Design of cryptographic primitives (algorithms), like block ciphers, stream ciphers, random-number generators, hash functions, MACs, key exchanges, public-key encryption or signature schemes. Also tag with the relevant type of primitive. If you ask about a known existing algorithm, also tag with its ...

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How would using only one s-box affect security of Blowfish?

Schneier says: Fewer and smaller S-boxes. It may be possible to reduce the number of S-boxes from four to one. Additionally, it may be possible to overlap entries in a single S-box: entry 0 ...
3
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1answer
351 views

How is an AES Encrypted Message Decrypted with Random Padding?

One thing I was surprised to learn about AES is that random padding can be added to the message to make it a multiple of block size. What I can not wrap my head around is how this random padding can ...
2
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1answer
292 views

Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?

I'm writing my own cryptosystem that uses One Time Pad and Diffie-Hellman to generate keys for the OTP. I am using Rails on the server side and Javascript for the client side. Please don't tell me ...
2
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2answers
220 views

Need 32-bit mixing function that has perfect avalanche between octets

for my hobby tinkering project, I need a mixing function that takes 32-bit input and has 32-bit output (and will, most likely, run in a 32-bit C environment) and the following property (independent of ...
4
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3answers
246 views

Can insecure algorithms be combined to form a secure algorithm?

This is hypothetical as I can't think of any reason to do this, but out of curiosity... Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite ...
28
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1answer
1k views

How is the MD2 hash function S-table constructed from Pi?

For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ...
1
vote
1answer
332 views

Can you explain partial private key extract algorithm in certificateless Public key cryptography?

Related to the algorithms of certificate-less Signature approach of Al-Riyami and Paterson… Why is there a need for a "partial private key extract algorithm"? Why should it be needed when ...
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3answers
574 views

random access stream cipher

Some time ago I was working in a pet project for a type of database engine. And I thought about securing the data in disk with encryption.. and since the main code was already developed.. I had a few ...
3
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1answer
359 views

How does the IV or initial counter increase internally for each block in AES CTR mode?

I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions. I could not see how the IV or initial counter increases in CTR mode. In general, how ...
3
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0answers
100 views

Hi Sec National algorithm

I'm trying to create a remote controller compatible with HiSec algorithm. It's so old that National (now Texas Instruments) discontinued NM95HS01/02 and docs are unavailable. Does anyone have the ...
0
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1answer
3k views

Are there any Truth Table to Boolean expression converters? [closed]

I am working on Bent functions that are of interest in cryptography. I developed an algorithm that construct such functions. However, I need some tools to calculate boolean expression from the truth ...
2
votes
1answer
203 views

Having 4096 bit keys and short (< 256 byte) messages, can I simply use the key as OTP?

Assumptions: Alice and Bob use (cryptographically secure, hardware-rng generated) 4096 bit keys. Each message is encrypted using a new key; meaning: once a key is used, it's destroyed. Alice and Bob ...
7
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1answer
757 views

What's wrong with MARS?

Why did the MARS cipher receive such a high number of negative votes in the AES competition? As I understand only MARS and Serpent implement measures to counter future cryptoanalytic attacks, so it ...
3
votes
1answer
631 views

Non-linearity of a boolean function

What's the definition of non-linearity of a boolean function? Roughly saying it is minimum number of times it equals any affine function. But I don't get it mathematically. For example, if $f = ...
5
votes
1answer
502 views

Where could I submit my algorithm?

I have come up with an encryption algorithm and I am looking for a place to possibly publish it. Any ideas?
3
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1answer
2k views

How much is slower GCM AES-128 than one of the stream chipher eSTREAM?

Evaluate the speed of the algorithm GCM AES-128 and compare it whith speed of one of the stream chipher in eSTREAM. Can someone give such an assessment?
4
votes
2answers
351 views

What (precisely) is a block cipher?

If I follow the wikipedia or crypto.stackexchange definition, any simple XOR encryption where the key is as long as the plain text should qualify as a secure block cipher. Now I thought what would ...
3
votes
1answer
173 views

Derive a public EC key from two public EC keys

Alice has two EC key pairs: $a_1$, $a_2$ are private keys (integers), $A_1$, $A_2$ are the corresponding public keys (points). Alice and Bob want to create a new public key $C$. Alice must prove that ...
0
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1answer
226 views

What is the difference between, and security of $Z_p$ and $F_p$?

While reading some papers, I found that sometimes $Z_p$ was used but sometimes $F_p$ was used ($p$ is prime). Usually, the author will only use their subgroups like this: choose a big prime factor of ...
3
votes
3answers
280 views

understanding pairing $e:G \times G \to G_T$ and ( Decision)BDH assumption

From DrLecter's comment, I know that DDH problem can be efficiently solved with this $$e(g^a,g^b)\stackrel{?}{=} e(g,g^z).$$ I have some trouble to understand this map $e:G \times G \to G_T$. Am I ...
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0answers
146 views

Career advice for our readers [closed]

I am a first year math PhD student with work experience and an MS in math. Do you have any advice regarding internships involved with cryptography and other mathematics other than the NSA? Thanks.
2
votes
2answers
278 views

Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...
18
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5answers
6k views

What is the lowest level of mathematics required in order to understand how encryption algorithms work?

What mathematical fields of knowledge would be required in order to get a good understanding of encryption algorithms? Is it basic algebra, or is there a "higher education" mathematical field ...
17
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9answers
3k views

Why not the one-time pad with pseudo-number generator

I am very new to cryptography (so be kind), but I have a question that may seem silly. If the one-time pad is the perfect cipher and impossible to crack, why would the following algorithm not be one ...
2
votes
1answer
2k views

Inverting the encryption equation of a symmetric cipher

I've just started a cryptography course. I am beginning to understand the concepts (I'm only in week 2) but I just can't get my head around the theories and principles when written as equations. I've ...
5
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2answers
799 views

What is an active S-Box?

I don't understand what an active s-box is (in reference of design criteria 8 of the DES). Because according to DES, all 8 s-boxes are used every round. But this is not what active means. So my ...
6
votes
1answer
608 views

Is the first version of the Message-Digest algorithm by Ronald Rivest publically available?

Diving into the history and evolution of the Message-Digest algorithm by Ronald Rivest, I have been able to track back papers from MD6 down to MD2. Yet, somehow I can not seem to be able to find any ...
4
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2answers
354 views

Is there any research about cryptography on nondeterministic Turing machines?

I know it's a highly theoretical topic, but I was wondering if there was any research out there about what cryptography would be like assuming that we had access to nondeterministic Turing machines. ...
4
votes
1answer
241 views

Fractal Merkle Traversal

I am studying Fractal Merkle Tree Traversal algorithm in the book “Post Quantum Cryptography” (PDF). On the [pag. 54] I don't understand this paragraph: We may determine the number of pebbles ...
13
votes
6answers
2k views

Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
4
votes
2answers
301 views

Advantages of combined PRNGs

This question is related to this one in intention, and this one in scope. Would I be guarding myself against future attacks on a single PRNG if I combine two (or more) together? I am thinking of ...
0
votes
1answer
87 views

Different patterns of different paterns, wildcard [closed]

I'm not realy experienced with programming and such but I am wondering if the following could be implemented in, lets say, python we have the following ciphertext sequence ...
2
votes
1answer
342 views

Primality testing (deterministic vs. non-deterministic)

I noticed that non-deterministic primality testing algorithms are more commonly used in practice while there is a deterministic algorithm e.g., AKS which runs in polynomial time? I am right? if so, ...
2
votes
1answer
313 views

How to prove a cipher resistant to differential cryptanalysis?

How do you prove that a cipher is resistant to differential cryptanalysis? It's said that Rijndael has been proven resistance to differential cryptanalysis. How do cryptographers do that?
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1answer
320 views

What operations are used in symmetric cryptography and why?

In continuation to Why are bitwise rotations used in cryptography?: what other operations are commonly used in symmetric cryptography? Are there particular operations on numbers that are good for ...
2
votes
1answer
200 views

Selecting bijective functions for permutations

How would one go about selecting an appropriate bijective function for introducing permutations into a cipher or hash? For example, $f(x) = x+1 \space mod \space n$ is a bijective function, but isn't ...
4
votes
7answers
600 views

A block cipher with independent keys for each round

I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher as secure as the original one ? Thank you. EDIT Some missing ...
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0answers
59 views

Are there any bi-bidirectionally indistinguishable Asymmetric Encryption Algorithms

I have been using Asymmetric Encryption for a while, and I have come across an interesting concept, and it would be cool if it could be done. Are there any Asymmetric Encryption Algorithms where the ...
6
votes
3answers
752 views

Why is “mod(n)” so central to most aspects of cryptography?

When I first started learning cryptography, I had my first a-ha moment when I fully appreciated the value of a One Time Pad and XOR and all the functions that attempt to emulate that OTP's randomness ...
2
votes
1answer
507 views

How are Predicate Encryption algorithms implemented?

After a lot of reading on the internet, i can't seem to figure out how Predicate Encryption works. As i read, it consists of 4 algorithms: ...
3
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1answer
46 views

Distributing blocks with validation and non-dependant list generation

Problem Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
2
votes
1answer
152 views

Is this algorithm secure?

I recently found this site, proposing a hashing algorithm for passwords. They describe the following: pad the password on both sides with SHA1(email) to ...
3
votes
2answers
444 views

Is there a way to do fair exchange between two parties who don't trust each other?

Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts $m_A$, Bob encrypts $m_B$) with their own key, and ...
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votes
1answer
96 views

AES encryption algorithm [closed]

What is the amount of decrease in the probability of decrypting a data encrypted using an AES algorithm? (That is by introducing each round out of ten whole rounds, how the probability of decryption ...
9
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7answers
3k views

Where can I begin to study the math behind modern cryptography?

Why do I start the word buffers in MD5 with those values specifically? What in the world motivated the decision to use the numbers 1, 1, 2, 3 for the mix columns stagein AES? And what kind of ...
5
votes
1answer
904 views

What are the constraints for an IV using AES in CBC mode?

I'm designing a protocol for use into a VPN software. The VPN frames are encapsulated into AES-256 CBC encrypted frames. I understand that IVs must be uniquely used for each message encrypted with ...
1
vote
0answers
263 views

Method and explanation for calculating difference in speed between DES and RSA

Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ...
7
votes
3answers
687 views

Is this encryption algorithm build from MD5 secure?

I'm being asked to use an encryption algorithm in my code, and besides the fact that I'm sure there will be implementation faults that lead to vulnerabilities, I also have concerns about the algorithm ...
5
votes
2answers
787 views

Are there any secure commutative ciphers?

This answer lists two commutative cipher algorithms - Pohlig-Hellman and SRA. However, they don't appear to be too secure. My question is, here there any commutative ciphers out there that are secure ...
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7answers
996 views

Turning a cipher into a hashing function

This is theoretical question. I'd like to know if it's possible (and what are eventually the consequences), not that I'm going to do it in one of my projects. ;) The first hashing functions created ...