Secure communication system with cross linked cryptographic codes

Claim 2

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for securing said message between said first and second terminals, said method comprising: encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; appending said first message authentication code to said first plurality of encrypted data blocks; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; appending said second message authentication code to said second plurality of encrypted data blocks; sending said message from said first terminal to said second terminal; receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 3

A method in accordance with claim 1, further comprising: comparing said calculated second message authentication code with said received second message authentication code; and disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 4

A method in accordance with claim 1, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 5

A method in accordance with claim 1, wherein said first initial vector equals zero.

Claim 6

A method in accordance with claim 1, wherein said second initial vector equals zero.

Claim 7

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for sending said message between said first and second terminals, said method for sending comprising: encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; appending said first message authentication code to said first plurality of encrypted data blocks; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; and appending said second message authentication code to said second plurality of encrypted data blocks.

Claim 8

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for sending said message between said first and second terminals, said method for sending comprising: encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; appending said first message authentication code to said first plurality of encrypted data blocks; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; and appending said second message authentication code to said second plurality of encrypted data blocks.

Claim 9

A method in accordance with claim 6, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 10

A method in accordance with claim 6, wherein said first initial vector equals zero.

Claim 11

A method in accordance with claim 6, wherein said second initial vector equals zero.

Claim 12

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said first and second packets being encrypted under a first cryptographic code key using a cipher block chaining mode and first initial vector input to form said first and second plurality of encrypted data blocks, said first plurality of encrypted data blocks being encrypted under a second cryptographic code key and a second initial vector, said second plurality of encrypted data blocks being encrypted under said second cryptographic code key using a cipher block chaining mode and a third initial vector input for said second packet, a method for receiving said message between said first and second terminals, said method for receiving comprising: receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 13

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said first and second packets being encrypted under a first cryptographic code key using a cipher block chaining mode and first initial vector input to form said first and second plurality of encrypted data blocks, said first plurality of encrypted data blocks being encrypted under a second cryptographic code key and a second initial vector, said second plurality of encrypted data blocks being encrypted under said second cryptographic code key using a cipher block chaining mode and a third initial vector input for said second packet, a method for receiving said message between said first and second terminals, said method for receiving comprising: receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 14

A method in accordance with claim 10, further comprising: comparing said calculated message authentication code with said received message authentication code; and disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 15

A method in accordance with claim 10, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 16

A method in accordance with claim 10, wherein said first initial vector equals zero.

Claim 17

A method in accordance with claim 10, wherein said second initial vector equals zero.

Claim 18

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for securing said message between said first and second terminals, said method comprising: encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet; selecting one of said encrypted data blocks in said first packet as the initial vector for forming said message authentication code for said second packet following said first packet; sending said message from said first terminal to said second terminal; receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 19

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for securing said message between said first and second terminals, said method comprising: encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet; selecting one of said encrypted data blocks in said first packet as the initial vector for forming said message authentication code for said second packet following said first packet; sending said message from said first terminal to said second terminal; receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 20

A method in accordance with claim 15, further comprising: comparing said calculated second message authentication code with said received second message authentication code; and disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 21

A method in accordance with claim 15, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.

Claim 22

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for sending said message between said first and second terminals, said sending method comprising: encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said message authentication code, said cipher block chaining mode having an initial vector input; and selecting one of said encrypted data blocks in a given packet as the initial vector for calculating said message authentication code for the packet following said given packet.

Claim 23

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, a method for sending said message between said first and second terminals, said sending method comprising: encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said message authentication code, said cipher block chaining mode having an initial vector input; and selecting one of said encrypted data blocks in a given packet as the initial vector for calculating said message authentication code for the packet following said given packet.

Claim 24

A method in accordance with claim 18, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.

Claim 25

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said message being encrypted under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks, said plurality of encrypted data blocks being encrypted using a second cryptographic code key using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet, a method for receiving said message between said first and second terminals, said receiving method comprising: receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 26

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said message being encrypted under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks, said plurality of encrypted data blocks being encrypted using a second cryptographic code key using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet, a method for receiving said message between said first and second terminals, said receiving method comprising: receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 27

A method in accordance with claim 20, further comprising: comparing said calculated second message authentication code with said received second message authentication code; and disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 28

A method in accordance with claim 20, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.

Claim 29

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for securing said message between said first and second terminals, said apparatus comprising: means for encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; means for encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; means for appending said first message authentication code to said first plurality of encrypted data blocks; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; means for appending said second message authentication code to said second plurality of encrypted data blocks; means for sending said message from said first terminal to said second terminal; means for receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 30

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for securing said message between said first and second terminals, said apparatus comprising: means for encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; means for encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; means for appending said first message authentication code to said first plurality of encrypted data blocks; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; means for appending said second message authentication code to said second plurality of encrypted data blocks; means for sending said message from said first terminal to said second terminal; means for receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 31

An apparatus in accordance with claim 23, further comprising: means for comparing said calculated second message authentication code with said received second message authentication code; and means for disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 32

An apparatus in accordance with claim 23, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 33

An apparatus in accordance with claim 23, wherein said first initial vector equals zero.

Claim 34

An apparatus in accordance with claim 23, wherein said second initial vector equals zero.

Claim 35

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for sending said message between said first and second terminals, said apparatus for sending comprising: means for encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; means for encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; means for appending said first message authentication code to said first plurality of encrypted data blocks; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; and means for appending said second message authentication code to said second plurality of encrypted data blocks.

Claim 36

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for sending said message between said first and second terminals, said apparatus for sending comprising: means for encrypting said message under a first cryptographic code key, using a cipher block chaining mode having a first initial vector input, to form said first and second plurality of encrypted data blocks; means for encrypting said first plurality of encrypted data blocks under a second cryptographic code key using said cipher block chaining mode having a second initial vector input for said first packet to form said first message authentication code; means for appending said first message authentication code to said first plurality of encrypted data blocks; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode having a third initial vector input for said second packet to form said second message authentication code; means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector for said second packet for forming said second message authentication code; and means for appending said second message authentication code to said second plurality of encrypted data blocks.

Claim 37

An apparatus in accordance with claim 28, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 38

An apparatus in accordance with claim 28, wherein said first initial vector equals zero.

Claim 39

An apparatus in accordance with claim 28, wherein said second initial vector equals zero.

Claim 40

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said first and second packets being encrypted under a first cryptographic code key using a cipher block chaining mode and first initial vector input to form said first and second plurality of encrypted data blocks, said first plurality of encrypted data blocks being encrypted under a second cryptographic code key and a second initial vector, said second plurality of encrypted data blocks being encrypted under said second cryptographic code key using a cipher block chaining mode and a third initial vector input for said second packet, an apparatus for receiving said message between said first and second terminals, said apparatus for receiving comprising: means for receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 41

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said first and second packets being encrypted under a first cryptographic code key using a cipher block chaining mode and first initial vector input to form said first and second plurality of encrypted data blocks, said first plurality of encrypted data blocks being encrypted under a second cryptographic code key and a second initial vector, said second plurality of encrypted data blocks being encrypted under said second cryptographic code key using a cipher block chaining mode and a third initial vector input for said second packet, an apparatus for receiving said message between said first and second terminals, said apparatus for receiving comprising: means for receiving said second packet including a received second plurality of encrypted data blocks and a received second message authentication code; means for encrypting said second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and said third initial vector input for said received second packet to form a calculated second message authentication code; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said third initial vector input.

Claim 42

An apparatus in accordance with claim 32, further comprising: means for comparing said calculated message authentication code with said received message authentication code; and means for disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 43

An apparatus in accordance with claim 32, wherein said selected one of said first plurality of encrypted data blocks of said first packet comprises the last of said first plurality of encrypted data blocks.

Claim 44

An apparatus in accordance with claim 32, wherein said first initial vector equals zero.

Claim 45

An apparatus in accordance with claim 32, wherein said second initial vector equals zero.

Claim 46

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for securing said message between said first and second terminals, said apparatus comprising: means for encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; means for encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet; means for selecting one of said encrypted data blocks in said first packet as the initial vector for forming said message authentication code for said second packet following said first packet; means for sending said message from said first terminal to said second terminal; means for receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; means for encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 47

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for securing said message between said first and second terminals, said apparatus comprising: means for encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; means for encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet; means for selecting one of said encrypted data blocks in said first packet as the initial vector for forming said message authentication code for said second packet following said first packet; means for sending said message from said first terminal to said second terminal; means for receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; means for encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 48

An apparatus in accordance with claim 37, further comprising: means for comparing said calculated second message authentication code with said received second message authentication code; and means for disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 49

An apparatus in accordance with claim 37, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.

Claim 50

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for sending said message between said first and second terminals, said sending apparatus comprising: means for encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; means for encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said message authentication code, said cipher block chaining mode having an initial vector input; and means for selecting one of said encrypted data blocks in a given packet as the initial vector for calculating said message authentication code for the packet following said given packet.

Claim 51

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, an apparatus for sending said message between said first and second terminals, said sending apparatus comprising: means for encrypting said message under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks; means for encrypting said plurality of encrypted data blocks using a second cryptographic code using a cipher block chaining mode to form said message authentication code, said cipher block chaining mode having an initial vector input; and means for selecting one of said encrypted data blocks in a given packet as the initial vector for calculating said message authentication code for the packet following said given packet.

Claim 52

An apparatus in accordance with claim 40, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.

Claim 53

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said message being encrypted under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks, said plurality of encrypted data blocks being encrypted using a second cryptographic code key using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet, an apparatus for receiving said message between said first and second terminals, said receiving apparatus comprising: means for receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; means for encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 54

In a cryptographic communication system including first and second terminals, said first and second terminals being connected via a telecommunications link, said cryptographic communication system providing a message comprising a plurality of packets, including at least first and second packets, each of said first and second packets comprising a respective first and second plurality of encrypted data blocks and a respective first and second message authentication code, said message being encrypted under a first cryptographic code using a cipher block chaining mode to form said plurality of encrypted data blocks, said plurality of encrypted data blocks being encrypted using a second cryptographic code key using a cipher block chaining mode to form said second message authentication code, said cipher block chaining mode having a respective initial vector input for each packet, an apparatus for receiving said message between said first and second terminals, said receiving apparatus comprising: means for receiving said message including received first and second packets at said second terminal, and including received first and second plurality of encrypted data blocks and received second message authentication code; means for encrypting said received second plurality of encrypted data blocks under said second cryptographic code key using said cipher block chaining mode and an initial vector for forming a calculated second message authentication code for said received second packet; and means for selecting one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet.

Claim 55

An apparatus in accordance with claim 42, further comprising: means for comparing said calculated second message authentication code with said received second message authentication code; and means for disconnecting said telecommunications link between said first and second terminals if said calculated second message authentication code is not substantially equal to said received second message authentication code.

Claim 56

An apparatus in accordance with claim 42, wherein said selected one of said first plurality of encrypted data blocks of said first packet as said initial vector for said second received packet comprises the last of said first plurality of encrypted data blocks.