Design of cryptographic protocols, i.e. ways of using algorithms (primitives) to achieve one or more security goals like integrity, confidentiality, authenticity (maybe together with non-security-related goals). If you ask about a specific protocol, tag with its name instead (or additionally, if ...
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1answer
97 views
Is this a sensible cryptographic protocol intending to reduce the impact of compromised security?
I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data.
The basic crux of it is that keys ...
-4
votes
0answers
28 views
pseudo random sequence and permutation functions [closed]
Iam doing my Master thesis in enhancing of an encryption algorithm by using of a pseudo random sequence generators to create a 16*16 shared table and apply a permutation function on it. one of the ...
3
votes
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 ...
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4answers
148 views
Increased CRC collision probability when adding bits to input message
The Scenario
I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ...
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1answer
105 views
Designing a security system from scratch with a custom protocol, suggestions needed
For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ...
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3answers
175 views
What kind of adversary is the cloud?
I just started some work on computation over encrypted data in the cloud. We're still in the early planning stages, and to really understand the kind of security we can offer I need to determine what ...
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1answer
58 views
How to hash a structure that needs to include that hash's outcome?
so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
6
votes
2answers
131 views
Have I understood pedersen commitment correctly?
I want to do a one-sided integer commitment scheme. I.e. the whole process must be non-interactive where I at one point first publicly reveal some data and then at a later time reveal the committed ...
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1answer
98 views
Is this scheme a provably fair random number generation?
I have thought up a method for generating random numbers between a client and a server which I hope is fair:
The client and server decide on a range in advance, $0$ trough $n-1$.
The server ...
2
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0answers
45 views
Relaxed trust criterion for mental poker server?
I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a ...
2
votes
0answers
21 views
Encryption with Deduplication [duplicate]
Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
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votes
2answers
142 views
Where to store the private key and the public key in a communication protocol
I want to create a simple secured connection protocol over TCP/IP.
I just want to connect from my mobile device to a server securely.
Firstly I thought to use an SSL connection, but I changed my ...
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1answer
33 views
Selecting a large NUMS Safe prime
Suppose I want to use the following simple hash function.
For a mesage $m$, take some public $a$ and prime $p$ and raise $a^m \bmod p$ (never mind the computational expense of this operation).
This ...
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votes
1answer
321 views
Is a steganographic technique which has a universal decoder novel/secure? [closed]
I've come up with an approach to steganography which needs review of both its cryptography and its math. There's a complete working implementation at https://github.com/bramcohen/DissidentX and the ...
3
votes
2answers
159 views
What crypto system allows for 3 parties: Party 1 who makes an assertion, Party 2 mutates the assertion, Party 3 validates it
I'm looking for the cryptographic equivalent of a Drivers license where the issuer can be verified, the issuer doesn't need to know who you showed the drivers license to, but also allows ...
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2answers
181 views
Diffie-Hellman key agreement with both Server Authentication and Perfect Forward Secrecy
I am trying to find the protocol with the least overhead, which still meets the following requirements:
Server Authentication of server identity to client. The client has an authentic copy of the ...
2
votes
1answer
249 views
Is a known plaintext, ciphertext, and public-key a viable attack on RSA?
Assume Alice and Bob are using RSA to create a common session key and Cindy is listening, attempting to obtain the session key.
Alice and Bob each have their public- and private-key pairs ...
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1answer
66 views
How to secure a mental poker protocol?
I would like to implement a mental poker protocol in a secure fashion. How should I go about that without (preferably) infringing on the Mental Poker Framework patent?
3
votes
3answers
150 views
Efficient Symmetric Mutual Entity Authentication Protocol
I am looking for an Authentication protocol for access control. Let's say both the client and server would share a symmetric secret (256 bit key) and the client wants to access the server. Access ...
3
votes
1answer
192 views
Is Truecrypt's multiple/cascading encryption safe?
Is Truecrypt use of cascading encryption safe? Is it useful? Truecrypt is arguably one of the most popular and widely used encryption applications in use today, yet it seems to use a very ...
0
votes
1answer
120 views
Digital signatures in SSL/TLS-like protocols
The TLS protocol includes an optional Server Key Exchange message that is signed by the server. It seems to me that this message is digitally signed only to prove to the client that the message ...
0
votes
0answers
23 views
How can I validate generated session keys in SRP-6a protocol
I have genereted two equal session keys on client and server successfully. But I couldn't understand how each other should validate that they have same session keys.
On the client I generated a SHA1 ...
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2answers
124 views
AES encryption with shared IV
Sorry about the horrible title, didn't now what to say.
I'm trying to avoid having to send an IV with every message purely to keep packet sizes down, so I thought of a method to establish a "IV ...
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0answers
40 views
SRP6a client server exchanged message order
In SRP6a, the public key of server is send after receiving the public key of client A. Its that okay that B send along together with s right after client send the username, and then later on client ...
2
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0answers
68 views
Why does the SRP6 calculation of B included a multiplier k = 3?
In SRP6 $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$?
(In SRP 6b, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP 6.)
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5answers
2k views
Guarding against cryptanalytic breakthroughs: combining multiple hash functions
Assume I want to design a protocol (or data format or similar) including some cryptographic hash, and want it to be as future-proof as possible, i.e. I want to avoid that breakthroughs in cryptography ...
2
votes
2answers
68 views
Zero-knowledge identification of the majority commitment
Alice is communicating with $n$ people. We do not assume that the $n$ people don't trust each other or trust Alice. Alice doesn't trust them either, and needs to assume that they will not form a ...
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1answer
42 views
Reference papers for protocol proving [closed]
I am working on few cloud cryptography protocols. i am new to protocol design, definitions and proving .
With some preliminary research i understand that there are two models of security proofs
one ...
4
votes
3answers
405 views
A proof-of-work random number generation system for Pokémon [closed]
(The original question that was here was considered too confusing, unclear, and rambling. You can still view it in the edit history, but the content is no longer useful by itself, and cannot be ...
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0answers
154 views
Cryptographic Protocol using NaCL
Why?
I wanted to add some security and privacy to a chat-type server for playing various games (with a few things that are done on the server to limit cheating). Going by the "Don't implement ...
2
votes
2answers
274 views
Benefit of combining classical substitution ciphers with modern cryptography
I know that a simple monoalphabetic substitution cipher is considered extremely weak, on account of linguistic frequency-analysis attacks. However, assume the following:
cleartext is encrypted ...
4
votes
1answer
83 views
How to construct yes/no - election protocol, such that only the result is revealed?
Can we use Threshold scheme to construct an (yes/no)-election protocol, such that every voter can give a positive or negative vote or he can abstain, and such that only the result of the election is ...
1
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3answers
115 views
Public keys and their protocols
I'm having difficulties understanding exactly what this protocol means:
$S \to D : \{N_S , S\}K_D$
$D \to S : \{N_S , N_D \}K_S$
$S \to D : \{N_D \}K_D$
"where $S$ represents the supervisor’s ...
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2answers
198 views
Are there any tools for modelling and analysis of Cryptographic protocols?
Iam designing few cryptographic protocols and am new to it.
Are there any well known tools that can be used to model/design these protocols ?
And also verify/Analyze their validity ?
If not a tool , ...
2
votes
2answers
82 views
What are the cryptographic assumptions in the Dolev Yao model?
In the Dolev Yao model for interactive protocols, the cryptographic primitive (encryption, for example) is considered as a blackbox.
Does blackbox here mean that the primitive is to be considered CPA ...
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votes
1answer
58 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} , . . . , ...
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2answers
130 views
Contruct a protocol to determine if three secret keys are different, without revealing any of them?
I am trying to find a protocol for this problem:
Three persons, $A$, $B$, and $C$, know secret numbers $s_{A}, s_{B}$, and $s_{C}$, respectively. They want to know whether their numbers are all ...
2
votes
0answers
97 views
Transforming simplest protocol into a Sigma-protocol
I have some questions from previous years exams, I hope you could help me with them. :)
Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
2
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1answer
143 views
Why are protocols often proven secure under the random oracle model instead of a hash assumption?
Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle?
I mean, is it possible to devise a protocol $P$ using a function $H$, and ...
1
vote
1answer
69 views
Comparing plaintext to contents of ciphertext
Given an authenticated mode of encryption, when comparing a plaintext string against the contents of a ciphertext, which approach is typically considered safer?
Encrypt the plaintext and compare ...
1
vote
0answers
99 views
Sigma-protocol for 3SAT problem
I have some questions from previous years exams, I hope you could help me with them. :)
Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
9
votes
2answers
301 views
How should one implement a delegated shared trust protocol?
Consider the following (probably naive) scenario.
Alice, who is very limited in her knowledge of security in general (clueless about securing a private key for example), wishes to delegate certain ...
3
votes
3answers
734 views
Should we sign-then-encrypt, or encrypt-then-sign?
We often want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
2
votes
2answers
249 views
Why do we need Hash by key?
(i'm just trying to find what am I missing...)
Assuming John have a clear text message , he can create a regular hash ( like md5 , or sha256) and then encrypt the ...
1
vote
0answers
100 views
Computer appliance protocol
I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
1
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1answer
94 views
Is secure remote snap possible?
Scenario:
We have a central server $S$.
We have a number of peripheral servers $P_i$
We have some individuals $U_j$
A given individual may be "known" to one or more peripheral servers. Each ...
1
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1answer
335 views
Can I combine two of SHA-3 candidates cryptography hash functions and obtain more secure Algorithm?
For example, Is possible to combine (Concatenate or Chain or XOR) Skein SHA-3 candidate with Grostl SHA-3 candidate to increase security?
Note: I just want more secure output and CPU cycles does not ...
3
votes
3answers
221 views
How to avoid a chicken and egg scenario with encrypting passwords?
I am working on application that allows users to upload files containing company data and then share those files with a list of other users that have specific roles within the system.
I want to ...
2
votes
1answer
151 views
Exact mathematical definition of simulation based security?
I've been trying to understand cryptographic protocols and how to define their security. The problem is that while I can understand what the intuitive definition says, I have trouble understanding how ...
2
votes
1answer
78 views
Data-validating protocol
I have to implement protocol of secure data transfer that can be described as
Alice selects data to send from finite set $m\in M$ (e.g. $M$ could be a column of values in database table)
Alice ...
