# All Questions

489 views

### Definition of cryptographic advantage vs. probability of success

In game-based security definitions, like for example the one defining IND-CPA security, a given cryptosystem is said to be secure if any probabilistic polynomial time adversary has only a negligible ...
222 views

### what is an injective trapdoor function?

The answer to this question at Crypto.SE is clear about what a trapdoor function is, but what makes a trapdoor function "injective"?
446 views

### Shamir's Secret Share [duplicate]

I'm not quite sure the benefits of working over a prime modulus in Shamir's secret share- but doesn't limiting the numbers you pull from make the secret easier to guess? Instead of being over the real ...
120 views

### Question about Fermat's little theorem

Why is $g^e \mod p = g^{e \mod (p-1)} \mod p$ if p is prime. I don't get it. It follows from Fermat's little theorem.
250 views

### Is it possible to translate a piece of language into your own without knowing the language? [closed]

I understand the the texts within the Voynich Manuscript are of an unknown language, and yet cryptographers are still working on it and still trying to decipher it. Does that mean that it is possible ...
510 views

### How terribly flawed is this design for key storage?

Dave here, with a plan for storing secrets. Threat model: Database and keyfile may (will?) be stored on un-trusted servers. Database contains many valuable secrets (passwords), encrypted by key ...
798 views

### Using IV buffer after altered inside a Rijndael CBC Encryption/Decryption process as IV for next message?

When sending a block to be decrypted or encrypted, with RijndaelCBC, we input the data to decrypt/encrypt and an IV for syncing and to prevent identical outputs for identical inputs. This question is ...
1k views

### Lagrange Interpolation for finite field GF(2^8), for Secret Reconstruction

I'm using Lagrange's Interpolation technique to reconstruct the secret from a set of point pairs (x,y). Since I only need the secret, not the whole polynomial, I have simplified the reconstruction ...
888 views

### Quadratic residue problem on composite integers

Its believed that the quadratic residue modulo $n=p·q$ for large primes $p$ and $q$ is intractable, which forms the basis of some cryptosystems. However, it is solvable if the factors of $n$ are know,...
135 views

### Three-way key exchange with elliptic curves without pairing

Assume that there are three users, each with their own secret key $d_i$ and the corresponding public key $Q_i = d_i \cdot P$, such that $Q_i$ is a point on an elliptic curve and $P$ is a base point on ...
1k views

### Is the salt value a secret or can it be stored in cleartext just like the IV? [duplicate]

From Wikipedia I read that the IV is used to randomise the mapping of cleartext to cipher text and that the IV is usually stored (in cleartext) together with the encrypted record. (http://en.wikipedia....
266 views

### Brute force attack on RSA - success criteria?

In a hypothetical discussion we ended up with a concrete question I'd like to find the answer to: If you try to brute force an RSA encryption, but the original vale which was encrypted was just ...
1k views

### Help with example RSA problem

While learning about RSA, I found this example problem. The answer is supposed to be "a 4-digit number that is a pattern of digits." I have computed it to be 16657 twice. OK, now to see if you ...
457 views

### Amateur question: two-way RSA?

Is this a sensible scheme for 2-way client/server communication? A client connects to a server. The server and client both generate RSA keys, and send over the public ones to each other. If the client ...
201 views

### Acceptable assumptions when proving security

Considering the output of a cryptographic primitive, like an encryption scheme (CBC, ...), a hash function or even the output of any schemes based on number theoretic assumptions, is it reasonable (...
256 views

### Indistinguishability attack example

I want solve the next exercise. The author defined the experiment for the cryptosystem $\Pi$, the adversary $A$ and the security parameter $n$ as follows $\mathsf{PRIV_{EAV}}(\Pi,A,n)$ The ...
525 views

### Is it worth applying a MAC on data in a HSM?

I'm building a basic HSM out of an Arduino, and am using the following scheme to store data: Master symmetric key $k_m$ stored in firmware (secure bit set to prevent trivial extraction). Secondary ...
415 views

### Efficient algorithm for remainder calculation over prime field for ECC implementation?

I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
633 views

### Partial decryption of large file in AES-GCM (or other modes)?

Lets assume a 4gig file that is internally made of 1 million pages of 4k bytes each (page). the file was originally AES-GCM encrypted these pages (or entire file) lives across the internet i.e. ...
4k views

### GPG vs PGP vs OpenSSH and management of them [closed]

What is the main difference of the three? Can I use only one of them for everything (e.g. GPG for SSH authentication) If I encrypt my private key with a pass-phrase, is it strong enough so that if ...
653 views

### Why are RSA keys encoded with ASN.1 for TLS?

Browser vendors use ASN.1 encoding for RSA certificates in the TLS protocol. RSA public keys are just a number, so why do we need encode them to something else? That increases the risk of security ...
578 views

### File encryption with one keypair?

I'm working on a program that uses an ECC keypair in a (password protected) PKCS12 file (.pfx) to encrypt files. I like this method because I think it will be higher security (using ECDH to negotiate ...
301 views

### Is there a problem with constructing a CSPRNG using MD5 or SHA1?

Is there any security concerns with building a CSPRNG using a broken hash function like MD5 or SHA1? The design is such that a CRC-like function is used for mixing entropy and MD5 is used as the ...
332 views

920 views

### How to jusify {e,n} is a valid RSA public key?

I have a two set of key {36,77} and {50,117}, How can validate if it is a valid RSA public keys? Is there any simple method?
329 views

### Are there any multiparty homomorphic encryption schemes?

Are there any multiparty homomorphic encryption schemes ? Most of the literature is about two party schemes . Is there any generalization made for n party ?
298 views

### Should I use md5 for my new application?

MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application? I don't think so, but I can't seem to convince anyone else that this is ...
346 views

### Relation between Threshold Cryptosystem and Secure Multiparty Computation ?

Is there any relation between secure multiparty computation and threshold cryptosystem ?
1k views

### What is the correct value for “certainty” in RSA key pair generation?

I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are. There is another ...
4k views

### Removing Padded Value in Decrypted Message

How to remove padded value in Decrypted Message? I am using AES Algorithm. Let's take this as the decrypted message: "abcdefghijklmn " There is a 2 space in ...
128 views

### How can I protect against the failure of a block or symmetric cipher?

Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of? Are some combination of ciphers ...
216 views

### RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?

Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
157 views

67 views

### Scalar Multiplication for Elliptic Curve

Let $\mathbb{E}$ be the elliptic curve $y^2 = x^3 + 6x \text{ mod } 11$ and consider the point $P = (2, 3)$ on it. How do I compute $3P$? I have been able to figure out what $2P$ is, $2P = (5,10)$. ...
20 views

### Can a compressed checksum be considered unique

I'm kind of guessing that the answer may be no. Since the compression is trying to reduce the output size using various optimization methods, this may cancel the properties of a hash algorithm. But ...
93 views

### Appropriate scrypt parameters when generating an scrypt hash

What values for CPU, memory and parallel difficulty should be used when generating an scrypt hash? i.e. ...
The Coursera course on Cryptography 1 has a section about Carter-Wegman MAC. Here is the image of slide: Now my question is both $F$ and $S$ output $n$-bit strings. We XOR two $n$-bit strings and we ...