# All Questions

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### The length of the shortest vector in Lattice

In Micciancio and Regev's paper "Lattice-based Cryptography",the length of the shortest vector is at least min{q, 2^{2*squart(nlog_qlog_(dert))}} . I want to ask why the paper chose the latter as the ...
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### Store and share data on web server

I'm developing an intranet for a company where admins are sharing a huge excel file containing all the necessary password, on the common TSE. I've managed making them encrypt it with a common password ...
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### Proof that LFSR (with XOR feedback and nonzero seed) will never hit state of all 0s

Does anyone know a good proof that a LFSR (with XOR feedback and seeded with non-zero starting state) will never enter zero state? It is obvious that a zero state will always get stuck in a zero ...
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### What exactly is a “garbled circuit”?

There are plenty of questions here about the details and how-to's of "garbled circuits", but I have not seen anything that defines what garbled circuits are. What exactly is a garbled circuit? What ...
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### How can I find all points on an elliptic curve?

I have an elliptic curve $$y^2=x^3 + 8 \times x + 6 \mod 13$$ How do I find all the points on this EC? Also, could you give me more examples?
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### Client side encryption / hashing of “person ID's” with password?

What we're looking for A solution where data is stored and retrieved (!) from a server using a person ID that can only be known at the client (form of ...
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### Given $g^a, Y$, is it hard to distinguish $e(g,g)^{ab}$ from a random value?

where $g$ is a group element in bilinear group $G$ $Y = M.e(g,g)^{ab}$ $M$ is a message Does anyone know the answer or suggest some material for reference? Many Thanks
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### Using the Unix epoch as nonce

Since a nonce must be unique and that time only goes forward, is it safe to use the Unix epoch as nonce ? My use case is be AES w/ GCM which recommends a nonce length of 12B. Current Unix time can be ...
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### How secure is encrypting with self-hash [duplicate]

I don't have much knowledge about cryptography beyond using libraries for it. So just wanted to understand if the following two cases differ sufficiently in security or is it just psychological: Say ...
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### Is it possible to turn an image (e.g. a photo) into a cryptographic hash? [closed]

I am looking for a way to turn an image (e.g. a photo captured on a phone) into a cryptographic hash (e.g. SHA256). Is this possible? If so, how?
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### Is security against semi honest adversary inheritable?

I have a two party protocol, let's call it $M$. At some point, there are $k$ steps, each one involving an oblivious transfer protocol, which is known to be secure against semi honest adversaries. ...
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### Decomposing an ideal in intersections

Let $R$ be an ring, and let $(a),(b)$ be the ideals generated by $a,b\in R^\times$ respectively. Let $c=a\cdot b$ and $(c)$ the ideal generated by $c$. I am supposing that, given $c$, it is ...
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### Using a single Ed25519 key for encryption and signature

The libsodium documentation contains a function crypto_sign_ed25519_pk_to_curve25519 that converts an Ed25519 key into a Curve25519 one, so it can be used for both ...
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### How long is the tag T in AES-GCM(Or: Can implementations freely choose t = len(T)?) [duplicate]

I've started to learn about GCM. In the paper I read on page 4 there is the equation: $$T = \text{MSB}_t(\text{GHASH}(H, A, C) \oplus E(K, Y_0))$$ It's clear to me that the function \$\text{MSB}_t(S)...