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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References l Peter Guttman's tutorial n about 500 slides covering cryptography, secure connection protocols, PKI, politics and more. l RSA Laboratories PKCS specifications n l SSL/TLS n TLS v 1.0 RFC - n SSL-v3 n openSSL l Certificates n