CN1323507C - The Processing Method of Short Packet in Block Encryption Algorithm - Google Patents

Abstract

The invention discloses a method for processing short packets in a packet encryption algorithm. The encryption process includes: after the sender encrypts the plaintext of the last complete packet, divides the obtained ciphertext packet into two parts, and uses one part as The ciphertext grouping of the short grouping; splicing the short grouping with the padding part to form a complete grouping; encrypting the complete grouping and sending it to the recipient; the decryption process includes: the recipient receives the last After the ciphertext of the complete group is grouped, the ciphertext group is decrypted; the decrypted group is divided into two parts, one of which is the plaintext of the short group; the other part is combined with the received ciphertext of the short group The groups are spliced to obtain a complete ciphertext group, and then the group is decrypted to obtain the plaintext of the last complete group. Applying the method described in the invention can improve the security of data transmission.

Description

The Processing Method of Short Packet in Block Encryption Algorithm

technical field

The invention relates to data encryption technology, in particular to a processing method for short packets in packet encryption algorithms.

Background technique

In a communication system, security is an important indicator to evaluate the performance of a communication system, especially in a wireless communication system, due to the characteristics of openness and mobility of a wireless communication system, the security of a wireless communication system is particularly important .

The IEEE 802.16d/e series protocol defines the protocol standard for wireless broadband fixed and mobile access air interface. In order to ensure the security of air interface data transmission, the above-mentioned series of protocols define a security sublayer (Privacy Sublayer), which is used to realize the authentication of wireless communication system users, key distribution and management, subsequent data encryption and authentication, etc. . After the authentication is completed, MS and BS also need to generate, distribute and manage the key for encrypting air interface data through the key management protocol (PKM). The result of the above PKM process is to generate a key for deriving The basic key of other key resources - authentication key (AK, Authorization Key). After obtaining key resources through authentication, MS and BS can realize secure transmission of air interface data through encryption algorithms.

IEEE 802.16d/e series protocols provide a variety of optional encryption algorithms, which encryption algorithm to use needs to be negotiated between the MS and the BS during the authentication message exchange process. The currently commonly used encryption algorithm is a block encryption algorithm. Before encryption using the block encryption algorithm, the sender first divides the plaintext data block that needs to be encrypted into several groups according to a fixed size m. The block encryption algorithm is Encrypted in units of packets. According to the agreement, in the specific application process, you can use a variety of different encryption modes, such as Electronic Code Book (ECB, Electronic Code Book) mode and Cipher Block Chaining (CBC, Cipher Block Chaining) mode, etc.

Among them, ECB is the simplest mode in block encryption algorithm. In this mode, the sender directly encrypts each packet independently using the same key Ki, and sends the encrypted result as a ciphertext packet to the receiver. After receiving each ciphertext packet, the receiver will perform independent decryption processing to directly obtain the plaintext of each packet. In ECB encryption mode, each packet is encrypted and decrypted independently.

CBC is an encryption mode commonly used in block encryption algorithms. In this mode, in addition to having a shared data encryption key Ki, both communicating parties will also negotiate to generate a CBC initialization vector (IV), the length of which is equal to the size of the packet m, used as the first An input when encrypting a block. The CBC encryption mode uses the following steps to process plaintext packets:

1. For the first group, first perform an XOR operation on CBC IV and the plaintext data of the first group, then encrypt the XOR result, and use the encrypted result as the ciphertext group of the first group;

2. Starting from the second group, corresponding to each group, first perform an XOR operation with the ciphertext group of the previous group and the plaintext data of the current group, and then encrypt the XOR result to obtain the encryption of the corresponding group Text grouping; here the key Ki used to encrypt each grouping is the same;

3. For the last packet, if the length of the packet is exactly equal to m, it will be treated the same as other packets; if its length is less than m, it will be called a short packet, and different encryption algorithms will use different processing for short packets method.

In the above two encryption modes, there are many encryption algorithms used to encrypt each packet, for example, Advanced Encryption Standard (AES, Advanced Encryption Standard) algorithm and Data Encryption Standard (DES, Data Encryption Standard) algorithm, etc. wait. The IEEE802.16d-2004 version stipulates that the DES algorithm based on the CBC mode can be used to encrypt each packet of service data. IEEE 802.16e/D7 stipulates that the AES algorithm based on CBC mode can be used in the 802.16 system to encrypt each packet of service data.

In the DES algorithm based on CBC mode and the AES algorithm based on CBC mode, the processing method for the last short packet whose length is less than m is the same. Here, the length of the short packet is set to n, and n<m, mainly including :

The sender directly performs an encryption operation based on the ECB mode on the ciphertext group of a complete group before the short group; takes the left n bits of the encrypted ciphertext group, and directly performs an XOR operation with the short group plaintext, The obtained result is used as the ciphertext group of the short group.

The encryption algorithm used here is the same as the encryption algorithm used when other packets are encrypted, which can be DES algorithm or AES algorithm, and the encryption key used is also the same as the encryption key used by other packets.

After receiving the ciphertext packets corresponding to each packet, the receiver uses the corresponding decryption algorithm to decrypt the previous complete packet; for the last short packet, the receiver first decrypts the ciphertext of the previous complete packet of the short packet The group is encrypted again based on the ECB mode, and the left n bits of the encrypted ciphertext group are used to perform an XOR operation with the ciphertext group of the short group, so as to obtain the plaintext corresponding to the short group.

It can be seen from this that in the existing encryption algorithms, the ciphertext of all short blocks is just the result of a simple XOR operation between the plaintext of the short block and a part of the ciphertext in the previous block, and there is essentially no The short packet is encrypted. In this way, network attackers can systematically change the content of the decrypted short block plaintext by changing some bits in the short block ciphertext. If the last short block does not contain important information, there will be no problem with this encryption algorithm. But if the last packet contains important information, there will be serious security risks.

In addition, for the encryption method using the DES encryption algorithm, since the DES algorithm is a symmetric encryption algorithm, in the process of encrypting the short packet, it is necessary to combine the plaintext of the last complete packet with that of the penultimate complete packet. The XOR result of the ciphertext block is encrypted twice with DES, which is equivalent to performing DES encryption on the XOR result and then DES decryption. In this way, the encryption operation on the plaintext of the short block is equivalent to using the first n bits of the ciphertext block of the penultimate complete block, the first n bits of the plaintext of the last complete block, and the plaintext of the short block. or the result of the operation. Therefore, if the network attacker obtains the plaintext of the short packet, he can deduce some of the plaintext bits of the penultimate packet; similarly, if the network attacker obtains the plaintext of the last complete packet, he can The plaintext of the short packet is easily obtained. In this way, secure transmission of data will not be possible.

Contents of the invention

In order to solve the above technical problems, the present invention provides a method for encrypting short packets, so as to improve the security of data transmission and eliminate the potential safety hazards in the prior art.

The method for processing short packets in the packet encryption algorithm of the present invention includes two processes of encryption and decryption, the packets include a short packet with a length of n and a complete packet with a length of m, and n is less than m;

The encryption process includes:

A. After encrypting the plaintext of the last complete block, the sender divides the obtained ciphertext block into two parts whose length is n and whose length is m minus n;

B. Use the padding part whose length is m minus n to splice with the plaintext of the short block to form a complete block with a length of m, encrypt the complete block as the ciphertext block of the last complete block, and send to the recipient;

C, using the ciphertext grouping part of length n obtained in step A as the ciphertext grouping of the short grouping, and sending it to the receiver;

The decryption process includes:

a. After receiving the ciphertext packet of the last complete packet, the receiver decrypts the ciphertext packet;

B, dividing the deciphered grouping corresponding to the splicing method described in step B into two parts with a length of n and a length of m minus n, wherein the part with the length of n is the plaintext of the short group;

c. Splicing the part whose length is m minus n in step b corresponding to the division method described in step A and the received ciphertext group of the short group to obtain a ciphertext group with a length of m, and then the ciphertext The packet is decrypted to obtain the plaintext of the last complete packet.

The encryption described in step A is to use the data encryption standard algorithm based on the ciphertext block chain mode to encrypt;

The decryption process described in step c is to use the data encryption standard algorithm based on the ciphertext block chaining mode for decryption.

The encryption described in step A is to adopt the Advanced Encryption Standard algorithm based on the ciphertext block chaining mode to encrypt;

The decryption process described in step c is to use the Advanced Encryption Standard algorithm based on the ciphertext block chaining mode for decryption.

The division described in step A is as follows: taking the first n bits of the ciphertext group as a part, and taking the remaining m-n bits as another part, or taking the first m-n bits of the ciphertext grouping as a part, and leaving n bit as another part.

The padding part described in step B is the part of length m-n divided by the ciphertext grouping described in step A;

The splicing described in step B is: placing the short packet plaintext in front of the padding part, or placing the padding part in front of the short packet plaintext;

The encryption described in step B is encrypted by using an encryption algorithm based on the electronic codebook mode;

The decryption described in step a is to use a decryption algorithm based on the electronic codebook mode for decryption.

The encryption algorithm based on the electronic codebook mode in the present invention is the advanced encryption standard algorithm based on the electronic codebook mode; the decryption algorithm based on the electronic codebook mode is the advanced encryption standard algorithm based on the electronic codebook mode.

The encryption algorithm based on the electronic codebook mode in the present invention is a standard data encryption algorithm based on the electronic codebook mode; the decryption algorithm based on the electronic codebook mode is a standard data encryption algorithm based on the electronic codebook mode.

The encryption key used when encrypting is the same encryption key used to encrypt other packets;

The decryption key used for decryption is the same as the decryption key used for decrypting other packets.

The padding part described in step B is any value whose length is m-n;

The splicing described in step B is: according to the division method described in step A, splicing the plaintext of the short block and the filling part, so that the position of the plaintext of the short block and the part of length n in the ciphertext block corresponding to the location;

The encryption described in step B is encrypted by using an encryption algorithm based on ciphertext block chaining mode;

The decryption described in step a is to use a decryption algorithm based on ciphertext block chaining mode for decryption.

According to the present invention, adopting encryption algorithm based on ciphertext grouping link mode to encrypt comprises:

B1, using the ciphertext group described in step A and the complete group described in step B to perform an XOR operation;

B2. Encrypt the XOR result above using the same encryption key as that used to encrypt other packets, to obtain the ciphertext packet of the last complete packet described in step B.

The decryption algorithm based on the ciphertext grouping link mode of the present invention comprises:

a1. Decrypt the ciphertext block of the last complete block described in step a using the same decryption key as the decryption key used to decrypt other blocks;

a2. According to the same splicing method as step B, splicing the padding part and the received ciphertext packet of the short packet into a complete ciphertext packet with a length of m;

a3. Perform an XOR operation on the decryption result obtained in step a1 and the complete ciphertext group obtained in step a2, and use the XOR result as the decryption result of the ciphertext group of the last complete group.

The encryption algorithm based on the ciphertext block chaining mode in the present invention is an advanced encryption standard algorithm based on the ciphertext block chaining mode; the decryption algorithm based on the ciphertext block chaining mode is the advanced encryption standard algorithm based on the ciphertext block chaining mode.

The encryption algorithm based on the ciphertext grouping chaining mode in the present invention is a data encryption standard algorithm based on the ciphertext grouping chaining mode; the decryption algorithm based on the ciphertext grouping chaining mode is a data encryption standard algorithm based on the ciphertext grouping chaining mode.

It can be seen that the application of the method described in the present invention can encrypt the short packet, which ensures the security of data transmission and eliminates the potential safety hazards of the prior art. In addition, the method of the present invention does not change the length of the data during the process of encrypting the short packet, thereby ensuring the transmission efficiency of the data.

Description of drawings

Fig. 1 is the flow chart of the method for encrypting short packets by the sender described in a preferred embodiment of the present invention;

Fig. 2 is a flow chart of a method for decrypting a short packet by the receiver according to a preferred embodiment of the present invention;

FIG. 3 is a flow chart of a method for encrypting a short packet by a sender according to another preferred embodiment of the present invention;

Fig. 4 is a flowchart of a method for encrypting a short packet by a receiver according to another preferred embodiment of the present invention.

Detailed ways

In order to solve the problems existing in the prior art, the present invention provides a method for processing short packets in a packet encryption algorithm. The main idea of the method is: fill the short packets into a Complete group, and then use the existing encryption algorithm to encrypt the complete group, so as to ensure that all plaintext data sent by the sender is encrypted, and improve the reliability of system data transmission.

The method of the present invention is applicable to the situation that the length of the plaintext of the data block to be encrypted is greater than the length m of the complete group, that is, the group contains at least one complete group with the length m after grouping.

Fig. 1 shows a flow chart of a sender encrypting a short packet according to a preferred embodiment of the present invention. Here, it is assumed that the data blocks that need to be encrypted are divided into k groups according to the size m of the complete group, and the length of the last short group is n, and n<m, as shown in Figure 1, in this embodiment, the sender The encryption process of the short packet mainly includes:

Step 101: After encrypting the plaintext P _k-1 of the last complete block, the sender divides the obtained ciphertext block C into two parts. One part has a length of n and is denoted as C _k , and the other part has a length of mn and is denoted as C'.

The encryption in this step may adopt the DES algorithm based on the CBC mode, or the AES algorithm based on the CBC mode. And the encryption key used when encrypting is the same as the encryption key used when encrypting other packets.

The method of dividing the obtained ciphertext group into two parts is also arbitrary. For example, the first n bits of C can be used as C _k , and the remaining part can be used as C', or the first mn bits of C _i can be used as C', and use the remaining part as C _k ; in addition, it is also possible to use other division methods without going beyond the scope of the present invention.

Step 102: splicing the C' part with a length of mn as the padding part  with the plaintext of the short packet P _k to form a complete packet P _k ' with a length of m, and encrypting the complete packet P _k ', A complete ciphertext block C _k-1 is obtained and sent to the receiver as the ciphertext block of the last complete block P _k-1 .

In this step, the splicing method can also be arbitrary, for example, the short block plaintext can be placed in front of C', and the C' part can also be placed in front of the short block plaintext.

The encryption described in this step can adopt the DES algorithm based on the ECB mode or the AES algorithm based on the ECB mode, and the encryption key used is the same as that used for encrypting other packets in the CBC mode.

Step 103: Send the C _k obtained in step 101 as the ciphertext packet of the short packet to the receiver.

Fig. 2 has shown the flow chart that according to the method described in this embodiment, the receiver performs decryption processing after receiving the above-mentioned grouping, as shown in Fig. 2, the described decryption process mainly includes:

Step 201: After receiving the ciphertext block C _k-1 of the last complete block, the receiver decrypts the ciphertext block to obtain a complete block P _k ';

Corresponding to step 102, if the encryption algorithm used when encrypting is the AES algorithm based on ECB, then in this step, the AES algorithm based on the ECB mode should be used for decryption; if the encryption algorithm used when encrypting is based on the ECB mode DES algorithm, the ECB-based DES algorithm should be used for decryption in this step; and the decryption key used for decryption is the same as that of other packets;

Step 202: Divide the complete packet P _k ' into two parts corresponding to the splicing method described in step 102, one part has a length of n, and the other part has a length of mn; wherein, the part with a length of n is the plaintext P of the short packet _k , the part whose length is mn is the C' described in step 101;

It can be seen from step 102 that the complete block P _k ' is spliced by the plaintext of the short block P _k and the part C' of length mn in the ciphertext block obtained by one encryption of the last complete block, Therefore, the splicing method corresponding to step 102 of P _k 'is divided into two parts, and the plaintext of the short packet P _k can be directly obtained;

Step 203: splicing the part C' of length mn in P _k ' corresponding to the division method described in step 101 with the received ciphertext C _k of the short group to obtain a complete ciphertext group C with a length of m, and then Decrypt the packet to obtain the plaintext packet P _k-1 of the last complete packet.

Wherein, the decryption corresponds to the encryption algorithm used in step 101. If the AES algorithm based on the CBC mode is used for encryption, the AES algorithm based on the CBC mode should be used for decryption; if the DES algorithm based on the CBC mode is used for encryption, then The DES algorithm based on CBC mode should be used for decryption. The decryption key used for decryption is also the same as that of other packets.

So far, the receiver can obtain the plaintext of the last complete packet and the short packet.

Fig. 3 shows a flow chart of the encryption processing of the short packet by the sender according to another preferred embodiment of the present invention. Here, it is assumed that the data blocks that need to be encrypted are divided into k groups according to the size m of the complete group, and the length of the last short group is n, and n<m, as shown in Figure 3, in this embodiment, the sender The encryption process of the short packet mainly includes:

Step 301: After encrypting the plaintext P _k-1 of the last complete block, the sender divides the obtained ciphertext block C into two parts. One part has a length of n and is denoted as C _k , and the other part has a length of mn and is denoted as C';

In this step, the encryption may adopt the DES algorithm based on the CBC mode, or may adopt the AES algorithm based on the CBC mode. Encryption is done with the same encryption key that was used to encrypt other full packets.

The method of dividing the obtained ciphertext block into two parts is also arbitrary. For example, the first n bits of the ciphertext block C can be used as C _k , and the remaining part can be used as C', or C _i The first mn bits of C' are taken as C', and the remaining part is taken as _Ck ; in addition, it is also possible to use other division methods without going beyond the scope of the present invention.

Step 302: Use the padding part  of length mn to splice the plaintext of the short packet P _k of length n to form a complete packet P _k ″ of length m, and encrypt the complete packet P _k ″ to obtain a complete The ciphertext block C _k-1 of is sent to the receiver as the ciphertext block of the last complete block P _k-1 .

In this step, the padding part [phi] used can be arbitrary, for example, can be m-n 0s or other arbitrary values.

The splicing described in this step should be carried out corresponding to the division method described in step 301. After splicing, the short packet P _k in the complete packet P _k ″ should correspond to the position of the C _k part in the ciphertext packet C.

In this step, the encryption may adopt the DES algorithm based on the CBC mode or the AES algorithm based on the CBC mode.

Since the encryption method using the CBC mode needs to first use the ciphertext group of the previous group to perform an XOR operation with the current group, therefore, in this embodiment, the encryption of the complete group P _k " using the CBC mode mainly includes:

Step 3021: use the ciphertext block C described in step 301 and the complete block P _k ” described in step 302 to perform an XOR operation;

Step 3022: Use the same encryption key as that used to encrypt other packets to encrypt the XOR result above to obtain the complete ciphertext block C _k-1 .

Step 303: Send the C _k obtained in step 301 as the ciphertext packet of the short packet to the receiver.

Fig. 4 has shown the flow chart that according to the method described in this embodiment, the recipient performs decryption processing after receiving the above packet, as shown in Fig. 4, the decryption process mainly includes:

Step 401: After receiving the ciphertext block C _k-1 of the last complete block, the receiver decrypts the ciphertext block to obtain a complete block P _k .

Corresponding to step 303, if the encryption algorithm used when encrypting is the AES algorithm based on CBC, then in this step, the AES algorithm based on the CBC mode should be used for decryption; if the encryption algorithm used during encryption is based on the CBC mode DES algorithm, then the CBC-based DES algorithm should be used for decryption in this step.

The decryption process based on CBC mode further includes:

Step 4011: Decrypt the ciphertext block C _k-1 of the last complete block using the same decryption key as that used to decrypt other blocks;

Step 4012: According to the same splicing method as in step 302, splicing the padding part  with a length of mn and the received ciphertext block C _k of the short block into a complete ciphertext block with a length of m;

Step 4013: Perform XOR operation with the decryption result obtained in step 4011 and the complete ciphertext block obtained in step 4012 to obtain a complete block P _k .

In contrast to the encryption process shown in Figure 3, the ciphertext block C _k-1 of the last complete block is a complete block composed of the short block plaintext P _k and the padding part  and the composition of the C _k and C' The result obtained after the XOR operation on the complete group and then the encryption operation. According to the characteristic of XOR operation, this result is mathematically equal to the result obtained by encrypting the complete group composed of P _k and C' and the complete group composed of C _k and the filling part  after XOR operation. Therefore, it can be seen that the complete packet P _k  obtained in step 4013 is formed by combining the plaintext of the short packet P _k and the ciphertext block C' of length mn.

Step 402: Divide the complete packet P _k  into two parts corresponding to the splicing method described in step 302, one part has a length of n, and the other part has a length of mn; wherein, the part with a length of n is the plaintext P of the short packet _k , the part whose length is mn is the C' described in step 301;

Step 403: splicing the part C' of length mn in P _k  corresponding to the division method described in step 302 with the received ciphertext C _k of the short group to obtain a complete ciphertext group C with a length of m, and then Decrypt this packet to obtain the plaintext packet P _k-1 of the last complete packet.

Wherein, the decryption corresponds to the encryption algorithm used in step 301. If the AES algorithm based on the CBC mode is used for encryption, the AES algorithm based on the CBC mode should be used for decryption; if the DES algorithm based on the CBC mode is used for encryption, then The DES algorithm based on CBC mode should be used for decryption. And the decryption key used for decryption is the same as the decryption key used for decrypting other packets.

So far, the receiver can obtain the plaintext of the last complete packet and the short packet.

It can be seen from the methods described in the above two embodiments that all packets sent by the sender to the receiver, including the ciphertext packets of the short packets, are all encrypted, so the reliability of data transmission can be guaranteed. Eliminate security risks of existing technologies. Moreover, the above encryption method does not increase the length of the transmitted data, thereby ensuring the efficiency of data transmission.

Claims (9)

1, a kind of in block encryption algorithm to the processing method of short grouping, it is characterized in that described method comprises two processes of encryption and decryption, described grouping comprises that length is that short grouping and the length of n is the complete packet of m, and n is arranged less than m;

Described ciphering process comprises:

After A, transmit leg were encrypted the plaintext of last complete packet, it was that n and length are two parts that m subtracts n that the ciphertext block that obtains is divided into length;

B, use length to subtract the filling part of n as m and the plaintext of described short grouping splices, form the complete packet that length is m, described complete packet is encrypted, the ciphertext block as described last complete packet sends to the recipient;

C, be the ciphertext block of the ciphertext block part of n, send to the recipient as described short grouping with the length that obtains in the steps A;

Described decrypting process comprises:

A, recipient are decrypted this ciphertext block after receiving the ciphertext block of described last complete packet;

It is that n and length are two parts that m subtracts n that b, the described connecting method of the corresponding step B of the grouping after will deciphering are divided into length, and wherein said length is that the part of n is the plaintext of described short grouping;

C, be that the described dividing mode of the corresponding steps A of part that m subtracts n is spliced with the ciphertext block of the described short grouping that receives with length among the step b, obtain the ciphertext block that length is m, again this ciphertext block is decrypted processing, obtains the plaintext of described last complete packet.

2, the method for claim 1 is characterized in that, steps A is described to be encrypted as employing and to encrypt based on the data encryption standard algorithm of cipher block chaining model;

The described decryption processing of step c is decrypted for adopting the data encryption standard algorithm based on cipher block chaining model.

3, the method for claim 1 is characterized in that, steps A is described to be encrypted as employing and to encrypt based on the Advanced Encryption Standardalgorithm of cipher block chaining model;

The described decryption processing of step c is decrypted for adopting the Advanced Encryption Standardalgorithm based on cipher block chaining model.

4, the method for claim 1 is characterized in that, steps A is described to be divided into: the preceding n position of described ciphertext block as a part, is subtracted the n position as another part and will be left m; Perhaps the preceding m with described ciphertext block subtracts the n position as a part, and will be left the n position as another part.

5, the method for claim 1 is characterized in that, the described filling part of step B is that the described length that is marked off by ciphertext block of steps A is the part that m subtracts n;

Step B is described to be spliced into: described short grouping expressly is placed on described filling part front, or described filling part is placed on described short grouping front expressly;

Step B is described to be encrypted as employing and to encrypt based on electronic codebook mode pattern cryptographic algorithm;

The described deciphering of step a is decrypted based on electronic codebook mode pattern decipherment algorithm for adopting.

6, method as claimed in claim 5 is characterized in that, described is Advanced Encryption Standardalgorithm based on the electronic codebook mode pattern based on electronic codebook mode pattern cryptographic algorithm; Described is Advanced Encryption Standardalgorithm based on the electronic codebook mode pattern based on electronic codebook mode pattern decipherment algorithm.

7, method as claimed in claim 5 is characterized in that, described is data encryption standard algorithm based on the electronic codebook mode pattern based on electronic codebook mode pattern cryptographic algorithm; Described is data encryption standard algorithm based on the electronic codebook mode pattern based on electronic codebook mode pattern decipherment algorithm.

As claim 1,2,3,5,6 or 7 described methods, it is characterized in that 8, the encryption key that uses is identical with other employed encryption keys that divide into groups of encryption when encrypting;

Employed decruption key is identical with other employed decruption keys that divide into groups of deciphering when deciphering.

9, the method for claim 1 is characterized in that, the described filling part of step B is that length is any number that m subtracts n; Step B is described to be spliced into: according to the described dividing mode of steps A, described short grouping is expressly spliced with described filling part, make that length is that n position partly is corresponding in described short grouping position expressly and the described ciphertext block;

Step B is described to be encrypted as employing and to encrypt based on the cipher block chaining model cryptographic algorithm;

The described deciphering of step a is decrypted based on the cipher block chaining model decipherment algorithm for adopting.

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