Questions tagged [terminology]

Questions about the meaning and proper use of specific technical terms or notation within cryptography.

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11
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4answers
3k views

What is the difference between a 'cipher' and a 'mode of operation'?

What is the difference between the term cipher (a name like RIJNDAEL) and mode of operation (like ECB)? Aren't these both terms for the encryption/decryption technique?
7
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2answers
2k views

What is the definition of "security beyond the birthday paradox"?

I'm reading a paper about MACs and I would like to be sure about the meaning of a security beyond the birthday paradox. Is there a definition?
4
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1answer
2k views

What is adversary's advantage in cryptography and why we use it?

The definition of adversary's advantage seems a bit odd for me and I am wondering why do we use it to measure the power of an adversary rather than just use the probability of a PPT adversary ...
16
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6answers
3k views

How exactly is "true randomness" defined in the realms of cryptography?

Especially in relation to stream ciphers, I frequently read about (sometimes theoretical, sometimes practical) attacks that are able to "distinguish a ciphertext from a truly random stream". What's ...
4
votes
1answer
435 views

What does it mean to be simultaneously hardcore?

In this paper the term "simultaneously hardcore" is defined as: "We say that a block of bits of $x$ are simultaneously hard-core for a one-way function $f(x)$, if given $f(x)$ they cannot be ...
3
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0answers
228 views

Precise meaning of various terms related to universal hash functions [closed]

I've been reading about universal hashing, but I'm confused by all these different terms and notations. Could someone help me understand the precise meaning or relation between the following terms: ...
10
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1answer
4k views

What is it meant by a "hybrid argument"?

Can anyone explain (or point to a reference for) what a hybrid argument is in a security proof, and when it's convenient or preferable to use it? Among some of the places where I've seen it mentioned,...
6
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2answers
21k views

What is the meaning of "trapdoor" in cryptography?

I do not really understand the meaning of a "trapdoor" in cryptography, so here are my questions: What is the meaning of trapdoor and how can I convert a word or string using a trapdoor in ...
17
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1answer
2k views

What is the origin of the word "Keccak"?

Where does the word or acronym Keccak come from? Guido Bertoni, Joan Daemen, Michael Peeters, and Gilles Van Assche. Keccak sponge function family main document. Submission to NIST (updated), 2009. "...
49
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6answers
10k views

Kerckhoffs’ principles – Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
6
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1answer
713 views

Difference between actual attacks and theoretical attacks on SHA cryptographic series

Could anyone tell me what the difference is between a theoretical attack (Like the one done on SHA-1) and an actual, practical attack (Like the one done on SHA-0)? Is a theoretical attack a proposed ...
9
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2answers
9k views

Definition and meaning of "semantic security"

I'm taking a Coursera cryptography course. The definition of semantic security is hard to understand. I tried to restate it with some slight changes (the word "efficient" was in the original ...
5
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1answer
2k views

Signature with appendix

I see sometimes signatures schemes with appendix. This is about signatures schemes in which the message is needed in the verification algorithm, that is, the ouput of the signature algorithm is of the ...
22
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4answers
19k views

The exact difference between a permutation and a substitution

I've noticed confusing definitions about permutation and substitution, preventing me from understanding the difference. A permutation changes the order of distinct elements of a set, but this can be ...
7
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1answer
3k views

What is a fair exchange scheme?

The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated. Is this a new field in cryptology or can someone give an ...
2
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1answer
162 views

What does "securely realize" mean?

I was wondering what "securely realizes" means. I see this in some cryptographic papers but I don't know what it means for a protocol to "securely realize" a function $F$. Is it just a fancy way of ...
5
votes
1answer
469 views

What does "adaptively secure" mean?

In a paper it says "In the generic group model, the PRF is adaptively secure for inputs of $\mathbb{Z}_q^n$". Maybe a stupid question, but what does "adaptively secure" mean exactly?
2
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2answers
594 views

What are unified addition and differential addition in elliptic curve point arithmetic?

A lot of papers use these terms but I do not find a proper explanation of them. Can somebody tell the meaning / difference / intuition / application and if possible with an example.
26
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2answers
23k views

Why is Diffie-Hellman considered in the context of public key cryptography?

In all textbooks I used the Diffie-Hellman key exchange is under "public key cryptography". As far as I can see it is a method to exchange a key to be used with a symmetric cryptographic algorithm, ...
2
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2answers
322 views

Name for identical operations for encryption and decryption

Is there a name for the property of a cryptographic algorithm that the operations for encryption and decryption are identical, i.e. $E_k(x) = D_k(x)$ and accordingly $E_k(E_k(x)) = x$? An example ...
3
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1answer
6k views

What are rounds in the context of ciphers?

Another recent question on security margin included in its answer the discussion of how many rounds are broken so far. What is the definition of a round?
8
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1answer
2k views

What is 'security margin'?

I have been academic papers about Rijndael, Serpent, and Twofish, and there is this term that is vague to me. I cannot find a tangible definition in google. Can someone briefly define, describe, and/...
1
vote
1answer
335 views

What does modular inversion mean?

I'm trying to implement an e-voting algorithm, which is described at the paper "Internet Voting Protocol Based on Improved Implicit Security" by Abhishek Parakh & Subhash Kak. At the Example 1 ...
7
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1answer
2k views

What does a "cycle" mean in cryptography benchmarks?

In this table of the "Crypto++ 5.6.0 Benchmarks", for example, cryptographic algorithm performance is measured in cycles per byte for symmetric ciphers, and in cycles per operation for asymmetric ...
9
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1answer
4k views

What is "Blinding" used for in cryptography?

What does "blinding" mean in cryptography, and where do we usually use it? Can you describe a sample implementation?
11
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1answer
6k views

What does Maj and Ch mean in SHA-256 algorithm?

I'm guessing they're some kind of standard function but what do they do and what do the names mean? A little explaination or link me to an article would be great.
6
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1answer
9k views

What is a trapdoor permutation?

Can anyone explain to me what a trapdoor one-way permutation is? Is RSA a trapdoor one-way permutation? Context: I was reading about ring signatures. On page 560, it describes steps to implementing ...
3
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3answers
212 views

The meaning of "scheme"

This question is a bit different from other questions here, but I think it is suitable to correctly understand the terminology of cryptography. Consider the following two sets of terms: Encryption ...
150
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2answers
144k views

What is the main difference between a key, an IV and a nonce?

What are the main differences between a nonce, a key and an IV? Without any doubt the key should be kept secret. But what about the nonce and the IV? What's the main difference between them and their ...
33
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8answers
43k views

Simply put, what does “perfect secrecy” mean?

I would like to ask for a clear (but maybe not so deep) explanation of what the term "perfect secrecy" means. As far as I have researched and understood, it has to do with probabilities of assuming ...
5
votes
1answer
6k views

Simulation-based security?

I've been reading Introduction to Modern Cryptography by Katz and Lindell as an introduction to cryptography. The book seems to use the term 'simulator' when it talks about a game like, for instance, ...
8
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2answers
2k views

Toy cipher -- does it have a name?

When I was perhaps nine years, I borrowed a book from the library on various maths and CS topics. It outlined various simple ciphers, including one that I used a lot, just for fun. I can't remember ...
11
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2answers
2k views

K out of N encryption

A friend just showed me how to combine padlocks to achieve a lock that opens when k out of n people turn their keys. I was ...
3
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0answers
213 views

Security of stream cipher based on Matrix multiplication GF(256) with randomized padding

The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components: The keyed function $F_k:\{0,1\}^{8n}\mapsto\...
10
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1answer
904 views

Are there any authoritative definitions of "key stretching"?

This is mostly a terminology question, but I suppose that it is best asked and answered here. After browsing the Internet I have come across a fair number of completely different definitions of the ...
7
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1answer
3k views

What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
52
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3answers
42k views

Definition of textbook RSA

What is the definition of textbook or "raw" RSA? What are some of the properties of textbook RSA? How does it differ from other schemes based on RSA?
41
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3answers
24k views

What are the differences Between “White-Box Cryptography” and “Code Obfuscation”?

I have been reading the question "What is a white-box implementation of a cryptographic algorithm?" and it led to this short article / Q&A which states in question 2: Q2: What is the ...

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