instruction stringlengths 15 30k |
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I am wanting to secure some highly sensitive data in a database. This would mean that the data needs to be encrypted and remain secure for 100 years if it were to fall into adversary hands. I also want to limit the amount of data that is vulnerable in plaintext at a time in RAM. This is so there is less chance of plain... |
I've been looking at the paper of Boneh, Boyen, Goh [*Hierarchical Identity Based Encryption with Constant Size Ciphertext*](https://eprint.iacr.org/2005/015.pdf)
which contains a general theorem (Theorem A.2) about the advantage of an attacker in the generic group model. It seems to be based on the idea that in the g... |
Consider the following experiment:
> Let there be a machine which runs (ie. continually clocks) an LFSR of size (ie. number of bits) $b$, having a button that, when pressed, extracts the next $t$ bits from the LFSR, prints them onto a paper ticket, deposits the ticket into a sealed, opaque urn, and *complements ever... |
Are LFSRs enough for this? |
Consider the following experiment:
> Let there be a machine which runs (ie. continually clocks) an LFSR of size (ie. number of bits) $b$, having a button that, when pressed, extracts the next $t$ bits from the LFSR, prints them onto a paper ticket, deposits the ticket into a sealed, opaque urn, and *complements ever... |
I'm not too familiar with the math involved with the exchange of keys, I've read it over several times, but math isn't my strong point. My understanding is that smart people are hard at work to overcome the difficulty of factoring the shared secret.
So assuming that quantum processors overcome the current implementa... |
Can Diffie-Hellman be scaled up or force-multiplied? |
I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of authentication is not an option.
One possible solution is to talk directly to `ssh-agent` and have it sign a constant tok... |
Is it safe to derive a password from a signature provided by ssh-agent? |
Then why don't we use xxxxxxx bits encryption? what stopping us from using a very lengthy key?
I am referring to the encryption we use with SSL
|
Is it true the longer the key length is the more secure the encryption? |
Like all things in life, there are tradeoffs to be balanced. SSL can use RSA keys, right? So why not generate 2 billion bit RSA keys? Well, the efficiency of RSA goes down significantly as more bits are added. With too large of keys, RSA would be impractical to use in real life.
Another answer to your question is t... |
> Is it true the longer the key length is the more secure the encryption?
No. Key length *does* put a lower bound on security, because it determines the complexity of brute force iteration of the key space or factoring, discrete log, etc. for some asymmetric algorithms. However, once you have a [long enough][1] key ... |
I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of authentication is not an option.
One possible solution is to talk directly to `ssh-agent` and have it sign a constant tok... |
I am learning about <a href="http://en.wikipedia.org/wiki/Hill_cipher">Hill Cipher</a> and know that it is a block cipher where each block of n letters (considered as an n-component vector) is multiplied by an invertible n × n matrix, again modulus 26.
The article did not touch on what happens if the the block of ... |
We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest enough decent random noise.
Now in theory you would imagine that there is a universal class or model of cipher that c... |
Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad? |
What is the output of an r-round Feistel network when the input is $(L_0, R_0)$ and each round function outputs all 0s, regardless of the input? |
What happens with the output of the round function and the previous half block? Nearly every Feistel networks XOR them. What happens if you XOR any block with an all "0" block? You get the previous block. Example in binary notation with 8-bit blocks:
$$ \text{0100 1100} \oplus \text{0000 0000} = \text{0100 1100}$$
... |
Thanks for the help in advance. I have a couple decades programming experience, but never had to deal with cryptography myself. So please bear with me while I lay out my lack of knowledge.
-
I'm creating a prototype for a messaging queue with some custom logic (can't re-use any existing solution).
One requirem... |
Some points towards an answer:
- Why Twofish? It did not win the AES competition, and is (thus) less widely available, especially in hardware.
- Twofish alone does not define an encryption algorithm, for it is a block cipher. You need to specify an [operating mode][1].
- On 1.: Since Twofish is a 128-bit block cip... |
Some points towards an answer:
- Why HMAC-SHA3? The security proof of HMAC holds only for Merkle-Damgård hashes (thus not including any member of the SHA3 familly); and there's not an accepted definition of HMAC-SHA3 even if we specify the output width. HMAC-SHA256 would be fine.
- Why Twofish? It did not win the A... |
What's the meaning of 160 bit Curve in Elliptic curve ? or 192 or 224 or 256 and etc.
And What is the standard for selecting this number of bit ? why they don't say 100 bit curve?
|
Some points towards an answer:
- Why HMAC-SHA3? The security proof of HMAC holds only for Merkle-Damgård hashes (thus not including any member of the SHA3 familly); and there's not an accepted definition of HMAC-SHA3 even if we specify the output width. HMAC-SHA256 would be fine.
- Why Twofish? It did not win the A... |
AES: Guess Password using the unencrypted text? |
It really depends on you block cipher mode of operation and likeliness between your files. With any proper implementation, it should really not, but since you don't really give any details about your encryption scheme, it's hard to tell.
(side-note: how do you derive the key from the password?) |
One can find up to date recommended key sizes for RSA at http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf for example. In short it suggests a key size of at least 2048 bits.
> Is it possible to find a history of government recommended key sizes
> for RSA going back to the invention of RSA? |
What is the history of recommended RSA key sizes? |
One can find up to date recommended key sizes for RSA at http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf for example. In short it suggests a key size of at least 2048 bits.
Is it possible to find a history of government recommended key sizes for RSA, going back to the invention of RSA?
|
I'm not a mathematician or anything - just a curious individual.
If RSA (textbook RSA that is) generates a digital signature by using the sender's private key, couldn't any cryptosystem (the only two that come to mind are RSA and ElGamal) capable of asymmetric encryption do the same?
For example, I've read that E... |
I'm looking to compare (for byte-for-byte equality) two binary files.
I already have the process down:
- Check for existence etc.
- Compare file lengths
- Use a hash or CRC of a sort (right now I use MD5) to look for an obvious inequality
- Finally, byte-for-byte compare them ([I have a way of doing this i... |
Comparing Files: Is it better to use multiple hash algorithms or just one? |
I know there are XEX, XTS and other ways to add tweak to block cipher without modifying cipher itself. However they are quite slow and/or complex.
If we assume we have a secure block cipher round function (like AES) with pseudo-independent round keys (generated with stream cipher). Is it safe to add tweak with same ... |
I'm looking to compare (for byte-for-byte equality) two binary files.
I already have the process down:
- Check for existence etc.
- Compare file lengths
- Use a hash or CRC of a sort (right now I use MD5) to look for an obvious inequality
- Finally, byte-for-byte compare them ([I have a way of doing this i... |
If RSA (textbook RSA that is) generates a digital signature by using the sender's private key, couldn't any cryptosystem (the only two that come to mind are RSA and ElGamal) capable of asymmetric encryption do the same?
For example, I've read that ElGamal is encryption only. Why can't ElGamal encryption (not DSA) do... |
I'm creating a prototype for a messaging queue with some custom logic (can't re-use any existing solution).
One requirement is to have all messages encrypted. There are three classes of nodes subscribing to the queue with the following permissions:
1. Read/Write access
2. Read-only access
3. Buffer/forwarder wi... |
We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest enough decent random noise.
Now in theory you would imagine that there is a universal class or model of cipher that c... |
This question comes to mind after seeing "custom" Bitcoin addresses with some special string at the beginning of the address. They are generated in the same way Bitcoins are "mined", continually hashing with a nonce + password to get some desired output.
My question is, is it just as hard to find `[HLOWRLD]M9VveeBL... |
Is it just as difficult to find a desired output in a hash digest, for MSB vs LSB? |
I have two devices which communicate via sms.
This communication should now be encrypted.
The devices can only send messages with the lenght of 160 characters.
So i am looking for an encryption system which can limit the length of the encypted message to 160.
Is there such a cryptography system?
Which syst... |
I came across these questions while studying for a crypto course, does anyone have any ideas on how to answer these?
(a) Random prime numbers of size 1536 bits are chosen to generate
an RSA modulus of size 3072 bits. Knowing that the number field sieve
factorization algorithm would succeed in factorizing an RSA m... |
I came across these questions while studying for a crypto course, does anyone have any ideas on how to answer these?
(a) Random prime numbers of size 1536 bits are chosen to generate
an RSA modulus of size 3072 bits. Knowing that the number field sieve
factorization algorithm would succeed in factorizing an RSA m... |
> What's the meaning of 160 bit Curve in Elliptic curve?
It's the size of the field, as the other answers explain. It affects the size of keys and signatures (which can be equal to the number or e.g. double it), as well as security and performance.
> Why they don't say 100 bit curve?
100-bit curves are [too sm... |
After reading through https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-0, I could understand that this option is useful when one has legacy SSL Servers which only support SSLv3.
But could not understand how this option helps even after reading couple of articles.
Can anyone help me in understanding this? |
How does TLS_FALLBACK_SCSV help? |
After reading through https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-0, I could understand that this option is recommened for use when one has legacy SSL Servers which only support SSLv3.
But could not understand how this option helps even after reading couple of articles.
Can anyone help me in underst... |
One can find up to date recommended key sizes for RSA at http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf for example. In short it suggests a key size of at least 2048 bits.
Is it possible to find a history of recommended key sizes for RSA, going back to the invention of RSA?
|
Consider the following experiment:
> Let there be a machine which runs (ie. continually clocks) an LFSR of size (ie. number of bits) $b$, having a button that, when pressed, extracts the next $t$ bits from the LFSR, prints them onto a paper ticket, deposits the ticket into a sealed, opaque urn, and *complements ever... |
Suppose I receive a list of 1 million coinflips, and I want to know how likely it is that the list was randomly generated.
My first thought would be to count the number of heads and tails, which should be evenly distributed (around 500.000). But suppose the distribution looks normal, its still possible the list cont... |
How do you test randomness? |
If i want to break quadruple DES (say EDED), what is complexity? Like for EDE, it is O(2^112). |
I need to know number of encryption/decryption operations? |
Encrypting twice with different modes? |
A long question here, but I really want to motivate why I'm confused.
Consider the following attack on the Schnorr Identification Scheme.
<ol>
<li>Alice chooses a random $k$, computes $\gamma = \alpha^k \pmod p$, and sends a message to Bob, containing her certificate and $\gamma$, of her intent to authenticate.... |
A long question here, but I really want to motivate why I'm confused.
Consider the following attack on the Schnorr Identification Scheme.
<ol>
<li>Alice chooses a random $k$, computes $\gamma = \alpha^k \pmod p$, and sends a message to Bob, containing her certificate and $\gamma$, of her intent to authenticate.... |
A long question here, but I really want to motivate why I'm confused.
Consider the following attack on the Schnorr Identification Scheme.
<ol>
<li>Alice chooses a random $k$, computes $\gamma = \alpha^k \pmod p$, and sends a message to Bob, containing her certificate and $\gamma$, of her intent to authenticate.... |
For part(a.ii), I am presuming that "enumerating candidate prime factors" means that we have a precomputed list of all 1536-bit primes, which we can simply test one at a time.
To determine average running time we can use the prime number theorem, which states that the number of primes less that $N$ is approximately ... |
For part(a.ii), I am presuming that "enumerating candidate prime factors" means that we have a precomputed list of all 1536-bit primes, which we can simply test one at a time.
To determine average running time we can use the prime number theorem, which states that the number of primes less that $N$ is approximately ... |
For part(a.ii), I am presuming that "enumerating candidate prime factors" means that we have a precomputed list of all 1536-bit primes, which we can simply test one at a time.
To determine average running time we can use the prime number theorem, which states that the number of primes less that $N$ is approximately ... |
Am I correct in assuming that HMAC_DRBG would return different results if I, e.g. first request 4 bytes followed by a request of another 4 bytes instead of asking for 8 bytes at once?
It seems that in [NIST SP800-90A](http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf) chapter 10.1.2.5: Generating Pseu... |
HMAC_DRBG Generate Process: requesting N bytes at once different from requesting N bytes in total? |
I do the following via the Linux CLI:
printf '\xff\xff\xff\xff\xff\xff\xff\xff' > plaintext.txt
openssl enc -bf-ecb -e -in plaintext.txt -out ciphertext.txt -nosalt -K FFFFFFFFFFFFFFFF -p
I then read the contents of ciphertext.txt with `<?= bin2hex(file_get_contents('ciphertext.txt')); ?>` and I get this... |
While reading a literature on signature schemes, I came across the concept of Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack. Can anyone point me to the paper where this notion was introduced first? Otherwise, may I ask for a paper/reference where the above-mentioned game is prop... |
What's the meaning of 160 bit Curve in Elliptic curve ? or 192 or 224 or 256 and etc.
And What is the standard for selecting this number of bit ? why they don't say 100 bit curve?
OK now By your answers I can change my questions in this way :
when we consider a curve in a prime field for example Weierstrass for... |
What's the meaning of 160 bit Curve in Elliptic curve ? or 192 or 224 or 256 and etc.
And What is the standard for selecting this number of bit ? why they don't say 100 bit curve?
|
> Is it true the longer the key length is the more secure the encryption?
No. Key length *does* put a lower bound on security, because it determines the complexity of brute force iteration of the key space or factoring, discrete log, etc. for some asymmetric algorithms. However, once you have a [long enough][1] key ... |
Some points towards an answer:
- Why HMAC-SHA3? HMAC and its security proofs have been devised for Merkle-Damgård hashes, and SHA3 is not one. HMAC-SHA256 would be fine (Updated per comment: the [Keccak submission][1] does endorse its use with HMAC, using a block size parameters of 576 (resp. 832, 1088, 1152) bits f... |
I am a newer.
My question is: what exactly means "Lernable with oracle query" program? And what is the impact of it? Does it mean that we can learn what exactly the program does or just enter input and receive the result of the program running in each step? Without knowing which mathematical action influenced it?
... |
It would be possible to implement the [HMAC][1] construction with [(draft) SHA-3][2], leading to HMAC-SHA3-224, HMAC-SHA3-256, HMAC-SHA3-384, HMAC-SHA3-512 (the last 3 digits are the output size $\ell$, where $\ell/8$ is the $L$ parameter in HMAC). All that's missing to apply the familiar
$$\text{HMAC}(K,\text{text})=... |
I was just reading these [notes](https://www.cs.bris.ac.uk/~nigel/FHE-MPC/Lecture6.pdf) on garbled (Yao) circuits and I just stuck trying to figure out how an implementation of Table 1 would work using RSA encryption. In RSA the public key is (n,e). So for the first row, for example, I guess that <img src="http://late... |
My question is: what exactly does it mean to say that a program is "learnable with oracle query"? And what is the impact of it? Does it mean that we can learn what exactly the program does or just enter input and receive the result of the program running in each step? Without knowing which mathematical action influence... |
There are a bunch of papers do research on resizable garbled circuits. But I wonder why garbled circuits cannot be reused?
For example, the constructor constructs a garbled circuit of "AND" like this:
$E_{K_{u}^0}(E_{K_{v}^0}(K_{w}^0))$,
$E_{K_{u}^0}(E_{K_{v}^1}(K_{w}^0))$,
$E_{K_{u}^1}(E_{K_{v}^0}(K_{w}^0))$,
... |
Why garbled circuits cannot be reused? |
Why can't garbled circuits be reused? |
In the `hashlib` module in python is a function called `m.update()` where `m` is a `hashlib.md5` object. My question, actually not specific to python, is how does this function work, such that:
m = hashlib.md5()
m.update("hello")
m.update(" world")
which is the same as if I would have done:
... |
So I'm reading a chapter in my networking book and it talks about substitution and transition ciphers ([Transition Cipher Wikipedia][1]). I know that most network security uses public key or symmetric, but I was wondering if these are also used. I ask because I'm not sure how they would quickly decode the message on th... |
Does the transition cipher have a network application? |
I am a french student and I read the post on the forums (http://crypto.stackexchange.com/questions/2249/how-does-one-attack-a-two-time-pad-i-e-one-time-pad-with-key-reuse). I need your help if possible.
I 'm 11 encrypted messages , all encrypted with the same key.
How should I proceed?
thank you in advance for y... |
So I'm reading a chapter in my networking book and it talks about substitution and transposition ciphers ([Transposition Cipher Wikipedia][1]). I know that most network security uses public key or symmetric, but I was wondering if these are also used. I ask because I'm not sure how they would quickly decode the message... |
Does the transposition cipher have a network application? |
In the definition of functional encryption ($FE$):
$FE.Setup(1^k)$ takes as input the security parameter $1^k$ and outputs a master public key $fmpk$ and a master secret key $fmsk$.
$FE.KeyGen(fmsk, f)$ takes as input the master secret key $fmsk$ and a function $f$ and outputs a key $sk_f$.
$FE.Enc(fmpk,x)$ ta... |
Can we run a probabilistic function on ciphertext with Functional Encryption (or Attribute Based Encryption)? |
In the definition of functional encryption ($FE$):
$FE.Setup(1^k)$ takes as input the security parameter $1^k$ and outputs a master public key $fmpk$ and a master secret key $fmsk$.
$FE.KeyGen(fmsk, f)$ takes as input the master secret key $fmsk$ and a function $f$ and outputs a key $sk_f$.
$FE.Enc(fmpk,x)$ ta... |
So I'm reading a chapter in my networking book and it talks about substitution and transposition ciphers ([Transposition Cipher Wikipedia][1]). I know that most network security uses public key or symmetric, but I was wondering if these are also used. I ask because I'm not sure how they would quickly decode the message... |
I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password.
The password was written on a paper slip, but I remember that it consisted of 30+ completely alphanumeric characters with some special symbols in between.
I have read that a GPU cluster will crack o... |
With the knowledge of the trapdoor, we are able to compute the same digest for differents messages.
I've read that given two messages $m$, $m'$ and two numbers $r$, $r'$ such that
$Ch(m,r)=Ch(m',r')$, computed by the owner of the trapdoor, we are able to find other collisions and sometimes we are able to find this... |
RC4 has a variable length key. Is it still necessary to use a key derivation function, such as [PBKDF2][1], to initialize it?
Would using a single character password weaken it's output when compared to a block cipher using, for example, the SHA-256 hash of that same single character password as the key?
[1]: ht... |
Does a stream cipher require a KDF when it's key is variable length? |
Recent fast Elliptic curve implementations for example the paper presented in Eurocrypt titled "Faster Compact Diffie Hellman : Endomorphism on the x - line" talks about protection against only timing attacks. Why so ?? If these methods are implemented in hardware then I think it should have been protected against powe... |
Recent fast Elliptic curve implementations for example the paper presented in Eurocrypt http://www.craigcostello.com.au/wp-content/uploads/Privacy2013.pdf talks about protection against only timing attacks. Why so ?? If these methods are implemented in hardware then I think it should have been protected against power ... |
Recent fast elliptic curve implementations, for example a presentation at Eurocrypt 2014 ([earlier presentation slides](http://www.craigcostello.com.au/wp-content/uploads/Privacy2013.pdf), [the paper](http://eprint.iacr.org/2013/692)) talks about protection against only timing attacks. Why only timing attacks?
If t... |
It all comes down to your threat model, right? Just because an implementation is done in hardware does not mean that power and fault attacks must be considered. If I host the hardware in my secure facility with armed guards at the door, but the hardware is connected to a machine which is connected to the internet, I mi... |
In RSA, the $p$ and $q$ should be randomly generated, and they are the same size. The difference between $p$ and $q$ should not be small.
Suppose that $u=|p-q|<20$ and $p \times q =2189284635403183$. Find the values of $p$ and $q$.
I have no idea how to compute $p$ and $q$. I use calculator to compute square roo... |
I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password.
The password was written on a paper slip, but I remember that it consisted of 30+ completely alphanumeric characters with some special symbols in between.
I have read that a GPU cluster will crack ol... |
Which mathematical operations does secp256k1 point multiplication use? |
$m$ is arbitrary value in $Z_n$, where n is RSA modulo. Then we do: $r_2=r_1 . m$, where $r_1$ is a random value such that $r_1\in Z^*_n$.
** My question is whether $r_2$ is a uniformly at random value in $Z_n$?
|
After studying philosophy and being a philosophy teacher, I took back studies 4 years ago and I did a bachelor in maths. I'm in maths grad school now (I'm 32), and I would like to work in cryptography. (I took as many algebra and arithmetic and logic courses as I could, and I'm studying Galois theory this semester.)
... |
I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password.
The password was written on a paper slip, but I remember that it consisted of 30+ completely random alphanumeric characters with some special symbols in between.
I have read that a GPU cluster will cra... |
$m$ is arbitrary value in $Z_n$, where n is RSA modulo. Then we do: $r_2=r_1 . m (modn)$, where $r_1$ is a random value such that $r_1\in Z^*_n$.
** Question(1): is $r_2$ a uniformly at random value in $Z_n$?
**Question(2): Would this: be secure $r_2=r_1 . m (modn)$ (where $m\in Z_p$ and $r_1\in Z^*_n$ )?
|
$m$ is arbitrary value in $Z_n$, where n is RSA modulo. Then we do: $r_2=r_1 . m (modn)$, where $r_1$ is a random value such that $r_1\in Z^*_n$.
** Question(1): is $r_2$ a uniformly at random value in $Z_n$?
**Question(2): Would this be secure: $r_2=r_1 . m (modn)$ (where $m\in Z_p$ and $r_1\in Z^*_n$ )?
|
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