But don’t worry, because I’m here to save the day and make this topic as entertaining as possible.
To set the stage, let’s set up our environment. We need a few packages installed on our machine, including `ecdsa` (duh), `hashlib`, and `os`. If you haven’t already done so, go ahead and install them using pip:
#!/bin/bash
# This script installs necessary packages for our environment setup.
# Install ecdsa package using pip.
pip install ecdsa
# Install hashlib package using pip.
pip install hashlib
# Install os-random package using pip.
pip install os-random
# Note: The original script had a typo, it should be "os-random" instead of "os". Also, it is not necessary to install all packages in one line.
# Alternatively, you can install all packages in one line using the following command:
# pip install ecdsa hashlib os-random
# Note: It is recommended to install packages separately to avoid any potential conflicts or errors.
# Lastly, it is important to mention that these packages are necessary for our script to run properly. The ecdsa package is used for elliptic curve cryptography, the hashlib package is used for hashing algorithms, and the os-random package is used for generating random numbers.
Now that we have our tools ready to go, let’s create a simple script that generates an ECDSA key pair (public and private), signs some data with the private key, and verifies it using the public key. Here’s what it looks like:
# Import necessary libraries
import hashlib # Importing hashlib library for hashing functions
from ecdsa import SigningKey, VerifyingKey # Importing SigningKey and VerifyingKey from ecdsa library
from ecdsa.util import randrange_from_seed__trytryagain # Importing randrange_from_seed__trytryagain function from ecdsa.util library
# Generate a new ECDSA key pair with NIST192p curve (default)
sk = SigningKey.generate() # Generating a new SigningKey object
vk = sk.verifying_key # Retrieving the verifying key from the SigningKey object
# Get the public key in PEM format for future use
with open("public.pem", "w") as f: # Opening a file named "public.pem" in write mode and assigning it to variable f
f.write(str(vk)) # Writing the string representation of the verifying key to the file
# Generate some data to sign and save it to a file
data = b"Hello, world!" # Creating a byte string to be used as data
with open("message.txt", "wb") as f: # Opening a file named "message.txt" in write mode and assigning it to variable f
f.write(data) # Writing the data to the file
# Sign the message using our private key (stored in memory)
signature = sk.sign_deterministic(data, hashfunc=hashlib.sha256) # Generating a signature for the data using the SigningKey object and the sha256 hashing function
# Save the signature to a file for future use
with open("signature.bin", "wb") as f: # Opening a file named "signature.bin" in write mode and assigning it to variable f
f.write(signature) # Writing the signature to the file
# Verify the signature using our public key (loaded from disk)
try:
with open("public.pem", "rb") as f: # Opening the "public.pem" file in read mode and assigning it to variable f
vk = VerifyingKey.from_pem(f.read()) # Retrieving the verifying key from the file and assigning it to variable vk
with open("message.txt", "rb") as f: # Opening the "message.txt" file in read mode and assigning it to variable f
message = f.read() # Reading the data from the file and assigning it to variable message
with open("signature.bin", "rb") as f: # Opening the "signature.bin" file in read mode and assigning it to variable f
signature = f.read() # Reading the signature from the file and assigning it to variable signature
assert vk.verify(signature, message, hashfunc=hashlib.sha256) # Verifying the signature using the verifying key, data, and sha256 hashing function
print("Good signature!") # Printing a success message if the signature is valid
except BadSignatureError: # Catching the BadSignatureError exception if the signature is invalid
print("BAD SIGNATURE!!!") # Printing an error message if the signature is invalid
Now the most common mistake people make when working with ECDSA signatures in Python: forgetting to hash the message before signing it. This is a big no-no, because if you don’t do this, your signature will be vulnerable to attacks like length extension and message recovery.
To prevent these issues, we need to use a cryptographic hash function (like SHA-256) to create a fixed-size digest of the message before signing it. This ensures that even if an attacker changes some parts of the original message, they won’t be able to forge a valid signature without knowing our private key.
In our script above, we use `hashlib` to hash the message using SHA-256 (which is the default algorithm in Python 3). However, if you want to use a different hash function or customize some other parameters of your ECDSA implementation, feel free to modify the code accordingly.
And that’s it! With this script, we can generate and verify ECDSA signatures with ease. Just remember to always hash the message before signing it, and you should be good to go.