Introduction and application of MD5 and Base64

MD5:
Concept:
MD5 is an irreversible message digest algorithm. A hash function widely used in the field of computer security,
Used to provide integrity protection for messages.
Effect:
Transform an arbitrary-length byte string into a fixed-size six-digit string.
The purpose is to make the capacity information "compressed" into a confidential format before signing the private key for digital signature software.
Application:
1. Conformance Verification:
When downloading from the Internet, software, various materials, some documents will provide MD5 control information. Philip? MD5 Check the software to check the downloaded, to see if the downloaded files are consistent with the sender.
Using the MD5 algorithm to enter the file verification scheme is widely used in software download station, forum database, System file security, etc. square face

2. Digital certificate:
Generates fingerprint (fingerprints) on a message (byte string) to prevent "tampering". For example, you write a paragraph in a file called Readme.txt, and you create a MD5 value on the Readme.txt and record it, and then you can spread the file to someone else if you change anything in the file, you'll find it when you recalculate the MD5. If there is a third-party certification body, with MD5 can also prevent the file author's "Repudiation", which is called Digital signature application.
3. Secure Access authentication:
For the login authentication of the operating system. When the user logs in, the system enters the password entered by the username? MD5 hash operation, and then go to and save in the file system MD5 value in the comparison, enter to determine whether the password is correct.
Through such steps, the system can determine the legality of the user login system without knowing the user's password. This avoids the user's password being known to users with system administrator privileges.

At the International Cryptography Conference in Saint-Barat, California, August 17, 2004, Professor Xiao, from Shandong, China, made a report to decipher MD5, HAVAL-128, MD4 and RIPEMD algorithms, and released the results of the MD series algorithm. Declared the world of the solid-like soup? Password Standard MD5 's fortress collapsed, triggering the great wave of cryptographic academics.
So are we safe with MD5? Don't worry about this, here's why:
1, our cattle?? The effect of the students is to find collisions, not can be reversed. MD5 is to get information digest, the main purpose is tamper-proof. It is difficult to tamper with the information and keep the MD5 intact.
2, the hardware equipment requirements are particularly high, and the program is only a collision, if you want to according to the known files, to construct a same MD5, and is a different content of the valid files, it is difficult to get on.
3, the use of MD5 algorithm does not need to pay any royalties, so in general (non-top secret application) How can be very safe.

Base64

Concept:
Base64 is a representation of binary data based on 64 printable characters. Base64 is a coding method.
Effect:
The idea of BASE64 encoding is to re-encode the data using 64 basic ASCII characters.
The use of BASE64 encoding is not readable, that is, the encoded data will not be directly visible to the human eye.
Application:
Base64 is mainly used to convert binary data into text data, which is convenient to use HTTP protocol, etc., is reversible. When dealing with text data, some binary data is represented, transmitted, and stored. Includes the MIME Email,email via mime, which stores complex data in XML.

Note: The primary role of Base64 is not to encrypt, but to avoid values that cannot be converted to display characters in "bytes".

Introduction and application of MD5 and Base64