HMAC Generator

import hmac
import hashlib
import base64
import secrets

# Generate HMAC-SHA256
key = secrets.token_bytes(32)   # 256-bit random key
message = "Hello, World!"

# Raw hex output
mac = hmac.new(key, message.encode(), hashlib.sha256)
print("HMAC-SHA256 (hex):", mac.hexdigest())

# Base64 output (common for API signatures)
mac_b64 = base64.b64encode(mac.digest()).decode()
print("HMAC-SHA256 (b64):", mac_b64)

# HMAC-SHA512
mac512 = hmac.new(key, message.encode(), hashlib.sha512)
print("HMAC-SHA512 (hex):", mac512.hexdigest())

# Constant-time verification (prevents timing attacks)
def verify_hmac(key: bytes, message: str, expected: str) -> bool:
    computed = hmac.new(key, message.encode(), hashlib.sha256).hexdigest()
    return hmac.compare_digest(computed, expected)

signature = mac.hexdigest()
print("Valid:  ", verify_hmac(key, message, signature))   # True
print("Invalid:", verify_hmac(key, "tampered", signature)) # False