Security and SecureICA Services

1. Jay Tomlin Technical Support February 2000 Now everything computes Security and SecureICA Services

2. Security Concepts and SecureICA Services Class Overview • Cryptography Overview • Various technologies and examples • SecureICA Services 1.22 • Overview • Server and client installation • Configuring SecureICA Services • Web clients and ICA files

3. Cryptography Overview • Cryptography Technologies • Public/Private Key Cryptography • PGP • Diffie-Hellman key agreement algorithm • Symmetric Key (a.k.a. Secret Key) Cryptography • SecureICA Services • Kerberos • UNIX, Windows 2000

4. Cryptography Overview • Public-key Cryptography • Each party maintains a pair of Keys, one public and one private • Messages encrypted with the public key can be decrypted using the private key • Dummies example: Inversion Public key: Multiply by x Private key: Divide by x • I give you my public key; you use it to encrypt the messages you send me • Then only I can decrypt those messages, using my private key • Example: PGP (“Pretty Good Privacy”), included with e-mail software Eudora

5. Cryptography Overview • Secret-key Cryptography • Also called Symmetric-key cryptography • Each party shares a common secret key • Messages encrypted with the secret key can be decrypted using the same secret key • Dummies example: ROT-13 Shift all letters 13 characters to the right, wrapping from Z to A. CITRIX becomes PVGEVK; PVGEVK becomes CITRIX. • Security depends on communicating the secret key safely • Example: RC5, SecureICA Services

6. Cryptography Overview • Diffie-Hellman Key Agreement Algorithm • Outlined in a 1976 IEEE article, “New Directions in Cryptography,” by Whitfield Diffie and Martin Hellman • Variation of public-key cryptography whose end result is a shared secret (symmetric) key • Allows two users to create a shared secret key without the need to communicate the key to one another

7. Cryptography Overview • Diffie-Hellman Algorithm Begin with a large prime P and any integer G such that G < P (both P and G may be publicly known) For every number N between 1 and P-1, there is a power k of G such that Gk = N mod P Alice generates a random private value a where a < P-2 Bob generates a random private value b where b < P-2 Alice’s public key X is Ga mod P Bob’s public key Y is Gb mod P Alice and Bob exchange public values X and Y Alice computes Gab = Ya mod P = k Bob computes Gab = Xa mod P = k Alice and Bob now both know the secret value k Algorithm relies on the mathematical property that (Ga mod P)b mod P = Gab mod P and (Gb mod P)a mod P = Gab mod P

8. Cryptography Overview • Diffie-Hellman Algorithm Begin with a large prime P and any integer G such that G < P (both P and G may be publicly known) For every number N between 1 and P-1, there is a power k of G such that Gk = N mod P Alice generates a random private value a where a < P-2 Bob generates a random private value b where b < P-2 Alice’s public key X is Ga mod P 63 mod 13 = 8 Bob’s public key Y is Gb mod P 69 mod 13 = 5 Alice and Bob exchange public values X and Y Alice computes Gab = Ya mod P = k 53 mod 13 = 8 Bob computes Gab = Xb mod P = k 85 mod 13 = 8 Alice and Bob now both know the secret value k Algorithm relies on the mathematical property that (Ga mod P)b mod P = Gab mod P and (Gb mod P)a mod P = Gab mod P Simple Example Let P = 13, G = 6, a = 3, & b = 9 Then: X = 8 & Y = 5 Secret: K = 8

9. Cryptography Overview • RC5 • Named after its inventor, Ron Rivest, RC is short for “Rivest Cipher” or “Ron’s Code” • RC5 is a “fast block cipher” symmetric key algorithm which transforms a block of plain text into a block of encrypted text of the same length (think ROT-13) • This fixed length is called the block size (usually 64 bits) • The encryption is performed by a shared secret key • Rounds denote the number of times each block is passed through the encryption algorithm • RC5 allows variable block sizes, key lengths, and numbers of rounds

10. Cryptography Overview • Kerberos • Developed at MIT (“Project Athena”) especially for UNIX computer networks • A dedicated Kerberos server maintains a database of all users’ private, symmetric keys • The Kerberos server uses these keys to authenticate users and generate “tickets” for client-server sessions • Ticket requests are encrypted using the user’s secret key; the Kerberos server decrypts the request and sends an encrypted ticket back to the client • In Windows 2000, at least one Domain Controller will act as the Kerberos Distribution Center (KDC)

11. Citrix SecureICA Services SecureICA Services • Currently two versions: Global (40-bit) and North American (40-, 56-, and 128-bit) • Performs end-to-end encryption of the ICA data stream • All ICA session traffic on TCP 1494 is encrypted (not ICA Browser traffic on UDP 1604) • Requires services installed at the Citrix server and a secure client

12. Citrix SecureICA Services SecureICA Services • SecureICA uses the RC5 algorithm to encrypt ICA commands • A pair of RC5 keys are negotiated for each session using the Diffie-Hellman key agreement algorithm • One symmetric key encrypts client-to-server traffic, the other is for server-to-client traffic • SecureICA uses a 64-bit block size, 12 rounds, and a 40-, 56-, or 128-bit key size during the session • Authentication is always encrypted using a 128-bit key, regardless of version or session key length

13. Citrix SecureICA Services SecureICA DLL’s • The following DLL’s perform the encryption for SecureICA Win32 clients and servers (found in system32): No encryption: pdc0n.dll 40-bit encryption: pdc40n.dll 56-bit encryption: pdc56n.dll 128-bit encryption: pdc128n.dll • For Win16 clients, the filenames are pdc0w.dll, pdc40w.dll, and so on • For DOS/DOS32 clients, the filenames are pdc0.dd_, pdc40.dd_, etc. • No Macintosh, UNIX, or Java clients yet

14. Citrix SecureICA Services Configuring SecureICA • Three places to configure Encryption preferences at the server: • At the listener or winstation • At the published application • Per user (Winframe only) • Per-user preferences not recommended in a mixed WinFrame/MetaFrame environment • Client must at least support the server’s requirements in order to connect • Also possible to filter Farm applications by encryption level (i.e., 40-bit clients won’t see 128-bit apps in their app set)

15. Citrix SecureICA Services ICA file syntax [WFClient]Version=2[ApplicationServers]Outlook=[Outlook]Address=OutlookInitialProgram=#OutlookDesiredHRES=640DesiredVRES=480DesiredColor=2TransportDriver=TCP/IPWinStationDriver=ICA 3.0EncryptionLevelSession=EncRC5-40[EncRC5-40]DriverNameWin32=PDC40N.DLLDriverNameWin16=PDC40W.DLL

16. Citrix SecureICA Services SecureICA Services 1.22 • SecureICA 1.21 works on WinFrame 1.7, WinFrame 1.8, TSE/Metaframe 1.0 and TSE/Metaframe 1.8 • SecureICA 1.22 will work on all of the above plus Metaframe 1.8 for Windows 2000 • Scheduled release: March 1, 2000 via downloadable maintenance upgrade • Global version has long been slated to increase its strength from 40- to 56-bit, but changes in US export regulation will probably allow us to export 128-bit encryption

17. Citrix SecureICA Services Export Regulations • Bill Clinton signed a law on January 14, 2000 relaxing U.S. Export restrictions • SecureICA 1.22 should consist of a single version (pending review) • Customers who upgrade from Global 1.21 to 1.22 will have their license automatically converted to a North American license • SecureICA license format: Domestic (128-bit): CTX-0004-10D7-XXXX-XXXXXX Global (40-bit): CTX-0004-10E7-XXXX-XXXXXX • Descriptions will be changed to read “128-bit Encryption” or “56-bit Encryption” instead of “North American” or “Global”

18. Now everything computes