# All Questions

139 views

### Witness and Commitment in Commitment schemes [closed]

In connection to a commitment scheme, how are witness and commitment different? Are 'Binding' and 'Hiding' properties defined w.r.t. witness and commitment or both?
358 views

### What is h in this RSA variant?

I am trying to implement a proposed improved algorithm of RSA . Here the author has increased the number of exponents. However I am unable to understand what $h$ is in the Key generation step. Can ...
1k views

### Open source implementations of Symmetric Searchable Encryption and Order Preserving Encryption [closed]

Are there open source implementations of SSE and OPE? Can anyone please point to sample codes, if available. EDIT If cryptDB is not an option, what other options are available? (Indeed, these ...
173 views

### A variant of Shamir secret sharing

Suppose implement the Shamir secret sharing as following: we select a degree $d$ polynomial $P$ with a zero coefficient of 0, and all other coefficents selected randomly from $Z_p$; and to this ...
79 views

### Hardness proof?

I am little curious about how do we calculate hardness proof of any cryptography algorithm? Also where can I find hardness proof for AES and AES-CBC ?
746 views

### what are DP and DQ in Encryption by RSA in c#

I want to know about these tags in RSA Encryption by private Key. when I use this code: ...
227 views

### Why are we not using multiple ciphers per message?

I am aware of at least rsa, elgamal-encryption, and variations of elliptic-curves relying on different problems and that those problems are considered hard. However, if someone figures out a way to ...
186 views

### Is SRP post-quantum secure?

Is SRP-6a post-quantum secure? If it is not post-quantum secure, do any post-quantum secure alternatives similar to SRP-6a exist?
44 views

### Is Attribute based encryption sub-class of Identity based encryption [duplicate]

I have a basic question related to Identity and Attribute based encryption. Construction of IBE scheme was first shown by Boneh et al. in 2001 and I think in 2004 Sahai and Waters introduced ...
230 views

### EC Public Key length in ASN.1 DER

I have two X.509 certificates in DER format. A: ...
409 views

### CDH problem and Square-DH problem

CDH problem roughly says that choose $U=g^u, V=g^v$ uniformly at random from cyclic group $G$, it's hard to compute $CDH(U,V)=g^{uv}$. Square-DH problem roughly says choose $U=g^u$ uniformly at ...
397 views

### Strength and weaknesses of this JavaScript charCodeAt based login script

I know of a company on their website who are using this very basic password login page written in JavaScript. This doesn't seem very secure at all, because in the html source code it shows where the ...
105 views

### Is One Time Pad something like this? [closed]

Alphabet: [A-Z] = [0-25] Plaintext = HELLO = 7 4 11 11 14 // QUESTION: do this key must be as long as plaintext? KEY: [QWERT] KEY = 16 23 4 17 19 Plaintext + Key = 23 27 15 28 33 Plaintext + Key (...
503 views

### Hierarchical Encryption

Is there a way to setup a hierarchical encryption using public key encryption? Let's say a higher level user can decrypt messages encrypted by lower level users. Is that possible? I guess it is only ...
397 views

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7k views

### Compare Blockmode CBC (with diffuser) against XTS

I have some problems in understanding the "advantage" of AES-XTS compared to CBC with diffuser. I read something about FileVault, in this paper they mention the two modes of operations XTS and CBC (...
301 views

### reducing false positives in searchable encryption

Practical techniques for searchable encryption proposed by Song et al. [1] have a false positive rate of $l/2^m$ where $l$ is left half of encrypted bits and $m$ is right half and $l+m=n$ where $n$ is ...
770 views

### Why should CAST5 and 3DES not be used for encrypting files over 4GB?

On https://www.gnupg.org/faq/gnupg-faq.html#define_cast, it says that Like 3DES, its 64-bit block size means it should not be used to encrypt files larger than 4Gb in size… How and why does the ...
610 views

### Possible Digital Signature Hack?

I am starting to learn more about cryptography and I just read more about how asymmetric keys can make a digital certificate, and I would like if someone could explain me why the following case can't ...
486 views

### Message encrypted with a LFSR based stream cipher

I am learning about LFSR sequence and I came across this question: A 16-bit message consists of two ASCII characters. This message was encrypted with a one-time pad, and the key for the one-time pad ...
78 views

### Bridging the gap between security proofs and “real-world” security

I've been studying cryptography for a little while. I understand fairly well the nuts and bolts of security proofs, but I'm having trouble reconciling the formal statements of security in these proofs ...
182 views

### INT_32_BE in PBKDF2

Trying to understand PBKDF2 in detail. It is clear that the password and the salt is given to the PRF (which is HMAC-SHA-1 in the specification). But what is the role of the INT_32_BE(i)? What does it ...
60 views

### Are there any obvious techncial faults in F. Ruiz's 2013 URSA javascript cryptography? [closed]

The link to the cryptography is here: http://prgomez.com/ursa/ I have found the following simple javascript system of encryption/decryption portable and easy to use for emails and messaging sites, ...
110 views

### Cipher built from GPU primitives [closed]

Is it feasible to build a cipher (or hash) out of GPU or DSP primitives (e.g. big matrix multiplication, Fast Fourier Transform, big block SIMD, or hardware H.264/AVC codec)? Preferably those are slow ...
246 views

### Does brute force attack use the program that created the ciphertext?

I've read several articles about brute force cryptanalytic attacks, but none explicitly say what algorithm is being run for each attempt, nor what criteria is used to declare an attempt a success or a ...
80 views

### NIZK Proof of knowledge N of M discrete logarithms (threshold)

It is well known how to produce a NIZK that curvepoints $aG$ and $aP$ have the same discrete logarithm $a$ with respect to the curvepoints they are multiplied by. There is also a way to prove that a ...
132 views

### Brute Force Attack Strategies

A Brute Force Attack obviously involves attempting to decrypt ciphertext (with the associated plaintext being known) using all possible encryption keys. Aside from attempting all possible ...
931 views

### Is there benefit to signing unencrypted emails?

I came to this article from another comment on Crypto StackExchange. After reading it, I am wondering if there is any benefit to using a digital signature on unencrypted S/MIME emails?
85 views

### Hash function and indifferentiability [closed]

What are the properties derived from the fact that a hash function is indifferentiable from a random oracle?
108 views

### See any problems with this search-specific homomorphic encoding strategy?

I'm imagining this for use in the scenario of cloud-stored client-encrypted email, where, when seeking to do a string search across messages, you don't want to have to download every stored message in ...
97 views

### Keccak and compression functions

Keccak follows a sponge construction. Can we say that Keccak employs a compression function? Generally speaking, for sponge constructions, can we say that there is an underlying compression function?
140 views

### Determining average number of hash calls to get a hash that begins with X

I have been attempting to find an answer to a self-study question: If I have a hash algorithm that outputs 256 binary bits, on average, how many times would I have to call the hash function so ...
195 views

### Roots of polynomial in Shamir secret sharing

I need to know whether one can obtain any roots of the polynomial in Shamir secret sharing if he possesses less than threshold shares. For instance in (t,n) if he has t-1 shares can he obtain any ...
96 views

### stream cipher computation cost [closed]

With AES-CTR the computation time to encrypt a message of lengh $n$ blocks is $n$ computations of the block cipher. What is the running time to encrypt a message of $n$ bits using a stream cipher, ...
50 views

### Group Dependent Language

The text below has been taken from the below paper Groth-Sahai Paper. The relevant part is highlighted in red. What does this group-dependent language mean in this context? From the definition of a ...
355 views

### Strategy to crack a presumed substitution cipher

The ciphertext given is: ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae I've done ...
439 views

### What is the (uncompressed) x,y-representation of a curve point on the P-256 NIST elliptic curve?

I am trying to understand the FIDO U2F Raw Message Format, especially the format in which a user public key should be provided. The documentation says the following: A user public key [65 bytes]. ...
965 views

### Key management for military GPS receivers

I wonder what encryption scheme is used in high-precision encrypted GPS streams (the so-called “P(Y) code”). If there's a master key needed, then it has to be in every device. Yet the master key doesn'...
294 views

### What is “msg = group.random(GT)” in Charm encryption schemes?

In many encryption schemes in Charm the random group message is used instead of a text-message: msg = group.random(GT) For example, in CP-ABE scheme, random ...
450 views

### what is the difference between IBE and ABE schemes

Can somebody explain in simple words. real life example light help and limitations of these schemes etc.
3k views

### SHA1 no longer considered secure for SSL Certificates — what about Cipher Suites?

Many browsers and Internet companies have recently claimed that SSL Certificates with a signature algorithm of SHA1 will imminently no longer be considered secure. Most notably, Google and Google ...
118 views

### Deprecation of RSA-SHA-1 in DKIM keys?

I recently noticed that OpenDKIM on my mail server is objecting to DKIM signatures from a client, saying their key is insecure. It may be that that's due to lack of secure DNS (confirmation anyone?) ...
339 views

### How do disk encryption programs solve the “IV problem”?

I was reading a paper on the "elephant diffuser" used in BitLocker and it got me wondering how other systems (e.g. TrueCrypt before it shutdown) solved the problem the elephant diffuser was meant to ...
132 views

### Basic question about design of program with data encryption

I need to store encrypted files on a hard disk. The actual code side is not important for me now (I plan to use C# and AES-GCM encryption from Bouncy Castle library, please tell me if you think that's ...
118 views

### simple encryption scheme turns out to be “somewhat homomorphic”

In the paper Fully Homomorphic Encryption over the Integers in the introduction: How do I calculate $r$ and $q$ of this equation in the picture? $r \approx 2^{\sqrt{\eta}}$ and $q \approx 2^{\eta^3}$...
239 views

### Fully Homomorphic Encryption over the Integers - perform an operation on an encrypted data

In Fully Homomorphic Encryption scheme represented here Fully Homomorphic Encryption over the Integers In the Evaluate process (see section “3.1 The Construction” of the paper): Evaluate(pk, C, c1, ...
173 views

### Is this modified Schnorr signature scheme secure?

Signing Let y = g^x, which is your public/private keypair. Let r = g^v, for random v Let c = H(M) Let z = (v + cx) mod q The signature is the pair (r,z) Verifying g^z = ry^c mod p We further ...
484 views

### What weaknesses in Hash_DRBG did NIST find and fix?

Matthew Green states in the Practical Kleptography presentation (video, at about 12:15) that Hash_DRBG (from SP800-90A) as originally proposed by NSA had potentially exploitable flaws or bugs and that ...
Short version: When generating a prime number of N bits, should I draw random numbers from the range $[0 , 2^n]$, or $[2^{(n-1)} , 2^n]$? Context: I'm trying to implement a toy-version of RSA as a ...