Converting an ECDSA signature to a DER-encoded format in Python

In this article, we will explore the process of converting an ECDSA signature from a hexadecimal string to a DER (Distinguished Encoding Rules)-encoded format using the Python libraries ecdsa and hashlib.

Required libraries

• ecdsa: for generating and verifying ECDSA signatures

• hashlib: for hashing and signing the input data

Code example

import ecdsa 




Import the ECDSA library
import hashlib 
Import the hash library
from ecc import ec 
Import the ecc module from the Ecc library

Define the ECDSA key and signature
pubKey = b'your_pub_key_hex_here'
signature = b'signature_hex_here'

Create a new VerifyingKey object with the provided public key
vk = ecdsa.VerifyingKey.from_string(bytes.fromhex(pubKey), curve=ecdsa.SECP256k1)

Define the SHA-256 hash function and an instance of the hashlib library
sha256_hash = hashlib.sha256()

Sign the input data with ECDSA (replace it with your own signature)
signing_data = bytearray()
vk.sign(signature, signing_data, sha256_hash)

Convert the DER encoded signature to a hexadecimal string
der_encoded_signature = bytes(signing_data).hex()
if vk.verify(bytes.fromhex(signature), bytes.fromhex(der_encoded_signature), hashlib.sha256, sigdecode=ecdsa.SigningHash.DER) == True:
print("Verification successful!")
else:
print("Verification failed!")

Explanation

• We first import the required libraries: ecdsa for generating and verifying ECDSA signatures and hashlib for hashing and signing.

• We define the ECDSA key (public and private) and the signature in hexadecimal format.

• We create a new VerifyingKey object with the provided public key.

• We define the SHA-256 hash function and an instance of the hashlib library to sign the input data with ECDSA.

• We use the vk.sign() method to convert the DER encoded signature into a hexadecimal string representing the DER encoded format.

• We verify the signature by comparing it with the original signature using the vk.verify() method. If they match, we print “Verification successful!” Otherwise, we print “Verification failed!”

Important notes

• Make sure you replace 'your_pub_key_hex_here' and 'signature_hex_here' with your actual public key and signature in hexadecimal format.

• The ecdsa.SigningHash.DER flag is used to encode the signature in DER format, which is a standard encoding scheme for ECDSA signatures.

• You may need to adapt the code to suit your specific needs or handle errors differently.

By following this example, you should be able to successfully convert an ECDSA signature from hexadecimal to DER encoded format using the Python libraries ecdsa and hashlib.

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