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2 answers

Formal verification in cryptography

I have seen in some places that people use formal verification and/or computer-aided verification for cryptography (tools like ProVerif, CryptoVerif, etc.). How do these approaches work?
user4936
33
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4 answers

What is the difference between known-plaintext attack and chosen-plaintext attack?

I am very confused between the concept of known-plaintext attack and chosen-plaintext attack. It seems to me that these two are the same thing, but it definitely is not. Can anyone explain to me how these two differ?
Tom Fabregas
33
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2 answers

Disadvantage AES-GCM

What are the disadvantages and weaknesses of AES-GCM mode for authenticated encryption? Why does the CAESAR competition say that it’s one of the goals to "find an AE scheme that offers an advantage over AES-GCM"? What advantage they are talking…
user2035863
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Is 80 bits of key size considered safe against brute force attacks?

I came across the KATAN family of ciphers for small domain input blocks. They cipher arbitrary block lengths: 32, 48 and 64, but their key size is 80 bits only. Is 80 bits of key size considered safe against brute force attacks with current state…
sashank
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33
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Reason why “XOR” is a linear operation, but ordinary “addition” isn’t?

I'm new in cryptography and try to read some articles in this field. Many of these articles talk about non-linear S-boxes, and nothing more on what they mean by their non-linearity. I have a simple question which I think will guide me through my…
Shnd
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33
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2 answers

In RSA, why is it important to choose e so that it is coprime to φ(n)?

When choosing the public exponent e, it is stressed that $e$ must be coprime to $\phi(n)$, i.e. $\gcd(\phi(n), e) = 1$. I know that a common choice is to have $e = 3$ (which requires a good padding scheme) or $e=65537$, which is slower but safer. I…
Martin
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33
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2 answers

Why do we need special key-wrap algorithms?

Wikipedia says: Key Wrap constructions are a class of symmetric encryption algorithms designed to encapsulate (encrypt) cryptographic key material. We are using these algorithms to encrypt (and authenticate) a key, using a symmetric algorithm…
Paŭlo Ebermann
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32
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ECDSA Compressed public key point back to uncompressed public key point

From the ECDH demo here, if I generate a private key for Alice I can get _ P = 1175846487558108474218546536054752289210804601041 Which gives the following public key point. X = 583857549063195252150226340830731484791130788759 Y =…
Ian Purton
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Theoretically, what if I were to change some magic numbers in, say, AES?

Purely theoretically. I know it's a bad idea to try to invent your own encryption and that's not the intention here. Just a thought experiment. Say, I change some or all of the magic numbers used in, say, AES (but this would also apply to other…
RobIII
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What is the practical impact of using System.Random which is not cryptographically random?

I recently noticed a .NET software using PBKDF to derive an encryption key from a password string. This password string was dynamically generated using System.Random. Now, I know that System.Random is not really cryptographically random and should…
learnerX
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32
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Prevent double-spending with decentralized digital currencies without all transactions being public?

A recent approach to creating a decentralized online currency, called Bitcoin, has been generating some interest. The goal is to have a way to transfer currency without a central authority and without double spending or counterfeiting. Their…
Artem Kaznatcheev
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Fixed point of the SHA-256 compression function

SHA256 Free Start Self Collision (Full 64 rounds) IVec: 72BF9EF1 27B82DFB F298F3B7 22B6C32C 18A54860 4C032D91 ADD7B85B 7ED1A4AC Block: 0000004D 0000006F 00000075 00000073 00000065 00000054 00000072 00000061 00000070 00000000 00000000 00000000…
Nathan.Mariels
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32
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3 answers

Applicability of IBM's projected 50-qubit quantum computer Q to cryptanalysis?

IBM announced Q, a project for a 50-qubit universal quantum computer, according to the press realease. Here is more PR spin, and the research sub-page. What would be the applicability of that to cryptanalysis?
fgrieu
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32
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Key derivation functions (KDF): What are they, what are their main purposes and how they can be used?

What are KDFs? What are their main purposes? How they can be used, in other words, what's their drill in a cryptography scheme?
Samuel Paz
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32
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4 answers

Why does Neumann think cryptography isn't the solution?

What did Peter G. Neumann mean by: If you think cryptography is the answer to your problem, then you don't know what your problem is. (eg: quoted in the New York Times, February 20 2001)
user2768
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