-1
votes
2answers
185 views

How to choose an algorithm

I have some understanding of Cryptography and I would like to know if there is a tool or website to help me choose an algorithm based on my own needs (I'm being vague in purpose). I'm looking for a ...
-1
votes
1answer
9k views

Decrypt files with original file CTB-Locker [closed]

I have problem called CTB-Locker. It encrypted all of my files on computer and since I have lot of documents that are very important I am in problems! As I read online CTB-Locker uses "elliptical ...
-1
votes
2answers
90 views

Reusing one-time-pad with random plaintext

I understand that by definition one-time-pad keys cannot be reused but I was thinking about the case where it is used to send random data and couldn't find anything on the subject so here is my idea: ...
-1
votes
1answer
72 views

what is the benefit of lcm in cryptography? [closed]

what is the benefit of lcm in cryptography? and what is the effect of lcm on public key? note * lcm = Least common multiple thanks
-1
votes
1answer
68 views

HMAC ipad and opad choice

It is written in the HMAC paper that the $ipad=0x36$ and $opad=0x5c$ were chosen such that it maximize the Hamming-Distance of the part of the key used in the inner and outer part of the HMAC process. ...
-1
votes
1answer
109 views

Reversing a Psuedo Crytographic Hash [closed]

I'm trying to get a better understanding of cryptographic hashing. Take the example transformation function below, is it possible to reverse this formula to solve/isolate for message[i]? ...
-1
votes
1answer
35 views

El gamal correctness

I tried to find online for the correctness of El-Gamal, but I couldn't find any good resource that will teach me how to show the correctness of El-Gamal, could any body show me how is it done?
-1
votes
1answer
80 views

What does $\mathbb Z_p^*$ contain?

I have a prime $p = 7$ and was tasked to select a random value in $\mathbb Z_p^*$ in my signature scheme. What does the full range of $\mathbb Z_p^*$ contain in this case? Is it $\{0...7\}$ or ...
-1
votes
1answer
185 views

Simplest code for 64-bit block RSA-like encryption/decryption and key generation

Looking for the simplest code in C. Need a set of functions that will first generate a public/private 64-bit key pair, and then the function to code/decode a given 64-bit block, no built-in checksum ...
-1
votes
1answer
64 views

Convert message to polynomial NTRU

How to make a message into a polynomial? I saw many answers to this question and yes, i know that here are some questions. But i did not get it. I think that i am making some mistakes. I took a word ...
-1
votes
1answer
170 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 ...
-1
votes
1answer
61 views

How to use the key from a Diffie Hellman exchange? [closed]

I watched a YouTube video about Diffie-Hellman called "Diffie-Hellman Key Exchange", and it said after doing some modulo operations with the public modulus and generator and the random private ...
-1
votes
1answer
101 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 ...
-1
votes
1answer
209 views

RSA given q, p and e?

I am given the q, p, and e values for an RSA key, along with an encrypted message. Here are ...
-1
votes
1answer
63 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?
-1
votes
1answer
125 views

What's the best packet cipher mode for use with UDP for example? Advantages or disadvantages of any alternatives?

Cipher modes typically assume data is streamed or read from a reliable channel with guaranteed ordering. However, many communication transports, such as UDP, are not reliable and don't guarantee order ...
-1
votes
1answer
82 views

I am new to Cryptography and I wonder if one can Suggest me Beginner Projects [closed]

Sorry for this kind of a question, but I really like to learn and improve in cryptography. At the moment I am following online lectures from https://class.coursera.org/crypto-011 , can anyone suggest ...
-1
votes
1answer
132 views

PGP message integrity : How can receiver of an email check the integrity using the sender's public key?

PGP message integrity: Basically, only private key can decrypt message encrypted with public key. But in the message integrity service in PGP does the reverse, where the Hash of the message if ...
-1
votes
1answer
117 views

Pseudo Random Generator with fixed Hamming Weight [closed]

I'm searching for way to generate secure pseudo random sequence with a fixed Hamming weight using a seed. I found below code but I need a seed to generate a sequence ... (and need know if is possible ...
-1
votes
1answer
59 views

How small are we talking about when defining the small public/private key exponent [duplicate]

I've been wondering about the 'small' part of the attacks on RSA, like the small public key exponent and the small private key exponent and what's not really clear is how small are we talking about? ...
-1
votes
1answer
260 views

Reverse engineering a single checksum byte [closed]

I am working to understand a system which saves a few bytes of data together with what appears to be a single checksum byte that provides a very naive guarantee that the data has not been tampered ...
-1
votes
1answer
96 views

How can the key size be calculated [closed]

If the decrypting key is 448, then what is the key size? Suppose I am encrypting a plain text with a key by choosing some random numbers between ...
-1
votes
1answer
145 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 ...
-1
votes
1answer
90 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 ...
-1
votes
1answer
259 views

How can I convert numbers into prime numbers?

I'm working with one-way accumulators, but I'm not knowledgable in cryptography. Is there an easy peasy way to hash numbers (or whatever) into prime numbers? Obviously I'd like it to be collision ...
-1
votes
1answer
60 views

Positioning of keys in encrypted text

I'm just looking at very simple encryption. I've noticed that the key is typically either at the front or at the back of the encrypted text. This is quite easy to break if you know the key. It can ...
-1
votes
1answer
102 views

How to create PSK key? [closed]

I'd like to create a PSK key to use with TLS-RSA-PSK-WITH-AES-256-CBC-SHA - what is the format of this key?
-1
votes
1answer
162 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
-1
votes
1answer
411 views

Number of possible keys in a Play fair cipher [duplicate]

So for the play fair case, the number of possible keys is : 26x26 = 676 possible keys But if we consider the repeated letters, how many unique keys will the play fair have? I mean how will ...
-1
votes
1answer
89 views

Adding “salt” to “doHash” function in Java [closed]

For one of my university projects I am being asked to "Improve the code to satisfy the pre-image resistance requirement." Basically the program is a basic encryption server system, and when I type a ...
-1
votes
2answers
115 views

Need Help Reversing my Encryption Algorithm [closed]

So I wrote a simple encryption algorithm (Not very secure, just a starting point. I don't want criticism on it.) and I have been having trouble finding a way to decrypt the text. The algorithm is here ...
-1
votes
1answer
131 views

How to determine which type of crypto is used in a text file? [closed]

is there a tool or a way to determine which type of crypto is used in this type of text: ...
-1
votes
1answer
160 views

Are the protocols DH-EKE, B-SPEKE, A-EKE, and SRP are considered challenge-response authenticaion mechanisms? [closed]

I got confused which one is considered challenge-response mechanism which one is not.
-1
votes
1answer
604 views

why RSA uses Semiprime numbers? [duplicate]

Why does RSA use semiprime numbers? Why not just use any big number ?? What is the advantage of the two original numbers being prime? Because factoring any big number will be difficult
-1
votes
1answer
140 views

Use of Different keys with PCBC

Currently I am having a doubt, while making a "DES PCBC" encryption on an image I observe a bit of the silhouette of the image (Probably because of the XOR between plaintext blocks and ciphertext ones ...
-1
votes
1answer
94 views

Paillier Crypto System : Pros and Cons? [closed]

Can you please list the pros and cons of the Paillier crypto system you have encountered or found?
-1
votes
1answer
116 views

Can someone explain how this unpadded RSA formula works?

Taken from http://en.wikipedia.org/wiki/Homomorphic_encryption, $\mathcal{E}(x_1) \cdot \mathcal{E}(x_2) = x_1^e x_2^e$ $\bmod\; m = (x_1x_2)^e \;$ $\bmod\; m = \mathcal{E}(x_1 \cdot x_2)$ What is ...
-1
votes
1answer
72 views

Is size Q equal to size SHA(Q)? [closed]

Assume d is a 128 bit random integer and P is base point of an elliptic curve and Q = dP is a point on the elliptic curve and SHA is a hash function with 128 bit output, my question is: Is size Q ...
-1
votes
1answer
72 views

The specification of modern, non-communicating cipher machinery [closed]

I'm looking for references, papers or guidance on a class of system which I have not seen widely discussed. Consider powerful electronic machinery which remains in the custody of communicating ...
-1
votes
1answer
2k views

AES: keylength and password length? [closed]

What is the difference between the keylength and the length of a password for AES-256?
-1
votes
1answer
183 views

Integer factorization via geometric mean problem

presume: we have A and B integers, and C - product of multiplication of A and B, A and B are prime numbers (strong or usual) G - is geometric mean of A and B (square root of C) also, we have: if B > ...
-1
votes
1answer
138 views

Which areas in CS will be (or have been) most affected by fully homomorphic cryptography? [closed]

I'm in the middle of planning a 5000ish word essay on fully homomorphic cryptography, the current practical implementations and their limitations. Which areas of CS as a subject have been (or will ...
-1
votes
2answers
356 views

Is triple des similiar to RSA in that they message size is limited to the key size?

Is triple des similiar to rsa in that the message size you can encrypt is limited (unlike AES)? Yes you can break the message size into parts and apply it, but I'm not interested in doing that so I ...
-1
votes
2answers
77 views

Book Didactic Security Notions [closed]

I want study more about cryptography reading papers, but I have a problems to understand few concepts: security notions, random oracle model, IND-CCA, ... etc. I began study this concepts by internet: ...
-1
votes
1answer
176 views

Obtaining a key that's using ice algorithm

I have a text file that has been processed by the SNOW steganography tool that uses ICE encryption. However, I do not know the key that would enable me to decrypt and retrieve the message hidden. ...
-1
votes
1answer
66 views

construct an election protocol for the following election problem..? [closed]

I am something new to election protocols and I am trying to construct an election protocol for the following problem: Let $A= \lbrace a_{1} , . . . , a_{n} \rbrace $ and $B = \lbrace b_{1} , . . . , ...
-1
votes
1answer
456 views

File Encryption/Decryption in ECB mode [duplicate]

Possible Duplicate: Removing Padded Value in Decrypted Message I tried to encrypt and decrypt a file in ECB mode using AES Algorithm but I encountered one problem during decryption, I don't ...
-1
votes
0answers
7 views

suitable method for encryption and desciption

I want to encrypt and store important data in mysql so that no one else can access its original form and I want to decrypt those data whenever required. Which encryption scheme is suitable for this ...
-1
votes
0answers
11 views

How does combining SHA256 with RIPE-MD160 compare to SHA256 + SHA-3?

Bitcoin stores its addresses as a combined SHA256 + RIPE-MD160 hash. Is it correct to assume this is done to prevent a failure in the algorithm? Since SHA3 was designed to be an alternative to ...
-1
votes
0answers
51 views

can you attack to this protocol? [on hold]

can you attack to this protocol? ‎$ ‎A‎\rightarrow{B}‎‎\quad:\ P{_B(r_1,A)}‎\\A‎\leftarrow‎{B}\quad:\ P{_A(r_1,r_2)}\\A‎\rightarrow‎{B}\quad:\ r_2‎$ ‎$P_A,P_B\ are\ public\ keys\ and\ r_1,r_2\ are\ ...

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