MD5 Detailed Manual. Which prawn to me.

MD5 has theoretically been broken.

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The MD5 information digest algorithm is a widely used cryptographic hash function that generates a 128-bit (16-byte) hash value to ensure that the message is transmitted in a complete and consistent manner. MD5 was designed by American cryptographer Ronald Linn Rivest and made public in 1992 to replace the MD4 algorithm.

The algorithm is specified in RFC 1321 standard. After 1996, the algorithm was proven to be weak and could be cracked, and for data that required a high degree of security, experts generally recommend switching to other methods of divination, such as the MD5 algorithm.

There is no collision protection, so it is not suitable for security authentication, such as SSL public key authentication or digital signatures.

and other uses.

The principle of MD5 algorithm can be briefly described as: MD5 code processes the input information with 512-bit packets, and each group is divided into 16 32-bit sub-packets, after a series of processing, the output of the algorithm is composed of four 32-bit packets, and the four 32-bit packets are cascaded by this type of cover.

A 128-bit hash value is generated.

The MD5 Message-digest Algorithm, a widely used cryptographic hash function, produces a 128-bit (16-byte) hash value to ensure that information is transmitted in a complete and consistent manner.

A brief description of the MD5 algorithm can be as follows: MD5 processes the input information in 512-bit packets, and each packet is divided into 16 32-bit subgroups, and after a series of processing, the output of the algorithm consists of four 32-bit packets, and the cascading of these four 32-bit packets will generate a 128-bit hash value.

In 1991, Rivest developed the more technically mature MD5 algorithm. It is added to MD4"Safety - straps"(safety-belts). Although MD5 is more complex than MD4, it is more secure.

This algorithm is obviously composed of four steps that are slightly different from the MD4 design. In the MD5 algorithm, the size of the information-digest and the necessary conditions for filling MD4 are exactly the same. Den Boer and Bosselaers have found pseudo-collisions in the MD5 algorithm, but there are no other cryptographic results that have been discovered.

What is MD5??? The full name of MD5 is message-digest

algorithm

A typical application of MD5 is to generate a message-digest of a message to prevent tampering. For example, there are many software under UNIX that have the same file name and file extension when **. MD5 files, in which there is usually only one line of text, are roughly structured as follows:

0ca175b9c0f726a831d895e269332461

This is the digital signature of the file. MD5 treats the entire file as a large text message, and through its irreversible string transformation algorithm, produces this unique md5 information digest. If there is any form of change in the content of the unsuccessful file in the process of propagating the file in the future (including manual modification or transmission errors caused by unstable lines in the process), as long as you recalculate the md5 of this file, you will find that the information summary is not the same, so you can be sure that what you get is only an incorrect file.

If there is a third-party certification body, using MD5 can also prevent the authorship of the document.

Repudiation", which is known as a digital signature application.

MD5 is also widely used in encryption and decryption techniques. For example, in UNIX, the user's password is encrypted in MD5 (or other similar algorithms) and stored in the file system. When a user logs in, the system calculates the password entered by the user as the md5 value, and then compares it with the md5 value saved in the file system to determine whether the password entered is correct.

Through such steps, the system can determine the legitimacy of the user's login to the system without knowing the user's password. This not only prevents the user's password from being known by a user with system administrator privileges, but also increases the difficulty of password cracking to a certain extent.

It is for this reason that one of the most used methods by hackers to decipher passwords right now is one known as"Run the dictionary"method. There are two ways to obtain a dictionary, one is a list of strings used as passwords collected on a daily basis, and the other is generated by the permutation and combination method of such things, and the md5 of these dictionary items is calculated by the md5 program

value, and then retrieve it in this dictionary with the md5 value of the target. Let's assume that the maximum length of the password is 8 bytes (8

bytes), and the password can only be letters and numbers, a total of 26 + 26 + 10 = 62 characters, and the number of entries in the dictionary is p(62,1)+p(62,2)....p

62,8), that is already a very astronomical number, and the storage of this dictionary requires a terabyte-level disk array, and this method also has a premise, that is, if you can obtain the password md5 value of the target account. This encryption technology is widely used in UNIX systems, which is an important reason why UNIX systems are more robust than ordinary operating systems.