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An Introduction to Security Concepts and Public Key Infrastructure (PKI)

An Introduction to Security Concepts and Public Key Infrastructure (PKI). Mary Thompson. Security Levels. Confidentiality Protection from disclosure to unauthorized persons Integrity Maintaining data consistency Authentication Assurance of identity of person or originator of data

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An Introduction to Security Concepts and Public Key Infrastructure (PKI)

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  1. An Introduction toSecurity Concepts andPublic Key Infrastructure (PKI) Mary Thompson

  2. Security Levels • Confidentiality • Protection from disclosure to unauthorized persons • Integrity • Maintaining data consistency • Authentication • Assurance of identity of person or originator of data • Non-repudiation • Originator of communications can't deny it later • Authorization • Identity combined with an access policy grants the rights to perform some action

  3. Security Building Blocks • Encryption provides • confidentiality, can provide authentication and integrity protection • Checksums/hash algorithms provide • integrity protection, can provide authentication • Digital signatures provide • authentication, integrity protection, and non-repudiation

  4. Keys • Symetric Keys • Both parties share the same secret key • Problem is securely distributing the key • DES - 56 bit key considered unsafe for financial purposes since 1998 • 3 DES uses three DES keys • Public/Private keys • One key is the mathematical inverse of the other • Private keys are known only to the owner • Public key are stored in public servers, usually in a X.509 certificate. • RSA (patent expires Sept 2000), Diffie-Hellman, DSA

  5. Hash Algorithms • Reduce variable-length input to fixed-length (128 or 160bit) output • Requirements • Can't deduce input from output • Can't generate a given output • Can't find two inputs which produce the same output • Used to • Produce fixed-length fingerprint of arbitrary-length data • Produce data checksums to enable detection of modifications • Distill passwords down to fixed-length encryption keys • Also called message digests or fingerprints

  6. Message Authentication Code MAC • Hash algorithm + key to make hash value dependant on the key • Most common form is HMAC (hash MAC) • hash( key, hash( key, data )) • Key affects both start and end of hashing process • Naming: hash + key = HMAC-hash • MD5 1 HMAC-MD5 • SHA-1 1 HMAC-SHA (recommended)

  7. Digital Signatures • Combines a hash with a digital signature algorithm • To sign • hash the data • encrypt the hash with the sender's private key • send data signer’s name and signature • To verify • hash the data • decrypt the signature with the sender's public key • the result of which should match the hash

  8. Elements of PKI • Certificate Authorities (CA) • OpenSSL, Netscape, Verisign, Entrust, RSA Keon • Public/Private Key Pairs - Key management • x.509 Identity Certificates - Certificate management • LDAP servers

  9. X.509 Identity Certificates • Distinguished Name of user • C=US, O=Lawrence Berkely National Laboratory, OU=DSD, CN=Mary R. Thompson • DN of Issuer • C=US, O=Lawrence Berkely National Laboratory, CN=LBNL-CA • Validity dates: • Not before <date>, Not after <date> • User's public key • V3- extensions • Signed by CA

  10. Certificate Authority • A trusted third party - must be a secure server • Signs and publishes X.509 Identity certificates • Revokes certificates and publishes a Certification Revocation List (CRL) • Many vendors • OpenSSL - open source, very simple • Netscape - free for limited number of certificates • Entrust - Can be run by enterprise or by Entrust • Verisign - Run by Verisign under contract to enterprise • RSA Security - Keon servers

  11. LDAP server • Lightweight Directory Access Protocol • Evolved from DAP and X.500 Identities • Used by CA's to store user's Identity Certificate • Open source implementations • Standard protocol for lookup, entry, etc. • Access control is implemented by user, password.

  12. SSL - OpenSSL • Secure message passing protocol • Developed by Netscape, now an IETF RFC (TLS Jan '99) • Protocol for using one or two public/private keys • to authenticate a sever to a client • and by requiring a client key to authenticates the client to the server • establish a shared symetric key (the session key) • uses the session key to encypt all data over the secure channel • Gives you authentication, message integrity and confidentiality • Everything except authorizaton

  13. SSL Handshake • Negotiate the cipher suite • Establish a shared session key • Authenticate the server (optional) • Authenticate the client (optional) • Authenticate previously exhanged data

  14. SSL handshake details • Client hello: • Client challenge • Available cipher suites (eg RSA + RC4/40 + MD5) • Server hello: • Server certificate • Connection ID • Selected cipher suite • Server adapts to client capabilities • Optional certificate exchange to authenticate server/client • Commercial sites only use server authentication

  15. SSL Handshake - details Client Server Generate Challenge Define Protocols Challenge Encryption protocols Return Server Certificate Generate connection ID Confirm Protocols Server Cert Verify server certificate Connection Id Encryption protocols Decrypt session key Generate server read/write Key pairs Generates session key Generate Client read/write key pairs Encyrpt session key (Session Key) Server's public key Encrypt random challenge phrase Decrypt and verify challenge phrase (Client's Challenge) Server Write Key

  16. SSL Handshake Client Authentication Client Server Generate new challenge Requests Client certificate Decrypt challenge (Challenge phrase) Server write key Decrypt Message Digest and Client Certificate Calculate message digest on Challenge and Server certificate [Message Digest & Client Certificate] Client private key Verify Client certificate and recompute message digest Done (Session Identifier) Server's write key

  17. Status • Single purpose CA’s e.g. Globus (SSLeay) Collaboratory, DOE-Grid (Netscape) • Enterprises slow to run CA’s • Many different Vendors - Verisign, Entrust, Netscape, RSA Security Keon • Incompatible Key and Certificate management between vendors • Certificates are not integrated with existing applications that need authorization • Large amount of corporate overhead in running a CA • Uncertain legal implications of issuing certificates • Lab is currently looking at the RSA Keon server as it has integration with ssh and NIS authorization

  18. Public Key Cryptography Standards - PKCS • PKCS 7 • Cryptographic Message Syntax Standard • PKCS 10 • Certification Request Syntax Standard - used by Netscape browser, IE, and SSL libraries • PKCS 11 • Cryptographic Token Interface Standard - An API for signing and verifying data by a device that holds the key • PKCS 12 • Personal Information Exchange Syntax Standard - file format for storing certificate and private key - used to move private information between browsers

  19. References • Peter Guttman's tutorial • http://www.cs.auckland.ac.nz/~pgut001/tutorial/ about 500 slides covering cryptography, secure connection protocols, PKI, politics and more. • RSA Laboratories PKCS specifications • http://www.rsasecurity.com/rsalabs/pkcs/ • SSL/TLS • TLS v 1.0 RFC - http://www.ietf.org/rfc/rfc2246.tx. • SSL-v3 http://www.netscape.com/eng/ssl3/draft302.txt • openSSL http://www.openssl.org/ • Certificates • http://futile.lbl.gov/mecury/cappt/index.html

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