Base64 encoding
1: Base64 is one of the most common encoding methods for transmitting 8Bit bytecode on the Internet. Base64 is a method of representing binary data based on 64 printable characters.
2: Base64 encoding is a process from binary to character. It can be used to transmit long identification information in the HTTP environment
3: The encoded data is a string, which contains characters: AZ, az, 0-9, +, /
A total of 64 characters: 26 + 26 + 10 + 1 + 1 = 64. In fact, it is 65 characters, "=" is the padding character
4: 64 characters need 6 bits to represent, and the value is 0~63
Base64 encoding process
1: The string "Xue" becomes "WHVl" after Base64 encoding. The number of data bits with a length of 3 bytes is 8*3=24, which can be accurately divided into 6*4
2: If the number of bytes of data is not a multiple of 3, then its number of bits is not a multiple of 6, so it cannot be accurately divided into 6-bit blocks. In this case, one or two zero-valued bytes need to be added after the original data, so that the number of bytes is a multiple of 3. Then, add one or two equal signs "=" after the encoded string to indicate the number of zero-valued bytes added. Example:
The string "Xu" becomes "WHU=" after Base64 encoding.
md5/SHA1 hash algorithm
1: MD5 algorithm:
1> Compressibility: For data of any length, the length of the calculated MD5 value is fixed.
2>Easy calculation: It is easy to calculate the MD5 value from the original data.
3> Modification resistance: any modification to the original data, even if only 1 byte is modified, the MD5 value obtained is very different.
4> Strong anti-collision: Knowing the original data and its MD5 value, it is very difficult to find a data with the same MD5 value (ie forged data)
2: SHA1 algorithm
and MD5 similar processing;
3: Encrypt user password, server Store user passwords are all MD5 values;
4: Compare whether the file has been modified, and generate MD5 values according to the content of the file;
