MD5 is (atleast when it was created) a standardized 1-way function that takes in data input of any form and maps it to a fixed-size output string, irrespective of the size of the input string.
Though it is used as a cryptographic hash function, it has been found to suffer from a lot of vulnerabilities.
The hash function generates the same output hash for the same input string. This means that, you can use this string to validate files or text or anything when you pass it across the network or even otherwise. MD5 can act as a stamp or for checking if the data is valid or not.
For example -
|Input String||Output Hash|
|computer science is amazing! I love it.||f3c5a497380310d828cdfc1737e8e2a3|
Check this out - If you are looking for MD5 hash of a String.
Create MD5 hash of a file in Python
MD5 hash can be created using the python's default module
Incorrect Way to create MD5 Hash of a file in Python
But, you have to note that you cannot create a hash of a file by just specifying the name of the file like this-
# this is NOT correct import hashlib print(hashlib.md5("filename.jpg".encode('UTF-8')).hexdigest())
Output of the above code-
The above value is NOT the MD5 hash of the file. But, it is the MD5 hash of the string
Correct Way to create MD5 Hash of a file in Python
You have to read the contents of the file to create MD5 hash of the file itself. It's simple, we can just read the contents of the file and create the hash.
import hashlib file_name = 'filename.jpg' with open(file_name) as f: data = f.read() md5hash = hashlib.md5(data).hexdigest()
MD5 Hash of Large Files in Python
In the above code, there is one problem. If the file is a 10 Gb file, let's say a large log file or a dump of traffic or a Game like FIFA or others. If you want to compute MD5 hash of it, it would probably chew up your memory. Here is a memory optimised way of computing MD5 hash, where we read chunks of 4096 bytes(can be customised as per your requirement, size of your system, size of your file etc.,). So, in this process we sequentially process the chunks and update it.
import hashlib # A utility function that can be used in your code def compute_md5(file_name): hash_md5 = hashlib.md5() with open(file_name, "rb") as f: for chunk in iter(lambda: f.read(4096), b""): hash_md5.update(chunk) return hash_md5.hexdigest()
Compare and Verify MD5 hash of a file using python
Here you can compare the original MD5 value that the source has generated and MD5 that you generate.
import hashlib file_name = 'filename.jpg' original_md5 = '5d41402abc4b2a76b9719d911017c592' with open(file_name) as f: data = f.read() md5_returned = hashlib.md5(data).hexdigest() if original_md5 == md5_returned: print "MD5 verified." else: print "MD5 verification failed."