# All Questions

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### Proving an encrypted message contains (but does not 100% consist of) a plain-text message?

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then concatenate X and Y, into Z. I encrypt Z, into "encrypt(Z,u) = Q". r is ...
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### Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
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### Requirements for the modulus in the Massey-Omura three pass protocol

In the Massey-Omura three pass protocol: How many bits long should the prime modulus $M$ be in order to be secure? Should the $M$ be secret? Should the $M$ be generated every time or it could be ...
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### Concepts for realization in applied cryptography [closed]

I'm a computer science student (not a mathematican) and I'm gonna to write a master degree diploma on applied cryptography. Specifically, I'd like to create a realization of some cryptographic stuff ...
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### Is Curve25519 vulnerable to private key exposure in the case of a bad RNG?

I'm really excited by what I've learned of advancements in elliptic-curve cryptography. Curve25519 seems to be a great choice at this point in time, but if I recall correctly, some elliptic curve ...
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### A periodic PRNG based on hash function?

I need a PRNG which provides 128 bytes numbers. Let's say that given a symmetric key $K$ and an internal state $s$ I use the PRF HMAC-SHA512 this way: The output is PRNG($K, s$) = ...
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### Are there ANY text strings that will generate the same SHA-512 Hash output? [duplicate]

Are there ANY text strings that will generate the same SHA-512 Hash output? Please provide an example, and how you came to that conclusion. I've tried thousands of variations, including ".." vs. "." ...
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### Proving an encrypted message contains (but does not 100% consist of) a plain-text message? [duplicate]

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then combine X and Y, into c(X,Y) = Z. I encrypt Z, into "encrypt(Z,u) = Q". r ...
290 views

### Formula for the number of expected collisions

Say we have a hash function that produces $n$ bit outputs. From the birthday problem that after around $\sqrt{2^n}$ different inputs to the has function, we can expect a collision. Say instead that ...
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### Why do we truncate the hash when using DSA?

All the articles I read on the web about DSA keep telling me that the size of the hash needs to be truncated so that the bit length is equal to or lesser than the bit length of the prime number of the ...
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### Is there any equivalent to the apache xml security library for JSON? [closed]

I'm talking about org.apache.xml.security(santurio) Is there any equivalent library that works with JSON and provides the same set of features? (mostly AES-128 with KEK support)
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### Privacy and Integrity in Public Cryptography

I'm trying to figure out which is the best way to get privacy and integrity together in public cryptography. Alice needs to send multiple files $f$ (may be big) to Bob. I've thought: Alice computes ...
161 views

### Are ideal hashes possible to create?

In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve). Hence, isn't it ...
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### What security authorities and standards reject $e=3$ in RSA, when, and with what rationale?

In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following: PKCS#1 allows ...
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### How feasible would it be to generate 300 million public key pairs in 8 hours?

Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time. What would be required in terms of ...
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### Is SipHash cryptographically secure?

I'm evaluating different hash algorithms for use in my application. One of the kind of algorithms I am looking at are cryptographically secure ones to protect against DOS attacks. SipHash seems ...