Cryptography – Key management
Reexamination Certificate
2000-03-22
2004-11-16
Barron, Gilberto (Department: 2132)
Cryptography
Key management
C380S278000, C380S281000
Reexamination Certificate
active
06819766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an improvement in computing systems and in particular to computer systems which manage keys for encrypted data.
2. Description of the Related Art
As confidential and sensitive data is increasingly stored on computer systems, or transmitted over communications networks, including the Internet, it is of increasing importance to have methods and systems to ensure the security of such data. Typically, such data is encrypted as it is stored or transmitted by a computer system and then decrypted when the data is to be accessed after being retrieved or received. Many different approaches are known to those skilled in the art and are available to permit users to encrypt and then decrypt computer data.
To encrypt data, data encryption keys are required. A typical encryption system takes as input the source data to be encrypted and an encryption key. For the same source data, but different encryption keys, a typical encryption system will create different encrypted data. It is intended that only a person knowing the encryption key will be able to decrypt the encrypted data.
It is a poor security practice if one encrypts all data using a single data encryption key or a single set of data encryption keys. This is because by reusing the same key or set of keys, more data are available for analysis of encrypted data (cryptanalysis) for a third party to break the encryption system. Therefore, to ensure the security of a series or collection of encrypted data, for each piece of data (or each occasion) to be encrypted in the series or collection, different data encryption keys are used.
The data encryption keys for each occasion are called session keys because an occasion usually corresponds to a communication session if data are transmitted over a communication network. The term “session key” is also applicable to occasions where no communication is involved but where data encryption is required. The more encrypted data or files one produces the more data encryption keystone has. Matching data encryption keys to the corresponding encrypted data becomes a key management problem if there are many instances of encrypted data and a correspondingly large number of data encryption keys.
Misplacing or losing data encryption keys, or mismatching the data encryption keys and encrypted data, result in the failure to decrypt the encrypted data. It is therefore important to be able to ensure that the correct data encryption keys are associated with the appropriate encrypted data. However, a method of associating the encryption keys with the encrypted data which is simple and easy to use for the party intended to retrieve the encrypted data will also be potentially simple and easy for unauthorized parties to use, to the detriment of the security of the encrypted data. This potential difficulty is present where the data encryption keys are stored or transmitted together with the encrypted data. Although such a simple system ensures that the encryption keys are available to the recipient or person intended to retrieve the data, others may also find the encryption keys and decrypt the encrypted message.
Security for such a system, where the encryption keys are included with the encrypted message, is not to store or transmit the encryption keys in an easily readable format but rather to encrypt the encryption keys themselves. This approach means that the data encryption keys will be encrypted by a key encryption key. This in turn leads to the problem how to transmit or store the key encryption key so that it remains secure.
In the prior art, a security infrastructure to solve the key management problems is often used. Such a security infrastructure may either involve a key distribution center for a symmetric encryption system or a certificate authority used in asymmetric encryption (public key encryption). A key distribution center generates symmetric key encryption keys and distributes them to users in a secure manner. For asymmetric encryption, a certificate authority issues a certificate to a user, which contains the user's public key and is digitally signed by the certificate authority. A user can generate session keys to encrypt data, then using the receiver's public encryption key the user will encrypt the session keys. The receiver can recover the session keys through decryption using the receiver's private decryption key. Encrypted data can be decrypted using the recovered session keys.
Both key distribution centers and certificate authorities are known to those skilled in the art. Use of such security infrastructures is made in sophisticated computer systems where data security is required. However, for most users, such an infrastructure is unavailable, expensive to implement it, or inconvenient.
It is therefore desirable to have a computer system which is capable of encryption key management without requiring a security infrastructure such as a key distribution center or a certificate authority.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided an improved system for managing keys for encrypted data.
According to another aspect of the present invention, there is provided a method for managing encryption keys for data comprising the steps of:
a) generating a session key;
b) encrypting the data using the session key, the encrypted data having a binary representation;
c) generating a key encryption key based on an initial vector, the initial vector being known only to a party encrypting the data and a party intended to decrypt the data;
d) encrypting the session key using the key encryption key, the encrypted session key having a binary representation;
e) generating a set of indices by a one-way transform mapping based on the length of the binary representation of the encrypted session key, the length of the binary representation of the encrypted data, and the initial vector; and
f) reformatting the binary representation of the encrypted data to generate an output set of binary data by interleaving the encrypted session key with the encrypted data by dividing the binary representation of the encrypted session key into segments and inserting the segments into the binary representation of the encrypted data at locations determined by the set of indices.
According to a further aspect of the present invention there is provided a method for the selective decryption of the data encrypted as described above, the decryption including the steps of:
a) regenerating the set of indices by using the one-way transform mapping based on the length of the binary representation of the encrypted session key, the length of the binary representation of the encrypted data, and the initial vector;
b) rebuilding the encrypted session key by using the regenerated set of indices to extract the segments of the binary representation of the encrypted session key from the output set of binary data and assembling the segments to form the encrypted session key;
c) rebuilding the encrypted data by using the regenerated set of indices to extract the binary representation of the encrypted data from the output set of binary data;
d) regenerating the key encryption key, using the initial vector;
e) regenerating the session key by decrypting the rebuilt encrypted session key using the regenerated key encryption key; and
f) decrypting the rebuilt encrypted data using the regenerated session key.
According to another aspect of the present invention, the above methods are implemented in which the number of elements in the set of indices is equal to the number of 8-bit bytes in the binary representation of the encrypted session key, in which each element of the set of indices is an index into the binary representation of the encrypted data, and in which each segment of the encrypted session key is one byte long, whereby the step of interleaving the encrypted session key with the encrypted data comprises the bytes of the binary representation of the encrypted session key being inserted at the byte
Barron Gilberto
Kinnamen, Jr. William A.
Stulberger Cas
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