MXPA98010503A - Methods and apparatus for multiple-iteration cmea encryption and decryption for improved security for wireless telephone messages - Google Patents

Abstract

An enhanced CMEA encryption system suitable for use in wireless telephony. A plaintext message is introduced into the system and subjected to a first iteration of a CMEA process, using a first CMEA key to produce an intermediate ciphertext. The intermediate ciphertext is then subjected to a second iteration of the CMEA process using a second CMEA key to produce a final ciphertext. Additional security is achieved by subjecting the plaintext and intermediate ciphertext to input and output transformations before and after each iteration of the CMEA process. The CMEA iterations may be performed using an improved use of a box function which adds permutations to a message or intermediate crypto-processed data. Decryption is achieved by subjecting a ciphertext message to the reverse order of the steps used for encryption, replacing the input and output transformations by inverse output and inverse input transformations, respectively, as appropriate.

Description

METHODS AND APPARATUS FOR CODING AND DECODIFICATION BY THE METHOD OF ALGORITHM OF CELLULAR MESSAGE CODING, OF MULTIPLE ITERATION. FOR IMPROVED SECURITY FOR MESSAGES VIA WIRELESS PHONE FIELD OF THE INVENTION The present invention relates generally to cryptography in cordless telephones. More particularly, the invention relates to an improved cryptographic system or cryptosystem for fast and secure encryption in a wireless telephone system without requiring large amounts of additional system resources.

ANl? SUBJECT OF THE INVENTION Wireless telephony uses messages for various purposes including, for example, transporting status information, reconfiguring modes of operation, handling call termination and transport systems, and user data such as the subscriber's electronic serial number and telephone number , as well as conversations and other data transmitted by the user. Unlike wired telephony, in which a central service station is connected to each subscriber by a wire, and therefore a REF degree is ensured. 29092 for the protection of illegal eavesdropping and misuse by an unauthorized party (attacker), wireless telephone service stations (ie, base stations) must transmit and receive messages via air signals, regardless of the physical location of the subscribers. Because the base station must be able to send and receive messages to and from a subscriber anywhere, the process of transmitting messages depends entirely on the signals received from, and sent to, the subscriber's equipment. Because the signals are transmitted by air, they can be intercepted by someone who performs illegal listening or an intruder with the correct equipment. If a signal is transmitted by a wireless phone in plain text, there is the danger that someone who performs illegal listening will intercept the signal and use it to pretend to be the subscriber, or to intercept private data transmitted by the user. Such private data may include the content of conversations. The private data may also include non-voice data transmitted by the user such as, for example, computer data transmitted over a modem connected to the cordless telephone and may also include a bank account or other private user information typically transmitted by the user. middle of pressing buttons. Someone who performs illegal listening, who is listening to a conversation or intercepting non-voice data can obtain private information from the user. The message content of an unencrypted telephone signal (ie, a plaintext signal) is relatively easily intercepted by a suitably adapted receiver. Alternatively, an intruder can intercept it within an established connection by using a higher transmitting power, send signals to the base station and pretend to be a part of the conversation. In the absence of coding application to the messages transmitted by the wireless signals, the unauthorized use of telephone resources, the illegal listening of messages and the pretending to be another person of the called or calling party during a conversation are possible. Such unauthorized intrusion and / or illegal listening has in fact proven to be a serious problem and is highly undesirable. The application of cryptography to wireless telephone applications offers a solution to the security problems described above, but the application of standard cryptography methods to wireless telephony has encountered significant difficulties due to the computationally intensive nature of these methods. Specifically, these methods are subject to the restrictions imposed by the desire to supply a small cordless handset and the processing power restriction imposed by the small size of the handset. The processing power present in typical wireless handsets is insufficient to handle the processing requirements of commonly known cryptographic algorithms such as DES (Data Coding Standard). The implementation of such a cryptographic algorithm commonly known in a wireless telephone system "; typical potentially increases the time needed to process signals (ie, encode and decode), thereby causing unacceptable delays for subscribers. A cryptographic system for wireless telephony is described in U.S. Patent 5,169,634 of Reeds.

("Reeds"), incorporated herein by reference. Reeds describes a cryptographic em incorporated into a cryptographic algorithm known as the Cell Message Coding Algorithm (CMEA) process. There is a desire to substantially improve this and other existing cryptographic ems for wireless telephony consistent with the resources available in this context.

BRIEF DESCRIPTION OF THE INVENTION The present invention advantageously solves these and other needs. In a method according to the present invention, first and second CMEA keys are generated. Plain text is entered and subjected to a first input transformation to produce a first input transformed message. The first input transformed message is processed by a first iteration of a CMEA process using the first CMEA key to produce a first intermediate ciphertext. This first intermediate encrypted text is subjected to a first output transformation to produce a first output transformed message. The first transformed output message is subjected to a second input transformation to produce a second input transformed message. The second input transformed message is processed by a second iteration of the CMEA process using the second CMEA key to produce a second intermediate ciphertext. The second intermediate encrypted text is subjected to a second output transformation to produce a second transformed output message. According to another aspect of the present invention, the first and second iterations of the CMEA process use tbox functions with permuted entries by secret shifts. According to another aspect of the present invention, the plain text can be processed by first and second iterations of the CMEA process using first and second CMEA keys, without being subjected to input and output transformations. The encoded or encrypted text can be decoded appropriately according to the teachings of the present invention by entering the ciphertext and reversing the order and reversing the applied steps to encode the plain text. The apparatus according to the present invention generates text and supplies it to an interface 1/0 which identifies it as generated text and supplies the text of the identification to an encoding / decoding processor which in turn encodes the text and It supplies a transceiver for transmission. When the apparatus receives a transmission via a transceiver, the transmission is identified as incoming encrypted text, and the encrypted text and identification is supplied to the encoding / decoding processor which decodes the encrypted text and supplies it as text to the processor I / Or for shipment to your destination. In a preferred embodiment, this apparatus is integrated into a wireless telephone using a standard microprocessor and a memory consistent with those currently typically used in such telephones. A more complete understanding of the present invention, as well as the additional features and advantages of the invention will be apparent from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram illustrating the CMEA key generation process of the prior art and the implementation of CMEA; Fig. 2 is a flowchart illustrating an improved CMEA coding method using multiple iterations CMEA, according to the present invention; Figure 3 is a flow diagram illustrating an improved CMEA coding method according to the present invention, which uses multiple iterations CMEA, each iteration is preceded by an input transformation and followed by an output transformation; Figure 4 is a detailed illustration of an input transformation suitable for use in a coding method according to the present invention; Figure 5 is a detailed illustration of an output transformation suitable for use in a coding method according to the present invention; Figure 6 is a flow chart illustrating a method according to the present invention for decoding text * encryption encoded by an improved CMEA process; And Figure 7 is a diagram illustrating a telephone equipment using the improved CMEA coding according to the present invention.

DESCRIPTION DETA ADA Figure 1 is a diagram illustrating the method 100 of the prior art using a CMEA key for encoding certain critical user data which can be transmitted during a call. The creation and description of the CMEA key is well known in the art. The CMEA key is used to create a secret array, tbox (z), of 256 octets. Alternatively, the tbox function can be implemented as a function call. This implementation reduces the use of RAM, but increases the processing time generally by an order of magnitude. In step 102, the unprocessed text is entered. In step 104, in the systems which implement tbox as a static table instead of as a function call, the static tbox table is derived. The tbox table is derived as follows: for each z in the interval 0 =. < 256, tbox (z) = C (((C (((C ((z.XOR kO) + kl) + z) XOR k2) + k3) + z) XOR k4) + k¿5) + z) XOR k6) + k7) + z, where "+" denotes the addition module 256, "XOR" is the Boolean XOR operator by bits, the "z" operator is the function argument, kO, .. ., k7 comprising the eight octets of the CMEA key and C () is the result of an eight-bit CAVE lookup table. CMEA comprises three successive stages, each of which alters each string of octets in the data buffer. In steps 106, 108 and 110, the first, second and third stages of the CMEA process are respectively performed, as will be described herein. A data buffer of d octets long, with each octet designated by b (i) as an integer in the range of 0 < . i < d, is encrypted in three stages. The first stage (I) of CMEA is as follows: 1. Initialize a variable z to zero, 2. For successive integer values of i in the range of 0 < í < d. to. from a variable q by q = z (+) minus octet of i, where (+) is the exclusive Boolean operator OR by bits, b. from the variable k by k = TBOX (q), c. update b (i) with: b (i) = b (i) + k mod 256, and d. update z with: z = b (i) + z mod 256. The second stage (II) of CMEA is: 1. for all the values of i in the interval of 0 < i < d (d - l) / 2: b (i) = b (i)? (b (d - 1 i) OR 1), where OR is the Boolean OR operator by bits.

The final stage or third stage (III) of CMEA is the decoding, which is inverse to the first stage: 1. Initialize a variable z to zero, 2. For successive integer values of i in the interval of 0 < i < gives. for a variable q by: q = z? lower order octet of i, b. for the variable k by: k = TBOX (q), c. update z with: z = b (i) + z mod 256, d. update b (i) with b (i) = b (i) -k mod 256. In step 112, the final processed output is provided. The CMEA process is self-reversible. That is, the same steps applied in the same order are used to encode plain text as to decode encrypted text. Therefore, there is no need to determine whether coding or decoding has been carried out. Unfortunately, it has been shown that the CMEA process is subject to an attack which will allow the recovery of the CMEA key used for a call. In order to provide added security to the user information, a coding system according to the present invention preferably performs two iterations of the CMEA process, with a different key used in each iteration. A first input transformation and a first output transformation are performed before and after the first iteration of the CMEA process, and a second input transformation and a second output transformation are performed after the second iteration of the CMEA process. An alternative coding system according to the present invention preferably improves the use of the tbox function by adding at least one permutation of the tbox entries in one or more iterations of the CMEA process. The improved use of the tbox function is described in our patent application serial number entitled "Methods and appliances for improved security expansion of a secret key in a search table for enhanced security, for wireless telephone messages "(" Methods and Apparatus for Enhanced Security Expansion of a Secret Key into a Lookup Table for Improved Security for Wireless Telephone Messages ") filed on the same date with the present application and incorporated herein by reference. In another aspect of the invention, the first and second iterations of the CMEA process can be performed, but without the input and output transformations before and after each iteration of the CMEA process Figure 2 is a flow chart showing the steps performed by a coding process 200 according to one aspect of the present invention The coding process of Figure 2 includes two iterations of the CMEA process described in connection with the discussion of Figure 1, with a different CMEA key used for each iteration.In step 202, plain text is entered into the coding process.In step 204, the plain text is encoded into a prime iteration using the CMEA process, using a first CMEA key. In step 206, the first iteration is completed and the intermediate cipher text is produced. In step 208, the intermediate ciphertext is subjected to a second iteration of the CMEA process, using a second CMEA key. In step 210, the final cipher text is produced. Figure 3 is a diagram illustrating coding process 300 according to another aspect of the present invention. In step 302, the plain text message is entered into the coding process. In step 304, the plain text message is subjected to a first input transformation to produce a first input transformed message. In step 306, a first input transformed message is submitted to a first iteration of a CMEA process using a first CMEA key to produce a first intermediate ciphertext. Preferably, the first iteration of the CMEA process uses an improved use of the tbox function in which each entry of the tbox function is subjected to a permutation. The improved use of the tbox function is described in our application mentioned above serial number. In step 308, the output of the first iteration of the CMEA process is subjected to a first output transformation to produce a first output transformed message. In step 310, the first intermediate encrypted text is subjected to a second input transformation to produce a second input message. In step 312, the intermediate ciphertext is subjected to a second iteration of the CMEA process, using a second CMEA key to produce an intermediate ciphertext. The second iteration of the CMEA process preferably uses the improved use of the tbox function described in our application mentioned above. In step 314, the second intermediate encrypted text is subjected to a second output transformation to produce a second transformed output message. In step 316, the second transformed output message is transmitted as final encrypted text. Fig. 4 is a diagram illustrating in detail the input transformation 400 which can suitably be used in the coding process 300 described in relation to Fig. 3. The reverse input transformation 400 is self-reversing. Each one of the bytes of input data j + 1, j + 1, j, ..., 2, 1 is processed XOR with a transformation octet. The transformation octet is a secret value which can be created using any of several techniques commonly used in art. Two transformation octets are preferably used and applied alternately to the octets of input data. The transformation byte I2 is applied to the input data octet j + 1, the transformation octet I1 is applied to the input data octet j, the transformation octet I2 is applied to the input data octet j-1, and so on The transformation application produces a new set of input data octets, j + 1 ', j', ..., 2 ', 1' which are then used as described above in relation to the discussion of Figure 3. Figure 5 is a diagram illustrating an output transformation 500 direct / reverse which can be used appropriately in the coding process 300 described in relation to figure 3. For the direct output transformation, each of the output data octets j + 1, j + 1, j ,. ..2, l is added with one octet of transformation. The transform octet is a secret value which can be created using any of a number of techniques commonly used in the art. For the reverse output transformation, the sum is substituted with a subtraction. The two transformation octets are preferably used and applied alternately to the octets of output data. The transformation byte 02 is applied to the output data octet j + 1, the transformation octet 01 is applied to the output data octet j, the transformation octet 02 is applied to the output data octet j-1, and so on. The transformation application produces a new set of output data octets j + 1 ', j', ..., 2 '1', which are subsequently used as described above in relation to the discussion of Figure 3 Because the coding system of the present invention requires the application of two keys, it is not self-reversible. That is, the same operations applied in the same order will not encode plain text or decode encrypted text. In addition, the output transformation described in relation to the discussion of Figure 1 is not self-reversing. Therefore, a separate decoding process is necessary, as described below. Figure 6 illustrates a decoding process 600 according to an aspect of the present invention. Essentially, the steps illustrated in Figure 3 are followed, but in reverse to the order shown in Figure 3. The first and second inverse input and output transformations are used in place of the input and output transformations of Figure 3. The first reverse input transformation is simply the second input transformation described above in relation to the discussion of Figure 3, and the second reverse input transformation is the first input transformation described above in relation to the discussion of Figure 3.

In step 602, the encrypted text message is entered into the decoding process. In step 604, the encrypted text message is subjected to a first reverse output transformation to produce a first reverse output transformed message. The first inverse output transformation is the inverse of the second output transformation described in relation to FIG. 3 and in greater detail in relation to FIG. 5. In particular, the addition step in the output transformation is canceled by a subtraction. in the reverse output transformation. In step 606, the first reverse output transform message is subjected to a first iteration of the CMEA process to produce a first intermediate decoded encrypted text message. The first iteration of the CMEA process preferably uses an improved use of the tbox function according to our request mentioned above serial number. The key used for this first iteration is the second CMEA key in the second input permutation tbox. In step 608, the first intermediate encrypted text is subjected to a first reverse input transformation, which is identical to the second input transformation described in connection with the discussion of FIG. 3, to * produce a first input transformed message reverse. Then, in step 610, the first reverse input transformed message is subjected to a second reverse output transformation, which is the inverse of the first output transformation described in relation to the discussion of FIG. 3, to produce a second Transformed message of reverse output. In step 612, the second reverse output transformed message is subjected to a second iteration of the CMEA process to produce a second intermediate decoded encrypted text message. The second iteration of the CMEA process preferably uses the improved use of the tbox function. The key used for this iteration of the modified CMEA process is the first CMEA key and the first tbox input permutation. In step 616, the second intermediate decoded encrypted text message is subjected to a second reverse input transformation, which is identical to the first input transformation described in relation to the discussion of FIG. 4 to produce a second transformed message of reverse entry. In step 618, the second iteration is completed and the second reverse input transformed message is transmitted as the final planar text. The coding described in relation to the discussion of Figure 2 can be similarly inverted. In order to decode a coded message according to the aspect of the invention described in relation to Figure 2 above, the decoding described in Figure 6 is executed, but without executing the inward and outward inverse transformations.

Because the decoding described in relation to Figure 6 can not be carried out simply by operating the coding described in relation to Figure 3, it is necessary for a device to use the coding and decoding systems according to the present invention for recognize when a message needs to be encoded and at what time it needs to be decoded. Figure 7 is a diagram showing a wireless telephone equipment 700 equipped to carry out a message transmission and encoding / decoding according to the present invention, which facilitates both recognition if a message needs to be encoded or decoded, and to perform the appropriate encoding or decoding. The telephone equipment 700 includes a transceiver 702, an input / output interface 704 (1/0), a coding / decoding processor 706 and a key generator 708. Key generator 708 receives and uses secret data stored for key generation. The secret data stored preferably they are stored in non-volatile memory 710 such as an EEPROM or Flash memory. The key generator 708 stores the keys generated in the memory 712. The aodification / decoding processor also includes the memory 714 for storing keys received from the key generator 708. A static tbox table can be produced and stored during coding and decoding which can be generated and used if you want to implement the tbox function as a static table, and other values. The telephone equipment 700 also includes a message generator 716 which generates messages to be encoded by the encoding / decoding processor 706 and transmitted by the transceiver 702. When an internally generated message is to be encoded and transmitted by the equipment 700 telephone, the message is transmitted from the message generator 712 to the interphase 704 1/0. The interface 704 1/0 identifies the message as an internally generated message to be encoded and transmits the message, along with the identification, to the coding / decoding processor 706. The coding / decoding processor 706 receives one or more keys from the key generator 708, which then uses it to encode the message. Preferably, the encoding / decoding processor 706 receives two keys from the key generator 708, which are then used to perform the double-iteration CMEA encoding using input and output transformations as described above in relation to FIG. The coding / decoding processor 706 submits the plain text message to a first input transformation to produce a first input transformed message. Subsequently, the first input transformed message is subjected to a first iteration of a CMEA process using a first CMEA key, to produce a first intermediate encrypted text message. The first iteration of the CMEA process can suitably use the improved use of the tbox function in which each introduced tbox function is subjected to a permutation. The first intermediate encrypted text message is subjected to a first output transformation to produce a first transformed output message. Then, the transformed output message is subjected to a second input transformation to produce a second input transformed message. The second input transformed message is then subjected to a second iteration of the modified CMEA process, using a second CMEA key, to produce a second intermediate encrypted text message. The second iteration process can also properly use the improved use of the tbox function. The output of the second iteration of the CMEA process is then subjected to a second output transformation to produce a second output transformed message. Finally, the second iteration is completed and the second output processed message is produced as well as the final encrypted text. Upon completion of the encoding, the final ciphertext can be stored in the memory 714, and is sent to the 704 I / O interface and the transceiver 702 for transmission.

When the coded message is received by the telephone equipment 700, the transceiver 702 does not pass to the interface 704 I / O. The interface 1/0 identifies the message as a coded message, and passes this identification, together with the message, to the coding / decoding processor 706. The encoding / decoding processor 706 receives one or more keys from the key generator 708 and decodes the message, preferably using a double iteration CMEA decoding process, as described in relation to figure 6. When the coding process 706 / decoding receives an encrypted text message from the 704 I / O interface, the encrypted text message is subjected to a first reverse output transformation to produce a first reverse output transformed message. The first inverse output transformation is the inverse of the second output transformation described in relation to FIG. 3, and in greater detail in relation to FIG. 5. In particular, the addition step in the output transformation is canceled by a subtraction in the reverse output transformation. Subsequently, the first iteration of the CMEA process is performed, preferably using the improved use of the tbox function to produce an intermediate decoded encrypted text message. The key used for this first iteration is the second CMEA key and the second input permutation tbox.

Then, the first intermediate decoded encrypted text message is subjected to a first reverse input transformation to produce a first reverse input transformed message. The first reverse input transformation is identical to the second input transformation described in relation to the discussion of Figure 3. The second reverse input transform message is then subjected to a second reverse output transformation to produce a second transformed message of reverse output. The second inverse output transformation is the inverse of the first output transformation described in relation to the discussion of Figure 3. Next a second iteration of the CMEA process is performed, preferably using the improved use of the tbox function, to produce a second intermediate decoded encrypted text message. The key used for this iteration of the modified CMEA process is the first CMEA key and the first tbox permutation. The second intermediate decoded encrypted text message is then subjected to the second reverse input transformation to produce a second reverse input transformed message. The second reverse input transformation is identical to the first input transformation described in relation to the discussion of Figure 3. The second reverse input transformed message is passed as plain text to the 704 I / O interface, where after it is directed for its final use.

The improvements described above to the CMEA process, while substantially increasing security, do not substantially increase processing or system resources, and are therefore suitable for use in an environment such as the wireless telephone system in which units such as mobile units often have limited processing power. Although the present invention is described in the context of the currently preferred embodiment, it will be recognized that a wide variety of implementations can be used by persons usually familiar with the art, consisting of the foregoing discussion and the claims that follow. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (22)

REIVINJPICATIONS

1. A method for encoding or encrypting data, characterized in that it comprises the steps of: entering a plain text message; perform an iteration of a CMEA process in the plain text to produce an intermediate ciphertext; and performing one or more additional CMEA iterations of the CMEA process of the intermediate encrypted text message, each additional iteration of the CMEA process before the final iteration produces an additional intermediate encrypted text message, the final iteration of the CMEA process produces an encrypted text message of final output.

2. The method according to claim 1, characterized in that each iteration of the CMEA process is performed using a different CMEA key.

The method according to claim 2, characterized in that each message entered in an iteration of the CMEA process is subjected to an input transformation before the iteration of the CMEA process and each output message of an iteration of the CMEA process is subjected to an output transformation after the iteration of the CMEA process.

4. The method according to claim 3, characterized in that each iteration of the CMEA process uses a tbox function with permuted entries by one or more secret offsets.

5. A data coding method, characterized in that it comprises the steps of: entering a plain text message; performing a first input transformation in the plain text message to produce a first input transformed message; performing a first iteration of a CMEA process in the first input transformed message, using a first CMEA key, to produce a first intermediate encrypted text message; and performing an output transformation on the first intermediate encrypted text message to produce a first transformed output message.

The method according to claim 5, characterized in that it further includes the steps of: performing a second input transformation on the first output transformed message to produce a second input transformed message; performing a second iteration of the CMEA process in the second input transformed message, using a second CMEA key to produce a second intermediate encrypted text message; and performing a second output transformation on the second intermediate encrypted text message to produce a second transformed output message.

The method according to claim 6, characterized in that the first input transformed message is subjected to a tbox function including the permutation of each input to a tbox function by a first and second secret offsets during the first iteration of the CMEA process and the second input transform message is subjected to a tbox function including the permutation of each input to the tbox function by a third and fourth secret shifts during the second iteration of the CMEA process.

A method for decoding an encrypted text message, characterized in that it comprises the steps of: entering an encrypted text message; performing a first reverse output transformation on the encrypted text message to produce a first reverse output transformed message; performing a first iteration of a CMEA process on the first reverse output transformed message, using a second CMEA key, to produce a first intermediate decoded encrypted text message; and performing a first reverse input transformation on the first intermediate decoded encrypted text message to produce a first reverse input transformed message.

The method according to claim 8, characterized in that it further includes the steps of: performing a second inverse output transformation on the first reverse input transformed message to produce a second reverse output transformed message; performing a second iteration of the CMEA process in the second reverse output transformed message, using a first CMEA key to produce a second intermediate decoded encrypted text message; and performing a second reverse input transformation on the second intermediate decoded encrypted text message to produce a second reverse input transformed message.

The method according to claim 9, characterized in that it further includes the steps of recovering the first, second, third and fourth offsets generated during the encoding of a plain text message to produce the encrypted text message and submitting the first message and transformed from the reverse output to a? tbox mutation including permutation of each tbox function introduced in the third and fourth shifts during the first iteration of the CMEA process and subjecting the second reverse processed message to a tbox function and including permutations of each input of the tbox function for the first and second displacements during the second iteration of the CMEA process.

11. A method for decoding an encrypted text message encoded by two iterations of a CMEA process, characterized in that it comprises the steps of: entering the encrypted text message; perform a first iteration of a CMEA process in the plain text message, use a single CMEA key to produce a first intermediate encrypted text message; and performing a second iteration of the CMEA process in the first intermediate encrypted text message, using a first CMEA key; and produce a final plaintext.

The method according to claim 11, characterized in that each iteration of the CMEA process is swapped by one or more secret shifts.

13. The method according to claim 12, characterized in that each message on which the CMEA process is performed, undergoes an inverse output transformation before the iteration of the CMEA process, and each-message produced by an iteration of the process CMEA undergoes a reverse input transformation after the iteration of the CMEA process.

14. A wireless coding telephone, characterized in that it comprises: a transceiver; an input / output interface for receiving and directing messages coming from the transceiver and for transmitting messages to the transceiver, the input / output interface is operative to differentiate a message that enters from a message that leaves and produce a signal that identifies to the message as a message that enters or a message that comes out; a message generator to receive user inputs and format the user inputs to a message that leaves, the message that leaves passes to the input / output interface; a memory to store secret data; a key generator for receiving secret data from the memory and using the secret data to generate one or more coding keys; an encoding / decoding processor, the encoding / decoding processor receives the message and a message identification signal from the input / output interface and a first and second coding keys from the key generator, the encoding processor / decoding is operative for each message that enters to: perform a first input transformation in the message to produce a transformed message; performing a first iteration of a CMEA process on the first input transformed message, using the first encoding key, to produce an intermediate encrypted text message; performing a first output transformation on the first intermediate encrypted text message to produce a first transformed output message; performing a second input transformation on the first transformed output message to produce a second input transformed message; performing a second iteration of the CMEA process in the second input transformed message using the second encoding key, to produce a second intermediate encrypted text message; performing a second output transformation on the second intermediate encrypted text message; and passing the second final intermediate encrypted text message to the input / output interface for appropriate addressing.

The coding telephone according to claim 14, characterized in that the first input transformed message is subjected to a tbox function including the permutation of each input tbox function by a first and second offsets during the first iteration of the CMEA process, and the second input transformed message is subjected to a tbox function including the permutation of each tbox function introduced by the third and fourth offsets during the second iteration of the CMEA process.

16. The coding telephone according to claim 14, characterized in that the encoding / decoding processor is operative for incoming messages to: perform a first reverse output transformation in the message to produce a first reverse output transformed message; performing a first iteration of a CMEA process in the message, using a second encoding key, to produce a first decoded intermediate encrypted text message; performing a first reverse input transformation on the first decoded intermediate encrypted text message; performing a second reverse output transformation on the first decoded intermediate encrypted text message to produce a second transformed output message first encoding key, for producing a second decoded intermediate encrypted text message; performing a second reverse input transformation on the second decoded intermediate encrypted text message; and passing the final output message to the entry / exit interface for appropriate addressing.

The coding telephone according to claim 16, characterized in that the first reverse output transformed message is subjected to a tbox function including the permutation of each tbox function introduced by the first and fourth offsets during the first iteration of the CMEA process., and the second reverse output transformed message is subjected to a function tbox including the permutation of each function tbox introduced by the first and second offsets during the second iteration of the CMEA process.

18. A method of encoding data of an encrypted text message previously encoded by multiple iterations of a plain text message, characterized in that it comprises the steps of: entering the encrypted text message, performing the first iteration of a CMEA process in the encrypted text to produce an intermediate decoded encrypted text; and performing one or more additional iterations of the CMEA process in the intermediate decoded encrypted text message, each additional iteration of the CMEA process before the final iteration produces an additional intermediate decoded encrypted text message, the final iteration of the CMEA process produces a message of flat text of final output.

19. The method according to claim 18, characterized in that each iteration of the CMEA process is performed using a different CMEA key.

20. The method according to claim 19, characterized in that the iterations of the CMEA process are applied in a reverse order from an order in which the iterations of the CMEA process were previously applied to perform data coding, and where each iteration of the process CMEA uses a CMEA key corresponding to the CMEA key previously used by a corresponding iteration of the CMEA process to perform data encoding in a previous plaintext message to produce the encrypted text message.

The method according to claim 20, characterized in that each message entered in an iteration of the CMEA process is subjected to an inverse output transformation before the iteration of the CMEA process, and each message output of the iteration of the CMEA process is undergoes a reverse input transformation subsequent to the iteration of the CMEA process, each inverse output transformation is the inverse of an output transformation performed after a corresponding iteration of the CMEA process previously used to perform data coding, and each input transformation Inverse is identical to an input transformation performed prior to a corresponding iteration of the CMEA process previously used to perform data encoding in a previous plaintext message to produce the encrypted text message.

22. The method according to claim 21, characterized in that each iteration of the CMEA process uses a tbox function that includes the permutation of each tbox function introduced by one or more secret shifts.