2.2 Password Technology
2.2.1 Calculation Safety
The technical foundation of information security is the password technology. Current various encryption algorithms have no theoretical security, only calculation
Fullness.
The contemporary cryptography requires three basic assumptions, namely:
Randomness assumptions: The random bit sequence that physically generates evenly distributed in a single region is possible.
Physical assumption: Physical protection of data stored in a single region is possible, number of long distance transmission
It is difficult to implement physical protection.
Calculation hypothesis: reasonable calculation time has one amount of boundary, and the one-way function is stored in a reasonable calculation time.
In the case, it is easier to ask for reverse difficulties.
The three basic assumptions of cryptography are the basic premise of information system design, but they can only approach them in reality, but cannot
From theory, the requirements of these three assumptions have been proven. Naturally, it is impossible to prove the security of a password algorithm.
.
A password algorithm has anti-breakage before it is in its use or in the information it protects.
The force is possible, and it can also be said to achieve the design safety goals. And expecting an algorithm to keep safely
Sexual is unrealistic, because the development of future mathematics may make the password cracking method achieved breakthrough progress. Not only theory
There is no way to exist in this algorithm, even in practical applications, due to cryptographic analysis methods and computer computing
The rapid development of power, it can be considered that the algorithm with calculation safety will no longer have calculation safety after a period of time.
Sex. Such an example can be seen everywhere, and the DES algorithm is one of them.
There is no way to prove the security of an encryption method; you can only prove unsafe or failure. This is
The so-called proves false. The examination of cryptographic experts - long review is currently owned, about safety
The only evidence that can be enabled.
2.2.2 Traditional password system
The traditional symmetric key system is based on replacement and replacement, and the security is calculated.
Take DES as an example, from it to the federal standard, it has always argued that it has been arguing. Controversy focus
The length of the key and the safety of the algorithm itself. For the current computing power, the 56-bit key length DES has already
Atten, it is dangerous, so the key length of the expert proposal is increasing. But this is just a time to increase password crack.
Moreover, it can still be crack in theory. In 1998, the Electronics New Foundation founded a violent cracking DES algorithm.
Computer. This computer is named DES deep crack, test 90 billion key per second; it can be found in average 4.5 days
A 56-bit DES key. In 1999, a Distributed Internet Key Finding the Distributed DES Key Named Distributed.net
The project can test 250 billion keys per second. DES's extension algorithm 3DES sets the key length to 112 bits, while most
Modern algorithms have at least 128-bit keys. US government new advanced encryption standard AES supports 128, 192 and 256-bit
Key length. Of course, using a longer key will affect the algorithm itself's add-secret speed (3 heavy DES algorithm in many environments)
It is too slow), which is also one of the weighs that must be made in terms of security and cost. Another problem is concentrated in each round
The S-box used in iteration, because the S-box design standard is not disclosed, therefore people suspect if they know the S-box structure method,
It is possible to find the weakness of the S box.
For DES's cryptographic analysis, the most promising is differential cryptographic analysis and linear password analysis. Although these two areas
The number of attacks required is significantly less than exhaustive attacks, but due to the prerequisites of the analysis, it is relatively high (for 56-bit dense
The length of the key, the former needs 247 options, the latter requires 247 plaintext), making these two methods for longer keys
There is only theoretical sense.
2.2.3 public key cryptosystem
The development of public key cryptography is the greatest revolution in the history of the entire password development. Public key algorithm based on mathematical letters
number. The security of contemporary public key cryptosystem relies on several mathematical problems, such as large numbers, discrete logarithms,
Discrete logarithm problems on the elliptic curve, etc., these problems have not been undesirable in mathematical proven, so the public key cryptographic system is not in theoretical security. In addition, the calculation speed of the public key password algorithm is large below the symmetric key algorithm.
In many password protocols, symmetrical encryption algorithm encrypts clear text messages, and then encrypt symmetrical encryption with public key algorithm.
The key used by the algorithm.
Take RSA as an example, it is based on large number decomposition problems in mathematics, so security depends on a large number of decomposition.
. Although large numbers are still a problem in mathematics, due to the continuous enhancement and factors of computer computing power
The decomposition algorithm has been continuously improved, and the RSA algorithm has been threatened. The secret article provided by the RSA Labs in 1999 has been
Decoups, its key length is 155 decimal, and the decomposition method used by the attacker is a general digital screening method. Therefore choosing
Be careful when the key length of the RSA, recently, the relatively secure key length of the cryptographic expert suggestion is 10
24 to 2048 bits.
In theory, there are three of the possible attacks of the RSA algorithm: exhaustive attack, mathematical attack, timing attack. among them
Time attacks are worth mentioning. Time attack is similar to the thief by observing others to turn the safe deposit of the safe deposit.
The test code, the attacker determines the private key by logging the time used by the computer decryption message. Timing attacks are not only available for attacks
Hit RSA, and can be used to attack other public key cryptosystems, because this attack is completely unpredictable and it is only
Depending on the plaintext, the timing attack has a big threat. Despite this, for the current computing power, take the above
The recommended key length, RSA is calculated.
.
2.2.4 Password Protocol
Password protocol, referring to two or more parties to use cryptography to complete a series of ordered steps for a task, the purpose is
In order to prevent attackers from implementing spoofing and illegal access information. Various cryptographic protocols focus on satisfying five basics in information security
One or more of this attribute. You can construct complex protocols based on simple protocols, or even an agreement
.
You can use a simple example to explain the importance of the password protocol, if there is no security key allocation scheme,
Then, the strength of the password algorithm is better and no good. The result is equivalent to establishing a super-security gate, while the gate
The key is lost at the door.
In theory, it proves that only one secret it is safe, but the first time I need to use the number of randhes once, this is
Unable to meet in the information system (see below); Second, various cryptographic protocols are the symmetric cryptographic system and public key described in the previous
The cryptographic system is constructed, and the two itself has no theoretical security; once again, the real application must be one
There is also a consideration of complexity and system cost. Therefore, it is actually just one part in a certain part,
It does not guarantee the security of the entire complex system.
2.2.5 Random
The random number is a very important component in password technology, almost a computer security system that uses encryption technology.
All random numbers, the unique values of the key, the protocol, etc., or the like or use to use the auxiliary information or the initialization vector. This
Safety of some systems often rely on randomness of these random numbers. If the randomness of the random is not safe enough, the whole system
The pool is likely to be broken by the attacker.
Real random number sequence satisfies unpredictability and non-repeatability, but the real random number is only God created.
Computers can only produce pseudo-random numbers. The father of the computer, Feng Niman, has pointed out: "Anyone who wants people to generate the arithmetic method
The number of people in the machine is in the confused state. "He said this, is a certainty object such as a computer
It is impossible to get true random things. The random number of the computer depends on the initial seed, if the seed is the same,
The resulting random sequence is the same. Taking the m-sequence random number generator as an example, it can get a random random number, but
In fact, its cycle cycle is relatively large, such as the 50-level M sequence random number generator's cycle cycle is 2
50 times, the output will still be repeated after a certain period of time, i.e., only a pseudo-random number. To produce a real random, you can only use the physical noise source by means of the strength of God. Unfortunately, real physics
The noise source is difficult to obtain, it is difficult to use directly in the information system, and the random number generated by the noise source after the circuit simulation
Although the random number created with God is quite close, it is not true to the real number. There are some examples in this regard: NSA is hard
Electronic interference diode is used in the circuit circuit, generate random numbers; some systems use air turbulence in disk drives or
It is the random arrival time of the continuous network packet, and the random arrival time of the continuous network packet. Of course, the random number and true
The difference between the number of characters can be ignored from a practical perspective, but it must be clear that both are strictly different.
, Can't wait. my country's existing WNG series random number generator chip is generated in accordance with the currency model, it is
The physical noise source chip of the work.
2.2.6 Public Key Infrastructure PKI
The current hotspot current hotspot is the public key infrastructure PKI, here is discussed in this regard.
PKI (Public Key Infrastructure) is the cornerstone of the e-commerce security technology platform, which is published by the public key
Password technology, digital certificate, certificate issuance agency (CA), and basic components such as security policies on public keys
Result. PKI is a system using public key technology to realize e-commerce security, is an infrastructure, network communication, network
The trading is to use it to ensure safe.
PKI is a system or platform for providing public key encryption and digital signature services to manage keys and certificates. One
The agency can establish a secure network environment by using the PKI framework management key and certificate. PKI mainly includes four departments
Certificate (X.509 V3) and certificate abolition list CRL (X.509 V2); CA / RA operation protocol; CA / RA operation protocol;
A Management Agreement; CA Policy. A typical, complete, and effective PKI application should have at least the following part:
Certificate Center CA, X.500 Directory Server, Security WWW Server, Web (Safety Tong) with High Strength Password Algorithm (SSL)
Letter platform), self-developing security application system, complete PKI.
In order to ensure the safety of information in e-commerce transactions (confidentiality, true integrity, and non-negotiation). Need to make
The parties of the transaction can trust each other and verify each other through a trust verification mechanism. This trust and trust verification mechanism are
Implementation is implemented by the digital certificate (that is, the identity of its identity) by participating in e-commerce.
Digital certificates are the identity proves in information exchange and business trading activities online, with uniqueness and
authoritative. To meet this requirement, you need to establish a organization that participates in the e-commerce alliances, which is specially responsible for numbers.
The issuance and management of certificates to ensure true and reliability of digital certificates. This institution is the Digital Certificate Certification Center (CERT
Ificate authority, hereinafter referred to as CA). CA is a key link to ensure online electronic transaction security, it produces
Digital certificates for all entities involved in the online trading. The main responsibilities of CA include: certificates, certificate updates
, Certificate abolition, certificate and CRL announcement, online query, certificate certification and development policy of certification status.
In order to promote the smooth development of e-commerce in China, some units and departments have built their own CA system.
Among them, there is more affected China Telecom CA Security Certification System (CTCA), Shanghai E-Commerce CA Certification Center (Sheca)
And China Financial Certification Center (CA), etc.
Despite some progress, the system designed and implemented fully applied PKI technology is also facing severe challenges. in
Some major problems must be solved before the PKI technology is widely used and effective. These issues include: sharing,
