Questions and Answers
What is a characteristic of symmetric encryption?
What can typically be a method to encrypt stored data?
Which statement about public-key encryption is true?
What is a common feature of hash functions?
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What does the term 'non-repudiation' refer to in digital signatures?
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Which is a common application of pseudorandom numbers?
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Which approach is NOT a typical method for archiving stored data securely?
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What does symmetric block encryption primarily achieve?
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What is often the primary purpose of encryption for transmitted data?
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Why is it essential to use randomly generated keys in encryption?
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Study Notes
Symmetric Encryption
- Provides confidentiality for transmitted or stored data, also known as conventional encryption or single-key encryption.
- Requires a strong encryption algorithm and secure sharing of a secret key between sender and receiver.
Attacking Symmetric Encryption
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Brute-Force Attacks:
- Involves trying all possible keys on ciphertext to find intelligible plaintext.
- On average, half of all possible keys must be tried for success.
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Cryptanalytic Attacks:
- Exploits algorithm characteristics and knowledge of plaintext attributes to deduce plaintext or key.
- Success compromises all messages encrypted with that key.
Popular Symmetric Encryption Algorithms
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Data Encryption Standard (DES):
- A 64-bit block size with a 56-bit key, produces a 64-bit ciphertext block.
- Considered insecure due to key length and has been extensively studied.
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Triple DES:
- Enhances DES by applying the algorithm three times with either two or three keys.
- Key length of 168-bits increases security against brute-force attacks but is slower in software.
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Advanced Encryption Standard (AES):
- Developed as a replacement for 3DES, using 128-bit data blocks with key sizes of 128, 192, or 256 bits.
- Selected Rijndael as the standard for its superior efficiency and security.
Practical Security Issues
- Symmetric encryption commonly applied to larger data sets rather than single blocks.
- Electronic Codebook (ECB) Mode: Simplest form of block encryption but can expose regularities in plaintext, risking cryptanalysis.
Types of Symmetric Encryption
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Block Ciphers:
- Process input in fixed-size blocks, providing an output block for each input.
- More common in applications.
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Stream Ciphers:
- Encrypt data continuously, outputting one element at a time, generally faster and more efficient.
Message Authentication
- Protects against alterations and verifies the authenticity and sequence of received messages.
- Can occur without confidentiality; combining both is recommended for stronger security.
Hash Function Requirements for Authentication
- Can process data of any size with a fixed-length output.
- Must be one-way resistant (pre-image resistant) and collision resistant.
Security of Hash Functions
- Attacks include cryptanalysis and brute-force methods.
- SHA is the most popular hash algorithm utilized.
Public-Key Encryption
- Proposed by Diffie and Hellman, operating on the basis of asymmetric keys (public and private).
- Public key encryption allows anyone with the public key to decrypt messages.
Applications of Public-Key Cryptosystems
- RSA: Widely used algorithm for encryption and digital signatures.
- Diffie-Hellman: Primarily for key distribution, not suitable for direct encryption or signatures.
- DSS (Digital Signature Standard): Allows for signatures but not encryption of data.
- Elliptic Curve: Supports signatures and encryption key distribution.
Requirements for Public-Key Cryptosystems
- Easy key pair creation and utilization for encryption/decryption.
- Computationally difficult for adversaries to derive private keys from public keys or recover original messages without the private key.
Asymmetric Encryption Algorithms
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RSA (Rivest, Shamir, Adleman):
- Developed in 1977, the most accepted public-key encryption method, works with integers for plaintext and ciphertext.### Diffie-Hellman Key Exchange
- Enables secure agreement on a shared secret key for symmetric encryption between two users.
- Primarily focused on key exchange without providing encryption capabilities.
Asymmetric Encryption Algorithms
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Digital Signature Standard (DSS)
- Provides functionalities for digital signatures using SHA-1.
- Not suitable for encryption or key exchange.
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Elliptic Curve Cryptography (ECC)
- Delivers security comparable to RSA but requires significantly smaller keys.
Digital Signature Definition
- Defined by NIST FIPS 186-4 as a cryptographic transformation mechanism that verifies:
- Origin authentication.
- Data integrity.
- Signatory non-repudiation.
- Functions as a data-dependent bit pattern generated from a data block.
Digital Signature Algorithms
- FIPS 186-4 specifies three algorithms:
- Digital Signature Algorithm (DSA).
- RSA Digital Signature Algorithm.
- Elliptic Curve Digital Signature Algorithm (ECDSA).
Random Numbers and Their Role
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Random Number Requirements
- Must exhibit uniform distribution for statistical fairness.
- Should be unpredictable to prevent future number prediction.
- Independence is key; no single number should be inferred from others.
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Pseudorandom Number Generation
- Often utilizes algorithmic methods, producing non-statistically random sequences.
- Pseudorandom numbers may pass randomness tests but remain predictable.
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True Random Number Generator (TRNG)
- Draws from nondeterministic sources, such as physical phenomena (e.g., radiation).
- Often included in modern processors for enhanced randomness.
Encryption Applications
- Commonly encrypts transmitted data, while encryption for stored data is less prevalent.
- Historical data can be recoverable until disk sectors are reused, even after erasure.
- Various approaches exist for encrypting stored data:
- Commercial encryption solutions.
- Back-end appliances.
- Library-based tape encryption.
- Background encryption for laptops/PCs.
Summary Insights
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Confidentiality and Symmetric Encryption
- Includes symmetric block encryption algorithms and stream ciphers.
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Message Authentication and Hash Functions
- Discusses authentication using symmetric encryption and secure hash functions.
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Public-Key Encryption
- Covers structure, applications, and requirements of public-key cryptography and asymmetric encryption algorithms.
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Key Management
- Involves digital signatures, public-key certificates, and symmetric key exchanges using public-key encryption.
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Random and Pseudorandom Numbers
- Highlights the importance of random number use in cryptographic applications.
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Practical Application of Encryption
- Focuses on the encryption of stored data and the mechanisms to protect it effectively.
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Description
Explore the key concepts of symmetric encryption in chapter 2 of 'Computer Security: Principles and Practice'. Understand the requirements for secure encryption and the importance of a strong encryption algorithm. This quiz will test your knowledge on essential cryptographic tools.