Key management method

Details Key management method Key management method

1999-08-11

2003-12-02

Peeso, Thomas R. (Department: 2132)

Cryptography

Key management

C380S278000, C713S156000, C713S168000, C713S169000

Reexamination Certificate

active

06658114

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to cryptographic communication, and in particular to a key management method to prevent illegal eavesdropping in a network system, wherein keys of the network system are divided into several family subkeys and several communication subkeys which are respectively preserved in plural trusted-key centers and are not available to any single trusted-key center, and in which communication keys are valid only during an authorized time period.
2. Description of the Related Art
FIG. 1
(Prior Art) is a diagram illustrating a current cryptographic network system. In
FIG. 1
, a trusted-key center CA is provided in the network system to preserve all session keys and to ensure data security, such as preventing passive eavesdropping and active tampering. When a user P
i
and another user P
j
want to communicate with each other on a telephone system or a communication system, the sender, e.g., the user P
i
, first passes a to-be-transferred message m to a cipher device
10
. The cipher device
10
then encrypts the input message m using a corresponding session key K
ij
and outputs the encrypted message E
kij
(m) to a decipher device
20
at the receiving terminal thereof. Thereafter, the decipher device
20
decrypts the encrypted message E
kij
(m) using the same session key K
ij
and then outputs the recovered message m to the receiver, e.g., the user P
j
.
In the cryptographic network system, once an eavesdropper P
k
is authorized to eavesdrop the communication between the user P
i
and the user P
j
, the trusted-key center CA will pass the corresponding session key K
ij
to the eavesdropper P
k
. However, the session key K
ij
preserved in the trusted-key center CA is not refreshed frequently, so the eavesdropper P
k
can still use the previously obtained session key K
ij
to eavesdrop the communication between the user P
i
and the user P
j
, even after the authority has expired.
Furthermore, due to a possible security compromise of the trusted-key center CA, a potential security risk is realized when all the session keys of a network system are stored in a single trusted-key center.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a key management method for a network system, wherein keys of the network system are divided into several family subkeys and communication subkeys which are respectively preserved in plural trusted-key centers and are not available to any single trusted-key center, in order to prevent compromise of secure communications in the network system.
It is another object of the present invention to provide a key management method for a network system, wherein communication keys are not valid except during an authorized time period to prevent illegal eavesdropping.
It is another object of the present invention to provide a key management method for a network system, wherein each of the trusted-key centers generates a time-related and irreversible hash value which is used to calculate communication keys of the network system, so that the communication subkeys preserved in each of the trusted-key centers can be refreshed at a lower frequency.
It is another object of the present invention to provide a key management method for a network system, wherein each of the trusted-key centers only preserve subkeys of an order of t
2
, where t is the number of all network users. Because it is very fast to compute a one-way hash function, the computation loading for each of the trusted-key centers is very low.
To achieve the above and other objects, the present invention provides a key management method to prevent illegal eavesdropping in a network system. This method includes the following steps. First, keys of the network system are divided into several family subkeys and several communication subkeys. Then, a few trusted-key centers are provided for respectively preserving a part of the family subkeys and one of the communication subkeys, and generating a one-way hash value involving the preserved communication subkey and an open information. Thereafter, each of the trusted-key centers passes the hash value to an eavesdropper according to an authority certificate. Each of the trusted-key centers interchanges the preserved family subkeys according to the authority certificate to obtain a session key which is passed to the eavesdropper. Then, the eavesdropper combines all the hash values from the trusted-key centers to obtain a corresponding communication key, which is accompanied by the session key, in order to eavesdrop an authorized communication.
In this key management method, the open information may be a current time. The hash value may be obtained by calculating a one-way hash function of a sum of the preserved communication subkey and the current time. The communication key may be combined by adding all the hash values from the trusted-key centers.


REFERENCES:
patent: 5757920 (1998-05-01), Misra et al.
patent: 5812784 (1998-09-01), Watson et al.

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