptophone was born and it kept fully open their source code and security protocol design

• The company (composed of several very good hackers) build up the product and started selling the hardware phones

• Unfortunately the protocol did not get public attention (also because of lack of independent separated specification/implementation) and did not get strong public auditing nor other interoperable use

• Now works on CSD and IP

• No IP specs has been released


ZRTP for CS telephony and RadioZRTP/S

• In 2008 Mr. Zimmermann developed jointly with KHAMSA (now PrivateWave) an extension of ZRTP to works again, like PGPhone already does in 1995, over traditional phone lines

• Resulting product is PrivateGSM CSD (Nokia)

• ZRTP/S is a communication and security protocol that works over traditional telephony technologies (GSM, UMTS, CDMA IS94a, PSTN, ISDN, SATCOM, BLUETOOTH)

• Basically it works over a ‘bitstream channel’ that can be easily represented like a ‘serial connection’ between two devices


ZRTP/S Tech sheet

• ZRTP/S can be, oversimplifying, a subset of a “compatible” RTP packet refactored to works over narrowband channels

• It works over very narrowband links (4800 - 9600bps)

• It works over high latency links (GSM CSD and SAT) with a “compressed” ZRTP handshake

• In order to works over most channel it require the usage of narrowband audio codecs with advanced DTX and CNG features (AMR 4.75, Speex 3.95, MELPe 2.4)

• Implemented in open source as additional module to libzrtp

• Soon to be released for public and community usage


Chocolate grade encryption?

• IMHO most of the remaining systems fit into the category of chocolate grade encryption

• Just say “We use AES” or “We use DH key exchange”

• No detailed encryption protocol specs

• No public review

• Claim “military-grade” and “unbreakable”

• Often claim incredible bit size like 16000 bit authentication or 46080 bit encryption

• Typically no support for PFS

• Typically vulnerable to local key compromise

• No, i will not refer to any name here


PIN to protect local keys? Wrong!• Example of chocolate grade encryption is with

digital certificate system based on user security PIN.

• You used the best asymmetric crypto

• You used the best symmetric crypto

• You designed a complex and full featured enterprise key management system (x509v3)

• But on mobile device no secure passphrase is possible for frequent use by users

• Poor keyboard

• Poor Password

As a result the overall security model is strong as much as the PIN strength used to unlock the application that protect the private key


• Type a passphrase here:

Pa;!sd83/1@sZ

Conclusion

To summarize

• Different technologies for different markets and use

• Market and technologies are fragmented

• The race to standardization will fire all non standard technologies

• Most standard technologies include support for proprietary extensions for crypto

• All standards (TLC, Government, Public Safety and IETF) must be open and not restricted to a wallet garden because of the risk that the history of GSM A5/1 repeat again

Conclusion

Voice communication securityPrivacy protection, existing solution and emerging technologies for

wiretapping and voice encryption

Crypto Lab (University of Trento)

24 Aug 2010

Fabio Pietrosanti (naif)

Email: [email protected]

Blog: http://infosecurity.ch


http://infosecurity.ch/