instruction stringlengths 15 30k |
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Just for fun, I want to encrypt a message that will take about 10 or so years to decrypt. My idea is to encrypt a message with AES-512 with a password one million decimal digits long.
Knowing not much about cryptography, is this any more difficult to decrypt than a shorter password? (I'm trying to prevent brute-forc... |
Are really, really long passwords any securer than short ones? |
I saw some time ago a post discussing the issues surrounding encryoption of speech/voice in voip and how it can leak information (can't find it now). Can someone provide an insight into some of the issues and how to mitigate them if one wants to use symmetric encryption to encrypt voice between two devices? Is asymmetr... |
Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side.
David Chaums paper gives a following figure:
$r$ - blinding factor
$e$, $d$ - public & private exponent
$Blinded\ message = Message \cdot r^{e}$
$Signature\ of\ a\ Blin... |
Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side.
David Chaums paper gives a following figure:
$r$ - blinding factor
$e$, $d$ - public & private exponent
$Blinded\ message = Message \cdot r^{e}$
$Signature\ of\ a\ Blin... |
I'm currently writing a paper about RSA (a self-chosen subject).
I'm writing about the key-generation in RSA, and I have problem finding the public exponent *e*.
I have chosen *p = 61* and *q = 53*.
Then I determined my modulus *n = p ⋅ q = 3233*
and my *phi(n) = (p-1)(q-1) = 3120*.
What bothers me is t... |
So here's the concept. Rather than storing 2 keys and using a random IV, which presents its own problems (key rotation, ensuring no key is used in more than 2^32 cycles, sharing the keys, etc), is it OK to derive the cipher key, authentication key and IV from a master key? It wouldn't stop the need for key rotation pol... |
How it works depends on the cipher, but the basic idea is that of a [trapdoor function][1].
>A trapdoor function is a function that is easy to compute in one direction, yet believed to be difficult to compute in the opposite direction (finding its inverse) without special information, called the "trapdoor".
Man... |
SHA-1 is a cryptographic [tag:hash] function that is no longer considered secure and should only be used for backward compatibility.
In 2006, [NIST issued a policy][1] stating that:
> "Federal agencies should stop using SHA-1 ... as soon as practical, and must use the SHA-2 family of hash functions for these appl... |
I'm not really familiar with blind signature schemes, so please take the following with a grain of salt, but what you describe looks like a really funny way to apply padding. Normally, one would pad the message (using a suitable padding scheme like [RSA-PSS](http://www.rsa.com/rsalabs/node.asp?id=2005)) _before_ the f... |
As I know, in Paillier cryptosystem, the encryption c of a message m is calculated as c=g^m r^n mod n^2
Now, I am wondering if I can derive g^m mod n^2 given that I know c, r, and n?
It seems that "mod n^2" operation does not constitute a finite field. Not every element has the corresponding multiplicative invers... |
Strange...
`WNZTNV` is repeated...
If i'm counting correct on position 1-6 and 22-27.
My guess would be the key length is a divider of 21? 7 seems to be consistent with the other information, but my knowledge of foreign languages is close to none, so i don't recognize anything readable in key or plaintext... ... |
As I know, in Paillier cryptosystem, the encryption $c$ of a message $m$ is calculated as $c=g^m r^n \bmod n^2$.
Now, I am wondering if I can derive $g^m \bmod n^2$ given that I know $c$, $r$, and $n$?
It seems that the "$\bmod\ n^2$" operation does not constitute a finite field. Not every element has the corres... |
Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle?
I mean, is it possible to devise a protocol $P$ using a function $H$, and then prove a theorem saying that $P$ is secure in a model $M$ given that $H$ is a collision-resistant function? What ... |
Why are protocols often proven secure under the random oracle model instead of a hash assumption? |
Since OCB-AES mode of authenticated encryption is the fastest way to provide authenticity and confidentiality without having to strive into questions like:"Encrypt then MAC, MAC then encrypt, Encrypt and MAC why it is not widely used or even become a standard? |
Why OCB-AES mode is not becoming a standard for authenticated encryption? |
A random oracle is an idealization of a hash function $H$: if hash functions were perfect they would **be** random oracles. This is why it is always easier to consider a hash function a random oracle when one proves something about a larger scheme. Those are "proofs in the random oracle model". [1]
That being said i... |
The [OCB mode of authenticated encryption][1] (used for example with AES) is the fastest way to provide authenticity and confidentiality without having to strive into questions like: [Encrypt then MAC, MAC then encrypt, Encrypt and MAC][2].
So why it is not widely used and didn't become a standard?
[1]: http:... |
Why is OCB-AES mode not becoming a standard for authenticated encryption? |
> can we assume that b breached number of keys, no matter what the quantity would not help an attacker discover the previous nor next key in the set without the original seed data?
No, you cannot assume it. Whether that holds depends upon what key generation algorithm you use. For good key derivation algorithms it... |
I was reading some articles about attacks on RSA system and I wonder about some generalization of the following theorem.
> Theorem (Coppersmith).
>
> Let $N=pq$ be an $n$-bit RSA modulus, where
> $p<q<2p$. Then given the $\frac{n}{4}$ least significant bits of $p$
> (that is $\approx$ half of LSB of $p$) or the... |
A message may be accompanied with a digital signature, a MAC or a hash. What assurances does each primitive provide to the recipient.
In your answer, please discuss for each primitive:
- **Integrity:** can the recipient be confident that the message has not been accidentally modified?
- **Authentication:** c... |
What is the difference between a digital signature, a MAC and a hash? |
The difference between a digital signature and a MAC is non-repudiation. A message with a digital signature proves that only the sender could have signed the message, whereas a message with a MAC proves that either the sender or the recipient could have signed the message.
Can an OpenPGP implementation, such as GPG,... |
Can I use PGP to sign a message without providing cryptographic non-repudation? |
Say I have
$k1 = "keyhere";
$k2 = "keyhere";
$rc4key = sha256($k1 . $seed);
$aeskey = sha256($k2 . $seed . $rc4key);
$input_data = "hello world";
$rc4 = new RC4 -> encrypt($input,$rc4key)
$aes = new AES -> encrpt ($rc4, $aeskey);
Meaning...
If I have two keys... |
RC4 encryption -> AES encryption = more or less secure than RC4 or AES alone? |
A message may be accompanied with a **digital signature**, a **MAC** or a message **hash**, as a proof of some kind.
Which assurances does each primitive provide to the recipient?
What kind of keys are needed?
|
These types of cryptographic primitive can be distinguished by the security goals they fulfill (in the simple protocol of "appending to a message"):
- **Integrity:** Can the recipient be confident that the message has not been accidentally modified?
- **Authentication:** Can the recipient be confident that the ... |
What are the differences between a digital signature, a MAC and a hash? |
What type of attack are you trying to prevent?
If it's a brute-force attack, AES-128 is *more* than sufficient. In the best case scenario, combining RC4 and AES gains you negligible additional security due to a [meet-in-the-middle attack](http://en.wikipedia.org/wiki/Meet-in-the-middle_attack).
Are you trying to ... |
I'm trying to calculate the size of a public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is that what I retrieve and the actual key size is off by 12 bytes, or 96 bits for that matter. I know there is at least always ... |
How much extra information is in a public key? |
In the Dolev Yao model, the cryptographic primitive (encryption, for example) is considered as a blackbox. My question is: does *blackbox* mean CPA security or does it require CCA security?
My guess is that CPA is sufficient (and it is the minimum requirement), since the adversary model is rather passive. But could ... |
What is the need for two private/public keys in twin elgamal?
I'm relatively new and would need some help. |
In the [Dolev Yao model][1] for interactive protocols, the cryptographic primitive (encryption, for example) is considered as a blackbox.
Does *blackbox* here mean that the primitive is to be considered CPA secure, or does it even require CCA security?
My guess is that CPA is sufficient (and it is the minimum req... |
What are the cryptographic assumptions in the Dolev Yao model? |
In Dolev-Yao and other formal models, the assumptions about adversary behavior are encoded via the grammar and entailment relation, and there's no mention of a specific computational definition of encryption security.
But your question is still meaningful, and can be interpreted as follows:
>If my encryption sche... |
In Dolev-Yao and other formal models, the assumptions about adversary behavior are encoded via the grammar and entailment relation, and there's no mention of a specific computational definition of encryption security.
But your question is still meaningful, and can be interpreted as follows:
>If my encryption sche... |
> **Possible Duplicate:**
> [RSA encryption with private key and decryption with a public key](http://crypto.stackexchange.com/questions/2123/rsa-encryption-with-private-key-and-decryption-with-a-public-key)
<!-- End of automatically inserted text -->
This wording is creeping everywhere ([e.g. there][1]): "I encr... |
Contruct a protocol to determine if three secret keys are different, without revealing any of them? |
On a practice question for my intro cryptography exam, it asks the following:
> Assuming that keys are chosen with equal likelihood, the shift cipher provides:
> A) computational security
> B) perfect secrecy
> C) semantic security
> D) none of the above
I chose "none of the above", thou... |
Can a shift cipher attain perfect secrecy? |
On a practice question for my intro cryptography exam, it asks the following:
> Assuming that keys are chosen with equal likelihood, the shift cipher provides:
> A) computational security
> B) perfect secrecy
> C) semantic security
> D) none of the above
I chose "none of the above", thou... |
I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall.
Basicly I attacked the final round first (K3) using the differential characteristic of 0x80800000 which yealds a differential of 0x02000000 with a probability of 1.
I have found four possibilities for the... |
Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side.
David Chaums paper gives a following figure:
$r$ - blinding factor
$e$, $d$ - public & private exponent
$Blinded\ message = Message \cdot r^{e}$
$Signature\ of\ a\ Blin... |
I read http://zucalg.forumotion.net/t8-on-the-construct-of-good-sboxes that's we do not know if exists an 8x8 sbox with differential uniformity = 2.
I suppose we cannot compute every possible sbox because there are 64! possible s-box. Am i right? It's this an np problem? |
I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay attacks don't work on ECSDA.
For this scenario, the public key, $Q = x \centerdot G$, where $x$ is the private key and $... |
Why doesn't this replay attack work on ECDSA? |
I'm trying to calculate the size of an RSA public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is that what I retrieve and the actual key size is off by 12 bytes, or 96 bits for that matter – for a 1024 bit key, I get ... |
How much extra information is in an RSA public key? |
Previously we visited the benefits of [elliptic curves for cryptography][1]. [Lattice based cryptography][2] is starting to become quite popular in academia. The primary benefit of lattice based crypto is the resistance to quantum algorithms. Are there other benefits to lattice based crypto? For example, speed, ciphert... |
What are the benefits of lattice based cryptography? |
I saw some time ago a post discussing the issues surrounding encryption of speech/voice in VoIP and how it can leak information (can't find it now). Can someone provide an insight into some of the issues and how to mitigate them if one wants to use symmetric encryption to encrypt voice between two devices? Is asymmetri... |
I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall.
Basically I attacked the final round first (K3) using the differential characteristic of 0x80800000 which yields a differential of 0x02000000 with a probability of 1.
I have found four possibilities for t... |
I'm trying to figure out block ciphers and this is the first time I've encountered the term "oracle adversary". It appears in the context of defining a PRP and a PRF. Can someone please explain what an "oracle adversary" can/cannot do? Or maybe help out with a link or something (I've tried looking it up myself, but I c... |
I [read](http://zucalg.forumotion.net/t8-on-the-construct-of-good-sboxes) that we do not know if there exists an 8x8 sbox with differential uniformity = 2.
I suppose we cannot compute every possible sbox because there are $64!$ possible s-boxes. Am I right? Is this problem in $NP$? |
In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT.
It's clear that adversaries should be at most probabilistic sub-exponential, because otherwise they could exhaust the message space. It's also clear that adversar... |
FIPS 186-3 specifies a method to generate DSA parameters.
Is there anything similar (official standard or widely-accepted recommendation) that shows how to generate the primes for multi-prime RSA? |
Are there any standards of multi-prime RSA key generation? |
Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else. If I understand right, this means that the same message could have possibly also been constructed by Alice, but not by Eve (who can observe, change, remove and inject messages).
The us... |
Can one have an authentic, but repudiable, message without a previously shared secret? |
Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else.
If I understand right, this means that the same message could have possibly also been constructed by Alice, but not by Eve (who can observe, change, remove and inject messages).
The... |
Does all $2^{bitlengt}$ states allways occure in a LFSR or can I choose my taps badly so some states are skipped and the period are shortend?
If so are there any (easy) way to prove the number of states that can occure in a LFSR? |
Do all $2^{\ell}$ (where $\ell$ is the bit length of the shift register) states always occur in a LFSR or can I choose my taps badly so some states are skipped and the period is shortened?
If so is there a way to prove the number of states that can occur in a LFSR? |
**Predicate encryption(PE)** arrived as a descendant of attribute based encryption. Attribute based encryption allows the encryptor to embody a policy to the ciphertext (Ciphertext-Policy based encryption) and the receipent to receive a key from a central trusted authority according to his attributes. If the attributes... |
Is there any semantic difference between predicate encryption and functional encryption? |
Suppose $g$ is a generator of an order $p$ cyclic group in which discrete logarithm is hard and $p$ is a prime (i.e., given $g^x$ for a random $x \in \{0,1,\ldots, p-1\}$, it is hard to recover $x$ except with $negl(\lambda)$, where $negl(\lambda)$ is a negligible function of the security parameter $\lambda$).
My qu... |
I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise).
On one hand you have [system's like](http://webapps.stackexchange.com/a/11362/6433) [LastPass](https://lastpass.com) which store all your passwo... |
Let's look at the risks.
## Encrypted password database
To steal your passwords, the attacker has to steal the database. Then she has two options: steal the master password or guess/bruteforce it. Once the attacker has the database and master password, she has access to your current accounts until you change stor... |
Let's look at the risks.
## Encrypted password database
To steal your passwords, the attacker has to steal the database. Then she has two options: steal the master password or guess/bruteforce it. Once the attacker has the database and master password, she has access to your current accounts until you change stor... |
Suppose $g$ is a generator of an order $p$ cyclic group in which discrete logarithm is hard and $p$ is a prime (i.e., given $g^x$ for a random $x \in \{0,1,\ldots, p-1\}$, it is hard to recover $x$ except with $negl(\lambda)$, where $negl(\lambda)$ is a negligible function of the security parameter $\lambda$).
My qu... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. It uses a public key ($n,e)$ where the modulus is the product of $u>2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). No other requirement is given by PKCS#1v2.
I know no **standard** about gene... |
Let's look at the risks.
## Encrypted password database
To steal your passwords, the attacker has to steal the database. Then she has two options: steal the master password or guess/bruteforce it. Once the attacker has the database and master password, she has access to your current accounts until you change stor... |
I'm having difficulties understanding exactly what this protocol means:
S → D : {NS , S}KD
D → S : {NS , ND }KS
S → D : {ND }KD
"where S represents the supervisor’s console and D represents the door controller and the other symbols have their usual security protocol meanings."
I understand N to be a no... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. It uses a public key ($n,e)$ where the modulus is the product of $u>2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). No other requirement is given by PKCS#1v2.
I know no **standard** about gene... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. It uses a public key ($n,e)$ where the modulus is the product of $u>2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). No other requirement is given by PKCS#1v2.
I know no **standard** about gene... |
I'm having difficulties understanding exactly what this protocol means:
$S \to D : \{N_S , S\}K_D$
$D \to S : \{N_S , N_D \}K_S$
$S \to D : \{N_D \}K_D$
"where $S$ represents the supervisor’s console and $D$ represents the door controller and the other symbols have their usual security protocol meanings."
... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. It uses a public key ($n,e)$ where the modulus is the product of $u>2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). No other requirement is given by PKCS#1v2.
I know no **standard** about gene... |
I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and [understand why certain features are implemented or not implemented][1] in the common ECC stacks.
**Question**
Namely, I'd like to know when should a non-standard ECC library (or related hardw... |
Is there a field guide to ECC for the IT Security layman? |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
Multi-prime RSA (also known as RSA-MP) is supported by [PKCS#1v2][1]. This standard supports a public key $(n,e)$ where the modulus $n$ is the product of $u≥2$ distinct odd primes: $n=\prod_{i=1}^u{r_i}$, with $1<e<n$ and $\gcd(r_i-1,e)=1$ (implying $e$ odd). The private exponent $d$ is such that $1<d<n$, and $e⋅d≡1\pm... |
I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and [understand why certain features are implemented or not implemented][1] in the common ECC stacks.
**Question**
Namely, I'd like to know when should a non-standard ECC library (or related hardw... |
http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
That has 3DES being used three times for each 64-bit block of random data desired. eg.
I = ede *K(DT)
R = ede *K(I XOR V) and a new V is generated by V = ede*K(R Xor I)
OpenSSL seems to be using 3DES in ECB mode:
http://www.opensource.apple.... |
I'm having difficulties understanding exactly what this protocol means:
$S \to D : \{N_S , S\}K_D$
$D \to S : \{N_S , N_D \}K_S$
$S \to D : \{N_D \}K_D$
"where $S$ represents the supervisor’s console and $D$ represents the door controller and the other symbols have their usual security protocol meanings."
... |
Your question is ill-posed; to determine whether they provide "security", we need a specification of what you mean by security.
So I'll answer about just one potential use of hash functions:
Are you thinking about using hashing together with encryption to try to protect the integrity of the message against tamper... |
N=pq (p and q are prime numbers)
m_1, ..., m_x are the messages, e and d are RSA encryption and decryption keys, respectively
I am given e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, m_x^d.
Is it possible for me to factor N or derive d from the above knowledge?
My tentative answer is "no" because this problem seems to be ... |
Is this attack for RSA possible? |
Chapter II of [Merkle's 1979 PhD thesis][1] is titled "One Way Hash Functions." The chapter appears to be the first reference to cryptographic hashing. The chapter has no references. Is there an earlier reference that I am not aware of?
[1]: http://www.merkle.com/papers/Thesis1979.pdf |
Did Merkle invent cryptographic hashing? |
I just find this pencil and paper cipher 'Felix' on this [site][1]
and I want to know how secure it is?
[1]: http://topcat.hypermart.net/felix.html |
The original question states that we are given $e,m_1,{m_1}^e,{m_1}^d,\dots,{m_x}^e,{m_x}^d$, but not $N$; and asks for $d$ or a factorization of $N$.
I suspect this is ill-posed, because if any of the ${m_j}$ is such that ${m_j}>1$, it is trivial to obtain $d$ from ${m_j}$ and ${m_j}^d$, as $d=\log({m_j}^d)/log(m_j... |
The original question states that we are given $e,m_1,{m_1}^e,{m_1}^d,\dots,{m_x}^e,{m_x}^d$, but not $N$; and asks for $d$ or a factorization of $N$.
I suspect this is ill-posed, because if any of the ${m_j}$ is such that ${m_j}>1$, it is trivial to obtain $d$ from ${m_j}$ and ${m_j}^d$, as $d=\log({m_j}^d)/log(m_j... |
i'm trying to figure out the best way to generate a cryptographically secure random number between 0 and 200 from a cryptographically random string of bytes (ie. read from /dev/urandom or some such)
i could do random[0] % 201 but then numbers 0-54 would be more likely than 55-200 which would make the resultant numbe... |
For a project I am working on, I have access to a CSPRNG that outputs a random integer in the interval $[0, 2^{n-1}]$ for any integer $n$ greater than 0. I cannot use the zero values, so I have my RNG code in a `while` loop that runs until the random number is `!==0`. For small $n$ it is very likely that the while loop... |
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