The fourth property
, the one-way property, states that it is easy to generate a code given a message but virtually impossible to generate a message given a code. This property is important if the authentication technique involves the use of a secret value (Figure 11.5e).
Why is the one-way property of encryption algorithms important?
Algorithms of one-way hash functions are often known to the public. They
provide security thanks to their properties
as one-way functions. Usually, a change of one bit of input data, causes changing about half of the output bits. … They are used for example in an message authentication algorithm HMAC.
What properties must a hash function have to be useful for message authentication?
To be useful for message authentication, the hash function H must have the following properties:
– H can be applied to a block of data of any size
. – H(x) is relatively easy to compute for any given x, making both hardware and software implementation practical.
In which mode of encryption if an attacker reorders the blocks of ciphertext then each block will still decrypt successfully?
In
the ECB mode
of encryption if an attacker reorders the blocks of ciphertext then each block will still decrypt successfully, however, the reordering may alter the meaning of the overall data sequence.
Which property guarantees it is impossible to find an alternate message with the same hash value as a given message?
The
fifth property, second preimage resistant
, guarantees that it is impossible to find an alternative message with the same hash value as a given message. This prevents forgery when an encrypted hash code is used (Figure 11.2b and Figure 11.3a).
Are there one-way functions?
There
is an explicit function f that has been proved to be one-way
, if and only if one-way functions exist. In other words, if any function is one-way, then so is f. Since this function was the first combinatorial complete one-way function to be demonstrated, it is known as the “universal one-way function”.
Are one-way functions Bijective?
According to the definition of Oded Goldreich’s book Foundations of Cryptography (Basic Tools),
a one-way function does not need to be a bijection
.
Can we use the hash function for the authentication?
A message authentication code (MAC) is similar to a cryptographic hash, except that it is based on a
secret
key. When secret key information is included with the data that is processed by a cryptographic hash function, the resulting hash is known as an HMAC.
What is the difference between a private key & a secret key?
2. In this, the same key (secret key) and algorithm is used to encrypt and decrypt the message. In public key cryptography, two keys are used, one key is used for encryption and while the other is used for decryption. … In private key cryptography,
the key is kept as a secret
.
What is digital signature authentication?
Digital signatures are
the public-key primitives of message authentication
. … They are used to bind signatory to the message. Similarly, a digital signature is a technique that binds a person/entity to the digital data. This binding can be independently verified by receiver as well as any third party.
What is CTR mode?
CTR (short for counter) is a
popular AES block cipher mode
in which every step can be done in parallel. CTR is similar to OFB as it also involves XOR-ing a sequence of pad vectors with the plaintext and ciphertext blocks. The main difference lies in how these pad vectors are generated.
Which of the following is the strongest hashing algorithm?
The current strongest encryption algorithms are
SHA-512
, RIPEMD-320, and Whirlpool.
Does AES use Feistel structure?
Explanation: It uses a 128-bit block size and a key size of 128, 192, or 256 bits. 2. Like DES, AES also
uses Feistel Structure
.
Which of the following is often called a keyed cryptographic hash function?
A keyed hash function (also known as
a hash message authentication code, or HMAC
) is an algorithm that uses a cryptographic key AND a cryptographic hash function to produce a message authentication code that is keyed and hashed.
What is hash coding?
(programming, algorithm) (Or “hashing”)
A scheme for providing rapid access to data items which are distinguished by some key
. Each data item to be stored is associated with a key, e.g. the name of a person.
What is second pre image resistance?
Second preimage resistance is
the property of a hash function that it is computationally infeasible to find any second input that has the same output as a given input
. … A hash function is said to be a one-way hash function (OWHF) if it is both preimage resistant and second preimage resistant.
