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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Why use an Initialization Vector (IV)?
Why use an Initialization Vector (IV)?
How are IV's used?
What are the advantages/disadvantages of using an IV?
Why use an IV instead of a longer key in which some section of the key is pubic?
What ...
8
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3answers
446 views
What is the best way to put a backdoor in an encryption system?
How can you put a backdoor into an encryption algorithm? Are there any techniques that can be used to reduce the time it takes to break a key?
I am looking for practical examples encryption schemes ...
7
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3answers
2k views
Can one generalize the Diffie-Hellman key exchange to three or more parties?
Does anyone know how to do a Diffie-Hellman or ECDH key exchange with more than two parties?
I know how to do a key exchange between 2 parties, but I need to be able to have a key agreement between 3 ...
6
votes
3answers
448 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 ...
6
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2answers
692 views
Why do block ciphers need a non-linear component (like an S-box)?
Why is there a requirement of "Non-Linear functions" as a component of many popular block ciphers (e.g. the S-box in DES or 3DES)?
How does it make the cipher more secure?
The only intuition I have ...
6
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3answers
226 views
Can nesting different ciphers with different keys ever decrease security?
Very related to this question but not addressed there.
Does the following construction risk introducing any vulnerabilities that render it less secure than using either of its individual components ...
6
votes
3answers
405 views
Counter mode secure hash algorithm
Ever since the SHA-3 competition, I've been wondering if it is possible to create a hash algorithm that is easier to parallelize. The current algorithms all seem to require building a tree of hashes. ...
6
votes
1answer
375 views
Why Addition Mod 32?
I was looking at the algorithm for Twofish, and I noticed that in some places a XOR is used, but in others, they use "addition modulo-32." What makes modulo-32 special? Why not always use XOR? Why not ...
6
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1answer
136 views
Are more complex algorithms easier to break with timing attacks?
Is there a point where increasing the complexity of an encryption algorithm will make it easier to break using a timing attack?
Or is there no connection here at all?
6
votes
1answer
207 views
How to choose constants in a cryptographic function?
A number of cryptographic functions have constants built in. For example, the constants used in RFC 2104 for HMAC, or the constants used in s-boxes (e.g., DES and AES), or MD5. In general, how are ...
6
votes
1answer
94 views
Abstracting primitives and modes of operation
I am developing a symmetric crypto library and have reached a roadblock. Looking at block ciphers, it is quite obvious that all block ciphers are trivially abstractable as a simple primitive ...
5
votes
2answers
332 views
Is it possible to create an easy to use encryption/decryption method that will never be comprimised?
In the comments of the question "Why programming languages don't provide simple encryption methods?" the following statement was made:
A well thought out, tested and understood standard that has ...
4
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3answers
766 views
Are there any simple and yet secure encryption algorithms?
Being very new to C++ and cryptography, I finally managed to implement a version of the Vinegere algorithm. I would like to try something a bit more complicated. I have looked at AES and DES and ...
4
votes
2answers
908 views
SHA-256 “midstate”
Recently I've been trying to implement some Bitcoin-related code, and I've stumbled upon a weird concept, a SHA-256 "midstate". Some explanation is given here.
The general concept is that Bitcoin ...
4
votes
3answers
231 views
Designing a key expander out of ciphers
Is it possible to compose or combine $n$ ciphers ($cipher_0, cipher_1, ... cipher_n$) in such a way that they generate $n$ ciphertexts from the same key, $k$, and that recovering the key, $k$, from ...
3
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6answers
304 views
Where can I begin to study the math behind modern cryptography?
I've been studying (more like breathing and eating) crypto for almost a year now, implementing algorithms, reading books, studying code, etc. The deeper I go in, the more I realize there is; I feel ...
3
votes
1answer
233 views
Do Cryptographic Hashing Algorithms operate only on Integers?
Do all the Cryptographic hashing algorithms operate only on integers (32 bit or 64 bit)? Is there any operation performed on Floating Point Numbers as well?
The reason I ask this is because I read ...
3
votes
2answers
1k views
Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509
What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"?
Edit:
I'm creating the ...
3
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2answers
177 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 ...
3
votes
2answers
175 views
Two step encryption
Is there any asymmetric cryptography algorithm which will allow recursive encryption.
...
3
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3answers
620 views
How can I create a fixed length output in my hash function?
I've been recently looking into the creation (and theory) of hash functions, however I just can't figure out how to turn a message into something of a fixed length.
At the moment, my theory of a hash ...
3
votes
1answer
213 views
Is XOR in a CBC-like mode secure?
Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively.
The first byte of ciphertext is computed like this:
$C_{1} = K_{1} \oplus P_{1}$
...
3
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1answer
129 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 ...
2
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5answers
606 views
Are there hash algorithms with variable length output?
I understand that for example MD5 produces a 128 bit hash value from a given text of variable size. My question is if there is a hash-like algorithm that will produce a hash value where one can ...
2
votes
1answer
71 views
Rapidly changing passwords?
Suppose you need to authenticate yourself to a program with the password - but the program's source code is public, the program doesn't have access to any private information and all your ...
2
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1answer
193 views
Padding for the TEA
Sorry if this is a noob questions, but I finally figured out how to implement the Tiny Encryption Algorithm in C++.
My question is what to do about padding the key and the plaintext? I know that ...
2
votes
1answer
85 views
Is the following scheme secure for different cipher
Let's say I have
two keys K1 and K2.
two messages M1 and M2 of the same length.
Cipher (E,D)
3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj)
In situation ...
2
votes
1answer
68 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 ...
2
votes
2answers
152 views
Algorithm Design for only Mutual Information Sharing
Bob and Alice each have a bit string they want to keep private. They each want to know what the bitwise AND of their two strings would be without telling the other or anyone else listening to their ...
2
votes
1answer
200 views
Verilog simulation & synthesis of Diffie-Hellman key exchange
Is there any freely available verilog implementaion of Diffie-Hellman key exchange?
I couldn't find anything using google. So, assuming its not there I started implementing on my own.
The code is ...
2
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0answers
77 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 ...
1
vote
2answers
157 views
How hard is to find the operators of an addition knowing the sum of them?
I want to learn whether or no there is a cryptographic primitive,scheme assumption that is based on the following hard problem if it is hard . By hard we mean that we have a polynomial adversary: The ...
1
vote
3answers
664 views
Does encrypting twice using the same block cipher produce a security weakness?
If I use the output of a cipher, for example a block cipher such as AES and encrypt it again with the same algorithm, I read that this introduces weaknesses into the overall security of the system.
...
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1answer
141 views
Which one is fastest? Karatsuba or Montgomery multiplication?
Is there any complexity analysis between Karatsuba and Montgomery multiplication algorithms? It seems that Karatsuba is more general in the sense that is not modulo tuned while Montgomery it is. Does ...
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2answers
95 views
Encryption algorithm which produces comparable results for substrings
I am wondering is there any encryption algorithm available which produces comparable string.
I am expecting the output as shown below.
...
1
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2answers
681 views
Symmetric vs. Asymmetric cryptographic approaches to data security
Ok. So, I now know the basic differences between them. But I'd love to know the deeper things, like:
Exactly why is the asymmetric approach slower than the symmetric?
Why does it make use of ...
1
vote
1answer
58 views
Cryptographic Algorithm/Protocol needed
I am trying to achieve the following:
Encrypted files are stored on users filesystem. The user uses my client to authenticate against a server. Once he is authenticated successfully he gets a token ...
1
vote
2answers
107 views
Fastest multiplication algorithm for efficient exponentiation in C++?
First I apologize if this question is better tailored for SO, but since I'm using the method for crypto stuff, I thought I'd ask anybody that might know here. Karatsuba algorithm does a pretty good ...
1
vote
1answer
77 views
How to hide bit frequency of the inter-packet delays covert channel?
I encode a hidden message as different delays between packets of another data stream.
My implementation now is that for each bit,
if the bit is 0, a inter-packet ...
0
votes
2answers
155 views
Idea for user/pass hashing to prevent rainbow tables, would it work?
I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
0
votes
1answer
79 views
Secure way to compare two secret numbers without disclosing them?
For example, two people want to know who is the older, without disclosing their age. Is there a secure way to do this without a third party involved?
0
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2answers
143 views
0
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1answer
133 views
Design criteria for AES
I hope somebody can help me understand the design criterias for AES. Therefore, I would be really thankful if somebody could explain "non-linearity" in this context.
A criteria for the s-box in AES ...
0
votes
1answer
80 views
Trapdoor implementation
Please refer to this secure index paper. On page#6, a trapdoor is defined as
...
0
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2answers
106 views
Bent Combining Functions
Bent functions are boolean functions with maximum nonlinearity and are widely studied for their potential applications in cryptography. Lets say you wanted to use a simple two input AND gate as a ...
0
votes
0answers
59 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 ...
-1
votes
1answer
178 views
ECC Cryptography
I want to know th basic understanding of ECC algorithm for cryptography.But I am not aware of the algorithm so please any one give me the basic understanding of the algorithm.
-2
votes
3answers
303 views
Crypto-Compression Algorithms?
I was wondering, whether there exist such algorithms/enciphering procedures which both compress and encrypt the input data. That means, for starters, the output will be both smaller in size and ...
-2
votes
2answers
181 views
Random Sequence Generator function
By someone's suggestion, I am posting this question from math.stackexchange.com.
I want to find out a function or algorithm, whichever is suitable, which can provide me a random sequence. Like
...
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votes
1answer
109 views
Same Size Crypto Algorithm?
I need to know there is any algorithm that crypts data in same size,
Any knowledge appriciated!
Thank you!
