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Mobile Security and Payment

Mobile Security and Payment. Nour El Kadri University Of Ottawa. Security. Keep in mind: Security requires an overall approach A system is as secure as its weakest component Securing network transmission is only part of the equation

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Mobile Security and Payment

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  1. Mobile Security and Payment Nour El Kadri University Of Ottawa

  2. Security Keep in mind: • Security requires an overall approach • A system is as secure as its weakest component • Securing network transmission is only part of the equation • The sad part is that people often prove to be the weakest link in the chain • Employee who hacks company’s billing database • Careless user who writes his/her PIN on the back of their handset and forget in on the bus

  3. The Role of Cryptography • SIM Module and Authentication centers in GSM Architecture • WAP Gateway security gaps and their solution in the new WAP protocol stack for built-in IP • How does cryptography complement such solutions? • What are the business implications?

  4. Network Transmission Security Requirements • Authentication • Confidentiality • Integrity • Non-repudiation Cryptography plays a central role in satisfying these requirements Other techniques include: • Packet acknowledgements • Checksums

  5. Cryptography Sender: plaintext  cipher text …. Using encryption algorithms Receiver cipher text plaintext …. Using a matching decryption algorithm

  6. Secret-Key or Symmetric Cryptography • Alice and Bob agree on an encryption method and a shared key. • Alice uses the key and the encryption method to encrypt (or encipher) a message and sends it to Bob. • Bob uses the same key and the related decryption method to decrypt (or decipher) the message.

  7. Advantages of Symmetric Cryptography • There are some very fast classical encryption (and decryption) algorithms • Since the speed of a method varies with the length of the key, faster algorithms allow one to use longer key values. • Larger key values make it harder to guess the key value-- and break the code -- by brute force.

  8. Disadvantages of Symmetric Cryptography • Requires secure transmission of key value • Requires a separate key for each group of people that wishes to exchange encrypted messages (readable by any group member) • For example, to have a separate key for each pair of people, 100 people would need about 5000 different keys.

  9. Public-Key Cryptography AKA Asymmetric Cryptography • Alice generates a key value (usually a number or pair of related numbers) which she makes public. • Alice uses her public key (and some additional information) to determine a second key (her private key). • Alice keeps her private key (and the additional information she used to construct it) secret.

  10. PK Cryptography – cont’d • Bob (or Carol, or anyone else) can use Alice’s public key to encrypt a message for Alice. • Alice can use her private key to decrypt this message. • No-one without access to Alice’s private key (or the information used to construct it) can easily decrypt the message.

  11. Public Key Cryptography Source: N. Sadeh

  12. Man-in-the-Middle Attack Solution: Certificate Authorities • Keys are certified, that means a third person/institution confirms (with its digital signature) the affiliation of the public key to a person

  13. Certificate Authorities Three types of organizations for certification systems (PKIs?): • Central certification authority (CA) • A single CA, keys often integrated in checking software • Example: older versions of Netscape (CA = Verisign) • Hierarchical certification system • CAs which in turn are certified by “higher” CA • Examples: PEM, Teletrust, infrastructure according to Signature Law • Web of Trust • Each owner of a key may serve as a CA • Users have to assess certificates on their own • Example: PGP (but with hierarchical overlay system)

  14. Hybrid Encryption Systems • All known public key encryption algorithms are much slower than the fastest secret-key algorithms. • In a hybrid system, Alice uses Bob’s public key to send him a secret shared session key. • Alice and Bob use the session key to exchange information.

  15. Digital Signatures • A digital signature is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document

  16. Digital Signatures Source: N. Sadeh

  17. Elliptic Curve Cryptography • ECC was introduced by Victor Miller and Neal Koblitz in 1985. • For DSA, RSA we need larger key length. • ECC requires significantly smaller key size with same level of security. • Benefits of having smaller key sizes : faster computations, need less storage space. • ECC ideal for constrained environments: Pagers ; PDAs ; Cellular Phones ; Smart Cards

  18. Key player • Certicom is a key player. • Acquired by Research in Motion (two days ago. • Verisign was bidding on the company too • This will set new research ahead in the wireless security arena

  19. Smart Cards Smart card: • A card that contains a processor, memory, and an interface to the outside world. • Vary based on the capabilities of the processor and size of the memory • A smart card needs a reader • Not very common in north America, but it is widespread in other places. • Problems: Lack of standard interfaces

  20. GSM’s SIM-Based Authentication

  21. Message Authentication Codes • Checksums • used mostly to verify the integrity of messages Use a hybrid approach • Recipient can verify both the authenticity and the integrity of the message • MACs are also referred to as “Message Integrity Codes”

  22. Security: The Combinations are Many • IPSec protocol has been adopted by GPRS • Negotiation of security parameters between sender and recipient • Negotiation carried out using Internet Key Exchange • Flexibility in adapting security parameters to mobile environments is very important • Keys might be stored on SIM or WIM modules • Limited memory and processing power • Low bandwidth and high latency

  23. Wired Equivalent Privacy Aka “WEP” • Represents Wi-Fi first attempt at security • Works at data link layer (Layer 2) • Uses static 40 or 104 bit keys for authentication and encryption. • Based on RC4 symmetric stream cipher. • Key stream generated from initial key, used to encrypt and decrypt data

  24. WAP Security: WTLS • Keys generally placed in normal phone storage. • New standards emerging (WAP Identity Module [WIM]) for usage of tamper-resistent devices. • Aside from crypto problems: • User interface attacks likely (remember SSL problems) • WTLS terminates at WAP gateway; MITM attacks possible.

  25. WAP Transaction layer WTP • Three classes of transactions: • Class 0: unreliable • Class 1: reliable without result • Class 2: reliable with result • Does the minimum a protocol must do to create reliability. • No security elements at this layer. • Protocol not resistant to malicious attacks.

  26. WAP Session Layer WSP • Meant to mimic the HTTP protocol. • No mention of security in spec except for WTLS. • Distinguishes a connected and connectionless mode. • Connected mode is based on a SessionID given by the server.

  27. Wireless Identity Module • Can be used to hold private and secret keys required by WTLS TLS and non-WAP applications • Computes crypto operations • “unwrapping master secret” • client signature in WTLS Handshake • key exchange (ECC WTLS Handshake) • It can also store certificates and generate keys • WIM does not necessarily need to be issued by the mobile operator • It can be implemented on the SIM card

  28. WMLScript SignText • Allows developers to write applications where users are prompted with a text that they reject or accept • Acceptance requires the user to punch his/her WIM PIN code and that results in the generation of a digital signature • DS is transmitted back to the content server

  29. WAP Security Models • Operator Hosts Gateway • Without PKI • With PKI • Content Provider Hosts Gateway • Static Gateway Connection • Dynamic Gateway Connection

  30. Operator Hosts Gateway

  31. Operator Hosts Gateway • Without PKI: • Advantages • No extra work for Content Provider • No extra work for user • System only requires one logical gateway • Disadvantages • Content Provider must trust Operator (NDA) • Operator can control home deck • Operator can introduce advertising

  32. Operator Hosts Gateway • With PKI: • Advantages • Content providers does not need to trust Operator. • Disadvantages • PKI Infrastructure must be in place.

  33. Content Provider Hosts Gateway • Static Gateway Connection • Advantages • Content Provider does not need to trust Operator • Content Provider can control home deck • OTA can be used to configure mobile terminal • Disadvantages • Mobile terminal may have limited number of gateway config sets (i.e., Nokia 7110 has 10) • Mobile Terminal needs to be configured. • OTA via WAP Push / SMS may not work with gateway / mobile terminal combination • Content Provider may have to pre-configure mobile terminals

  34. WTLS Class 2 SSL Operator WAP Gateway Internet WAP Gateway Content Provider Web Server SSL Content Provider Hosts Gateway

  35. Content Provider Hosts Gateway • Dynamic Gateway Connection • Advantages • Content Provider does not need to trust Operator. • Content Provider does not need to worry about mobile terminal configuration • Disadvantages • Operator needs to trust Content Provider. • Deployment very slow.

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