CN112367159B - A hybrid encryption and decryption method and system for safe storage of medical data - Google Patents

Abstract

The invention relates to a mixed encryption and decryption method for medical data security storage, which comprises the steps that a sender encrypts a key for DES encryption by utilizing RSA to form a ciphertext CK, a digital signature is formed by utilizing an RSA decryption key and a public encryption key together, a plaintext is encrypted by utilizing DES, the digital signature is combined with the encrypted plaintext and the encrypted digital signature to form a ciphertext C, and then the ciphertext C is sent; the receiving party receives the ciphertext C, decrypts the key K in the ciphertext C by using the RSA decryption key Kdb, and then decrypts the plaintext and the digital signature MA by using the key K. The invention carries out double encryption on the encrypted information, strengthens the safety intensity of the algorithm, inherits the characteristics of a public key encryption system, does not need to worry about related problems of key management, and is an ideal scheme for the safety storage of medical data.

Description

A hybrid encryption and decryption method and system for safe storage of medical data

technical field

The invention relates to the field of data encryption, in particular to a hybrid encryption and decryption method and system for safe storage of medical data.

Background technique

Data encryption technology is the most commonly used and most important technology to ensure network information security, and it is also the most important research direction in cryptography. Cryptography is an emerging interdisciplinary subject that studies the encryption, decryption and transformation of data information. The study of cryptography abroad is earlier, and many practical encryption algorithms have been proposed, such as DES (Data Encryption Standard), RSA (Rivest-Shamir-Adleman), AES (Advanced Encryption Standard) and ECC (Elliptic Curves Cryptography) algorithms. The more famous ones in China are Liu's encryption algorithm and so on. The various performances of the cryptographic system are mainly determined by the cryptographic algorithm. Different algorithms determine different cryptosystems, and different cryptosystems have different advantages and disadvantages. Some algorithms are fast and simple, but the encryption and decryption keys are the same, and the key management is difficult; some algorithms have convenient and safe key management, but the calculation cost is large and the processing speed is slow.

Data encryption technology is known as the core technology of information security. It is mainly divided into symmetric encryption and asymmetric encryption, with DES algorithm and RSA algorithm as typical representatives respectively. The DES algorithm is a block encryption algorithm with high computational efficiency and fast encryption speed, but its security depends on the key, while the RSA algorithm is an algorithm based on the decomposition of large numbers, using a dual-key system of public key and private key, which is difficult to crack It is equivalent to decomposing the product of two large prime numbers, so the RSA algorithm has high security, but its calculation overhead is large and the encryption speed is slow. Although there is no effective method to decipher them in a short period of time, with the continuous development of computer software and hardware, the performance of computers is changing with each passing day, and these traditional data encryption algorithms are no longer safe.

Data encryption technology is to process the data to be protected (also known as plaintext) according to a certain encryption transformation method (encryption algorithm), so that it can be transformed into unrecognizable data (ciphertext). The reverse process of data encryption, that is, the process of recovering plaintext from ciphertext according to the corresponding decryption transformation method (decryption algorithm), is called data decryption. In encryption technology, key-based encryption algorithms can be divided into two categories: symmetric encryption technology and asymmetric encryption technology, among which the most influential symmetric encryption and asymmetric encryption technology are data encryption DES algorithm and RSA algorithm.

At present, there are many researches on DES and RSA algorithms at home and abroad, some improve DES algorithm and RSA algorithm alone, and some do mixed research on DES and RSA algorithms, such as: encryption algorithm based on triple DES, fast encryption algorithm based on RSA And the mixed data encryption algorithm based on DES and RSA, etc., but these algorithms either only focus on security and ignore the complexity of calculation, or speed up the efficiency of calculation but the security cannot be guaranteed, even if there are both security and computational complexity Taking both into account, it is difficult to implement and has low practicability. Therefore, a hybrid encryption scheme with high security performance and fast operation speed is urgently needed in this field.

Contents of the invention

The purpose of the present invention is to provide a hybrid encryption and decryption method and system for safe storage of medical data, which solves the problems of insufficient security, slow calculation speed and practicality of the important algorithms DES and RSA in the current symmetric encryption technology and asymmetric encryption technology. Therefore, a hybrid encryption scheme with high security performance, fast operation speed and good practicability is proposed.

To achieve the above object, the present invention provides the following scheme:

A hybrid encryption method for safe storage of medical data, said method comprising:

Generate a key K for DES encryption;

Using RSA to encrypt the key K to form ciphertext CK;

Get the RSA public encryption key Keb;

Using the RSA decryption key together with the public encryption key Keb to form a digital signature MA;

Using the key K to encrypt plaintext and the digital signature MA;

Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C;

Send ciphertext C.

Optionally, the specific form of the ciphertext CK is: CK.Keb(K)=CK.

Optionally, the specific form of the ciphertext C is: C=K(plaintext, MA)+CK.

A hybrid encryption system for safe storage of medical data, said system comprising:

DES key generation unit, is used for generating the key K that is used for DES encryption;

A first encryption unit, configured to encrypt the key K with RSA to form ciphertext CK;

A public encryption key acquisition unit, used to obtain the RSA public encryption key Keb;

A first digital signature generating unit, configured to use the RSA decryption key and the public encryption key Keb to form a digital signature MA;

A second encryption unit, configured to use the key K to encrypt plaintext and the digital signature MA;

A ciphertext generation unit, configured to combine the encrypted plaintext and the encrypted digital signature MA with the ciphertext CK to form a ciphertext C;

The sending unit is used to send the ciphertext C.

A hybrid decryption method for safe storage of medical data, said method comprising:

Receive ciphertext C;

Decrypt the key K in the ciphertext C with the RSA decryption key Kdb;

The plaintext and the digital signature MA are decrypted by using the key K.

Optionally, after decrypting the plaintext and the digital signature MA by using the key K, the method further includes:

Get the public key Kea;

Using the public key Kea and the decryption key Kdb to confirm the identity of the signature information;

digitally processing the signature information to form the receiver's signature information;

Send the receiver's signature information to the sender to confirm receipt of the information.

Optionally, after sending the receiver's signature information to the sender to confirm receipt of the information, further include:

Both sender and receiver delete said key K.

A hybrid decryption system for safe storage of medical data, said system comprising:

a receiving unit, configured to decrypt the key K in the ciphertext C by using the decryption key Kdb;

The decryption unit uses the key K to decrypt the plaintext and the digital signature MA.

Optionally, it also includes a receiver processing unit for

Get the sender's public key Kea;

Using the public key Kea and the decryption key Kdb to confirm the identity of the signature information;

digitally processing the signature information to form the receiver's signature information;

Send the receiver's signature information to the sender to confirm receipt of the information.

A hybrid encryption and decryption method for safe storage of medical data, said method comprising:

The sender generates the key K for DES encryption;

Using RSA to encrypt the key K to form ciphertext CK;

Get the RSA public encryption key Keb;

Using the RSA decryption key together with the public encryption key Keb to form a digital signature MA;

Using the key K to encrypt plaintext and the digital signature MA;

Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C;

Send the ciphertext C to the receiver;

The receiver uses the RSA decryption key Kdb to decrypt the key K in the ciphertext C;

The plaintext and the digital signature MA are decrypted by using the key K.

According to the specific embodiments provided by the invention, the invention discloses the following technical effects:

The invention double-encrypts the encrypted information, strengthens the security strength of the algorithm, and realizes local independence, avoiding the threat of the key being cracked violently.

The hybrid encryption scheme provided by the invention inherits the characteristics of the public key encryption system, so there is no need to worry about key management issues, and it is an ideal scheme for safe storage of medical data.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without paying creative labor.

FIG. 1 is a control flow diagram of a hybrid encryption method for safe storage of medical data provided by Embodiment 1 of the present invention.

Fig. 2 is a schematic diagram of the composition of the hybrid encryption system for safe storage of medical data provided by Embodiment 1 of the present invention.

Fig. 3 is a control flow diagram of the hybrid decryption method for safe storage of medical data provided by Embodiment 2 of the present invention.

Fig. 4 is a schematic diagram of the composition of the hybrid decryption system for safe storage of medical data provided by Embodiment 2 of the present invention.

FIG. 5 is a control flow diagram of a hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

FIG. 6 is a schematic diagram of the TDEA encryption and decryption process of the hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

FIG. 7 is a schematic diagram of the encryption and decryption process of the HDDES algorithm of the hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

Fig. 8 is a comparison diagram of the encryption time of the DES and RSA algorithms in the hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

FIG. 9 is a schematic diagram of a hybrid encryption scheme based on HDDES and IPNRSA for a hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

Fig. 10 is a comparison diagram before and after encryption of medical electronic medical record data according to the hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

Fig. 11 is a comparison diagram before and after decryption of medical electronic medical record data according to the hybrid encryption and decryption method for safe storage of medical data provided by Embodiment 3 of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The purpose of the present invention is to provide a hybrid encryption and decryption method and system for safe storage of medical data, which solves the problems of insufficient security, slow calculation speed and practicality of the important algorithms DES and RSA in the current symmetric encryption technology and asymmetric encryption technology. problem of poor sex.

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Embodiment one:

As shown in Figure 1, a hybrid encryption method for safe storage of medical data, assuming that the sender is A (the encryption key is Kea, the decryption key is Kda), and the receiver is B (the encryption key is Keb, and the decryption key is Kda). The key is Kdb), the implementation steps of the above encryption scheme are as follows

A1, generate the key K for DES encryption;

The sender generates the key K for DES encryption. In order to improve data security, each key K is only used once. The DES key can be any 56-bit number, so users can generate it randomly. Since the length of the DES key is only 56 bits, its processing efficiency is extremely high.

A2. Using RSA to encrypt the key K to form ciphertext CK;

The sender obtains the receiver's RSA public encryption key Keb from the key server, and encrypts the DES key K with Keb to form the ciphertext CK.Keb(K)=CK. The advantage of the public encryption key is that it does not need to pass the key through a secure channel, which greatly simplifies the key management, but the encryption and decryption of the actually transmitted data requires a dedicated key.

A3. Obtain the RSA public encryption key Keb;

A4. Utilize the RSA decryption key and the public encryption key Keb to form a digital signature MA;

The sender generates the information that needs to be signed, and uses its own RSA decryption key Kda and Keb to form a digital signature MA. The original concept and goal of the development of the RSA algorithm is to make the Internet safe and reliable, aiming to solve the problem of using the public channel transmission of the DES algorithm key. It not only solves this problem well, but also can be used to complete the digital signature of the message .

A5, using the key K to encrypt plaintext and the digital signature MA;

A6. Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C;

After the sender uses K to encrypt the plaintext and signed information, and then forms a ciphertext C together with Ck and sends it to the receiver. C=K(plaintext, MA)+CK.

A7. Send ciphertext C.

The DES algorithm and the RSA algorithm are well-tested and excellent algorithms in data encryption, but there are still deficiencies in processing efficiency and key management. The following two algorithms are introduced separately.

The Data Encryption Standard (DES) algorithm is a block encryption algorithm, which uses 64bit (byte) as a packet to encrypt data, including 8bit parity, and the effective key length is 56bit. The encryption and decryption of the DES algorithm use the same algorithm (key sequence is different), and its security depends on the key used.

The specific process of the DES encryption algorithm is to divide the 64bit data into two parts (L, R) of 32bit on the left and right, use the XOR operation, and use the symbol express. The encryption process can be summarized as follows:

The 64bit plaintext is initially transformed, and recorded as IP.

Perform 16 iterative operations on the plaintext after the initial transformation, which are respectively marked as T ₁ , T ₂ ,...,T ₁₆ . Each iteration is divided into left and right parts, each 32 bits, expressed as (L _n , R _n ). The relationship between adjacent two iterations is as follows (1) and (2):

L _n =R _n-1 (1)

Among them, K _n represents 16 subkeys with a length of 48 bits used in 16 iterations. They are all generated by transforming the 56bit key, and each subkey is different.

After the iterative operation, it is processed by an end transformation IP ^-1 . The final transformation and the initial transformation are inverse transformations, that is, the conditions are satisfied:

IPIP ^-1 = 1 (3)

Described DES encryption process can be expressed simply with following formula (4):

DES(m)＝IP ^-1 (T ₁₆ (...(T ₂ (T ₁ IP(m))))) (4)

The DES decryption process can be simply expressed by the following formula (5):

DES(m)＝IP ^-1 (T ₁ (···(T ₁₅ (T ₁₆ IP(m))))) (5)

The RSA algorithm is mainly proposed based on the difficulty of large number decomposition, because it is very easy to find the product of two large prime numbers, but it is very difficult to factorize the product. Therefore, the product of two large prime numbers can be publicly used as the public key, and the prime number can be used as the private key generation factor. Then wanting to use the public key and the ciphertext to decipher the plaintext is equivalent to decomposing the product of two large prime numbers, which is very difficult, that is to say, the security of the RSA algorithm is based on the difficulty of decomposing the factors of the multiplication of large prime numbers.

The specific encryption and decryption methods of the RSA algorithm are summarized as follows:

Select two large prime numbers p and q with similar digits, but the values of p and q cannot be close.

Calculate the product n=p×q and φ(n)=(p-1)×(q-1), where n represents the product of two large prime numbers.

The encryption key e ₁ is chosen arbitrarily, so that e ₁ and (p-1)×(q-1) are relatively prime, that is, gcd(e,φ(n))=1.

Calculate the decryption key e ₂ such that e ₁ e ₂ =1modφ(n), that is, e ₁ and e ₂ are mutually inverse, and e ₂ and n are mutually prime.

The encryption function is: The decryption function is: /> where m is the plaintext and c is the ciphertext. {e ₁ ,n} is the public key, e ₂ is the private key, and generally the length of n is greater than or equal to 1024 bits.

When RSA encrypts data plaintext M, it first divides the plaintext M into data packets of appropriate size, and then encrypts each packet separately. The length of each packet should be smaller than n bits.

In terms of encryption and decryption processing efficiency, the DES algorithm is superior to the RSA algorithm, because the length of the DES key is only 56 bits, so the processing speed of the RSA algorithm is significantly slower than the DES algorithm when processing multiple word lengths.

In terms of key management, the RSA algorithm is more superior than the DES algorithm, because the RSA algorithm can distribute the encryption key in a public form, and it is easy to update the encryption key, and for different communication objects, the RSA algorithm only needs to It is enough to keep your own decryption key secret; while the DES algorithm requires the secret distribution of the key before communication, the replacement of the key is difficult, and for different communication objects, the DES algorithm needs to generate and store different keys.

Both the DES algorithm and the RSA algorithm have better security, and there is currently no effective method to decipher them in a short time. It is impossible for the DES algorithm to implement digital signature and identity authentication in principle, but the RSA algorithm can be easily implemented.

Generally speaking, the DES algorithm and the RSA algorithm have their own advantages and disadvantages, so the present invention designs an encryption scheme that combines the advantages of DES and RSA while avoiding their respective disadvantages. The basic principle is: before data communication, use the DES algorithm to encrypt the plain text of the message, and at the same time use the RSA algorithm to encrypt the DES key and realize the digital signature. If both network users who transmit confidential information use the symmetric encryption system DES and the RSA asymmetric key encryption system to transmit the key of DES, the high-speed simplicity of DES and the convenience and security of RSA key management can be fully utilized. . At the same time, for the above method, the present invention also provides a hybrid encryption system for safe storage of medical data, as shown in Figure 2, the system includes:

DES key generation unit, is used for generating the key K that is used for DES encryption;

A first encryption unit, configured to encrypt the key K with RSA to form ciphertext CK;

A public encryption key acquisition unit, used to obtain the RSA public encryption key Keb;

A first digital signature generating unit, configured to use the RSA decryption key and the public encryption key Keb to form a digital signature MA;

A second encryption unit, configured to use the key K to encrypt plaintext and the digital signature MA;

A ciphertext generation unit, configured to combine the encrypted plaintext and the encrypted digital signature MA with the ciphertext CK to form a ciphertext C;

The sending unit is used to send the ciphertext C.

The hybrid encryption method and system for safe storage of medical data provided by the embodiments of the present invention, on the basis of the traditional DES and RSA algorithms, first analyze the advantages and disadvantages of DES, and combine the triple DES encryption algorithm (Triple Data Encryption Algorithm, TDEA) and independent subkey DES encryption algorithm (Independent Sub Key DES Algorithm, ISKDES) advantages, the DES algorithm is improved, a hybrid double DES encryption algorithm (Hybrid double DES encryption algorithm, HDDES), and then The method of judging prime numbers that affects the speed of RSA algorithm modular exponentiation is studied in detail. On the basis of not affecting the security of RSA, the original prime number judging method is improved, and an RSA algorithm based on improved prime number judging (RSA algorithm based on improved prime number decision, IPNRSA), and finally combine HDDES encryption algorithm and IPNRSA encryption algorithm to form a hybrid encryption scheme based on HDDES and IPNRSA, which can effectively store medical data safely. It has the advantages of fast speed and high safety performance, and has good practicability.

Embodiment two:

As shown in Figure 3, a hybrid decryption method for safe storage of medical data, said method comprising:

B1. Receive ciphertext C; the receiver receives ciphertext C sent from the sender.

B2, use the RSA decryption key Kdb to decrypt the key K in the ciphertext C;

After receiving the ciphertext C, the receiver uses its own decryption key Kdb to decrypt the DES key K in C.

B3. Using the key K to decrypt the plaintext and the digital signature MA.

B4. Obtain the public key Kea;

B5. Use the public key Kea and the decryption key Kdb to confirm the identity of the signature information; the receiver uses the sender's public key Kea and its own decryption key Kdb to authenticate the signature information.

B6. Digitally process the signature information to form signature information of the receiver;

B7. Send the receiver's signature information to the sender to confirm receipt of the information.

B8. Both the sender and the receiver delete the key K.

The key length of the DES algorithm is too short, the encryption unit is only 64-bit binary, and 8 bits are used for parity check or other communication overhead, so the effective key is only 56 bits. So this will inevitably reduce the security of DES. With the development of computer performance, a method of brute force cracking the DES key has been found, and as computers become more and more powerful, DES with a 56-bit key cannot support applications with high security requirements.

And the DES algorithm has a weak key. There are 12 semi-weak keys and 4 weak keys in the DES algorithm. Because the key is divided into two parts during the process of generating the subkey, if the two parts are divided into all 0s or all 1s, the subkey generated in each round is the same. When the key is all 0 or all 1, or half of 1 or 0, a weak or semi-weak key will be generated, which will reduce the security of DES.

At present, there are mainly the following ways to attack the RSA algorithm:

Brute force cracking: try all private keys; mathematical attack: factorize the product of two prime numbers; timing attack: depends on the execution time of the decryption algorithm. In order to prevent the forced cracking of the RSA algorithm, an extra-long key must be used, so the more digits of the two large prime numbers p and q selected, the better, but this also makes the key generation speed, encryption and decryption speed faster come slower. For the remaining two attacks, since the security of RSA is based on the difficulty of multiplying and integrating large prime numbers, it is currently almost impossible to crack or very expensive to crack.

However, RSA algorithm key generation is cumbersome. Because two large prime numbers p and q must be used to generate the RSA key, it is limited to the prime number generation technology, and it is almost difficult to use one-time encryption. And its encryption speed is slow. The RSA algorithm not only has high security that DES does not have, but also the algorithm process is very easy to understand. However, behind the high security is actually at the expense of encryption speed. Large prime numbers such as p and q in RSA are randomly generated using a deterministic quality number judgment algorithm. The encryption time between RSA and DES is almost a hundred times different.

Therefore, the present invention combines the two encryption algorithms, learns from each other, and forms a hybrid encryption scheme based on HDDES and IPNRSA, so that it can effectively store medical data safely. In addition, the hybrid encryption scheme based on HDDES and IPNRS inherits the characteristics of the public key encryption system, so there is no need to worry about key management related issues, and it is an ideal scheme for the safe storage of medical data. At the same time, the embodiment of the present invention also provides a hybrid decryption system for safe storage of medical data, as shown in Figure 4, the system includes:

a receiving unit, configured to decrypt the key K in the ciphertext C by using the decryption key Kdb;

The decryption unit uses the key K to decrypt the plaintext and the digital signature MA.

The receiver processing unit is used to obtain the public key Kea of the sender;

Using the public key Kea and the decryption key Kdb to confirm the identity of the signature information;

digitally processing the signature information to form the receiver's signature information;

Send the receiver's signature information to the sender to confirm receipt of the information.

The hybrid decryption method and system for safe storage of medical data provided by the embodiment of the present invention first expands the original 64-bit key to 128-bit, which reduces the risk of being attacked by exhaustion if the key is too short, and then draws on the advantages of multiple encryption of the TDEA algorithm , double-encrypt the encrypted information to strengthen the security strength of the algorithm. Finally, refer to the characteristics of the ISKDES algorithm to map the 12-bit key to achieve local independence and avoid the threat of the key being brute-forced. The two complement each other, and because Only double encryption is higher than the TDEA algorithm in terms of operating efficiency.

Embodiment three:

As shown in Figure 5, a hybrid encryption and decryption method for safe storage of medical data, said method comprising:

The sender generates the key K for DES encryption;

Using RSA to encrypt the key K to form ciphertext CK;

Get the RSA public encryption key Keb;

Using the RSA decryption key together with the public encryption key Keb to form a digital signature MA;

Using the key K to encrypt plaintext and the digital signature MA;

Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C;

Send ciphertext C;

The recipient receives the ciphertext C, and uses the RSA decryption key Kdb to decrypt the key K in the ciphertext C;

The plaintext and the digital signature MA are decrypted by using the key K.

The present invention at first analyzes the shortcoming of symmetric encryption algorithm DES, and the shortcoming analysis of DES is specifically as follows:

1. The key length is too short. The encryption unit of the DES algorithm is only 64-bit binary, and 8 bits are used for parity check or other communication overhead, so its effective key is only 56 bits. So this will inevitably reduce the security of the DES algorithm. With the development of computer performance, a method of brute force cracking the DES key has been found, and as computers become more and more powerful, DES with a 56-bit key cannot support applications with high security requirements. Due to these obvious shortcomings of DES, the National Institute of Standards and Technology no longer conducted research on DES in 1997, but instead studied its alternative method, the Advanced Encryption Standard (AES).

2. Weak keys exist. There are 12 semi-weak keys and 4 weak keys in the DES algorithm. Because the key is divided into two parts during the process of generating the subkey, if the two parts are divided into all 0s or all 1s, the subkey generated in each round is the same. When the key is all 0 or all 1, or half of 1 or 0, a weak or semi-weak key will be generated, which will reduce the security of DES.

Then, research and analyze the improved DES algorithm at home and abroad to improve the shortcomings of the DES algorithm, as follows:

There are still many deficiencies in the improved DES algorithm, for example, its data transmission rate is low, it is not suitable for long-term data protection, and it is easy to be cracked by the differential key. Therefore, scholars at home and abroad have made many attempts to improve the DES algorithm. Under this background, the more influential triple DES algorithm (TDEA) and independent subkey DES algorithm (ISKDES) have been proposed successively.

Triple DES algorithm: Because the traditional DES algorithm key length is short and easy to be cracked, in order to make up for this deficiency, researchers proposed a triple DES encryption algorithm (TDEA), which triples the key length of DES, And three different keys are used for triple encryption and decryption. The encryption process is: first encrypt with the first key k ₁ , then decrypt with the second key k ₂ , and finally encrypt again with the third key k ₃ , that is, C=Ek ₃ (DK ₂ (Ek ₁ M )). The decryption is in reverse order, that is, M=Dk ₁ (EK ₂ (Dk ₃ C)). The core of TDEA is to use k ₁ , k ₂ , k ₃ to perform multiple encryptions on the plaintext, and the key length is three times that of DES. The specific implementation process of the TDEA algorithm is shown in Figure 6. Figure 6(a) is the encryption process of the TDEA algorithm, and Figure 6(b) is the decryption process of the TDEA algorithm. Although this method increases the length of the key and improves the security strength of the algorithm, Brute force cracking is effectively avoided, but its calculation time is increased by f-1 times, and f represents a multiplicity. For example, the time complexity of triple encryption is increased by 3-1=2 times, and the time complexity of decryption is also increased by 3-1=2 times, so the operating efficiency is very low. In addition, although the key number of bits in TDEA is 168 bits, the threat of brute force cracking is still unavoidable for the current computing power.

DES algorithm with independent subkeys: The key to the ISKDES algorithm depends on using different randomly generated subkeys for encryption, that is, the subkeys in each iteration are not generated with the same 56-bit binary key. Since each of the 16 iterations uses a 48-bit key, the modified DES key length of ISKDES becomes 768 bits. This method can greatly increase the difficulty of exhaustive decryption, thereby improving the encryption strength of DES, but the length of the key is too long, and the overhead becomes larger.

Drawing on the above two excellent algorithm ideas (triple DES algorithm and independent subkey DES algorithm), a hybrid double DES encryption algorithm (HDDES) is designed, as follows:

On the basis of TDEA algorithm and ISKDES algorithm, a hybrid double DES encryption algorithm (HybridDouble DES Encryption Algorithm, HDDES) is proposed. The algorithm expands the key of DES from 64 bits to 128 bits, and after mapping through the mapping table (as shown in Table 1), it is divided into two subkeys (each subkey is 64 bits), respectively Denoted as key1 and key2, then use the 16 subkeys generated by key1 to encrypt the plaintext to generate ciphertext 1, and then use the 16 subkeys generated by key2 to encrypt the ciphertext 1 to generate ciphertext 2, so that through double Encryption to enhance security strength. The specific process of the HDDES algorithm is shown in Figure 7, Figure 7(a) is the encryption process of the HDDES algorithm, and Figure 7(b) is the decryption process of the HDDES algorithm.

97 98 52 twenty one 101 86 103 54 105 3 107 twenty three 109 83 89 112 17 18 19 20 100 twenty two 108 twenty four 25 26 27 28 29 30 31 32 49 50 51 9 53 104 55 56 57 123 59 60 61 62 63 64 81 82 110 84 85 102 87 88 111 90 91 92 93 94 95 96 65 35 67 68 69 37 71 72 40 74 75 76 117 127 79 80 43 116 106 4 114 6 125 8 9 10 121 12 13 118 15 16 113 5 115 2 77 14 119 41 11 122 58 124 7 126 78 128 33 34 66 36 70 38 39 73 120 42 1 44 45 46 47 48

Table 1 128-bit key mapping table of TDEA

The HDDES algorithm is specifically:

Input: plaintext M, 128-bit key mapping table

Output: double encrypted ciphertext C, double decrypted plaintext M

1. Extended key length: expand the original DES 64-bit key to 128-bit length;

2. Key mapping processing: input the 128-bit key and map it according to the mapping table in Figure 5, and get two sub-keys key1 and key2, each with 64 bits;

3. Generate sub-keys: process the two sub-keys key1 and key2 to obtain 16 sub-keys respectively;

4. Double encryption of plaintext: After inputting the plaintext, encrypt once with key1 and then encrypt twice with key2 to generate ciphertext C;

5. Output double-encrypted ciphertext C;

6. Double decryption of plaintext: After inputting the ciphertext, first decrypt it once with key2, and then use key1 for the second decryption to restore it to plaintext M;

7. Output double decrypted plaintext M;

Then analyze the asymmetric encryption algorithm RSA, the shortcomings of RSA are analyzed as follows:

At present, there are mainly the following methods for attacking RSA: ①forced cracking: try all private keys; ②mathematical attack: factorize the product of two prime numbers; ③timing attack: depends on the execution time of the decryption algorithm. In order to prevent the forced cracking of the RSA algorithm, an extra-long key must be used, so the more digits of the two large prime numbers p and q selected, the better, but this also makes the key generation speed, encryption and decryption speed slower Slower and slower. For the remaining two attacks, since the security of RSA is based on the difficulty of multiplying and integrating large prime numbers, it is currently almost impossible to crack or very expensive to crack.

1. Key generation is cumbersome. Because two large prime numbers p and q must be used to generate the RSA key, it is limited to the prime number generation technology, and it is almost difficult to use one-time encryption.

2. The encryption speed is slow. The RSA algorithm not only has high security that DES does not have, but also the algorithm process is very easy to understand. However, behind the high security is actually at the expense of encryption speed. The following compares the encryption time of a set of simple data (2KB data volume) by the DES algorithm and the RSA algorithm to further illustrate their encryption speed gap. Specifically As shown in Figure 8. Among them, large prime numbers such as p and q of RSA are randomly generated by using a deterministic quality judgment algorithm. It can be seen that the encryption time of RSA and DES is almost a hundred times different.

Investigate and analyze the RSA algorithm improved at home and abroad for the shortcomings of RSA. The latest research and analysis of RSA is as follows:

The RSA algorithm is an algorithm based on the decomposition of large numbers. Since the decomposition of large numbers is a recognized mathematical problem, the security of RSA is very high. Although the computer hardware is updated rapidly and the performance of the computer continues to break through the limit, it still takes a lot of time to decompose a large number. In addition, in order to cope with the rapid development of computer computing power, the RSA algorithm gradually increases the length of the key, but the encryption speed of the RSA algorithm is precisely limited by the key generation speed. In order to solve the problem of encryption speed of RSA algorithm, researchers at home and abroad generally adopt two methods. The first method is to improve the realization of the key algorithm and take certain measures to speed up its operation speed. The present invention also starts from this aspect and studies how to improve the generation of the RSA key and improve its operation speed. The second method is to find a new public key encryption algorithm to replace RSA, such as the public key encryption algorithm based on elliptic curve (ECC). Research is still theoretical.

Since the core algorithm of RSA is the modular exponentiation operation of large prime numbers, that is, the self-multiplication of large numbers to obtain the modulus, so to improve the efficiency of the RSA algorithm, it is necessary to solve the problem of the operation speed of the modular exponentiation operation in RSA, and the core of the modular exponentiation operation is complicated. The degree depends on the modulo operation, and the modulo operation includes division operations. For a computer, a division operation requires several addition, subtraction, and multiplication operations, which is quite time-consuming, so it is assumed that the RSA algorithm can be used to reduce the modulus. operation or even avoid the modulo operation, the performance of the RSA algorithm will be significantly improved. Based on this, under the premise of ensuring the safety of the RSA algorithm, the present invention studies in detail the method for judging the prime number that affects the speed of the RSA algorithm modular exponentiation, and carefully compares the advantages and disadvantages of the deterministic and probabilistic two kinds of prime number judging algorithms, and then Using the Montgomery fast power algorithm to optimize the classic probabilistic quality number judgment algorithm—Miller-Rabin algorithm, an improved fast prime number judgment algorithm (Improved fast prime number judgment algorithm, IFPNJA) is proposed, and finally IFPNJA is applied to the RSA algorithm to form a An RSA algorithm based on improved prime number decision (IPNRSA).

Judgment method of prime number: The method of judging prime number is generally divided into two categories: one is deterministic quality number judgment algorithm, and the other is probabilistic quality number judgment algorithm. Determining the quality number judgment algorithm is as its name suggests, that is, hundreds of percent of the numbers generated by it are prime numbers, but it has certain restrictions. Although the probabilistic quality and number judgment algorithm cannot guarantee 100% generation of prime numbers, it has no major restrictions and the speed of generating prime numbers is faster than the deterministic judgment algorithm. In general, probabilistic quality and number judgment algorithms are mostly used in real life. Although it cannot guarantee 100% prime numbers, generating non-prime numbers is a small probability event after all, and probabilistic quality and number judgment algorithms can quickly and irregularly generate false numbers. A prime number that meets most needs.

The divisibility algorithm is the most commonly used in determining the quality number judgment algorithm, that is, the divisibility test. The principle of the algorithm is that all integers used as divisors are smaller than n, and n represents the product of two large prime numbers. If any of these numbers is arbitrary If a number is divisible by n, then n is a compound number. The divisibility algorithm is very inefficient, and its bit operation complexity is exponential.

Famous algorithms in the probabilistic property number judgment algorithm include: Miller-Rabin algorithm, Solovay-Strassen algorithm, Lehman algorithm, etc., because the present invention is improved at Miller-Rabin probability property number judgment algorithm and is limited in length, so only Miller-Rabin The algorithm is introduced in detail, and the other several famous algorithms will not be described in detail.

Introduction to the Miller-Rabin algorithm: If n is an odd prime number, then n-1=2 ^r m, r is a non-negative integer, m is a positive odd number, and a is any positive integer that is prime to n, then a ^m ≡ 1(mod n) or for some h (0≤h≤r-1), the equation a ^w ≡-1(mod n) holds, where w=2 ^h m. It can be proved that the error probability of the Miller-Rabin algorithm is at most 4 ^-1 . If n passes t tests, the probability that n is not a prime number will be 4 ^-t , and the error probability of Solovay-Strassen algorithm and Lehman algorithm are both 2 ^-t .

Since the efficiency of the deterministic property number judgment algorithm is very low and the complexity is high, it is not suitable for the modular exponentiation operation of the RSA algorithm, so the present invention directly adopts the probabilistic property number judgment algorithm to improve the modular exponentiation operation of the RSA algorithm. From the principles of each probabilistic quality and number judging algorithm, it can be seen that the probability of the Miller-Rabin algorithm judging the prime number is much higher than the other two mainstream algorithms, so the present invention selects the Miller-Rabin algorithm to improve, and the introduction here can greatly reduce the number of models. The algorithm of exponentiation—the Montgomery fast exponentiation algorithm optimizes the Miller-Rabin algorithm to form an improved fast prime number judgment algorithm (IFPNJA). The specific process is as follows:

Input: large numbers A, B, Miller-Rabin algorithm, modulus N.

Output: the fast modular multiplication result of large numbers A and B.

Initial input: input two large numbers A, B and modulus N.

Select the base: choose a positive integer R that is relatively prime to N as the base, and at the same time require that when R is 2 ^k , N must satisfy: 2 ^k-1 ≤ N ≤ 2 ^k , and require GCD(R, N) = 1, Here R can be any base, and in the present invention, for the convenience of processing, a power based on 2 is used.

Montgomery's fast power multiplication: use Montgomery's fast power algorithm to simplify the Miller-Rabin algorithm to perform modular multiplication operations on large numbers A and B, that is, Montgomery(A,B,N)=ABR ^-1 (modN).

Output the fast modular multiplication result of large numbers A and B.

The main advantage of IFPNJA adopting Montgomery's fast exponentiation algorithm is to convert division into shift operation, which not only simplifies the calculation process, but also improves the efficiency of large number exponentiation operation.

In order to improve the judgment efficiency of IFPNJA applied to the RSA algorithm, the present invention directly eliminates all even numbers and numbers divisible by 5 at the initial stage of prime number generation, and selects 53 small prime numbers to form a screening array for in-depth screening, and then applies IFPNJA to the RSA algorithm Modular exponentiation for quick screening. All screening methods complement each other to form an RSA algorithm (IPNRSA) based on improved prime number judgment. The specific improvement steps of IPNRSA are as follows:

Input: plaintext M, Miller-Rabin algorithm, random large array N.

Output: encrypted ciphertext C, decrypted plaintext M.

Random large number generation: Randomly generate a set of large arrays N except even numbers and numbers divisible by 5.

Large array screening: select 53 small prime numbers and use the remainder method to screen the large array N.

Optimizing the Miller-Rabin algorithm: Optimizing the Miller-Rabin algorithm using Montgomery's fast power algorithm.

Generate large prime numbers p, q: Combine the above steps and IFPNJA to generate two large prime numbers p, q.

RSA encrypted plaintext: Input the plaintext M, use two large prime numbers p and q to generate an RSA key to encrypt the plaintext to generate ciphertext C.

Output encrypted ciphertext C.

RSA decrypts the plaintext: Input the ciphertext C, use two large prime numbers p and q to generate an RSA key to decrypt the ciphertext to generate plaintext M.

Output the decrypted plaintext M.

Based on the advantages of the above two improved algorithms, HDDES and IPNRSA, they use different stages of EMR data in medical electronic records (that is, perform hybrid encryption) to form a hybrid encryption scheme for safe storage of medical data, as follows:

Because the encryption and decryption process of the symmetric encryption algorithm (such as DES) is very fast and the encryption efficiency is very high, it is very suitable for the encryption of medical electronic medical record data EMR with a fast update frequency and a large amount of data. It is easy to be stolen, so the security is not high, the encryption and decryption of asymmetric encryption algorithm (such as RSA) is very slow, the encryption efficiency is very low, and it is not suitable for the encryption of medical record data, but due to the difficulty of cracking and the key Not afraid of being stolen, so the security is extremely high. Therefore, in order to solve this problem, the present invention adopts a hybrid encryption scheme combining symmetric encryption and asymmetric encryption, that is, adopts HDDES and IPNRSA to select hybrid encryption for medical data. The specific process is shown in Figure 9 As shown, the overview is as follows:

The sender encrypts the plaintext of the medical data with the HDDES key to obtain the encrypted ciphertext.

The sender then encrypts the HDDES key information with the public key of IPNRSA to obtain the encryption key.

The sender sends out the mixed information of encrypted ciphertext and encryption key.

After receiving the mixed information, the receiver uses the private key of IPNRSA to decrypt the encryption key to obtain the HDDES key.

The recipient then uses the decrypted HDDES key to decrypt the encrypted ciphertext to obtain the plaintext of the medical data.

The above hybrid encryption strategy based on HDDES and IPNRSA not only improves the efficiency of encrypted medical data EMR but also ensures the security of medical data EMR transmission.

The present invention uses real medical electronic medical record data pictures (EMR pictures) to encrypt and decrypt, and the experimental results are shown in Figures 10 and 11, and the experimental analysis is as follows.

The plaintext encryption effect of medical data pictures is obvious. From the left half of Figure 10, it can be seen that the text part of the medical data picture before encryption is clearly visible, and then the encrypted text of the medical data picture is obtained after the encryption operation (see the right half of Figure 10), as can be seen from the right half of Figure 10 It can be seen that almost all text parts cannot be recognized by human eyes, and they all appear in the form of garbled characters when the operation of viewing the source file is performed in the background, which fully demonstrates the encryption effectiveness of the hybrid encryption scheme proposed by the present invention.

The ciphertext decryption effect of medical data pictures is obvious. From the left half of Figure 11, it can be seen that the medical data picture before decryption is blurred and almost unrecognizable, and then the ciphertext of the medical data picture is obtained after the decryption operation (see the right half of Figure 11), which is similar to the left half of Figure 10 Comparing some original images, it is obvious that the images before and after encryption and decryption are almost lossless, which fully demonstrates the decryption effectiveness of the hybrid encryption scheme proposed by the present invention.

The present invention discusses the advantages and disadvantages of triple DES encryption algorithm (Triple Data Encryption Algorithm, TDEA) and independent subkey DES encryption algorithm (Independent Sub Key DES Algorithm, ISKDES), on the basis of TDEA algorithm and ISKDES algorithm, proposes a A hybrid double DES encryption algorithm (Hybrid Double DESEncryption Algorithm, HDDES). The HDDES algorithm combines the advantages of both TDEA and ISKDES. HDDES first expands the original 64-bit key to 128-bit, which reduces the brute force attack when the key is too short. Then learn from the advantages of multiple encryption of the TDEA algorithm to double-encrypt the encrypted information to strengthen the security strength of the algorithm. Finally, refer to the characteristics of the ISKDES algorithm to map the 12-bit key to achieve partial independence and avoid the key being The threat of brute force cracking, the two complement each other, and because there is only double encryption, the operating efficiency is higher than that of the TDEA algorithm.

At the same time, the present invention also discusses the advantages and disadvantages of two kinds of prime number judging algorithms, deterministic and probabilistic, and proposes an improved fast prime number judging algorithm (IFPNJA) on the basis of the Miller-Rabin probabilistic prime number judging algorithm. The main advantage of Montgomery's fast exponentiation algorithm is to convert division into shift operation, which not only simplifies the calculation process, but also improves the efficiency of large number exponentiation operation. Finally, IFPNJA is applied to the RSA algorithm to form an RSA algorithm based on improved prime number decision (IPNRSA).

Due to the advantages and disadvantages of the symmetric encryption algorithm and the asymmetric encryption algorithm in the face of fast update frequency and huge data volume of medical electronic medical record data EMR, the present invention combines the HDDES encryption algorithm and the IPNRSA encryption algorithm to learn from each other to form a HDDES-based The hybrid encryption scheme with IPNRSA enables it to effectively store medical data securely. In addition, the hybrid encryption scheme based on HDDES and IPNRSA inherits the characteristics of the public key encryption system, so there is no need to worry about key management related issues, and it is an ideal scheme for the safe storage of medical data.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other. As for the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and for the related information, please refer to the description of the method part.

In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; meanwhile, for those of ordinary skill in the art, according to the present invention Thoughts, there will be changes in specific implementation methods and application ranges. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. A hybrid encryption method for safe storage of medical data, characterized in that the method comprises: Generate a key K for DES encryption; Using RSA to encrypt the key K to form ciphertext CK; Get the RSA public encryption key Keb; Using the RSA decryption key together with the public encryption key Keb to form a digital signature MA; Using the key K to encrypt plaintext and the digital signature MA; Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C; Send ciphertext C; The DES is specifically: ① Extended key length: expand the original DES 64-bit key to 128-bit length; ② Key mapping processing: input the 128-bit key and map it according to the mapping table, and map to get two sub-keys key1 and key2, each sub-key is 64 bits; ③ Generate sub-keys: process the two sub-keys key1 and key2 to obtain 16 sub-keys respectively; ④Double encryption of plaintext: After inputting the plaintext, first encrypt it once with key1 and then encrypt it twice with key2 to generate DES ciphertext; The RSA is specifically: Random large number generation: Randomly generate a set of large arrays N except even numbers and numbers divisible by 5; Large array screening: select 53 small prime numbers and use the remainder method to screen the large array N; Optimize the Miller-Rabin algorithm: use the Montgomery fast power algorithm to simplify the Miller-Rabin algorithm to perform modular multiplication operations on large numbers A and B, that is, Montgomery(A,B,N)=ABR ^-1 (modN); Generate large prime numbers p, q: Combine the above steps and IFPNJA to generate two large prime numbers p, q; RSA encrypted plaintext: Input the plaintext M, use two large prime numbers p and q to generate an RSA key to encrypt the plaintext to generate RSA ciphertext. 2. the hybrid encryption method facing the safe storage of medical data according to claim 1, characterized in that, The specific form of the ciphertext CK is: CK.Keb(K)=CK. 3. the hybrid encryption method facing the safe storage of medical data according to claim 1, characterized in that, The specific form of the ciphertext C is: C=K(plaintext, MA)+CK. 4. A hybrid encryption system for safe storage of medical data, characterized in that the system comprises: DES key generation unit, is used for generating the key K that is used for DES encryption; A first encryption unit, configured to encrypt the key K with RSA to form ciphertext CK; A public encryption key acquisition unit, used to obtain the RSA public encryption key Keb; A first digital signature generating unit, configured to use the RSA decryption key and the public encryption key Keb to form a digital signature MA; A second encryption unit, configured to use the key K to encrypt plaintext and the digital signature MA; A ciphertext generation unit, configured to combine the encrypted plaintext and the encrypted digital signature MA with the ciphertext CK to form a ciphertext C; a sending unit, configured to send the ciphertext C; The DES is specifically: ① Extended key length: expand the original DES 64-bit key to 128-bit length; ② Key mapping processing: input the 128-bit key and map it according to the mapping table, and map to get two sub-keys key1 and key2, each sub-key is 64 bits; ③ Generate sub-keys: process the two sub-keys key1 and key2 to obtain 16 sub-keys respectively; ④Double encryption of plaintext: After inputting the plaintext, first encrypt it once with key1 and then encrypt it twice with key2 to generate DES ciphertext; The RSA is specifically: Random large number generation: Randomly generate a set of large arrays N except even numbers and numbers divisible by 5; Large array screening: select 53 small prime numbers and use the remainder method to screen the large array N; Optimize the Miller-Rabin algorithm: use the Montgomery fast power algorithm to simplify the Miller-Rabin algorithm to perform modular multiplication operations on large numbers A and B, that is, Montgomery(A,B,N)=ABR ^-1 (modN); Generate large prime numbers p, q: Combine the above steps and IFPNJA to generate two large prime numbers p, q; RSA encrypted plaintext: Input the plaintext M, use two large prime numbers p and q to generate an RSA key to encrypt the plaintext to generate RSA ciphertext. 5. A hybrid decryption method for medical data safe storage according to the hybrid encryption method for safe storage of medical data according to claim 1, wherein the method comprises: Receive ciphertext C; Decrypt the key K in the ciphertext C with the RSA decryption key Kdb; The plaintext and the digital signature MA are decrypted by using the key K. 6. The hybrid decryption method for safe storage of medical data according to claim 5, wherein, after said decrypting said plaintext and said digital signature MA using said key K, further comprising: Get the public key Kea; Using the public key Kea and the decryption key Kdb to confirm the identity of the signature information; digitally processing the signature information to form the receiver's signature information; Send the receiver's signature information to the sender to confirm receipt of the information. 7. The hybrid decryption method for safe storage of medical data according to claim 6, characterized in that, after sending the recipient's signature information to the sender to confirm receipt of the information, the method further includes: Both sender and receiver delete said key K. 8. A hybrid decryption system oriented to the secure storage of medical data according to the hybrid decryption method for secure storage of medical data according to claim 5, wherein the system comprises: a receiving unit, configured to decrypt the key K in the ciphertext C by using the decryption key Kdb; The decryption unit uses the key K to decrypt the plaintext and the digital signature MA. 9. The hybrid decryption system facing medical data safe storage according to claim 8, characterized in that, Also includes a receiver processing unit for obtaining the sender's public key Kea; Using the public key Kea and the decryption key Kdb to confirm the identity of the signature information; digitally processing the signature information to form the receiver's signature information; Send the receiver's signature information to the sender to confirm receipt of the information. 10. A hybrid encryption and decryption method for safe storage of medical data, characterized in that the method comprises: The sender generates the key K for DES encryption; Using RSA to encrypt the key K to form ciphertext CK; Get the RSA public encryption key Keb; Using the RSA decryption key together with the public encryption key Keb to form a digital signature MA; Using the key K to encrypt plaintext and the digital signature MA; Combining the encrypted plaintext and encrypted digital signature MA with the ciphertext CK to form ciphertext C; Send the ciphertext C; The recipient receives the ciphertext C, and uses the RSA decryption key Kdb to decrypt the key K in the ciphertext C; Using the key K to decrypt the plaintext and the digital signature MA; The DES is specifically: ① Extended key length: expand the original DES 64-bit key to 128-bit length; ② Key mapping processing: input the 128-bit key and map it according to the mapping table, and map to get two sub-keys key1 and key2, each sub-key is 64 bits; ③ Generate sub-keys: process the two sub-keys key1 and key2 to obtain 16 sub-keys respectively; ④Double encryption of plaintext: After inputting the plaintext, first encrypt it once with key1 and then encrypt it twice with key2 to generate DES ciphertext; The RSA is specifically: Random large number generation: Randomly generate a set of large arrays N except even numbers and numbers divisible by 5; Large array screening: select 53 small prime numbers and use the remainder method to screen the large array N; Optimize the Miller-Rabin algorithm: use the Montgomery fast power algorithm to simplify the Miller-Rabin algorithm to perform modular multiplication operations on large numbers A and B, that is, Montgomery(A,B,N)=ABR ^-1 (modN); Generate large prime numbers p, q: Combine the above steps and IFPNJA to generate two large prime numbers p, q; RSA encrypted plaintext: Input the plaintext M, use two large prime numbers p and q to generate an RSA key to encrypt the plaintext to generate RSA ciphertext.