# All Questions

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### Statistical tests for PRNG that generates a sequence which is not binary

Is there a pratical application to PRNG that generates a sequence which is not a binary one? A ternary, quaternary sequence, for instance. If so, how can we test this? Is there any alternative test ...
65 views

### ECFP harder than ECDLP ?

Given two points $P$ and $Q = \sum_{i=1}^{n} x_i.P$ over $E_p(a, b)$ for $x_1,x_2,...,x_n \in \mathbb F_p$. The Elliptic Curve Factorization Problem (ECFP) is to find the points ...
10 views

### Why does HS1-SIV use the universal hash function the second time?

HS1-SIV uses HS1-Hash twice: once with the message as input, and the second time with the authentication tag as input. The second use seems somewhat strange to me: assuming that the core is a strong ...
128 views

### How to prove the security of block ciphers

I see very often proofs of security for asymmetric crypto algorithms, for instance, using reductions to known hard problems, or game based proofs... In the field of protocols (like authentication) it ...
55 views

### Can one extend the nonce of ChaCha/Salsa20 by XORing the extra bits with the key?

Can one extend the ChaCha and Salsa20 nonces by XORing the extra nonce bits with the key? My reasoning is as follows: the Rumba compression function allows attackers to supply any 48-byte input to ...
37 views

### Weil Pairing - Miller's Algorithm

I'm trying to implement Weil Pairing using Miller's algorithm. I have got couple of questions. How to select $m$? As stated in this link page 13, I interated from $1$ to order of point $P$ such that ...
19 views

### PHP Apple News HASH HHMAC

I am having a problem generating the signature key in PHP as describred in the Apple nes API documentation found here: ...
68 views

### Here I am like a [on hold]

I don't know if it's the place to ask this, but I realy don't know where to look for this information. I heard someone says "Here I am like a..." And that sentence reminded me of something I have ...
17 views

### TLS 1.2 PRF Cipher Suite Specification

I am upgrading our assembler SSL/TLS implementation to support TLS 1.2 and am reviewing RFC5246 specification for TLS 1.2. It states that the PRF is now part of the cipher suite specification but ...
1k views

### Does composing multiple substitution ciphers improve security?

Will using two substitution ciphers one after the another be more secure than using single substitution cipher?
49 views

### Is ChaCha12 considered 256-bit secure?

ChaCha20 is considered 256-bit secure (no attack faster than brute force). However, the best known cryptanalysis that I know of is on ChaCha7. That gives ChaCha20 a rather large security margin ...
71 views

### Is a PRF applied to a secure MAC also a secure MAC?

Suppose I apply a PRF to a secure MAC. Do I still have a secure MAC?
34 views

### Converting a 5-bit s-box to its bit-sliced format

I'm currently trying to convert a 5-bit sbox (the one from this cipher: http://primates.ae/wp-content/uploads/primatesv1.02.pdf) to its bit-sliced format (i.e. to a boolean network). Most papers ...
27 views

### Fully or partially Decrypting Data with Multiple keys

Is there any good paper or research carried out till now that a data is encrypted by a single key or onwer(user) and their are 2 or more decryption keys. One key can decrypt the entire data. Other ...
42 views

### Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
24 views

### Algorithm to rotate values in a predefined manner

I will start with an example. Some beacon like estimote Beacons use something called secure ID. The ID transmitted by the beacon change every 10 minutes autonomously without contacting the server. ...
77 views

### Is it possible to combine two hash functions in such a way that cracking the constructed hash would require cracking the constituent hashes? [duplicate]

Suppose A is some arbitrary hash function, for example BCrypt or MD5. And B be some other arbitrary hash function, maybe SHA256 or SCrypt. Let ...
67 views

### How would an attacker perform an exhaustive key search on a block cipher using ECB mode?

Do you always assume from Kerchoff's principle, that the attacker has access to everything but the decryption key? That is, am I to assume that to perform an exhaustive key search, the attacker has a ...
68 views

### Is every point on an elliptic curve of a prime order group a generator?

If the order of elliptic group is prime then every point is a generator of that group. I tested the above statement on some elliptic curves and found it true. Does that really work on all curves? Is ...
75 views

### Is double AES-CBC encryption with the same key and IV unsafe?

If some plaintext encrypted twice with the same AES function (CBC-mode), same IV and same key, is it possible to retrieve either the key or the plaintext?
37 views

### Triple DES with 2 keys

Suppose triple DES is performed by choosing two keys $K_1$ and $K_2$ and computing $C = T (T (T (L, K_1), K_2), K_2)$. How to attack this modified version with a meet-in-the-middle attack, in which ...
50 views

### How to define order according to domain parameters in elliptic curve pairing groups

According to domain parameters, as an example Type 1 pairing domain parameters are ...
195 views

I was researching about hash, and I thought, If sites store passwords with hash algorithms, then can't this happen: User A has the password 'hello' User B finds out the hash code of the password of ...
28 views

If I want to generate a few one-time pads, is it OK to just read required number of bytes from /dev/urandom without weakening information-theoretical security?
90 views

### Probabalistic Polynomial-time Algorithms & One-way functions

I've been reading up on probabilistic polynomial-time algorithms and one-way functions, and I was hoping to get some guidance on the topic. A textbook I'm reading states the following for one of the ...
103 views

### If we should not reuse primes in DH, shouldn't we not reuse ECDH elliptic curve properties?

An article How is NSA breaking so much crypto? describes NSA's methods for breaking encryption. If a client and server are speaking Diffie-Hellman, they first need to agree on a large prime number ...
30 views

### How are the IVs of SHA512/256 and SHA512/224 calculated?

This seems odd to me, because there are a lot of resources out there saying that the initializer values of SHA512 and SHA384 are the first 64 bits of the fractional parts of the square roots of prime ...
102 views

### Is multiplicative blinding less secure than additive?

It's easy to see that additive blinding (e.g., $x+r$ for secret x and random r) is perfectly secure in a finite field (this is a one-time-pad) and statistically secure for $r$ uniformly distributed in ...
29 views

### How much does using the same $H$ for all messages weaken GCM?

How much is GCM weakened by using the same MAC key $H = E_K(0^*)$ for all messages that use the same key (which is what GCM actually does) instead of using $E_K(N||0_{32})$ (which is different for ...
50 views

### Which AES encryption do banks use? [on hold]

I'm trying to find what size keys banks use for symmetric and asymmetric encryption. I know that the symmetric one is smaller because they want it to be fast but I can't find any information on their ...
37 views

### Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key ...
79 views

### Difference left-or-right CPA security, IND-CPA security

I am trying to understand the notion of left-or-right-CPA (LOR-CPA) security for private-key encryption schemes introduced in my lecture. If I understood it correctly so far, the only difference to ...
127 views

### CP-ABE for threshold cryptography

I would like to know if there is any research work using CP-ABE for threshold cryptography? I want to know also if applying CP-ABE for threshold cryptography would overcome other techniques.
277 views

### To what extent is WhatsApp's statement on secure messaging realistic?

As those of you who use WhatsApp Messenger probably know, with their recent update chats and calls are now encrypted. Here's what WhatsApp claims: Messages you send to this chat and calls are now ...
329 views

### Blinding twice in RSA

I understand that if you have a message $m$, you can blind it by selecting a random $r$ and then multiplying $r^e\times m \pmod{n}$ Someone else then signs it with $d$, raising to the power of $d$: ...
17 views

### Create composite group for pairing in JPBC

We use bilinear map $S = (G, G_T , e(\cdot, \cdot))$ of composite order $n = s \times n'$ with two subgroups $G_s$ and $G_n'$ of $G$. Random generators $w \in G$, $g \in G_s$, and $φ \in G_n'$ are ...
49 views

### Is it safe to encrypt data using XOR along with CSPRNG seeded with a truly random number?

I was wondering a couple of days ago whether I could reverse the normal encryption order to produce a good AES based cipher variant. The method is as follows: Two users, Alice and Bob, each have a ...
51 views

### How distinct are the meanings of the terms “CSPRNG,” “DRBG” and “stream cipher”?

Are there universal, consensus definitions for the following terms? Cryptographically secure pseudo-random number generator ("CSPRNG") Deterministic random bit generator ("DRBG") Stream cipher ...
60 views

### Strength of $H(k\|H(m))$ as a MAC algorithm

What is the strength of $H(k \| H(m))$ compared to HMAC? Compared to $H(m \| k)$? What is the strength in bits of a given key/output size?
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### Can anyone tell whether combinational has higher frequency of operation than sequential or vice-versa?

I have designed SHA3 algorithm in 2 ways - combinational and sequential. The sequential design is giving frequency of operation as 700MHz while the combinational one is giving 0.5MHz so i want to ask ...
166 views

### Sorting over encrypted data with different symmetric keys

I'm working on a security project. I need to perform a sorting on the lists of encrypted integers and strings. The encryption used is symmetric. The clients send the encrypted data in a list to the ...
26 views

### Partial-Message Collisions on Iterated Hash Functions

In Cryptography Engineering by Ferguson et al it says the following is a problem with iterated hash functions: Because hashing $m$ and $m'$ leads to the same value, $h(m||X) = h(m'||X)$... for all ...