instruction stringlengths 15 30k |
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I am currently investigating use of [EAX][1] mode for a dedicated application and following useful clarifications received from my previous [post][2] , to consider according to my applicable input security requirements (separate keys for encryption and authentication) either :
- the Baseline solution where EAX is ... |
Is it possible to insert a key derivation function when using EAX? |
The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" (similar to EFS perhaps), issued to a human ("Mr CSO") or an application ("My cat photo app"). Certs would be off existin... |
Using EC keying material as KDF for symmetric file encryption? |
The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" (similar to EFS perhaps), issued to a human ("Mr CSO") or an application ("My cat photo app"). Certs would be off existin... |
No, you definitely shouldn't change the internal guts of EAX. That would invalidate the security proof and might introduce subtle security problems. (You can look at EAX', a minor tweak to EAX which was suggested for standardization -- but was eventually discovered to have a serious but non-obvious flaw that was intr... |
Are there Cryptography certifications variants of CISSP ( Certified Information Systems Security Professional)? Like a CISSP exams, but only for cryptography? |
Are there Cryptography certifications variants of CISSP? |
I'm designing a scheme for management of a small number of cryptographic keys (<100 at any given time) and I had an idea. Rather than storing all the keys, could I just store one master key and use a KDF to derive the particular key I need by varying the salt in a certain way? For example, if I need the second encrypti... |
Is this key management scheme secure? |
The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" (similar to EFS perhaps), issued to a human ("Mr CSO") or an application ("My cat photo app"). Certs would be off existin... |
The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" (similar to EFS perhaps), issued to a human ("Mr CSO") or an application ("My cat photo app"). Certs would be off existin... |
**i'm performing el gamal encryption algorithm and using the additive homomorphic property so the product of two ciphertexts is the encryption of the sum of the plaintexts.
the problem is that i need to return the original plain text sum values
how could i get it using decryption
is there an algorithm i can follow k... |
The situation involves a single party (single certificate) who would want to AES encrypt a file that they can later decrypt. Assume the EC certificate + EC keys have a purpose i.e. "File encryption" (similar to EFS perhaps), issued to a human ("Mr CSO") or an application ("My cat photo app"). Certs would be off existin... |
Using single EC cert/keying material to derive symmetric encryption key (for storage)? |
How can we construct a (pseudo) random permutation from a (pseudo) random function ?
I've seen a method from Luby-Rackoff which allows to construct a PRP of length $2N$ from a PRF of input/output length $N$. Is there a method to keep the same length $N$ ?
Thank you. |
Construct a random permutation from a random function? |
As generator (g) is use in DH how to find combination of prime p and g? eg: if we choose p=23 its generator is 7(given in book) how to find it? |
how to find generator (g) in a cyclic group? |
I have been using Asymmetric Encryption for a while, and I have come across an interesting concept, and it would be cool if it could be done.
Are there any Asymmetric Encryption Algorithms where the Encryption Key and the Decryption Key cannot be deciphered from one another? |
As generator $g$ is use in DH how to find combination of prime $p$ and $g$? eg: if we choose $p=23$ its generator is $7$ (given in book) how to find it? |
How to find generator $g$ in a cyclic group? |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation that have constraints on $e$. How hard will depend :
- Heavily, on exactly what values of the public modulus $N$ and its bit size $n$ are acceptable for a given signature $S$. This var... |
I'm assuming you meant "how to **efficiently** find generator $g$ in a cyclic group?"
**Small groups**
For small values $p$, bruteforce is efficient.
**Large groups with known factorization of group order**
The order of the group $\mathbb{Z}_p^*$ is $p-1$. The order of every element divides the order of the... |
I'm performing el gamal encryption algorithm and using the additive homomorphic property so the product of two ciphertexts is the encryption of the sum of the plaintexts.
the problem is that I need to return the original plain text sum values
how could I get it using decryption
is there an algorithm I can follow kno... |
Mike gave you the answer for the specific question you asked. I'll try to give you an answer to the question you should have asked:
> For Diffie-Hellman, what criteria should I use to select a secure $p$ and $g$?
This question is important, because not every large cyclic group is actually secure. It turns out t... |
When setting up a nonce/IV and counter (e.g. for AES-GCM-128), why are the nonce/IV and counter restricted to specific sections (e.g. random nonce/IV in first 8 bytes and counter in last 8 bytes)? This results in the last 8 bytes always starting off at a predictable value (0), reduces uniqueness (only 8 bytes of random... |
Why restrict nonce/IV and counter to specific sizes? |
How can we construct a (pseudo) random permutation from a (pseudo) random function ?
I've seen a method from Luby-Rackoff which allows to construct a PRP of length $2N$ from a PRF of input/output length $N$. Is there a method to keep the same length $N$ ?
I'm looking for a method different from simply truncating ... |
I am wondering whether the following form is a one way function with collision resistance.
$ax^2+by^2 \mod p$, where $a$ and $b$ are given, and $p$ is a prime number.
Since QR(quadratic residue) $x^2 \mod p$ is one way, $ax^2 \mod p$ is also one way.
$by^2$ is further considered.
So, my guess is that the fo... |
I'm taking coursera cryptography course, slightly restated definition of semantic security is the following:
> The adversary chooses two messages: $m_0, m_1$.
> One of theese messages is ciphered: $c \leftarrow E(k, m_b)$.
> The adversary has to guess which message was ciphered.
>
> There are two events: $M_b = ... |
I'm taking coursera cryptography course. The difinition of semantic security is hard to understand. I tryed to slightly restate it (the word "efficient" was in the original definition). Do i get it right?
> The adversary chooses two messages: $m_0, m_1$.
> One of theese messages is ciphered: $c \leftarrow E(k, m_b)... |
I'm taking coursera cryptography course. The difinition of semantic security is hard to understand. I tryed to slightly restate it (the word "efficient" was in the original definition). Do i get it right?
> The adversary chooses two messages: $m_0, m_1$.
> One of theese messages is ciphered: $c \leftarrow E(k, m_b)... |
I'm taking coursera cryptography course. The definition of semantic security is hard to understand. I tryed to slightly restate it (the word "efficient" was in the original definition). Do i get it right?
> The adversary chooses two messages: $m_0, m_1$.
> We encrypt one of these messages: $c \leftarrow E(k, m_b)$.... |
>What if it could? What does this definition mean in practice?
Consider $M_0=$ *attack* and $M_1=$ *don't attack*. If the adversary can distinguish which message you are sending to your troops, they can optimize their strategy to defeat you.
Another example. Say you are casting a yes ($1$) no ($0$) vote for a pro... |
For Java I'm only aware of the Bouncy Castle implementation of Salsa20. However, that version is ***significantly*** slower than AES-CTR and ARC4.
There are plenty of libraries in C, but are there any good implementations of this stream cipher in Java?
|
Fast Salsa20 in java? |
I'm taking coursera cryptography course. The definition of semantic security is hard to understand. I tried to slightly restate it (the word "efficient" was in the original definition). Do I get it right?
> The adversary chooses two messages: $m_0, m_1$.
> We encrypt one of these messages: $c \leftarrow E(k, m_b)$.... |
I am reading my lecture and I found this definition.
Let be $F$ be a family of hash functions, that is, a parameterized set
$$F=\{g_k:\{0,1\}^{*}\rightarrow\{0,1\}^{n}|k\in K\},$$
where $n\in \mathbb{N}$ and $K$ is a finite set.
Which could be an example of F? |
The event of Snowden invokes an intereting cryptograpic problem. At present, who can or how to say something confidentially to Snowden?
Claim: I have no any particular political orientation. The above question is merely a cryptographic challenge. The meta assumption is
1. You trust someone, denoted by Snowden,... |
Cryptographic Challenge: How to Say Something Confidentially to Snowden? |
1. Generate a file of cryptographically strong random data at least as long as the message to be sent. This will allow communicating the secret using the random data as a one-time-pad. I.e., produce the ciphertext by using a bit-by-bit combining function such as XOR.
2. Purchase a plane ticket for an international ... |
1. Generate a file of cryptographically strong random data at least as long as the message to be sent. This will allow communicating the secret using the random data as a one-time-pad. I.e., produce the ciphertext by using a bit-by-bit combining function such as XOR.
2. Purchase a plane ticket for an international ... |
1. Generate a file of cryptographically strong random data at least as long as the message to be sent. This will allow communicating the secret using the random data as a one-time-pad. I.e., produce the ciphertext by using a bit-by-bit combining function such as XOR.
2. Purchase a plane ticket for an international ... |
The event of Snowden invokes an intereting cryptograpic problem. At present, who can or how to say something confidentially to Snowden?
Claim: I have no any particular political orientation. The above question is merely a cryptographic challenge. The meta assumption is
1. You trust someone, denoted by Snowden,... |
The event of Snowden invokes an intereting cryptograpic problem. At present, who can or how to say something confidentially to Snowden?
Claim: I have no any particular political orientation. The above question is merely a cryptographic challenge. The meta assumption is
1. You trust someone, denoted by Snowden,... |
I'm performing ElGamal encryption algorithm and using the additive homomorphic property so the product of two ciphertexts is the encryption of the sum of the plaintexts.
The problem is that I need to return the original plaintext sum values.
How could I get them using decryption?
Is there an algorithm I can follow... |
[revised to better highlight the semi-realistic (2.) where an easy attack might work for $e=3$ by sneaking a forged $N$ of about $368$ bits even if the original modulus is much bigger]
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation... |
[revised to better highlight the semi-realistic (2.) where an easy attack might work for $e=3$ by sneaking a forged $N$ of about $368$ bits even if the original modulus is much bigger]
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation... |
[revised to better highlight the semi-realistic (2.) where an easy attack might work for $e=3$ by sneaking a forged $N$ of about $368$ bits even if the original modulus is much bigger]
It seems conceivable to go beyond [Poncho's great answer][1] and make the public key $(N,e)$ acceptable by a standard implementation... |
I'm trying to create a good scheme for generating passwords in my systems management scripts. What I'd like to do is have a secret key (let's say `hello123`), which I keep only on trusted management machines. I'd then like to combine that with a "password identifier" (for example `testing-db-pass`), and produce some AS... |
I am studying Lamport-Diffie signature scheme and in my lecture present the follow algorithm for attempting to invert the one way function $f$, where $f$ is used to compute the public key of this signature from the private key $sk=\left(\begin{array}{rrrrrr}
x_{1,0} & x_{2,0} & \cdots & x_{l,0} \\
x_{1,1} & x_{2,1}... |
When using PGP type public encrypted communication, would it be a good idea to generate a new
public for each message and attach that in the new public key in the reply to back to sender mail body? Idea is you start the communication with the known public key from a key server, but for each new message/chat message yo... |
Generate a new public/private key pair for each new message? |
Can an encryption scheme (deterministic or not) be viewed as a pseudorandom function taking as input a message and returning a value of the same bit-encoding length ?
Thank you. |
If neither of the 'big two' of TLS Handshake and IKE are appropriate in a given situation, what alternative Authenticated Key Exchange (AKE) standards exist and are recommended?
Many protocols have been proposed in the literature over the past 20+ years, though only a small subset have made it into standards of some... |
What current authenticated key exchange standards exist? |
Can an encryption scheme (deterministic or not) be viewed as a pseudorandom permutation taking as input a message and returning a value of the same bit-encoding length ?
Thank you. |
I am wondering whether the following form is a one way function with collision resistance:
$$ax^2+by^2 \mod p$$
where $a$ and $b$ are given, and $p$ is a prime number.
Since the QR (quadratic residue) $x^2 \mod p$ is one way, $ax^2 \mod p$ is also one way.
The same goes for $by^2$.
So, my guess is that the for... |
One runtime platform provides an API that supplies PKCS#5 padding for block cipher modes such as ECB and CBC. These modes have been defined for the triple DES, AES and Blowfish block ciphers. The other platform API only provides PKCS#7 padding.
Are PKCS#5 padding and PKCS#7 padding compatible?
|
I am studying Lamport-Diffie signature scheme. In the [lecture][1] present the algorithm $A'$ for attempting to invert the one way function $f$, where $f$ is used to compute the public key. My question is Why to use this algorithm $A'$ to prove the Theorem 1?, Why I cann't use other any algorithm?
[1]: http://w... |
I am studying Lamport-Diffie signature scheme. In the [lecture][1] present the algorithm $A'$ for attempting to invert the one way function $f$, where $f$ is used to compute the public key. My question is Why to use this algorithm $A'$ to prove the Theorem 1?, Why I cann't use other any algorithm (for example Grover, ... |
For a protocol where the server presents its signature to prove authenticity (e.g. IKE/SIGMA/STS with only one party authenticated), it's essential that the signing is extremely cheap, while verification can be almost arbitrarily expensive.
RSA appears to be the worst alternative, but what about DSA vs. ECDSA? Is th... |
DSA, RSA, ECDSA etc - which one is cheapest for signing? |
What is the ideal system for an encryption scheme ? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an encryption scheme do we have a well known application describing an ideal system for an encryption, maybe the one-time pad ?
... |
I'm taking coursera cryptography course. The definition of semantic security is hard to understand. I tried to slightly restate it (the word "efficient" was in the original definition). Do I get it right?
> The adversary chooses two messages: $m_0, m_1$.
> We encrypt one of these messages: $c \leftarrow E(k, m_b)$.... |
The Snowden situation raises an intereting cryptograpic problem. At present, how can something be sent confidentially to Snowden?
Claim: I have no particular political orientation. The above question is merely a cryptographic challenge. The meta assumption is
1. You trust someone, denoted as Snowden, but Snowd... |
I want to modify a standard block cipher in the following way. I replace each round key by a key picked at random. Is this block cipher more secure than the original one ?
Thank you. |
Is this encryption key sharing okay to use? Or is much better to use ECIES?
G = base point
a = Alice’s private key
b = Bob’s private key
A = aG = Alice’s public key
B = bG = Bob’s public key
Cx = x coordinate of C
Alice and Bob share an AES key…
Alice makes C = aB
Bob makes C = bA
The c... |
Is this ECC encryption key sharing method okay? |
How did they factor RSA-704? |
I like know What's a relation between **attack** and **attack model**. For example: Let $\Pi$ the Lamport signature scheme, this signature has its security based in the one way function. Exists the Grover algorithm (**attack**), such that invert this function with complexity $O(2^{n/3})$. Furthermore are the algorithms... |
Given a random bit string $R=r_1r_2\cdots r_n$, let us encrypt each bit $c_i=E(r_i,k_i)$ where $k_i$ is taken from the stream of encryption key. Suppose that an attacker can guess correct $r_i$ from $c_i$ with probability $p>1/2$. Then, the probability that the attacker can recover correct $R$ from $C=(c_1,\cdots,c_n)$... |
How to compute the attacker's probability? |
Given a random bit string $R=r_1r_2\cdots r_n$, let us encrypt each bit $c_i=E(r_i,k_i)$ where $k_i$ is taken from the stream of encryption key. Suppose that an attacker can guess correct $r_i$ from $c_i$ with probability $p>1/2$. Then, the probability that the attacker can recover correct $R$ from $C=(c_1,\cdots,c_n)$... |
Given a random bit string $R=r_1r_2\cdots r_n$, let us encrypt each bit $c_i=E(r_i,k_i)$ where $k_i$ is taken from the stream of encryption keys. Suppose that an attacker can guess the correct $r_i$ from $c_i$ with probability $p>1/2$. Then, the probability that the attacker can recover correct $R$ from $C=(c_1,\cdots,... |
The probability of recovering the string $R$ is the same with both of your scheme. The reason is that your second scheme can be separated into two independent parts. In the first part, you just transform $R$ into $R'$ using only your step 1 (this is invertible and from $R'$ you can recover $R$).
In the second part, ... |
I am reading my lecture and I found this definition:
> Let be $F$ be a family of hash functions, that is, a parameterized set
> $$F=\{g_k:\{0,1\}^{*}\rightarrow\{0,1\}^{n}|k\in K\},$$
> where $n\in \mathbb{N}$ and $K$ is a finite set.
Which could be an example of $F$? |
Is this encryption key sharing okay to use? Or is much better to use ECIES?
$G$ = base point
$a$ = Alice’s private key
$b$ = Bob’s private key
$A = aG$ = Alice’s public key
$B = bG$ = Bob’s public key
$C_x$ = x coordinate of $C$
Alice and Bob share an AES key:
* Alice makes $C = aB$
* Bob ma... |
First up, I think your question is less something for crypto.SE and would fit better in the security.SE corner. Nevertheless, here goes:
> ...except his name or identity...
That's in itself already describes your problems when it comes to security and cryptography.
1. Problem due to lack of verification opt... |
First up, I think your question is less something for crypto.SE and would fit better in the security.SE corner. Nevertheless, here goes:
> ...except his name or identity...
That's in itself already describes your problems when it comes to security and cryptography.
1. Problem due to lack of verification opt... |
First up, I think your question is less something for crypto.SE and would fit better in the security.SE corner. Nevertheless, here goes:
> ...except his name or identity...
That's in itself already describes your problems when it comes to security and cryptography.
1. Problem due to lack of verification opt... |
Suppose that tomorrow is July 7, 2050 and Snowden is still stayed in Sheremetyevo airport. Further, let us suppose that quantum computation and quantum commincation are available to everyone, and Snowden's laptops are also quantumly-made. My question is: Who can or how to say something confidentially to Snowden? (See h... |
Snowden Challenge II: Can we solve Snowden challenge quantumly? |
Suppose that tomorrow is July 7, 2050 and Snowden is still stayed in Sheremetyevo airport. Further, let us suppose that quantum computation and quantum commincation are available to everyone, and Snowden's laptops are also quantumly-made. My question is: Who can or how to say something confidentially to Snowden? (Pleas... |
I was reading up on CryptoCat's (pretty ridiculous) programming issues and how is dramatically reduced the key search space ([link to bug synopsis][1])
One thing that caught my eye was
>So 2^54.15 turns into 2^27.08
Unless I'm missing something, the impact of the fractional exponent is negligible. So, any ide... |
Decimal point in keyspace notations? (eg 2^54.15)? |
As expressed, this is not possible. A zero-knowledge proof cannot be non-interactive. The reason is that any non-interactive proof can be forwarded to a third party who will accept it. This is excluded by standard definitions of zero-knowledge.
Could you rephrase you question and explain more precisely what you expe... |
When using a “sponge function” to create a cryptographic hash, we can look at the flat sponge claim, which flattens the claimed success probabilities of all attacks using a single parameter: the claimed capacity *c*<sub>claim</sub>
Is there any way to actually verify the probability of that claim - in this case: pot... |
Is it possible to actually verify a “sponge function” security claim? |
I was just looking at some [NIST PRNG recommendations][1], specifically at Hash_DRBG. I read briefly through the algorithm, and even though it is not overly complex, it still seems unnecessary to me. I asked myself how I would implement a (cryptographically secure) PRNG on top of a Hash algorithm (SHA256 or SHA512), wh... |
I was just looking at some [NIST PRNG recommendations][1], specifically at Hash_DRBG. I read briefly through the algorithm, and even though it is not overly complex, it still seems unnecessary to me. I asked myself how I would implement a (cryptographically secure) PRNG on top of a Hash algorithm (SHA256 or SHA512), wh... |
I was just looking at some [NIST PRNG recommendations][1], specifically at Hash_DRBG. I read briefly through the algorithm, and even though it is not overly complex, it still seems unnecessary to me. I asked myself how I would implement a (cryptographically secure) PRNG on top of a Hash algorithm (SHA256 or SHA512), wh... |
I was just looking at some [NIST PRNG recommendations][1], specifically at Hash_DRBG. I read briefly through the algorithm, and even though it is not overly complex, it still seems unnecessary to me. I asked myself how I would implement a (cryptographically secure) PRNG on top of a Hash algorithm (SHA256 or SHA512), wh... |
Is there a problem with signing a message like this?
p = the Elliptic Curve prime
G = base point
a = Alice’s private key
A = aG = Alice’s public key
e = hash(message)
Jx = x coordinate of J
In my target 32-bit microcontroller I am using p-256 and SHA256. Thus e will typic... |
Is there a problem with this non-ECDSA message signing? |
I'd like to refer you to the [other answer](http://crypto.stackexchange.com/a/9042/5231) in the original question. Suppose your laptop and Snowden's laptop are both capable of quantum communication. Suppose there is also a quantum phone book, or a quantum DNS service. When his passport got revoked, Snowden's address is... |
I'd like to refer you to the [other answer](http://crypto.stackexchange.com/a/9042/5231) in the original question. Suppose your laptop and Snowden's laptop are both capable of quantum communication. Suppose there is also a quantum phone book, or a quantum DNS service. When his passport got revoked, Snowden's address is... |
Section 4.9.2 of FIPS PUB 140-2 specifies, amongst other things, a "Continuous random number generator test." Here are the relavant bits:
> 1. If each call to a[n] RNG produces blocks of n bits (where n > 15), [...] Each subsequent generation of an n-bit block shall be compared with the previously generated block. ... |
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