In existing research results, they can mainly be divided into four kinds in reducing the cost of the key management: hierarchical key management scheme, key compression scheme based on symmetric encryption, identity-based key compression scheme, and other related solutions.
However, the main drawback of hierarchical key management scheme was that only under certain conditions can it achieve effective key compression. This was because the node key can only access to the subtree of the node, if authorized files were from different branches, which in turn would increase the number of users' private keys.
 proposed a key compression scheme based on symmetric encryption.
Intended for undergraduate computer and electrical engineering students with intermediate level mathematics and computer systems experience, this volume uses the MATLAB numerical computing and modeling program to demonstrate the underlying processes of key compression
functions without overwhelming the student with complex algorithms.
Dr Chin Chye Koh, director of product management for Nevion's Ventura family of products, said that the efficient aggregation of video signals across IP networks for content distribution of any kind--unidirectional, bidirectional, unicast or multicast--as well as key compression
and multiplexing technologies have farreaching implications for IP transport.
And finally, the newly developed 4 to 10 Station XSpress from OYSTAR Manesty conforms to the cGMP (current Good Manufacturing Practices) and allows customers to analyze key compression
If key compression
is employed, however, the order of different nodes in a tree may vary.
Pass-Phrases/Key Compression - Rather than forcing a user to come up with a secure but easy-to-remember short password, some systems have implemented support for pass-phrases and key compression. Simply put, pass-phrases are long passwords.
In order to support these long passwords, but still use them with the DES and other encryption algorithms, key compression is used.