# All Questions

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### Roots in modulo field

I have a point $(X,Y)$ on an elliptical curve $E(a,b)$ where $a=-3$ and $B$ is a large number that is in hexadecimal from -51BD. To compress this point oficially in a program, we know that every $X$ ...
16 views

### Timestamp assignment and meaning

I have an entity A sending a message to another, B. An encrypted message is signed with a timestamp TB, and then the whole thing is signed again with a new key and new timestamp TA. What i'm ...
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### Modulo Square Roots [duplicate]

Here's my issue and someone can help me understand it so I can program it correctly. I have a point(X,Y) on an Elliptical Curve E(a,b) where a=-3 and B is a large number that is in hexidecimal from ...
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### Retrieve timestamp from TOTP value

TOTP (Time-based One-Time Password) as I understand is an algorithm that uses the current time as a variable along with a shared key to generate a secured token. Wiki page for reference: ...
52 views

### Using machine-learning techniques for data-dependent operations in ciphers

From 'Methods of Symmetric Cryptanalysis' by Dmitry Khovratovich, The data-dependent operations are one of the most controversial design concepts. We say that an operation is data-dependent, if it ...
63 views

### Arithmetic modulo 1

In the context of lattice-based cryptography, in particular the Learning With Errors (LWE) problem, I see some definitions given in terms of equations modulo 1 (see for example, Appendix A of this ...
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### Why is proving “parties' views are simulatable” enough in semi-honest model?

To prove a protocol is secure in semi-honest model, we have to prove: the view of each party, on each possible pair of inputs, can be efficiently simulated based solely on its own input and and ...
67 views

### point decompression on a elliptical curve

I'm programming an elliptical curve cryptography system and I'm having difficulty with decompressing points. The following information is from my project specification as to my understanding: Given a ...
50 views

### What approach is used here? [closed]

Here is an image hidding some information. I need to discover, what is the hidden text. I tried to interpret this as 27 letter alphabet(with space) in columns, tried this with Ceasar cipher. No ...
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### Oblivious transfer variation question

Now I am doing a variation of the oblivious transfer, I have to use 2 people, pebbles, and boxes. I need to find out if who has a larger number between Alice and Bob (variation of Yao's Millionaires' ...
136 views

### Will X9.31 remain a secure & acceptable deterministic random generator beyond 2015?

I am actually looking for available crypto libraries including a deterministic random generator for the purpose of a dedicated crypto key generator unit. I have a simple question about the X9.31 based ...
43 views

### Soundness of GRC.com Haystack padding concept [migrated]

I was wondering how sound is the concept presented by the Gibson Research Corporation (see below if you do not want to follow the link) about simple passwords (= very easy to remember) with the ...
48 views

### What cipher algorithm is this routine using? [closed]

I transfered a code routine from Java to Python: ...
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### Requirement for the length of a HMAC tag?

I've seen NIST requirements about key length. What about the output lengths ? Is 112 bits enough for the HMAC output length ? Can we truncate the tag to keep only 112 bits ? Thank you
41 views

### Factoring a number who has factors with same number of digits

I am working on a factoring problem. I have a number that is a product of two prime numbers, both with same numbers of digits (20-30 digits). I was searching online for algorithms that are good for ...
51 views

### how to represent message as an integer between $1$ and $n-1$ [closed]

I am trying to implement simple El-Gamal cryptosystem. And I can't understand how to represent message as an integer between $1$ and $n-1$. The only thing that comes to my mind is: if $n$ bit length ...
67 views

### Generation of strong primes

It seems that this is pretty difficult to find large (above 1024 bits) strong primes, or at least such primes p where (p-1) has a very large prime factor. Is there any information regarding the ...
104 views

### Rounds in cryptography

I need to make it clear I know nothing about crypto so in that context I'm hoping to clear up some confusion: As I understand it a "round" in a cipher is one encryption operation and a cipher like ...
128 views

### In cryptographic protocols, what protects against an attacker dropping messages?

In some cryptographic protocols I have seen messages protected for confidentiality, authenticity, replaying attacks, reordering attacks, etc. What protects a protocol from an attacker in a ...
26 views

### Encrypt algorithm [duplicate]

Is it possible to encrypt an algorithm? What I mean by this is have a remote/cloud computer execute a program that will process some data... And the remote computer would not be able to know anything ...
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### Corporate PKI - SHA1 deprecation [closed]

Here is the context. Suppose you have a corporate PKI with : AC_Root (offline in safe store - SHA1 signature) SubRootA ans SubrootB (offline in safe store - SHA1 signature) SubSubRootC, ...
233 views

### RFC 6979 - Why not simply hash the message & the private key for deterministic ECDSA?

Why go through the trouble of using the HMAC_DRBG process, instead of simply hashing [message | private key] to calculate $k$ for deterministic ECDSA? If the ...
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### block cipher algorithms with variable block lengths

Rijndael supports block lengths of 128, 192 and 256. AES does not but Rijndael does. What other algorithms support variable block lengths? Or is Rijndael unique in that regard?
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### transforming RC2 keys to have effective minimum length in implementations with fixed effective lengths

mcrypt's implementation of RC2 has a fixed effective length of 1024 bits, however, it is possible to simulate keys with effective lengths between 1-1024 by doing something like this: ...
42 views

### Does SHA-1 hash have quasi commutative property? [closed]

Although I have tested with a program and found negative answer, I want to be sure.
39 views

### Encryption using elliptic curves

What is currently the best way to actually encrypt a message using elliptic curves? I'm looking for an algorithm like ElGamal, but more efficient, since ElGamal outputs a tuple of two points for every ...