instruction stringlengths 15 30k |
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How is "post-quantum security" proven/shown? |
I have read some content on trusted execution environment, and I like to ask exactly how it improves hashing. What I read online states "...PCRs) which hold various measurements in a shielded location in a manner that prevents spoofing." This was from Wikipedia. My question is does this mean one does not have visibilit... |
I have read some content on trusted execution environment, and I like to ask exactly how it improves hashing. What I read at [Wikipedia’s “Trusted_Execution_Technology” article](https://en.wikipedia.org/wiki/Trusted_Execution_Technology) states:
> ...PCRs) which hold various measurements in a shielded location in a... |
Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair:
$$ A: (P_A, S_A), B: (P_B, S_B)$$
What is the most an adversary C can do while impersonating one of the parties (we assume there is no authentication employed). For e... |
What is the most an adversary can do in the context of public key masquerading? |
Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair:
$$ A: (P_A, S_A), B: (P_B, S_B)$$
What is the most an adversary C can do while impersonating one of the parties (we assume there is no authentication employed). For e... |
I am familiar with public key signatures, but I was wondering if there is a method to accomplish the following.
Suppose I publish a file (say a PDF article) on a peer to peer network. How can I generate some sort of public key or signature which will allow one peer to prove to another peer that they have a copy of t... |
Can Grover's Algorithm be combined with a meet-in-the-middle attack? |
We all know and love the meet-in-the-middle attack which basically makes double encryption pointless using a time-memory-tradeoff. Now there was recently the recommendation by the NSA to use double encryption to protect sensitive data adequately from quantum attackers.
This made me ask myself:<br>
**Can one combine... |
I am familiar with public key signatures, but I was wondering if there is a method to accomplish the following.
Suppose I publish a file (say a PDF article) on a peer to peer network. How can I generate some sort of public key or signature which will allow one peer to prove to another peer that they have a copy of t... |
The latest AMD programmer manuals, dated June 2015, include the `RDRAND` instruction in the instruction set. For completeness, it lacks `RDSEED`. Confer, [AMD64 Architecture Programmer’s Manual Volume 3: General-Purpose and System Instructions](http://support.amd.com/TechDocs/24594.pdf), page 278.
The description in... |
You could be able to reduce the space required for a meet-in-the-middle attack, if you follow a similar idea as [the application of Grover's algorithm on collisions][1]. Suppose you have two layers of $n$-bit encryption:
1. Partition the inner keyspace into $2^{n/4}$ parts of size $2^{3n/4}$.
2. For each partition ... |
You could be able to reduce the space required for a meet-in-the-middle attack, if you follow a similar idea as [the application of Grover's algorithm on collisions][1]. Suppose you have two layers of $n$-bit encryption:
1. Partition the inner keyspace into $2^{n/4}$ parts of size $2^{3n/4}$.
2. For each partition ... |
Secure against what and for what purpose?
MD5 remains too fast for human typed passwords. You should use something like bcrypt or PBKDF or sha256crypt where there are a tunable amount of thousands to millions (or more) rounds of hashing to generate each hash.
`f(x) := md5(x) ++ md5('abc' ++ x)` will be just as... |
I was wondering if the following hash function
f(x) := md5(x) & md5('abc'&x)
(with & as concatenation operator) is secure.
This schema can be even extended like this:
g(x) := md5(x) & md5('abc'&x) & md5('def'&x)
To find a collission in f(x), following requirements would be met:
f(x)=f(x'),... |
Is md5(x)&md5(y&x) secure? |
I have calculated the affine points on the curve $x^2 + y^2 = 1 − 3x^2y^2$
Using $y^2 = \frac{1-x^2}{1+3x^2}$ I got the following points:
$(0,1),(0,10),(1,0),(1,11),(2,2),(2,9),(3,4),(3,7),(7,3),(7,8),(9,2),(9,8),(10,0),(10,11),(11,1),(11,10)$
Total comes to be 16 points. But what I know is that total points s... |
Secure against what and for what purpose?
MD5 remains too fast for most human typed passwords. You should use something like bcrypt or PBKDF or sha256crypt where there are a tunable amount of thousands to millions (or more) rounds of hashing to generate each hash. You really don't want to allow users to try seve... |
Secure against what and for what purpose?
MD5 remains too fast for most human typed passwords. You should use something like bcrypt or PBKDF or sha256crypt where there are a tunable amount of thousands to millions (or more) rounds of hashing to generate each hash. You really don't want to allow users to try seve... |
Perhaps the situation should be concretized a little.
<blockquote>
A and B both have a public/private key pair:
</blockquote>
Does A already know $P_B$, and vice versa? If not, then $C$ can send to A the $P_C$ saying it's «$P_B$» (similar for B, $P_C$ substitutes $P_A$), and become a typical man-in-... |
Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair:
$$ A: (P_A, S_A), B: (P_B, S_B)$$
and A already knows about B's public key but has no proof of authenticity.
What is the most an adversary C can do while impersonati... |
Assuming that you're paranoid before storing your file (distributed across a shared location), which will be the best case scenario? |
File Security - Would it be better to split a file and then encrypt, or vice versa? |
Assuming that you're paranoid before storing your file (distributed across a shared location), which will be the best case scenario: splitting the file first and then encrypting or encrypting first and then splitting? |
Would it be better to split a file and then encrypt, or vice versa? |
In the Wikipedia article on Block Ciphers, it says [about the Electronic Code Block mode][1]:
> The disadvantage of this method is that identical plaintext blocks are
> encrypted into identical ciphertext blocks; thus, it does not hide
> data patterns well. In some senses, it doesn't provide serious message
> con... |
I read ECB is bad because the same plaintext outputs the same ciphertext. Isn't that a requirement of a cipher? |
How to calculate Enc(-m) from Enc(m) in Pailler encrypto system? |
How to calculate Enc(-m) from Enc(m) in Paillier cryptosystem? |
I asked this question on stackoverflow.com and was told to post it on this site instead. :)
A way to prevent timing attacks for hash string comparison is to perform additional HMAC signing in order to randomize the verification process (see https://www.nccgroup.trust/us/about-us/newsroom-and-events/blog/2011/februar... |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
A way to prevent timing attacks for hash string comparison is to perform additional HMAC signing in order to randomize the verification process (see [Double HMAC Verification][1]).
In addition to the second HMAC hashing for each hash, a random salt of random length is added to both in order to make the hashing timi... |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
$c(y) = (03)y^3 + (01) y^2 + (01) y + (02)$
Let $d = (01)b$ in the AES field GF(16).
Provide exact equations for the bits $d_i, 0 \leq i \leq 7$, in terms of the bits $b_i$ of b.
Can some give me an example or hint? I don't know where to start.. |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
> $c(y) = (03)y^3 + (01) y^2 + (01) y + (02)$
> Let $d = (01)b$ in the AES field GF(16).
> Provide exact equations for the bits $d_i, 0 \leq i \leq 7$, in terms of the bits $b_i$ of b.
Can some give me an example or hint? I don't know where to start.. |
> $c(y) = (03)y^3 + (01) y^2 + (01) y + (02)$
> Let $d = (01)b$ in the AES field $GF(2^8)$.
> Provide exact equations for the bits $d_i, 0 \leq i \leq 7$, in terms of the bits $b_i$ of b.
Can some give me an example or hint? I don't know where to start.. |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
Historically messages in languages that use alphabets have been encrypted manually according to some kind of algorithm (e.g. mono- and poly-alphabetic ciphers). But how would messages be encrypted in a semagram-based language like Chinese? |
How were semagrams encrypted in the pre-digital era? |
A way to prevent timing attacks for hash string comparison is to perform additional HMAC signing in order to randomize the verification process (see [Double HMAC Verification][1]).
In addition to the second HMAC hashing for each hash, a random salt of random length is added to both in order to make the hashing timi... |
I'm studying for a cryptography test and I came across this question:
>*Assume a language has three letters: A=1111, B=0011 and C=1010. Two words in this language are encrypted with a one-time pad and by using the same binary key sequence. The first four bits for both corresponding cipher texts are, respectively: $... |
Historically messages in languages that use alphabets have been encrypted manually according to some kind of algorithm (e.g. mono- and poly-alphabetic ciphers). But how wew messages encrypted in a semagram-based language like Chinese? |
> Will this successfully prevent a timing attack?
Strictly speaking you should be checking if [openssl_random_pseudo_bytes](http://php.net/manual/en/function.openssl-random-pseudo-bytes.php) happens to be returning cryptographically strong numbers or not. If not, an attacker could guess be able to launch a timing at... |
I would like to compress data before encrypting and storing it in a MySQL DB to reduce space requirements. At present, all is handled by a server-based script, although implementation through a web server is possible, also.
Various comments on the insecurity of compression plaintext prior to encryption, related to ... |
I would like to compress data before encrypting and storing it in a MySQL DB to reduce space requirements. At present, all is handled by a server-based script. In the future, the DB may also be accessible via a web interface.
Various comments on the insecurity of compression plaintext prior to encryption, related t... |
I would like to compress data before encrypting and storing it in a MySQL DB to reduce especially bandwith requirements. At present, all is handled by a server-based script. In the future, the DB may also be accessible via a web interface.
Various comments on the insecurity of compression plaintext prior to encrypt... |
Say I have a graph of messages like this:
A
|
B
/ \
C D
By including the parent hash in the message to be hashed I can show that B is a child of A, and C and D are children of B.
For example
Hash("This is message A") = ab3ed
Hash("This is message B + ab3ed") = ... |
The problem is as follows:
There are two parties, both of whom would like to HMAC a message with a key. Although the keys are known to one another, both parties do not trust that the other one created a truly random key.
The HMAC result must not be easily attackable by a third party. So it is necessary the final ... |
The problem is as follows:
There are two parties, both of whom would like to HMAC a message with a key. Although the keys are known to one another, both parties do not trust that the other one created a truly random key.
The HMAC result must not be easily attackable by a third party. So it is necessary the final ... |
How to key an HMAC with keys from separate mutually untrusted parties? |
I'm running through a protocol specifiation (LoRaWAN), and I'm puzzled by the crypto. The data is encrypted and authenticated in the following way:
- a unique 128-bit key is used;
- the plaintext is first encrypted in classical counter mode with AES, with counter = fixedData1 | nonce | blockCounter;
- a MAC is... |
I'm running through a protocol specification (LoRaWAN, [pdf][1]), and I'm puzzled by the crypto. The data is encrypted and authenticated in the following way:
- a unique 128-bit key is used;
- the plaintext is first encrypted in classical counter mode with AES, with counter = fixedData1 | nonce | blockCounter;
-... |
I'm practising for a cryptography test and came across this question:
>Let us assume that for a specific elliptic curve the formulas for the computation of $(x_3, y_3)=R+S$ are given by:
>
>$X_3=\sigma^2-x_1-x_2\ (\textrm{mod}\ p)$
>
>$Y_3=\sigma(x_1-x_3)-y_1 \ (\textrm{mod}\ p)$
>
>$\sigma = \frac{y_2-y_1}{x_2... |
>I understand that $16\cdot 7\equiv 10 \bmod 17$, but where does the $7$ come from? Also, why is $5^{−1}\equiv 7 \bmod 17$ shouldn't that equal zero..?
When working with modular arithmetic, $a^{-1}$ (if it exists) is a number $b$ such that $a\cdot b\equiv 1$. So, because $5\cdot7\equiv 1\bmod{17}$, we say that $5^{-... |
I am familiar with public key signatures, but I was wondering if there is a method to accomplish the following.
Suppose I publish a file (say a PDF article) on a peer to peer network. How can I generate some sort of public key or signature which will allow one peer to prove to another peer that they have a copy of t... |
I'm designing a cryptography assignment for a college security course, and one of the problems is to perform a simple meet-in-the-middle attack on a 2-round, 2-key cipher. Since we want this to be a reasonable attack for students to mount on their own laptops or school computers, the cipher needs to be very fast to com... |
Block Cipher Without Key Schedule? |
I would like to use different EC keys for different purposes in an app, and I would like to easily see the purpose for which particular key (pair) was generated.
With ~65K attempts, I can generate a key-pair where the first byte of both the public and private key are equal to a particular "purpose code" byte value.
... |
Are EC public/private keys significantly weakened by having a known byte? |
I'm designing a cryptography assignment for a college security course, and one of the problems is to perform a simple meet-in-the-middle attack on a 2-round, 2-key cipher.
Since we want this to be a reasonable attack for students to mount on their own laptops or school computers, the cipher needs to be very fast to ... |
I [sometimes][1] [see][2], in [discussions][3] of symmetric ciphers, reference to the 'key agility' of a particular algorithm. It seems to be related to the difficulty of switching encryption keys, but I don't understand more than that.
Can anyone give a good explanation of 'key agility' and some contexts in which i... |
I would like to use different EC keys for different purposes in an app, and I would like to easily see the purpose for which particular key (pair) was generated.
With ~65K attempts, I can generate a key-pair where the first byte of both the public and private key are equal to a particular "purpose code" byte value.
... |
How do we solve Shammir 2,3 sharring scheme where arithmetic is modulo? |
Alice and Bob want to play a coin flipping game. Alice wins if the coin flips head.
They choose to trust a independent third party that generates a random beacon (such as NIST).
Alice has a message known only to her.
The result is the first bit of hash(message, beacon)
1. Alice and Bob may not be able to ... |
Suppose that there is a place in a security proof where the behavior of an oracle differs from the corresponding real execution (for example, the decryption oracle rejects a ciphertext but in the real world the decryption function accepts it). Let us assume also that the probability of this situation is not negligible ... |
I am using a PGP method to encrypt and decrypt messages shared between users A and B.
Upon the start of a message exchange is the initialization of the public and secret keys by both Users.
Lets say that User A downloads the message exhange app and he adds his friend (through phone number). He then wants to initializ... |
**The first question:** what is the **exact definition** of semantically secure?
Basically, a cryptosystem is semantically secure if given the public key and the ciphertext, an adversary cannot learn any partial information of the plaintext.
However, the above statement is quite vague to me. For example, what doe... |
why is "semantically secure" important for cryptosystems? |
**The first question:** what is the **exact definition** of semantically secure?
Basically, a cryptosystem is semantically secure if given the public key and the ciphertext, an adversary cannot learn any partial information of the plaintext.
However, the above statement is quite vague to me. For example, what doe... |
Why is "semantically secure" important for cryptosystems? |
If one wishes to encrypt one can either use a pseudo random generator to generate a long sequence and then xor it with plaintext, similarly he can use the seed as key to encrypt the plaintext using block encryption.
If encryption is not of paramount concern, which runs faster, pseudo random generator or block encrypt... |
Pseudo random generator vs Block Encryption, which is faster? |
Suppose that there is a place in a security proof where the behavior of an oracle differs from the corresponding real execution (for example, the decryption oracle rejects certain types of ciphertexts but in the real world the decryption function accepts them). Let us assume also that the probability of this situation ... |
Suppose that there is a place in a security proof where the behavior of an oracle differs from the corresponding real execution (for example, the decryption oracle rejects certain types of ciphertexts but in the real world the decryption function accepts them). Let us assume also that the probability of this situation ... |
If one wishes to encrypt one can either use a pseudo random generator to generate a long sequence and then xor it with plaintext, similarly he can use the seed as key to encrypt the plaintext using block encryption.
If encryption is not of paramount concern, which runs faster, pseudo random generator or block encrypti... |
Pseudo random generator vs block encryption, which is faster? |
Suppose I want to use LTV scheme from this paper https://eprint.iacr.org/2013/094.pdf to compute homomorphically a function.
But the multiplication operation is more expensive than the additive one.
So, if multiplication is the counterpart of an AND gate and addition is the counterpart of an OR gate, why not implemen... |
How to toggle a bit homomorphically ? |
Let me try to answer your second question, and hopefully shed some light on the first one in doing so.
When we encrypt a message, it's because we want to keep *something* about that message secret. But what *is* it that we actually want to protect?
Let's say the message we're encrypting is `AGENT DOE REPORTS 2... |
I was reading this paper https://eprint.iacr.org/2014/816.pdf "Bootstratpping in less than one second" but I didn't understand it throughly. What's the point to build a cheap NAND gate ? Maybe to build cheaper AND and OR gates based on this NAND gate and then follow the approach of Regev's type cryptosystems? Or maybe ... |
How to use this homNAND gate? |
How is bitslicing faster? |
> What's the point to build a cheap NAND gate ?
Because it's a complete operation; you can build any circuit with a sufficiently large pile of them.
> Maybe to build cheaper AND and OR gates based on this NAND gate and then follow the approach of Regev's type cryptosystems?
You could build AND and OR gates wit... |
I'm running into very contradictory opinions when try to understand if weak elliptic curves exist. I'm not interested in the case when a curve's weakness is attributed to properties of an EC's prime, because those cases have been already explored, e.g. here: http://wstein.org/edu/2010/414/projects/novotney.pdf
I wan... |
Do Weak Eleptic Curves Exist? |
I'm running into very contradictory opinions when try to understand if weak elliptic curves exist. I'm not interested in the case when a curve's weakness is attributed to properties of an EC's prime, because those cases have been already explored, e.g. here: http://wstein.org/edu/2010/414/projects/novotney.pdf
I wan... |
Do Weak Elliptic Curves Exist? |
I'm running into very contradictory opinions when try to understand if weak elliptic curves exist. I'm not interested in the case when a curve's weakness is attributed to properties of an EC's prime, because those cases have been already explored, e.g. here: http://wstein.org/edu/2010/414/projects/novotney.pdf
I wan... |
As fgrieu pointed out, Alice and Bob must have somehow come to some kind of agreement before the random beacon is generated.
Would either of these techniques work for you?
use the random beacon directly
------------------------------
They could agree ahead of time that "Alice wins if the first random bit sent b... |
I have a cryptography homework question, in the question it says a cryptographic hash function in the form of f(x) = g^x mod n , where n is a very large prime (1024bits), g is a generator for {1, 2, . . . , n − 1}, and x is
possibly much more than 1024 bits in length. Comment on how well the function satisfies pre-im... |
I have a cryptography homework question, in the question it says a cryptographic hash function in the form of $f(x) = g^x \bmod n$ , where $n$ is a very large prime (1024bits and more), $g$ is a generator for $\{1, 2, . . . , n − 1\}$, and $x$ is
possibly much more than 1024 bits in length. Comment on how well the fu... |
What if we were substitute the ANDs with XORs in some homomorphic encryption scheme like BGV(https://eprint.iacr.org/2011/277.pdf), LTV ( https://eprint.iacr.org/2013/094.pdf) ? It may be more efficient ?
For example if we can substitute an AND with 6 XORs, we would achieve a better efficiency for some choice of the p... |
What about using only XOR gates in homomorphic encryption? |
I've been wrestling with a problem, and I was hoping if someone else had a bright idea.
Here's the problem: I have two sides, Alice and Bob. Alice has a single high entropy string $A$, and Bob has a number of high entropy strings $B_i$, one of which may be $A$. What we would like to do is have Alice send a single ... |
Is there a way to optimize a linear scan while preserving anonymity? |
I'm educating myself about cryptography. I know this is a long one, but please, bear with me. :) Now I have a scenario in my mind and I'd like to ask if what I've thought is sound (enough), what more to take into account and possible pointers.
**Describing the scenario**
1. Let's assume there are *producers*, *P... |
Am am auditing some software that includes compiled in DH parameters (2048 bits).
- I can't be sure who generated the DH parameters or how they were generated.
Question:
- Can DH parameters be weak if they were generated improperly or
made intentionally weak?
- Is it possible to *test* DH parameters, t... |
I am a beginner in cryptography and I am interested for several weeks on this for my chat application.
Basically, it is a centralized model. All messages are stored and potentially visible by authorities or server administrators.
Here the global functioning of the chat :
- Each person may register with a nick... |
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