Wide–Mouth Frog (protocol)

From Bauman National Library
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The origin of the protocol name is not known. This is one of the simplest key-agreement protocols, that use the trusted third party. It was invented by M. Burrows, M. Abadi and R. Needham in 1989. Some modifications of this algorithm were invented later.



Users and who desire to start messaging, have to be familiar to (Key distribution center) and have shared secret keys with it. The generation of these keys is not a part of the protocols, they should be obtained earlier.


  1. generates a random session key , that will be used in communication with . Then puts together a package for : a timestamp , 's identificator and a session key are encrypted with the key, shared between and and sent to with 's identificator.
  2. chooses the corresponding key and decrypts the package. After that, he forms a package for , that contains a new timestamp, 's identificator and the session key . He decrypts the package with the key, shared between and and sends it to :
  3. decrypts the package and gets the session key and also ID of the user, with whom the connection is established ().

Modified version


During the investigations, some vulnerabilities of the protocol has been found. For example, malefactor can make to open more connections, than were requested, by simple repeating the messages from . In the modified version, after the steps from the basic version, check the correctness of the established connection. It sends to a random number and waits to get from the same number, increased by .


Initial conditions are the same as in the basic version.



M. Burrows, M. Abadi, R. Needham A Logic of Authentication. — Research Report 39, Digital Equipment Corp. Systems Research Center — Feb. 1989. — http://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-39.pdf

Bruce Schneier Applied Cryptography. — Wiley, 1996. — pp. 56 et seq. — ISBN 978-0-471-11709-4.