instruction stringlengths 15 30k |
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State of the art techniques for Anonymous Authentication? |
For a CBC mode cipher, which is what POODLE applies to, you **don't encrypt or decrypt <br>individual bytes, but rather blocks**, formed by adding padding to the actual data bytes. <br>For encryption in general every byte can be any value 0 to 255, and the SSL spec allows the padding_length byte to be almost any value,... |
For AES CBC, can I encrypt the IV with AES ECB and the same key and include it with the message? |
All of the information on asymmetric encryption I can find uses key-exchanging to get a mutual symmetric key.
what I am trying to do is encrypt a message with a public key and have it only readable by someone with the private key. I don't even want the sender to be able to read it after it's be encrypted. I don't ca... |
Way to do single key-pair asymmetric encryption? |
All of the information on asymmetric encryption I can find uses key-exchanging to get a mutual symmetric key.
what I am trying to do is encrypt a message with a public key and have it only readable by someone with the private key. I don't even want the sender to be able to read it after it's be encrypted. I don't ca... |
Does anyone know of an efficient way of breaking a modified Caesar cipher via brute-force?
The way I'm currently trying to crack it is as follows:
1. Generate all possible key combinations ( 5 numbers between 1 & 25)
2. Use the generated key to "decipher" the message
3. Use frequency analysis on deciphered mess... |
Does anyone know of an efficient way of breaking a modified Caesar cipher (where the key is a set of numbers (the amount of shift) that is repeated throughout the plaintext, e.g. {1,2,3,4,5}) via brute-force?
The way I'm currently trying to crack it is as follows:
1. Generate all possible key combinations ( 5 num... |
All of the information on asymmetric encryption I can find
<br>
uses key-exchanging to get a mutual symmetric key.
What I am trying to do is encrypt a message with a public key and have it only readable by someone with the private key. I don't even want the sender to be able to read it after it's been encrypted.... |
Is there a way to do single key-pair asymmetric encryption? |
Consider the following five events:
1. Correctly guessing a random 128-bit AES key on the first try
2. Winning a lottery with 1 million contestants
3. Winning a lottery with 1 million contestants 5 times in a row.
4. Winning a lottery with 1 million contestants 6 times in a row
5. Winning a lottery with ... |
What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; lets say watching movies in Netflix. I am looking for schemes that prevents linkability, and also schemes that allows lin... |
I have two points on an elliptic curve $P(x_1,y_1)$ and $Q(x_2,y_2)$ and a scalar value $x$, where $P=x \cdot Q$. What is the best way that I could figure out the value of $x$?
Given that I know all the necessary key and constants. (a,b,p,G,nA,PB...) |
How to find the integer multiplicand from given two points? |
Consider the following five events:
1. Correctly guessing a random 128-bit AES key on the first try
2. Winning a lottery with 1 million contestants
3. Winning a lottery with 1 million contestants 5 times in a row.
4. Winning a lottery with 1 million contestants 6 times in a row
5. Winning a lottery with ... |
Does anyone know of an efficient way of breaking a modified Caesar cipher (where the key is a set of numbers (the amount of shift) that is repeated throughout the plaintext, e.g. {1,2,3,4,5}) via brute-force?
The way I'm currently trying to crack it is as follows:
1. Generate all possible key combinations ( 5 num... |
I am restricted on a certain environment involving PHP and unable to implement new memory hard hashes such as scrypt. Also, cryptanalysis of script shows time-memory tradeoff problems which is a concern.
My current key derivation is simply an iteration of hmac (password + salt). But it seems that using AES or other... |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, cryptanalysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of hmac (password + salt). But it seems that usin... |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, cryptanalysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that usin... |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, analysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that using AES... |
All of the information on asymmetric encryption I can find uses key-exchanging to get a mutual symmetric key.
What I am trying to do is encrypt a message with a public key and have it only readable by someone with the private key. I don't even want the sender to be able to read it after it's been encrypted. I do... |
we are dealing with cryptography in school right now and superficially went over the Rabin cryptosystem with the (apparently usual) example of p=7 and q=11 etc (we didn't do RSA).
<br>I understand that there are many results when you try to reverse $15 = m^2 mod 77$. E.g. m^2 = 77+15, 77*2+15,77*3+15 and so on.
<br>W... |
I am pentesting a database that where I found data which was base64 encoded. I tried the usual method of decoding `base64`, which didn't work.
Later, I found in database a field called `base64_custom_key`. How do I decrypt a base64 encoded message with a key?
For eg.
The key looks like `gP9jOzA75VyIW6FRuHZim... |
I have seen this prior post: http://crypto.stackexchange.com/questions/17635/elliptic-curve-based-blind-signature-implementation
Currently I'm sizing up how difficult it would be to attain Elliptic Curve Blind signatures for an application I'm working on.
I did see this posting from @DrLecter which was very inf... |
I have seen this prior post: http://crypto.stackexchange.com/questions/17635/elliptic-curve-based-blind-signature-implementation
Currently I'm sizing up how difficult it would be to attain Elliptic Curve Blind signatures for an application I'm working on.
I did see this posting from @DrLecter which was very inf... |
> What i don't understand is how it gets easier to reverse this function when you know the primes that you used to calculate the divisor
Well, we know how to compute square roots modulo a prime; that is, how to solve the problem $a \equiv x^2 \pmod p$, for prime $p$ (assuming, of course, if there is a solution; ther... |
I have seen this prior post: http://crypto.stackexchange.com/questions/17635/elliptic-curve-based-blind-signature-implementation
Currently I'm sizing up how difficult it would be to attain Elliptic Curve Blind signatures for an application I'm working on.
I did see this [posting from @DrLecter](http://crypto.sta... |
I want to implement AES-128-GCM in assembler using Intel AES-NI instructions. I have found reference code in the [Intel AES-NI Whitepaper][1] but I don't see code for the GCM mode there (or indeed any use of the PCLMULQDQ instruction). Do I miss something in this document? Or could somebody point me to another similarl... |
Reference AES-NI assembler code for AES-128-GCM? |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, analysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that using AES... |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, analysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that using AES... |
I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity.
My key derivation function currently looks like this:
![enter image description here][1]
Please note that `scrypt` could just as easily be subbed out for `PBKDF2` or `bcr... |
We are dealing with cryptography in school right now and superficially went over the Rabin cryptosystem with the (apparently usual) example of p=7 and q=11 etc (we didn't do RSA).
I understand that there are many results when you try to reverse $15 = m^2 \pmod{77}$. E.g. $m^2 = 77+15, 77*2+15,77*3+15$ and so on.
... |
I am new in Cryptography and I saw this question in a note I solved it but I'm not sure about my answers.
> Let $F : \{0, 1\}^n × \{0, 1\}^n→ \{0, 1\}^n$ be a secure PRF (i.e. a PRF where the key space,
input space, and output space are all $\{0, 1\}^n$) and say $n = 128$. Which of the following is a secure PRF. In... |
> I think number 1 is PRF because the input key of each F is different
That is correct, though I might not give full marks for your reasoning. The XOR of two PRFs is PRF. The probability that a random $k1||k2$ has $k1 = k2$ is negligible.
> number 2, 3, 4 are PRF because $x+k$ term could be any string of $\{0, 1\... |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt. Also, analysis of script shows time-memory tradeoff problems, which is a concern.
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that using AES... |
I am trying to understand how Attribute Base Encryption (ABE) works. So, after downloading libfenc library from [here][1], I built the source code on Ubuntu 12.04 without any error. Afterward, I tried to follow the library [commands][2] as follow:
- Create the master secret and public parameters:
`abe-setup ... |
How does ABE decryption works? |
I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt (and I am not trying to compete with the likes of scrypt).
My current key derivation is simply an iteration of HMAC (password + salt). But it seems that using AES or other encryption ci... |
Please consider a case where we have a master key MS that is used in pseudo-random function to generate a set of pseudo-random values. Then we use key derivation function to derive a key from each of pseudo-random values. Assume all the keys are long enough (in security context).
-------------------
**Question**: ... |
Can a key derived from key derivation function be considered as a secure key? |
I'm currently doing a project on RSA, and have just come across this website.
https://www.namecheap.com/support/knowledgebase/article.aspx/798/67/what-is-an-rsa-key-used-for
On here, it says that
> Since encrypted data transmission takes too much time in case of asymmetric encryption, this kind of encryption ... |
Exactly how slow is asymmetric encryption? |
I'm currently doing a project on RSA, and have just come across this website.
https://www.namecheap.com/support/knowledgebase/article.aspx/798/67/what-is-an-rsa-key-used-for
On here, it says that
> Since encrypted data transmission takes too much time in case of asymmetric encryption, this kind of encryption ... |
Is it feasible to have data encrypted at different levels?
I'd like to encrypt an xml database (such as used in [www.keepass.info][1]) whereby two keys can exist:
1. <kbd>Key #1</kbd> decrypts the entire database file
2. <kbd>Key #2</kbd> decrypts a subset of the database file
Is this technically possible/re... |
> What i don't understand is how it gets easier to reverse this function when you know the primes that you used to calculate the divisor
Well, we know how to compute square roots modulo a prime; that is, how to solve the problem $a \equiv x^2 \pmod p$, for prime $p$ (assuming, of course, if there is a solution; ther... |
> Can formulae for equivalent year cost be constructed to determine the parameters as functions of time since those tests were performed?
Yes, but you have to make a lot of assumptions. First, though, note that the paper says:
> We caution again that these values are very approximate [...] Nevertheless, we believ... |
I am trying to understand how Attribute Base Encryption (ABE) works. So, after downloading libfenc library from [here][1], I built the source code on Ubuntu 12.04 without any error. Afterward, I tried to follow the library [commands][2] as follow:
- Create the master secret and public parameters:
`abe-setup ... |
Assume that eve who masquerades as a legitimate host and convinces Carol to
make an authentication attempt.(Carol want to handshake with steave(host))
Thus, eve can get values, A = g^a, M1 = H(A,B',K')
For a guessing password P', eve can calculate following :
x' = H(s,P') -> v' = g^x' (eve can get random stri... |
Why does the Secure Remote Protocol have resistance of dictionary attack? |
How to check the signature without the predetermined function in ECDSA from openssl? |
The property of SRP is that:
- If the attacker is a passive listener to an exchange between a client and a server, he learns nothing about the shared password
- If the attacker is a participant in the exchange with either a client or a server with the password (or modifies the exchange between the client and the ... |
Assume that Eeve who masquerades as a legitimate host and convinces Carol to
make an authentication attempt. (Carol wants to handshake with Steve – a host)
Thus, Eve can get values $A = g^a, M1 = H(A,B',K')$
For a guessing password $P'$, Eve can calculate the following :
$x' = H(s,P') \rightarrow v' = g^{x'}$... |
I'm building a SHA1 rainbow table to crack basic passwords (i.e. upto 10 character, 0-9,a-z). But I can't seem to calculate that golden ratio that would give me the most coverage.
Also is there anyway to estimate the coverage of the table? As at now, after building the table I'm using a brute-force attack to check ... |
What's the perfect chain length : number of chains ratio for Rainbow Tables? |
Miller Rabin - Error probability of .5 a possibility? |
I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people citing his anonymous credential system paper (oai.cwi.nl/oai/asset/1745/1745A.pdf) and his hhttp://chaum.com/publications/... |
This question comes from a (nitpicking) comment by me in [this SO question][1].
I said that using the half of the output from a 256 bit hash function is worse than using a 128 bit hash function. My reasoning is that the contract of the 256 bit function takes into account the full lenght output so you can find more c... |
Taking half of a X bits hash key as secure as using a X/2 bit hash function? |
In the paper [Pinocchio: Nearly Practical Verifiable Computation][1], there are some polynomials $v_k(x)$, $w_k(x)$ and $y_k(x)$ representing the structure of there circuit. However, as in the "concrete example" in page 3, the description of $v_k(x)$ are table items like $v_1(r_5) = 0$ and $v_1(r_6) = 1$, where $r_5$ a... |
How to calculate $v_k(s)$ in Quadratic Arithmetic Program? |
I'm building a SHA-1 rainbow table to crack basic passwords (i.e. up to 10 character, 0-9,a-z). But I can't seem to calculate that golden ratio that would give me the most coverage.
Also is there anyway to estimate the coverage of the table? As at now, after building the table I'm using a brute-force attack to chec... |
What's the perfect chain length : number of chains ratio for rainbow tables? |
I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people citing his [anonymous credential system paper][1] and [his
paper][2].
Can someone explain in simple language (and si... |
This question comes from a (nitpicking) comment by me in [this SO question][1].
I said that using the half of the output from a 256 bit hash function is worse than using a 128 bit hash function. My reasoning is that the contract of the 256 bit function takes into account the full length output so you can find more c... |
Are there known constructions which allow to sign a message M
(let's say it will be sent as clear text) using a stream cipher C
and a symmetric secret key K?
So, we have M, C, K and we want to send M|S
where S = SIGN(C,K,M) and | is the concatenation operator.
|
How to use a stream cipher to sign a message? |
Key Derivation Function (KDF): Can a key derived from KDF be considered as a secure key? |
Consider a case where we have a master key MS that is used in pseudo-random function to generate a set of pseudo-random values. Then we use key derivation function to derive a key from each of pseudo-random values. Assume all the keys are long enough (in security context).
-------------------
**Question**: In the ... |
A. Lenstra et al. had a paper in 2012 "Ron was wrong, Whit is right", in which one reads: "What surprised us most is that many thousands of 1024-bit RSA moduli, including thousands that are contained in still-valid X.509 certificates, offer no security at all." Has that surprise been satisfactorily explained in the mea... |
What followed findings of A. Lenstra et al. concerning shared factors of practical RSA moduli? |
Yes, this is exactly what KDFs and PRFs are designed for. That is, no *reasonably efficient* attacker will be able to tell if you used an actual random key or something generated from the KDF/PRF. This is of course assuming that your initial seed/master secret was of sufficient entropy.
The practice of deriving man... |
Yes, this is exactly what KDFs and PRFs are designed for. That is, no *reasonably efficient* attacker will be able to tell if you used an actual random key or something generated from the KDF/PRF. This is of course assuming that your initial seed/master secret was of sufficient entropy, and the way you derive the vario... |
I'm trying to understand how AES guarentees security. One of the named points on the web is that AES uses a non-linear step (the *SubBytes step*). But how exactly does the Rijndael key schedule add security? It sounds like a wide question, but for me, not exactly an expert, it's hard to understand.
*Help is apprecia... |
How does non-linearity (S-box) add security to AES? |
Assume that an scheme used to secure specific system Π=(Gen,Enc,Dec), thought have indistinguishable multiple encryption in the presence of an eavesdropper, For any adversary A can break the scheme with `Pr[PrivKmult A,Π(n) = 1] ≤ 1/2 + negl(n)`, Some PPT Adversary x break this scheme with probability `Pr[PrivKmult x,... |
I want to derive $n$ keys from a master key.
I pick a master key $mk$ and use pseudo-random function (PRF) to generate $n$ pseudo-random values, $v_i=PRF(mk,i)$ where $1\leq i \leq n$.
Next, I use key derivation function to generate $n$ keys: $k_i=KDF(v_i)$, where $1\leq i \leq n$. Note that key derivation must be... |
Can Pseudorandom values be used as secure keys? |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ SHA-256 per second, that is over $2^{83.7}$ SHA-256 per year. I'm guessing that a fraction of NSA's budget would allow this organization to do much better.
Here is said raw data as a graphic. Renewed growth in the 2013-2014 peri... |
On the section 5.4 of the paper [Improved Security for a Ring-Based Fully Homomorphic Encryption Scheme][1], the authors explain how to discard some bits of the ciphertexts to get smaller ciphertexts and smaller evaluation keys.
The function *Discard* simply takes a ciphertext $c$ and an integer $i$ (number of words... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ SHA-256 per second, that is over $2^{83.7}$ SHA-256 per year. I'm guessing that a fraction of NSA's budget would allow this organization to do much better.
Here is said raw data as a graphic. Renewed growth in the 2013-2014 peri... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ SHA-256 per second, that is over $2^{83.7}$ SHA-256 per year. I'm guessing that a fraction of NSA's budget would allow this organization to do much better.
Here is said raw data as a graphic. Renewed growth in the 2013-2014 peri... |
Assume that an scheme used to secure specific system $Π=(Gen,Enc,Dec)$, thought have indistinguishable multiple encryption in the presence of an eavesdropper, For any adversary $A$ can break the scheme with $\Pr[\text{PrivKmult}^A_Π(n) = 1] \leq 1/2 + \text{negl}(n)$, Some PPT Adversary $x$ break this scheme with proba... |
Assume that a scheme used to secure a specific system $Π=(Gen,Enc,Dec)$ which is thought have indistinguishable multiple encryption in the presence of an eavesdropper.
For any adversary $A$ that can break the scheme with
$\Pr[\text{PrivKmult}^A_Π(n) = 1] \leq 1/2 + \text{negl}(n)$
some PPT adversary $x$ breaks... |
I want to implement the ATV-FHE scheme as described here https://eprint.iacr.org/2013/094.pdf and based on it I want to compare homomorphically a vector of integers. Would this be a valuable application, something that is both new and useful ?
By new, I mean that the integer comparison I want to implement is for a m... |
How about a homomorphic integer sorting in a MPC context? |
New to StackExchange, so please bear with the newbie.
At my current job we are often creating many ssh keys with ssh-keygen (RSA). One thing I have noticed is that the first few characters (say the first 5 or so) are consistently the same. These are all created on the same computer. Is this to be expected? I am just... |
Why are the first 4-6 characters from ssh-keygen (RSA) the same everytime? |
New to StackExchange, so please bear with the newbie.
At my current job we are often creating many ssh keys with ssh-keygen (RSA). One thing I have noticed is that the first few characters (say the first 5 or so) of the private key are consistently the same. These are all created on the same computer. Is this to be ... |
Lets assume we have a DRGB(deterministic random bit generator) which is seeded by a good true RBG(random bit generator). Before any bit has been read from the DRBG, the entropy is clearly the number of bits of the seed.
But is entropy lost, when I read out the bits of the DRBG?
From an information theoretical poin... |
Will entropy be lost by using a DRBG? |
I want to implement the ATV-FHE scheme as described by Adriana López-Alt, Eran Tromer, Vinod Vaikuntanathan: [_On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption_][1] ([ePrint][2] revised 2014, originally in [Proceeding of STOC 2012][3]); and based on it I want to compare homomorph... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ SHA-256 per second, that is over $2^{83.7}$ SHA-256 per year. I'm guessing that a fraction of NSA's budget would allow this organization to do much better.
Here is this data redrawn in hashes per year with a $\log_2$ vertical sc... |
Lets assume we have a DRGB (deterministic random bit generator) which is seeded by a good true RBG (random bit generator). Before any bit has been read from the DRBG, the entropy is clearly the number of bits of the seed.
But is entropy lost, when I read out the bits of the DRBG?
From an information theoretical... |
New to StackExchange, so please bear with the newbie.
At my current job we are often creating many ssh keys with ssh-keygen (RSA). One thing I have noticed is that the first few characters (say the first 5 or so) of the private key are consistently the same. These are all created on the same computer. Is this to be ... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ hashes per seconds, where one hash is two nested SHA-256, that is over $2^{84.7}$ SHA-256 per year. I'm guessing that the NSA could do much better with a fraction of it's budget.
Here is this data redrawn in SHA-256 per year wit... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ hashes per seconds, where one hash is two nested SHA-256, that is over $2^{84.7}$ SHA-256 per year. I'm guessing that the NSA could do much better with a fraction of it's budget.
Here is this data redrawn in SHA-256 per year wit... |
According to [this source][1], bitcoin mining nowadays (Nov. 2015) tops $50\cdot10^{15}$ hashes per seconds, where one hash is two nested SHA-256, that is over $2^{84.7}$ SHA-256 per year. I'm guessing that the NSA could do much better with a fraction of it's budget.
Here is this data redrawn in SHA-256 per year wit... |
My question maybe will be stupid, but my problem is that I do not understand why stram ciphers need a key and also a nonce. As far as I understand, the keystream is generated with the nonce. The same key can be reused with a different nonce. Wouldn't be simpler just to use a new key each time? If I understand good, to ... |
Why srteam ciphers use nonce? |
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