KR20090024604A - Method of transmitting and receiving data in wireless communication system - Google Patents

Abstract

A method for transmitting and receiving data is provided to intensify the security without large change of the system by using an encryption algorithm variably. An encryption algorithm is selected among at least two encryption algorithms or more(S72). At least a part of data block is encrypted by the selected encryption algorithm(S74). The encrypted data block is transmitted to the receiving side. The identification information for distinguishing the encryption algorithm used for encryption is transmitted to the receiving side. The identification information is included in the header of the encrypted data block and is transmitted. The identification information is the operation result using the index of the encryption algorithm used for encryption and the unique identifier of the receiving side.

Description

Method of transmitting and receiving data in wireless communication system

The present invention relates to a wireless communication system, and more particularly, to a method for transmitting and receiving data in a wireless communication system and a method for performing encryption or decryption for transmitting and receiving data.

Since an air interface is an open medium that anyone can access, a security problem is a very important issue in a mobile communication system that communicates through an air interface. Data security is a method for protecting data from malicious users. Data security is essential to provide various services requiring high security such as e-commerce and Internet banking.

In the 3GPP WCDMA system, which is a standard method of asynchronous mobile communication systems, two technologies, ciphering and integrity protection, are used to secure data. Encryption is used in a specific protocol layer of the transmitting side, that is, RLC (Radio Link Control) or MAC (Medium Access Control) layer, and encrypts the mask generated by the encryption algorithm in units of data and bits to be transmitted. Integrity checking is used when RRC message is transmitted in RRC (Radio Resource Control) layer, and attaches field called Message Authentication Code for Integrity Protection (MAC-I) to the beginning of RRC message.

1 is a flowchart illustrating a call connection process used in a WCDMA system. In FIG. 1, the base station and the terminal generate a CK, which is a key value for encryption, through an authentication & security process, and the base station informs which encryption algorithm the terminal for encryption uses. The procedure after the authentication and security process is performed through encryption.

2 is a diagram for explaining an encryption and decryption method used in a WCDMA system. In FIG. 2, encryption at the sender (terminal or RNC) generates a mask for encryption based on various unique input parameters and adds it with each bit of the data block (RLC PDU or MAC SDU) (XOR operation) to encrypt it. Generate data. The receiving side can recover data normally by performing decryption on the encrypted data using the mask used at the transmitting side. In a conventional WCDMA system, when a call is established between a network and a terminal, encryption and decryption are performed using one encryption algorithm until the connection is terminated.

As described above, when encryption and decryption are performed using only one encryption algorithm from call establishment to termination, security may be weakened because unique parameters necessary for encryption / decryption may be exposed to the outside. There is this. In particular, as the call connection time becomes longer, the above problem is increased.

The present invention has been made to solve the problems of the prior art as described above, an object of the present invention is to provide a scheme that can enhance the security function in the mobile communication system.

Disclosed herein is a method of using a particular encryption algorithm selected from at least two or more encryption algorithms when encrypting data to be transmitted from a sender to a receiver. The specific encryption algorithm may be variably selected for each data block unit. In order to decrypt the encrypted data at the receiver side, it is necessary to know what encryption algorithm is used at the time of encryption. The receiving side decrypts the encrypted data received from the transmitting side using the encryption algorithm indicated by the identification information.

Encryption may be performed at a specific protocol layer at the sender. In this case, encryption is performed on at least a portion of the upper layer data block transmitted from the upper layer in the protocol layer, and identification information for identifying the encryption algorithm used at the time of encryption is added to the upper layer data block. header). The identification information may use a result of a predetermined operation using an index of the encryption algorithm used for the encryption and a unique identifier of the receiver.

According to the present invention, by using the encryption algorithm variably there is an effect that can enhance the security without major changes in the existing system in the mobile communication system.

The construction, operation, and other features of the present invention will be readily understood by the embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which technical features of the present invention are applied to an Evolved Universal Mobile Telecommunications System (E-UMTS).

3 is a diagram illustrating a network structure of an E-UMTS. The E-UMTS system is an evolution from the existing WCDMA UMTS system and is currently undergoing basic standardization work in the 3rd Generation Partnership Project (3GPP). E-UMTS is also called a Long Term Evolution (LTE) system. For details of technical specifications of UMTS and E-UMTS, refer to Release 7 and Release 8 of the "3rd Generation Partnership Project; Technical Specification Group Radio Access Network", respectively.

Referring to FIG. 3, an E-UTRAN consists of base stations (hereinafter, abbreviated as 'eNode B' or 'eNB'). The eNBs are connected via an X2 interface. The eNB is connected to a user equipment (hereinafter abbreviated as UE) through an air interface and is connected to an Evolved Packet Core (EPC) through an S1 interface. The EPC includes a Mobility Management Entity (MME) / System Architecture Evolution (SAE) gateway.

Layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in communication systems. L2 (second layer), L3 (third layer) can be divided into, wherein the physical layer belonging to the first layer provides an information transfer service (Information Transfer Service) using a physical channel, The radio resource control (hereinafter referred to as RRC) layer located in the third layer plays a role of controlling radio resources between the terminal and the network. To this end, the RRC layer exchanges RRC messages between the UE and the network.

4 is a schematic diagram of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). In FIG. 2, the hatched portion shows the functional entities of the user plane and the unhatched portion shows the functional entities of the control plane.

5A and 5B illustrate a structure of a radio interface protocol between a UE and an E-UTRAN. FIG. 3A is a control plane protocol configuration diagram and FIG. 3B is a user plane protocol configuration diagram. . The wireless interface protocol of FIGS. 3A and 3B is horizontally composed of a physical layer, a data link layer, and a network layer, and vertically, a user plane for transmitting data information. It is divided into a user plane and a control plane for transmitting a control signal. The protocol layers of FIGS. 3A and 3B are based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in communication systems, based on L1 (first layer), L2 (second layer), It may be classified as L3 (third layer).

The physical layer, which is the first layer, provides an information transfer service to an upper layer by using a physical channel. The physical layer is connected to the upper medium access control layer through a transport channel, and data between the medium access control layer and the physical layer moves through the transport channel. Then, data is moved between different physical layers, that is, between physical layers of a transmitting side and a receiving side through physical channels. In E-UMTS, the physical channel is modulated by an orthogonal frequency division multiplexing (OFDM) scheme, thereby utilizing time and frequency as radio resources.

The medium access control (hereinafter, referred to as MAC) layer of the second layer provides a service to a radio link control layer, which is a higher layer, through a logical channel. The Radio Link Control (hereinafter referred to as RLC) layer of the second layer supports reliable data transmission. The PDCP layer of the second layer performs a header compression function to reduce unnecessary control information so that data transmitted using IP packets such as IPv4 or IPv6 can be efficiently transmitted in a wireless section where bandwidth is relatively low. do.

The radio resource control layer (hereinafter referred to as RRC) layer located at the bottom of the third layer is defined only in the control plane, and the configuration and resetting of the radio bearer (abbreviated as RB) are performed. It is responsible for the control of logical channels, transport channels and physical channels in relation to configuration and release. In this case, RB means a service provided by the second layer for data transmission between the terminal and the UTRAN.

Downlink transmission channels for transmitting data from the network to the UE include a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, and a downlink shared channel (SCH) for transmitting user traffic or control messages. There is. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH or may be transmitted through a separate downlink multicast channel (MCH). Meanwhile, the uplink transmission channel for transmitting data from the terminal to the network includes a random access channel (RAC) for transmitting an initial control message and an uplink shared channel (SCH) for transmitting user traffic or control messages.

Above logical channels, logical channels mapped to transport channels include BCCH (Broadcast Channel), PCCH (Paging Control Channel), CCCH (Common Control Channel), MCCH (Multicast Control Channel), MTCH (Multicast Traffic Channel) ).

In the E-UMTS system, the OFDM scheme is used in downlink, and the SC-FDMA (Single Carrier-Frequency Division Multiple Access) scheme is used in uplink. The OFDM system, which is a multi-carrier method, is a system for allocating resources in units of a plurality of subcarriers in which a part of carriers is grouped, and uses Orthogonal Frequency Division Multiple Access (OFDMA) as an access method.

In the physical layer of an OFDM or OFDMA system, active carriers are divided into groups and transmitted to different receivers for each group. The radio resource allocated to each UE is defined by a time-frequency region of two-dimensional space and is a set of consecutive subcarriers. In an OFDM or OFDMA system, one time-frequency domain is divided into rectangles determined by time coordinates and subcarrier coordinates. That is, one time-frequency region may be divided into a rectangle partitioned by symbols on at least one or more time axes and subcarriers on a plurality of frequency axes. Such a time-frequency region may be allocated to an uplink of a specific UE or a base station may transmit the time-frequency region to a specific user in downlink. To define such a time-frequency domain in two-dimensional space, the number of consecutive subcarriers starting at a position separated by the number of OFDM symbols in the time domain and an offset from a reference point in the frequency domain should be given.

In the E-UMTS system, which is currently under discussion, a 10 ms radio frame is used, and one radio frame includes 20 subframes. That is, one subframe is 0.5 ms. One resource block is composed of one subframe and 12 subcarriers each having a 15 kHZ band. In addition, one subframe includes a plurality of OFDM symbols, and some symbols (eg, first symbols) of the plurality of OFDM symbols may be used to transmit L1 / L2 control information.

FIG. 6 illustrates an example of a physical channel structure used in an E-UMTS system. One subframe includes an L1 / L2 control information transmission area (hatched part) and a data transmission area (unhatched part). do.

7A and 7B illustrate a downlink (DL) and uplink (UL) second layer structure of an E-UMTS system, respectively. The second layer (Layer 2) is composed of three sub-layers (MAC layer, RLC layer and PDCP layer), each sub-layer performs the respective functions defined by the protocol.

The encryption / decryption method according to an embodiment of the present invention may be implemented in any sublayer of the second layer. That is, according to an encryption / decryption method according to an embodiment of the present invention, data to be transmitted to a receiving side may be encrypted by any sublayer among the MAC layer, the RLC layer, and the PDCP layer, which are sublayers of the second layer of the transmitting side. The corresponding sublayer on the side can decrypt the encrypted data received from the sender. Hereinafter, an embodiment of performing encryption in the PDCP layer will be described.

7A and 7B, the PDCP layer includes an ROHC entity and a security entity. The ROHC entity performs a header compression function to reduce unnecessary control information in order to efficiently transmit data transmitted using an IP packet such as IPv4 or IPv6 in a relatively low bandwidth wireless section. The security entity performs functions for security of data to be transmitted to a receiver. An encryption function according to an embodiment of the present invention may also be performed by the security entity. Alternatively, an encryption function according to an embodiment of the present invention may be performed by another entity other than the security entity.

8 is a flowchart illustrating an encryption process in a PDCP layer according to an embodiment of the present invention.

Referring to FIG. 8, the PDCP layer receives a PDCP SDU (Service Data Unit) from an upper network node or an upper layer [S71]. The PDCP SDU refers to one data block as a data unit delivered to the PDCP layer from an upper node or an upper layer. The PDCP layer selects a specific encryption algorithm to perform encryption on the PDCP SDU received from the higher node or higher layer among at least two encryption algorithms [S72]. If it is determined that encryption is not required, it may be decided not to perform encryption. The PDCP layer attaches a PDCP header to the PDCP SDU to configure a PDCP PDU [S73]. The PDCP header may include a plurality of fields according to functions performed in the PDCP layer. One field thereof is an encryption algorithm index field and includes identification information for identifying an encryption algorithm selected for encryption. The receiver determines what encryption algorithm is used for data encryption using the identification information, and decrypts the data encrypted using the encryption algorithm. The PDCP PDU may include at least one PDCP SDU.

9 schematically illustrates a data format of a PDCP PDU according to an embodiment of the present invention. The PDCP PDU includes a PDCP header and a PDCP SDU, and the PDCP header includes an encryption algorithm index field. The encryption algorithm identification information included in the encryption algorithm index field may be an index of the selected encryption algorithm. Table 1 describes an example of the correspondence relationship between the encryption algorithm index and the encryption algorithm.

Encryption algorithm index Encryption algorithm 00 No ciphering 01 X 10 Y 11 Reserved

In Table 1, it is assumed that the PDCP layer can use two types of encryption algorithms, 'X' and 'Y', to encrypt data. For example, when the PDCP layer selects an encryption algorithm of 'X' for encryption of a specific PDCP PDU, the encryption algorithm index field includes '01', which is an index of the selected encryption algorithm. When the PDCP layer determines not to perform encryption on a specific PDCP PDU, the encryption algorithm index field includes a corresponding index '00'.

In another embodiment, the predetermined operation result value using the index of the encryption algorithm and the unique identifier of the receiving side (for example, the terminal) that will receive the encrypted data, instead of the index itself of the encryption algorithm selected as the identification information, is used. It can be included in the encryption algorithm index field. That is, since the encryption algorithm index itself may be exposed to the outside when repeatedly transmitted, the encryption algorithm index itself is intended to enhance security by scrambling by a unique operation and a predetermined operation of the terminal. Examples of the unique identifier of the terminal include a Cell Radio Netwrok Temporary Identity (C-RNTI), an International Mobile Subscriber Identity (IMSI), and a Temporary IMSI (TMSI). Equation 1 is an example of an operation algorithm for scrambling the encryption algorithm index and the C-RNTI of the terminal.

new CAI = (CAI + (C-RNTI mod 4)) mod 4

In Equation 1, new CAI is identification information included in the encryption algorithm index field, and CAI is an index of the selected encryption algorithm.

Referring back to FIG. 8, the PDCP layer performs encryption on the PDCP PDU using the selected encryption algorithm [S74]. In this case, encryption may be performed on all or part of the PDCP PDU. For example, in the PDCP PDU structure of FIG. 8, encryption may be performed only on a payload portion or a PDCP SDU portion, or only on the remaining PDCP PDU portions except for an encryption algorithm index field. The PDCP PDU having been encrypted is delivered to the lower layer RLC layer.

10 schematically illustrates a data format of a PDCP PDU according to another embodiment of the present invention. FIG. 10 illustrates an embodiment in which an encryption algorithm index field including encryption algorithm identification information is included in a body part instead of a PDCP header part. In FIG. 10, the encryption algorithm index field is assigned to the Most Significant Bits (MSB) portion of the PDCP body. As another example, it is also possible to include the encryption algorithm index field in the Least Significant Bits (LSB) portion or any intermediate portion of the PDCP body.

In the embodiment of FIG. 10, the portion in which encryption is performed according to the encryption algorithm selected from all PDCP PDUs is a PDCP body portion. Accordingly, since encryption is also performed on the encryption algorithm index field, the receiving side cannot know what encryption algorithm is applied unless the PDCP PDU received from the transmitting side is deciphered. Since the receiving side should identify the encryption algorithm applied by using the identification information included in the encryption algorithm index field and then perform decryption afterwards, the encryption algorithm index field includes identification information for identifying the encryption algorithm applied to the corresponding PDCP PDU. It is not desirable to make it. Accordingly, the embodiment of FIG. 10 proposes a method of previously selecting an encryption algorithm to be applied to a PDCP PDU to be transmitted after the PDCP PDU and including the identification information in the encryption algorithm index field. For example, the encryption algorithm index field of the Nth PDCP PDU may include identification information for identifying an encryption algorithm to be applied to the (N + 1) th PDCP PDU. According to the promise of the transmitting side and the receiving side, identification information for identifying an encryption algorithm to be applied to any PDCP PDU to be transmitted after the N th PDCP PDU may be selectively included in the encryption algorithm index field of the N th PDCP PDU.

11 is a diagram for describing a data encryption method according to an embodiment of the present invention. In Fig. 11, unlike the encryption method according to the prior art, the encryption algorithm is variably selected from two or more. The encryption algorithm can be varied periodically or aperiodically. For example, the encryption algorithm may be performed by changing the encryption algorithm for each PDCP PDU, or the encryption algorithm may be changed at any time determined by the transmitter without a certain period.

In FIG. 11, PLAINTEXT BLOCK is data before encryption, and is encrypted through bit operation with MASK to form CIPHERTEXT BLOCK. The CIPHERTEXT BLOCK is transmitted to the receiver through the radio section, and the receiving side recovers the original PLAINTEXT BLOCK by generating and decrypting the same MASK through the encryption algorithm used at the transmitter. The MASK is generated by encryption parameters selected from CK, COUNT-C, BEARER, DIRECTION, LENGTH, etc. and a selected encryption algorithm. In addition to the f8 algorithm used in 3GPP, various encryption algorithms may be used. Among the above parameters, CONUNT-C is a value related to a sequence number of a data block in which encryption such as PDCP PDU is performed, and changes over time.

The data decoding process at the receiving side according to an embodiment of the present invention will be briefly described as follows. In the embodiment of FIG. 9, the PDCP layer of the receiving side determines what encryption algorithm is used for encryption through the identification information included in the encryption algorithm index field included in the header of the PDCP PDU received from the transmitting side. Then, the encrypted portion of the PDCP PDU is decrypted using the corresponding encryption algorithm. In the case of the embodiment of FIG. 10, the receiving side receives the N-th PDCP PDU and obtains encryption algorithm identification information to be applied to the (N + 1) -th PDCP PDU through the encryption algorithm index field in advance. Thereafter, the receiving side receives the (N + 1) th PDCP PDU and performs decryption according to the encryption algorithm identification information previously obtained.

As described above, the encryption / decryption method according to an embodiment of the present invention may be implemented not only in the PDCP layer but also in the RLC layer or the MAC layer. In this case, the encryption is preferably performed at the last stage of the layer where encryption is performed, and the decryption is preferably performed at the first stage of the layer where decryption is performed.

 The above embodiments are those in which the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is also evident that the claims may be incorporated into claims that do not have an explicit citation in the claims, or may be incorporated into new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, embodiments of the invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), and FPGAs (fields). programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

1 is a flowchart illustrating a call connection process used in a WCDMA system.

2 is a diagram for explaining an encryption and decryption method used in a WCDMA system.

3 is a diagram illustrating a network structure of an E-UMTS.

4 is a schematic diagram of an E-UTRAN.

5A and 5B illustrate a structure of a radio interface protocol between a UE and an E-UTRAN. FIG. 3A is a control plane protocol configuration diagram and FIG. 3B is a user plane protocol configuration diagram. .

6 shows an example of a physical channel structure used in an E-UMTS system.

7A and 7B illustrate a downlink (DL) and uplink (UL) second layer structure of an E-UMTS system, respectively.

8 is a flowchart illustrating an encryption process in a PDCP layer according to an embodiment of the present invention.

9 schematically illustrates a data format of a PDCP PDU according to an embodiment of the present invention.

10 schematically illustrates a data format of a PDCP PDU according to another embodiment of the present invention.

11 is a diagram for describing a data encryption method according to an embodiment of the present invention.

Claims (30)

In the data transmission method at the transmitting side of a wireless communication system, Performing encryption on at least a portion of the data block using an encryption algorithm variably selected from among at least two encryption algorithms; Transmitting the encrypted data block to a receiving side; And Transmitting identification information for identifying an encryption algorithm used for the encryption to the receiving side. The method of claim 1, The encryption algorithm used when performing encryption is selected in units of data blocks, data transmission method. The method of claim 1, And said identification information is a result of a predetermined operation using an index of an encryption algorithm used for said encryption and a unique identifier of said receiving side. The method of claim 1, And the identification information is included in a header of the data block on which the encryption is performed and transmitted. The method of claim 4, wherein And encryption is performed only on the remaining part of the data block except for the header. The method of claim 1, And the identification information is included in the body portion of the data block on which the encryption is performed and transmitted. The method of claim 6, The body portion including the identification information, characterized in that the encryption is performed, the data transmission method. The method of claim 1, And the data block is any one of an RLC PDU, a MAC PDU, and a PDCP PDU. A method of performing encryption at a specific protocol layer of a sender for data transmission from a wireless communication system to a receiver, Performing encryption on at least a portion of a lower layer data block comprising at least one higher layer data block delivered from an upper layer using an encryption algorithm variably selected from among at least two encryption algorithms; And And adding a header containing identification information for identifying an encryption algorithm used for the encryption, to the lower layer data block on which the encryption has been performed. The method of claim 9, The encryption algorithm used when performing the encryption, characterized in that the selection of the lower layer data block unit, encryption method. The method of claim 9, And the identification information is a result of a predetermined operation using an index of an encryption algorithm used for the encryption and a unique identifier of a receiving side. The method of claim 9, And the specific protocol layer is any one of an RLC layer, a MAC layer, and a PDCP layer. A data receiving method at a receiving side of a wireless communication system, Receiving from the sender a block of data encrypted by a cryptographic algorithm that is variably selected from among at least two cryptographic algorithms; Receiving identification information from the transmitting side for identifying an encryption algorithm used for the encryption; And Performing decryption on the received data block using an encryption algorithm identified by the identification information. The method of claim 13, The encryption algorithm used when performing encryption is selected in units of data blocks, data receiving method. The method of claim 13, And said identification information is a predetermined calculation result value using an index of an encryption algorithm used for said encryption and a unique identifier of said receiving side. The method of claim 13, And the identification information is included in a header of the data block and received. The method of claim 16, And encrypting is performed only on the remaining part of the data block except for the header at the transmitting side. The method of claim 13, And the data block is any one of an RLC PDU, a MAC PDU, and a PDCP PDU. In the data transmission method at the transmitting side of a wireless communication system, Performing encryption on at least a portion of the first data block using an encryption algorithm variably selected from among at least two encryption algorithms; Transmitting the encrypted first data block to a receiving side; And Transmitting identification information for identifying an encryption algorithm to be used for a second data block to be transmitted after the first data block to the receiving side. The method of claim 19, The encryption algorithm used when performing encryption is selected in units of data blocks, data transmission method. The method of claim 19, And the identification information is included in a portion in which encryption is performed in the first data block and transmitted. The method of claim 21, And the portion in which the encryption is performed is a body portion. A method of performing encryption at a specific protocol layer of a sender for data transmission from a wireless communication system to a receiver, Generating a lower layer data block comprising at least one higher layer data block transferred from the upper layer and identification information for identifying an encryption algorithm to be used for encryption; And Performing encryption on at least a portion of the lower layer data block using an encryption algorithm that is variably selected from at least two or more encryption algorithms. The method of claim 23, wherein The encryption algorithm used when performing the encryption, characterized in that selected in the upper layer data block unit, encryption method. The method of claim 23, wherein And the identification information is information for identifying an encryption algorithm to be applied when encrypting an N-th lower layer data block after the lower layer data block. The method of claim 25, And the identification information is included in a portion in which encryption is performed in the lower layer data block. The method of claim 26, And the portion in which the encryption is performed is a body portion. In a wireless communication system, a method for decrypting data transmitted by being encrypted at a transmitting side in a specific protocol layer at a receiving side, Receiving from the transmitting side a second data block comprising identification information for identifying higher layer data and an encryption algorithm to be used for encryption of the first data block; And And performing decryption on the second data block using an encryption algorithm identified by identification information included in the third data block received from the transmitting side. The method of claim 28, And the identification information is included in a portion in which encryption is performed in the data block. The method of claim 29, And a portion in which the encryption is performed is a body portion.

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