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Questions and Answers
What is the original message to be encrypted called?
What is the original message to be encrypted called?
Plaintext
What is the process of converting plaintext into ciphertext called?
What is the process of converting plaintext into ciphertext called?
Enciphering or encryption
What is the term for the encrypted message?
What is the term for the encrypted message?
Ciphertext
What is the term for the key that is used for both encryption and decryption?
What is the term for the key that is used for both encryption and decryption?
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What is the term for the process of recovering plaintext from ciphertext?
What is the term for the process of recovering plaintext from ciphertext?
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The decryption algorithm is the reverse of the encryption algorithm.
The decryption algorithm is the reverse of the encryption algorithm.
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A cipher is also referred to as a cryptographic system.
A cipher is also referred to as a cryptographic system.
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Cryptanalysis is the study of attacks against cryptographic systems.
Cryptanalysis is the study of attacks against cryptographic systems.
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Cryptology is the science of studying ciphers.
Cryptology is the science of studying ciphers.
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What are the two inputs for an encryption algorithm?
What are the two inputs for an encryption algorithm?
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The key used in a symmetric cipher is the same for both encryption and decryption.
The key used in a symmetric cipher is the same for both encryption and decryption.
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What is the difference between a block cipher and a stream cipher?
What is the difference between a block cipher and a stream cipher?
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An asymmetric cipher uses the same key for both encryption and decryption.
An asymmetric cipher uses the same key for both encryption and decryption.
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The key used in symmetric encryption is often referred to as a symmetric key.
The key used in symmetric encryption is often referred to as a symmetric key.
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All classical encryption algorithms are symmetric.
All classical encryption algorithms are symmetric.
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What is the objective of Cryptanalysis?
What is the objective of Cryptanalysis?
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What does Kerkhoff's principle state?
What does Kerkhoff's principle state?
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What are the two general approaches to attacking a conventional encryption scheme?
What are the two general approaches to attacking a conventional encryption scheme?
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In a brute-force attack, what is the attacker trying to do?
In a brute-force attack, what is the attacker trying to do?
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On average, it takes trying half of all possible keys in a brute-force attack to be successful.
On average, it takes trying half of all possible keys in a brute-force attack to be successful.
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If a brute-force or cryptanalytic attack is successful, the impact is only for the current intercepted message.
If a brute-force or cryptanalytic attack is successful, the impact is only for the current intercepted message.
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Cryptanalytic attacks can be classified by the amount of information available to the attacker.
Cryptanalytic attacks can be classified by the amount of information available to the attacker.
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Which of these is NOT a type of cryptanalytic attack?
Which of these is NOT a type of cryptanalytic attack?
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The ciphertext-only attack is the most difficult to defend against because the attacker has the most information.
The ciphertext-only attack is the most difficult to defend against because the attacker has the most information.
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The ciphertext-only attack is completely insecure if it cannot resist ciphertext-only attacks.
The ciphertext-only attack is completely insecure if it cannot resist ciphertext-only attacks.
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What is the goal of the known-plaintext attack?
What is the goal of the known-plaintext attack?
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The known-plaintext attack is closely related to what is called a probable-word attack.
The known-plaintext attack is closely related to what is called a probable-word attack.
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In a chosen-plaintext attack, the attacker can choose the plaintext and observe the resulting ciphertext.
In a chosen-plaintext attack, the attacker can choose the plaintext and observe the resulting ciphertext.
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In a chosen-ciphertext attack, the attacker can choose any ciphertext to obtain its plaintext by having it decrypted.
In a chosen-ciphertext attack, the attacker can choose any ciphertext to obtain its plaintext by having it decrypted.
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Classical encryption techniques are no longer relevant in modern cryptography.
Classical encryption techniques are no longer relevant in modern cryptography.
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What is the goal of studying classical encryption techniques?
What is the goal of studying classical encryption techniques?
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Older versions of RSA encryption were susceptible to chosen-ciphertext attacks.
Older versions of RSA encryption were susceptible to chosen-ciphertext attacks.
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In a chosen-ciphertext attack, the attacker chooses the ciphertext to analyze.
In a chosen-ciphertext attack, the attacker chooses the ciphertext to analyze.
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Study Notes
Symmetric Cipher Model
- A secret key is shared by the sender and recipient.
- Plaintext is inputted into the encryption algorithm (e.g., DES).
- Ciphertext is transmitted.
- Ciphertext is inputted into the decryption algorithm (reverse of encryption).
- Plaintext is output.
Basic Terminology
- Plaintext: The original message to be encrypted.
- Ciphertext: The encrypted message.
- Enciphering/Encryption: The process of converting plaintext into ciphertext.
- Encryption Algorithm: Performs the encryption process, taking plaintext and a secret key as input.
Deciphering/Decryption
- Decryption Algorithm: Recovers plaintext from ciphertext, using the ciphertext and the secret key as input.
Cryptography & Cryptanalysis
- Cipher/Cryptographic System: A scheme for encryption and decryption.
- Cryptography: The science of studying ciphers.
- Cryptanalysis: The science of studying attacks against cryptographic systems.
- Cryptology: The combination of cryptography and cryptanalysis.
Ciphers
- Symmetric Cipher: Uses the same key for encryption and decryption.
- Block Cipher: Encrypts a block of plaintext at a time (typically 64 or 128 bits).
- Stream Cipher: Encrypts data one bit or one byte at a time.
- Asymmetric Cipher: Uses different keys for encryption and decryption.
Symmetric Encryption
- Also known as conventional, secret-key, or single-key encryption.
- Sender and recipient share a common key.
- All classical encryption algorithms are symmetric.
- The only type of cipher prior to the invention of asymmetric-key ciphers in the 1970s.
- Widely used.
Symmetric Encryption (Mathematical)
- Y = E(X) or Y = E(K, X)
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X = D(Y) or X = D(K, Y)
- X = plaintext
- Y = ciphertext
- K = secret key
- E = encryption algorithm
- D = decryption algorithm
- Both E and D are known to the public.
Cryptanalysis
- Objective: To recover the plaintext of a ciphertext or, more commonly, the secret key.
- Kerkhoff's Principle: The adversary knows all details about a cryptosystem except the secret key.
- Brute-Force Attack: Tries every possible key until a successful decryption of the ciphertext is achieved. (This approach is computationally intensive and time-consuming, particularly with increasingly strong encryption keys)
- Non-Brute-Force Attack (Cryptanalytic Attack): Exploits the nature of the encryption algorithm to guess the secret key.
Steps of a Block Cipher (Example)
- Step 1: Get Text: Obtain the plaintext to be encrypted.
- Step 2: Convert to Binary: Convert the plaintext into its binary representation.
- Step 3: Break into 64 bit blocks: Divide the binary data into fixed-size blocks (typically 64 bits).
- Padding: Data may need to be padded according to the specific cipher to handle plaintext that doesn't neatly divide into the appropriate block size.
Ciphertext-Only Attack
- The attacker only has access to the ciphertext.
- This is generally considered the easiest attack to defend against due to the limited information available.
- An encryption scheme is considered insecure if it cannot withstand a ciphertext-only attack.
Known-Plaintext Attack
- The attacker has access to the plaintext and its corresponding ciphertext.
- The attacker uses this information to analyze the encryption scheme and potentially derive the secret key.
- A common cryptanalytic attack used in block ciphers.
Chosen-Plaintext Attack
- The attacker can choose plaintext messages to be encrypted.
- The attacker then analyzes the resulting ciphertexts to derive information about the secret key or the encryption technique employed.
Chosen-Ciphertext Attack
- The attacker chooses ciphertext messages and receives the corresponding decrypted plaintexts.
- This technique allows the attacker to infer information about the secret key used in the encryption system.
Classical Encryption Techniques
- These encryption techniques provide a foundation and introduction to basic concepts and terminology essential for understanding the processes behind modern cryptography.
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Description
This quiz covers the fundamental concepts of cryptography, including symmetric cipher models, basic terminology such as plaintext and ciphertext, and the processes of encryption and decryption. Test your understanding of how algorithms are used in securing information.
