Method and system for selecting encryption keys from a plurality of encryption keys
A method and system of alternatively selecting an encryption key used to transmit a known number data bits and providing sufficient information to inform the receiving part of the selected encryption key is presented. In one embodiment of the invention, a plurality of encryption keys are available to the parties of the communication network. The transmitting party selects an encryption key used to encrypt a message block based on the data content of a previously transmitted message block. The receiving party, having received, and decrypted, a previously transmitted message block has sufficient information to determine the encryption key used to encrypt a subsequent data block and is able to decrypt the subsequently transmitted message.
1. A method to encrypt a data message having a plurality of message data blocks prior to transmitting said message data blocks over a network, said method comprising:
extracting data values from at least two of said message data blocks;
selecting encryption keys from among a plurality of encryption keys dependently upon said extracted data values, respectively; and,
encrypting subsequent ones of said message data blocks using said selected encryption keys, respectively.
2. The method of claim 1 , wherein said extracted data value is determined using a known number of bits.
3. The method of claim 2 , wherein said known number of bits are distributed among at least one data byte of said one of said message blocks.
4. The method of claim 2 , wherein said known number of bits are located in a first byte of said one of said message blocks.
5. The method of claim 2 , wherein said known number of bits are located in a last byte of said one of said message blocks.
6. The method of claim 1 , wherein said step of extracting further comprises limiting said extracted data value to a known range.
7. The method of claim 6 , wherein said known range is determined using modulo-arithmetic.
8. The method of claim 6 , wherein said known range is associated with a number of said stored encryption keys.
9. A method to encrypt a data message having a plurality of message data blocks prior to transmitting said message data block over a network, said method comprising:
extracting a data value from at least one of said message data blocks;
selecting an encryption key from among a plurality of encryption keys dependently upon said extracted data value; and
encrypting at least a subsequent one of said message data blocks using said selected encryption key;
wherein said extracting, selecting and encrypting are iteratively repeated for others of said message data blocks.
10. The method of claim 9 , further comprising:
receiving each of said encrypted message data blocks;
decrypting each said received, encrypted message data block using a key based on a prior received message data block;
extracting a data value from each said decrypted massage data block.
11. The method of claim 10 , wherein each said received message block corresponds to at least one unencrypted message data block.
12. The method of claim 10 , wherein said received message data block corresponds to a synchronizing indicator.