instruction stringlengths 15 30k |
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How does partial key escrow work? |
What are the ***"standard procedures in cryptanalysis"*** to analyze unknown ciphertext?
In other words: Are there any protocols, officially acknowledged checklists or something like that which represent a ***"standard"*** approach in cryptanalysis to analyze unidentified ciphertext? If yes, which ones would that be... |
What are the standard procedures in cryptanalysis to analyze unknown ciphertext? |
What are the ***"standard procedures in cryptanalysis"*** to analyze unknown ciphertext?
In other words: Are there any protocols, officially acknowledged checklists or something like that which represent a ***"standard"*** approach in cryptanalysis to analyze unidentified ciphertext? If yes, which ones would that be... |
*TWhat are the standard procedures in cryptanalysis to analyze unknown ciphertext? |
What are the ***"standard procedures in cryptanalysis"*** to analyze unknown ciphertext?
In other words: Are there any protocols, officially acknowledged checklists or something like that which represent a ***"standard"*** approach in cryptanalysis to analyze unidentified ciphertext? If yes, which ones would that be... |
What are the standard procedures in cryptanalysis to analyze unknown ciphertext? |
What are the ***"standard procedures in cryptanalysis"*** to analyze unknown ciphertext?
In other words: Are there any protocols, officially acknowledged checklists or something like that which represent a ***"standard"*** approach in cryptanalysis to analyze unidentified ciphertext? If yes, which ones would that be... |
First of all, for elliptic curves based on a prime field $F_p$, we always work with a prime $p$ that is the same size as our target subgroup.
The reason is quite simple: we could work in a proper subgroup based on a larger curve, but what would that buy us? It becomes more costly (as all our internal computations a... |
I am working on an occasionally connected app. To allow the users to authenticate I created a profile which is encrypted and placed on the users machine.
The first byte of the file contains the IV length followed by the IV and then encrypted using Aes where the key is the users password hashed using SHA256.
Wi... |
You might look at [EAX][1] mode, which combines a block cipher in CTR mode with a CMAC. However, EAX does differ from generic Encrypt-than-MAC in that EAX uses a single master key, which would be an absolute no-no for Encrypt-then-MAC. Normally using the same key for both purposes is quite dangerous, but EAX is expli... |
I've previously answered this question over at [How will security need to be changed if P=NP?](http://security.stackexchange.com/q/12802/971) (on our sister site, the IT Security Stack Exchange). In addition, see the answers to [What would be the scenario if P = NP for RSA algorithm?](http://security.stackexchange.com... |
What are the ***"standard procedures in cryptanalysis"*** to analyze unknown ciphertext?
In other words: Are there any protocols, officially acknowledged checklists or something like that which represent a ***"standard"*** approach in cryptanalysis to analyze unidentified ciphertext? If yes, which ones would that be... |
Given a message $M$ and a signature $S$, is it feasible to find a RSA public key $(n,e)$ such that $S$ verifies as a valid signature on $M$ (using this public key)?
What if we're given one public key $(n,e)$ where the signature verifies (presumably, the public key of the original signer), and we want to find a secon... |
Is my one time pad cipher secure? |
I know for a fact that DES is not a group, but are any of the Triple-Des versions a group? Why, or why not?
|
Is Triple-DES a group? |
The first hole I see is that you're using the random generator `urandom`. How do you know that the sequence generated by this function is truly random?
The second hole is that you're saving the key as plaintext! |
Scenario: a class that is not mandatory. The teacher wants a protocol that will satisfy the following requirements:
1. It must record each student's assistance.
2. A student X should not be able to say that another student Y went to the lecture.
3. The teacher should not be able to know who attended the lessons... |
In recent weeks the concept of (perfect) forward security/secrecy has
been mentioned a lot, primarily in the context of the shocking
revelations about NSA eavesdropping. As far as I'm aware, this concept
was introduced by C. G. Günther in [1]. Unfortunately [1] only sketches
the concept but does not give a securit... |
Do you have a specific application domain in mind?
I do not know of any *formal* definition that spans multiple application domains.
A formal definition of Perfect Forward Secrecy for the domain of key exchange protocols is included in this paper:
[Beyond eCK: Perfect Forward Secrecy under Actor Compromise and E... |
You have various options. Basically, your goal is to ensure that the plaintext you decrypt was the exact same plaintext you encrypted. (Trivially, this excludes re-ordered plaintext.)
**If the receiver can wait for all the packets to arrive before decrypting:**
The solution is simple: Use an authenticated encrypt... |
I have a 64 bit integer. It has some sort of signature so that one can be sure it is valid.
Anyone may increase the integer, update the signature, and remove all trace of the old signature. But it is not permitted to reduce the integer.
Many updates are permitted.
Is there a scheme such that, given $n$ and pub... |
**If the receiver can wait for all the packets before decrypting:**
This case is simple, since your final goal is to ensure that the plaintext you decrypt was the exact same plaintext you encrypted. (Trivially, this includes rejecting re-ordered plaintext.) Use an Authenticated Encryption (AE) scheme (eg, CCM, GCM, ... |
**If the receiver can wait for all the packets before decrypting:**
This case is simple, since your final goal is to ensure that the plaintext you decrypt was the exact same plaintext you encrypted. (Trivially, this includes rejecting re-ordered plaintext.) Use an [Authenticated Encryption][1] (AE) scheme (eg, CCM, ... |
In order to setup an authenticated shared secret key between two clients, I am faced with the choice between two possibilities:
- A: Let users set a (low-entropy) shared password and then perform PAK-DH (as described [here](http://tools.ietf.org/html/rfc5683), for example).
- B: Generate a high-entropy shared key a... |
Scenario: a class that is not mandatory. The teacher wants a protocol that will satisfy the following requirements:
1. It must record each student's attendance.
2. A student X should not be able to say that another student Y went to the lecture.
3. The teacher should not be able to know who attended the lessons... |
Let E be an elliptic curve over a finite field Fp. Given n be a positive integer and Q be a point on E, assume that Q=nP, how can we find this P? We can assume that n|p-1. If n is "small", I would imagine that it is possible using division polynomials. Is it a difficult problem if n is large enough?How difficult it is?... |
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:
`Setup()` - (outputs `MSK` - Master Secret Key and `PK` - Public Key)
`Encrypt(PK, text)` - (outputs `CT` - ciphertext)
`GenKey(MSK, predicate)` - (outputs a `Token`)... |
How are Predicate Encryption algorithms implemented? |
I have an idea for a system that would be outsourcing some brute force calculations to many users in hopes of finding divisors of a number. However, there is a possibility that a given number would be prime, or that it would not have a divisor in a given range.
For example, a computer might be tasked to look for a d... |
Proof of work for determining whether a number is prime? |
I have an idea for a system that would be outsourcing some brute force calculations to many users in hopes of finding divisors of a number. However, there is a possibility that a given number would be prime, or that it would not have a divisor in a given range.
For example, a computer might be tasked to look for a d... |
**Background**
Microsoft certifies Windows 7/8 as well as Server 2008 R2 and 2012 to be FIPS-140-2 compliant. Actually they certify just a small crypto core, bcrypt.dll (the library, which is unrelated to bcrypt, the key derivation function). Microsoft's FIPS-140-2 architecture is [detailed here][1]. Also, their FIP... |
Windows 8/Server 2012: Passes FIPS-140-2 despite failing AES-GCM for IV != 96 bits long? |
Let $E$ be an elliptic curve over a finite field $F_p$. Given $n$ be a positive integer and $Q$ be a point on $E$, assume that $Q=nP$, how can we find this $P$? We can assume that $n|p-1$. If $n$ is "small", I would imagine that it is possible using division polynomials. Is it a difficult problem if $n$ is large enough... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend heavily on:
- If the adversary has a large supply of $S$ (I assume she is content with success for one $S$), or/and a large supply of... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend heavily on:
- If the adversary has a large supply of $S$ (I assume she is content with success for one $S$), or/and a large supply of... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend heavily on:
- If the adversary has a large supply of $S$ (I assume she is content with success for one $S$), or/and a large supply of... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend heavily on:
- If the adversary has a large supply of $S$ (I assume she is content with success for one $S$), or/and a large supply of... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend heavily on:
- If the adversary has a large supply of $S$ (I assume she is content with success for one $S$), or/and a large supply of... |
Why the Lamport - Diffie signature is quantum resistance?. Where I will be able to find quantum attempts to attack this signature scheme?. |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
I'm trying to learn more about the Subgroups implementation of Microsoft UProve. I'm unsure if they are [Schnorr Groups][1] or use a different foundation?
Can anyone point me to the technical reading required to understand the implementation? (anything appropriate for a determined, yet fledgling novice would b... |
What type of groups does Microsoft's U-Prove use (Schnorr... etc?) |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
I'm new to the field of cryptography, but I want to make the web a better web by setting up the sites that I host with Perfect Forward Secrecy. I have a list of questions regarding the setup of Perfect Forward Secrecy. Here it goes:
- Can my choice of certificate authority hinder the use of Perfect Forward Secrec... |
[U-Prove Recommended Parameters](http://research.microsoft.com/apps/pubs/default.aspx?id=166972) describes the groups used by U-Prove.
For the subgroup variant it references Appendix A.1.1.3 of FIPS186-3 which is about groups for finite-field based DSA. AFAIK these groups are Schnorr groups, even though NIST never r... |
I am trying to understand the design of Tor(onion router). I am reading the original paper on the 2nd generation onion routing system. Where, under integrity checking on streams, they say, "When Alice negotiates a key with a new hop, they each initialize a SHA-1 digest with a derivative of that key. Then they each incr... |
Tor's integrity verification system? |
In the beginning SSL handshake, the client sends a list of supported ciphersuites (among other things). The server then picks one of the ciphersuites, based on a ranking, and tells the client which one they will be using.
This step is the one that determines whether or not the future connection will have perfect fo... |
Forgive the very novice question, but...
Given an algorithm which, upon inputting an unchanging 4-character string, generates a variable 6-character string, but having no idea what the algorithm is other than it is at least partially based on the date, is it possible/practical to discover the algorithm based on 15 o... |
Seemingly simple (?) decryption question |
presume:
we have A and B integers, and C - product of multiplication of A and B, A and B are prime numbers (strong or usual)
G - is geometric mean of A and B (square root of C)
also, we have: if B > A => G/A = B/G (from geometric mean properties)
so: since G is float number, then GCD(G*10^x,C) > 1 and I can with t... |
If I interpret your question correctly, your unchanging 4-character input is probably just a PIN code that unlocks the use of the device. In this case, the sequence of 6-character strings is a series of one-time password to unlock access to a remote device.
Under this assumption, they is no simple way to predict the... |
presume:
we have A and B integers, and C - product of multiplication of A and B, A and B are prime numbers (strong or usual)
G - is geometric mean of A and B (square root of C)
also, we have: if B > A => G/A = B/G (from geometric mean properties)
so: since G is float number, then GCD(G*10^x,C) > 1 and I can with t... |
In the book Cryptographic Engineering, it is said that fixing p, q, g for a key negotiation protocol based on DH is a bad idea (page 228 1st ed).
But allowing for flexible p, q and g requires a lot of checks and protocol tricks (e.g. requesting a lower bound on p / q)
Why do we need this flexibility? Isn't DH sec... |
Why use variable p, q, g for Diffie-Hellman? |
In the book Cryptographic Engineering, it is said that fixing p, q, g for a key negotiation protocol based on DH is a bad idea (page 228 1st ed).
But allowing for flexible p, q and g requires a lot of checks and protocol tricks (e.g. requesting a lower bound on p / q)
Why do we need this flexibility? Do we add so... |
While reviewing NIST SP800-90 publication for pseudo random numbers generation, I noted that no stream cipher was considered among the various specified solutions
From that I also noted in listing the other NIST SP800 publications that finally (unless error from my part) no Stream Cipher appears today approved / rec... |
Stream Cipher no more considered by NIST? |
When a block cipher key length is greater than the block length, is it the case that for keys $k_0, k_1$ (with $k_0 \not= k_1$) and plaintext message $m$ that $E_{k_0}(m) = E_{k_1}(m)$? |
How can I use SSL/TLS with Perfect Forward Secrecy? |
When a block cipher key length is greater than the block length, is it the case that for some keys $k_0, k_1$ (with $k_0 \not= k_1$) and plaintext message $m$ that $E_{k_0}(m) = E_{k_1}(m)$? |
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 (PRP/PRF).
Now that I'm learning about the math behind various lemmas, I see a recurring theme regarding "take the mo... |
Why is "mod(n)" so central to most aspects of cryptography? |
Your question first calls for a remark, the XOR itself already is an instance of taking a modulo. Namely, XOR is just another name for addition modulo 2. As a consequence, using modulo n can be seen as a generalization of the XOR to larger sets. A simple example is Caesar's cipher which adds a key modulo 26 (the size o... |
I read about STS + variants being insecure in the SIGMA paper, which then proposes SIGMA as a replacement. Are the SIGMA variants still considered secure or are there some other protocol that's currently recommended to use? |
Authenticated DH, what protocols are secure? |
If the 'big two' of TLS and IPSEC aren't appropriate in a given situation, where can you find up to date information on the existence and security of Authenticated Key Exchange (AKE) protocols?
So many protocols have been proposed in the literature over the past 20+ years, and deficiencies of one type or another hav... |
Where to find up to date information on authenticated key exchange protocols? |
__What is consistent, special or useful about mod(n) that makes it so consistently used by cryptographers such as XOR is?__
The operation's result is finite - you're working in a field/ring with it. Now there are various ways to work in fields and rings, but moduli are easy to understand and analyze and come pre-shi... |
While reading [NIST SP 800-90A, "Recommendation for Random Number
Generation Using Deterministic
Random Bit Generators"](http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf), I noted that no stream cipher was included among the various specified solutions.
I also noted that, at least as far as I could... |
Are stream ciphers no longer considered by NIST? |
Forgive the very novice question, but...
Given an algorithm which, upon inputting an unchanging 4-character string, generates a variable 6-character string, but having no idea what the algorithm is other than it is at least partially based on the date, is it possible/practical to discover the algorithm based on 15 o... |
Here is a good guide for [deploying forward secrecy on your SSL server](https://www.net-security.org/article.php?id=1856).
To answer your specific questions: As far as I know, you should be able to use any CA. The choice of forward secrecy doesn't come from the certificate; it comes from the list of ciphersuites yo... |
to understand RSA better I am doing a little calculation by hand, this is what I got:
Choosing:
$p = 3$
$q = 5$
$n = 15$
$\phi(pq) = 2 * 4 = 8$
$e > \phi(n) => e = 13$
$e*d = 1 mod 8$
$13 * d = 1 mod 8$
$(13 * 5) mod 8 = 1$
So there has to be $m <= n$ and I choose $m = 7$
Encryption:
... |
RSA by hand - did I do something wrong? (c = m on encryption) |
to understand RSA better I am doing a little calculation by hand, this is what I got:
Choosing:
$p = 3$
$q = 5$
$n = 15$
$\phi(pq) = 2 * 4 = 8$
$e > \phi(n) => e = 13$
$e*d = 1 mod 8$
$13 * d = 1 mod 8$
$(13 * 5) mod 8 = 1$
So there has to be $m <= n$ and I choose $m = 7$
Encryption:
... |
to understand RSA better I am doing a little calculation by hand, this is what I got:
Choosing:
$p = 3$
$q = 5$
$n = 15$
$\phi(pq) = 2 \cdot 4 = 8$
$e > \phi(n) => e = 13$
$e \cdot d = 1 \mod 8$
$13 \cdot d = 1 \mod 8$
$(13 \cdot 5) \mod 8 = 1$
So there has to be $m \le n$ and I choose $m ... |
Is it possible to send Messages over TLS with out Encryption.If so Which cipher suite is needed for this? |
Recently NSA published [two new algorithms](http://eprint.iacr.org/2013/404.pdf), Simon and Speck. In the abstract they say
>The aim of SIMON and SPECK is to fill the need for secure, flexible, and analyzable lightweight block ciphers.
so as the question title says, what does 'analyzable' mean? BTW I found the pu... |
What does NSA mean by 'Analyzable'? |
Out of the two deterministic random bit generators defined in section 10.1 of [NIST SP 800-90A][1] (i.e. based on hash functions), which one is cryptographically stronger?
1. Hash-DRBG (Section 10.1.1)
2. HMAC-DRBG (Section 10.1.2)
Is there any other criteria to select between these two?
[1]: http://csrc.... |
How much stronger is RSA-2048 compared to RSA-1024? It is hard to imagine very big numbers. So what would be your way to explain the difference to someone who doesn't know much about cryptography? |
How much stronger is RSA-2048 compared to RSA-1024? |
Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm?
I'm thinking of something like this:
Client $C$ knows $g$, $p$, $q$ and $g^S$.
1. $C \rightarrow S : \{ g^C \} $
2. Server ... |
Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm?
I'm thinking of something like this:
Client $C$ knows $g$, $p$, $q$ and $g^s$.
1. $C \rightarrow S : \{ g^c \} $
2. Server ... |
Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm?
I'm thinking of something like this:
Client $C$ knows $g$, $p$, $q$ and $g^s$.
1. $C \rightarrow S : \{ g^c \} $
2. Server... |
Let us say there is exist a permutation matrix n x n for some large n. Then, there are n! possible permutations. If one to use brute-force to find the secrete permutation among n! possibilities, is there a parallel way to find such permutation?
thanks |
can permutation matrix be found in parallel processing technique? |
I'm looking to fill in the gaps of my knowledge of lattices. Can anyone point me towards papers or books that introduce lattice crypto assuming a fairly solid math background?
Mods: Feel free to close this if it's not the proper format. I'm not exactly clear on the literature request policy. |
I am reading the page 38 in this [book][1] (Equation (8) and (9)). My question Why to compute the verification key $Y$, $f$ is applied $2^w-1$ times?. Are there any security notions involved?
[1]: http://www.e-reading-lib.org/bookreader.php/135832/Post_Quantum_Cryptography.pdf |
Let us say there exists a permutation matrix $n \times n$ for some large $n$. Then, there are $n!$ possible permutations. If one to use brute-force to find the secret permutation among $n!$ possibilities, is there a parallel way to find such permutation?
thanks |
Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm?
In other words, we will replace $SIG_S(Data)$ in some protocol with this scheme. The steps described below can be merged with what... |
Other considerations aside, is it possible to use DH with an established public key (together with fixed g, p, q) to safely authenticate a server instead of using some signing algorithm?
In other words, we will replace $SIG_S(Data)$ in some protocol with this scheme. The steps described below can be merged with what... |
Imagine multiple parties executing a secure multiparty computation protocol to evaluate a function securely. Let Alice be one of the parties who is intended to get all the partial results and combine these partial results into complete result at the end of the protocol.
In practice , if Alice's machine is compromis... |
What kind of adversary is a compromised party? |
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