Encryption Flashcards

When is Cryptography Needed?

• Required when communicating over insecure channels to ensure only the intended recipient can read the message.

Message Appearance Before Encryption

• Looks like a normal email format with header details (To, From, Subject) followed by the actual message.

Message Appearance After Encryption

• Transformed into gibberish; format includes encrypted content, e.g., "-----Begin PGP Message----" followed by random characters.

PGP (Pretty Good Protection)

• Provides strong encryption for secure communication.

Symmetric Cryptography

• Uses a single shared key to encrypt and decrypt messages.
• Method includes applying the same key and "Exclusive OR" (XOR) rule which outputs 1 only if one bit is 1.

Steps of Symmetric Cryptography

• Encrypt at the sender's device.
• Send the encrypted message to the recipient.
• Decrypt message at the recipient's device using the same key.

Goal of Cryptography

• To guarantee that only the intended recipient can read the message.

Constraints of Symmetric Cryptography

• Security is compromised if the shared key is lost or stolen.
• Ensuring the correct recipient has the key is critical.

Ensuring Key Sharing

• If a secure channel is available, the key can be securely transmitted, allowing messages to be sent without encryption.

Asymmetric Cryptography (AC)

• Employs two mathematically linked keys: a public key for encryption and a private key for decryption.

Decryption Limitations in AC

• Cannot decrypt messages with the same key used for encryption (public/private).

Private Key Creation

• Generated by the user and never transmitted over a network, ensuring security.

Public Key Access

• Public keys are freely available to anyone wanting them.

Steps of Asymmetric Cryptography

• Sender encrypts using recipient's public key.
• Encrypted message is sent to the recipient.
• Recipient decrypts the message using their private key.

Goal of Asymmetric Cryptography

• Similar to symmetric: ensure that only the intended recipient can read the message.

Constraints of Asymmetric Cryptography

• Best suited for short messages due to inefficiency.
• Private keys need to be securely kept.
• Verification of public key authenticity is crucial.

Key Requirements for AC

• Four keys are generally needed for proper functionality.

AC Notes

• Not efficient for web browsing or e-commerce.
• Despite resolving key distribution issues, it doesn't fully address other cryptography concerns.

Use of Digital Signatures

• Offers assurance that: the message originates from the claimed sender, and has not been altered during transmission.
• Recognized as legally binding since June 2000.

Security Comparison

• Digital signatures provide superior security compared to traditional handwritten signatures.

Digital Signature Process Steps

• Message signed using sender's private key.
• Encrypted again with recipient's public key.
• Sent as double-encrypted message.

Verification of Sender and Integrity

• Only the sender could have created the message due to reversible encryption with a private key, ensuring authenticity and integrity.

E-commerce Encryption Approach

• Adopts a hybrid model, combining both asymmetric and symmetric encryption for efficiency and security.

Hybrid Encryption Process in E-commerce

• Public key of the receiver is obtained.
• Symmetric key is encrypted using this public key and sent.
• Upon receiving, the recipient decrypts using their private key to access the symmetric key for further secure transactions.

Security Concerns in Key Exchange

• Potential risks include impersonation or counterfeit public keys leading to security breaches.

Diffie-Hellman Key Exchange

• A method combining asymmetric and symmetric approaches to establish a shared secret key without direct key exchange.

Understanding MOD

• MOD operation finds the remainder after division, with limited results based on the divisor.

Example of Diffie-Hellman Key Usage

• Alice and Bob use shared prime numbers and generate private and public keys to securely exchange a shared secret key.

General Formula Overview for Key Exchange

• Variables defined: secret (private) keys a and b, and public results A and B based on modular mathematical operations.

Test your knowledge on encryption and cryptography concepts with these flashcards. Learn when cryptography is necessary and how messages appear before and after encryption. Perfect for students or anyone interested in secure communication.