10
votes
1answer
225 views

Can Skein be used as a secure MAC in format H(k || m)?

Can Skein be used as a secure MAC in format H(k || m)? I understand it can work with HMAC, but it is fine as a one-pass MAC in the format above and resists length extension attacks. Is this ...
2
votes
1answer
132 views

Shamir's Secret Sharing of modular inverse

Given a secret $K \bmod q$ which is shared among entities $E_1,…,E_n$ using polynomial Shamir's Secret Sharing, how can the inverse of $k$ be shared without revealing $k$ and $k^{-1}$?
0
votes
0answers
76 views

Cryptodefense ransom use RSA-2048. Any chance with known plaintext attack? [duplicate]

The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048. Personally, I have been victim of cryptodefense: 40000 files encrypted... I'm not going to pay anything ...
3
votes
1answer
223 views

When is it safe to not use authenticated encryption?

I have read the post Why should I use Authenticated Encryption instead of just encryption? When is it safe to not use authenticated encryption? I assumed hard drive volume encryption or per file ...
2
votes
1answer
459 views

In the STS Authentication Protocol, why are the signatures encrypted?

From Wikipedia: (1) Alice → Bob : g^x (2) Alice ← Bob : g^y, E_K(S_B(g^y, g^x)) (3) Alice → Bob : E_K(S_A(g^x, g^y)) I know there should be something I'm missing,...
1
vote
0answers
65 views

Is container format relevant to security of encrypted message inside?

Still trying to design a fully binary cryptography container format for my mobile app, I am here asking if container is ever relevant. Thanks to Apple, I cannot use GPG directly because I can neither ...
3
votes
1answer
460 views

Security benefits of Ed25519 generating signatures deterministically

I am reading on the Ed25519 curve, and I am trying to understand a claim. Here is the claim: Foolproof session keys. Signatures are generated deterministically; key generation consumes new ...
3
votes
1answer
203 views

Encrypting a short phrase into two keys. both with length of 32letters

It doesn't need to be crazy secure. I wanted to figure out if there's a popular practice when encrypting a short phrase (less than 32 letter long) into two keys (two strings 32 length). Doesn't need ...
1
vote
1answer
710 views

Decrypting a small Message using RSA with a Private Key [closed]

If I have a private key of (43, 341). What would be the steps I need to take to decrypt a small message using RSA? I have looked ...
1
vote
1answer
243 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 ...
6
votes
1answer
278 views

Proving the possession of signature in zero-knowledge

Does anybody know an efficient mechanism to prove the possession of a digital signature (e.g. RSA) on a certain attribute (message) in zero-knowledge? That is, without revealing the actual signature (...
1
vote
0answers
60 views

Mapping integers to Ed25519 and back again?

I would like to map integer values to points on Ed25519, and then back again. Is there a technique that takes advantage of the specific structure of Ed25519?
4
votes
1answer
403 views

Is knowing the private key of RSA equivalent to the factorization of $N$?

Given the RSA modulus $N$ the fastest method to factor it is of sub-exponent order. But, now if I know the private key $d$ of RSA, does that mean I can factor $N$ efficiently?. It intuitively seems ...
0
votes
1answer
356 views

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?
0
votes
0answers
34 views

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 ...
1
vote
1answer
173 views

Does AES 256 really make sense in hybrid crypto systems when the PKI is the bottleneck?

AES 256 is used widely in hybrid crypto systems (e.g. SSL/TLS). According to keylength.com a 2048 bit public key corresponds to 112 bits of security. Does it make sense to use AES 256 in this ...
2
votes
1answer
416 views

Is the DES algorithm in OPENSSL random?

Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext ...
1
vote
1answer
57 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 ...
17
votes
6answers
940 views

Can I encrypt user input in a way I can't decrypt it for a certain period of time?

I run a baseball league and would like to do silent auctions for free agents. This would require teams to enter their highest bid and the highest bidder at the end of the auction period would win. ...
9
votes
2answers
2k views

Does Microsoft use Dual_EC_DRBG by default?

So, as we all know, Dual_EC_DRBG contains an NSA back door. At this point, there is no reason to call it a "potential" or even an "alleged" back door; the presence is obvious even to the NY Times. As ...
2
votes
1answer
166 views

What are the two parts of SHA1's compression function called?

SHA1's compression function has two distinct parts: one where 16 words are expanded into 80 words, and one where the 80 words are used over 80 rounds. Are there specific names or terms for each of ...
1
vote
1answer
184 views

Can 64-bit “PRINCEcore” practically be brute forced?

There is a cipher called PRINCE proposed in ASIACRYPT two years ago. See the paper: “PRINCE – A Low-latency Block Cipher for Pervasive Computing Applications” The cipher divides the 128-bit key into ...
4
votes
1answer
390 views

How can k3d3/ed25519-java's performance be improved?

I tried asking this on stackoverflow because I thought it might be a simple coding question and didn't want to clutter up this amazing stack, but I received no responses. CodesInChaos showed me that ...
7
votes
4answers
605 views

How to argue to a paranoid that RSA is safe?

From today's standpoint, most people would claim RSA to be secure. However, to my knowledge, this is purely based on the speculation that no one knows a computational feasible way to find a $d$ for ...
2
votes
3answers
610 views

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 ...
1
vote
1answer
169 views

Block cipher encryption of decryption with the same key

With block chipers can I assume that Enc(k,Dec(k,m))=m Meaning if I decrypt something with a key k and then encrypt the result with the same key k, do I get what ...
1
vote
0answers
103 views

Shor's Algorithm values

I'm working with Shor's algorithm and I have a question regarding the following step $$a^r -1 = (a^{r/2}+1)(a^{r/2}-1)=0 \pmod n$$ Now what is going to be the result if ${r/2}$ was -1? this will ...
2
votes
2answers
896 views

DES with actual 7 byte key

Do we have any library or any mechanism where we can use true 7 byte key for DES instead of 8 byte key. I need it for keys analysis in DES and 8 byte key requirement for associated library is creating ...
1
vote
2answers
172 views

Are ZKPPs possible with server-side hashed passwords?

A basic ZKPP (Zero Knowledge Password Proof) is based on the server being able to challenge the client, and the client can then prove it knows the password (in such a way that is verifiable to the ...
5
votes
2answers
395 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 ...
3
votes
1answer
357 views

Is ISAAC Cipher Cryptographically Secure?

http://en.wikipedia.org/wiki/ISAAC_(cipher) This question was asked before but the answers seem vague, and I want to know about ISAAC specifically, not ISAAC+. It seems some cryptanalysis was ...
3
votes
2answers
423 views

What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
0
votes
1answer
59 views

find $x$, given $\{c_ix = k_i + y_i\}_{i=[1,n]} $

Given $$c_1x = k_1 + y_1 $$ $$c_2x = k_2 + y_2 $$ $$\vdots $$ $$c_nx = k_n + y_n $$ where the values of $\{c_1 \ldots c_n \}$ and $\{ k_1 \ldots k_n \}$ are known, and $x, \{y_1 \ldots y_n \}$ are ...
1
vote
1answer
137 views

Generating the keys for the RSA cryptosystem in probabilistic polynomial time

In general every public key cryptosystem ``has'' a probabilistic polynomial time algorithm $G$ such that $G(1^k)=(\textrm{public key}, \textrm{private key=trapdoor})$; $G$ is called the key generator. ...
4
votes
1answer
178 views

Understanding hash entropy

I have been told that one advantage of using a hash function is that it spreads entropy over all input bits. But it also seems to be true that a bad hash algorithm can make things less random. But how ...
1
vote
1answer
318 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 ...
-1
votes
1answer
98 views

Symmetry for finite cyclic groups (Z/pZ)∗

How well is it known that for $i$ such that $1 \leq i \leq \frac{p − 1}2$: $$ g^{i+(p−1)/2} = g^{i−1+(p−1)/2} − g^i + g^{i−1} \pmod p $$ Whilst working in the finite cyclic group of prime moduli $(Z/...
0
votes
1answer
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?
67
votes
11answers
6k views

Is modern encryption needlessly complicated?

RSA, DES, AES, etc. all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
1
vote
1answer
43 views

Why Distance-128 relation in Plain texts is reflected in Cipher texts

The two text having relation as "\x10\x11" → "\x90\x91" (80+10) will have relation after encryption/decryption also in RC4. Following code clearly describes the problem I am mentioning. ...
0
votes
3answers
392 views

Would it be possible to create a game where one would need to decrypt a simple encryption?

This might sound pretty weird, but I was thinking of a game a person could play alone with a pen and paper. I got this idea where the person would write a random four letter string on a paper, and ...
1
vote
0answers
60 views

Smart card Strong authentication / Verification ( fingerprints)

I'm trying to make a strong authentication software and embedded software in a java card. I have found many papers and publications about the subject… too much information to process and I'm working ...
4
votes
4answers
2k views

Pseudocode for constant time modular exponentiation

I'm looking to implement modular exponentiation (for RSA) in constant time, but most of the examples I've found are more mathematical descriptions of the operations. Are there any references with ...
2
votes
3answers
141 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 ...
2
votes
2answers
257 views

reverse an identicon to its source string

Identicons are used to create unique images based on IP address or strings. Lots of programs are available to generate identicons based on an input string. My ...
4
votes
4answers
2k views

Assistance Cracking Classical Cipher

Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble. ...
1
vote
0answers
58 views

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 ...
2
votes
1answer
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: ...
1
vote
1answer
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 ...
2
votes
1answer
339 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). ...

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