DaddyTrap / MD5_cpp

Course Homework, not for production environment.

MD5 C++ Implementation

Just a homework. NOT for production environment.

How to use it

#include "md5.h"
#include <iostream>

using std::cout;
using std::endl;

void simple() {
  MD5 md5("string to md5");
  auto res = md5.digest().getHexResult();
  cout << res << endl;
}

void useUpdate() {
  MD5 md5;
  md5.update("string");
  md5.update(" to ").update("update").digest();
  auto res = md5.getHexResult();
  cout << res << endl;
}

void readFile() {
  MD5 md5;
  md5.update("path_to_file", MD5::UPDATE_TYPE::UPDATE_FILE);
  auto res = md5.digest().getHexResult();
  cout << res << endl;
}

How is the class designed

Reference: RFC 1321 and my teacher's courseware

Step 1 (Append Padding) and Step 2 (Append Length) in RFC 1321 can be delayed, and Step 3 (Intialize MD Buffer) can be done in the class's initialize time. So, this implementation first proceeds Step 4 (Process Message in 16-Word Blocks) except the final block. (Step 1 and 2 are only applied on the final block)

When callling update(), the new data will be appended to the buffer -- which carrys the final block of the last update(). This means m1 and m2 are the same in the following code.

MD5 m1, m2;
m1.update("123456").digest();
m2.update("123").update("456").digest();

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As for the private method process(), it will process the current buffer. It won't clear the buffer, it is update() 's work to update buffer and call process().

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Files won't be fully read by one reading operation, which means this implementation won't use too much memory. (Depends on the constexpr in md5.h called FILE_READ_BLOCK_SIZE)

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More explanations on the code are in the code comment block.

Test it

Part of the test suite can be found in RFC 1321, others are generated by python's hashlib library. (Yes, I trust it to be a correct implementation!)

Check the file md5_test.cpp !