User sensitive data protection system based on cloud service and block chain

Abstract

According to the user sensitive data protection system based on the cloud service and the block chain, an SM3 algorithm is adopted to fuse biological characteristics and dynamic tokens to generate an encryption credential, high-security identity authentication is achieved, differential fragmentation encryption is carried out on data based on semantic classification, Rabin threshold fragmentation and AES + ECC double-layer encryption is adopted for data of the highest security level, and the security level of the data is improved. A dynamic node optimization model is designed; an optimization coefficient is calculated according to the capacity, the transmission rate and the fault rate; the storage efficiency is improved by more than 40% in combination with a time period regulation factor; the node temperature and the vibration frequency are monitored in real time through a sensor; and verifying the validity period of the dynamic token and the fragment permission mark by using an intelligent contract to realize GDPR compliance fine-grained access control. The system remarkably improves the anti-attack capability and storage reliability of data, and is suitable for high-sensitivity scenes such as highway toll collection, finance and medical treatment.

Description

Technical Field

[0001] The present invention belongs to the field of data security technology, and in particular relates to a user sensitive data protection system based on cloud services and blockchain. Background Art

[0002] With the rapid development of cloud computing and blockchain technology, the storage and protection of user sensitive data face dual challenges. In existing technologies, mainstream solutions can be divided into the following two categories:

[0003] 1. Data protection solutions based on centralized cloud storage typically rely on encryption services provided by a single cloud service provider, using AES or RSA algorithms to centrally encrypt and store data. However, if the centralized server is attacked (such as SQL injection or DDoS), it may lead to a complete data leak. In addition, the permission policy is hard-coded in the central server and cannot dynamically adapt to multi-user collaboration scenarios. At the same time, data is encrypted and stored in a holistic form. If some storage nodes are damaged, there is a lack of effective sharding redundancy mechanism, and full recovery requires relying on backup servers, which takes up to several hours.

[0004] 2. Blockchain-based distributed storage solutions. These solutions distribute data across blockchain nodes and leverage smart contracts for operational auditing. However, they still suffer from the following issues: Simple node selection strategies (such as random assignment or round-robin) fail to account for real-time node performance differences. Experiments show that when node transmission rate differences exceed 50%, data storage latency increases by over 30%. Most solutions only implement a single layer of encryption for complete data storage, allowing attackers to obtain the entire ciphertext by stealing a single node, making them vulnerable to quantum computing brute force attacks. Furthermore, the physical state of storage nodes (temperature, humidity) is not monitored, requiring manual intervention to repair data loss caused by hardware failures.

[0005] Existing technologies that combine cloud services and blockchain still have technical bottlenecks such as lack of dynamic optimization, disconnection between sharding and encryption, and insufficient compliance. Summary of the Invention

[0006] In response to the above-mentioned shortcomings, the present invention provides a user sensitive data protection system based on cloud services and blockchain. The dual-engine architecture based on cloud service dynamic optimization and blockchain security enhancement reduces the risk of data leakage, reduces transmission delays, improves the fault tolerance of redundant design, and meets the requirements of GDPR data privacy regulations.

[0007] The present invention is achieved through the following technical solutions:

[0008] A user sensitive data protection system based on cloud services and blockchain, including a user identity authentication module, a data preprocessing module, a blockchain node management module, a distributed storage module, a dynamic monitoring and migration module, and an access control module;

[0009] The user identity authentication module is used to verify the user's identity through multi-factor biometrics. Specifically, the user terminal collects facial images and fingerprint information, encrypts them locally, and transmits them to the authentication server; the server calls a pre-stored biometric template for comparison. If a match is successful, a one-time dynamic token (OTP) is generated using the SM3 algorithm and bound to the user's identity ID; the dynamic token is associated with the user's private key to generate an encrypted access credential, which includes a timestamp and the scope of access rights;

[0010] The data pre-processing module is used to segment and encrypt sensitive data, specifically including: performing semantic analysis on the data based on a preset sensitive word library, and dividing the security level according to personal identity, financial account, and health information;

[0011] Select the fragmentation strategy based on the security level: For the highest security level data, use (N, K) threshold fragmentation based on the Rabin algorithm to split the data into N ≥ 5 fragments, where any K = 3 fragments can reconstruct the original data;

[0012] Execute for each data segment in turn:

[0013] First layer of encryption: Use the AES-256 algorithm to generate a symmetric key Ksym to encrypt the data fragment;

[0014] Second layer encryption: uses the elliptic curve encryption algorithm to encrypt Ksym with the user's public key PKuser to generate the key encapsulation ciphertext Ckey;

[0015] Bind the Ckey to the encrypted data fragment, add the fragment sequence number and data hash value to form the final ciphertext fragment;

[0016] The blockchain node management module is used to dynamically select storage nodes, specifically including: periodically obtaining node performance data from the cloud service provider API, including: storage capacity remaining value Cr, bit B; average transmission rate Cs, unit Mbps; historical failure rate Fr, calculated as the percentage of node downtime in the past 30 days;

[0017] The node selection coefficient YX is calculated using the following formula:

[0018]

[0019] Where Cr_max, Cs_max, and Fr_max are the preset maximum reference values, k is the dynamic adjustment factor, and its value range is 0.8 to 1.2. x1+x2+x3=1, and x1=0.4, x2=0.4, and x3=0.2;

[0020] Select the first three nodes with the highest YX values ​​as the primary storage nodes, and the rest as backup nodes;

[0021] The distributed storage module is used to store ciphertext fragments in blockchain nodes, specifically including:

[0022] Call the smart contract to bind each ciphertext shard to the physical address of the storage node and generate a data location index table;

[0023] The following information is recorded in the new block in the blockchain ledger: shard storage timestamp; storage node ID; shard hash value, calculated using SHA-256; associated smart contract address;

[0024] The dynamic monitoring and migration module is used to monitor node status in real time and trigger migration, specifically including:

[0025] Deploy sensors on storage nodes to periodically collect the following parameters:

[0026] Temperature value T, unit ℃, sampling frequency 1 time / minute;

[0027] Humidity value H, unit %RH, sampling frequency 1 time / minute;

[0028] Network delay D, in milliseconds, measured using the ICMP protocol;

[0029] Migration is triggered when any of the following conditions are met:

[0030] T>40℃ or H>70% or D>500ms;

[0031] The migration process includes:

[0032] Select the node with the second highest YX value from the list of backup nodes;

[0033] Copy the original node data shards to the new node through the P2P protocol;

[0034] Update the storage node ID and positioning index table in the blockchain ledger;

[0035] The access control module is used to verify user permissions and decrypt data, specifically including: when a user submits an access request, he needs to provide encrypted access credentials and the ID of the data shard to be accessed;

[0036] The smart contract executes the following verification chain:

[0037] Verify the validity period of the dynamic token and the legitimacy of the signature. The validity period shall not exceed 5 minutes.

[0038] Query the blockchain ledger for the user's permission to the target shard, which can be read / write / deny.

[0039] Verify that the hash value of the data shard is consistent with that when it was stored;

[0040] If all verifications pass, the smart contract returns the corresponding Ckey to the user. The user uses the private key SKuser to decrypt and obtain Ksym, and then decrypts the data shard.

[0041] As a further improvement of the present invention, in the sharding strategy, for financial account data, (N=7, K=4) threshold sharding is adopted, and each shard is stored in nodes in different geographical areas; the shard sequence number is embedded in the ciphertext header in binary encoding form, and a CRC-32 check code is attached.

[0042] As a further improvement of the present invention, the dynamic adjustment factor k is determined as follows: when the system is in a high-load period from 9:00 to 18:00 every day, k=1.2 to give priority to nodes with high transmission rates; and k=1.0 in other periods.

[0043] As a further improvement of the present invention, when verifying permissions, if a user requests access to multiple shards, the smart contract needs to verify that the permission marks of all shards are "allowed"; for the reorganization of decrypted data shards, it is necessary to obtain the decryption results of at least K shards, and verify the integrity of the shards through the Rabin algorithm.

[0044] As a further improvement of the present invention, the sensor data acquisition further includes measuring the vibration frequency Fv of the node device by an accelerometer, in Hz. When Fv>200 Hz for 10 seconds, data migration is forcibly triggered.

[0045] As a further improvement of the present invention, the blockchain ledger adopts the following structure to store operation logs:

[0046] Each block contains the Merkle tree root hash, and the leaf nodes are the hash values ​​of the sharding operation records;

[0047] Operation records include: storage / migration / deletion operation type, executor's digital signature, and data shard ID.

[0048] As a further improvement of the present invention, after decrypting the data shards, the user terminal needs to locally calculate the hash value of the reconstructed data and compare it with the original hash recorded in the blockchain account book. If there is any inconsistency, an alarm is triggered and access is terminated.

[0049] The present invention adopts a system architecture of two-factor dynamic authentication, hierarchical sharding encrypted storage, dynamic node optimization algorithm, environmental perception migration extreme and on-chain smart contract control to build a sensitive data protection system that combines cloud-chain collaboration, sharding management and control, and environmental perception. Through dynamic policy optimization, layered security reinforcement, and real-time environmental response, it solves the contradictions in security, efficiency, and reliability in the integration of cloud storage and blockchain, and provides a full life cycle solution for sensitive data protection. Two-factor dynamic authentication integrates biometrics (face / fingerprint) and a one-time dynamic token (OTP), generates encrypted credentials through the SM3 algorithm, and realizes high-security identity verification. Hierarchical sharding encrypted storage is based on a sensitive vocabulary to automatically identify data types (identity / finance / health), divide security levels, and use Rabin threshold sharding for highly sensitive data (such as 7 shards require 4 shards to reconstruct), combined with AES+ECC double-layer encryption to ensure that data cannot be restored if a single node is leaked. The dynamic node optimization algorithm constructs a quantitative evaluation model to dynamically calculate the node optimization coefficient (YX value) based on storage capacity, transmission rate, and failure rate. It also introduces a time-based adaptive adjustment factor (k) to prioritize high-speed nodes during high-load periods, improving system response efficiency. The environmentally aware migration mechanism uses sensors to monitor node temperature, humidity, and network latency in real time. When thresholds are exceeded, P2P data migration is automatically triggered. The storage location index is then updated synchronously with the blockchain ledger to ensure data traceability.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] 1. The present invention adopts a node selection algorithm based on a multi-dimensional quantitative evaluation of capacity, rate and failure rate, and designs a dynamic adjustment factor (k) to achieve adaptive optimization of storage strategy during the storage period. Compared with the traditional polling strategy, the storage efficiency is improved by more than 40%.

[0052] 2 The present invention designs a three-level protection system of "semantic classification → threshold sharding → differential encryption", which forces multi-region shard storage of financial data (N=7, across 3 geographical regions), and embeds CRC checksum and binary serial number in the shard header to prevent tampering and sequence disorder of the shards.

[0053] 3. This invention combines physical sensor monitoring (temperature / humidity / vibration) with blockchain storage, defines a hard migration threshold (such as temperature > 40°C), and achieves lossless data migration through the P2P protocol, reducing the data loss rate caused by hardware failure by 90%.

[0054] 4. This invention embeds the principle of “minimum necessary permissions” in permission verification, the access token automatically expires (5 minutes), and supports the “right to be forgotten” required by GDPR - the shard key association is destroyed with one click through the smart contract.

[0055] 5. This invention adopts the ECC+SM3 national secret algorithm combination, and the shard key encapsulation ciphertext (Ckey) can be seamlessly replaced with a quantum-resistant encryption module to cope with future quantum computing attack threats. DETAILED DESCRIPTION

[0056] The present invention is further described below. In the examples, unless otherwise specified, the technical means used are conventional technical means in the art.

[0057] Example 1

[0058] A user sensitive data protection system based on cloud services and blockchain, including a user identity authentication module, a data preprocessing module, a blockchain node management module, a distributed storage module, a dynamic monitoring and migration module, and an access control module;

[0059] The user identity authentication module is used to verify the user's identity through multi-factor biometrics. Specifically, the user terminal collects facial images and fingerprint information, encrypts them locally, and transmits them to the authentication server; the server calls a pre-stored biometric template for comparison. If a match is successful, a one-time dynamic token (OTP) is generated using the SM3 algorithm and bound to the user's identity ID; the dynamic token is associated with the user's private key to generate an encrypted access credential, which includes a timestamp and the scope of access rights;

[0060] The data pre-processing module is used to segment and encrypt sensitive data, specifically including: performing semantic analysis on the data based on a preset sensitive word library, and dividing the security level according to personal identity, financial account, and health information;

[0061] Select the fragmentation strategy based on the security level: For the highest security level data, use (N, K) threshold fragmentation based on the Rabin algorithm to split the data into N ≥ 5 fragments, where any K = 3 fragments can reconstruct the original data;

[0062] In the sharding strategy, for financial account data, (N=7, K=4) threshold sharding is adopted, and each shard is stored in nodes in different geographical areas; the shard sequence number is embedded in the ciphertext header in binary encoding form, and a CRC-32 check code is attached.

[0063] Execute for each data segment in turn:

[0064] First layer of encryption: Use the AES-256 algorithm to generate a symmetric key Ksym to encrypt the data fragment;

[0065] Second layer encryption: uses the elliptic curve encryption algorithm to encrypt Ksym with the user's public key PKuser to generate the key encapsulation ciphertext Ckey;

[0066] Bind the Ckey to the encrypted data fragment, add the fragment sequence number and data hash value to form the final ciphertext fragment;

[0067] The blockchain node management module is used to dynamically select storage nodes, specifically including: periodically obtaining node performance data from the cloud service provider API, including: storage capacity remaining value Cr, bit B; average transmission rate Cs, unit Mbps; historical failure rate Fr, calculated as the percentage of node downtime in the past 30 days;

[0068] The node selection coefficient YX is calculated using the following formula:

[0069]

[0070] Wherein, Cr_max, Cs_max, and Fr_max are preset maximum reference values, k is a dynamic adjustment factor with a value range of 0.8 to 1.2, x1+x2+x3=1, and x1=0.4, x2=0.4, and x3=0.2; the value of the dynamic adjustment factor k is determined as follows: when the system is in the high-load period from 9:00 to 18:00 every day, k=1.2 to give priority to nodes with high transmission rates; and k=1.0 in other periods.

[0071] Select the first three nodes with the highest YX values ​​as the primary storage nodes, and the rest as backup nodes;

[0072] The distributed storage module is used to store ciphertext fragments in blockchain nodes, specifically including:

[0073] The smart contract is called to bind each ciphertext shard to the physical address of the storage node and generate a data location index table. When verifying permissions, if the user requests access to multiple shards, the smart contract needs to verify that the permission marks of all shards are "allowed". For the reorganization of decrypted data shards, the decryption results of at least K shards need to be obtained, and the shard integrity must be verified through the Rabin algorithm.

[0074] The following information is recorded in the blockchain ledger to the new block: shard storage timestamp; storage node ID; shard hash value, calculated using SHA-256; associated smart contract address. The blockchain ledger uses the following structure to store operation logs:

[0075] Each block contains the Merkle tree root hash, and the leaf nodes are the hash values ​​of the sharding operation records;

[0076] Operation records include: storage / migration / deletion operation type, executor's digital signature, and data shard ID.

[0077] The dynamic monitoring and migration module is used to monitor node status in real time and trigger migration, specifically including:

[0078] Deploy sensors on storage nodes to periodically collect the following parameters:

[0079] Temperature value T, unit ℃, sampling frequency 1 time / minute;

[0080] Humidity value H, unit %RH, sampling frequency 1 time / minute;

[0081] Network delay D, in milliseconds, measured using the ICMP protocol;

[0082] Migration is triggered when any of the following conditions are met:

[0083] T>40℃ or H>70% or D>500ms;

[0084] Sensor data collection also includes measuring the vibration frequency Fv of the node device through an accelerometer, in Hz. When Fv>200Hz for 10 seconds, data migration is forcibly triggered.

[0085] The migration process includes:

[0086] Select the node with the second highest YX value from the list of backup nodes;

[0087] Copy the original node data shards to the new node through the P2P protocol;

[0088] Update the storage node ID and positioning index table in the blockchain ledger;

[0089] The access control module is used to verify user permissions and decrypt data, specifically including: when a user submits an access request, he needs to provide encrypted access credentials and the ID of the data shard to be accessed;

[0090] The smart contract executes the following verification chain:

[0091] Verify the validity period of the dynamic token and the legitimacy of the signature. The validity period shall not exceed 5 minutes.

[0092] Query the blockchain ledger for the user's permission to the target shard, which can be read / write / deny.

[0093] Verify that the hash value of the data shard is consistent with that when it was stored;

[0094] If all verifications pass, the smart contract returns the corresponding Ckey to the user. The user uses the private key SKuser to decrypt and obtain Ksym, and then decrypts the data shard.

[0095] After decrypting the data fragments, the user terminal needs to calculate the hash value of the reconstructed data locally and compare it with the original hash recorded in the blockchain account book. If there is any inconsistency, an alarm will be triggered and access will be terminated.

[0096] Application Example 1

[0097] The system of Example 1 is applied to high-speed vehicle statistics and billing, mainly used to manage highway vehicle traffic data management, and the specific steps are as follows:

[0098] 1. Vehicle Identity Authentication

[0099] Multi-factor authentication:

[0100] The vehicle sends an encrypted identification code (including license plate number and vehicle ID) through the ETC device, while the toll booth camera captures the license plate image;

[0101] The authentication server compares the ETC identification code with the license plate OCR recognition result, and generates a dynamic token (OTP) after matching. The algorithm is OTP = SM3 (vehicle ID || timestamp || toll station number);

[0102] Generate a pass credential {vehicle ID, OTP, permission: [pass record read], validity period: 3 minutes}.

[0103] 2. Pass Data Fragmentation and Encryption

[0104] Data classification:

[0105] Vehicle traffic data is categorized into: basic information (license plate, vehicle model), billing information (mileage, rate), and statistical information (traffic flow, time period distribution);

[0106] Billing information is marked as the highest security level (Level 3).

[0107] Sharding and encryption:

[0108] Sharding strategy: Rabin (5,3) threshold sharding is used for billing data, dividing it into 5 fragments, and any 3 of them can be reconstructed;

[0109] Multi-layer encryption:

[0110] 1. AES-256: Generates an independent key Ksym for each shard to encrypt data;

[0111] 2. ECC encryption: Use the road section management public key PKroad to encrypt Ksym and generate Ckey;

[0112] Fragment identification: A binary serial number (such as 00101) and a CRC-16 checksum are appended to the fragment header. The ciphertext format is [serial number|CRC|C_{key}|ciphertext].

[0113] 3. Blockchain Node Storage

[0114] Node selection:

[0115] Obtain performance parameters from the road segment server (nodes A / B / C) and provincial data center (node ​​D):

[0116] Node A: Cr = 10TB, Cs = 1Gbps, Fr = 0.3%;

[0117] Node D: Cr = 50TB, Cs = 5 Gbps, Fr = 0.1%;

[0118] Calculate the optimal coefficient (k = 1.2 during peak hours):

[0119]

[0120] Nodes D and A are preferred for storing billing data shards.

[0121] Distributed storage:

[0122] Store 5 shards on node D (3 shards) and node A (2 shards);

[0123] The smart contract records the shard hash and storage path to the blockchain ledger and generates an index:

[0124] {"Shard ID":"T001-2","Node Address":"10.200.1.101","Associated Road Section":"G80 Guangkun Expressway","Merkel Root":"0x7b2e...9a4f"}.

[0125] 4. Abnormal Monitoring and Migration

[0126] Environmental monitoring:

[0127] Node D deploys a temperature and humidity sensor, which detects a temperature of T = 45°C (threshold ≤ 40°C).

[0128] Network delay D = 600 ms (threshold ≤ 500 ms).

[0129] Migration execution:

[0130] 1. Select backup node B (YX=0.28) to replace node D;

[0131] 2. Migrate shard data through the IPFS protocol and update the node address in the blockchain ledger to 10.200.1.102;

[0132] 3. Synchronously modify the billing system data index table to ensure uninterrupted billing queries.

[0133] 5. Data Access and Billing Settlement

[0134] Permission request: The section administrator submits the OTP and shard ID list [T001-1, T001-3, T001-5].

[0135] Smart Contract Verification:

[0136] Verify OTP validity period (≤3 minutes) and digital signature;

[0137] The administrator's permission to the shard in the query ledger is marked as "read";

[0138] Verify shard hash consistency (migrated data matches the original hash).

[0139] Decryption and billing:

[0140] Return the Ckey of the three shards, and decrypt it using the road segment private key SKroad to obtain Ksym;

[0141] After decrypting the fragments, the complete billing data (mileage = 150km, rate = 0.5 yuan / km) is reassembled using the Rabin algorithm, and the chargeable amount is calculated to be 75 yuan;

[0142] The local verification reconstructed data hash is consistent with the blockchain record to confirm the accuracy of billing.

[0143] 6. Anti-tampering test

[0144] Simulate an attacker to tamper with one shard of node A. Due to CRC check failure and hash mismatch, the system automatically refuses to decrypt.

[0145] The dynamic node selection in this application example makes the billing data query response time ≤200ms (traditional solutions ≥800ms), and the dynamic token expires in 3 minutes, preventing historical access records from being abused for a long time, which complies with the requirements of the "Cybersecurity Law".

[0146] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention is defined by the claims. Persons skilled in the art may make various modifications or equivalent substitutions to the present invention within the spirit and scope of protection of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present invention.

Claims

1. A user sensitive data protection system based on cloud services and blockchain, characterized by: It includes user identity authentication module, data preprocessing module, blockchain node management module, distributed storage module, dynamic monitoring and migration module and access control module; The user identity authentication module is used to verify the user's identity through multi-factor biometrics. Specifically, the user terminal collects facial images and fingerprint information, encrypts them locally, and transmits them to the authentication server; the server calls a pre-stored biometric template for comparison. If a match is successful, a one-time dynamic token is generated. The dynamic token is generated using the SM3 algorithm and bound to the user's identity ID; the dynamic token is associated with the user's private key to generate an encrypted access credential, which includes a timestamp and the scope of access rights; The data pre-processing module is used to segment and encrypt sensitive data, specifically including: performing semantic analysis on the data based on a preset sensitive word library, and dividing the security level according to personal identity, financial account, and health information; Select the fragmentation strategy based on the security level: For the highest security level data, use (N, K) threshold fragmentation based on the Rabin algorithm to split the data into N ≥ 5 fragments, where any K = 3 fragments can reconstruct the original data; Execute for each data segment in turn: First layer of encryption: Use the AES-256 algorithm to generate a symmetric key Ksym to encrypt the data fragment; Second layer encryption: uses the elliptic curve encryption algorithm to encrypt Ksym with the user's public key PKuser to generate the key encapsulation ciphertext Ckey; Bind the Ckey to the encrypted data fragment, add the fragment sequence number and data hash value to form the final ciphertext fragment; The blockchain node management module is used to dynamically select storage nodes, specifically including: periodically obtaining node performance data from the cloud service provider API, including: storage capacity remaining value Cr, bit B; average transmission rate Cs, unit Mbps; historical failure rate Fr, calculated as the percentage of node downtime in the past 30 days; The node selection coefficient YX is calculated using the following formula: Where Cr_max, Cs_max, and Fr_max are the preset maximum reference values, k is the dynamic adjustment factor, and its value range is 0.8 to 1.

2. x1+x2+x3=1, and x1=0.4, x2=0.4, and x3=0.2; Select the first three nodes with the highest YX values ​​as the primary storage nodes, and the rest as backup nodes; The distributed storage module is used to store ciphertext fragments in blockchain nodes, specifically including: Call the smart contract to bind each ciphertext shard to the physical address of the storage node and generate a data location index table; The following information is recorded in the new block in the blockchain ledger: shard storage timestamp; storage node ID; shard hash value, calculated using SHA-256; associated smart contract address; The dynamic monitoring and migration module is used to monitor node status in real time and trigger migration, specifically including: Deploy sensors on storage nodes to periodically collect the following parameters: Temperature value T, unit ℃, sampling frequency 1 time / minute; Humidity value H, unit %RH, sampling frequency 1 time / minute; Network delay D, in milliseconds, measured using the ICMP protocol; Migration is triggered when any of the following conditions are met: T>40℃ or H>70% or D>500ms; The migration process includes: Select the node with the second highest YX value from the list of backup nodes; Copy the original node data shards to the new node through the P2P protocol; Update the storage node ID and positioning index table in the blockchain ledger; The access control module is used to verify user permissions and decrypt data, specifically including: when a user submits an access request, he needs to provide encrypted access credentials and the ID of the data shard to be accessed; The smart contract executes the following verification chain: Verify the validity period of the dynamic token and the legitimacy of the signature. The validity period shall not exceed 5 minutes. Query the blockchain ledger for the user's permission to the target shard, which can be read / write / deny. Verify that the hash value of the data shard is consistent with that when it was stored; If all verifications pass, the smart contract returns the corresponding Ckey to the user. The user uses the private key SKuser to decrypt and obtain Ksym, and then decrypts the data shard.

2. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: In the sharding strategy, for financial account data, threshold sharding (N=7, K=4) is adopted, and each shard is stored in nodes in different geographical regions; The fragment sequence number is embedded in the ciphertext header in binary code form, and a CRC-32 checksum is appended.

3. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: The dynamic adjustment factor k is determined as follows: when the system is in the high-load period from 9:00 to 18:00 every day, k=1.2 to give priority to nodes with high transmission rates; and k=1.0 in the rest of the time.

4. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: During permission verification, if a user requests access to multiple shards, the smart contract must verify that the permission marks of all shards are "allowed." For the reorganization of decrypted data shards, it is necessary to obtain the decryption results of at least K shards and verify the integrity of the shards using the Rabin algorithm.

5. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: The sensor data collection also includes measuring the vibration frequency Fv of the node device through an accelerometer, in Hz. When Fv>200 Hz for 10 seconds, data migration is forcibly triggered.

6. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: The blockchain ledger uses the following structure to store operation logs: Each block contains the Merkle tree root hash, and the leaf nodes are the hash values ​​of the sharding operation records; Operation records include: storage / migration / deletion operation type, executor's digital signature, and data shard ID.

7. The user sensitive data protection system based on cloud services and blockchain according to claim 1 is characterized by: After decrypting the data fragments, the user terminal needs to calculate the hash value of the reconstructed data locally and compare it with the original hash recorded in the blockchain account book. If there is any inconsistency, an alarm will be triggered and access will be terminated.

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