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Questions and Answers
What is the maximum estimated time for Eve to launch a collision attack using a hash function with a 64-bit digest?
What is the maximum estimated time for Eve to launch a collision attack using a hash function with a 64-bit digest?
How many tests are needed to successfully perform a collision attack on MD5?
How many tests are needed to successfully perform a collision attack on MD5?
What is the digest size of the SHA-1 hash function?
What is the digest size of the SHA-1 hash function?
Which hash function is described to be resistant to collision attacks based on the Random Oracle Model?
Which hash function is described to be resistant to collision attacks based on the Random Oracle Model?
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What is the relationship between a message digest and a message authentication code (MAC)?
What is the relationship between a message digest and a message authentication code (MAC)?
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Which statement accurately describes the essential difference between a document and its fingerprint compared to a message and its message digest?
Which statement accurately describes the essential difference between a document and its fingerprint compared to a message and its message digest?
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How long would it theoretically take to launch a collision attack on SHA-1 if tests can be performed at 230 per second?
How long would it theoretically take to launch a collision attack on SHA-1 if tests can be performed at 230 per second?
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What are the three criteria that a cryptographic hash function must satisfy?
What are the three criteria that a cryptographic hash function must satisfy?
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What is the purpose of a modification detection code (MDC)?
What is the purpose of a modification detection code (MDC)?
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How many tests does SHA-512 require to find a collision with a probability of 1/2?
How many tests does SHA-512 require to find a collision with a probability of 1/2?
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Why can a conventional lossless compression method like StuffIt not be used as a cryptographic hash function?
Why can a conventional lossless compression method like StuffIt not be used as a cryptographic hash function?
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What does second preimage resistance in a cryptographic hash function prevent?
What does second preimage resistance in a cryptographic hash function prevent?
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Which of the following statements about collision resistance is true?
Which of the following statements about collision resistance is true?
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In the Random Oracle Model, what is the primary function of the oracle?
In the Random Oracle Model, what is the primary function of the oracle?
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What is a significant limitation of using a checksum function as a cryptographic hash function?
What is a significant limitation of using a checksum function as a cryptographic hash function?
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What aspect of document integrity can a fingerprint verify?
What aspect of document integrity can a fingerprint verify?
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What is the primary output size of the SHA algorithm?
What is the primary output size of the SHA algorithm?
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Which SHA version added in FIPS 180-2 does NOT exist?
Which SHA version added in FIPS 180-2 does NOT exist?
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What role do the 80 constants, K0 to K79, serve in the SHA-512 algorithm?
What role do the 80 constants, K0 to K79, serve in the SHA-512 algorithm?
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What key feature is employed by the SHA-512 compression function?
What key feature is employed by the SHA-512 compression function?
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If the first hexadecimal digits of buffers A, B, and C are 0x7, 0xA, and 0xE respectively, what is the leftmost hexadecimal digit of the resulting Majority function?
If the first hexadecimal digits of buffers A, B, and C are 0x7, 0xA, and 0xE respectively, what is the leftmost hexadecimal digit of the resulting Majority function?
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What aspect of SHA-1 has raised concerns about its future applications?
What aspect of SHA-1 has raised concerns about its future applications?
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Which function in SHA-512 is responsible for providing output based on the majority of input bits?
Which function in SHA-512 is responsible for providing output based on the majority of input bits?
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Which of the following SHA versions was introduced as a part of the revised Secure Hash Standard?
Which of the following SHA versions was introduced as a part of the revised Secure Hash Standard?
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Which property of a cryptographic hash function ensures that it is computationally infeasible to find two different inputs that produce the same hash output?
Which property of a cryptographic hash function ensures that it is computationally infeasible to find two different inputs that produce the same hash output?
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What is the primary purpose of a Message Authentication Code (MAC)?
What is the primary purpose of a Message Authentication Code (MAC)?
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How can HMAC security be compromised?
How can HMAC security be compromised?
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Which of the following is a characteristic of a cryptographic hash function that allows it to detect changes in a message?
Which of the following is a characteristic of a cryptographic hash function that allows it to detect changes in a message?
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Which method is employed to achieve non-repudiation in digital signatures?
Which method is employed to achieve non-repudiation in digital signatures?
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What is the significance of using a pseudorandom function (PRF) in cryptography?
What is the significance of using a pseudorandom function (PRF) in cryptography?
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In the context of digital signatures, what role does the public key play?
In the context of digital signatures, what role does the public key play?
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What is the primary purpose of creating a message digest (MDC) when sending a message?
What is the primary purpose of creating a message digest (MDC) when sending a message?
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Which of the following elements are crucial for message authentication?
Which of the following elements are crucial for message authentication?
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Which hashing technique ensures that the original password cannot be easily retrieved from stored data?
Which hashing technique ensures that the original password cannot be easily retrieved from stored data?
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Why does the security of a Message Authentication Code (MAC) depend on the underlying hash algorithm?
Why does the security of a Message Authentication Code (MAC) depend on the underlying hash algorithm?
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What is a significant disadvantage of using public-key encryption for message authentication?
What is a significant disadvantage of using public-key encryption for message authentication?
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In the context of symmetric message encryption, which statement is true?
In the context of symmetric message encryption, which statement is true?
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What occurs when signing a message using the sender's private key followed by encrypting with the recipient's public key?
What occurs when signing a message using the sender's private key followed by encrypting with the recipient's public key?
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What is a potential issue related to the use of PKCS in public-key encryption?
What is a potential issue related to the use of PKCS in public-key encryption?
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Which factor contributes to the requirement of recognizing corrupted messages in public-key encryption?
Which factor contributes to the requirement of recognizing corrupted messages in public-key encryption?
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What is the primary violation that occurs when an oracle uses a formula h(M) = M mod n to create message digests?
What is the primary violation that occurs when an oracle uses a formula h(M) = M mod n to create message digests?
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According to the pigeonhole principle, if a hash function produces 4-bit digests and accepts 6-bit messages, how many different messages can correspond to a single digest?
According to the pigeonhole principle, if a hash function produces 4-bit digests and accepts 6-bit messages, how many different messages can correspond to a single digest?
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How many digests should Eve create to have more than a 50% probability of finding an original message with a 64-bit digest?
How many digests should Eve create to have more than a 50% probability of finding an original message with a 64-bit digest?
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If Eve can generate 2^30 messages per second, how long would it take her to find a preimage for a 64-bit digest?
If Eve can generate 2^30 messages per second, how long would it take her to find a preimage for a 64-bit digest?
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In the case of a collision attack with a 64-bit digest, how many digests would Eve need to create to exceed a probability of 50% in finding two messages with the same digest?
In the case of a collision attack with a 64-bit digest, how many digests would Eve need to create to exceed a probability of 50% in finding two messages with the same digest?
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What characteristic of a cryptographic hash function is directly challenged by a collision attack on a 64-bit digest?
What characteristic of a cryptographic hash function is directly challenged by a collision attack on a 64-bit digest?
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What does the 'k' represent in the generalized version of the pigeonhole principle related to message digests?
What does the 'k' represent in the generalized version of the pigeonhole principle related to message digests?
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When evaluating the security of a digest size of 64 bits against different types of attacks, which attack is the digest least secure against?
When evaluating the security of a digest size of 64 bits against different types of attacks, which attack is the digest least secure against?
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Study Notes
Cryptography and Network Security Week 9-11
- This week covers message integrity, cryptographic hash functions, cryptographic hash function criteria, preimage resistance, second preimage resistance, collision resistance, random oracle model, and message authentication.
Message Integrity
- Cryptography systems typically provide secrecy/confidentiality but not integrity.
- Integrity ensures the message hasn't been altered.
- Preserving document integrity: Using a fingerprint (analogous to a digital fingerprint/message digest). Alice places her fingerprint at the bottom of a document.
- Electronic equivalent of document/fingerprint pair: message/digest pair.
- A hash function converts a message into a fixed-size digest.
Cryptographic Hash Function Criteria
- Preimage resistance: Given a hash, it is computationally infeasible to find the original message producing that hash.
- Second preimage resistance: Given a message and its hash, it is computationally infeasible to find a different message with the same hash.
- Collision resistance: It is computationally infeasible to find two different messages with the same hash.
Random Oracle Model
- Introduced in 1993 by Bellare and Rogaway.
- Serves as an ideal mathematical model for hash functions.
- Assumes the hash function is a random oracle. This means that the hash function acts like a random function—it maps inputs to outputs in a completely unpredictable way.
Message Authentication
- A message digest by itself does not authenticate the sender.
- Modification detection code (MDC): Digest created by cryptographic hash function.
- Message authentication code (MAC): Needed for authenticating the sender.
- A MAC uses a secret key known only to the sender and receiver.
Attack Types and Algorithms
- Preimage Attack: Given a digest, find the original message
- Second Preimage Attack: Given a message, find another message with the same digest.
- Collision Attack: Find two different messages with the same digest.
- The difficulty of the attacks increase proportionally to 2n (preimage), 2n (second preimage), and 2n/2 (collision), where n is the number of bits in the digest/hash value.
- Example 11.2: A checksum function is not a cryptographic hash function.
Additional Points
- Cryptographic hash functions are important for message integrity and authentication when data needs to persist longer than its encryption.
- A 64-bit digest offers security against preimage attacks but not collision attacks; a 128-bit digest is preferred for better security.
- SHA-1 and MD5 were popular hash functions, but are now considered vulnerable to attack due to improvements in computer processing and discovery of weaknesses in the algorithms.
- SHA-2 (e.g. SHA-512) was introduced as a replacement for previous versions to increase security, but still relies on iteration and can be attacked by a cryptanalytic attacks.
- Whirlpool: An iterated hash function that uses a symmetric-key block cipher in place of the compression function; the block cipher is a modified AES cipher.
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Description
Test your knowledge on cryptographic hash functions with this quiz. Explore questions about collision attacks, digest sizes, and essential differences between message digests and MACs. Discover the requirements for secure hash functions and their use in data integrity.
