Cryptographic Operations

def encrypt(message: bytes, pub_key: PublicKey) -> bytes:
    """
    Encrypts the given message using PKCS#1 v1.5.

    Parameters:
    - message: bytes - the message to encrypt (max length: k-11 bytes where k is key size in bytes)
    - pub_key: PublicKey - the public key to encrypt with

    Returns:
    bytes - encrypted message as bytes

    Raises:
    - OverflowError: when the message is too large for the key size
    """

import rsa

# Generate keys
(public_key, private_key) = rsa.newkeys(2048)

# Encrypt a message
message = b'Hello, World!'
encrypted = rsa.encrypt(message, public_key)

# Encrypted data is the same length as the key
print(f"Encrypted length: {len(encrypted)} bytes")

def decrypt(crypto: bytes, priv_key: PrivateKey) -> bytes:
    """
    Decrypts the given message using PKCS#1 v1.5.

    Parameters:
    - crypto: bytes - encrypted message to decrypt
    - priv_key: PrivateKey - the private key to decrypt with

    Returns:
    bytes - decrypted message as bytes

    Raises:
    - DecryptionError: when decryption fails (wrong key, corrupted data, etc.)
    """

import rsa

# Decrypt the message
try:
    decrypted = rsa.decrypt(encrypted, private_key)
    print(decrypted.decode('utf-8'))  # Convert bytes to string
except rsa.DecryptionError:
    print("Decryption failed - wrong key or corrupted data")

def sign(message: bytes, priv_key: PrivateKey, hash_method: str) -> bytes:
    """
    Signs a message using the private key.

    Parameters:
    - message: bytes - the message to sign
    - priv_key: PrivateKey - the private key to sign with
    - hash_method: str - hash algorithm ('SHA-1', 'SHA-224', 'SHA-256', 'SHA-384', 'SHA-512', 'MD5')

    Returns:
    bytes - signature as bytes

    Raises:
    - ValueError: for unsupported hash methods
    """

def sign_hash(hash_value: bytes, priv_key: PrivateKey, hash_method: str) -> bytes:
    """
    Signs a pre-computed hash value.

    Parameters:
    - hash_value: bytes - the hash to sign (must match hash_method)
    - priv_key: PrivateKey - the private key to sign with  
    - hash_method: str - hash algorithm used to create hash_value

    Returns:
    bytes - signature as bytes
    """

import rsa

# Sign a message
message = b'Important document content'
signature = rsa.sign(message, private_key, 'SHA-256')

# Sign a pre-computed hash
import hashlib
hash_obj = hashlib.sha256(message)
hash_bytes = hash_obj.digest()
signature = rsa.sign_hash(hash_bytes, private_key, 'SHA-256')

def verify(message: bytes, signature: bytes, pub_key: PublicKey) -> str:
    """
    Verifies a message signature.

    Parameters:
    - message: bytes - the original message
    - signature: bytes - the signature to verify
    - pub_key: PublicKey - the public key to verify with

    Returns:
    str - the hash method used for signing ('SHA-256', etc.)

    Raises:
    - VerificationError: when signature verification fails
    """

def find_signature_hash(signature: bytes, pub_key: PublicKey) -> str:
    """
    Finds the hash method used in a signature.

    Parameters:
    - signature: bytes - the signature to analyze
    - pub_key: PublicKey - the public key used for verification

    Returns:
    str - the hash method name ('SHA-256', etc.)

    Raises:
    - VerificationError: when signature cannot be processed
    """

import rsa

# Verify a signature
try:
    hash_method = rsa.verify(message, signature, public_key)
    print(f"Signature valid - signed with {hash_method}")
except rsa.VerificationError:
    print("Signature verification failed")

# Determine hash method without full verification
try:
    hash_method = rsa.find_signature_hash(signature, public_key)
    print(f"Signature uses {hash_method}")
except rsa.VerificationError:
    print("Cannot determine hash method")

def compute_hash(message: Union[bytes, BinaryIO], method_name: str) -> bytes:
    """
    Computes a hash of the given message.

    Parameters:
    - message: bytes or file-like object - data to hash
    - method_name: str - hash algorithm ('SHA-1', 'SHA-224', 'SHA-256', 'SHA-384', 'SHA-512', 'MD5')

    Returns:
    bytes - computed hash value

    Raises:
    - ValueError: for unsupported hash methods
    """

import rsa

# Hash a message
message = b'Data to hash'
hash_value = rsa.compute_hash(message, 'SHA-256')

# Hash a file
with open('document.txt', 'rb') as f:
    hash_value = rsa.compute_hash(f, 'SHA-256')

class CryptoError(Exception):
    """Base class for all cryptographic errors."""

class DecryptionError(CryptoError):
    """Raised when decryption fails due to wrong key, corrupted data, or padding errors."""

class VerificationError(CryptoError):
    """Raised when signature verification fails due to invalid signature or wrong key."""