Digital certificate is a series of data that identifies the identity information of all parties in network communication, and its function is similar to that of ID card in real life. It is published by an authoritative organization, and people can use it to identify each other in communication.

The simplest certificate contains a public key, a name, and.

Digital signature. Generally speaking, the certificate also includes the valid time of the key, the name of the certificate authority, the serial number of the certificate and other information. The format of the certificate follows the international standard ITUT X.509

The standard X.509 digital certificate contains the following contents:

Version information of the certificate;

Serial number of certificates, each certificate has a unique serial number;

The signature algorithm used by the certificate;

The name of the certificate issuer, and the naming rules generally adopt X.500 format;

The validity period of the certificate, now the universal certificate generally adopts UTC time format, and its timing range is1950-2049;

The name of the certificate owner, and the naming rules generally adopt X.500 format;

The public key of the certificate owner;

Signature of the certificate issuer on the certificate.

Using digital certificate and symmetric and asymmetric cryptography to establish a strict identity authentication system to ensure that information will not be stolen by others except the sender and receiver; Information is not tampered with during transmission; The sender can confirm the identity of the receiver through the digital certificate; The sender cannot deny his information.

2. Why use a digital certificate?

Thanks to the technology of Internet e-commerce system, customers who shop online can get the information of businesses and enterprises very conveniently and easily, but at the same time, it also increases the risk of abusing some sensitive or valuable data. Both buyers and sellers must ensure that all financial transactions conducted on the Internet are true and reliable, and all parties to the transaction, such as customers, businesses and enterprises, have absolute confidence. Therefore, the Internet e-commerce system must ensure very reliable security technology, that is, it must ensure the four elements of network security, namely, the confidentiality of information transmission, the integrity of data exchange, the undeniability of sending information and the certainty of the identity of traders.

Confidentiality of information

Business information in the transaction needs to be kept confidential. For example, if you know the account number and user name of a credit card, you may be stolen. If the information of ordering and payment is known by competitors, you may lose business opportunities. Therefore, in the information dissemination of e-commerce, encryption is generally needed.

The certainty of trader's identity

The two sides of online transactions are probably strangers, thousands of miles apart. In order to make the transaction successful, we must first confirm the identity of the other party. Merchants should consider whether the customer is a liar or not, and customers will also worry about whether the online shop is a black shop that plays fraud. Therefore, it is the premise of the transaction to confirm the identity of the other party conveniently and reliably. For banks, credit card companies and sales stores that provide services to customers or users, in order to carry out service activities safely, confidentially and reliably, identity authentication must be carried out. For the relevant sales stores, they don't know the card number of the credit card used by customers, and the stores can only give the credit card confirmation to the bank. Banks and credit card companies can use all kinds of confidentiality and identification means to confirm whether the customer's identity is legal, and at the same time, they should also prevent the problem of refusal to pay, and confirm the order and order collection information.

undeniable

Due to the ever-changing business conditions, once the transaction is reached, it cannot be denied. Otherwise, it will inevitably harm the interests of one party. For example, when ordering gold, the price of gold is low, but after receiving the order, the price of gold rises. If the acquirer can deny the actual time of receiving the order, or even the fact of receiving the order, then the orderer will suffer losses. Therefore, all links in the communication process of electronic transactions must be undeniable.

Nonmodifiability

Due to the ever-changing business conditions, once the transaction is reached, it should not be denied. Otherwise, it will inevitably harm the interests of one party. For example, when ordering gold, the price of gold is low, but after receiving the order, the price of gold rises. If the acquirer can deny the actual time of receiving the order, or even the fact of receiving the order, then the orderer will suffer losses. Therefore, all links in the communication process of electronic transactions must be undeniable.

Digital security certificate provides a way to verify identity on the Internet. The security certificate system mainly adopts public key system, and others include symmetric key encryption, digital signature and digital envelope.

We can use digital certificates and establish a strict identity authentication system by using symmetric and asymmetric encryption technologies to ensure that information will not be stolen by others except the sender and receiver; Information is not tampered with during transmission; The sender can confirm the identity of the receiver through the digital certificate; The sender cannot deny his information.

3. The principle of digital authentication

Digital certificate adopts public key system, that is, a pair of matching keys are used for encryption and decryption. Each user sets a specific private key that only he knows, and uses it to decrypt and sign; At the same time, a public key is set to be made public by myself and enjoyed by a group of users for encryption and signature verification. When sending confidential documents, the sender uses the public key of the receiver to encrypt the data, and the receiver uses its own private key to decrypt the data, so that the information can reach the destination safely and correctly. The encryption process is guaranteed to be irreversible by digital means, that is, only the private key can be used for decryption.

RSA is commonly used in public key cryptosystems. Its mathematical principle is to decompose a large number into the product of two prime numbers, and encrypt and decrypt them with two different keys. Even if the plaintext, ciphertext and encryption key (public key) are known, the decryption key (private key) cannot be deduced by calculation. According to the current level of computer technology, it will take thousands of years to crack the RSA key of 1024. Public key technology solves the management problem of key distribution, and merchants can disclose their own public keys while retaining their private keys. Shoppers can encrypt the sent information with a well-known public key and transmit it safely to merchants, who can then decrypt it with their own private keys.

If the user needs to send encrypted data, the sender needs to use the digital certificate (public key) of the receiver to encrypt the data, and the receiver uses its own private key to decrypt the data, thus ensuring the security and confidentiality of the data.

In addition, users can realize the integrity and validity of data through digital signature, and only need to encrypt data with private key. Because the private key only belongs to the user, it can guarantee the uniqueness of the signature file, that is, the data is signed and sent by the signer himself, and the signer cannot or cannot deny it; The data has not been modified during the period from issuing to receiving, and the issued document is true.

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4. How are digital certificates issued?

Digital certificates are issued by certification centers. Root certificate is the basis of establishing trust relationship between certification center and users. Users must download and install digital certificates before they can use them.

Certification center is a management organization that can issue digital certificates to users to confirm their identity. In order to prevent the forgery of digital certificates, the public key of the certification center must be reliable, and the certification center must publish its public key or provide the electronic certificate of the superior certification center to prove the validity of its public key. The latter method leads to the emergence of multi-level authentication centers.

The process of issuing digital certificates is as follows: the user generates his own key pair and sends the public key and some personal identification information to the authentication center. After authentication, the authentication center will perform some necessary steps to ensure that the request is indeed sent by the user. Then, the certification center will issue a digital certificate to the user, which contains information such as the user and his key, as well as a digital certificate confirming the public key of the certification center. When users want to prove the legitimacy of their public keys, they can provide this digital certificate.

5. Encryption technology

Because data may be eavesdropped by intruders and lose confidential information during transmission, encryption technology is the main security measure in e-commerce and the most commonly used security measure. Encryption technology is to use technical means to turn important data into garbled (encrypted) transmission, and then restore (decrypt) by the same or different means after reaching the destination.

Encryption includes two elements: algorithm and key. Encryption algorithm is a step of combining ordinary text (or understandable information) with a number (key) to produce incomprehensible ciphertext. Keys and algorithms are equally important for encryption.

A key is an algorithm used to encode and decode data. In terms of security, we can ensure the information communication security of the network through appropriate key encryption technology and management mechanism. The cryptographic system of key encryption technology can be divided into symmetric key system and asymmetric key system.

Accordingly, data encryption technology can be divided into two categories, namely symmetric encryption (private key encryption) and asymmetric encryption (public key encryption). Symmetric encryption is represented by data encryption standard (DNS) algorithm, and asymmetric encryption is usually represented by RSA(Rivest Shamir Ad 1eman) algorithm. Symmetric encryption has the same encryption key and decryption key, but asymmetric encryption has different encryption keys and decryption keys. The encryption key can be made public, and the decryption key needs to be kept secret.

6. Symmetric encryption technology

Symmetric encryption adopts symmetric cryptography, which is characterized by using the same key for file encryption and decryption, that is, the encryption key can also be used as the decryption key. This method is called symmetric encryption algorithm in cryptography. Symmetric encryption algorithm is simple and fast to use, with short key and difficult to decipher. In addition to the data encryption standard (DNS), another symmetric key encryption system is the International Data Encryption Algorithm (IDEA), which is better than DNS in encryption and does not require such high computer functions. The IDEA encryption standard is used by PGP (quite good privacy) systems.

There are several problems in symmetric encryption algorithm in e-commerce transactions;

(1) It is necessary to provide a secure channel for both communication parties so as to negotiate a * * * same key when communicating for the first time. Direct face-to-face negotiations may be unrealistic and difficult to implement, so the two sides may need to negotiate by mail, telephone and other relatively unsafe means;

(2) The number of keys is difficult to manage. Because each collaborator needs to use different keys, it is difficult to adapt to a large number of information exchanges in the open society;

(3) Symmetric encryption algorithms generally cannot provide information integrity authentication. It cannot verify the identity of the sender and the receiver;

(4) The management and distribution of symmetric keys is a potentially dangerous and troublesome process. Symmetric encryption is realized on the basis of confidentiality. Both parties using symmetric encryption technology must ensure that they use the same key, ensure the safety and reliability of key exchange between them, and set up procedures to prevent key leakage and change keys.

7. Asymmetric encryption technology

1976, American scholars Dime and Henman proposed a new key exchange protocol, which solved the problems of public information transmission and key management, and allowed the two communication parties to exchange information on insecure media and reach a consistent key safely. This is the "public key system". Compared with symmetric encryption algorithm, this method is also called asymmetric encryption algorithm.

Different from symmetric encryption algorithm, asymmetric encryption algorithm needs two keys: public key and private key. The public key and the private key are a pair. If the data is encrypted with the public key, it can only be decrypted with the corresponding private key. If the data is encrypted with a private key, it can only be decrypted with the corresponding public key. Because encryption and decryption use two different keys, this algorithm is called asymmetric encryption algorithm.

The basic process for traders to exchange confidential information by using asymmetric encryption algorithm is as follows: trader A generates a pair of keys and discloses one of them to other traders as a public key; Trader B who obtains the public key encrypts confidential information with the key and sends it to trader A; Party A decrypts the encrypted information with another private key saved by itself. Party A can only decrypt any information encrypted with its own public key with its own private key.

Asymmetric encryption algorithm has good confidentiality, and does not need end users to exchange keys, but encryption and decryption take a long time and are slow, so it is not suitable for encrypting files, but only suitable for encrypting a small amount of data.

In the Window NT security system of Microsoft, the public key system is mainly used to encrypt the private key. If each user wants to encrypt data, he needs to generate a pair of his own key pairs. The public key and asymmetric encryption and decryption algorithm in the key pair are public, but the private key should be properly kept by the key owner.

The actual process of encrypting and transmitting files using public keys includes four steps:

(1) The sender generates its own private key and encrypts it with the receiver's public key, and then transmits it to the receiver through the network;

(2) The sender encrypts the file to be transmitted with its own private key, and then transmits the encrypted file to the receiver through the network;

(3) The receiver decrypts with its own public key to obtain the sender's private key;

(4) The receiver decrypts the file with the sender's private key to obtain the plaintext form of the file.

Because only the receiver has its own public key, even if others get the encrypted private key of the sender, the security of the private key is guaranteed because it cannot be decrypted, thus ensuring the security of the transmitted file. In fact, the above two encryption and decryption processes are realized in the process of file transmission: the encryption and decryption of the file itself and the encryption and decryption of the private key are realized by the private key and the public key respectively.

8. Digital signature technology

Encrypting files only solves the confidentiality problem of transmitted information, and other means are needed to prevent others from destroying the transmitted files, and how to determine the identity of the sender. This means a digital signature. In e-commerce system, digital signature technology plays a particularly important role, which is used for source authentication, integrity service and non-repudiation service in e-commerce security service. In e-commerce, a perfect digital signature should have the ability that the signer can't deny it, others can't forge it, and can verify the authenticity in front of a notary.

There are many ways to realize digital signature. At present, public key encryption technology is widely used in digital signature, such as PKCS (public key cryptography standards), digital signature algorithm, x.509 and PGP(Pretty Good Privacy) based on RSA data security. 1994 The American Institute of Standards and Technology issued the digital signature standard, which made the public key encryption technology widely used. The public key encryption system adopts asymmetric encryption algorithm.

The current digital signature is based on public key system, which is another application of public key encryption technology. The main way is that the message sender generates a hash value (or message digest) of 128 bits from the message body. The sender encrypts this hash value with his own private key to form the sender's digital signature. Then, the digital signature will be sent to the recipient of the email as an attachment. The receiver of the message first calculates the hash value (or message digest) of 128 bits from the received original message, and then decrypts the digital signature attached to the message with the public key of the sender. If the two hash values are the same, the receiver can confirm that the digital signature belongs to the sender. The original message can be authenticated by digital signature.

Signing a written document is a means to confirm the document, which has two functions: first, because a person's signature is difficult to deny, it confirms the fact that the document has been signed; Second, because the signature is not easy to forge, it confirms the true facts of the document.

There are similarities between digital signature and written document signature. Using digital signature can also confirm the following two points: first, the information was sent by the signer; Second, the information has not been modified from release to receipt. In this way, digital signatures can be used to prevent electronic information from being tampered with because it is easy to be modified, or to send information in the name of others. Or send (receive) a letter and deny it.

There are three widely used digital signature methods, namely: RSA signature, DSS signature and Hash signature. These three algorithms can be used separately or together. Digital signature is realized by encrypting and decrypting data through cryptographic algorithm, and digital signature can be realized through DES calculation and RSA algorithm. However, these three technologies are more or less flawed, or there are no mature standards.

The biggest convenience of using RSA or other public key cryptography algorithms is that there is no key distribution problem (the more complex the network, the more network users, the more obvious its advantages). Because public key encryption uses two different keys, one is the public key and the other is the private key. The public key can be stored in the system directory, in the unencrypted e-mail, on the yellow pages of the telephone (business telephone) or on the bulletin board, and any user on the Internet can obtain the public key. The private key is user-specific and held by the user himself, and can decrypt the information encrypted by the public key.

The digital signature technology in RSA algorithm is actually realized by a hash function. The characteristic of digital signature is that it represents the characteristics of a file. If the file changes, the value of the digital signature will also change. Different files will get different digital signatures. One of the simplest hash functions is to accumulate the binary code of the file and take the last few digits. Hash function is public to both parties who send data.

DSS digital signature is jointly developed by National Institute of Standardization and National Security Bureau. Because it is promulgated and implemented by the US government, it is mainly used by companies that have business dealings with the US government, and other companies rarely use it. It is only a signature system, and the US government does not advocate the use of any encryption software that weakens the government's eavesdropping ability, believing that this is in the national interest of the United States.

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Hash signature is the most important digital signature method, also known as digital digest or digital fingerprint. Unlike RSA digital signature, which is a separate signature, this digital signature method closely links the digital signature with the information to be sent, which is more suitable for e-commerce activities. Compared with transmitting the contract and signature separately, combining the contents of the business contract with the signature will increase the credibility and security. The encryption method of digital digest, also known as SHA (Secure Hash Algorithm) or MD5 (MD standard of message digest), was designed by RonRivest. This coding method uses a one-way hash function to "abstract" the plaintext to be encrypted into a series of ciphertexts with 128 bits. This series of ciphertexts, also known as digital fingerprints, have a fixed length and different plaintext abstracts must be consistent. In this way, this string of abstracts can be used as a "fingerprint" to verify whether the plaintext is "true".

Only by adding digital signature and verification can the secure transmission on the open network be truly realized. The file transfer process with digital signature and verification is as follows:

(1) The sender first obtains the digital signature from the original text with a hash function, then encrypts the digital signature with the developer's private key with a public key system, and attaches the encrypted digital signature to the original text to be sent;

(2) The sender selects a key to encrypt the file and transmits the encrypted file to the receiver through the network;

(3) The sender encrypts the key with the public key of the receiver and transmits the encrypted key to the receiver through the network;

(4) The receiver decrypts the key information with its own private key to obtain the plaintext of the key;

(5) the receiver decrypts the file with the secret key to obtain an encrypted digital signature;

(6) The receiver decrypts the digital signature with the public key of the sender to obtain the plaintext of the digital signature;

(7) The receiver recalculates the digital signature with the obtained plaintext and hash function, and compares it with the decrypted digital signature. If the two digital signatures are the same, it means that the file was not destroyed during transmission.

If a third party impersonates the sender to send a file, because the receiver uses the sender's public key when decrypting the digital signature, as long as the third party does not know the sender's private key, the decrypted digital signature and the calculated digital signature must be different. This provides a secure way to confirm the identity of the sender.

A secure digital signature assures the receiver that the file really comes from the purported sender. Since the private key of the signature is only kept by the sender himself, no one else can make the same digital signature, so he cannot deny that he participated in the transaction.

Although both the encryption and decryption process of digital signature and the encryption and decryption process of private key use public key system, the implementation process is just the opposite, and the key pairs used are also different. Digital signature uses the sender's key pair, the sender encrypts with his own private key, and the receiver decrypts with the sender's public key. This is a one-to-many relationship: anyone who owns the sender's public key can verify the correctness of the digital signature, while the encryption and decryption of the private key use the receiver's key pair, which is a many-to-one relationship: anyone who knows the receiver's public key can send encrypted information to the receiver, and only the only person who owns the receiver's private key can decrypt the information. In fact, users usually have two pairs of keys, one for encrypting and decrypting digital signatures and the other for encrypting and decrypting private keys. This method provides higher security.

9. Digital timestamp technology

In the development of e-commerce, digital signature technology has also been developed. Digital timestamp technology is a variant of digital signature technology.

Time is very important information in e-commerce transaction documents. In a written contract, the date of signing the document is as important as the signature to prevent the document from being forged and tampered with. DTS(digita 1 Time Stamp Service) is one of the security services of online e-commerce, which can provide the security protection of date and time information of electronic files, and is provided by a specialized agency.

If a timestamp is added to a signature, it is a digital signature with a digital timestamp.

Time stamp is an encrypted voucher document, which includes three parts:

(1) Abstract); Time stamp of the file;

(2) Date and time when 2)DTS received the document;

(3) Digital signature of DTS.

Generally speaking, the process of time stamp generation is as follows: users first encrypt files that need time stamps with Hash codes to form abstracts, and then send the abstracts to DTS. DTS encrypts (digitally signs) the file after adding the date and time information of receiving the file summary, and then sends it back to the user.

The time when the document is signed in writing is written by the signer himself, but the digital time stamp is not. It was added by the authentication unit DTS according to the time when DTS received the document.

10.SSL security protocol

SSL security protocol was originally designed and developed by Netscape Communications Company, also called "Secure Sockets Layer Protocol", which is mainly used to improve the security coefficient of data between applications. The whole concept of SSL protocol can be summarized as: a protocol to ensure the security of transactions between any client and server with secure sockets, which involves all TC/IP applications.

SSL security protocol mainly provides three services:

Legitimacy authentication of users and servers

Authenticate the legitimacy of users and servers so that they can ensure that data will be sent to the correct clients and servers. Both the client and the server have their own identification numbers, which are numbered by the public key. In order to verify whether the user is legitimate, the Secure Sockets Layer protocol requires digital authentication when shaking hands to exchange data to ensure the legitimacy of the user.

Encrypt data to hide the transmitted data.

The encryption technologies used in Secure Sockets Layer protocol include symmetric key technology and public key technology. Before the data exchange between the client and the server, the initial handshake information of SSL is exchanged, which is encrypted by various encryption technologies to ensure its confidentiality and data integrity, and authenticated by digital certificates. This can prevent illegal users from deciphering.

Protect the integrity of data

Secure Sockets Layer protocol provides information integrity service by using hash function and secret sharing method, and establishes a secure channel between client and server, so that all services processed by Secure Sockets Layer protocol can reach their destinations completely and accurately during transmission.

It should be noted that the Secure Sockets Layer protocol is a protocol to ensure the security of computer communication and protect the communication dialogue process. For example, when a client connects to a host, it should first initialize the handshake protocol and then establish SSL. Enter the dialogue. Until the end of the session, the Secure Sockets Layer protocol will encrypt the whole communication process and check its integrity. Such a conversation period counts as a handshake. In the HTTP protocol, every connection is a handshake, so compared with HTTP. The communication efficiency of Secure Sockets Layer protocol will be higher.

(1) connection stage: the customer greets the service provider through the network, and the service provider replies;

(2) Password exchange stage: the password recognized by both parties is exchanged between the client and the server, generally using RSA cryptographic algorithm, and some using Diffie-Hellmanf and Fortezza-KEA cryptographic algorithms;

(3) conference password stage: customers and service providers generate conference passwords for mutual calls;

(4) check stage: check the password obtained by the service provider;

(5) Customer authentication stage: verifying the credibility of customers;

(6) In the terminal stage, customers and service providers exchange terminal information.

When the above actions are completed, the data transmission between them will be encrypted, and the other party will recover the encoded data after receiving the data. Even if the thief gets the coded data on the network, he can't get readable and useful data without the original cryptographic algorithm.

When sending, the information is encrypted with a symmetric key, and the symmetric key is encrypted with an asymmetric algorithm, and then two packets are bundled together for transmission.

The process of receiving is just the opposite of sending. First, open the package encrypted with the symmetric key, and then decrypt it with the symmetric key.

In the process of e-commerce transaction, due to the participation of banks, according to SSL protocol, customers' purchase information is first sent to merchants, who then forward the information to banks. After verifying the legality of customer information, the bank informs the merchant that the payment is successful, and the merchant then informs the customer that the purchase is successful and sends the goods to the customer.

SSL security protocol is the earliest network security protocol used in e-commerce in the world, and it is still used by many online stores. In traditional mail-order activities, customers first look for commodity information, and then remit money to merchants, who send goods to customers. Here, merchants can be trusted, so customers pay merchants first. In the early days of e-commerce, merchants were also worried that customers would not pay after purchase or use expired credit cards, so they hoped the bank would certify them. SSL security protocol is produced under this background.

The basic point of SSL protocol operation is the merchant's commitment to the confidentiality of customer information. But in the above process, we can also notice that SSL protocol is beneficial to merchants and not to customers. Customer information is transmitted to the merchant first, and then transmitted to the bank after the merchant reads it, so the security of customer information is threatened. It is necessary for merchants to authenticate customers, but in the whole process, merchants lack authentication for customers. In the initial stage of e-commerce, this problem has not attracted people's attention because most of the participants in e-commerce are large companies with high reputation. With the rapid increase of manufacturers participating in e-commerce, the authentication problem of manufacturers is becoming more and more prominent, and the shortcomings of SSL protocol are completely exposed. SSL protocol will be gradually replaced by new e-commerce protocols (such as SET).

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1 1. Set the security protocol.

Dealing with e-commerce on the open Internet to ensure the security of data transmission between buyers and sellers has become an important topic of e-commerce. In order to overcome the shortcomings of SSL security protocol, meet the growing security needs of electronic transactions, and meet the market requirements for transaction security and cost performance, VISA international organizations and other companies such as MasterCard, Microsoft, IBM, etc. * * * Jointly formulated the Secure Electronic Transaction Bulletin (SET). This is an open electronic payment system specification, based on electronic money established for online transactions. On the premise of retaining the customer's credit card authentication, SET adds the authentication of merchant identity, which is very important for transactions that need to pay money. Because of its reasonable design, SET protocol has won the support of many large companies and consumers, and has become the industrial standard of global network, and its transaction form will become the norm of "e-commerce" in the future.