The document provides an overview of a course on PKI (Public Key Infrastructure) technology. It outlines the topics that will be covered over two days, including secret key cryptography algorithms like AES and RSA, digital certificates, certificate authorities, and practical PKI applications like S/MIME, SSL, and IPSEC. The objectives of the course are to understand cryptographic fundamentals, public key infrastructure elements and how they interact, and why PKI is useful for enabling e-commerce and enhancing security.

1. Introduction to PKI Technology Sylvain Maret Février 2002 Version 2.01

2. Course Map Day One Introduction Key Terms Cryptosystems Services, Mechanisms, Algorithms Cryptography in History Cryptanalysis

3. Course Map Day One Secret-Key Cryptography AES Public-Key Cryptography RSA Diffie-Hellman Message Digests Random Numbers Key Length

4. Course Map Day One Message Authentication Code (MAC, HMAC) Digital Signature RSA, DSS / DSA, ElGamal Hybrid Cryptosystems RSA Key Wrapping Diffie-Hellman PKCS Standard Smart Card End of day one

5. Course Map Day Two Questions to day one ? Revision quiz ! PKI introduction Digital certificates X.509 certificates (Demo) Certificate Revocation (Demo) Certification Authorities RA, LRA Data Repositories (LDAP)

6. Course Map Day two S/MIME: How it works ? SSL: How it works ? IPSEC: How it works ? Open discussion Encryption references site s

7. Course Objectives Understand cryptographic fundamentals and how cryptographic technology is applied in a Public Key Infrastructure Know the elements of Public Key Infrastructure and how they interact with each other Understand and be able to describe some of the practical applications of PKI Understand why PKI is an attractive technology to enable e-commerce and enhance security

8. PKI, WHY? The rise of public data networks. Internet is a new platform for business relationships: E-business Business rules need to be “translated” into this new “language”. Hope behind PKI: to preserve classical business rules in this new virtual world.

9. Drawbacks for E- business Let’s say you have an electronic contract which you need to distribute to another party over the Internet… With existing Internet tools like www and e-mail you lose a lot compared to paper No assurance that the contract has been signed No guarantee that the contract is authentic No assurance of the contract’s source Basically, it is worth than the paper where everything is printed on!

10. About needs... You need to know who you are dealing with (Authentication) You need to keep private things private (Confidentiality) You need to make sure that people do not cheat (Non-Repudiation) You need to be sure that information has not been altered (Integrity)

11. If PKI is the answer then… What is the question? On the Internet no one knows you're a dog!

12. Key Terms A message will be defined as plaintext or cleartext The process of disguising a message to hide its substance is encryption The encrypted message is referred to as ciphertext Decryption is the process turning ciphertext back into plaintext

13. Key Terms Cryptography is the science allowing messages to be kept secure Cryptoanalysis is the art and science of breaking ciphertext Cryptology is the mathematics field Cryptologist are theoretical mathematicians

14. Cryptosystems A cryptosystem is a collection of cryptographic algorithms, cryptographic keys, and all possible plaintexts and their corresponding ciphertexts.

15. Security Services Authentication : Provides the assurance of someone’s identity Confidentiality : Protects against disclosure to unauthorized identities Non-Repudiation : Protects against communications originator to later deny it Integrity : Protects from unauthorized data alteration

16. Security Mechanisms Three basic building blocks are used: Encryption is used to provide confidentiality and integrity protection Digital Signatures are used to provide authentication, integrity protection and non-repudiation Checksums / hash algorithms are used to provide integrity protection and can provide authentication

17. Cryptography Algorithms All Cryptosystems are based on only three algorithms: 1 - Secret-Key algorithms 2 - Public-Key algorithms 3 - Message-Digest algorithms

18. Services, Mechanisms, Algorithms A typical security protocol provides one or more services Services Mechanisms Algorithms Services are built from Mechanisms Mechanisms are implemented using Algorithms SSL, IPSEC, TLS, SSH, etc... Signatures Encryption Hashing DSA RSA RSA DES SHA MD5

19. Security Protocol Layers The further down you go, the more transparent it is The further up you go, the easier it is to deploy Application Presentation Session Transport DataLink Physical Application Presentation Session Transport Network DataLink Physical Network S/MIME, PGP SSL, TLS, SSH IPSEC Hardware link encryption

20. Cryptography in History 2000 B.C. Hieroglyphics Cryptography as an Art Ancient Chinese First to transform messages in Ideographs for privacy India First “Networks spies” using phonetics encryption (Javanese or reverse speaking) Mesopotamia Numbers associate to letters (cuneiform table)

21. Cryptography in History ATBASH cipher: In the Bible ABCDEFGH… (clear) ZYXWVU…(encrypted) Skytale Cipher (Greek) key: stick papyrus enrolled Polybius square (Greek)

22. Cryptography in History Runiques Stones by Vikings (Arts)

23. Cryptography in History World War II: Electromechanical cryptography Rotor based machine transforming plaintext into ciphertext, using electrical signals as encryption key Example: Enigma machine used by Germans Ciphers were not new, but their processing was… 1970-today: New ciphers: based on numbers properties issued from Mathematical theories RSA: Prime numbers factorization Diffie-Hellman: discrete logarithm ECDSA: Elliptic curve cryptography

24. Cryptanalysis Two categories of security levels Computationally secure: Question of time and money (Brute force attack) (Most of the cryptosystems: DES, 3DES, IDEA, RSA, DH etc.) Unconditionally secure: Can “never” be broken independently of the resources One-time pads

25. Several Cryptanalytic Attacks Ciphertext only Brute force attack and dictionary attacks on keys Chosen ciphertext Start from a known ciphertext and try to appear as someone else to get information from others behavior Known Plain ciphertext Derive the key from knowledge of both plain and ciphertext

26. Secret-Key Cryptography

27. Secret-Key Cryptography Use a secret key to encrypt a message into a ciphertext Use the same key to decrypt the ciphertext into the original message Secret-key cryptography is referred also as symmetric cryptography or conventional cryptography The secret key is also known as session key or bulk encryption key

28. Secret-Key Cryptography Let us imagine Alice and Bob who use Secret-Key to protect their messages Plaintext Ciphertext Secret-Key

29. Secret-Key Cryptography How to share the Secret-Key ? Alice and Bob can use the phone, fax, a meeting point, etc. But!?: Could someone steal the key? How to proceed without partner knowledge?

30. Secret-Key Cryptography The Advantages Implementation is efficient to encrypt large volume of data (100 to 1’000 faster than Public-Key Cryptography) Simple to implement in either software or hardware Most of the algorithms are well know and secure Seem to be safe to brute force attack Widely used

31. Secret-Key Cryptography The Disadvantages Hard to share Secret-Keys Large number of keys No non-repudiation (Signature) Subject to interception (Secret-Key)

32. Secret-Key Cryptography Number of needed keys Suppose Alice, Bob and Chris want to use Secret-Key Cryptography! They need only 3 keys

33. Secret-Key Cryptography Increase of keys number Suppose they want to add Dawn and Eric Now they need ten keys

34. Secret-Key Cryptography If n persons want to communicates we have this formula: Key’s number = ((n)*(n-1)) / 2 As example: A company of 60’000 people = 1’799’970’000 keys!

35. Secret-Key Cryptography Block cipher: Encrypts data in predefined block size Most well-known ciphers are block ciphers Stream cipher: Encrypts data stream, one-bit at the time Only few algorithms use it

36. Secret-Key Cryptography Common Secret-Key Ciphers DES Triple DES (3DES) RC2 IDEA Blowfish CAST-128 Skipjack RC4 (Stream cipher) etc.

37. Secret-Key Cryptography DES Data Encryption Standard (1973) by IBM World Standard for 20 years DES was broken in 22 hours (DES challenge III, January 18th, 1999) Key size = 56 bits Block cipher Recommendation: should be replaced by 3DES for high confidentiality requirements !

38. Secret-Key Cryptography Triple DES (3DES) Block cipher Encrypt + decrypt + encrypt with 2 (112 bits) or 3 (168 bits) DES keys DES’s replacement for Banking (1998) Recommendation: Use it for high confidentiality!

39. Secret-Key Cryptography RC2 Designed by Ron Rivest from RSA Block cipher Key size = up to 2048 Encryption speed: independent from the key size Trade secret from RSA, posted on the net in 1996 Designed as a DES’ replacement Faster than DES Recommendation: like DES but faster!

40. Secret-Key Cryptography CAST-128 Designed by C.Adams and S. Tavares (1993) Block cipher Key size = 128 bits Used in PGP 5.x Recommendation: unknown

41. Secret-Key Cryptography IDEA International Data Encryption Algorithm Designed by X.Lai and J. Massey (ETH Zurich) in 1990 Block cipher Key size = 128 bits More efficient than DES for software implementation Used in PGP Recommendation: Better than DES

42. Secret-Key Cryptography Blowfish Designed by B. Schneier in 1993 Optimized for high-speed execution on 32-bit processors Block cipher Key size = up to 448 bits key Recommendation: Use for fast performances and with a maximum key size

43. Secret-Key Cryptography Skipjack Designed by NSA (National Security Agency) Block cipher Key size = 80 bits Recommendation: Inadequate for long term security (key size too short)

44. Secret-Key Cryptography GOST Acronym for “GOsudarstvennyi STandard” Russian answer to DES Key size = 256 bits Recommendation: Incompletely specified to give an answer...

45. Secret-Key Cryptography RC4 Designed by Ron Rivest from RSA Stream cipher Key size = up to 2048 bits Optimized for fast software implementation Trade secret from RSA, posted on the net in 1994 Very fast Used in SSL, Lotus Note, Windows password encryption, Oracle etc. Recommendation: Highly recommended for long keys (>40 bits)

46. Secret-Key Cryptography Many, many others There is no good reason not to use one of above proven algorithms!

47. Secret-Key Relative Performance RC4 Blowfish, CAST-128 Skipjack DES, IDEA, RC2 3DES, GOST FAST SLOW

48. AES National Institute of Standard and Technology expressed a formal call for algorithm on 09.1997 The aim is to define the “next century’s” symmetric encryption standard or Advanced Encryption Standard AES1 conf. (08.98): 15 potential candidates AES2 conf. (03.99): 5 retained candidates Final choice expected for summer 2001

49. AES candidates MARS (IBM) RC6 (RSA Laboratories) Rijndael (J. Daemen, V. Rijmen) Serpent (R. Anderson, E. Biham, L. Knudsen) Twofish (B. Schneier - Counterpane)

50. AES requirements Block cipher of minimum 128 bits Must implement symmetric keys of 128, 192, 256 bits Must be efficient on software and hardware basis (high speed encryption)

51. Public Key Cryptography

52. Public-Key Cryptography Use two distinct keys, one public and one private The private is kept secret The public can be freely shared Referred as asymmetric cryptography A public-key and its corresponding key are mathematically related A public-key and its associated private-key are called a key-pair

53. Public-Key Cryptography A message encrypted with a public-key can be only decrypted by the private-key A message encrypted with a private-key can be only decrypted by the public-key (Signature)

54. Public-Key Cryptography Suppose Alice wants to send a message to Bob using Public-Key Cryptography Plaintext Plaintext Ciphertext Bob’s public key Bob’s private key

55. Public-Key Cryptography How to obtain the public-key ? Any publishing way can be used to get the public-key (Directory servers, Phone, Web server, Newspapers etc.) No more confidentiality issues in key distribution

56. Public-Key Cryptography Advantages No secret sharing Fewer keys No prior relationship needed Easier to administrate Offers useful mechanisms like digital signature (offering non repudiation)

57. Public-Key Cryptography Disadvantages Not efficient (slow) to encrypt large volume of data Keys need to be much longer than with secret-key encryption Impossible to encrypt a plaintext with size > key

58. Types of public-key algorithm A public-key algorithm is reversible if encryption and decryption can be processed with either a private or a public-key A public-key algorithm is irreversible if a private-key is mandatory for encryption Key exchange algorithm: neither used for encryption nor decryption (Diffie-Hellman)

59. RS A Inventors: Rivest, Shamir, Adleman in 1977 Most popular Provide confidentiality, digital signature and key exchange Key length up to 4096 Plaintext length < Key length Ciphertext size = Key size

60. RSA RSA is protected by a patent. Patent expires on 20th September 2000 Relies on irreversible mathematics functions (Prime numbers)

61. Diffie-Hellman Published in 1976 by W. Diffie and M. Hellman Oldest known public-key cryptosystem Key agreement algorithm Enables secret-key exchange without prior knowledge Agrees on shared secret used in conjunction with a secret-key Cryptosystem (DES, 3DES, IDEA, etc.)

62. Diffie-Hellman: How it works ? Alice’s private key Bob’s private key Alice’s public key Bob’s public key = Share Secret Key Share Secret Key

63. DSA Compliant to D igital S ignature S tandard (DSS) Published in 1994 Irreversible algorithm (encryption with private key only) Used in Digital signature only Performance tuned for smart cards

64. Comparative Public-Key table

65. Message-Digest Algorithms

66. Message-Digest Algorithms Take a variable-length message and produce a fixed-length digest as output The fixed-length output is called the message digest, a digest or a hash A message-digest algorithm is also called a one-way hash algorithm or a hash algorithm

67. Message-Digest Algorithms Input Message Fixed-length Digest Hash Function

68. Message-Digest Algorithms Message-Digest Algorithms properties required to be cryptographically secure It must not be feasible to determine the input message based on its digest It must not be possible to find an arbitrary message that has a particular, desired digest It should be impossible to find two messages that have the same digest (collision) It should be very sensitive to input message changes

69. Message-Digest Algorithms Some Common Message-Digest Algorithms MD2: 128-bit-output, deprecated, by Ronald Rivest MD4: 128-bit-output, broken, by Ronald Rivest MD5: 128-bit-output, weaknesses, by Ronald Rivest SHA-1: 160-bit-output, NSA-Designed RIPEMD-160: 160-bit-output Haval: 128 to 256 bit-output (3 to 5 Passes) CRC-32: 32-bit-output Recommendation: Use SHA-1

70. Message-Digest Algorithms Message-Digest at work Creation of digital signatures Creation of MAC, HMAC Creation of secret-key with a passphrase File checksum (FTP server, Patches, etc.) FIA (File Integrity Assessment like Tripwire)

71. Random Numbers Random numbers are usually required to generate cryptographic keys or challenge. Two main categories (PRNG) Pseudo Random Number Generator uses a deterministic algorithm to generate a pseudo random number based on a seed (mouse, keyboard, etc..) A random number generator generates truly unpredictable numbers. Based generally on special hardware (white noise, radioactive-decay, etc…)

72. Random Numbers

73. Random Numbers A very secure cryptosystem can be broken if it relies on random numbers that can be guessed Netscape browser using SSL broken! Some PRNG Yarrow from B. Schneier CryptPack etc.

74. Keys Length To break a secret-key cryptosystem with “no weakness”, an attacker must try each possible key. This is called a brute force attack To break a public-key cryptosystem an attacker should use “smarter” brute force attack based on mathematics Key space dimension = 2n (n:keylength)

75. Keys Length

76. What is the right key size ? The goals of cryptography are to make the value of encrypted information less than the money spent to decrypt it ! the value of information usually decreases over tim e

77. RSA’s Challenge on DES (III) Method: splitting the Key space for distributed Brute Force Attack (space dimension = 2n , where n is the key-length) Starting date: 18.01.99. Ending: 22h15 min. later… Brute Force Attack frequency: 245 Billions keys/sec. Platforms: Cray/Sun/SGI/Pentium etc..

78. RSA’s Challenge on RSA-155 Key-length: 512 bits = 155 digits Method: Prime number factorization Starting Date: August 99. Ending: 5 months later Time: 35.7 CPU years Platforms: SGI/Sun/Pentium etc. 292 computers

79. Keys’ time of life Most of the time, session keys are changing (IPSec, etc.) to enforce security Can be triggered by time or by encrypted data quantity

80. Public-Key vs Secret-key

81. Message Authentication Code

82. Message Authentication Code MAC is a fixed-length data item that is send together with a message to prove integrity and origin Provide authentication and integrity without confidentiality Also referred as message integrity code (MIC) Most common form is HMAC ( Hashed Mac) Example: HMAC-MD5

83. Message Authentication Code + Input Message HMAC Secret-Key Hash Function

84. Digital Signature

85. Digital Signature Digital signature is a data item that guarantees the origin and integrity of a message The signer of the message uses a signing key The recipient uses a verification key to verify the origin and integrity Signing key = private-key Verification key = public-key

86. Digital Signature By using his own private key, the signer can not repudiate the fact he has signed the message This mechanism provide non-repudiation Think about the difference with MAC …

87. Digital Signature: Basics Plaintext Simple signature using PRIVATE-key Plaintext Ciphertext (Signature) Alice’s private key Alice’s public key

88. Digital Signature: How it works? Alice’s private key Signature Alice’s Public key Signature Plaintext MD1 = MD2 ??? Plaintext Digest

89. Digital Signature Why signing a message involves Hashing ? Signature (data item) is too big Performance (public-key is very slow) Possible attack (known plaintext attack)

90. Common Signature Algorithms RSA Well known Export limitation DSA Similar to RSA (algebraic properties of numbers) Non-reversible algorithm, suitable for digital signature only ElGamal Another cipher for digital signature only

91. Hybrid Cryptosystems

92. Hybrid Cryptosystems A Hybrid Cryptosystem combines the best features of both Secret-Key and Public-Key cryptography Used to exchange session key to initiate a symmetric encryption Example: PGP, SSL, IPSEC using Diffie-Hellman or RSA

93. Example: Diffie-Hellman and Secret-Key cryptosystem = Share Secret Key Share Secret Key Plaintext Plaintext Ciphertext Asymmetric Symmetric

94. RSA Key wrapping encryption Suppose Alice wants to send an encrypted text to Bob across the Internet , using RSA key wrapping

95. RSA Key wrapping encryption How it works ? Alice creates a session key, which is a one-time-only secret-key Alice encrypts the data with the session key Alice encrypts the session key with Bob’s public-key Alice sends the ciphertext + the encrypted session key to Bob

96. RSA Key wrapping encryption

97. RSA Key wrapping decryption How it works ? Bob receives the message from Alice Bob uses his private-key to recover the temporary session key Bob uses the session key to decrypt the ciphertext

98. RSA Key wrapping decryption

99. RSA Key wrapping question ? How sure can Alice be about Bob’s presumed public-key ?

100. Man in the Middle Attack!

101. SSH: How it works ?

102. SSH SSH = Secure Sh ell Originally developed in 1995 as a secure replacement for rsh, rlogin,rcp, ftp, telnet Originally implemented in Finland Available worldwide About 3’000’000 users around the world

103. SSH Also allows port forwarding (tunneling over SSH) X11 connection forwarding SSH v2 submitted to IETF Can be run and used in a short space of time Many SSH clients available Secure CRT F-Secure Java Client etc.

104. SSH: Why ? Attacker with sniffer Network Original TCP Packet Login: rome Password: abc123 Unix Host Telnet to Unix Host

105. SSH-1 Protocol (Hybrid Crypto) TCP Auth request SSH Client Server DATA Client performs TCP handshake with the server at port 22 for SSH standard port Start authentication process. Client send authentication request Server decrypt the session key with the two private keys. Begin bulk encrypted data exchange. Client encrypts Server decrypts request, encrypts and sends response S S 22 Session The server responds with two keys. Host key 1024 bit RSA and a Server key 768 bit RSA (Generated hourly) Client verify host key and generate a secret key that is used for bulk encryption then encrypt this secret key twice with Host and Server public keys and send it to the server SSH Symmetric Encrypted data SSH Handshake Public Key

106. SSH Ciphers SSH v1 RSA DES, 3DES, Blowfish, IDEA SSH v2 Diffie-Hellman for key exchange algorithm DSA, RSA 3DES, Blowfish, IDEA, Twofish, Arcfour, Cast-128

107. SSH Authentication Multiple Authentication mechanisms Static password (protected by SSH encryption) RSA or DSA authentication (client decrypts challenge from server) Plug-in authentication (Securid, Radius, ldap, PAM *) “ .rhosts or /etc/hosts.equiv” (Based on IP address)

108. SSH Authentication (RSA/DSA) Client decrypts “challenge” from server Provides “strong” authentication (client uses his private-key plus a PIN code) Server sends encrypted challenge with client’s public key Client decrypts challenge and sends it to the server The challenge is chosen randomly

109. SSH Tunneling mode SSH Server HTTP 127.0.0.1 1999 Encrypted SSH tunnel Clear text Web server DMZ Corporate Net SSH Client

110. PKCS

111. PKCS Public Key Cryptographic Standard (PKCS) Standardization of public-key algorithmic, in order to maintain interoperability Developed by RSA Laboratories, a consortium of information technology vendors and academic institutions. Apple Microsoft Compaq Lotus Sun MIT etc.

112. PKCS list #1: Encrypting and signing using RSA public key cryptosystem #3: Key agreement with Diffie-Hellman key exchange #5: Encrypting with a secret key derived from a password #7: Syntax for message with digital signature #8: Format for private key information #9: Attribute type for use in other PKCS standard #10: Syntax for certification request #11: Define a cryptoki programming interface (API for smart cards) #12: Portable format for storing and transporting private keys #13: Encrypting and signing data using elliptic curves cryptography #14: Standard for pseudo number generation #15: Standard to store credentials on tokens

113. Smart Card

114. Smart Card Smart Cards consist of a chip (processor or/and memory), a contact plate and a piece of plastic (ISO 7810 - 54x85x0.8 mm) Smart Cards are used for multi-applications GSM, Banking, Medical, E-Commerce, Pay TV, etc .

115. Smart Card and PKI Storing the private-key and/or X.509 certificate on the Smart Card Provide Strong Authentication Something you have, Something you know Access protected by a PIN (like credit card) Types of Smart Card Memory Cards PKI smart cards using Crypto-processor (RSA, etc.) Some Smart Card are “brute force” protected

116. Smart Card Standard (interface) PKCS #11 also call Cryptoki Interface for the communication to Smart Card Netscape, RSA PC/SC and their Crypto API http://www.pcscworkgroup.com/ Bull, Gemplus, HP, Intel, Microsoft, Schlumberger Siemens, SUN, Toshiba

117. Smart Card Reader Keyboard USB Serial PCMCIA Diskette reader SCSI

118. Today’s Smart Card Drawbacks Hardware... Multi-Services rarely used Users leave Smart Card on the reader

119. Quiz !

120. Quiz! Describe Secret-Key ? Advantages / Disadvantages Describe Public-Key ? Advantages / Disadvantages Describe Messages Digest ? Describe Digital Signature and verification ? Differences between MAC and signature? Describe two Hybrid Cryptosystems ? Describe a challenge response based authentication?

121. PKI Introduction

122. PKI introduction The aim of PKI is to integrate all the previous mechanisms and algorithms into a coherent and efficient structure. It will answer the following fundamental security needs: Authentication Confidentiality Non-Repudiation Integrity The basis of PKI relies on the concept of certificates

123. PKI basis function PKI will include at least: One Certificate Authority who delivers certificates One Directory who stores active Certificates and/or Revoked Certificates One Registration Authority who allows certificates’ enrollment One centralized Management

124. Remember Alice, Bob and Charlie... Bob has no proof of the “link” between Alice’s public-keys and her identities So What ?

125. Third Trusted Party No more Charly Implicit Trust Trusted Authority Direct Trust Direct Trust

126. Digital Certificates A public-key certificate is a bond between n an entity’s public-key and one entity The entity can be: A person A role (Manager Director) An organization A piece of hardware (Router, Server, IPSEC, SSL, etc.) A software process (JAVA Applet) A file (Image, Databases, etc.) etc.

127. Digital Certificates A Public-key certificate provides assurance that the public-key belongs to the identified entity A Public-key certificate is also called a digital certificate, digital ID or certificate The entity identified is referred to as the certificate subject If the certificate subject is a person, it is referred to as a subscriber

128. Digital Certificates A certificate is like a passport ...

129. How to obtain a certificate As with passports, you give proof of your identity to an official (or trusted) authority. The authority checks this proof. The authority delivers a signed passport . This procedure is defined as an “enrollment” Instead of “enrolling” for a passport we’ll enroll for digital certificate.

130. Digital Certificates Graphical representation of a certificate

131. Demo: certificate view

132. X.509 Certificate Standard X.509 is a standard for digital certificate by International Telecommunications Union (ITU) First published in 1988 (V1.0) Version 2.0 (1993) adds two new fields Current version is v3.0 (1996) and allows additional extension fields

133. X.509 Basic Certificate Fields Version: X509 version 1,2 and 3 Certificate serial number: Integer assigned by the CA (unique) Signature algorithm identifier: RSA/MD5 etc. Issuer name: name of CA having signed and issued the certificate Validity period: time interval Subject name: the entity name (this name must be unique = distinguished name (DN) )

134. X.509 Basic Certificate Fields Subject public-key information: contains the public-key plus the parameters Issuer unique identifier: optional field Subject unique identifier: optional field Extensions: may provide additional data for specific applications.

135. How to build a Certificate X.509 Certificate CA’s Signature X.509 Fields Public key Identity etc. Digital Signature Process CA

136. How to verify a certificate ? Obtain the Signer’s (CA) public-key Pass the X.509 fields into the message digest algorithm and keep the digest (= your digest 1) Decrypt the Certificate signature with the Signer’s (CA) public-key. The decrypting plaintext will be the digest (= your digest 2) Compare the digest 1 with the digest 2 Does this match together?

137. Verifying a certificate? MD1 = MD2 ??? CA’s public key CA’s Signature X.509 Fields Public key Identity etc.

138. A few words about CAs Entities that issue and manage digital certificates including maintaining revoking publishing status information CAs’ security policy defined in CPS (Certification Practice Statement) Security measures to guarantee CA’s integrity Security measures to check enrollment’s identity Trust level relies upon CPS and not technology

139. Few words about CAs PKI security relies on CA’s private-key secrecy Should never be acceded Should be backed-up Solution: store it inside dedicated tamperproof hardware

140. Type of CAs Private CAs: Hold by a private entity (Company, Administration, the Military) Public CAs: Verisign, Swisskey, GTE, Thawte, Global-sign, Certplus, etc.

141. Registration Authority (RA) A Registration Authority is the entity receiving the certification requests and managing them before sending them to the CA. RA acts as a front end. As in hybrid CAs, the registration authority can be separate from the CA itself. In this case we talk about Local Registration Authority (LRA) Multiple sites for big companies Distributed environment

142. LDAP X.500 Directories required more effort and complexity than most companies were prepared to invest L ightweight D irectory A ccess P rotocol was proposed by the Internet community LDAP uses the X.500 naming conventions but simplifies the way you interact with a directory

143. LDAP LDAP is a “front end” that is used to implement simple directory services An LDAP Server may be implemented over: a full X.500 Directory a database a flat file Most of structured data set CA will use LDAP to publish certificates and CRLs

144. Certificate Revocation Certificate Revocation: Mechanism used by the CA to publish and disseminate revoked certificates Revocation is triggered in the following cases: Key compromise CA compromise Cessation of operation Affiliation change etc...

145. Certificate Revocation Several data structures exist to publish revocation CRL (Certificate Revocation List) ARL (Authority Revocation List) CRT (Certificate Revocation Trees) by Valicert Also Online query mechanisms OCSP (Online Certificate Status Protocol)

146. CRL’s publication and retrieval Certificate-using applications must be aware of revoked certificates Get CRL via ldap Get CRL via FTP, Http, Https, etc. Check certificate status via OCSP Etc. Problem to solve: Revocation delay ! Not yet fully standardized (Delta CRLs, OCSP etc.)

147. OSCP LDAP OCSP FTP, http others OCSP over http PKI enable Applications Pushing Revocation OCSP Responder CA Backend

148. Trust Because a CA has a certificate itself and represents the highest possible trust level, the CA has its self-signed certificate A self-signed certificate is a Root Certificate or Meta-Introducer A certificate-using application (any X.509 holders) must trust the Root certificate Importing a Root certificate into such an application is called Bootstrapping a CA

149. Trusted Root certificates Many applications (as http browsers) have already embedded root certificates

150. Let’s be practical! User enrolls for certificate http://www... User mailed retrieval PIN User retrieves certificate http://www... Admin Approves request http://www... User mailed acknowledgement Admin mailed notification RA CA User Security Officer LDAP Certificate installed

151. PKI Standards Some standard organizations: IETF PKI Working Group (PKIX) ITU SPKI RSA with PKCS

152. PKI Summary Based on Certificates (X.509) Trusted third party (CA) (L)RA CRL Data repositories Mechanisms and protocols between all these elements

153. S/MIME

154. S/MIME S ecure M ultipurpose I nternet M ail E xchange Developed by RSA, Microsoft, Lotus, Banyan, and Connectsoft in 1995 Implemented at application layer Build on top of PKCS #7 and PKCS #10 Very strong commercial vendor acceptance Netscape, Microsoft, Lotus, etc. IETF developed S/MIME v3 (last version) Use X.509 certificates

155. S/MIME S/MIME provides four services:

156. S/MIME Ciphers Symmetric encryption 3DES 168 bit DES 56 bit RC2 128, 64 and 40 bit Public-Key RSA 512 to 1024 bit

157. S/MIME dual Key ? Dual Key Pair One key pair for encryption One key pair for signature and non repudiation CA must support key backup and recovery Key pair for encryption generated on the CA itself ! Draw back: Not all Email client support Dual Key Pair

158. SSL / TLS

159. SSL S ecure S ockets L ayer TCP/IP socket encryption Provides end-to-end protection of communications sections Confidentiality protection via encryption Integrity protection with MAC’s Usually authenticates server using a digital signature (option) Can authenticate client (option)

160. SSL History SSL v1 designed by Netscape in 1994 Netscape internal usage SSL v2 shipped with Navigator 1.0 and 2.0 Microsoft proposed PCT (Private Communications Technology), which overcame some SSL v2 shortcomings SSL v3 latest version The progresses of PCT were echoed in SSL v3 TLS v1 developed by IETF

161. SSL Protocol The SSL protocol runs above TCP/IP The SSL protocol runs below higher-level protocols such as HTTP or IMAP

162. SSL Ports from IANA nsiiops 261/tcp # IIOP Name Service over TLS/SSL https 443/tcp # http protocol over TLS/SSL smtps 465/tcp # smtp protocol over TLS/SSL (was ssmtp) nntps 563/tcp # nntp protocol over TLS/SSL (was snntp) imap4-ssl 585/tcp # IMAP4+SSL (use 993 instead) sshell 614/tcp # SSLshell ldaps 636/tcp # ldap protocol over TLS/SSL (was sldap) ftps-data 989/tcp # ftp protocol, data, over TLS/SSL ftps 990/tcp # ftp protocol, control, over TLS/SSL telnets 992/tcp # telnet protocol over TLS/SSL imaps 993/tcp # imap4 protocol over TLS/SSL ircs 994/tcp # irc protocol over TLS/SSL pop3s 995/tcp # pop3 protocol over TLS/SSL (was spop3) msft-gc-ssl 3269/tcp # Microsoft Global Catalog with LDAP

163. SSL Ciphers The SSL protocol supports the use of a variety of different cryptographic algorithms or ciphers DES (56) 3DES (168) RC4 (40 or 128) RC2 (40) Fortezza (96) IDEA (128) SHA-1, MD5 DSA RSA (Key exchange)

164. SSL Handshake Negotiate the cipher suite Establish a shared session key Authenticate the server (Optional) Authenticate the client (Optional)

165. SSL Handshake TCP Hello GET URL Client Server DATA Client performs TCP handshake with the server at port 443 for HTTPS which is HTTP in SSL Start Cipher negotiation. Client sends SSL HELLO containing ciphers supported by the client and a random number. Start pass secret. Server sends it’s CERTIFICATE. Client and Server exchange CHANGE CIPHER SPEC and FINISH messages. Begin bulk encrypted data exchange. Client encrypts and sends HTTP GET. Server decrypts request, encrypts and sends response Server sends FINISH and closes with TCP handshake S A SSL connection consists of an SSL handshake followed by bulk encrypted protocol S 443 Cert The server responds with a HELLO containing the ciphers to use and a random number. Note the server selects the ciphers to be used. RSA, RC4 and MD5 are most common. Client uses certificate to encrypt the pre-master Secret and sends to Server. Both compute bulk encryption KEYS from secret and random numbers. Bulk Encrypted HTTP Protocol Symmetric SSL Handshake Asymmetric 0.2 - 4 KB

166. Client authenticate server Is today's date within the validity period? Is the issuing CA a trusted CA? Does the issuing CA's public-key validate the issuer's digital signature? Does the domain name in the server's certificate match the domain name of the server itself?

167. Demo: Wrong URL !

168. Server authenticate client Does the client's public-key validate its digital signature ? (challenge) Is today's date within the validity period? Is the issuing CA a trusted CA? Does the issuing CA's public-key validate the issuer's digital signature? Is the user's certificate listed in a CRL?

169. SSL Tunneling SSL can provide tunneling to transport TCP port over an encrypted channel Some tunneling software can use client and server authentication using Certificates X.509 Some tunneling programs Webtop (Sun/Netscape) Stunnel bjorb, Jonama SSLProxy Celo Communicationss (SSR)

170. SSL Hardware accelerator RSA key exchange is very CPU Intensive 200 Mhz NT box allows about a dozen concurrent SSL handshakes Use Multiple server Use Hardware encryption (Intel-IPIVOT, Ncipher, Rainbow, etc.)

171. SGC Server Gated Cryptography Allows strong encryption on a server basis Originally available only to “qualified financial institutions” Requires a special SGC server certificate from: Verisign Global-ID Thawte SuperCert GlobalSign HyperSign128 Etc.

172. SGC Enables strong encryption for export’s browser Procedure: Browser is export version: 40 bit cipher only ! Browser connect to SGC-enabled server with 40 bits cipher Server send his SGC-tagged certificate to browser Browser verifies server certificate and detect that is issued by a CA root certificate which is tagged to enable SGC Browser enabled 128 bit ciphers and force a SSL/TLS renegotiation with the stronger cipher suite.

173. TLS T ransport L ayer S ecurity IETF standardized evolution of SSL v3 Update Mac layer to HMAC Updated for newer algorithms Substantially similar to SSL v3 Cleanup of SSL v3 Aka SSL v3.1 Standardized by RFC 2246 (Jan 1999)

174. Installing a SSL Web Server Create the key-pair: Public and Private-Keys Each server includes programs to generate these Generate a CSR (Certificate Signing Request) This adds Information about your server and yourself Send the CSR to a CA (Certificate Authority) and wait for your Certificate For instance Verisign, or a internal CA Install the Certificate

175. Demo: unknown certificate

176. IPSEC

177. IPSec introduction Stands for IP Security Provide site-to-site and/or host-to-site encryption and/or authentication Driven by the IETF Mandatory for IPv6, optional for IPv4

178. IPSec: two main ”Blocks” IPSec deals with two main “blocks” IPSec - Encryption and Authentication ESP - Encapsulating Security Payload AH - Authentication Header Two modes: Tunnel and transport IPSec - Key management IKE, Skip, Manual IPSEC

179. IPSec: ESP and AH The AH (Authentication Header) is a protocol providing authentication only The ESP (Encapsulation Protocol) is an IPSEC protocol for packet encryption and encapsulation. Both protocols offer integrity check with authentication

180. IPSec Tunnel mode Each datagram is captured by the security gateway, encapsulated inside an IPSEC packet and sent to a remote security gateway, which “decapsulates” it, and sends the original datagram to its original destination The two security gateways create a ‘tunnel’ through which data is passed The two hosts (and their applications) are unaware of the encapsulation process

181. IPSec Tunnel mode IP TCP Application UDP IP TCP Application UDP IP AH/ESP Protected Data IP AH/ESP Protected Data Protected Traffic Hosts IPSec gateway

182. IPSec Transport mode In transport mode, the two hosts serve as a security gateway and encrypt their own data In this case, there is no need for a tunnel, nor for the double IP header The two hosts are aware of the encapsulation (since they perform it)

183. Transport mode Protected Traffic IP TCP Application UDP IP TCP Application UDP

184. Security Associations (SA) The SA is shared by the two communicating parties - it provides indications on the algorithms, the keys, the lifetimes and other algorithm dependant information The SPI (Security Parameter Index) is a number and serves as an index to the SA Each SA has two SPIs: incoming & outgoing

185. SPI and SA (Basics) SPI: 0x1234567 Encryption (ESP): DES Authentication (AH): SHA-1 DES Key: 0x1615613651365365326536 SHA-1: 0x32676362736347672672644 SPI: 0x1234567 SA

186. IPSec Key management In order to create the SA, the two parties need to exchange all the security parameters, as well as the keys. Several methods of key management: Manual keying or manual IPSec (statically defining SPI and SA). SKIP (Simple Key Interchange Protocol by SUN Microsystems) ISAKMP/OAKLEY or IKE: automatic key management using DH Photuris alternative to IKE using DH

187. Manual IPSec On each gateway a specific SA is defined (according S/WAN) for each remote gateway (SPI, Cipher, Keys, Hash etc.) Drawback: Very heavy management Static keys: less security Often used between different IPSec vendors Cisco to Check Point for instance

188. Manual IPSec SA SPI SA SPI

189. IKE Key management IKE is widely used (OSPF, IPSec etc..) SA proposal and negotiation is done using IKE Peers may be authenticated using X.509 certificate Each IPSec gateway holds a X.509 certificate SA negotiation starts after cross authentication Alternate method for authentication: Authentication is provided by pre-shared secrets Drawback: heavy key management etc.

190. IKE Key management using PKI SA SPI SA SPI Negotiation with Automatic Key Management X509 X509

191. Questions?

192. Pour plus d’informations e-Xpert Solutions SA Sylvain Maret Route de Pré-Marais 29 CH-1233 Bernex / Genève +41 22 727 05 55 [email_address]