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Create MD5 Hash of a file in Python

Create MD5 Hash of a file in Python

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 StringOutput Hash
hi49f68a5c8493ec2c0bf489821c21fc3b
debugpointerd16220bc73b8c7176a3971c7f73ac8aa
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 hashlib.

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-

03e6eda992afdeda6b2acaed17722515

The above value is NOT the MD5 hash of the file. But, it is the MD5 hash of the string filename.jpg itself.

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.

The process of creating an MD5 hash in python is very simple. First import hashlib, then encode your string that you want to hash i.e., converts the string into the byte equivalent using encode(), then pass it through the hashlib.md5() function. We print the hexdigest value of the hash m, which is the hexadecimal equivalent encoded string.

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 the hash. So, in this process, let's say there are 1000 such chunks of the file, the hash_md5 is updated 1000 times.

At the end we return the hexdigest value of the hash m, which is the hexadecimal equivalent encoded string.

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

You need to verify the MD5 hash at the server or at some other point or logic in your code.

To verify the MD5 hash you will have to create the MD5 hash of the original file again.

Then 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."

The process of MD5 creation and verification is easy as we discussed above. Happy Coding!

NOTE : Please do not use this to hash passwords and store it in your databases, prefer SHA-256 or SHA-512 or other superior cryptographic hash functions for the same.

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I'm glad that you found the content useful. Happy Coding.