def share_data_via_blockchain(categorized_data, user):
    """
    Share medical data via social blockchain.
    
    Args:
        categorized_data (dict): Categorized data with sensitivity level.
        user (dict): User information including permissions.
    
    Returns:
        str: Hash value (HV) or None.
    """
    # Stage I: Checking user permission
    user_permissions = user.get("permissions", [])
    data_sensitivity = categorized_data['sensitivity']
    
    if data_sensitivity not in user_permissions:
        print("Access Denied: User does not have permission to access this data.")
        return None
    
    # Stage II: Retrieving HV from IPFS and uploading to social blockchain
    ipfs_data_store = {
        1: "hash_public_data",
        2: "hash_widespread_data",
        3: "hash_restricted_data",
        4: "hash_limited_data",
        5: "hash_sensitive_data"
    }
    
    hv = ipfs_data_store.get(data_sensitivity, None)
    if not hv:
        raise ValueError("No hash value found for the given sensitivity level.")
    
    # Simulating upload to the social blockchain
    print(f"Uploading hash value {hv} to the social blockchain...")
    blockchain_record = {
        'hash': hv,
        'user': user['id'],
        'timestamp': '2024-11-27'
    }
    print(f"Blockchain record created: {blockchain_record}")
    
    # Stage III: Returning hash value
    return hv