34
votes
Digital signature that is only verifiable by one specific person
What you seem to be looking for is deniable authentication.
This is actually a somewhat stronger property than what you're asking for: it guarantees that the recipient (let's call him Bob) cannot ...
- 45.7k
33
votes
Accepted
Examples of modern, widely used ciphers that suddenly fell?
This question is quite broad by specifying a sudden fall to cryptanalysis and therefore my answer might not be as complete as you wish it to be.
If by "become practically attackable, or close enough ...
- 9,909
26
votes
Is secp256r1 more secure than secp256k1?
The curves secp256r1 and secp256k1 have comparable security.
If we consider only the best known attacks today, they have very close security.
Both curves are defined over prime fields and have no ...
- 6,814
26
votes
Accepted
What was NIST’s reason to switch naming from MD… (Message Digest) to SHA… (Secure Hashing Algorithm)?
When NIST introduced SHA-0 in 1993, they – for the first time – switched their naming convention from MD-n to SHA-n
Actually, MD-n was not NIST's naming conventions; it was RSA Security's (a private ...
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22
votes
Accepted
Does AES-NI offer better side-channel protection compared to AES in software?
Yes, AES-NI was specifically designed to be constant-time and thus offers better side-channel protection than (some) software implementations. Note however that these day there exist quite fast side-...
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21
votes
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Developing algorithm for detecting plain text via frequency analysis
As otus suggests in the comments, it's better to first calculate the frequency of each letter in the decrypted message, and then compare the frequency distribution to what would be expected for ...
- 45.7k
19
votes
Accepted
Use case for extendable-output functions (XOF) such as SHAKE128/SHAKE256
As of now I can think of four different applications for XOFs.
Note that some change the padding depending on the requested output size and so the outputs are truly unrelated, Skein does this.
...
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17
votes
Difference between “ECDH with cofactor key” and “ECDH without cofactor key”?
First, a bit of background. If we refer to the size of an elliptic curve group as $n$, we select an elliptic curve with $n = hq$, where $q$ is a large prime, and $h$ is a small integer called the ...
- 140k
16
votes
Accepted
Is every point on an elliptic curve of a prime order group a generator?
This is true of any group of prime order, over elliptic curves or not. This is due to Lagrange's Theorem which states that the order of a subgroup $H$ of group $G$ divides the order of $G$.
Since ...
- 721
16
votes
Does AES-NI offer better side-channel protection compared to AES in software?
With regards to timing-based side channels (those that can potentially be exploited remotely, as opposed to, say, power analysis), the AES-NI opcodes are constant-time. See for instance Intel ...
- 86.1k
16
votes
Accepted
Is Bruce Schneier Applied Cryptography, Second ed. up to date?
The Applied Cryptography Second Edition goes back to 1996. Although there is a 20th-anniversary edition, 2015, it is not updated as one thought. If you look for Schneier's style, you may look at the
...
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15
votes
Status of Algebraic Eraser key exchange?
The first part of this partial self-answer uses additional information I received from Professor Simon R. Blackburn, one of the author of the recent attack.
The method used to generate parameters is ...
- 134k
15
votes
Accepted
Why cannot I assume that cryptography published in venues/journals handled by the same publishers as prestigious journals is serious?
In addition to the (good) response of kodlu, let me clarify a point which, I think, is the source of the confusion.
Springer, IEEE, Elsevier, etc, are publishers. What this means is that they are ...
- 18.5k
14
votes
Accepted
Is there an encryption format that preserves length and only outputs alphanumerics?
Both of the other answers tackle the question of encryption in a particular format, but I would argue that neither of them is necessarily a good fit for your use case. You want to be able to generate ...
- 31.8k
14
votes
Digital signature that is only verifiable by one specific person
Lets say Alice wants to send Bob a sensitive message, she wants to prove to Bob that it came from her, but she doesn't want Bob to be able to prove that to anyone else.
A MAC is a good way of doing ...
- 162
13
votes
Accepted
Where can I find a description of the SHA-0 hash algorithm?
The reference on SHA(-0) is FIPS 180 (archived scan) of 1993 May 11. The standard itself is referenced on the NIST website, but that links to another scan lacking page 1 and the one before, thus ...
- 134k
13
votes
Accepted
Who is the inventor of the OFB block cipher mode of operation?
It's difficult to be sure of the attribution here, but my best guess would be Carl M. Campbell Jr., from the (later renamed to Mastercard) Interbank Card Association.
Soon after the DES was ...
- 12.2k
12
votes
Accepted
What was the NSA's reasoning for making their bitwise combination functions in SHA-1 the way they did?
What choice did they have?
F1 is a bitwise function with three inputs and one output. There are $2^8 = 256$ such functions. Only 70 of them are "unbiased" (i.e. have as many 0 and 1 outputs in their ...
- 31.8k
11
votes
Is there a string that's hash is equal to itself?
Yes, you can create many such functions.
For instance, lets build such a function based on SHA512. Generate some random value $m_0$ and generate a hash of it. It is important, because there is no ...
- 2,573
11
votes
Accepted
Opinion from "military institution" about the academic work
Here is a blog where Scott Aaronson wrote about this, including a link to the NSA document. That link is however now broken, but the blog contains all of the needed text. An alternative copy of the ...
- 27.4k
11
votes
Accepted
Clarification of the provable cryptography controversies
In general, that article seems to be referring to the "Another Look At..." line of work. Many of the papers are collated on this website.
There are a number of "controversies" you ...
- 10.8k
10
votes
Accepted
How to prove that a function is not pseudorandom?
Before answering the actual question, I will offer some general advice.
It is important to pay attention, both in class and to the textbook you are reading. If learning how to solve such exercises is ...
- 8,042
10
votes
Accepted
Which cryptography technique does not increase the size of the plain data?
The standard answer to this question is format-preserving encryption (FPE). FPE is a class of techniques that allow you to encrypt data while preserving some of its format (which can include its ...
- 4,616
10
votes
Accepted
Efficiency of oblivious algorithms vs non-oblivious algorithms?
Yes. There is an $\Omega(\log n)$ lower bound on ORAM. Therefore directly using ORAM to transform a non-oblivious algorithm to oblivious algorithm would incur a logN overhead. It is an open problem to ...
- 376
9
votes
Accepted
What is "witness encryption"?
In very short:
Assume you have an NP problem, stated as some condition to be met. Since it is a NP condition, the computational complexity to find a satisfying input (called the witness for the ...
- 12.5k
9
votes
Is secp256r1 more secure than secp256k1?
Here's a good amount of hard data on a variety of curves, well-analysed and the findings summarised in a readable way:
http://safecurves.cr.yp.to/
The article linked from this answer is not nearly ...
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9
votes
Use case for extendable-output functions (XOF) such as SHAKE128/SHAKE256
NIST has yet to standardize any accepted uses for these functions. As they said in response to a comment on the SHA-3 draft (pdf) which questioned this:
The text in Section 7 on conformance ...
- 31.8k
9
votes
Accepted
Where in the FIPS documents is it stated that SHA-1 is not secure?
Much of what NIST publishes about cryptographic algorithms is in Special Publications. In this case it is SP 800-131 (pdf) where they describe transitioning away from old algorithms and key sizes.
...
- 31.8k
8
votes
Accepted
How does the HOTP dynamic truncation function generalize to longer hashes?
I managed to find it out by reproducing the test vectors.
TL;DR: The standard assumes that you use the low 4 bits of the last byte of the hash, regardless of its length. So replace 19 in the original ...
- 31.8k
8
votes
What was the first MD5 collision ever constructed?
Even though Dobbertin could not provide a real collision of MD5, I would say that Hans Dobbertin first publicly described MD5 collision(s) in "The Status of MD5 After a Recent Attack" (PDF) – that was ...
- 17.7k
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