KR20010001539A - Terminal for secure communication in CDMA system and methods for transmitting information using encryption and receiving information using decryption - Google Patents

Abstract

PURPOSE: A method for encrypting/decrypting data from the terminal of a CDMA(code division multiple access) wireless communication system having data protection function is provided to keep data secret at the other places except both transmitting and receiving terminals by protecting the data with a block cipher or a cipher key. CONSTITUTION: A vocoder packet information bit is generated by coding of an input signal into a specific size of information bit. The coded vocoder packet information bit is block-encrypted. The encrypted vocoder packet information bit is formed as a CDMA frame by combination with a frame quality indicator and encoder tail bits. Finally, the CDMA frame is transmitted to a base station through a frequency band allocated in a process of convolutional encoding, interleaving and band expanding. Therefore, the CDMA frame is kept secret safely during transmitting.

Description

Terminal for secure communication in CDMA system and methods for transmitting information using encryption and receiving information using decryption}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code division multiple access (CDMA) communication system in accordance with IS-95, IS-95A, and IS-95B standards, and more particularly for a CDMA wireless communication system having an information protection function. A terminal, an encryption transmission method and a decryption reception method.

In the CDMA communication system using the IS-95, IS-95A, and IS-95B schemes, as shown in FIG. 1, a voice of a caller is a predetermined size (for example, 8 kbps) by a variable rate vocoder. Compresses the bit and transmits it through the allocated frequency band through the reverse traffic channel, and then recovers the original information bit through the forward traffic channel as shown in FIG. It is a digital communication system in which communication is performed by restoring the original voice. That is, in the reverse traffic channel illustrated in FIG. 1, a frame structure is formed by attaching a frame quality indicator and a tail encoder to a vocoder packet. Each CDMA frame is transmitted through an allocated frequency band through a process of convolutional encoding, interleaving and spread spectrum. In the forward traffic channel shown in FIG. 2, the original information bit (for example, 8.6 Kbps) is recovered through the reverse process from the process shown in FIG. 1, and then the original voice is recovered from the vocoder. By restoring, communication is made.

Existing Digital Cellular System (DCS) or Personal Communication System (PCS) terminals may be confused by abnormal causes and hear other people's conversations, or they may be exposed to others without their knowledge. There is. In addition, with the help of a telecommunications operator or the mobilization of experts who are familiar with CDMA equipment, it is virtually possible to recover the original call by detecting information bits passed only by the vocoder at the radio base station or the wireless exchange. Recently, the problem of communication interception has been discussed as a serious social problem, and there are many cases where information of important companies has been leaked.

U.S. Patent 5,727,064A, one of the information protection methods used in the existing CDMA communication system, attaches a scrambler to a longcode generator, and is required to modify or change the IS-95 standard. Not only is it not applicable to DCS or PCS, there are limitations to allowing different groups of users to communicate using different secret keys.

The present invention is to solve the above problems, in the (D) Digital Cellular System (DCS) or PCS (Personal Communication System) using the CDMA system (1) without any modification of the operator's mobile communication system, (2) Independent of the vocoder, it communicates securely from illegal activities such as eavesdropping by encrypting / decrypting using block ciphers such as DES (Data Encryption Standard), Triple DES, or SNAKE for transmitting and receiving terminals. It is an object of the present invention to provide a CDMA wireless communication system terminal, an encryption transmission method and a decryption reception method that enable the information protection function.

1 illustrates the structure of a conventional CDMA reverse traffic channel modulator.

2 shows the structure of a CDMA forward traffic channel demodulator according to the prior art.

3 is a block diagram of an embodiment of a terminal for a CDMA wireless communication system according to the present invention.

Figure 4 illustrates the structure of the DES algorithm that can be used in the present invention.

FIG. 5 illustrates the structure of a single iteration of the DES algorithm shown in FIG. 4.

6 is a flowchart illustrating an embodiment of a process of encrypting and transmitting information bits in a terminal of a CDMA wireless communication system according to the present invention.

7 is a flowchart illustrating an embodiment of a decryption reception process of an encrypted information bit in a terminal of a CDMA wireless communication system according to the present invention.

In order to achieve the above object, an embodiment of a terminal in a CDMA wireless communication system according to the present invention comprises: an encoder for generating vocoder packet information bits by compressing an input signal into information bits of a predetermined size; An encryptor for block encrypting the vocoder packet information bits generated by the encoder; A CDMA framer configured to configure an IS-95 CDMA frame by adding a frame quality indicator and encoder tail bits to the vocoder packet information bits encrypted by the encoder; A CDMA frame transmitter for transmitting a CDMA frame configured in the CDMA framer to a base station through an allocated frequency band through convolutional coding, interleaving, and spread spectrum; A CDMA frame receiver which receives a signal from the base station and reproduces a CDMA frame; A CDMA deframer for extracting encrypted vocoder packet information bits from the CDMA frame reproduced by the CDMA frame receiver; A decryptor for decrypting the encrypted vocoder packet information bits extracted from the CDMA deframer; And a decoder for decoding the vocoder packet information bits decrypted by the decoder.

In order to achieve the above object, a method of protecting and transmitting information bits in a terminal of a CDMA wireless communication system according to the present invention includes (a) encoding an input signal into information bits having a predetermined size to generate vocoder packet information bits. step; (b) block encrypting the encoded vocoder packet information bits; (c) constructing a CMDA frame by adding a frame quality indicator and encoder tail bits to the encrypted vocoder packet information bits; And (d) transmitting the CDMA frame to a base station through an allocated frequency band through convolutional coding, interleaving, and spread spectrum according to an IS-95 standard.

In order to achieve the above another object, a method of receiving an encrypted information bit in a terminal of a CDMA wireless communication system according to the present invention comprises the steps of: (a) receiving a signal from a base station to play a CDMA frame; (b) extracting encrypted vocoder packet information bits from the reproduced CDMA frame; (c) a decryptor for decrypting the encrypted vocoder packet information bits; And (d) decoding the decrypted vocoder packet information bits.

That is, according to the present invention, the voice transmitted by the CDMA communication system shown in FIGS. 1 and 2 is restored to the original voice by an illegal means which is not desired by the caller in an intermediate process such as a base station. Block ciphers between the vocoder and the CDMA framer on the reverse traffic channel, and between the vocoder and the CDMA deframer on the forward traffic channel, in order to prevent intrusion and misuse for economic or mental damage. Therefore, to ensure secure communication by encrypting and decrypting, respectively.

In order to implement this, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

1. Structure of sending and receiving terminal

3 is a block diagram showing the structure of a traffic channel of a wireless terminal including a transmitter-side encryptor 340 and a receiver-side decoder 350 of a wireless terminal, which is the core of the present invention. . In FIG. 3, the main part of the present invention is included in the block drawn by the dotted line.

Referring to FIG. 3, the encryptor 340 used in the reverse traffic channel stores all or part of the vocoder packet information bits 341 in the CDMA encoder 300 inputted at 20 ms intervals, or is stored in the secret or exchanged in a secure manner. The key 360 is encrypted using a block cipher 370 such as SNAKE, DES, or Triple DES, and an encrypted vocoder packet information bit 342 is generated and transmitted to the CDMA framer 310. Meanwhile, the decryptor 350 used in the forward traffic channel may store all or a portion of the encrypted vocoder packet information bits 352, which are input from the CDMA deframer 320 in 20 ms periods, or are stored therein or exchanged in a secure manner. The key 360 is used to decrypt the same block cipher 370 as the sender such as SNAKE, DES, and Triple DES, recover the vocoder packet information bit 351, and transfer the same to the CDMA demodulator 330. It consists of a means.

The CDMA framer 310 includes a frame quality indicator (e.g., 12 bits, 9200 bps) and encoder tail bits (e.g., an encoded vocoder packet information bit (e.g., 172 bits, 8600 bps). For example, 8bit) is attached to a 9600bps frame, and the CDMA deframer 320 performs the reverse process.

2. Encryption and Decryption

Encryption of the sender vocoder packet information bits 341 and decryption of the receive-side encrypted vocoder packet information bits 352 are performed in units of bytes by block ciphers 370 such as SNAKE and DES. Since only the information bits corresponding to multiples of 8 are encrypted or decrypted. For example, for the IS-95A 9600bps frame, since the number of information bits is 172 (= 8 × 21 + 4) bits, only 21 bytes are encrypted / decrypted. If there is a large amount of computation to encrypt / decrypt, only some of them (eg 8 bytes) are encrypted / decrypted. In addition, when the output of the encoder 300 is silent (1/8 rate), encryption / decryption may not be performed in order to prevent generation of noise. The encoder 340 and the decoder 350 are performed after the vocoder finishes encoding every 20 ms, and are implemented in software or hardware.

Data encryption standard selected as Federal Information Processing Standard 46 (FIPS PUB 46) by the US National Institute of Standards and Technology (NIST) in 1977 for Encryption and Decryption For example, consider using (Data Encryption Standard: DES).

4 shows the structure of the DES algorithm, and FIG. 5 shows the structure of a single iteration using 64 bits of text and a 56 bits secret key. For example, if only the first 8 bytes of 172 bits are encrypted and decrypted. At this time, the 64-bit plain text (for example, 01 23 45 67 89 ab cd e7) of FIG. 4 corresponds to the first 8 bytes of the vocoder packet information bits 172 bits 341 transmitted from the encoder 300, and 56 bits The key (for example, 01 23 45 67 89 ab cd) represents the secret key 360 shared between the transmitting and receiving terminals. 64bits Cipher Text (e.g. c9 57 44 25 6a 5e d3 1d) via Encryptor 340 encrypted vocoder packet information bits (342) 172 bits Is made.

The decryption process is the reverse of the encryption process. The encrypted 8-bytes (e.g. c9 57 44 25 6a 52 d3 1d) of the encrypted vocoder packet information bits 352 from the CDMA deframer 320 (e.g. For example, decrypting 01 23 45 67 89 ab cd) in the reverse order of the encryption process yields decrypted 64 bits (eg, 01 23 45 67 89 ab cd). The vocoder packet information bits 172 bits 351 made by attaching the remaining 108 bits to the decoder 330 are decoded to decode the original voice.

As such, a block cipher such as DES, Triple DES, or SNAKE is used for encryption and decryption.

3. Enabling and disabling the security mode

In addition, for a call with a terminal that does not implement the information protection scheme as described above, if a specific key promised at the beginning of a call is input, the sender terminal is set or released as a security mode. The terminal side receiving the key is also set or released in the same security mode as the transmitting side. Security mode setting using this specific key can be done either by (1) alerting before call setup is made, or (2) during call setup after call setup. Security mode can be set and released.

The Security_Mode 380 is input as a predetermined first key for requesting a security mode in a reverse traffic channel. Then, the first predetermined pattern (that is, the pattern distinguished from the vocoded voice) corresponding to the security mode setting is transmitted to the counterpart terminal through the information bit of the traffic channel. In response, the counterpart terminal receives the confirmation and switches the security mode to On. When the call is terminated or when a predetermined second key for requesting a security mode is input in a reverse traffic channel, the predetermined second pattern corresponding to the release of the security mode is entered. (I.e., the pattern which is also distinguished from the vocoded voice) is transmitted to the counterpart terminal through the information bit of the traffic channel. Then, the counterpart terminal receives the confirmation, switches to the security mode off, and returns to the normal mode. By this method, it is possible to repeat setting and releasing the security mode even during a call. This security mode setting may use a signaling channel with the help of a telecommunications provider.

The first key and the second key used for setting and releasing the security mode are selected from keys that do not affect the call. For example, the END key used to end a call cannot be used as a first key and a second key used for setting and releasing a security mode, but a SEND key can be used.

When setting the security mode, the secret cipher of a block cipher to be used may be transmitted together or a method for determining the secret key may be transmitted together. This method is described in detail in Sharing the private key on the next page.

4. Processing of Mute

When the encryptor 340 and the decoder 350 are silent, bypass is enabled through a MUTE_Tx 343 or MUTE_Rx 353 signal, and Security_Mode 380 according to the security mode of the terminal. Allow bypass through the terminals.

Encryptors and Decryptors Depending on Security Mode and Silence Coder Security_Mode on Security_Mode off Decoder Security_Mode on Security_Mode off Mute_Tx on bypass bypass Mute_Rx on bypass bypass Mute_Tx off encryption bypass Mute_Rx off encryption bypass

As shown in Table 1, when the Security_Mode 380 is released, both the Encryptor 340 and the Decryptor 350 are bypassed, and even when the Security_Mode 380 is set, MUTE_Tx or When MUTE_Rx is on, the encryptor 340 or the decoder 350 is bypassed.

MUTE_Tx 343 and MUTE_Rx 353 correspond to the mute of the vocoder packet of the current frame (typically, when the power amount of the voice for 20 ms is below the reference value, i.e., there is no voice between words). As information indicating whether or not information is contained, it can be displayed using a flag or the like when implemented by software, and can be processed as a separate signal when implemented by hardware. Security_Mode 380 is also information indicating whether the current security mode is set or released.

When processing at fixed rate, mute is not processed separately, but when processing at variable rate like PCS currently used in Korea, vocoder packet is 1 when mute occurs. It is processed at a ratio of / 8 so that it is easy to know that the corresponding frame is mute without any additional processing, so that no new logic is required for the implementation of the present invention.

5. Sharing a Secret Key

The block ciphers used for the sender 340 and the receiver 350 use the same algorithm and the same secret key. This requires sharing a secret key between distant senders and receivers.

The first method is to pass the secret key created by the sender to the receiver when setting the security mode. For example, when the security mode is set, a predetermined pattern (e.g., 5555 ... 555 (172 bits) information bit is set in the IS-95 9600bps frame to set the security mode. Hexadecimal), then use the 128-bits (when the 128-bit secret key) in the next frame as the secret key or transmit the secret key encrypted with the MasterKey. When using MasterKey, all terminals share the same MasterKey, and this MasterKey is kept only by the responsible authority.

The second method is to designate one of the keys (for example, 100 128-bits keys) stored in the same way in the transmitting and receiving terminals when setting the security mode. That is, for example, 168 bits of 172 bits information bits in an IS-95 9600bps frame are sent in a specific pattern (e.g., 5555 ... 5 (Hexadecimal)), which means security mode setting, and the rest. 8bits is the index of 256 secretly stored secret keys. At this time, the stored secret keys may be composed of secret keys provided by the terminal company and secret keys directly input by the subscriber.

In the third method, two subscribers exchange only the “secret key” through a separate call. At this time, the exchanged secret key is made by (1) subscriber's direct input or (2) terminal's random number generation function. The secret key exchanged in this way is specified and used when setting the security mode using the second method.

6 shows an example of a flowchart of a transmitting terminal. That is, this is an example of setting a secret mode during a call and sharing a secret key using an index.

Referring to FIG. 6, when the power source of the transmitting terminal is first turned on, an initialization operation of the transmitting terminal is performed (step 600). Thereafter, when the user requests a call by inputting a key provided in the transmitting terminal, the call is set (steps 605 and 610). At this time, if the input key is a key for turning on the security mode, the security mode of the transmitting terminal is turned on, and a predetermined pattern indicating security on and a plurality of patterns provided in the transmitting terminal are provided. The index of the selected secret key among the secret keys is included in the information bits of the traffic channel (steps 615, 620, 625, and 630). On the other hand, if the input key is a key for turning off the security mode, the security mode of the transmitting terminal is turned off, and a predetermined pattern indicating the security off is included in the information bit of the traffic channel. (Steps 615, 620, 635). If the key for the security mode is not input, the vocoder (encoder) compresses the input signal into information bits of a predetermined size to generate vocoder packet information bits (step 645). If the security mode is on and the vocoder packet information bits are not muted, the vocoder packet information bits are encrypted using the block cipher and the secret key, and otherwise bypassed (steps 650, 655 and 660). The encrypted or unencrypted vocoder packet information bits are composed of CDMA frames by attaching frame quality indicators and encoder tail bits. The CDMA frames are allocated through a frequency band allocated through convolutional encoding, interleaving, and spreading. It is transmitted to the base station (step 665, 670). If the call is maintained, step 615 or less is repeated, and when the call ends, the security mode is changed to the normal mode and step 605 or less is repeated.

Each function related to the encryptor 340 and the decryptor 350 of the terminal for a CDMA wireless communication system having the information protection function according to the present invention is applied to a terminal for a general CDMA wireless communication system or an application specific integrated circuit (ASIC). ) May be implemented by hardware.

FIG. 7 is a flowchart illustrating a receiver terminal corresponding to the case of FIG. 6.

Referring to FIG. 7, when the power of the receiver terminal is first turned on, an initialization operation of the receiver terminal is performed (step 700). Thereafter, when a ring and a call are received, the receiving terminal sets up a call with the transmitting terminal (steps 705 and 710), receives a signal from the base station, and reproduces the CDMA frame ( Step 715), the vocoder packet information bits are extracted from the reproduced CDMA frame (step 720). At this time, if the security mode pattern is included in the information bits of the received traffic channel, and the security mode pattern indicates that the security mode is on, the plurality of secrets included in the receiving terminal are checked by checking the index included in the information bits of the traffic channel. The secret key corresponding to the index is determined among the keys, and the security mode of the receiving terminal is turned on (steps 725, 730, 735, and 740). On the other hand, if the security mode pattern is included in the information bits of the received traffic channel, and the security mode pattern indicates the security mode off, the security mode of the receiving terminal is turned off (steps 725, 730, and 745). Then, if the security mode of the receiving terminal is turned on and the encrypted vocoder packet information bits are not muted, the encrypted vocoder packet information bits are decrypted using a block cipher and a secret key, and otherwise bypassed. (Steps 750, 755, 760). The decoded or bypassed vocoder packet information bits are decoded by the vocoder (decoder) (step 765). If the call is maintained, repeating step 715 or less, and if the call ends, the security mode is changed to the normal mode and repeating step 705 or less.

Since the greatest effect of the present invention is transmitted in the form of encrypted information bits other than the terminal, even if the encryption algorithm and the secret key are not known correctly even if the encrypted information bits are recovered by a highly specialized method, It is impossible to decode it into a vocoder packet. For example, if you know the type of blockcipher using a 128-bit secret key but do not know the secret key, you can use a Pentium PC to decrypt one encrypted vocoder packet. Assuming 1ms, it takes 2 ⁷⁰ years of unimaginable time to mobilize a million Pentium personal computers and find their keys at the same time.

Another effect of the present invention is that there is no need to modify an existing DCS or PCS base station or switch in a radio call between the same carrier (eg, 011 to 011 and 019 to 019). In the case of a radio call between the same carriers, since the vocal code is not decoded to the original voice in the intermediate process, so-called double coding may be performed in some cases, but it is generally bypassed. This is because the encrypted vocoder packet is delivered to the counterpart terminal intact. In other words, even in the case of a radio call between different operators (eg, 011 to 017), a safe call can be made without intervening vocoder decoding and encoding processes.

Lastly, the present invention provides a means for sharing a secret key simply and securely, so that different user groups can communicate using different secret keys, so that their own security network can be easily established even among small groups.

Claims (26)

In a terminal in a CDMA wireless communication system, An encoder for compressing an input signal into information bits of a predetermined size to generate vocoder packet information bits; An encryptor for block encrypting the vocoder packet information bits generated by the encoder; A CDMA framer configured to configure a CDMA frame by adding a frame quality indicator and encoder tail bits to the vocoder packet information bits encrypted by the encoder; A CDMA frame transmitter for transmitting a CDMA frame configured in the CDMA framer to a base station through an allocated frequency band through convolutional coding, interleaving, and spread spectrum; A CDMA frame receiver which receives a signal from the base station and reproduces a CDMA frame; A CDMA deframer for extracting encrypted vocoder packet information bits from the CDMA frame reproduced by the CDMA frame receiver; A decryptor for decrypting the encrypted vocoder packet information bits extracted from the CDMA deframer; And And a decoder for decoding the vocoder packet information bits decoded by the decoder. The method of claim 1, wherein the encryptor Encrypt using any block cipher and secret key, including DES, Triple DES, and SNAKE, The decryptor And decrypting using the secret key shared by the block cipher and the counterpart terminal. The method of claim 2, wherein the encryptor A terminal for a CDMA wireless communication system having an information protection function, characterized in that encryption is set and released according to a security mode set by a user. The method of claim 3, wherein the encryptor Generating a predetermined pattern corresponding to setting and releasing of the security mode, including the generated predetermined pattern in the information bits of the traffic channel, and transmitting the generated pattern to the counterpart terminal; The decryptor A terminal for a CDMA wireless communication system having an information protection function, characterized by setting and releasing decryption by the predetermined pattern. The method of claim 4, wherein the encryptor In setting the security mode, include the secret key in the information bit of the traffic channel, The decryptor CDMA wireless communication system terminal having an information protection function, characterized in that for decrypting the encrypted vocoder packet information bits using a secret key included in the information bits of the traffic channel. The method of claim 4, wherein the encryptor In setting the security mode, the secret key is encrypted with a predetermined master key and included in the information bit of the traffic channel. The decryptor CDMA wireless communication with an information protection function characterized by decrypting the encrypted secret key included in the information bit of the traffic channel with the predetermined master key, and decrypting the encrypted vocoder packet information bit using the decrypted secret key. Terminal for system. The method of claim 4, wherein the encryptor And a plurality of secret keys, including the index of the selected secret key of the plurality of secret keys in the information bit of the traffic channel when the security mode is set, and encrypting the vocoder packet information bit using the selected secret key. , The decryptor And sharing the plurality of secret keys provided in the encryptor, and decrypting the encrypted vocoder packet information bits using a secret key selected by an index included in the information bits of the traffic channel. Terminal for CDMA wireless communication system. The method of claim 1, wherein the encoder Generate a transmission silence signal indicating whether the generated vocoder packet information bits are muted; The encryptor If the transmission silence signal indicates silence, the vocoder packet information bit is not encrypted, The CDMA deframer Generate a reception silence signal indicating whether the extracted encrypted vocoder packet information bits are muted; The decryptor And if the received mute signal indicates mute, the encrypted vocoder packet information bits are not deciphered. The method of claim 1, wherein the encryptor Encrypting only some or all of the information bits of the vocoder packet information bits, The decryptor CDMA wireless communication system terminal having an information protection function, characterized in that for decrypting only part or all of the encrypted information bits of the encrypted vocoder packet information bits. In the method of transmitting and protecting the information bits in the terminal of the CDMA wireless communication system, (a) encoding the input signal into information bits having a predetermined size to generate vocoder packet information bits; (b) block encrypting the encoded vocoder packet information bits; (c) constructing a CMDA frame by adding a frame quality indicator and encoder tail bits to the encrypted vocoder packet information bits; And (d) encrypting the information bits in the terminal of the CDMA wireless communication system, wherein the CDMA frame is transmitted to a base station through an allocated frequency band through convolutional coding, interleaving, and spread spectrum. Transmission method. The method of claim 10, wherein step (b) A method of encrypting and transmitting information bits in a terminal of a CDMA wireless communication system, characterized by encrypting using an arbitrary block cipher and secret key including DES, Triple DES, and SNAKE. The method of claim 11, wherein step (b) A method of encrypting and transmitting information bits in a terminal of a CDMA wireless communication system, characterized in that encryption is set and released according to a security mode set by a user. The method of claim 12, wherein step (b) And generating a predetermined pattern corresponding to the setting and releasing of the security mode and including the predetermined pattern in the information bit of the traffic channel. The method of claim 13, wherein step (b) And encrypting the information bits in the terminal of the CDMA wireless communication system, wherein the secret key is included in the information bits of the traffic channel when the security mode is set. The method of claim 13, wherein step (b) And encrypting the secret key with a predetermined master key in the information bit of the traffic channel when the security mode is set. The method of claim 13, wherein step (b) In setting the security mode of the CDMA wireless communication system, including the index of the selected secret key of the plurality of secret keys in the information bits of the traffic channel, and encrypting the vocoder packet information bits using the selected secret key Method of encrypting information bits in a terminal. The method of claim 10, wherein step (b) Checking whether the generated vocoder packet information bits are mute, and if not, encrypting the vocoder packet information bits, and encrypting the information bits in the terminal of the CDMA wireless communication system. The method of claim 10, wherein step (b) And encrypting only a part of the information bits of the vocoder packet information bits. A method for receiving an encrypted information bit at a terminal of a CDMA wireless communication system, (a) receiving a signal from a base station and reproducing a CDMA frame; (b) extracting encrypted vocoder packet information bits from the reproduced CDMA frame; (c) a decryptor for decrypting the encrypted vocoder packet information bits; And and (d) decrypting the decrypted vocoder packet information bits. The method of claim 19, wherein step (c) A method of decrypting and receiving encrypted information bits in a terminal of a CDMA wireless communication system, characterized by decrypting using a block cipher, which is one of DES, Triple DES, and SNAKE, and a secret key. The method of claim 20, wherein step (c) The security mode is set and released by a predetermined pattern included in the information bits of the received traffic channel, and the decryption is determined by the security mode. Decryption reception method. The method of claim 21, wherein the secret key And a secret key included in an information bit of a traffic channel received when the security mode is set. The method of claim 21, wherein the secret key And a secret key obtained by decrypting a key value included in the information bit of the received traffic channel with a predetermined master key when the security mode is set. The method of claim 21, wherein the secret key Method of decrypting and receiving encrypted information bits in a terminal of a CDMA wireless communication system, characterized in that the secret key determined by the index included in the information bits of the traffic channel of the set of the security mode of the plurality of secret keys provided in the terminal. The method of claim 19, wherein step (c) Confirming whether or not the encrypted vocoder packet information bits are muted, and if not, decrypting and receiving the encrypted information bits in the terminal of the CDMA wireless communication system. The method of claim 19, wherein step (c) And decrypting only a part of the encrypted information bits of the encrypted vocoder packet information bits.