Management technology of key management

1, symmetric key management. Symmetric encryption is based on * * * confidentiality. Both parties who use symmetric encryption technology must ensure that they use the same key, ensure that the key exchange between them is safe and reliable, and at the same time, they must establish procedures to prevent key leakage and change keys. In this way, the management and distribution of symmetric keys will become a potentially dangerous and tedious process. The symmetric key is managed by public key encryption technology, which makes the corresponding management simpler and safer, and also solves the reliability and authentication problems in pure symmetric key mode. Traders can generate a unique symmetric key for each exchanged information (such as each EDI exchange) and encrypt the key with the public key, and then send the encrypted key to the corresponding traders together with the information encrypted with the key (such as EDI exchange). Because each information exchange student has a unique key, each transaction party no longer needs to maintain the key, and no longer needs to worry about the leakage or expiration of the key. Another advantage of this method is that even if a key is leaked, it will only affect one transaction, and will not affect all the trading relationships between the two parties. This method also provides a secure way for trading partners to issue symmetric keys.

2. Public key management/digital certificate. Trading partners can use digital certificates (public key certificates) to exchange public keys. The ITU standard X.509 defines digital certificate, which is equivalent to the ISO/IEC 9594-8: 195 standard jointly issued by ISO and IEC. A digital certificate usually contains a name that uniquely identifies the certificate owner (that is, the counterparty), a name that uniquely identifies the certificate publisher, the public key of the certificate owner, the digital signature of the certificate publisher, the validity period of the certificate, the serial number of the certificate, and so on. Certificate issuer is generally called Certification Authority (CA) and is trusted by all parties to the transaction. Digital certificate can identify traders, and it is one of the widely used technologies in e-commerce.

3. Standards and specifications related to key management. At present, relevant international standardization organizations have begun to formulate technical standards and specifications on key management. The Information Technology Committee (JTC 1) under ISO and IEC has drafted international standards and specifications on key management. The specification mainly consists of three parts: one is the key management framework; The second is to use the mechanism of symmetry technology; The third is the mechanism of technology asymmetry. This specification has now entered the voting stage of the draft international standard and will soon become a formal international standard.

digital signature

Digital signature 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. Digital signature can realize the authentication and non-repudiation of the original message.

ISO/IEC JTC 1 has been drafting relevant international standards and specifications. The preliminary name of this standard is "Digital Signature Scheme with Attachment for Information Technology Security Technology", which consists of an overview and an identity-based mechanism. According to records, in 400 BC, the ancient Greeks invented the permutation code. 188 1 year, the world's first telephone secrecy patent appeared. During the Second World War, the German military started the Enigma cipher machine, and cryptography played a very important role in the war.

With the development of information and digital society, people's awareness of the importance of information security and confidentiality is constantly improving, so in 1997, the American National Bureau of Standards published and implemented the American Data Encryption Standard (DES), and private forces began to fully participate in the research and application of cryptography, using DES, RSA, SHA and other encryption algorithms. With the increasing demand for encryption strength, AES and ECC have appeared recently.

Using encryption technology can achieve the following purposes:

Confidentiality: prevent the user's identity or data from being read.

Data integrity: prevent data from being changed.

Authentication: Ensure that the data comes from a specific party.

2. Introduction of encryption algorithms According to the different types of keys, modern encryption technologies can be divided into two categories: symmetric encryption algorithm (key encryption) and asymmetric encryption algorithm (public key encryption).

Symmetric key encryption system uses the same key for encryption and decryption, and both parties must obtain this key and keep it secret.

The encryption key (public key) and decryption key (private key) used in asymmetric key encryption system are different. In symmetric encryption algorithm, only one key is used to encrypt and decrypt information, that is, the same key is used for encryption and decryption. Commonly used algorithms are: DES (Data Encryption Standard): Data encryption standard, which is fast and suitable for encrypting a large amount of data.

3DES(Triple DES): Based on DES, a piece of data is encrypted three times with three different keys, which is more powerful.

AES (Advanced Encryption Standard): Advanced encryption standard, which is the next generation high-speed and high-security encryption algorithm standard;

In June 2000, NIST (National Institute of Standards and Technology) announced the adoption of a new key encryption standard selected from 65,438+05 candidate algorithms. Rijndael was chosen as the future AES. Rijndael was founded by researchers Joan Damon and Vincent Rimen in the second half of 1999. AES is increasingly becoming a practical standard for encrypting various forms of electronic data.

The American Institute of Standards and Technology (NIST) formulated a new advanced encryption standard (AES) specification on May 26th, 2002.

Algorithm principle AES algorithm is based on permutation and permutation operation. Arrangement is to rearrange data, and replacement is to replace one data unit with another. AES uses several different methods to perform permutation and permutation operations.

AES is an iterative symmetric key block cipher. It can use 128, 192 and 256-bit keys to encrypt and decrypt data with 128 bits (16 bytes). Unlike public key encryption using key pairs, symmetric key encryption uses the same key to encrypt and decrypt data. The number of bits of encrypted data returned by block cipher is the same as that of input data. Iterative encryption uses a circular structure in which input data is repeatedly permuted and replaced.

AES and 3DES algorithm name algorithm type key length speed decryption time (the construction machine tries 255 keys per second) Resource consumption AES symmetric block cipher 128, 192, 256 bits high149 billion years low 3DES symmetric feistel cipher 1 12 bits or.

RSA: Invented by RSA Company, it is a public key algorithm that supports variable-length keys, and the length of the file block to be encrypted is also variable.

DSA (Digital Signature Algorithm): Digital signature algorithm, which is a standard DSS (Digital Signature Standard);

ECC (Elliptic Curve Cryptography): Elliptic Curve Cryptography.

1976, because symmetric encryption algorithm can no longer meet the needs, Diffie and Hellman published an article entitled "New Trends in Cryptography", which introduced the concept of public key encryption. RSA algorithm was proposed by Rivet, Shamir and Adelman.

With the progress and perfection of large integer decomposition method, the improvement of computer speed and the development of computer network, RSA keys need to be continuously increased to ensure data security. However, the increase of key length greatly reduces the speed of encryption and decryption, and the hardware implementation becomes more and more unbearable, which brings a heavy burden to applications using RSA, so a new algorithm is needed to replace RSA.

In 1985, N.Koblitz and Miller proposed that elliptic curves should be applied to cryptographic algorithms based on the discrete logarithm problem ECDLP in point groups on elliptic curves over finite fields. ECDLP is a more difficult problem than factorization, and it is exponentially difficult.

Principle-difficult problem on elliptic curve The definition of discrete logarithm problem on elliptic curve ECDLP is as follows: Given prime number P and elliptic curve E, for Q=kP, find a positive integer K less than P when P and Q are known. It can be proved that it is easy to calculate q from k and p, but it is difficult to calculate k from q and p.

By matching the addition operation on the elliptic curve with the modular multiplication operation on the discrete logarithm, and matching the multiplication operation on the elliptic curve with the modular power operation on the discrete logarithm, the corresponding cryptosystem based on the elliptic curve can be established.

For example, corresponding to the Diffie-Hellman public key system, we can realize it on the elliptic curve in the following ways: select the generator P on E, which requires that there are enough group elements generated by P, and the communication parties A and B choose A and B respectively, which are confidential, but aP and bP are public, and the key used for communication between A and B is abP, which is unknown to the third party.

The corresponding ELGamal cryptosystem can be implemented on elliptic curves in the following ways:

Embedding plaintext M into Pm point on E, selecting a point B∈E, and each user selecting an integer A, 0.

K = kG[ where k and g are points on Ep(a, b), and k is an integer less than n (n is the order of point g)]

It is not difficult to find that given k and g, it is easy to calculate k according to the law of addition; But given k and g, it is relatively difficult to find k.

This is the difficult problem of elliptic curve encryption algorithm. We call point G as the base point, and k (k

Compared with RSA, ECC has absolute advantages in many aspects, mainly in the following aspects:

Strong anti-attack ability. With the same key length, it is many times more resistant to attack.

The calculation amount is small and the processing speed is fast. The overall speed of ECC is much faster than RSA and DSA.

Small storage space. Compared with RSA and DSA, ECC has much smaller key size and system parameters, which means that it takes up much less storage space. This is of great significance to the application of encryption algorithm in IC card.

Low bandwidth requirements. When encrypting and decrypting long messages, the three types of cryptosystems have the same bandwidth requirements, but when applied to short messages, the ECC bandwidth requirements are much lower. The low bandwidth requirement makes ECC have a broad application prospect in the field of wireless networks.

These characteristics of ECC will replace RSA and become a general public key encryption algorithm. For example, the maker of SET protocol has made it the default public key cryptography algorithm in the next generation SET protocol.

The following two are the security and speed comparison between RSA and ECC. Breakthrough time (MIPS year) RSA/DSA (key length) ECC key length RSA/ ECC key length ratio is105121065:10 7681326:/. 1010:10 2100600 35:1RSA and ECC safety module length safety generator 1.2B Safe3.0 163. 1, 023-bit RSA(ms) key pair generates 3.8 4, 708.3 signature 2.1(ecnra) 228.43.0 (ecdsa) authentication 9.9 (ecnra)12.710.7 (ecdsa) diffie-hellman key exchange 7.3 1, 654.0 RSA and ECC speed comparison hashing algorithm, also known as this conversion, is a compressed mapping, that is, the space of hash value is usually much smaller than that of input, and different inputs may be hashed into the same output, so it is impossible to uniquely determine the input value from the hash value. Simply put, it is the function of compressing messages of any length into message digests of fixed length.

Hash algorithm is mainly used for encryption algorithm in the field of information security. It converts some information with different lengths into 128 bits of garbled code, which is called hash value. In other words, hashing is to find the mapping relationship between data content and data storage address. Hash is a refinement of information, and its length is usually much smaller than that of information, and it is a fixed length. A strongly encrypted hash must be irreversible, which means that no part of the original information can be inferred from the hash result. Any change of input information, even if there is only one bit, will lead to obvious change of hash result, which is called avalanche effect. Hash should also prevent conflicts, that is, two pieces of information with the same hash result cannot be found. Hash results with these characteristics can be used to verify whether the information has been modified.

One-way hash function is generally used to generate message digest, key encryption and so on. Common ones are:

MD5 (Message Digest Algorithm 5): It is a one-way hash algorithm developed by RSA Data Security Company.

SHA (Secure Hash Algorithm): Data operation of any length can generate a value of 160 bits;

In 1993, Secure Hash Algorithm (SHA) was proposed by National Institute of Standards and Technology (NIST) and published as a federal information processing standard (FIPS publication 180). 1995, a revised version of FIPS PUB 180- 1 was released, commonly called SHA- 1. SHA- 1 is based on MD4 algorithm, and its design largely imitates MD4. Now it has become one of the most secure hash algorithms and is widely used.

Principle SHA- 1 is a data encryption algorithm. The idea of this algorithm is to receive a plaintext and then convert it into ciphertext (usually smaller) in an irreversible way. It can also be simply understood as the process of taking a series of input codes (called pre-mapping or information) and converting them into short and fixed number of output sequences, that is, hash values (also called information digest or information authentication codes).

The security of one-way hash function lies in its strong one-way operation process of generating hash value. If the password is embedded in the input sequence, no one can generate the correct hash value without knowing the password, thus ensuring its security. SHA blocks the input stream according to each block of 5 12 bits (64 bytes) to generate a 20-byte output, which is called information authentication code or information digest.

The maximum length of the input message in this algorithm is no more than 264 bits, and the output message is 160 bits. The input is processed in groups of 5 12 bits. SHA- 1 irreversible, anti-collision, good avalanche effect.

Digital signature can be realized by hash algorithm. The principle of digital signature is to convert the plaintext to be transmitted into message digest through a function operation (different plaintext corresponds to different message digest), and encrypt the message digest and transmit it to the receiver together with the plaintext. The receiver decrypts and compares the new message digest generated by the accepted plaintext with the message digest sent by the sender. The comparison results are consistent, indicating that the plaintext has not been changed. If it is inconsistent, it means that the plain text has been tampered with.

MAC (Information Authentication Code) is a hash result, in which part of the input information is a password, and only the participants who know this password can calculate and verify the validity of the MAC code again. The generation of MAC is shown in the following figure. Comparison between input information password hash function information authentication code SHA- 1 and MD5, since they are all derived from MD4, SHA- 1 is very similar to MD5. Accordingly, their strength and other characteristics are similar, but there are some differences:

Security of forced supply: The most significant and important difference is that SHA- 1 abstract is 32 bits longer than MD5 abstract. Using brute force technology, the difficulty of generating any message to make its digest equal to that of a given message is 2 orders of magnitude for MD5 and 2 orders of magnitude for SHA- 1. In this way, SHA- 1 is more powerful against forced attacks.

Security of cryptanalysis: Due to the design of MD5, it is vulnerable to cryptanalysis attacks, while SHA- 1 is not vulnerable to such attacks.

Speed: On the same hardware, SHA- 1 runs slower than MD5. Comparison between symmetric algorithm and asymmetric algorithm

The above summarizes the principles of the two encryption methods. Generally speaking, there are several differences:

First, in management, public key cryptography algorithm can achieve its goal with less resources, and in the distribution of keys, the difference between them is exponential (one is n, the other is n). Therefore, private key cryptography algorithm is not suitable for wide area network, and more importantly, it does not support digital signature.

Secondly, in terms of security, public key cryptography is almost impossible to crack because it is based on unsolved mathematical problems. For the private key encryption algorithm, it is theoretically impossible to crack in AES, but from the perspective of computer development. Public keys have more advantages.

Thirdly, in terms of speed, the software implementation speed of AES has reached several megabytes or tens of megabytes per second. It is 1000 times of the public key, and if it is implemented by hardware, the proportion will be expanded to1000 times.

The choice of encryption algorithm In the last chapter, symmetric decryption algorithm and asymmetric encryption algorithm have been introduced. Many people wonder: Which one should be used in actual use?

It should be determined according to its own use characteristics. Because the speed of asymmetric encryption algorithm is much slower than that of symmetric encryption algorithm, when we need to encrypt a large amount of data, we suggest using symmetric encryption algorithm to improve the encryption and decryption speed.

Symmetric encryption algorithm can't realize signature, so the signature can only be asymmetric algorithm.

Because the key management of symmetric encryption algorithm is a complicated process, which directly determines its security, asymmetric encryption algorithm can be considered when the data volume is small.

In practice, we usually use asymmetric encryption algorithm to manage the key of symmetric algorithm, and then use symmetric encryption algorithm to encrypt data. In this way, we combine the advantages of two kinds of encryption algorithms, which not only realizes the advantages of fast encryption, but also realizes the advantages of safe and convenient key management.

If the encryption algorithm is selected, how many bits of key will be used? Generally speaking, the longer the key, the slower the running speed, which should be selected according to the security level we actually need. Generally speaking, 1024 bits are recommended by RSA, 160 bits by ECC and 128 by AES.

The application of cryptography in modern times, with the popularization of commercial applications of cryptography, public key cryptography has received unprecedented attention. In addition to the traditional password application system, PKI system is mainly based on public key cryptography, providing encryption, signature, authentication, key management, distribution and other functions.

Secure communication: Secure communication is the driving force of cryptography. When the public-private key cryptosystem is used for secure communication, the information receiver can only decrypt the information if he knows the corresponding key.

Digital signature: Digital signature technology can replace the traditional handwritten signature, and from the perspective of security, digital signature has a good anti-counterfeiting function. It has a wide application environment in government agencies, military and commercial fields.

Secret * * * sharing: Secret * * * sharing technology refers to splitting a secret message into n pieces of information through cryptographic technology, which is called * * * sharing factor and distributed to n members. Only * * sharing factors of k(k≤n) legal members can recover the secret message, and neither they nor m(m≤k) members know the secret message. Secret sharing technology can be used to control any secret information, commands, etc. It needs to be controlled by many people.

Authentication function: transmit sensitive information on the open channel, verify the authenticity and integrity of the message by signature technology, and verify the identity of the communication subject by verifying the public key certificate.

Key management: key is a fragile and important part of the security system, and public key cryptosystem is a powerful tool to solve key management; Public key cryptosystem is used for key negotiation and generation, and both parties in secure communication do not need to enjoy secret information in advance; Use public key cryptosystem for key distribution, protection, key storage and key recovery.

In addition to the above general functions, the following systems can also be designed and implemented based on public key cryptosystem: secure e-commerce system, electronic cash system, electronic election system, electronic bidding system, electronic lottery system and so on.

The emergence of public key cryptosystem is the basis of cryptography from traditional government and military applications to commercial and civil applications. At the same time, the development of Internet and e-commerce has opened up a broader prospect for the development of cryptography.

The future of encryption algorithm With the improvement of calculation methods, the acceleration of computer running speed and the development of network, more and more algorithms have been cracked.

At the 2004 International Crypto Conference (Crypto'2004), Professor Wang Xiaoyun of Shandong University in China gave a report on decoding MD5, HAVAL- 128, MD4 and RIPEMD, which shocked the top international cryptographers present and meant that these algorithms would be eliminated from the application. Subsequently, SHA- 1 was also announced to be cracked.

There are three attack experiments that have an impact on DES in history. 1997, using 70,000 computers in various countries at that time, the key of DES was cracked in 96 days. 1998, the electronic frontier foundation (EFF) cracked the DES key in 56 hours with a special computer made of $250,000. 1999, EFF completed the cracking work in 22 hours 15 minutes. Therefore. DES, which has made outstanding contributions, can no longer meet our growing demand.

Recently, a group of researchers successfully decomposed a 5 12-bit integer factorization factor, announcing the cracking of RSA.

We say that the security of data is relative, and it can be said that under certain conditions, it is safe for a certain period of time. With the development of hardware and network, or the appearance of another Wang Xiaoyun, the commonly used encryption algorithms may be cracked in a short time. At that time, we had to use longer keys or more advanced algorithms to ensure the security of data, so the encryption algorithm still needs to be continuously developed and improved to provide higher encryption security strength and operation speed.

Look at these two algorithms, one is from DES to 3DES and then to AES, and the other is from RSA to ECC. Its development prospect is considered from the following aspects: simplicity of key, low cost, simplicity of management, complexity of algorithm, security of confidentiality and rapidity of calculation. Therefore, the future development of the algorithm must also proceed from these perspectives. In practice, the two algorithms are often combined, and a new algorithm combining the advantages of the two algorithms will appear in the future. At that time, the realization of e-commerce will be faster and safer.