2
votes
1answer
55 views

Security of MSS

I have started reading about the Merkle Signature Scheme. I am a little confused about why it is believed to be secure against quantum attacks, couldn't the hash function be attacked? What would make ...
-2
votes
1answer
104 views

OTP - Reuse key BUT add IV, is it secure enough?

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
1
vote
1answer
98 views

Will adding space to the Vigenère block make it truly unbreakable?

I just have gotten into cryptography and learned about the Vigenère block. I think it's a very good idea because, if used correctly, it is unbreakable. But the only downsite is, the key must be the ...
0
votes
0answers
90 views

Vigenère cipher frequency analysis not working

I'm writing a C++ program to use the Kasiski method to crack the Vigenère cipher. I'm testing it with a bit of Shakespeare encrypted with the key ABCDEFGHIJKL. It ...
0
votes
1answer
150 views

Finding Vigenère cipher key(s) [closed]

How can we find the key used with a Vigenère cipher in small number of steps? If we have text like: Peit Wokm! Mhfa fepatgb ets bvvrvxmea ebte bae twkd qiqi ...
2
votes
1answer
108 views

Words in “index of coincidence” in relation to the Vigenère cipher

I am trying to interpret the formula for index of coincidence from here… I am not understanding $f_i$. How can I calculate $f_i$ in this context? Is this the appearance of single word like ...
3
votes
1answer
135 views

Why must the sender and receiver be synchronised in synchronous stream ciphers?

I would like to know why the sender and receiver must be synchronized in synchronous stream ciphers as said in synchronous stream cipher. Why is there no synchronization between the sender and ...
1
vote
2answers
165 views

Why are there no OTP ciphers?

We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site). The strength of the OTP is not that it is unable to find a word without the key but you ...
-1
votes
1answer
312 views

Factoring large numbers

I am trying to factor few integers that are each between 115 and 135 digits long. I was wondering if anyone knew of any efficient methods or any programs that I could use to find the two primes $p$ ...
1
vote
1answer
286 views

Use curve25519 for ElGamal crypto [duplicate]

DJB described curve25519 in his paper which can be found here (PDF). It seems that the main purpose was for Diffie-Hellman key exchange. I think this means that Discrete Log is supposed to be hard on ...
0
votes
2answers
52 views

Getting the encryption/has algorithm used for modem configuration file [closed]

Hello guys I have backed up my modem configuration file and found the username and password is in clear text; the files shows the username and the password is : ...
0
votes
1answer
329 views

Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312

Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312. Just some guidance/help with this problem would be greatly appreciated not sure how to ...
2
votes
1answer
277 views

Perfectly secure shift cipher

Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. I want to show that $P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone ...
1
vote
1answer
113 views

Block Cipher Modes

I have a question here asking the following: Why do block ciphers need the use of blocking modes? To encrypt messages larger than the size of the block. To avoid having the same block ...
2
votes
0answers
387 views

Chi-Squared Step of Vigenere Cipher Decryption

So, I have been assigned an assignment where I had to solve a Vigenere cipher. Following along with this webpage I managed to get all the way to the chi-squared step. But, that is the problem. Upon ...
3
votes
4answers
699 views

Do any non-US ciphers exist?

Plenty of ciphers come out of the USA from government research or selection competitions. AES and DES are examples. Are there any public ciphers produced by other states, China or Iran for example? ...
2
votes
1answer
660 views

Isn't a simple Vernam cipher as secure as known symmetric key algorithms?

I have just read little about the Vernam cipher and the problems of implementing it. But, in practice, would not the key, if generated by a commonly used programming language's ...
1
vote
0answers
63 views

RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one ...
2
votes
1answer
398 views

inverse problem about scalar multiplication on elliptic curve

Let $E$ be an elliptic curve over a finite field $F_p$. Given $n$ be a positive integer and $Q$ be a point on $E$, assume that $Q=nP$, how can we find this $P$? We can assume that $n|p-1$. If $n$ is ...
2
votes
1answer
216 views

Is this ECC encryption key sharing method okay?

Is this encryption key sharing okay to use? Or is much better to use ECIES? $G$ = base point $a$ = Alice’s private key $b$ = Bob’s private key $A = aG$ = Alice’s public key $B = bG$ = Bob’s public ...
1
vote
1answer
75 views

What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?

I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between i^Q mod P = 1 Lacking a specific name I can call this mathematical ...
3
votes
3answers
197 views

Establishing encryption key using shared secret

I need to establish some security on a network of 8 bit microcontrollers. very limited RAM, CPU and packet sizes. I have zeroed in on a shared secret based scheme. Setting up shared secret is out of ...
4
votes
1answer
152 views

Prime factorization

What is the largest integer that can be factored by modern algorithm like Msieve and GGNFS in a time less than 5 hours with normal computers? For example, can an integer like ...
2
votes
2answers
527 views

Using ECB as RSA encryption mode, but encrypted messages are unique

As I understand, ECB should not be used as encryption mode unless you are encrypting single blocks of data which are always unique and only are encrypted once. I have a collection of ids represented ...
3
votes
1answer
671 views

bcrypt - collision-resistance against chosen salt and work factor?

Would it be difficult to find $\:$ cost,salt,input,password0,password1 $\:$ such that bcrypt(cost,salt,password0,input) = bcrypt(workfactor,salt,password1,input) and $\:$ password0 != password1 $\:$ ...
1
vote
0answers
29 views

HMAC for encrypted authentication token: recommended iteration number [duplicate]

In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance ...
-1
votes
2answers
198 views

SQL-Like queries in CRYPTDB doesn't work [closed]

I have downloaded and built Cryptdb and it works well. Most of queries on encrypted database run without any issue but, the query with LIKE key word receives an ...
3
votes
1answer
114 views

Do hand-based hash functions / MACs exist?

Is there research on a hash function or a MAC that can be executed without computers? I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using ...
8
votes
2answers
1k views

Simple protocol for 1-out-of-2 oblivious transfer

I'm trying to explain the concept of 1-out-of-2 oblivious transfer to folks who haven't seen this idea before. I can explain what properties it provides, but it's also helpful if I can show a simple ...
1
vote
1answer
186 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
2
votes
2answers
3k views

Why is HMAC-SHA1 still considered secure?

This Q & A http://security.stackexchange.com/questions/33123/hotp-with-as-hmac-hashing-algoritme-a-hash-from-the-sha-2-family says that the security of HMAC-SHA1 does not depend on resistance to ...
-2
votes
1answer
75 views

Is algorithm with more than $2^{word size}$ words secure? [closed]

Let's say we have a feistel cipher or feistel pseudo-random permutation with 8-bit function (S-box) similar to Treyfer, but with much bigger block size like 16MB. Here is example of such pseudo-random ...
3
votes
0answers
35 views

El-Gamal and Lines on Planes

I've been thinking about a geometric picture for El-Gamal. The idea is to understand the set $\{(my^{x},g^x) \mid x \in Z_p\}$ (the set of encryption of $m$ for fixed $g$ and $y$) by taking the ...
7
votes
1answer
154 views

Secret key and Decryption oracle in the revised Fujisaki-Okamoto transformation

Recently, Fujisaki and Okamoto provided a revised version of the Fujisaki-Okamoto transformation [1], a generic transformation for achieving IND-CCA2 security in the Random Oracle model. This new ...
1
vote
1answer
208 views

Why is the public/private key length used in libsodium so much shorter than needed for RSA [duplicate]

Reading the libsodium source I see that is uses a key length of 32 bytes (256 bit) for private/public key encryption. For RSA private/public key encryption a key length of 2048 (or 4095) bit is ...
3
votes
2answers
221 views

AES and Homomorphic Encryption

Is it possible to do the following? Input would be to generate a new AES key, encrypt the private data with that key, encrypt the AES key with the FHE key, and send the FHE-encrypted AES key along ...
-1
votes
1answer
49 views

Cardinality of the key space $\{0,1\}^\ell$

Imagine we have a scheme whose key is chosen from the set $\{0,1\}^\ell$. My question is: What is the size of key space for this scheme?
9
votes
3answers
1k views

Elliptic Curves of different forms

Looking at http://safecurves.cr.yp.to/ to find a safe curve, I find that most curves described here are of a different form from that generally used. In Bouncy Castle, for example, ...
5
votes
1answer
457 views

Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ...
1
vote
2answers
95 views

If you have a file and XOR every bit with a random bit, can you extract any information?

Say you have a file that is not random, and you XOR every bit with a random bit (not pseudo, but really random). Can someone who sees only the result extract any information from it? Obviously, it ...
2
votes
1answer
146 views

Why in Android kernel CSPRNG state is saved?

I am reading about the security internals of Android. In the book Android Security Internals, in chapter on Cryptographic Providers, there is a para stating: On Android, CSPRNG implementations are ...
4
votes
1answer
141 views

Implementing AES MixColumns with fewest XOR gates

I'm playing with Contiki (O.S. for constrained devices such as sensors and micro-controllers) and particularly with the AES encryption in software (the one available in Contiki source code). I'm ...
0
votes
0answers
51 views

Type of values that can be accumulated in bilinear map (multiplicative) accumulator reg.

Is there any restriction that the members to be accumulated in bilinear map (multiplicative) accumulator need to be relatively prime to P? Where P is the order of group.
2
votes
2answers
115 views

cipher text only attacks on deterministic homomorphic encryption schemes

If we consider a set of numbers say a set $s=\{a,b,c,d\}$ , where $a,b,c,d>1$ and the numbers $a, b, c, d$ do not share any relation between them , i.e. for any two numbers, $n_1,n_2\in s$ the ...
2
votes
3answers
349 views

Point decompression on an elliptic curve

I'm programming an elliptic curve cryptosystem and I'm having difficulty with decompressing points. The following information is from my project specification as to my understanding: Given a point ...
2
votes
0answers
141 views

Proxy re-encryption mod operations

I managed to implement the proxy re-encryption scheme from http://eprint.iacr.org/2009/189.pdf in Python 2.7, however I am having performance issues. As it is, I can run the algorithm for key sizes up ...
4
votes
2answers
190 views

In a group, is it hard to calculate the base $g$ given $g^a$ and $a$?

Discrete logarithm, that is: calculate $a$ given $g$ and $g^a$, is assumed to be a hard problem in some groups. Is it also hard to calculate $g$ given $g^a$ and $a$?
-1
votes
1answer
99 views

Montgomery and Galois fields

I'm a little bit confused about the design of a RSA module in VHDL. My question isn't directly related to hardware design. I've read a lot of publications and I bought also a book. In one publications ...
3
votes
1answer
93 views

Device intercommunication with commands

I want to create a smart house project, and in that I bought some simple RF modules. Those modules don't support crypto out of the box but I want to connect them to a device that I would program to ...
3
votes
1answer
109 views

NTRU less secure than previously thought?

A new paper (https://eprint.iacr.org/2015/552.pdf) says: This makes it possible to asymptotically and heuristically break the NTRU cryptosystem in subexponential time (without contradicting its ...

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