Java programming implementation of hexadecimal string XOR operation code example

I haven't written a blog for a long time. I feel so busy in the last year. I can't finish all kinds of work. I believe many office workers will feel this way. Recently, a check bit needs to be calculated for the NFC card writing operation. In general, most of the check bits are obtained by XOR operation of the first few bytes.

Now let me talk about the scenarios I use:

Write a 16 byte data into the CPU card (such as traffic card), and the last byte is the check code - the first 15 bytes of XOR.

I began to find some algorithms written by others on the Internet. I found that the calculation results were wrong or the writing was too complex, so I wrote one myself. I feel it is relatively simple. Now I share it with you and hope to communicate with you.

Section 1: what is XOR operation (mainly from Baidu Encyclopedia, familiar children's boots can be skipped)

definition:

Exclusive or, English is exclusive or, or abbreviated as XOR

XOR is a mathematical operator. It is applied to logical operations. The mathematical symbol of XOR is' ', and the computer symbol is XOR. Its algorithm is:

ab=(¬a∧b)∨(a∧¬b)

If the values of a and B are different, the XOR result is 1. If the values of a and B are the same, the XOR result is 0.

XOR is also called semi addition, and its algorithm is equivalent to binary addition without carry: in binary, 1 represents true and 0 represents false, then the algorithm of XOR is 00 = 0, 10 = 1, 01 = 1 and 11 = 0 (the same is 0 and the difference is 1). These algorithms are the same as addition, but without carry.

XOR is abbreviated as XOR, EOR, EX-OR

There are three operators in the program: XOR, XOR.

The usage is as follows

z=xy

z=xxory

Operation rules:

1.aa=0

2.ab=ba

3.abc=a(bc)=(ab)c;

4. D = ABC can deduce a = DBC

5.aba=b.

6. If x is binary number 0101, y is binary number 1011

Then xy = 1110

Only when the two comparison bits are different, the result is 1, otherwise the result is 0

That is "0 if the two inputs are the same, 1 if they are different"!

Logic:

Logical expression: F = ab'a'b ((ab'a'b) '= ab ⊙ a'B', ⊙ is the same or operation)

The truth table of XOR logic is shown in Figure 1

The logic symbol is shown in Figure 2. The relationship of XOR logic is: when AB is different, output P = 1; When AB is the same, the output P = 0. '' is an XOR operation symbol, and XOR logic is also a combination of and or non logic. Its logical expression is:

P=AB

As can be seen from Figure 1, the rule of XOR operation is

00=0,01=1

10=1,11=0

Pithy formula: take 0 for the same and 1 for the different

In fact, XOR is defined in English as either one (isone), but not both, that is, when only one is true (1), take true (1).

effect:

It is widely used in computers. XOR is generally used as the logical symbol of XOR. It is also useful:

True = false = true

False = true

False = false

True = false

Or:

TrueFalse=True

FalseTrue=True

FalseFalse=False

TrueTrue=False

Some computer languages use 1 for true and 0 for false, so the two bytes are bitwise XOR as follows

Here are two binary values for XOR calculation:

In reality, decimal values are used. Let's take a look at the XOR calculation of two decimal values:

52=？

1. All values will be converted to binary before XOR calculation:

5 and 2 are converted to binary: 0101 and 0010 respectively

2. Convert the result 0111 to decimal: 7

3. So 52 = 7

Clever use:

Different from other languages, the XOR of C language and C + + language does not use XOR, but uses "^", and the typing method is shift + 6. (while "^" in other languages generally means power)

If it is necessary to exchange the values of two variables, in addition to borrowing intermediate variables for exchange, XOR can also be used to exchange only two variables, such as:

Detailed explanation:

be careful:

a=a^b^(b=a);// This kind of form is incorrect UB behavior and will have different results in different compilers. Do not use it

This completes the exchange of a and B.

To sum up: the XOR value of the same variable and another variable is equal to itself.

Use case: it can be used in one or more links of the encryption algorithm to make the algorithm more complex, difficult to crack and more secure. [1]

Section 2: implemented in Java language:

Note: the above method is for XOR operation between one byte of a hexadecimal string, such as XOR operation for fifteen byte hexadecimal string:

1312f70f900168d900007df57b4884 split first: 13 12 F7 0f 90 01 68 D9 00 7d F5 7b 48 84 13 XOR 12 -- > 1 1 XOR F7 -- > F6 XOR 0f -- > F9 62 xor 84-->e6

That is, the one byte check code obtained is: E6 supplement, which adds a simple calling method to some friends for reference only:

Then call in the main function or other methods:

Code is the check code obtained.

summary

The above is all about the code example of hexadecimal string XOR operation in Java programming. I hope it will be helpful to you. Interested friends can continue to refer to other related topics on this site. If there are deficiencies, please leave a message to point out. Thank you for your support!