How is digital signature process carried out?

A digital signature is a cryptographic mechanism that allows verifying the authenticity and integrity of an electronic document.

The process of digital signing typically involves the following steps:

1. Hash generation: The original document is processed through a hash function (e.g., SHA-256), which creates a unique short representation of the data.

2. Encrypting the hash with a private key: The resulting hash is encrypted using the sender's private key (part of an asymmetric key pair). This is the digital signature.

3. Attaching the signature to the document: The signature along with the document is sent to the recipient.

4. Signature verification:

   • The recipient generates a hash from the received document.
   • Decrypts the digital signature using the sender's public key.
   • Compares both hashes. If they match, the document has not been altered and the signature is authentic.

Example in Python using the cryptography library:

from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric import padding, rsa
from cryptography.hazmat.primitives import serialization

# Key generation (usually keys already exist)
private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)
public_key = private_key.public_key()

data = b"Important message"

# Signing data
signature = private_key.sign(
    data,
    padding.PSS(
        mgf=padding.MGF1(hashes.SHA256()),
        salt_length=padding.PSS.MAX_LENGTH
    ),
    hashes.SHA256()
)

# Verifying the signature
try:
    public_key.verify(
        signature,
        data,
        padding.PSS(
            mgf=padding.MGF1(hashes.SHA256()),
            salt_length=padding.PSS.MAX_LENGTH
        ),
        hashes.SHA256()
    )
    print("Signature is valid")
except Exception:
    print("Signature is invalid")

Thus, a digital signature ensures security and trust in electronic document exchange.