Converting an ECDSA Signature to 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 creating and verifying ECDSA signatures

• hashlib: for hashing and signing 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 using the provided public key
vk = ecdsa.VerifyingKey.from_string(bytes.fromhex(pubKey), curve=ecdsa.SECP256k1)

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

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

Convert the DER-encoded signature to a hexadecimal string
der_encoded_signature = bytes(signaturedata).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

• First, we import the necessary libraries: “ecdsa” for creating 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 using the provided public key.

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

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

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

Important Notes

• Make sure to 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. This is the standard encoding scheme for ECDSA signatures.

• You may need to adjust the code to suit your specific requirements or handle errors differently.

Following this example, you should be able to successfully convert an ECDSA signature from hexadecimal to DER encoded using Python’s ecdsa and hashlib libraries.

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