All Questions

267 views

Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA? [closed]

I'm not talking about scytale, but encryption like RSA, DES, etc... How did exactly civil cryptography evolve after WWII?
474 views

Subtracting a point in elliptic curve cryptography?

I've had lots of practice adding points for my crypto class. However I've run into a situation where I need to subtract two points for decryption: ...
122 views

Can I use the ChaCha core as a 256-bit to 256-bit one-way function?

I'm looking to implement Lamport signatures as a little fun project, and I need a fast one way function that maps $\{0,1\}^{256} \rightarrow \{0,1\}^{256}$. I was wondering whether I could safely use ...
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684 views

If RSA is limited to 117-200 bytes or so, is that a very limited use case?

Am I missing something, or is RSA very very limiting when it comes to ecrypting data when it comes to the actual message size? I have read that you can only encrypt a message of around 117 to 200 ...
379 views

Is there a way to do fair exchange between two parties who don't trust each other?

Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts $m_A$, Bob encrypts $m_B$) with their own key, and ...
338 views

Counter Mode: static IV but different keys [duplicate]

Given we are using AES counter mode, suppose we randomly generate several keys, all of them are using same IV (say, zeros). Does this lead to any security issue? I know that in CTR mode, same key-iv ...
1k views

SHA256 HMAC brute force with chosen plaintext attacks

This is a follow up to Is It Possible To Reconstruct a Cryptographic Hash's Key I am using a SHA-256 HMAC function on a single-word input: sha256hmac(privatekey,word) = output. The private key length ...
707 views

Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?

The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
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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?
1k views

Known-plaintext attack on Blowfish in ECB mode

The protection scheme I faced recently seems so weak nowadays that a simple exhaustive key search would be enough to recover the user key in an acceptable amount of time (it's OK, since almost no ...
328 views

How to compute the dot product on encrypted values?

Is there a practical homomorphic encryption scheme that can give reasonable execution time results in computing a dot product: $$a_1*b_1 + a_2*b_2 +a_3*b_3 +\ldots+ a_n*b_n$$ I imagine the scheme will ...
108 views

How hard are discrete logarithms problems in $\mathbb Z^{*}_{n}$ and $\mathbb Z^{*}_{n^2}$, where $n$ is the RSA $n=pq$

Use the notations form the Wikipedia article Paillier Cryptosystem , assume that the chipertext $c$ and $c^{\lambda} \mod n^2$ are both given, is it possible to compute $\lambda$ easily?
383 views

Symmetric encryption mode where ciphertext size is plain text size

I've had many questions on Stackoverflow on how to minimize the output of a cipher - during encryption of course - to the same size as the input. Obviously this is possible for a single block of ...
1k views

Why is RSA encryption significantly faster than decryption?

I am designing an implementation of RSA . I recorded computation times in Java by using System.currentTimeMillis(). It returned an encryption time of 0.05 ms and ...
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If Bob steals Alice's private key, how exactly would he read her encrypted documents?

So Bob grabs Alice's secret key when she isn't looking and her encrypted files, doesn't he need to know her passphrase to read her files? What I am reading is that no he does not need it but as far ...
184 views

Format Preserving Encryption for 32 or 64 bit plaintext values

I am looking for a Format Preserving Encryption implementation to apply to either a 32-bit or a 64-bit integer. It looks like AES/FFX mode is just what I need in terms of established security ...
187 views

Small Encryption Exponent

I am trying to crack an unpadded RSA set up for a homework. I have public key (R,e) and encrypted message E. ...
117 views

Straightforward method for hampering frequency analysis on deterministic encryption

I'm brainstorming some different ways of making deterministic encryption more secure. I want to use deterministic encryption to preserve searchability over the keywords in a document set. However, I ...
124 views

AES-CTR-256 Sub Keys With Encrypted Sub Key Index

I was working with some encryption and I decided to put a spin. To preface this would be used to encrypt multiple files. You start with a key file generated from random data. For example you could ...