Post on 04-Jan-2016
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DRM 1
Digital Rights Managementthe Good, the Bad and the Ugly
Mark Stamp
Department of Computer Science
San Jose State University
stamp@cs.sjsu.edu
DRM resources at http://www.cs.sjsu.edu/faculty/stamp/DRM/
DRM 2
Who Am I?
1992: PhD, Texas Tech
1992-1993: WPI
1993-2000: NSA
2000-2002: MediaSnap, Inc.
2002-Present: SJSU
DRM 3
What was MediaSnap?
Silicon Valley startup companyo Founded June 2000o I joined in December 2000
Maximum of 15 employees Not a dot-com Funded by In-Q-Tel (CIA VC fund) Digital rights management (DRM)
product
DRM 4
Why MediaSnap? NSA provided
o Job securityo “Tenure” after 1 yearo Interesting work, good people, etc., etc.
Why leave NSA for startup company? Three reasons…
1. Money 2. Money3. Money
(salary)(benefits)
(worthless stock options)
DRM 5
Outline of Talk What is DRM? Overview of MediaSnap DRM system Overview of streaming media DRM
model MediaSnap’s competitors TCG/NGSCB Non-technical issues Enterprise DRM Conclusions
DRM 6
DRM Overview
DRM 7
What is DRM?
“Remote control” problem Digital book example Digital music, video, etc. Enterprise document protection Privacy-enhancing technology?
DRM 8
Persistent Protection Restrictions on use after delivery For example
o No copyingo Limited number of reads/playso Time limits: do not open until
Christmaso No forwardingo Etc.
DRM 9
What to Do? The honor system?
o Stephen King’s, The Plant Give up?
o Internet sales? HIPAA? SOA? etc. If you can’t beat ‘em, join ‘em... Lame software-based DRM?
o The standard DRM system today Better software-based DRM?
o MediaSnap’s goal Tamper-resistant hardware?
o Closed systems: Game Cube, etc.o Open systems: TCG/NGSCB for PCs
DRM 10
Is Crypto the Answer?
Attacker’s goal is to recover the key In standard crypto scenario, attacker has
o Ciphertext, some plaintext, side-channel info, etc. In DRM scenario, attacker has
o Everything in the box (if not more) Crypto was not designed to solve DRM
problem!
DRM 11
Current State of DRM At best, security by obscurity
o A derogatory term in the security world Secret designs
o In violation of Kerckhoffs Principle Crypto is king
o “Whoever thinks his problem can be solved using cryptography, doesn’t understand his problem and doesn’t understand cryptography.” --- Attributed by Roger Needham and Butler Lampson to each other
DRM 12
Rules to the DRM Game The analog hole
o When content is rendered, it can be captured in analog form
o DRM cannot prevent attack via the analog hole
Human nature matterso Absolute DRM security is impossibleo Want something that “works” in practiceo What works depends on context
DRM lives in no man’s lando Somewhere between CS and MIS
DRM 13
Software-based DRM Strong software-based DRM is
impossible We can’t really hide a secret in software To do so, we would have to prevent
software reverse engineering (SRE) User of system with full admin privilege
can break anti-SRE protection Bottom line: The killer attack on
software-based DRM is software reverse engineering
DRM 14
MediaSnap DRM
DRM 15
MediaSnap DRM Overview Server side
o Secure Document Server (SDS) Client side
o PDF plugin (reader)
DRM 16
Protecting a Document
SDSRecipient
Senderencrypt
persistentprotection
DRM 17
Accessing a Document inTethered Mode
SDSRecipient
Sender
key
Request key
DRM 18
Accessing a Document inUntethered Mode
SDSRecipient
Senderkey
DRM 19
Tethered vs Untethered Tethered advantages
o Server controls accesso Document can be “shredded” (Authentica)o Key is less exposed
Untethered advantageso Can access data without network
connectiono Key is “more exposed”
MediaSnap implemented both modes
DRM 20
Security Issues Server side (SDS)
o Protect keys, authentication data, etc.o Apply persistent protection
Client side (Reader/PDF plugin)o Protect keys, authenticate user, etc.o Enforce persistent protection
Remaining discussion concerns client
DRM 21
Security Overview
Obscurity
Tamper-resistance
DRM 22
Anti-debugger
Encrypted code
Tamper-Resistance
DRM 23
Obscurity Applied to
o Key managemento Authenticationo Caching (keys, authentication, etc.)o Encryption and “scrambling”o Key parts (data and/or code)o Multiple keys/key parts
Obscurity can only slow down attacker --- the persistent attacker wins!
DRM 24
Other MediaSnap Features Code tamper checking (hashing)
o Must know what code is executing Anti-screen capture
o Prevent most obvious attack on documents Watermarking
o In theory, can trace stolen contento In practice, watermarking is disappointing
“Unique-ification” (or metamorphism)o Break once, break everywhere (BOBE)
resistant
DRM 25
Other Measures/Concerns General code obfuscation
o Collberg and Thomborsono Questions concerning actual strength
Code “fragilization” (guards)o Code hash checks itselfo Any change should cause code to break
Can we trust OS?o How can we protect ourselves?
DRM 26
DRM for Streaming Media
DRM 27
Attacks on Streaming Media
Spoof stream between endpoints Man in the middle Capture stream
o Malicious software stealing stream at client end
Replay/redistribute data
DRM 28
Design Scrambling algorithms
o Encryption-like algorithmso Many such algorithms avaliable
Negotiation of random algorithmo Server and client must share algorithm
Decryption at receiver endo Remove strong encryption
De-scrambling in device drivero Remove scrambling just prior to rendering
DRM 29
Scrambling Algorithms
Server has a large set of scrambling algorithms: M = {1,2,3,4,…,N}
A client has a subset of algorithms, LIST = {12,45,2,37,23,31}
The LIST is stored on client, encrypted with server’s key: E(LIST,Kserver)
DRM 30
Server-side Scrambling
On server side
datascrambled
dataencrypted
scrambled data
Server must scramble data with an algorithm the client supports
Server must securely communicate algorithm choice to client
DRM 31
Scrambling Selection
Scrambling algorithm “database” distributed to clients
List is random subset of algorithms
Alice(client)
Bob(server)
E(LIST, K)
E(m,Ks)
scrambled (encrypted) datausing Alice’s m-th algorithm
DRM 32
Client-side De-scrambling
On client side
datascrambled
dataencrypted
scrambled data
Keep plaintext away from attacker Proprietary device driver
o Scrambling algorithms “baked in”o Able to de-scramble at last moment
DRM 33
Why Scrambling? Uniqueness or metamorphism If a scrambling algorithm is known to be
broken, server does not choose it If client has too many broken algorithms,
server can force upgrade Proprietary algorithm harder to reverse
engineer We cannot trust crypto strength of
proprietary algorithms, so we also encrypt
DRM 34
Why Uniqueness? The threat is reverse engineering (SRE) Reverse engineering a standard crypto
algorithm is easy (unnecessary) Reverse engineering a scrambling
algorithm is potentially much more difficult We also encrypt so not violating Kerchoffs
Principle (at least not too much…) This is clearly security by obscurity and
I’m not ashamed to admit it!
DRM 35
Exploit Systems and DRM
DRM 36
Exploit Systems Exploit Systems (ES) management
consists entirely of musicianso Not all of them are on drugso They offered me a job with huge salary…o Payable as soon as the get funding
Exploit Systems international office?o A coffee shop in Palo Alto
Only in Silicon Valley…
DRM 37
Exploit Systems Exploit Systems is a “peer offering
service” Their web site is (purposely?) vague on
the definition of “peer offering service” But I happen to know what they are
doing... ES tries to gently coerce people into
paying for content obtained from a peer-to-peer (P2P) network
DRM 38
P2P File Sharing: Query Suppose Alice requests “Hey Jude” Black arrow: query Red arrow: positive response
Frank
Ted Carol Pat
MarilynBobAlice Dean
Fred
Alice can select from: Carol, Pat
Carol
Pat
DRM 39
P2P File Sharing with ES Suppose Alice requests “Hey Jude” Black arrow: query Red arrow: positive response
ExploitSystems
Ted Carol Pat
MarilynBobAlice Dean
Fred
Alice selects from: Bill, Ben, Carol, Joe, Pat Bill, Ben, and Joe have legal content!
BillBenJoe
CarolPat
DRM 40
Exploit Systems Bill, Ben and Joe look legitimate Goal is to have at least half of top 10 be
Exploit Systems (ES) responses If “victim” clicks on ES response
o DRM protected (legal) content downloadedo Then small payment required to play
Victim can choose not to payo But then must download againo Is it worth the hassle to avoid paying $0.25?o ES content also offers extras
DRM 41
Exploit Systems A very clever idea Piggybacking on P2P network Weak DRM works well here
o Pirated content already existso DRM only needs to be more hassle to break
than hassle of clicking and waiting (a few times)
Current state of Exploit Systems?o Very little interest from the music industryo Lots of interest from the “adult” industry
DRM 42
Enterprise DRM
DRM 43
Why Enterprise DRM? Health Insurance Portability and
Accountability Act (HIPAA)o Medical records must be protectedo Fines of up to $10,000 “per incident”
Sarbanes-Oxley Act (SOA)o Protect documents of interest to SECo Also Draconian penalties
DRM required for regulatory compliance
DRM 44
What’s Different in Enterprise DRM?
Technically, it is similar to e-commerce But motivation for DRM is different
o Regulatory complianceo Not to make money, but to not lose money!
Human dimension is also much differento Legal threats are far more plausible
Legally, corporation is probably off the hook provided active attack is necessary
DRM 45
Enterprise DRM Moderate DRM security is sufficient Policy management issues
o Easy to set policies for groups, roles, etc.o Yet policies must be flexible
Authentication issueso Must interface with existing systemo Must prevent network authentication
spoofing (authenticate the authentication server)
Enterprise DRM is a solvable problem
DRM 46
Case Study I Sarbanes-Oxley Act (SOA) Requires retention/tagging of all
documents related to SEC disclosure DRM software
o Tag new documents created by SOA authors
o Allow any SOA author to modify tagged doc’so Read-only access for non-SOA authors
Transparent to users --- comply by default!
DRM 47
Case Study II Access control without authentication Example: A large automotive company
wants to limit access to documents too Company employees authoring documents o Partner company employees to whom
documents are electronically distributed o Other partner company employees to whom
the documents are purposely re-distributed
DRM 48
Case Study II Accomplished via simple shared
password Modest security requirement
o Met with minimal complexityo Works with any partner’s system
Risk of unauthorized password sharingo Acceptable due to legal obligations
Deployment will reach 10’s of thousands Modest DRM software suffices
DRM 49
DRM Nonsense
DRM 50
Silly DRM
We’ll only consider a few exampleso Patently obviouso Crypto claimso Extremely silly stuffo Adobe’s “Respect” modelo Microsoft’s MS-DRM
DRM 51
InterTrust“…a company whose business model
appears to rely entirely on legal filings against Microsoft.”
DRM 52
Absurd Crypto Claims
Q: How does Atabok security compare to the competition?
A: The majority of service providers offer the ability to encrypt at 128 bits. Atabok encrypts your content with 256-bit encryption, which is exponentially more secure.
DRM 53
Extremely Silly
SecretSeal’s five radical innovationso Hieroglyphic passwordso Variable-length encrypted keyso “Morphogenetic” encryption algorithmo No encryption formula in softwareo The use of public keys
Do these guys still exist?
DRM 54
Adobe’s “Respect” Model Adobe eBooks and PDF protection Adobe documentation: “It is up to the
implementors of PDF viewer applications to respect the intent of the document creator by restricting access to an encrypted PDF file according to passwords and permissions contained in the file.”
Fail to “respect the intent” and goto jail!o First prosecution under DMCA
DRM 55
MS-DRM (version 2)
MS-DRM: an early Microsoft DRM attempt MS-DRM employed
o Weak proprietary block cipher (MultiSwap) o Multiswap used for hashingo No controlled executiono No obfuscation, no individualization, etc.
Hard to believe this was serious DRM effort!
DRM 56
Microsoft’s NGSCB
DRM 57
Next Generation Secure Computing Base
NGSCB pronounced “n scub” (the G pronounces like a U after migrating to the right)
Will be part of Microsoft’s Longhorn OS TCG (Trusted Computing Group)
o Led by Intel, TCG makes special hardware NGSCB is the part of Windows that will interface
with TCG hardware TCG/NGSCB formerly TCPA/Palladium
o Why the name changes?
DRM 58
NGSCB The original motivation for TCG/NGSCB
was digital rights management (DRM) Today, it is promoted as general
security-enhancing technologyo DRM just one of many potential applications
Depending on who you ask, TCG/NGSCB iso Trusted computingo Treacherous computing
DRM 59
Motivation for TCG Closed systems: Game consoles,
smartcards, etc.o Good at protecting secrets (tamper resistant)o Good at forcing people to payo Limited flexibility
Open systems: PCso Incredible flexibilityo Poor at protecting secretso Poor at protecting their own software
TCG goal is to provide closed system security benefits on an open system
“A virtual set-top box inside your PC” --- Rivest
DRM 60
TCG/NGSCB
TCG provides tamper-resistant hardwareo Secure place to store cryptographic keyo Keys (or other secrets) secure even from a
legitimate user with full admin privileges TCG hardware is in addition to ordinary
hardware, not in place of it PC has two OSs --- usual OS and special
“trusted” OS to deal with TCG hardware NGSCB is Microsoft’s version of secure OS
DRM 61
NGSCB Design Goals According to Microsoft
Provide high assuranceo High confidence that system behaves
correctlyo Correct behavior even if system is under
attack Provide authenticated operation Protection against hardware tampering
is not a design goal of NGSCBo Hardware tampering is the domain of TCG
DRM 62
Disclaimer NGSCB details are sketchy Based on talk presented at RSA
Conference 2004, Microsoft has not worked out all of the details
What follows are my best guesses This should all become much
clearer in the not-too-distant future
DRM 63
NGSCB Architecture
Nexus is the Trusted Computing Base in NGSCB The NCA (Nexus Computing Agents) talk to
Nexus and LHS
Left-hand side (LHS) Right-hand side (RHS)
untrusted
trusted
Nexus
NCANCA
User space
KernelRegular OS
Drivers
Application
Application
DRM 64
NGSCB NGSCB “feature groups”
1. Strong process isolationo Processes do not interfere with each
other2. Sealed storage
o Data protected (tamper resistant hardware)
3. Secure patho Paths to and from I/O protected
4. Attestationo “Things” securely authenticated o Allows TCB to be extended via NCAs
1.,2. and 3. aimed at malicious code
DRM 65
Process Isolation Curtained memory Process isolation and the OS
o Trusted OS protected from insecure OSo Isolate trusted OS from BIOS, device drivers
Process isolation and NCAs o NCAs isolated from software they do not
trusto Trust determined by users --- to an extent…o User can disallow a trusted NCAo User cannot allow an untrusted NCA
DRM 66
Sealed Storage Sealed storage contains secret data
o If code X wants access to secret, a hash of X must be verified (must be sure X is trusted)
o Implemented via symmetric key cryptography
Confidentiality of secret is protected since only accessed by trusted software
Integrity of secret is assured since it’s in sealed storage
DRM 67
Secure Path Secure path for input
o From keyboard to Nexuso From mouse to Nexus
Secure path for outputo From Nexus to the screen
Details are vague
DRM 68
Attestation (1) Secure authentication of things
o Authenticate devices, services, code, etc.o Separate from user authentication
Public key cryptography usedo Certified key pair requiredo Private key not user-accessibleo Sign and send result to remote system
Nexus “extended” via attestation of NCAso This is a major feature
DRM 69
Attestation (2) Public key required to verify attestation
o Verification (i.e., public key) reveals the usero Anonymity is lost
Trusted third party (TTP) can be usedo TTP verifies signatureo Then TTP vouches for signature to recipiento Anonymity preserved (except to TTP)
Claimed support for zero knowledge proofso Verify knowledge of a secret without revealing
ito Anonymity “preserved unconditionally”
DRM 70
NGSCB Compelling Apps (1)
Type a Word document in Windows Move document to RHS
o Trusted area Read document carefully Digitally sign the document What you see is what you sign
o Virtually impossible to assure this on your PC!
DRM 71
NGSCB Compelling Apps (2)
Digital Rights Management (DRM) DRM problems solved by NGSCB Protect secret --- sealed storage
o Impossible without something like NGSCB Scraping data --- secure path
o Can’t prevent without something like NGSCB
Positively ID users --- attestationo Higher assurance with NBSCB
DRM 72
NGSCB Design Principles According to Microsoft
Everything in Windows must work in NGSCB User is in charge of
o Which Nexuses (Nexii?) will run on systemo Which NCAs will run on systemo Which NCAs allowed to identify the system, etc.
No external process can enable Nexus or NCA Nexus does not block, delete or censor any
data (NCA does, but NCAs must be authorized by user)
Nexus source code publicly available
DRM 73
NGSCB Critics
There are many critics --- we consider two
Ross Andersono Perhaps the most influential critico One of the harshest (extreme?) critics
Clark Thomborsono Lesser-known critico More rational (IMHO)
DRM 74
Anderson’s NGSCB Criticism (1)
Digital object controlled by its creator, not user of machine where it currently resides
Why?o Creator can specify the NCAo If user does not accept NCA, access is deniedo Aside: Such control is good in MLS applications
MS Word could encrypt documents with key only available to Microsoft products, then…o Very difficult to stop using Microsoft products!
DRM 75
Anderson’s NGSCB Criticism (2)
Files from a compromised machine could be blacklisted (e.g., to prevent music piracy)
Suppose “everyone in China uses same copy of Microsoft Word”o If you stop this copy from working on all NGSCB
machines, Chinese users will not use NGSCBo Instead, make all NGSCB machines refuse to
open documents created with this instance of Word!
I’m not convinced…
DRM 76
Anderson’s NGSCB Criticism (3)
Going off the deep end? “The Soviet Union tried to register and
control all typewriters. NGSCB attempts to register and control all computers.”
“In 2010 President Clinton may have two red buttons on her desk --- one that sends missiles to China and another that turns off all of the PCs in China…”
DRM 77
Thomborson’s NGSCB Criticism
NGSCB acts like a security guard By passive observation, NGSCB “security
guard” can see lots of sensitive information How to know NGSCB is not spying on you? According to Microsoft
o Nexus software will be publico NCAs can be debugged (for app development)o NGSCB is strictly “opt in”
But… release version of NCA not debuggable and versions have different hash values!
DRM 78
NGSCB Bottom Line (1) TCG/NGSCB provides a trusted OS
buried within an open platform Without something similar, PC may lose
outo Particularly in entertainment-related areas
With NGSCB it is claimed that users will lose some control over their PCs
But users must choose to “opt in”o If user does not opt in, what has been lost?
DRM 79
NGSCB Bottom Line (2)
NGSCB is a trusted system Only a trusted system can break
securityo By definition, an untrusted system is not
trusted with security critical taskso If untrusted system does not perform as
expected, security is not at risko Also by definition, a trusted system is trusted
with security critical taskso If trusted system does not perform as
expected, security is at risk
DRM 80
DRM Conclusions
DRM 81
My DRM Theories My theories, which are mine… DRM for e-commerce
o Strong DRM in software is impossibleo Moderate DRM is possible in some caseso Weak DRM is OK if business model supports
ito Charging $1/song is not supportable given
P2P, high speed Internet connections, etc.o NGSCB may tilt the balance somewhat
DRM in enterpriseo Legal mandates driving adoptiono Realistic legal threat enhances DRM greatly
DRM 82
Conclusions Current DRM systems are weak
o Ironically, weak systems have worked better than (moderately) strong systems, at least so far
o Stronger systems more complex/cumbersome Ideal software-based DRM…
o Individual content is non-trivial to attacko Overall system survives repeated attackso In other words, BOBE-resistanto Is this possible?
DRM 83
DRM References M. Stamp, Digital rights management: The technology
behind the hype, Journal of Electronic Commerce Research, http://www.csulb.edu/web/journals/jecr/issues/20033/paper3.pdf
M. Stamp, Risks of digital rights management, Communications of the ACM, http://www.csl.sri.com/users/neumann/insiderisks.html#147
M. Stamp, Digital rights management: For better or for worse?, ExtremeTech, http://www.extremetech.com/article2/0,3973,1051610,00.asp
E.J. Sebes and M. Stamp, Enterprise digital rights management: ready for prime time? http://www.bcr.com/bcrmag/2004/03/p52.asp
P. Biddle, et. al., The darknet and the future of content distribution, http://crypto.stanford.edu/DRM2002/darknet5.doc
DRM 84
NGSCB References NGSCB: Trusted Computing Base and
Software Authentication, http://www.microsoft.com/resources/ngscb/documents/ngscb_tcb.doc
P. England, et al, A Trusted Open Platform, http://www.cs.cornell.edu/People/egs/syslunch-spring04/palladium.pdf
E. Cram, Migrating Applications to NGSCB, http://www.intel.com/idf/us/fall2003/presentations/F03USSCMS22_OS.pdf
R. Merritt, Cryptographers Sound Warnings on Microsoft Security Plan, http://www.eetimes.com/sys/news/OEG20030415S0013