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KembaraXtra -Computer Science -World Wide Web
Core Attributes
Distributed
HTTP (HyperText Transfer Protocol)
ii.Server hello: Server selects the encryption methods. The server provides its public key.
iii.The client encrypts a string of bytes with the server's public key, and sends it to the server.
iv.Server decrypts using its private key. Both compute a shared secret key for symmetric encryption.
v.All further data is encrypted using the shared secret key.
The Searchable Web
Core Attributes
Distributed
- Definition: No central authority controls web content.
- Implications:
- Anyone can host a web server and publish content.
- Organizations/countries can block access.
- Governments can shut down illegal content.
- Key Point: The web is open and not centrally controlled.
- Definition: Every web resource has a unique address (URL).
- URL Components:
- Scheme: Protocol (e.g., HTTP, HTTPS).
- Authority:
- Hostname (e.g., travel.example.com).
- Optional: Username, Port Number.
- Path: Location of resource on server (like a file system path).
- Query: Modifies the resource returned (format varies by site).
- Relative URLs:
- Omit scheme, hostname, or full path.
- Interpreted relative to the current context.
- Practical URL Reading Example:
- Uses HTTP protocol.
- Server: travel.example.com.
- Path: /destinations/carolinas.
- Query: location=beach (shows beach locations).
- Definition: Web resources reference each other via hyperlinks.
- Hyperlinks: One-way references, no permission needed.
- Hypertext: Documents connected by hyperlinks.
HTTP (HyperText Transfer Protocol)
- Purpose: Transferring web resources (reading, creating, updating, deleting).
- Foundation: Based on TCP/IP for reliable data transfer and addressing.
- Model: Request and response.
- Client sends an HTTP request.
- Server replies with an HTTP response.
- GET: Retrieve a resource (no modification).
- PUT: Create/modify a resource at a specific URL.
- POST: Create a new resource as a child of an existing URL.
- DELETE: Remove a resource.
- Usage:
- GET is most common (used for browsing and loading resources).
- Servers often restrict PUT, POST, DELETE.
- Format: 3-digit number.
- Classes:
- 100s: Informational.
- 200s: Success.
- 300s: Redirection.
- 400s: Client error.
- 500s: Server error.
- Examples:
- 200 OK: Success.
- 301 Moved Permanently: Redirect to a new URL.
- 401 Unauthorized: Authentication required.
- 403 Forbidden: Access denied.
- 404 Not Found: Resource not found.
- 500 Internal Server Error: Server-side error.
- Request:
- First line: Method URL HTTP/Version (e.g., GET /documents/hello.txt HTTP/1.1).
- Headers: Additional information.
- Optional message body.
- Response:
- First line: HTTP/Version Status Code Response Phrase (e.g., HTTP/1.1 200 OK).
- Headers.
- Optional message body.
- Purpose: Encrypt data transmitted over the internet.
- Encryption: Encoding data to be unreadable without decryption.
- Cryptographic Key: Secret sequence of bytes used for encryption/decryption.
- Encryption Types:
- Symmetric: Single shared key for both encryption and decryption.
- Asymmetric:
- Public key: Encrypts data.
- Private key: Decrypts data (kept secret).
- Security:
- Prevents interception and modification of data.
- Encrypts the entire HTTP request (URL, headers, body).
- TLS (Transport Layer Security): Protocol used to encrypt HTTP requests (formerly SSL).
- HTTPS Handshake:
ii.Server hello: Server selects the encryption methods. The server provides its public key.
iii.The client encrypts a string of bytes with the server's public key, and sends it to the server.
iv.Server decrypts using its private key. Both compute a shared secret key for symmetric encryption.
v.All further data is encrypted using the shared secret key.
The Searchable Web
- Entry Point: Often accessed through search engines.
- Search Engines: Non-standard, proprietary systems (e.g. Google). """
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