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Questions about the construction and analysis of protocols and algorithms for secure computation and communication (including authentication, integrity, and privacy aspects).

1 vote
Accepted

NSA Recommended Cryptography Algorithms changes from a single paper

There are many examples in cryptography. Much of progress in cryptography is driven by academic research. …
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2 votes

A question on RSA

They're not weak for use with RSA. You don't cite where you got that misconception from, so it's hard for me to respond or identify the source of your confusion -- but you have a faulty premise. Giv …
D.W.'s user avatar
  • 166k
4 votes

Encrypting a 180-bit plaintext into a 180 bit ciphertext with a 128-bit block cipher

One approach is to use what is known as format-preserving encryption. For instance, you could use VIL mode or FFX mode. I recommend you spend some quality time on Cryptography.SE and with some resea …
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  • 166k
1 vote

dining metaphysicians problem

See https://en.wikipedia.org/wiki/Secure_multi-party_computation and a good textbook on theoretical cryptography. …
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3 votes

Blockchain cipher suitable for preschoolers

No cryptography is needed. You just need a way to randomly pick one student in the room, in a fair way. This could be done with numbered balls in a box, or any number of other ways. …
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0 votes

What's the correct term for this analog of cryptography?

As @mhum suggests, looking at techniques from the field of steganography is probably an excellent starting point... but you might also be interested in subliminal channels.
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1 vote

Trustless exchange without a third party

This is known as the fair exchange problem. There's lots of research on the topic; see the link for an overview and starting point.
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0 votes

Proof of non-receipt of the file

Cryptography probably isn't especially useful for enabling Alice to tell whether the user got the right file, but it is useful for enabling the user to tell whether they got the right file. … I don't know of any way that cryptography can allow the user to prove he didn't get the right thing from Bob. As a simple case, suppose the user claims he received nothing from Bob. …
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1 vote

Can the program determine the frequency of the CPU or is it impossible?

In certain very specific situations, you might be able to use software-based attestation. See, e.g., the following seminal paper: Pioneer: Verifying Code Integrity and Enforcing Untampered Code Exe …
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3 votes

Why is fully homomorphic encryption so slow?

In some sense, it's not surprising that FHE is a lot slower than traditional cryptography. FHE imposes some very strong requirements on the encryption scheme. … Algorithms for black box fields and their application to cryptography. Dan Boneh, Richard Lipton. CRYPTO '96. …
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2 votes
Accepted

How does the Goldreich-Levin Theorem imply the existence of secure pseudorandom generators?

It sounds like your issue is just understanding the notation. Commas indicate concatenation. $\odot$ denotes the dot product. So, $f(x)$ is $|x|$ bits long, $r$ is $|x|$ bits long, and $x \odot r$ is …
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2 votes

Collision resistant hash function

There's a problem with the formal details of your definition of collision-resistance: if we take it seriously, then no function (whose output is shorter than its input) can ever be collision-resistant …
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1 vote

Finding the private key in BB84 quantum cryptography

The first stage of the BB84 protocol involves throwing away any measurements where the measurements were performed with a different basis. After throwing those away, we are left with the following bi …
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2 votes
Accepted

Is there a zero-knowledge protocol for bit vector agreement?

I think you actually want secure multi-party computation, not zero-knowledge proofs. In secure multi-party computation, Alice has a secret input $a$, Bob has a secret input $b$, and we want to comput …
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14 votes
Accepted

Why did RSA encryption become popular for key exchange?

There is no strong technical reason. We could have used Diffie-Hellman (with appropriate signatures) just as well as RSA. So why RSA? As far as I can tell, non-technical historical reasons dominate …
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