# All Questions

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### RSA Proof - Is Z(n) closed under multiplication

In RSA proof it can be proved that $\mathbb{Z}^*_n$ is closed under multiplication. Can it be also proved that $\mathbb{Z}_n$ is closed under multiplication? If yes, then how?
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### Bit strength of combining hash functions? [duplicate]

Suppose there are hash functions H1 and H2 with bit strength of H1 and H2 is n1 and n2. A new good hash function is generated by combining H1 and H2. What will be the bit strength of these combined ...
292 views

### Is $G$ a secure PRG?

Is the following function a secure PRG? Given $F$ is a secure PRG and $k$ is choosen random from key space $K$. $$G(x) = F(k,x) \oplus F(k,x \oplus 1^s)$$ My solution is $x \oplus 1^s = x'$ ...
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Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
1k views

### How do RSA and ECDSA differ in signing performance?

Signature algorithms with elliptic curves have smaller output sizes compared to RSA for the same level of security. What about the processing time to generate a signature ? I've seen figures giving ...
58 views

### How is an X.509 public key used for TLS?

Wikipedia's TLS article says: The client responds with a ClientKeyExchange message, which may contain a PreMasterSecret, public key, or nothing. (Again, this depends on the selected cipher.) This ...
254 views

### Is there a flaw in this ECC blind signature scheme?

Recently I've found the following work on the internet: An ECC-Based Blind Signature Scheme The paper claims to be an ECDSA blind signature however it seems that their scheme has a flaw in it. The ...
248 views

### PRG existance and P versus NP

how can we prove that if there is a secure PRG then P!=NP or in reverse order?(is there any reduction?) a secure PRG is a pseudo random generator that for every eficient (running in probabilistic ...
441 views

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### How do I produce a stream of secure random numbers from AES-Counter mode?

I have just made my own program to encipher, using AES in counter mode, and have validated it using NIST data. So I know I have done it properly. I have read that AES-CTR can produce a stream of ...
329 views

### AES and One Time Passwords

I have used AES to secure my short term wireless network(1 day lifetime). The same symmetric key is used for securing entire network traffic. is it possible to improve security with onetime password ...
55 views

### From Factorisation of semiprimes to breaching confidentiality

If someone or some group found an efficient way to factor large composites with two distinct prime divisors, would this make it easier to decode any messages?
755 views

### Analyzing ECB's and CBC's resistence to a known-plaintext attack

I'm trying to analyze the strength of a block cipher with CBC mode or with ECB mode on the scenario of an exhaustive search attack with knowledge of pairs of plaintext – ciphertext (known plaintext ...
886 views

### PRF and hash functions

Is there a difference between PRF and a hash function? For example: Creation of a secret key is using PRF and creating a secret key is using hash function.
408 views

### in Bilinear pairings, what is the difference between Type 2 and Type 3?

in Bilinear pairings, what is the difference between Type 2 and Type 3? I understand in Type 2, there exists an efficiently computable homomorphic function $\phi : G_2 \rightarrow G_1$ , which is not ...
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### Does not using padding mean a lack of security?

I've read several texts which say that if the entire plaintext is a multiple of the block-size padding is not required (and not using padding would not mean a loss of security). I generally disagree ...
35 views

### Is the CONF key sharing Problem equivalent to discrete log problem?

If there a proof in the literature which says the CONF Problem is equivalent to solving the discrete log ? Let $g$ be a generator of a cyclic group $\mathbb{G}$ of prime order $q$ CONF problem: ...
142 views

### About using mistakes as part of a code

Could a code be developed where one uses intentional errors say in english, as a text to encode? For example someone might have a message 'Agent X must report to station 5'. This could be distorted ...
177 views

### Accelerated hashing on consumer-grade CPU?

Question is a follow-up to this one. The question was about accelerating SHA1. I am writing an application, where I do have a choice of hash algorithm, as long as it's a strong one. I want to be able ...
49 views

### Undefined $E_y(1,r_{i,j,1})$ notation in cryptography paper, suspect ElGamal-like

I'm trying to understand a paper that uses the notation $E_y(1,r_{i,j,1})$ (full text available in link, used just once on Page #35, 6th page of pdf, Section 3.3, Step 1c) in the context of an ...
401 views

### How do you test the security of your cipher?

I got asked this question and I didn't know what to answer. How do you test the security of your cipher? What comes to my mind now would be to test it with famous attacks: padding attacks, ...
244 views

### Why must IV be sent with each packet?

I was reading about Encrypt-then-MAC and everywhere I go it seems people include the IV with the ciphertext generated for each message then MAC that and send all the information concatenated. Why do ...
3k views

### Why is Triple DES not vulnerable to meet in the middle attacks?

Consider the Triple DES encryption calculated as: $$C= E_{K_1}(D_{K_2}(E_{K_1}(P))).$$ For a chosen plaintext attack, given plaintext $P$, we compute the result of $D_{K_2}(E_{K_1}(P))$ and store ...
352 views

### Can XEX or XTS modes be used with only one tweak?

XEX Mode (with two tweaks) is the following scheme: $X = E_{k}(I) \otimes \alpha^j \\ C = E_{K}(P \oplus X) \oplus X$ where $I$ and $j$ are both tweaks (sector number and block number respectively). ...