A session key is a randomly generated key used to secure communications between a user and another computer or between two computers. It’s called a symmetric key since the same key is used for both encrypting and decrypting messages. Each session gets its unique session key, which is discarded once the session ends. This contrasts with public keys, which use two different keys: a public one for encryption and a private one for decryption.
In cryptography, every encryption method relies on keys. Asymmetric encryption involves two keys, allowing one party to encrypt data with a public key while the recipient decrypts it with their private key. Session keys, used in symmetric encryption, are temporary and specific to each communication session. When a new session begins, a new session key is generated.
A session usually refers to an interaction between a user and a web server, often involving an exchange of data, like a request for a webpage. It starts when a user’s device sends out a request and wraps up once all data packets are exchanged, such as during a login. Some interactions don’t require a clear request-response dynamic. For example, signing into a web service needs information to be sent and stored without needing back-and-forth requests.
When Alice sends a message, the system encrypts it with a session key and includes a timestamp. When the server receives it, it decrypts the message using the same key to authenticate Alice’s identity and the time of the message.
Sessions can take different forms:
- An HTTP session tracks interactions between a browser and a web server to record user activity.
- A TCP session creates a logical connection between two network hosts based on transport layer segments.
- A Telnet session allows for remote server interaction.
A session lasts as long as communication occurs or until it times out. If they want to reconnect after it expires, new session keys must be generated.
Cryptographic session keys play a crucial role in securing information to combat identity theft. They simplify the encryption and decryption process and can either be fixed or dynamically created from existing keys. Session keys add an extra layer of security by being discarded after each use, making it harder for potential attackers to access or decrypt information. They’re also faster to use than asymmetric keys, particularly in real-time applications.
However, session keys come with some drawbacks. Their simplicity makes them less secure compared to asymmetric keys, raising concerns for data integrity. If reused across sessions, they risk exposure, compromising the integrity of exchanged data. Since the same key encrypts and decrypts information, malicious actors could potentially intercept it during transmission or while stored on a server. The more data processed with one session key, the higher the chances of it being subject to cryptanalysis.
HTTPS relies on session keys to encrypt data transmitted between the user’s browser and a website, ensuring private connections. For example, when a user enters sensitive information for a purchase, the browser encrypts it with a session key before sending it to the website’s server, which then decrypts it with the same session key.
To secure an HTTPS connection, a TLS handshake initiates a series of steps. It starts with the server sending its SSL certificate to the client. The client verifies this certificate, then encrypts a random number using the public key. During this handshake, the session key is established, responsible for encrypting most data exchanged. If the handshake fails, the connection remains insecure, leaving it open to potential eavesdropping.
Several key concepts relate to session keys:
- A Master Encryption Key (MEK) safeguards the integrity of other encryption keys and generates session keys for communication.
- A Key Encryption Key (KEK) encrypts other keys, such as those that encrypt sensitive data.
- A Content Encryption Key (CEK) encrypts specific content for storage or transmission and can be further encrypted using a KEK.
Staying informed about encryption best practices is critical, particularly as technology evolves. Keeping cryptographic measures updated is essential to ward off ongoing threats, especially in cloud environments and with emerging technologies like quantum computers.