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Questions and Answers
A ______ can use a keyed hash in various ways with a message, often to create a digital signature.
A ______ can use a keyed hash in various ways with a message, often to create a digital signature.
MAC
A MAC is a cryptographic ______ that condenses a variable-length message to a fixed-sized authenticator.
A MAC is a cryptographic ______ that condenses a variable-length message to a fixed-sized authenticator.
checksum
A digital signature provides a way to ensure the ______ of a message, in addition to its authenticity.
A digital signature provides a way to ensure the ______ of a message, in addition to its authenticity.
integrity
Using a ______ cipher in chaining mode can be used to create a MAC, where the final block is used as the MAC.
Using a ______ cipher in chaining mode can be used to create a MAC, where the final block is used as the MAC.
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A hash function should have a ______ property, meaning it is infeasible to find x such that H(x) = h given h.
A hash function should have a ______ property, meaning it is infeasible to find x such that H(x) = h given h.
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Message authentication is concerned with validating the identity of the ______ of a message.
Message authentication is concerned with validating the identity of the ______ of a message.
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The ______ effect is a desirable property of cryptographic hash functions, where a small change in the input leads to a significant change in the output.
The ______ effect is a desirable property of cryptographic hash functions, where a small change in the input leads to a significant change in the output.
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In a keyed hash function, the ______ is used to condense the message and verify its authenticity.
In a keyed hash function, the ______ is used to condense the message and verify its authenticity.
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If symmetric encryption is used, the receiver knows the sender must have created it because only the sender and receiver know the ______ used.
If symmetric encryption is used, the receiver knows the sender must have created it because only the sender and receiver know the ______ used.
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The Data Authentication Algorithm (DAA) is a MAC based on ______ in CBC mode.
The Data Authentication Algorithm (DAA) is a MAC based on ______ in CBC mode.
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Block ______ can be used as hash functions, but the resulting hash value is too small and susceptible to attacks.
Block ______ can be used as hash functions, but the resulting hash value is too small and susceptible to attacks.
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The ______ algorithm was originally designed by NIST & NSA in 1993 and was revised in 1995 as SHA-1, a US standard for use with DSA signature scheme.
The ______ algorithm was originally designed by NIST & NSA in 1993 and was revised in 1995 as SHA-1, a US standard for use with DSA signature scheme.
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A digital signature provides ______ and authentication, whereas a MAC only provides authentication.
A digital signature provides ______ and authentication, whereas a MAC only provides authentication.
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A Message Authentication Code (MAC) is generated by an algorithm that creates a small fixed-sized block depending on both the message and some ______.
A Message Authentication Code (MAC) is generated by an algorithm that creates a small fixed-sized block depending on both the message and some ______.
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In public-key encryption, if the sender signs the message using their ______ and then encrypts with the recipient's public key, it provides both secrecy and authentication.
In public-key encryption, if the sender signs the message using their ______ and then encrypts with the recipient's public key, it provides both secrecy and authentication.
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When selecting a cryptographic hash algorithm, it is important to consider the ______ of the hash function to ensure security.
When selecting a cryptographic hash algorithm, it is important to consider the ______ of the hash function to ensure security.
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It is generally regarded as better to compute the MAC ______ encryption.
It is generally regarded as better to compute the MAC ______ encryption.
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A MAC provides assurance that the message is unaltered and comes from the ______.
A MAC provides assurance that the message is unaltered and comes from the ______.
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Study Notes
Hash Functions
- A hash function takes an input message of any size and produces a fixed-length output.
- Requirements for hash functions:
- Can be applied to any sized message
- Produces fixed-length output
- Easy to compute
- One-way property: given a hash output, it is infeasible to find an input message
- Weak collision resistance: given an input message, it is infeasible to find another message with the same hash output
- Strong collision resistance: it is infeasible to find any two messages with the same hash output
- Avalanche effect: a small change in the input message should result in a significantly different hash output.
Simple Hash Functions
- Simple hash functions based on XOR of message blocks are not secure because an attacker can manipulate the message to produce the same hash output.
- Birthday attacks: an attacker can generate multiple variations of a message and its hash output, and then find a pair with the same hash output by exploiting the birthday paradox.
Block Ciphers as Hash Functions
- Block ciphers can be used as hash functions, but the resulting hash output is too small (64-bit) and vulnerable to attacks.
- Using a block cipher in CBC mode without a key can produce a hash output, but it is still vulnerable to attacks.
Secure Hash Algorithm (SHA)
- SHA was originally designed by NIST & NSA in 1993 and revised in 1995 as SHA-1.
- SHA-1 is a US standard for use with DSA signature schemes and is specified in FIPS 180-1 and RFC3174.
Message Authentication Code (MAC)
- A MAC is a cryptographic checksum that condenses a variable-length message into a fixed-sized authenticator using a secret key.
- Requirements for a MAC:
- Given a message and MAC, it is infeasible to find another message with the same MAC
- MACs should be uniformly distributed
- MAC should depend equally on all bits of the message
- MAC can be used to detect changes to a message and ensure its authenticity.
Using Symmetric Cipher for MAC
- Any block cipher can be used to generate a MAC by encrypting the message in CBC mode and using the final block as the MAC.
Data Authentication Algorithm (DAA)
- DAA is a MAC based on DES in CBC mode, but it is no longer secure due to its small MAC size.
Message Authentication
- Message authentication is concerned with protecting the integrity of a message, validating the identity of the originator, and providing non-repudiation of origin.
- Three alternative functions for message authentication are message encryption, MAC, and hash functions.
Message Encryption
- Message encryption provides a measure of authentication if symmetric encryption is used, as the receiver knows the sender must have created it.
- Public-key encryption provides no confidence of the sender, but signing the message using the sender's private key and encrypting with the recipient's public key provides both secrecy and authentication.
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Description
This quiz covers the fundamentals of hash functions, including their requirements and properties. Learn about the importance of hash functions in cryptography and their applications in digital signatures. Test your knowledge on hash functions and their attributes.
