In order to well maintain the ecological operation of the PoC contribution proof mechanism and ensure the security of the increasingly demanding "cloud storage" function, the CyberVein technical team has proposed a basic method to verify the availability and integrity of files-PDP data integrity verification protocol , Is to insert multiple encrypted bytes "sentinel" into the data block to "defend", and integrate the strict PDP detection mechanism to make the data block semi-encrypted but unreadable and non-intrusive. Every step of the entire process will be written into the blockchain, tamper-proof and traceable. Next, I will analyze this based on the relevant official information. Maybe you only need to spend these 3 minutes to read carefully to have a certain understanding of PDP.
Is PDP a heavenly book? It's just that you didn't read it right. I
believe many people will think that the technical principle is like a heavenly book, such as a description of CVT in its PDP mechanism: "PDP can check whether the remote cloud server retains a file, which is composed of a collection of n blocks. The data owner processes the data file to generate some metadata to store it locally. Then the file is sent to the server, and the owner deletes the local copy of the file. The owner verifies the ownership of the file in the challenge response protocol." Above this The meaning of the passage is probably the PDP scheme in CVT. When you store a file on the chain, the cloud server will use N "blocks" to store the file separately, and the local disk can delete the original file to free up more Space for you. There is no need to worry about the loss of files, because the nodes will record and supervise together.
Now let’s talk about it. If you can operate this PDP data integrity verification protocol, what should you do?
PDP has been around for 20 years and is currently the most widely used and most mature storage integrity certification mechanism in the distributed storage field. It can quickly determine whether the data on the remote node is complete, and is mainly used to detect the integrity of large data files. An application scenario of CVT's PDP mechanism is as follows: For
example, a PDP application scenario:
1. Arthur requires Bobo to store a set of information;
2. Arthur does not store this set of information for many reasons, such as insufficient memory or storage on his own computer Not safe;
3. After a while, Arthur asked Chloe to confirm whether Bobo still stored this set of information;
4. Of course, Chloe did not understand the content of this set of information, but was just a witness.
Note: In order to facilitate understanding, we have Role substitution: Arthur is the user, Bobo is the storage miner, and Chloe is the third-party reviewer (hereinafter referred to as TPA).
The completion of this application scenario has the following two aspects:
1. The setup phase (you must first have a tool to complete the task):
1. In the initialization phase,
Arthur inserts her hard disk into the computer, the computer and the hard disk read and write the PDP software at the same time, assign the variables to the default values, and set the controls to the default state. Arthur will have his own key after successful registration.
2. The user runs the key generation algorithm to generate a key pair (pk, sk).
Arthur runs the key according to the instructions, and the algorithm and key pair (pk, sk) are generated.
3. The stored file is divided into blocks F=( m1, m2,..., mn)
block refers to classification, which is convenient for searching in the future. File F is stored in blocks in the PoC system. These blocks have a fixed amount of storage (depending on the space contributed by the miners), and they can also be linked to other blocks. If the saved file is small, you only need to put it in one block. If the saved file is large, the more parts will be divided into other blocks, and an empty block will be created, which will link to all other parts of the file. This empty block is similar to a large envelope, which will cover all parts of the entire file.
4. Run the data block label generation algorithm to generate a homomorphic label set Φ for each data block in the file,
that is, after Arthur has classified the stored files, he will mark the files of her stored blocks, and this mark will be broadcast to all data blocks. Keep bottom
5. Arthur saves the data file F and signature collection Φ into the cloud at the same time, deletes the local {F, Φ}
The file F stored by Arthur is authenticated and uploaded to the "cloud database", and passed The system searched and found Bobo with enough storage space, that is, Bobo whose files were stored in the "cloud database".
At this time, Arthur's local disk space will not be occupied, because Bobo has already stored the file F. According to the size of storage file F (178MB), Bobo will receive corresponding token rewards.
2. Challenge stage (if you want to find this file)
1. As the verifier, the user or TPA periodically initiates integrity verification requests.
Arthur can initiate a verification request when he wants to check whether the file F is still in the cloud intact, or if he needs to download the file again. Of course, Arthur can also entrust Chloe to verify that the file F exists in Bobo in its entirety.
2. Randomly pick c block indexes {s1, s2,...,sc} from the file F block index set [1, n], and select a random number vi for each index si, and combine the two to generate The challenge request is sent to the server.
At this time, Arthur followed the PDP operation (don't be afraid, there are related instructions and steps, basically no brains), and the system will automatically generate a "search warrant" and send it to the "cloud database".
3. The server as the prover, according to the data file {F,Φ} stored on its server, invokes the evidence generation algorithm and the integrity evidence P, and returns it to the verifier.
The server will quickly index the file F. If the file is complete, it will feed back the "Proof in the Cloud P" to Arthur in real time to confirm that Bobo has stored the file F in its entirety, and has not been lost or deleted.
4. After the verifier accepts the evidence, it executes the evidence detection algorithm to verify whether the evidence is correct.
If Chloe conducts the investigation and collects the "Proof P in the cloud" on behalf of him, Arthur is still worried, and can use the evidence detection algorithm to verify the authenticity and validity of the "Proof P in the cloud".
The minimalism of PDP data integrity verification protocol
The traditional methods of uploading and downloading files or browsing web pages all require location-based addressing to obtain information from the server one at a time. Once the server fails, is restricted or is attacked, the file will be lost or the webpage cannot be opened (error 404), or the IP will be deleted or the server will be shut down, which will make the user unable to use the file. If this file is needed by many people, then everyone has to download it before it can be used, causing a huge waste of storage space. PDP is both decentralized and minimal. You need to upload or download files in the future, no longer need to run to the central server, and there is no problem of information loss or tampering, which can realize file sharing and save storage space . PDP actually reconstructs the way we transmit, obtain, and store information, completely change the way we view information, and become a part of our daily lives.
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