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Questions and Answers
A secret key is not used in the decryption process.
A secret key is not used in the decryption process.
False (B)
Block ciphers typically operate on blocks of 32 bits.
Block ciphers typically operate on blocks of 32 bits.
False (B)
Encryption and decryption processes always involve the use of algorithms.
Encryption and decryption processes always involve the use of algorithms.
True (A)
Confusion in cryptography refers to methods that simplify the relationship between plaintext and ciphertext.
Confusion in cryptography refers to methods that simplify the relationship between plaintext and ciphertext.
Stream ciphers generate data in fixed-size blocks.
Stream ciphers generate data in fixed-size blocks.
Microdots and image-word techniques are used in cryptography to hide information in transit or storage.
Microdots and image-word techniques are used in cryptography to hide information in transit or storage.
A reverse cipher encrypts a message by rearranging the letters in alphabetical order.
A reverse cipher encrypts a message by rearranging the letters in alphabetical order.
Cryptology encompasses both the study of cryptography and cryptanalysis.
Cryptology encompasses both the study of cryptography and cryptanalysis.
In-transit encryption secures data after it is received and before it is sent.
In-transit encryption secures data after it is received and before it is sent.
At-rest encryption involves encrypting data after it has been written to memory.
At-rest encryption involves encrypting data after it has been written to memory.
The black-box model assumes that attackers have complete access to the implementation of the cipher.
The black-box model assumes that attackers have complete access to the implementation of the cipher.
A chosen-plaintext attacker can perform encryption queries for plaintexts of their choice.
A chosen-plaintext attacker can perform encryption queries for plaintexts of their choice.
Columnar transposition is a technique that completely changes the plaintext symbols during encryption.
Columnar transposition is a technique that completely changes the plaintext symbols during encryption.
Instance deduction allows a cryptanalyst to find the plaintext of an intercepted ciphertext.
Instance deduction allows a cryptanalyst to find the plaintext of an intercepted ciphertext.
Gray-box models allow attackers to have complete access to the cipher's implementation.
Gray-box models allow attackers to have complete access to the cipher's implementation.
Ciphertext-only attackers have access to both the ciphertext and the associated plaintext.
Ciphertext-only attackers have access to both the ciphertext and the associated plaintext.
The Feistel network is a structure used in many asymmetric ciphers.
The Feistel network is a structure used in many asymmetric ciphers.
Diffusion in cryptography refers to spreading the influence of plaintext and key bits over the ciphertext.
Diffusion in cryptography refers to spreading the influence of plaintext and key bits over the ciphertext.
The Data Encryption Standard (DES) algorithm can handle key sizes greater than 128 bits.
The Data Encryption Standard (DES) algorithm can handle key sizes greater than 128 bits.
Cryptanalysis involves the process of encrypting messages to secure communications.
Cryptanalysis involves the process of encrypting messages to secure communications.
The Rijndael algorithm is capable of using keys that are 128 bits or more.
The Rijndael algorithm is capable of using keys that are 128 bits or more.
Symmetric cryptography uses a single key for both encryption and decryption processes.
Symmetric cryptography uses a single key for both encryption and decryption processes.
Ciphertext is the original readable data before any encryption takes place.
Ciphertext is the original readable data before any encryption takes place.
The term 'cryptography' specifically refers to the use of ciphers to communicate openly.
The term 'cryptography' specifically refers to the use of ciphers to communicate openly.
Flashcards
Cipher Cryptography
Cipher Cryptography
Protecting communication through codes, making messages readable only to intended recipients.
Cryptography
Cryptography
Process of communicating secretly using ciphers and cryptanalysis (breaking codes).
Symmetric Cryptography
Symmetric Cryptography
Encryption/decryption use the same secret key, shared between sender and receiver.
Plaintext
Plaintext
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Encryption Algorithm
Encryption Algorithm
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Ciphertext
Ciphertext
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Diffusion
Diffusion
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Cryptographic Algorithm
Cryptographic Algorithm
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Encryption
Encryption
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Decryption
Decryption
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Cipher Algorithm
Cipher Algorithm
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Secret Key
Secret Key
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Cryptology
Cryptology
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Block Cipher
Block Cipher
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Stream Cipher
Stream Cipher
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In-transit encryption
In-transit encryption
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At-rest encryption
At-rest encryption
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Encryption in use
Encryption in use
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Black-box Model
Black-box Model
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Gray-box Model
Gray-box Model
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White-box Model
White-box Model
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Ciphertext-only attack
Ciphertext-only attack
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Known-plaintext attack
Known-plaintext attack
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Study Notes
Cipher Cryptography
- Cryptography is the science of secure communication, using ciphers to protect messages.
- Cryptanalysis is the process of breaking secret communications.
- Cryptography uses algorithms to transform messages, making them unreadable to unauthorized users.
Symmetric Cryptography
- Plaintext: Original message.
- Encryption Algorithm: Mathematical operations to scramble the plaintext.
- Ciphertext: Scrambled message after encryption.
- Secret Key: Used both for encryption and decryption.
- Decryption Algorithm: Reverses encryption using the secret key to recover the plaintext.
- Block Ciphers: Operate on fixed-size blocks (e.g., 64 or 128 bits).
- Stream Ciphers: Generate a stream of pseudorandom bits (e.g., one bit or byte at a time).
- Confusion: Techniques to hide relationships between plaintext, ciphertext, and key.
- Diffusion: Spreading the influence of plaintext and key bits throughout the ciphertext.
Data Encryption Systems (DES)
- DES: Creates fixed-length block ciphers with a secret key.
Advanced Encryption Standard (AES)
- AES: Uses the Rijndael algorithm with a variable key size (e.g., 256 bits).
Cipher Methods
- Cipher: Method to transform a message to conceal its meaning.
- Algorithms involve private and public key generation, digital signing, and message verification.
- Reverse Cipher: Encrypts a message by reversing the order of characters.
Brute Force Technique
- Attack Models: Assumptions about attackers' capabilities (e.g., black-box, gray-box, white-box models).
- Black-box Model: Limited access to the cipher.
- Gray-box Model: Some access to the cipher's implementation.
- White-box Model: Full access to the cipher's implementation.
- Ciphertext-only attack (COA): Access only to ciphertext.
- Known-plaintext attack (KPA): Access to both ciphertext and plaintext.
- Chosen-plaintext attack (CPA): Ability to encrypt chosen plaintexts.
Categories of Breaking an Algorithm
- Total Break: Finding the key.
- Global Deduction: Finding an alternate algorithm.
- Instance/Local Deduction: Determining plaintext from ciphertext.
- Information Deduction: Obtaining some key or plaintext information.
- Unconditional Security: Cannot be broken even with infinite resources.
Transposition Cipher
- Transposition Ciphers: Change the order of characters in the plaintext but don't replace them.
- Columnar Transposition: A transposition cipher where the plaintext is arranged in a matrix, then reordered.
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