Crack the simple login system with NOP method

Catalog

One . Crack the object

Two . Preliminary analysis

3、 ... and . use OD debug

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One . Crack the object

A simple login system （ Please test in a legal environment ）.

Two . Preliminary analysis

After trying , We found that the login window has only three login opportunities .

Unsuccessful login each time , There will be “ user Wrong password also n Second chance ” Tips .

3、 ... and . use OD debug

OD： One 32 Bit assembly analysis debugger

OD website ：OllyDbg Chinese station

First drag the login system into OD（ Or use OD open ）.

Enter the string search interface （ Right click — Chinese search engine — Intelligent search ）.

By preliminary analysis , We get “ user Wrong password also n Second chance ” keyword , Try searching this string , So as to determine the relevant process .

ps: It is not recommended to search a string in a whole sentence , It is recommended to search for some keywords , Because the string display may be split into multiple lines .

Successfully found the relevant string , Double click this line to return to the debugging page .

 

Then start looking for key points .

Found a jump to the line before the key string , And the conditions hold , perform .

ps: The jump arrow shows Red Then the condition holds , Indicates execution ; The jump arrow is grayed out , Don't execute .

 

Look down again .

Found the second jump , Skip key strings directly , And the conditions hold , perform .

Compare the two jumps , We found that the first jump is the key jump , Because it skips " Landing successful " link .

We came to the first jump , Lower breakpoint （ Switch ）.

 

 

Back to the system , No response after entering the password , The system is suspended .

In this case, you can directly execute the empty instruction , Invalidate a jump , Do the following .

( Right healthy - Binary system - use NDP fill )

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Back to the system , You can log in directly .

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