Questions and Answers
When is cryptography needed?
When there is an insecure communication channel and you want to send this message in a way that ensures that only the intended recipient can read it.
How does a message look like before encryption?
like a normal message
How might a message look after encryption?
the actual message looks like gibberish
What does PGP stand for?
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What is symmetric cryptography?
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What are the steps of symmetric cryptography?
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What is the goal of cryptography?
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What are the constraints of symmetric cryptography?
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How do you ensure Computer1 and Computer2 have the SAME key?
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What is Asymmetric Cryptography?
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What can you NOT decrypt a message using in asymmetric cryptography?
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Who creates private keys in Asymmetric Cryptography?
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Who can use public keys?
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What are the steps to Asymmetric Cryptography?
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What is the goal of Asymmetric Cryptography?
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What are the constraints of Asymmetric Cryptography?
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How many keys are required for Asymmetric Cryptography?
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Is Asymmetric Cryptography good for ecommerce?
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How is the goal of Asymmetric Cryptography and a digital signature different?
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How do you ensure the recipient that the message is authentic and hasn't been changed?
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What is a digital signature?
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What is more secure, a human signature or digital signature?
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What is step 1 of the digital signature process?
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What is step 2 of the digital signature process?
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What is step 3 of the digital signature process?
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What is step 4 of the digital signature process?
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What is step 5 of the digital signature process?
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Could anyone other than Computer1 have sent the message?
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Could the message have been changed en route?
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Can only the intended recipient read the message?
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Which type of encryption does ecommerce use?
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Why doesn't asymmetric encryption work for ecommerce?
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Why doesn't symmetric encryption work for ecommerce?
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What is the objective of ecommerce's encryption?
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What is step 1 in Web-Based Commerce encryption?
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What is step 2 in Web-Based Commerce encryption?
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What is step 3 in Web-Based Commerce encryption?
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What is step 4 in Web-Based Commerce encryption?
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What is a benefit of Web-Based Commerce encryption?
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What are scenarios that might pop into your head if you are wondering how do I know that I actually retrieved your public key?
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What is Diffie-Hellman Key Exchange?
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What is MOD?
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How many options for MOD are there when you divide by 4?
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What is 17 MOD 4?
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How does Diffie-Hellman Key Exchange work?
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Study Notes
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.
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Description
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.