8. Bluetooth with WAP

Bluetooth and WAP (Wireless Application Protocol) technologies fundamentally address different problems. Mobile users with wireless devices use WAP to access and interact with information and services over the Internet instantly. The WAP architecture is designed to enable standard off-the-shelf Internet servers to provide services to wireless devices.  In addition, when communicating with wireless devices, WAP uses many Internet standards such as XML, UDP and IP. The WAP wireless protocols are based on Internet standards such as HTTP and TLS but have been optimized for the unique constraints of the wireless environment. Bluetooth on the other hand is a local area low power radio link between devices (only). Many of the usage scenarios for Bluetooth also involve one of the devices communicating over the air using WAP.

 

A model of protocol layering in WAP in Figure 10. Wireless Transport Layer Security (WTLS) (based on SSL) is designed to function on connection-oriented and/or datagram transport protocols. Security layer is as optional layer above the transport layer. WTLS supports four cryptographic operations - digital signing, stream cipher encryption, block cipher encryption and public key encryption. In digital signing, one-way hash functions (SHA, MD5, etc.) are used as input to a signing algorithm. A digitally-signed element is encoded as an opaque vector <0..216-1>, where the length is specified by the signing algorithm and key. In stream cipher encryption, the plain text is exclusive OR-ed with an identical amount of output generated from a cryptographically secure keyed pseudorandom number generator. In block cipher encryption, every block of plain text encrypts to a block of cipher text done in CBC (Cipher Block Chaining) mode, and all items which are block-ciphered are an exact multiple of the cipher block length. Lastly, in public-key encryption, a public-key algorithm is used to encrypt data that can be decrypted with the matching private-key.

 

Figure 10: Wireless Application Protocol Model


The WTLS Handshake Protocol involves (D-H exchange) the following steps:

  1. Exchange messages to agree on algorithms, exchange random number;
  2. Exchange the necessary cryptographic parameters (RSA) for the client and server to agree on a pre-master secret;
  3. Exchange certificates and authenticate both parties;
  4. Generate a master secret from pre-master secret and exchanged random number;
  5. Provide security parameters to the record layer;
  6. Verify the parameters and authenticate each other.