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Z39.50 and Cryptography

Explore the relevance of cryptography in the Z39.50 protocol for authentication, confidentiality, integrity, and non-repudiation. Learn about symmetric and public-key encryption, digital signatures, SSL, and securing Z39.50 with symmetric keys.

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Z39.50 and Cryptography

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  1. Z39.50 and Cryptography ZIG July 13th 2000 Poul Henrik Jørgensen, mailto:phj@dbc.dk DBC www.dbc.dk

  2. Is Cryptography Relevant to Z39.50? • Authentication:identify users (and servers) internally. • Confidentiality: keep searches, responses (and users) secret to from others. • Integrity: prevent tampering with searches and responses. • Non-repudiation:prove the transactions. Poul Henrik Jørgensen, DBC

  3. Security Threats • Spoofing:Masquerading as one of the parties. • Eavesdropping:Snooping on traffic between parties. • Tampering:Forgery or modification of messages. • Repudiation:Denying the transaction. Poul Henrik Jørgensen, DBC

  4. Symmetric Encryption • A single common encryption key is used to encode and decode messages • Both sender and receiver must know the common key • The common key need to be exchanged beforehand by some other secure method • Symmetric encryption is simple and fast • But - key management is impractical with large number of senders and receivers! Poul Henrik Jørgensen, DBC

  5. Public-key Cryptography • Public-key(PK) encryption algorithms use pairs of matched (asymmetric)keys for encryption and decryption. • Each user has a Public key and a corresponding Private (secret) key • Public-key cryptography is used to exchange symmetric keys securely. • Public-keys are also used to validate digitalsignatures. Poul Henrik Jørgensen, DBC

  6. Public-key Usage • Alice creates a new symmetric session-key. • Alice encrypts the session-key by means of Bob’s public key. • Alice transmits the encrypted message containing the session-key to Bob. • Bob decrypts Alice’s message with the session-key by means of his private key. • Alice and Bob both encrypt and decrypt subsequent messages by means of the session-key. Poul Henrik Jørgensen, DBC

  7. Digital Signatures and Certificates • Sender”sign” messages by means of his private secret key. • Recipient verify the senders signature by means of the senders public key. • The senders identity is certified by means of a”Certificate” which is digitally signed by a trusted third party. Poul Henrik Jørgensen, DBC

  8. Secure Socket Layer (SSL) • SSL is a communication layer on top of TCP/IP • SSL is supported by current browsers • Browser request a copy of a HTTPS servers’ certificate • Browser verify identity of the server by checking the certificate and the digital signature • Browser create a symmetric session key Poul Henrik Jørgensen, DBC

  9. Secure Socket Layer cont. • Browser encrypt the session key by means of the HTTP servers public key and transmits the session key to the server • Session data is encrypted and decrypted both ways at both ends by means of the symmetric session key • http://developer.netscape.com/tech/security/ssl/howitworks.html Poul Henrik Jørgensen, DBC

  10. Z39.50 and Symmetric Keys • A new Z39.50 Init Request option may specify use of a symmetric encryption algorithm within a Z39.50 session • Symmetric encryption key must be exchanged outside of the Z39.50 protocol, e.g. based on a predefined user password • Only Z39.50 user data is encrypted – not protocol elements Poul Henrik Jørgensen, DBC

  11. Z39.50 and Symmetric Keys cont. • Encryption and decryption must be handled by Z39.50 server and client applications. • This solution require limited changes to Z39.50 toolkits in order to handle a new Init Request option. • Z39.50 servers and clients must be modified to encrypt- and decrypt data via passwords or other symmetric keys. Poul Henrik Jørgensen, DBC

  12. Z39.50 with Symmetric Keys Encryption Toolkit Encryption Toolkit ZS-Client Application ZS-Server Application Z-Client Toolkit Z-Server Toolkit Z39.50 Session Poul Henrik Jørgensen, DBC

  13. Z39.50 and SSL • Z39.50 over SSL offers a complete security solution • Transparent to Z39.50 server and z-client applications • Require no changes to the Z39.50 protocol • Require a compatible Z39.50 toolkit on both z-server and z-client that utilise a SSL library • May require key certificates on Z39.50 server Poul Henrik Jørgensen, DBC

  14. Z39.50 Over SSL Z-Client Application Z-Server Application ZS-Client Toolkit ZS-Server Toolkit Encrypted Z39.50 Session SSL Toolkit SSL Toolkit Poul Henrik Jørgensen, DBC

  15. Summary • Security is primarily relevant to identify Z39.50 users • Confidentiality of queries and presented data may also be an issue • SSL require Z39.50 SRPM toolkits to utilise SSL libraries, but is transparent to z-servers and clients • Simple symmetric keys may require modifications to Z39.50 protocol and to z-servers and clients www.portia.dk/zigjuly2000/z3950crypto.htm Poul Henrik Jørgensen, DBC

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