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Questions and Answers
What is the purpose of Bob's public key in Public-Key Cryptography?
What is the purpose of Bob's public key in Public-Key Cryptography?
- To encrypt messages from Alice (correct)
- To decrypt messages from Alice
- To ensure message integrity
- To sign messages for Alice
What is the role of Alice's private key in digital signatures?
What is the role of Alice's private key in digital signatures?
- Decrypting the message
- Verifying the sender's identity
- Encrypting the message
- Creating the signature (correct)
In Public-Key Cryptography, what does Bob use to decrypt an encrypted message from Alice?
In Public-Key Cryptography, what does Bob use to decrypt an encrypted message from Alice?
- Alice's private key
- A symmetric key
- Bob's public key
- Bob's private key (correct)
What property should a cryptographic hash function possess to be considered secure?
What property should a cryptographic hash function possess to be considered secure?
What is the purpose of a digital certificate in secure communication?
What is the purpose of a digital certificate in secure communication?
How does Public-Key Cryptography differ from symmetric-key cryptography?
How does Public-Key Cryptography differ from symmetric-key cryptography?
What is the purpose of a Message Authentication Code (MAC)?
What is the purpose of a Message Authentication Code (MAC)?
In public-key cryptography, what is the role of a digital certificate authority (CA)?
In public-key cryptography, what is the role of a digital certificate authority (CA)?
Which cryptographic hash function is mentioned in the text examples?
Which cryptographic hash function is mentioned in the text examples?
What makes a password strong according to the text?
What makes a password strong according to the text?
How does Alice ensure data integrity when sending a message to Bob using a shared secret key?
How does Alice ensure data integrity when sending a message to Bob using a shared secret key?
In a symmetric cryptosystem, what is used for both encryption and decryption?
In a symmetric cryptosystem, what is used for both encryption and decryption?
Which type of cryptosystem requires each pair of communicating parties to share a separate secret key?
Which type of cryptosystem requires each pair of communicating parties to share a separate secret key?
What is the main advantage of public-key cryptography over symmetric-key cryptography?
What is the main advantage of public-key cryptography over symmetric-key cryptography?
Which component of a cryptosystem defines the set of possible encryption keys?
Which component of a cryptosystem defines the set of possible encryption keys?
What does the Caesar Cipher do to each letter in the plaintext?
What does the Caesar Cipher do to each letter in the plaintext?
Which cryptosystem involves sharing a public key for encryption and a private key for decryption?
Which cryptosystem involves sharing a public key for encryption and a private key for decryption?
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Study Notes
Message Authentication Codes (MACs)
- MACs ensure data integrity and allow Alice and Bob to detect tampering if they share a secret key.
- The process involves computing a hash (H) of the message (M) and the shared secret key (K), and sending the message and the hash to Bob.
Digital Certificates
- A digital certificate is a binding between an identity and a public key, digitally signed by a Certificate Authority (CA).
Passwords
- A password is a short sequence of characters used to authenticate someone via a secret they know.
- A strong password includes:
- Upper and lower case characters
- Special characters
- Numbers
Password Storage
- A password is typically stored in a password file, encrypted using a hash function.
Public-Key Cryptography
- Bob has two keys: a private key (SB) and a public key (PB), which he broadcasts widely.
- Alice uses Bob's public key to encrypt her message, and Bob uses his private key to decrypt the message.
- Separate keys are used for encryption and decryption.
Public Key Distribution
- Only one key pair is needed for each recipient, with the private key kept secret and the public key shared widely.
Digital Signatures
- Public-key encryption provides a method for digital signatures.
- To sign a message, Alice encrypts it with her private key, creating a digital signature that can be decrypted by anyone using her public key.
Cryptographic Hash Functions
- A cryptographic hash function is a checksum on a message that is one-way and collision-resistant.
- It is easy to compute the hash, but hard to find the original message given only the hash.
Encryption and Decryption
- Encryption and decryption algorithms are chosen so that it is infeasible for someone other than Alice and Bob to determine the plaintext from the ciphertext.
- Ciphertext can be transmitted over an insecure channel, while keeping the plaintext secure.
Cryptosystem
- A cryptosystem consists of:
- The set of possible plaintexts
- The set of possible ciphertexts
- The set of encryption keys
- The set of decryption keys
- The correspondence between encryption keys and decryption keys
- The encryption algorithm
- The decryption algorithm
Caesar Cipher
- A simple substitution cipher where each letter is replaced with the one "three over" in the alphabet.
Symmetric Cryptosystems
- Alice and Bob share a secret key, used for both encryption and decryption.
- Symmetric key distribution requires each pair of communicating parties to share a separate secret key.
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