instruction stringlengths 15 30k |
|---|
The proof of [FO hybrid encryption](http://knot.kaist.ac.kr/seminar/archive/33/33.pdf) is hard to understand. Especially, how the chanllenger responce the decryption queries when the challenger can only have some encryption queries?
Can someone explain it to me , thank you very much
|
The proof of [FO hybrid encryption](http://knot.kaist.ac.kr/seminar/archive/33/33.pdf) is hard to understand. $\:$ Especially, how does the challenger
<br>
respond to the decryption queries when the challenger can only have some encryption queries?
<br>
Can someone explain it to me?
|
Is there any known techniques for using time-space tradeoff for speeding up symmetrical crypto breaking? Kind of like rainbow tables speed up breaking hashes by using huge precomputed tables.
Is something similar possible for symmetrical cryptos like AES? If not, why? Is there a difference between block and stream c... |
Is there a time-space tradeoff attack for breaking symmetrical cryptos? |
I am studying in CSE and in my recent exam paper, A question was asked as:
Construct a playfair cipher for **Plaintext: semester5** and **key:*technology***.
Generally as we are taught yet, there is no example of playfair matrix substitution for numeric value.
So, what to do with number 5? Is there any trick f... |
The idea you have is: lets say we have a known plaintext/ciphertext pair; can we use a precomputed table to speed up the recovery of the key?
Well, the main problem with that precomputed tables don't actually speed up the search time, if you count the time taken to generate the precomputed table. What the table pre... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
Is there any known techniques for using time-space tradeoff for speeding up symmetrical crypto breaking? Kind of like rainbow tables speed up breaking hashes by using huge precomputed tables.
Is something similar possible for symmetrical cryptos like AES? If not, why? Is there a difference between block and stream c... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
I am not aware of a scheme that fulfills your requirements as defined above, but:
If your goal is that Bob can sign a message such that only Alice can verify it and she can proof no one else that this message was sent by Bob then chameleon signatures aka deniable signatures are the tool you are looking for.
Schem... |
**If the message is random** each additional signature halves the security level. **If the message is chosen by the attacker**, two signatures (of messages where each bit differs) are enough for a complete break.
A security level of about 64 bits can be broken by a determined attacker, and a level of 32 bits can be ... |
Preliminary: Almost [the same article][1] is available for free without breaking any law, nor downloading 5GB (formatting is shifted by at most one third of a page). It is also (as well as all other articles of IACR crypto conferences from 2000-2011) in the [IACR Online Proceedings][2], specifically in the FSE 2008 sec... |
Preliminary: Almost [the same article][1] is available for free without breaking any law, nor downloading 5GB (formatting is shifted by at most one third of a page). It is also (as well as all other articles of IACR crypto conferences from 2000-2011) in the [IACR Online Proceedings][2], specifically in the FSE 2008 sec... |
If you happen happen to have a message m ∈ Zn \ Z*n, RSA works but not secure. How likely is it going to happen? |n|=1024 bits |p| = 512 bits |q| = 512 bits.
Thanks! |
The variable of a polynomial is traditionally noted $x$, not $X$; and, when dealing with LFSRs, the polynomial is seldom considered a function. Thus I'll rewrite the polynomial as $P(x)=x^4+x^3+1$, a polynomial of degree $n=4$.
This is a polynomial with coefficients in the [field][1] $\operatorname{GF}(2)$, also not... |
I don't know why you would even consider using it.
In its current state, the NIST's Randomness Beacon is not yet fit for cryptographic use and the project itself describes itself being a [*“prototype implementation”* in *“research status”* under the lead of ITL](http://www.nist.gov/itl/csd/ct/nist_beacon.cfm). End ... |
I don't know why you would even consider using a prototype implementation for security purposes.
In its current state, the NIST's Randomness Beacon is not yet fit for cryptographic use and the project itself describes itself being a [*“prototype implementation”* in *“research status”* under the lead of ITL](http://... |
First up: Don't believe the hype! Especially if things can easily be proven wrong. What I mean is that your *`NIST have just launched a new service…`* is incorrect, as the NIST Randomness Beacon project is known to me (and others) **since 2011**. Furthermore, this project was awarded a multi-year grant from NIST's Inno... |
One question I had to answer in my crypto exam today was:
> Do we need symmetric cryptosystems?
As it stands, that's probably a debatable question, so I'd like to reformulate this as:
> Are there any situations where symmetric cryptosystems could not be replaced by asymmetric cryptosystems without serious down... |
Do we need symmetric cryptosystems? |
First up: Don't believe the hype! Especially if things can easily be proven wrong. What I mean is that your *`NIST have just launched a new service…`* is incorrect, as the NIST Randomness Beacon project is known to me (and others) **since 2011**. Furthermore, this project was awarded a multi-year grant from NIST's Inno... |
I hear a lot about why Montgomery curves are used in ECC, and one reason is that the same algorithm can be used to do both point addition and doubling (this is not true for the Weierstrass normal form).
What are the most prominent unsafe features of curves, and ways one can screw up an ECDH implementation? Are ther... |
Bitcoin relies on generating a smaller random number then the difficulty, thus is vulnerable to a truncated preimage attack (you just need to find a certain number of leading zeroes).
What is the current status of attacking truncated second preimages of SHA-256? |
Bitcoin relies on generating a smaller random number then the difficulty, thus is vulnerable to a truncated preimage attack (you just need to find a certain number of leading zeroes).
I believe this is called a near preimage attack.
What is the current status of attacking truncated second preimages of SHA-256? |
Scroll to the end for tl;dr.
Regarding your contrived example: Alice doesn't have Bob's keypair, but sends a message in such a way that only Bob can read it, eg. puts it in a dead-drop. So she takes out her pen and writes
> Hey Bob, could you sign and send me $X$ along with your public key? Here's mine: $P_A$
... |
Preliminary: Almost [the same article][1] is available for free without breaking any law, nor downloading 5GB (formatting is shifted by at most one third of a page). It is also (as well as all other articles of IACR crypto conferences from 2000-2011) in the [IACR Online Proceedings][2], specifically in the FSE 2008 sec... |
Preliminary: Almost [the same article][1] is available for free without breaking any law, nor downloading 5GB (formatting is shifted by at most one third of a page). It is also (as well as all other articles of IACR crypto conferences from 2000-2011) in the [IACR Online Proceedings][2], specifically in the FSE 2008 sec... |
Bitcoin mining relies on generating a smaller hash than the so-called _difficulty_, thus is vulnerable to a truncated preimage attack (you just need to obtain a certain number of leading zeroes).
I believe this is called a near preimage attack.
What is the current status of attacking truncated second preimages of... |
Near preimages, applicable to Bitcoin? |
Is truncating a SHA512 hash to the first 160 bits as secure as using SHA1? |
Bitcoin mining relies on generating a smaller hash than the so-called _target_, thus is vulnerable to a truncated preimage attack (you just need to obtain a certain number of leading zeroes).
I believe this is called a near preimage attack.
What is the current status of attacking truncated second preimages of SHA... |
Bitcoin mining relies on generating a smaller hash than the so-called [_target_][1] (a function of the so-called [_difficultly_][2]), thus is vulnerable to a truncated preimage attack (you just need to obtain a certain number of leading zeroes).
I believe this is called a near preimage attack.
What is the current... |
In the paper for Fortuna the authors say that you can use any good digest algorithm (obviously as long as its output is 256 bit) and then they recommend double SHA-256.
Why? What's the benefit? What happens if I use single SHA-256 or RIPEMD-256, for example? |
Why does Fortuna RNG use double SHA-256? |
Yes, you have the basic idea. Session-id info is stored (cached) at both ends; ticket is stored only at client, encrypted by server. Both re-use the "key exchange" which in SSL/TLS is actually key exchange combined with authentication; although authentication can be both directions (server and client) and thus an "exch... |
For all $c_0\leftarrow m_0 \oplus k$ there exists a $k'$ such that $c_1 \leftarrow m_1 \oplus k'$, where $m_0 \neq m_1$ and $c_0 = c_1$.
Assuming a truly random $k$, the first assignment is a one-time pad. If we were to repeat the process over all $m \in M$, we would create a Stirling set of the first kind.
To ... |
How can I prove the following:
> If $f$ is a one-way function, then it is an uninvertible function?
<sup>[CSL759: Cryptography and Network Security, Page 2, Problem 2.2.a](http://www.cse.iitd.ac.in/~shweta/HW/HW1.pdf)</sup> |
In Public key infrastructure, the MD5 of a piece of data is encrypted with the private key of a sender and this encrypted MD5 – along with the data – is again encrypted using an algorithm like AES or 3DES.
Here, the private key of a sender is used to encrypt with AES… is that correct?
This is a rough implementat... |
An RSA key pair consists of the private key $(n,d)$ and a public key $(n,e)$ such that $de \equiv 1 \bmod{\lambda(n)} $.
Usually one chooses a small $e$ and computes $d$ by inverting it modulo $\lambda(n)$. This makes things computationally easy for the user of the public key, but makes it expensive to use the priva... |
Is it secure to choose d in a RSA key pair? |
What is the the point of an "online" mode for an *authenticated* cipher? I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from such a feature. Usually, the "messages" that are encrypted and authenticated are not too long and I think that this is du... |
Use cases for *online* authenticated encryption? |
Can we have separate key for separate blocks which we get while operating a plain text message using CBC encryption model? If yes, what are it's advantage? Please enlighten me. |
Can CBC encryption have separate keys for separate blocks of plain text? |
The [AugPAKE](http://tools.ietf.org/html/draft-irtf-cfrg-augpake-01#section-2.3.1) spec says it can be implemented over elliptic curves. This sounds very promising, but they don't actually back that claim. Can this really be achieved? If so, how would one go about mapping the existing protocol to elliptic curves? |
Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties?
If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the first megabyte of the resulting ciphertext would this render the remaining ciphertext 100% immune to crypt analysis ? ... |
Alice signs a message $m$ with her private key, yielding a signature ($r$,$s$).
I want to prove to someone else that I have this signature, but I don't want them to have the knowledge of what ($r$,$s$) is.
Is there a transformation I can apply to ($r$,$s$) to yield a new signature ($r'$,$s'$), such that someone w... |
I'm very new to cryptography and encryption so I apologize if the answer to this is well known, but I can't find anything in my research.
The crux of the problem is the need to store data on an offline device which cannot be trusted. Is it possible to encrypt the data in such a way that it cannot be read by the devi... |
What is the the point of an "online" mode for an *authenticated* cipher?
I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from such a feature.
Usually, the "messages" that are encrypted and authenticated are not too long and I think that th... |
Use cases for “online” authenticated encryption? |
There are three blind card game players. Each player does not trust any other, even prejudicing other two players may not be blind, or there may be others in the room, peeking at their cards.
In order to protect from glimpsing their hands, each player puts each of his cards into separate locked box, each box having ... |
While reading Shamir, Rivest and Adleman's paper on "Mental Poker", I've met a mention of system such that `E_a(E_b(x)) == E_b(E_a(x))`, without however disclosing details on it, with `E_a(x)` being 'encrypt plaintext x with key a'.
Do any existing secure modern cryptosystems have this property, and how is it called... |
The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\to\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function $g:\{0,1\}^s\to\{0,1\}^*$ selected at random.
But what if the key parameter isn't selected at random? What, more exactly, might and might not be... |
What might be assumed about a PRF if the key has been chosen? |
The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function $g:\{0,1\}^s\mapsto\{0,1\}^*$ selected at random.
But what if the key parameter isn't selected at random? What, more exactly, might and migh... |
The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function $g:\{0,1\}^s\mapsto\{0,1\}^*$ selected at random.
But what if the key parameter isn't selected at random? What, more exactly, might and migh... |
What is the the point of an "online" mode for an *authenticated* cipher?
I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from such a feature.
Usually, the "messages" that are encrypted and authenticated are not too long and I think that th... |
I know the question is rather unusual, but let me clarify what I'm searching for:
There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of other persons.
Now $Alice$ has to encrypt one $t_i$ with a $pk_j$ for arbitrary $i,j$. Each key and plaintext shou... |
Is Encryption without knowing the input directly possible at all? |
I know the question is rather unusual, but let me clarify what I'm searching for:
There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of other persons.
Now $Alice$ has to encrypt one $t_i$ with a $pk_j$ for arbitrary $i,j$. Each key and plaintext shou... |
I know the question is rather unusual, but let me clarify what I'm searching for:
There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of other persons.
Now $Alice$ has to encrypt one $t_i$ with a $pk_j$ for arbitrary $i,j$. Each key and plaintext shou... |
The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function $g:\{0,1\}^s\mapsto\{0,1\}^*$ selected at random.
But what if the key parameter isn't selected at random? What, more exactly, might and migh... |
Data : uuid + int + nonce
Signature: DCMA(sha256(Data) )
To verify the signature:
decrypt(Signature) == sha256(data)
So if the data, hash function, and public_key is known, why the need to hash?
====================================
second question, if the same Data with different nonce ... |
Why the need to hash before signing small data? |
I’ve got two questions:
1. I’m doing the following:
Data : uuid + int + nonce
Signature: DCMA(sha256(Data) )
To verify the signature:
decrypt(Signature) == sha256(data)
So if the data, hash function, and public key are known, why is there a need to hash?
2. If the same `... |
Assuming the alert protocol is encrypted AFTER a session has been established and the structure below, how does the client know whether to expect encrypted data or not?
http://en.wikipedia.org/wiki/Transport_Layer_Security#Alert_protocol |
I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server.
Key encapsulation: a 128-bit symmetric key is generated and asymmetrically encrypted.
Data encapsulation: a 96-bit IV is generated, the plaintext is encrypted with AES-GCM using the generated ... |
I originally posted this question on bitcoin SE (http://bitcoin.stackexchange.com/questions/24092/is-it-possible-to-weaken-a-bitcoin-private-key-by-using-it-elsewhere) but they suggested that it might be better to ask it here on crypto SE since you would probably have more expertise...I hope you don't mind (especially ... |
Is it possible to weaken a bitcoin private key by 'using' it elsewhere? |
The paper "[Proofs of Space: When Space is of the Essence](https://eprint.iacr.org/2013/805)" proposes a scheme that allows a client to prove that it has read/write access to at least $B$ bytes of memory. Basically, the server gives the client a function $f$ that requires at least $B$ bytes to compute, and the client ... |
I originally posted this question on [Bitcoin.SE](http://bitcoin.stackexchange.com/questions/24092/is-it-possible-to-weaken-a-bitcoin-private-key-by-using-it-elsewhere) but they suggested that it might be better to ask it here on Crypto.SE since you would probably have more expertise… I hope you don't mind (especially ... |
Is it possible to weaken a bitcoin private key by “using” it elsewhere? |
I originally posted this question on [Bitcoin.SE](http://bitcoin.stackexchange.com/questions/24092/is-it-possible-to-weaken-a-bitcoin-private-key-by-using-it-elsewhere) but they suggested that it might be better to ask it here on Crypto.SE since you would probably have more expertise… I hope you don't mind (especially ... |
Which of the one ([HKDF][1] or [TLS1.1+ PRF][2]) is more secure and why?
[1]: http://tools.ietf.org/html/rfc5869
[2]: http://tools.ietf.org/html/rfc5246#section-5 |
HKDF vs TLS PRF. Which of the one is better? |
I’ve got two questions:
1. I’m doing the following:
Data : uuid + int + nonce
Signature: ECDSA(sha256(Data) )
To verify the signature:
decrypt(Signature) == sha256(data)
So if the data, hash function, and public key are known, why is there a need to hash?
2. If the same ... |
I'll start with the last point and use the notation for ECDSA from the [wikipedia article](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA).
> Does it make any more difference if there is data that is known to have been signed by the private key and the signature(s) are known and the raw data is known?
When using... |
Is it possible to weaken a bitcoin private key by 'using' it elsewhere? |
While reading Shamir, Rivest and Adleman's paper on "Mental Poker", I've met a mention of system such that $E_a(E_b(x)) == E_b(E_a(x))$, without however disclosing details on it, with $E_a(x)$ being “encrypt plaintext $x$ with key $a$”.
Do any existing secure modern cryptosystems have this property, and how is it ca... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
What are the increased possibilities (if any) of being able to crack a private key given the following:
1. The associated bitcoin (ECDSA Secp256k1-based) public key is known.
2. The private key has been used to generate a public key from a different ECDSA curve and that public key is also known.
3. It is known tha... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
Let $(d_1,Q_1)$ and $(d_2,Q_2)$ be ECC key pairs over two **different** elliptic curves (say NIST P-224 and NIST P-256). According to the Elliptic Curve Discrete Logarithm Problem (ECDLP), if the private keys were generated randomly, it is infeasible to find $d_1$ from $Q_1$ (or $d_2$ from $Q_2$).
Now, say we know $... |
Let $(d_1,Q_1)$ and $(d_2,Q_2)$ be ECC key pairs over two **different** elliptic curves (say NIST P-224 and NIST P-256). According to the Elliptic Curve Discrete Logarithm Problem (ECDLP), if the private keys were generated randomly, it is infeasible to find $d_1$ from $Q_1$ (or $d_2$ from $Q_2$).
Now, say we know $... |
It is unclear if you wanted to compare TLS 1.1 PRF or TLS 1.2 PRF. Different TLS versions have different PRFs. Assuming you meant TLS 1.1 PRF although you linked TLS 1.2 RFC.
TLS 1.1 PRF
-----
Short: HKDF is commonly a better choice than TLS 1.1 PRF, but not always.
Consider these aspects:
- HKDF is a gen... |
[This page](http://www.cryptosystem.net/aes/tools.html) by Nicolas T. Courtois mentions *Geometric Generalised T' Method*. It is described as
> an advanced geometric algorithm, never published, for finding extra linearly independent equations at a given degree, which would normally be found by Gröbner bases techniq... |
What is the Geometric Generalised T' Method? |
First of all I do not know your implementation, but it seems that you have some basic misunderstandings.
> `Signature: ECDSA(sha256(Data) )`
[ECDSA](http://en.wikipedia.org/wiki/Elliptic_Curve_DSA) is typically implemented in a way that you do not explicitly hash the data prior to passing it to the signing algo... |
1)I would like to know how to test hardware random number generators.
2)What techniques ,tools or tricks to solve the problem ?
3)Any practical difficulties, implementation complexities etc |
testing hardware random number generators? |
1. I would like to know how to test hardware random number generators.
2. What techniques, tools or tricks to solve the problem ?
3. Any practical difficulties, implementation complexities etc. |
Testing hardware random number generators? |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.