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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222 views
Existing works on pre-computing ElGamal ephermal keys
I was playing around with a problem in e-voting schemes that use additive homomorphic encryption to tally votes, namely that at the end of the day somebody (or somebodies, if the secret material has ...
2
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1answer
276 views
Replay attack prevention under strict conditions
Say I have a request-response protocol and the task to make it immune to replay attacks. The requirements are as follows:
The defense mechanism cannot rely on the clocks of the parties.
The defense ...
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2answers
69 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
196 views
Is this authenticated one-way communication protocol secure?
I am looking to see if this one-way communication protocol is secure. Assume Alice wants to send Bob a message (and doesn't need Bob to reply in the same session/channel - think email). Bob knows ...
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1answer
156 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
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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 ...
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1answer
445 views
Is this design of client side encryption secure?
I want to build a secure file storage web application. Users should be sure that server doesn't know how to decrypt files so encryption should take place at client side (i.e. in Javascript) and TLS ...
2
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1answer
207 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 ...
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1answer
60 views
Are there any signature schemes that protect against collusion by multiple parties?
Say I want to verify the identity of Alice, but Alice could be colluding with Bob to fool me. Is there any way to verify Alice's identity and also be sure that Bob is not impersonating Alice, e.g. ...
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46 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
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0answers
22 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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72 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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98 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) ...
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8answers
468 views
Does a public key absolutely need to be used to initiate an encrypted session?
I am a software developer working on an application with the .NET platform. This application needs to provide a secure connection and encrypt all data between the client and the server. It is a ...
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2answers
210 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 , ...
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2answers
131 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 ...
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1answer
122 views
How to collect, process, and transmit data securely?
In my question "Authenticating data generated by a particular build of an open source program", Dave Cary requested that I post a question stating my real problem on a high level rather than the ...
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1answer
49 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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3answers
117 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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1answer
343 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 ...
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2answers
84 views
How can I protect against the failure of a block or symmetric cipher?
Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of?
Are some combination of ciphers ...
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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 ...
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1answer
51 views
Proving item association without revealing one of the associated items
I'm a total noob when it comes to cryptography but I believe this falls under the "zero knowledge" category.
I have two associated pieces of information:
tag — known by both parties. Unique per ...
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1answer
102 views
Secure Remote Protocol - Are these 2 equations equivalent?
I'm implementing the Secure Remote Protocol that is specified to have this equation for the parameter S, the premaster secret.
...
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1answer
126 views
synchronization of counters in HOTP
How is synchronization of counter values achieved in the HOTP protocol?
As I understand it, the server increments its counter value only if a match (of the OTP value) is found. What happens at ...
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1answer
161 views
ID-Secret Scheme
I have an ID-Secret scheme and I'd like to hear if there are any vulnerabilities present.
Party 1 and Party 2 hold some credentials, an ID and a Secret.
Party 1 Creates this message:
...
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1answer
112 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 ...
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1answer
72 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?
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1answer
141 views
Deniability of OTR messaging
I've been looking at the off-the-record messaging protocol, and there is something about its deniability property that seems strange to me.
Consider the following scenario:
In the course of an ...
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1answer
674 views
Use of nonces in Kerberos and Needham–Schroeder protocols
Can you please explain me what is the reason of using nonces in the Needham-Schroeder and in the Kerberos protocols for Key Transport.
In particular :
Can you explain me the use of $N_A$?
And ...
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1answer
59 views
Distributed knowledge problem
I need a way to distribute knowledge among multiple parties - lets start with two. The idea is while the knowledge is originally created by one party I need to transform it into a situation where no ...
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2answers
192 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 ...
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1answer
77 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 ...
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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 ...
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1answer
140 views
Is it possible take a piece of data in secret?
I want something like this, but in a digital sense:
You and others walk into a room. Everyone knows who each of you are and everyone is doing their best to figure out what piece of paper each ...
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0answers
100 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. ...
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102 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 ...
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0answers
94 views
Setting protocol parameters to achieve concrete security
Background
One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
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2answers
107 views
Combating traffic analysis over request-response protocols
Suppose I am to design a request-response protocol (similar HTTP). For the sake of simplicity let us assume that this is a "chat" protocol where the client can only perform two actions:
Contribute a ...
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1answer
103 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 ...
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3answers
109 views
Is it possible to ensure security with zero pre-shared information?
Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information?
I know ...
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1answer
62 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 ...
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2answers
126 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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1answer
119 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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1answer
129 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 ...
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1answer
93 views
Combatting traffic shape analysis with spurious packets
I was reading a question about combatting traffic analysis, and a thought occured. If I send random junk messages periodically, would that defeat traffic analysis?
The messages would contain some ...
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2answers
96 views
Distinguishing Encryption Methods from the Output
Suppose that you see all IP communication packets between two computers for a day, as they pass through a connecting router, and this amounts to 10MB. You additionally know that all data transmission ...
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27 views
BAN Logic, Problem to Idealize the protocols
I'm studying the BAN logic.
In the application of it, there is a step,where I have to idealize the protocol
that I'm analyzing.
I have problems to make this.
Anyone that has expertise in BAN logic ...
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2answers
102 views
Proper Way to Encrypt Data with Two Keys?
I'm going to develop a system that will have two keys. One supplied and generated by the system that's specific to an individual user and one from the user.
I plan on using AES.
Does it make sense ...
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28 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 ...
