# All Questions

217 views

### Pseudorandom generator and AE-secure encryption

How would you answer the following question (I have to translate it from German): The existence of a pseudorandom generator implies the existence of a AE-Secure encryption scheme (AE = ...
504 views

### Key Scheduling of International Data Encryption Algorithm (IDEA)

How to perform the key scheduling in International Data Encryption Algorithm (IDEA), I took a research but I can't understand how to perform it, "further groups of eight keys are created by rotating ...
2k views

### Traditional DES scheme in Unix crypt function

In a security context course, we need to reproduce the old DES hashing scheme in the crypt program, on an old unix system. I am actually reading the crypt page on wikipedia: The traditional ...
188 views

### RSA encryption input range - plaintexts that map to ciphertexts?

According to the wiki article on the RSA encryption function, the valid range of input $m$ is $0 \leq m \lt n$. However I have found that the following values of $m$ always return themselves when ...
662 views

### Cryptanalysis of S-DES - Equations

I am trying to derive equations for s and t in the cryptanalysis of a Simple DES algorithm, but I haven't been able to deduce it....
542 views

### How do I calculate the maximum plain text length allowable for a certain cipher text length?

I am encrypting and storing sensitive values in the database. I have a set max length in the database, but in order to provide useful user feedback, I'd like to know the max input I should allow for a ...
253 views

### Is stretching hash several times basically the same as bcrypt?

As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
157 views

### MISTY1 Implementation error

I am trying to implement MISTY1. It's RFC, RFC2994, contains psuedocode that I basically copy and pasted into Code::Blocks. However, I managed to mess that up somehow. After 2 days, I still have not ...
1k views

### AES-CMAC passes every test except two

i wrote this code: ...
239 views

### Looking for cipher that uses one ciphertext

I'm new to Cryptography so please free to edit my question for clarity and add the appropriate tag. I'm trying to research if the following is possible. Suppose John has a message that he ...
167 views

### Idea for secure password hash-likes, is this feasible/usable/workable?

(Hand moved from stackoverflow.com,due to suggestion) Since breaking password hashes has become a new passtime for scriptkiddies, I thought of the problem and came up with a novel(?) idea. store ...
854 views

### What is the time complexity of the RC4 encryption & decryption algorithms?

I'm trying to figure out what the time complexity of RC4 encryption & decryption algorithms is, in big-O-notation.
1k views

### Can md5 be used for encrypting data?

I know that md5 shouldn't be used for password hashing because of collisions and possibility of making dictionary attacks e.g. using rainbow tables. But what about ...
8k views

### c# Correct Triple Des Block Encryption Usage

I found the below code online, but in its original state, the encryption was not using any padding (Padding.None), and was encrypting in blocks of 8. I wasn't able to get this code to properly encrypt ...
28 views

### Some terms related to secret sharing: Optimality, What does it mean?

In any secret sharing scheme we have to develop step by step. After constructing such scheme we need to reduce share size. Why? e.g. Robust secret sharing scheme is modified Shamir secret sharing ...
55 views

### AES encryption for pairwise identifiers

I'd like to map a random ID of 16 bytes (sourceID) to another random ID of 16 bytes (targetID). The operation should: only be reversible by me be deterministic There are about 1 million source ...
251 views

### Is there a administrator key that can decrypt all ciphertexts encrypted with different keys by different persons in a group?

here is the scenario: $A, B, C, \ldots, Z$ are in a group with a administrator $Admin$, each of the users in the group has his own key $Key_A, Key_B$, and so on... everyone encrypt his own ...
55 views

### Safe MD5 digest

So I've heard that MD5 is broken because it's possible to engineer collisions. So instead we should use, say, SHA256. The problem which SHA256 digests is that they are long. So I've come up with this: ...
62 views

### Does sending the same message with 2 different keys in OTP leak information?

Suppose a common message ($M$) is XOR'ed with two different keys $K_1,K_2$ producing two ciphertexts $C_1,C_2$. Thus, $$M \oplus K_1 = C_1\\ M \oplus K_2 = C_2$$ On observing $C_1$ and $C_2$, an ...
63 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 ...
77 views

### Multilinear Pairing in Cryptography

I want to create 2 Bilinear Pairing $e_1$,$e_2$ such that $$e_1:G_0 \times G_0 \rightarrow G_1$$ $$e_2:G_1 \times G_1 \rightarrow G_T$$ and use this to encrypt a message $M$ in the form M e_2(e_1(...
46 views

### Tackling encryption problems with “Zipf's law”?

I am new to cryptography and was wondering if it would be possible to semi-reliably "decrypt" an encrypted message by using the statistical distribution of symbols (/letters/numbers) in the encrypted ...
66 views

### what is meaning of operator “ := ” in cryptography?

I've seen := used in several cryptography papers where the this symbol has been used instead of assignment operator ($\leftarrow$ ) or equal sign (=), but never with an accompanying explanation. It'...
141 views

### Is Threefish the only cipher with 1024 bits of security?

Threefish has up to a massive 1024 bits of security. Is it the only cipher with such overkill security?
113 views

### Understanding Hash function notations

I am implementing a Certificateless Cryptography Algorithm by referencing the paper An Efficient Certificateless Encryption for Secure Data Sharing in Public Clouds. In this paper on page no. 4 during ...
87 views

### Block cipher block and key sizes

Is there any point in making block size less than key size in block cipher? For example, Russian GOST symmetric cipher uses 256-bit keys to encrypt 64-bit blocks. That means there are many keys which ...
252 views

### Do I need to use a MAC with asymmetric encryption?

The internet has drilled into me that when I delivery any symmetrically encrypted data, I should also deliver a MAC to authenticate it before any decryption occurs. Do I also need to do this if I use ...
57 views

### What is the advantage of Pseudosquare?

Pseudosquares ,which are not square but Jacobi symbol are still 1, are used in some cryptographic algorithm. What is the advantage of them over the exact squares? If we used squares instead of ...
63 views

### What are the possible security issues when exporting a plaintext database to a file like this?

Say I have plaintext database with key-value pairs of usernames and passwords. Then I iterate through the database, encrypt the passwords, and write the username and encrypted password pairs to file ...
74 views

### multiplicative inverse in galois field $2^8$

I am trying to compute the multiplicative inverse in galois field $2^8$.The question is to find the multiplicative inverse of the polynomial $x^5+x^4+x^3$ in galois field $2^8$ with the irreducible ...
48 views

### ChaCha20 core vs ideal unkeyed PRP

I know that the ChaCha20 core (without the initial constant) is not an ideal PRP and must not be used as such. I also know that $\text{ChaChaCore}(0) = 0$. Are there any other differences?
46 views

### Is it possible to brute force a single smaller variable in $\operatorname{HMAC-SHA512}(k, a\ ||\ b\ ||\ c\ ||\ d)$?

Given $c' = \operatorname{HMACSHA512}(k, a\ ||\ b\ ||\ c\ ||\ d)$ and the 32-bit integers $a$, $b$, $c$, and $d$ is it feasible to alter $b$ and produce a valid MAC under the unknown key? I ...
51 views

### Merkle signature scheme

I was browsing the Wikipedia article on Merkle signature schemes and noted that it says: The number of possible messages must be a power of two[…] Why is that? ...
41 views

### What information about the ciphertext can an attacker discern if a key is used too many times?

Suppose that I use Blowfish or XTEA (both secure block ciphers with 64-bit block size) in CTR mode. In these cases, I need to change the key after $2^{16}$ blocks to avoid leaking information with ...
126 views

### Is all of encryption based on xor?

For a long time I've been under the impression that all of encryption uses xor at its basic level. Is this true? What other method could be used to encrypt plaintext with a key? Asymmetrically, as ...
23 views

### How is the usual way of using PKCS5/7 when a weird data is given?

PKCS5/7 pads the remaining data elements with a binary representation of how many space requires padding. This is useful and compact but what should I do in the following sample scenario below ? ...
60 views

### Unkeyed, fast, one-way PRP

Are there any fast, secure, one-way, unkeyed almost-pseudorandom permutations? I am looking for something that can hide a MAC, without requiring a secret key and while being much faster than public ...
59 views

### NIST HMAC Test vectors

I am searching test vectors of the HMAC-SHA256 primitive to verify the correctness of an implementation. Without hesitation I go on the NIST website to see what they offer. While reading the ...
70 views

### How to split up $GF(2^{128})$ into smaller fields?

I've heard that it's possible to split up $GF(2^{128})$ into copies of several smaller fields like $GF(4)$ so as to make the math easier in some cases. How do you do that? I know how it works for ...
45 views

Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)?
109 views

### SHA256 for large files

I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size. What should be my input after 1st 64KB ...
40 views

### Are there any disadvantages of using libsodiums helpers for en-/decoding/comparision instead of the native ones?

Libsodium has some helpers, which allow hexdecimal decoding, encoding and also constant-time string comparison. So if you use the php binding libsodium-php you ...
409 views

### How is El Gamal different from Diffie Hellman Key Exchange [duplicate]

I am Reading RSA and Public-Key Cryptography by Mollin and I can't make out how El Gamal is different from Diffie Hellman Key Exchange. Any thoughts?
113 views

### Is super encryption (aka “multiple encryption”) always good?

I'm trying to use super encryption (also known as “multiple encryption”) with AES in CFB mode with IV and password salting and AES in CTR mode both without padding. I first use AES CFB and then AES in ...
55 views

### What happens if you multiply a point with its order on complete Edwards curves?

I was recently working with some ECC crypto and stumbled across the following phrase on the SafeCurves page: The rational points of a complete Edwards curve are the pairs (x,y) of elements of ...
82 views

### What libraries do people use to implement and evaluate cryptography protocols?

I want to implement this credential system: “Anonymous Credentials Light” (PDF). The implementation would involve some zero-knowledge proof and some exponentiation. For some basic group computations ...
284 views

### Lightweight Asymmetric encryption algorithm

I'm an embedded systems researcher, and new in the crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially considering the time needed for key ...
88 views

### RSA message integrity

I wish to send some small data that RSA alone can encrypt, and I send a shared secret along with it. ...