# Tag Info

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The correct answer would be: 1 . “Cryptography is under the security field”. Let me try to explain it a bit… Cryptography Modern cryptography concerns itself with 4 objectives: Confidentiality: the information cannot be understood by anyone for whom it was unintended. Integrity: the information cannot be altered in storage or transit between sender ...

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"PRNG" means "Pseudorandom Number Generator" which means that a sequence of numbers (bits, bytes...) is produced from an algorithm which looks random, but is in fact deterministic (the sequence is generated from some unknown internal state), hence pseudorandom. Such pseudorandomness can be cryptographically secure, or not. It is cryptographically secure if ...

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Randomness is not a property of strings of bits (or characters of any sort). Rather it is a property of the process that generates those strings. However, it is convenient to conflate the string with the thing that produced the string, and thus to speak about strings being “random” or “not random”. The string 00000, for example, is random if it was the ...

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"Cycles" are CPU instruction cycles. Cycles per byte roughly measures how many instructions, in a given instruction set, are needed to produce each byte of output. They're a reasonably-good relative measure of the performance of different algorithms. Generally, when you measure an algorithm's cycles per byte, you use carefully controlled conditions. You ...

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There are multiple metrics for work or effort needed: Amount of operations it takes (one operations is, for instance, one invocation of hash function or number of modular multiplication operations) Amount of money it takes Amount of memory it takes Amount of time it takes Strength in bits Amount of operations Usually, if amount of operations is large ...

7

In this context 'security margin' is a measure for how much better we need to get at analyzing a cipher to break it. Such advances in cryptoanalysis require new ideas of how one might attack a cipher. Thus estimating how strong a cipher is, is hard. Ultimately we can only tell something is broken, after we've broken it. We typically look at a few ...

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As noted in this answer and this answer to another question, permutation is just a mathematical term for a function $\sigma:X{\rightarrow}X$ that maps a finite set $X$ onto itself, in such way that for each $y \in X$ there exists exactly one $x \in X$ such that $\sigma(x) = y$. This is also equivalent to how the term substitution is used in cryptography, so ...

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Thought I'd begin with some references for you that might be of interest. These terms are used as key 'selling points' for a number of schemes, including many of the CAESAR submissions. Some examples using the terms specifically are given below - most of which are from CAESER because I have the zoo in-front of me: "Online": OCB, Ascon, CBA, APE, NORX ...

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A "generic attack" against a cryptographical primitive is one that can be run independently of the details of how that cryptographical primitive is implemented. The most obvious case is a cipher that takes an $N$ bit key; the generic attack of brute force takes a ciphertext, and attempts to decrypt it with all $2^N$ keys; when we find the known (or ...

6

Fair exchange protocols aren't new by any means, but there is a lack of layman-friendly material out there, unfortunately. I think the high prevalence of theoretical cryptography in fair exchange protocols may be partially responsible for that. At any rate, here is the basic idea behind a fair exchange protocol. Suppose you have two parties, Alice and Bob, ...

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This is a simple substitution cipher, specifically a mixed/deranged alphabet cipher. See wikipedia's description: Substitution of single letters separately—simple substitution—can be demonstrated by writing out the alphabet in some order to represent the substitution. This is termed a substitution alphabet. The cipher alphabet may be shifted or reversed ...

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In my practice (Smart Cards, often using DES and increasingly AES) Key Expansion is often used to designate production of subkeys in a block cipher. This process is often a mere bit extraction, as part of the algorithm's Key Schedule. Key Diversification is, almost exclusively, the process of producing a device key from its serial number (or other ...

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The Diffie-Hellman key exchange is a public-key technology. It is (by itself) not an encryption algorithm (or signature algorithm), though. Here is the basic function: (All calculations here happen in a discrete group of sufficient size, where the Diffie-Hellman problem is considered hard, usually the multiplicative group modulo a big prime (for classical ...

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According to J.-P. Aumasson (who's one of the authors of another SHA-3 finalist, BLAKE, and who participated in the cryptanalysis of Keccak), the name "Keccak" is a variant spelling of "Kecak", a type of Balinese dance. So far, that's the most authoritative reference I've been able to come up with. It should be noted that naming crypto primitives after ...

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Circuits can be expressed using very simple operations. For example, a boolean circuit consists of only two types of gates, addition and multiplication (where the input values are each 1 bit). Furthermore, (boolean) circuits can describe any computation. This is very nice when it comes to fully-homomorphic encryption. All we have to do is provide a way to ...

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It sounds like you're basically asking for a definition of the word "cipher". I agree that it's somewhat fuzzy and complicated — that's mainly because "cipher", on its own, is not a precisely defined technical term in modern cryptography, but a descriptive word whose meaning, like that of most other English words, has evolved gradually over time. So, ...

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Randomness is the information loss of any causal relationship between events. The universe needn't be a clockwork universe for the assumption of pervasive causality - if events are "sticky" and accrue localised causality in the same way that a molecular cloud accretes into stars and planets. The underlying cause of the speed of light might also be the prime ...

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A mode of operation is an explicit method by which we use a block cipher (eg AES) to do more than just encrypt one block of data. For example, it may allow us to encrypt multiple blocks of data (eg ECB,CBC etc), provide us with some authenticated encryption (eg GCM) or a method for encrypting disc storage (eg XTS). Rijndael,DES etc are block ciphers. That ...

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To be concise, true randomness boils down to the selected data being causally unrelated. That is, if each piece of data is the result of no common cause, then there is no relation by which the rest of the data can be predicted or inferred. So being unpredictable is a consequence of being truly random, but it is the lack of causal relationship that is the ...

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I have seen that used in the context of session keys, to describe how a key is tied to an identity without any certificate relative to that key could only be known by another identified party, without assurance that this party ever held that key. For example, one generates a random symmetric key, encrypts it using (say) RSA and a public key, and sends the ...

5

Cryptography is just one way towards security. It can solve some issues of security but not all of them. Careful coding for instance has nothing to do with cryptography. Appropriate memory allocation is not correlated with crypto but it is an aspect of security. Cryptography can mitigate confidentiality, integrity, secure computations, etc issues

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Many block ciphers are defined by specifying a round and then running that specification multiple times. For example, in AES, a round consists of the operations SubBytes, ShiftRows, MixColumns, AddRoundKey. That is one round and, to get AES, you run that multiple times (plus some setup and some post-processing). Thus a round is defined by each cipher and ...

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I don't have my copy of Katz & Lindell in front of me, but using the term "simulator" in the context of, say, an IND-CPA definition, is not exactly in line with standard usage in current literature. (But still an ok choice of words which is excusable for a textbook.) Here's the breakdown of "game-based" vs. "simulation-based" definitions: Both styles ...

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As @CodesInChaos explains: It might refer to blind signatures. It also might refer to a method to harden (typically) RSA implementations against timing/side-channel attacks, by blinding the data before operating on it. Example: suppose you are writing code to decrypt data, i.e., to compute $y=x^d \bmod n$, given the input $x$. The naive way to do is just ...

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Quoting from "On beating the hybrid argument" (by Bill Fefferman, Ronen Shaltiel, Christopher Umans and Emanuele Viola; 2012): The hybrid argument allows one to relate the distinguishability of a distribution (from uniform) to the predictability of individual bits given a prefix. The argument incurs a loss of a factor k equal to the bit-length of the ...

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A "cipher" is the algorithm which encrypts and decrypts data, while the "cipher-mode" defines how the cipher encrypts and decrypts it. In other words: ciphers are the cryptographic algorithms that you use to encrypt/decrypt data, while cipher-modes define the "mode of operation" for applying the cipher. Both are complementary and can be chosen separately. ...

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The pseudo-preimage is the problem of finding $(IV, M)$ given $t$ such that $H(IV, M) = t\$.

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Look up the words sound/complete from logic. Complete roughly means that a method can solve every instance. Sound roughly means that the answer it gives is correct. For example, assume that we have a program that's supposed to tell when an element belongs to a set. A sound program will only answer "yes" when the element actually belongs to the set. An ...

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My understanding of the term 'pepper' is that it more matches your definition 2, in that a pepper is an unknown salt, which makes it a cryptographic secret, but not a key. However, in use it is not as limited by either of your definitions: The pepper can be different (or random) for all users (like a salt). The pepper can be the same for all users (like a ...

3

Linear functions when expressed as polynomials only have terms of degree 1 or 0. Non-linear functions have at least one term of degree 2 or higher. For example, here is a linear boolean function: $y = ax + bz + c$, where $y$ is the output bit, $x$ and $z$ are input variables, and $a$, $b$, and $c$ are constants. Notice that none of the variables are ...

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