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20-771: Computer Security

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  1. 20-771: Computer SecurityLecture 11: Windows 2000 III Robert Thibadeau School of Computer Science Carnegie Mellon University Institute for eCommerce, Fall 2002

  2. Today’s lecture • Windows 2000 Access II • File Encryption/Decryption

  3. This Week • Read WS 10,11 XML Security More Windows Security

  4. Windows C-2 Security Model It must be possible to control access to a resource by granting or denying access to individual users or named groups of users. Memory must be protected so that its contents cannot be read after a process frees it. Similarly, a secure file system, such as NTFS, must protect deleted files from being read. Users must identify themselves in a unique manner, such as by password, when they log on. All auditable actions must identify the user performing the action. System administrators must be able to audit security-related events. However, access to the security-related events audit data must be limited to authorized administrators. The system must be protected from external interference or tampering, such as modification of the running system or of system files stored on disk.

  5. Win 2000 Security A User User/groups Rights-e.g., delegation Active Directory DACLs for Authorization Files & Other Objects Internal Privacy : File Encryption YOU! Certs for Authentication username kerberos Services Some-other-time.. password Certs for Integrity Active Directory SACLs for Audit certificate Other Machines Web Visitor Web Site IIS – IE5 Secure Network Privacy SSL & IPSec Windows 2000 IPAAA Model User Agents DACLs File Encrypt Kerberos Authenticode SACLs Smartcard IPSec

  6. Domain Trees Domain Controller Prof Domain Controller Domain Controller Domain Controller Domain Controller Prof Prof Prof Prof User Accounts Prof Prof Prof

  7. Example AD for company “reskit.com”

  8. Some Hierarchies

  9. Object Naming • An object has exactly one name, the distinguished name (DN). • The DN uniquely identifies the object and contains sufficient information for a client to retrieve the object from the directory. The DN of an object may be quite long and difficult to remember. Moreover, the DN of an object may change. Since the DN of an object is composed of the RDN of the object and its ancestors, a rename of the object itself or any ancestor will change the DN. • http://msdn.microsoft.com/library/default.asp?url=/library/en-us/netdir/adschema/w2k/A_name.asp • Object globally unique identifier (GUID) • A 128-bit number, guaranteed to be unique. Objects have a GUID assigned when they are created. The GUID is never changed, even if the object is moved or renamed. Applications can store the GUID of an object and be assured of retrieving that object no matter what the current DN is. • User Principal Name—Security Principals (users and groups) each have a "friendly" name, the User Principal Name (UPN),which is shorter than the DN and easier to remember. • The User Principal Name is composed of a "shorthand" name for the user and the DNS name of the domain tree where the user object resides. For example, user James Smith in the microsoft.com tree might have a UPN of "JamesS@Microsoft.com."

  10. Windows Authorization

  11. MSDN Links • How DACLs work http://msdn.microsoft.com/library/default.asp?url=/library/en-us/security/security/how_dacls_control_access_to_an_object.asp • File & Directory http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/file_security_and_access_rights.asp • String for ACE http://msdn.microsoft.com/library/default.asp?url=/library/en-us/security/security/ace_strings.asp • http://msdn.microsoft.com/library/default.asp?url=/library/en-us/security/security/access_mask.asp

  12. Windows Default ACE order • Denial ACEs first then Allow ACEs • Within this, Specific to Object then non Specific

  13. First Time Manager Mistake • Something doesn’t work • You make yourself “everything” • Still doesn’t work. • Problem : NT/2000 Security looks at you and makes you the MINIMUM capable of your groups • A Users group is pretty powerless • Select your groups very carefully to have the power you need

  14. Fine Grained Permissions • Give meaning to “full”, “modify”, etc. • Built-ins • Traverse folder/ execute file • List folder/ read data • Read attributes • Read extended attributes • Create files/ write data • Create folders/ append data • Write attributes • Write extended attributes • Delete subfolders and files • Delete • Read permissions • Change permissions • Take ownership

  15. Special Identities • System (only the OS of Local) : restricted root for SUID type actions. • Creator Owner (like “self group” in unix : only a directory!) • Users get permissions of CreatorOwner (like Special Bits) • Everyone (an automatic group assignment for all users including guests) • Network (an automatic group assignment for users/guests that are not Local and who have been granted remote access) • Interactive (Local users/guests who have been granted access)

  16. Features of Win 2000 • Multiple methods of authenticating internal and external users • Protection of files through easy to use encryption • Protection across network through transparent encryption • Per-property access control for objects (many more detailed uses than read, write, and execute) • Smart card support for authentication and hiding private keys • Transitive trust relationships between domains • Public Key Infrastructure (PKI – Certs handled transparently). • Code itself is routinely authenticated as to its source using PKI.

  17. Complex Many Hierarchies Lots of How-To Learn only MS Use only MS 2000 Simple underlying model MMC/ Active Directory / ACLs Hierarchies are easy to browse/search Only ONE way to configure Good online docs, good HCI Bad News Good News

  18. What is your recommendation? • Machines have to be 128 megabytes • Think domain trees. • Inheritance • Build a root • Build a department • Add in other departments • Web Servers • Build a root • Build a web server • Add in other departments

  19. Build a root? • The root should include • A top-level domain controller • A top-level certificate server • A top-level kerberos server • Possibly, a top-level SQL Server • Possibly, an exchange server (mail) • Possibly, a DNS server • If Intranetting: an IIS server • These servers don’t have to be big-time machines but do have to be reliable • Disk mirroring is built into NT/2000 • Offsite backup replication (IPSec) • These machines should be under major lock and key. • Entry should be local console although remote is supported in Windows 2000.

  20. Win 2000 Security A User User/groups Rights-e.g., delegation Active Directory DACLs for Authorization Files & Other Objects Internal Privacy : File Encryption YOU! Certs for Authentication username kerberos Services Some-other-time.. password Certs for Integrity Active Directory SACLs for Audit certificate Other Machines Web Visitor Web Site IIS – IE5 Secure Network Privacy SSL & IPSec Windows 2000 IPAAA Model File Encrypt

  21. Encrypting File • Think like SSL and others: uses RSA for authentication/authorization and Private Session Key for actual encryption/decryption • This means system has private key that it can use for decryption • Encrypted Data Recovery Policy (EDRP) • Workgroup (LOCAL Domain) this is local • In Domain, it is only with the Domain Administrator

  22. One DESX Key, Many Certs FILE OR DIRECTORY Administrator CERT /Public Key M Symmetric/Private/DESX/Encrypt/Decrypt Key A UserQ CERT /Public Key Q Symmetric/Private/DESX/Encrypt/Decrypt Key A UserR CERT /Public Key R Symmetric/Private/DESX/Encrypt/Decrypt Key A Some can be certs in Data Decryption Field or Data Recover Field

  23. File Encryption / Recovery Certificate • The symmetric encrypting key is encrypted using the public key derived from your EFS certificate. • The resulting encrypted data, along with your display name and a hash of the certificate, is stored in a named stream in the file that contains EFS metadata. • When EFS decrypts a file, it uses your private key to decrypt the symmetric encrypting key. EFS then uses the symmetric key to decrypt the data.

  24. File Encryption is DES • Actually DESX but the idea is the same: it operates like XOR : the number of bits is the number of tries needed to guess the key brute force (without studied cryptoanalysis). • 40 bits for International • 56 bits for US • 128 bits can be downloaded from MS Support • File Encryption Key Uses a Random (40, 56 or 128 bit) Number (randomness is probably very good, but not “cypher quality”) • You can bet somebody somewhere has characterized the non-randomness already (haven’t seen a publication) • This means WHAT? You should know the answer to this!

  25. Sidebar 3000 bit encryption • Answer: Yes, but…. • It won’t hurt but it probably doesn’t matter. 128 bit is • 1.70141183460469e+38 • 1 in 170,141,834,604,690,000,000,000,000,000,000,000,000 tries • Slightly better than 6 in 9999 (your PIN on your bank account)… • 86,400 seconds in a day, 31,500,000 in a year. 3,150,000,000 in 100 years. • Need 54,000, 000,000, 000,000, 000,000,000,000 Guesses a Second (div by 2) • 54 billion trillion operations per second with the expectation that in 50 years you’ll get it. • On the other hand, feel free.

  26. Process • You right click and set property to encrypt a file/directory • If you don’t have a user public/private keypair one is *automatically generated in the background* in your domain • Done once, you are done forever. • You can have others – need management • The private/public key pair gains access to the session key for the file.

  27. When it won’t work • System bit set (system files can’t be encrypted) • Compressed files (files *marked* compressed). • Read-Only files (this is because the file has to be written, temporarily, to be read). • FAT32 or any other FS than NTFS • Copy should be checked • Works because the file owner is always the file owner.

  28. Cipher utility • Why would you want to encrypt an encrypted file? Try being administrator and user. • Data Decryption Field (certs), and Data Recovery Field (certs) • Encrypt a file as a user, and see if you can decrypt it as somebody else (who is the default recovery manager). • Note: efsrecvr.exe as the Encrypted File System RECoVeR program you can use. You can also do this by right clicking and the security properties, owner.

  29. Cert (X.509) EFS Solution • Many certs can hide the SAME private/ symmetric/ session FEK (file encryption/decryption key) for a file. • These certs are SPECIAL FILE ENCRYPTION CERTS (using the user’s private/public key) • http://support.microsoft.com/support/kb/articles/Q273/8/56.ASP • The file can have several depending on the CERT which is user – Data Decryption Field • The file can have several recovery agents can have several depending on the CERT which is the recovery agent user.

  30. User and Kernel Mode • MS has decided to keep encryption/decryption in Kernel Mode • This requires careful user Mode handling (NTFS calls EFS in complete privacy) • Cryptographic Provider (right now, the Microsoft Base – defined for cryptoAPI. Could be smart card or external code/box). • There is another secret mode (SMI) that MS doesn’t use.

  31. CryptoAPI : EFS Components User Mode USER APPLICATION CryptoProvider RSA & Private Key STORE CryptoAPI Encrypts Communication NTFS EFS Msdn.microsoft.com search KSecDD “Inside Encrypting File System” Kernel Mode

  32. CryptoAPI : EFS Components User Mode BIOS Real Mode Phoenix Technologies Device Responsibility USER APPLICATION CryptoProvider RSA & Private Key STORE CryptoAPI Encrypts Communication NTFS EFS Msdn.microsoft.com search KSecDD “Inside Encrypting File System” Kernel (Real) Mode

  33. Problems with File Encryption System • There is no integrity checking on files (PAAA only)? • WRONG : There is, I, but only for the encryption header not the files themselves • The symmetric key is not necessarily just yours • You and anybody else allowed • Recovery cert owner. • Note, the EFS symmetric key in your local X.509 is *not yours* but is the file or directory’s – the container’s. (Uses special “hidden” certs) • But! A private key is used to open the certs encrypted with the public key. You have to steal a private key of an RSA pair. • Many attacks • Clear text file may exist (not deleted) • Crypto-API is in the clear (NOT kernel) • You can’t revoke the File Encryption Certificate

  34. File Encryption Experience • Ease of use • Is there a way to have truly private files here?

  35. Encrypting File System (EFS) • Think like SSL and others: uses RSA for authentication/authorization and Private Session Key for actual encryption/decryption

  36. Win 2000 Security A User User/groups Rights-e.g., delegation Active Directory DACLs for Authorization Files & Other Objects Internal Privacy : File Encryption YOU! Certs for Authentication username kerberos Services Some-other-time.. password Certs for Integrity Active Directory SACLs for Audit certificate Other Machines Web Visitor Web Site IIS – IE5 Secure Network Privacy SSL & IPSec Windows 2000 IPAAA Model User Agents DACLs File Encrypt Kerberos Authenticode SACLs Smartcard IPSec

  37. IPSec Classic Network Attacks • Snooping • Spoofing (TCP sequence numbers) • Password Compromise • Denial of Service Attacks (DoS) • TCP SYN : open tons of TCP connections • SMURF : drown with ping • Teardrop : fragmentation reassembly • Ping of Death : fake fragmentation parameters • Man-in-the-middle Attacks • Application-Level Attacks • Key Compromise

  38. IPSec is End to EndIPAxx • Client – to – Client • Transport Mode • One Authenticates but doesn’t encrypt • One Authenticates and Encrypts • Gateway – to – Gateway • Tunnel Mode (client to client is encapsulated) • Authenticates, Encrypts, and also hides source and destination!

  39. IPA… • Integrity • Uses a hash (called signature or fingerprint) • Authentication • Preshared key authentication • Nonce to confirm shared key • Kerberos authentication (essentially the same) • PK certs • Confidentiality/Privacy/Encryption • DES (3DES, triple DES) • CBC (Cipher Block Chaining) • Very akin to One Time Pad philosophy (approximates it).

  40. IPSec Detail • Authentication Header (AH) • Encapsulating Security Protocol (ESP) • Orig IP Header + AH + TCP + DATA (transport mode) • Authenticates whole packet • Orig IP Header + ESP Header + TCP + DATA + ESP Trailer + ESP Authentication (transport mode) • Authenticates whole ESP but not IP Header • Encrypts TCP-Trailer • New IP Header + ESP Header + Orig IP Header + TCP + DATA + ESP Trailer + ESP Authentication • Authenticates whole ESP but not IP Header • Encrypts Original IP header to ESP Trailer

  41. Uses Cyphersuite • Calls it “security parameters index” • Encryption DES or 3DES • Hash SHA1 or MD5 • Session Key (…not in a cyphersuite) • Diffie-Hellman provides the method of arriving at a shared secret to manage key exchange • Also uses RSA (see RFC)

  42. Three Flavors of Network Security in IPSec • Not Secret but it is Authentic! • Secret and Authentic – Client to Server • But Routing is KNOWN • Secret and Authentic and Routing (Inside Firewall/Gateway) is Secret Too. • Tunnelled through the Open Infrastructure, Gateway-to-Gateway • Defaults include: using if you can, and requiring use (on pain of failure to communicate at all).

  43. Features of Win 2000 • Multiple methods of authenticating internal and external users • Protection of files through easy to use encryption • Protection across network through transparent encryption • Per-property access control for objects (many more detailed uses than read, write, and execute) • Smart card support for authentication and hiding private keys • Transitive trust relationships between domains • Public Key Infrastructure (PKI – Certs handled transparently). • Code itself is routinely authenticated as to its source using PKI.

  44. Windows Core Security

  45. Guarding what’s Yours Sustainable Business Models Product Service Technology Policy Business of Security

  46. Online Purchasing Has A Lot Of Room For Growth How often do you purchase items online?

  47. Key Internet Shopping Groups Purchase items online very/fairly often Age18-29 Age30-39 Collegegraduates Upscale Know-ledgable All computer owners

  48. Consumers Clearly See The Advantages To Online Shopping What is the biggest advantage of shopping online? Convenient, at-homeshopping Easier to compareprices/find deals Greater selection Direct delivery Online discounts

  49. Nearly All Consumers Have Concerns About Online Shopping Don’t worry about the security of my personal information on the Internet NS Concerned about security of personal info on Internet, but benefits/convenience of using Internet outweigh concerns Very concerned about security of personal info on Internet, and unwilling to release any info to a Web site

  50. Security Concern Clearly Impacts Online Shopping Habits How often do you purchase items online? Not concerned about security Concerned, do it anyway Very concerned about security