instruction stringlengths 15 30k |
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The message format includes a datetime field in the clear. Is it okay to also use this field (or some hash thereof) as the initialization vector?
Edit: In this case, CBC is the mode being used. |
There are several uses of cryptographic algorithms in the protocol.
## Accounts/Transactions
To move money from one account to another, you need to collect some data (the previous transaction(s) which got you the money, the target account, the amount you want to transfer) and *sign them*, using the private key wh... |
Are there any evidence (other than not being cracked so far) that the [Bitcoin protocol][1] is secure? "How secure" is it?
(I realize that this might not qualify as a meaningful question - feel free to edit if you can improve it. Also, if you liked this question, you might like the [Bitcoin Proposal][2].)
[1]... |
Since the input is base-10 and the output is base-16, the output actually looks bigger than the input.
Do you have access to a binary code implementation? Disassembling or debugging that would be easiest.
How many hashed pair samples do you have access to? Can you generate more with chosen inputs?
What was the... |
I'm not sure I get your Q? but does these links help
__http://people.csail.mit.edu/rivest/crypto-security.html#Software
(DES - Eric Young's implementation)
http://www.tero.co.uk/des/
http://www.opensource.apple.com/source/OpenSSL/OpenSSL-26/openssl/crypto/aes/
__http://www.opensource.apple.com/sourc... |
The message format includes a datetime field in the clear. Is it okay to also use this field (or some hash thereof) as the initialization vector?
In this case, CBC is the mode being used. |
Before anyone suggest it, I've yet to pick up "Applied Cryptography" I'm planning on picking it up the next time I visit amazon.
I know that the keys are somehow mathematically related, and I know that they're somehow generated via prime numbers, but how exactly are they related? I realize that it'd probably be best... |
I understand this may not be the best place to ask a question like this, but I believe that this community may be the best/only place I can ask such a question.
I have inputs and outputs from an in-house hash developed years ago and the developer is no longer working with us any more. I need to determine the proces... |
In principle, the answer is yes. Any signature scheme can be converted in a black-box way to yield a symmetric-key encryption scheme. Both of the two primitives are equivalent to one-way functions under black-box reductions.
One way to do it:
1. A signature scheme yields a one-way function in a very straight-for... |
In principle, the answer is no, with an asterisk. Signature schemes are equivalent to one-way functions under black-box reductions. Public-key encryption scheme implies the existence of key agreement.
Impagliazzo & Rudich famously proved that **there is no black-box reduction from one-way functions to key agreement... |
In principle, the answer is no, with an asterisk. Signature schemes are equivalent to one-way functions under black-box reductions. Public-key encryption scheme implies the existence of key agreement.
Impagliazzo & Rudich [famously proved](http://cseweb.ucsd.edu/~russell/secret.ps) that **there is no black-box redu... |
Cryptographic hash functions (like everything else a traditional computer does) can be described as a set of binary operations, XOR, register rotate, and binary addition being very common. These translate directly to a classic computer science problem known as "binary satisfiability" or SAT.
SAT problem has been pro... |
I'm not sure I get your Q? but do these links help
__http://people.csail.mit.edu/rivest/crypto-security.html#Software
(DES - Eric Young's implementation)
http://www.tero.co.uk/des/
http://www.opensource.apple.com/source/OpenSSL/OpenSSL-26/openssl/crypto/aes/
__http://www.opensource.apple.com/source/... |
Im starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. i have a book about it that im going through, but it seems to skip something, which is causing my confusion. more likely its me thats constantly missed a line or something.
the book giv... |
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book about it that I'm going through, but it seems to skip something, which is causing my confusion. more likely it's me who is constantly missed a line or something.
the book... |
I have a customer with an Access database (ugh!) in which credit cards are stored in plaintext (yikes!), so amongst other changes I'm doing in the app, I'm applying some encryption in there.
I've used Rijndael as the algorithm of choice, but I'm struggling to find the correct approach to storing the encryption/decry... |
Where do I securely store the key for a system where the source is visible? |
According to the Wikipedia entry for this psuedorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have several questions about this :
1. If it hasn't been cracked since 1987, why is it not considered to be a candidate for a "one way function... |
According to the [Wikipedia entry][1] for this pseudorandom number generator, there is no public cryptanalysis for this device since it was invented back in 1987 by C.G. Gunther. I have several questions about this:
1. If it hasn't been cracked since 1987, why is it not considered to be a candidate for a "one way fu... |
But he did get a US patent for it: [Generator for generating binary ciphering sequences][1]
In fact, it looks very similar to [A5/1 and 2][2] which were used in the GSM spec. The designers of A5/1 were doubtless [aware of the ASG paper][3]. It would be really interesting to find out if they licensed it or simply wor... |
But he did get a US patent for it: [Generator for generating binary ciphering sequences][1]
In fact, it looks very similar to [A5/1 and 2][2] which were used in the GSM spec. The designers of A5/1 were doubtless [aware of the ASG paper][3] as it was presented in Europe the very same year. It would be really interest... |
> If it hasn't been cracked since 1987, why is it not considered to be a candidate
> for a "one way function" like the RSA crypto system, the discrete logarithm system, etc.?
This generator looks like suitable for a stream cipher, i.e. it is a one-way function (of type N -> *, i.e. fixed length input, variable-leng... |
A stream cipher, RSA, or whatever you designate by the expression "discrete logarithm system", are **not** "one-way functions". In particular, asymmetric encryption algorithms and digital signature algorithms provide functionality which is not doable (or not with the same usability) with only the "scrambling" technique... |
Suppose I need to store login information for a third-party website for a few users, how would I go about doing it?
Since I am logging into a third party website, I need the password in plain-text, not hashed. And no, the website in question does not provide any API.
In addition, the server I am using is accessib... |
How should I store passwords that need to be available in plain text? |
I found the below code online, but in its original state, the encryption was not using any padding (Padding.None), and was encrypting in blocks of 8. I wasn't able to get this code to properly encrypt / decrypt data so I was forced to have it encrypt the full length of the text. Is there something fundementally wrong w... |
The RP in ECC would be to find a1,...,an (integers) given P and Q1..Qn (points in the EC) such that P = a1*Q1 + ... + an*Qn.
Is it hard when DH-like assumption holds in the EC?
Is is hard in secp256k1 or Curve25519?
|
Is the Representation Problem hard on elliptic curves? |
I'm looking to incorporate more crib usage in breaking ciphers in unknown enciphering schemes, or at least to gleam what information I may. This seems to be a big hurdle to me, and I'm looking for references on incorporating cribs into decryption schemes.
Can you recommend any? |
Hugo Krawczyk has a paper titled [The Order of Encryption and Authentication for Protecting Communications (or: How Secure Is SSL?)](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.106.5488&rep=rep1&type=pdf).
It identifies 3 types of combining authentication (MAC) with encryption:
1. Encrypt then Authent... |
I would like to improve the performance of hashing large files, say for example in the tens of gigabytes in size.
Normally, you sequentially hash the bytes of the files using a hash function (say, for example SHA-256, although I will most likely use Skein, so hashing will be slower when compared to the time it takes... |
> password = sha1 ( mainPassword . domainName . number )
> Is this secure enough?
Answer is no. Let me explain. The only part that is really unknown in the above is `mainPassword`. The rest can easily be guessed by a hacker. If your original password is weak (not many characters, no digits, no specials characters),... |
I currently use the following method to have a different password on every website.
password = sha1 ( mainPassword . domainName . number )
Here are the questions:
1. Is this secure enough? I mean if somebody know my algorithm and one or many passwords, could he find easily one of my other password? Up unti... |
Is something wrong with this algorithm in terms of security? |
I'm looking to incorporate more crib usage in breaking ciphers in unknown enciphering schemes, or at least to gleam what information I may. This seems to be a big hurdle to me, and I'm looking for references on incorporating cribs into decryption schemes.
Now allow me to clarify. By "crib" I mean a word or a set of ... |
> Is Method 2 any less secure than Method 1, in terms of collisions
> being more possible and/or probable?
You are just producing more values which can be used to attempt collisions, but if you pick a big enough hash space, the difference is the same as between a molecule in the ocean and a drop in the ocean.... No... |
I currently use the following method to generate a different password on every website I have to login.
password = sha1 ( mainPassword . domainName . number )
Here are the questions:
1. Is this secure enough? I mean if somebody know my algorithm and one or many passwords, could he find easily one of my oth... |
Systems that do this already exist, such as [SuperGenPass][1]. To address your questions in order:
> I mean if somebody know my algorithm and one or many passwords, could
> he find easily one of my other password?
Easily? No. As long as SHA1 remains a secure hash function (which is currently the case, but all ha... |
I currently use the following method to generate a different password on every website I have to login:
`password = sha1 ( mainPassword . domainName . number )`
Here are my questions:
1. Is this secure enough?
I mean if somebody know my algorithm and one or many passwords, could he find easily one of my ot... |
If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existance, the number of English words known by the choosing algorthm, the number of English words assumed by the attacker?
Does the language matter, is the average entropy per word in Germ... |
How should I calculate the entropy of a password? |
If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existence, the number of English words known by the choosing algorithm, the number of English words assumed by the attacker?
Does the language matter, is the average entropy per word in Ger... |
I would like to improve the performance of hashing large files, say for example in the tens of gigabytes in size.
Normally, you sequentially hash the bytes of the files using a hash function (say, for example SHA-256, although I will most likely use Skein, so hashing will be slower when compared to the time it takes... |
Even if RSA decided to cancel the [*Factoring Challenge*][1] it seems that some teams keep working on it. According to Wikipedia, [RSA-768][2] has been factored in late 2009. What are the current large integer factorization algorithms and what the mathematical principles behind them? What are the ways for improvement (... |
We discuss a lot of topic and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy galculated in the general case? |
What is entropy? |
We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy calculated in the general case? |
In information theory, entropy is the measure of uncertainty associated with a random variable. In terms of Cryptography, entropy must be supplied by the cipher for injection into the plaintext of a message so as to neutralise the amount of structure that is present in the unsecure plaintext message. How it is measur... |
You may already be aware of this but have a look at the following article relating to different integer factorization algorithms. It is a bit outdated, however, it should give you an idea of the different algorithms available, and the theory behind them.
[Integer Factorization Algorithms by C. Barnes, 2004](http://... |
You may already be aware of this but have a look at the following article relating to different integer factorization algorithms. It is a bit outdated, however, it should give you an idea of the different algorithms available, and the theory behind them.
[Integer Factorization Algorithms by C. Barnes, 2004](http://... |
I've been reading a paper [1], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference.
In homomorphic encryption we have an encryption operation $E_k: P \rightarrow C$, where $P$ is the set of plain texts and $C$ is the set of cipher texts. We ... |
I have read [this question][1] regarding white-box Cryptography, and it led to this [short article / Q&A][2] which states in question 2:
> Q2: What is the difference with code obfuscation?
> Related and
> complementary techniques for protecting software implementations but
> with different security goals inclu... |
Came across this while refreshing my Cryptography brain cells.
From the **RSA** algorithm I understand that it somehow __depends on the fact__ that given a **large prime number (A)** it is computationally impossible to derive at the **two prime numbers (B & C) whose product it is**.
But that isn't the Fermat Theo... |
What is the relation between RSA & Fermats little theorem? |
> White-box cryptography is aimed at **protecting secret keys** from
> being disclosed in a software implementation.
A cryptography algorithm gets the key and plaintext(encryption mode)/ciphertext(decryption mode) as input and outputs the ciphertext/plaintext.
A white box implementation of the cryptography algorit... |
I've been reading a paper [[1][1]], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference.
In homomorphic encryption we have an encryption operation $E_k: P \rightarrow C$, where $P$ is the set of plain texts and $C$ is the set of cipher texts... |
In the past I have used the Chi-squared test to check the statistical randomness of my generator. Is this a good test to use? Are there other tests? |
What tests can I do to ensure my PRNG is working correctly? |
To walk you through RSA from start to end, here's how it works.
1. Choose two large distinct primes $p$, $q$. Calculate $n=pq$.
2. Calculate $\phi(pq)$. This happens to be $(p-1)(q-1)$.
3. Choose $e$ such that $gcd(e, \phi(p,q)) = 1$ and $e < $\phi(p,q)$.
4. Compute $de = 1 \mod \phi(p,q)$.
5. Do some crypto; $c... |
> White-box cryptography is aimed at **protecting secret keys** from
> being disclosed in a software implementation.
A cryptography algorithm gets the key and plaintext(encryption mode)/ciphertext(decryption mode) as input and outputs the ciphertext/plaintext.
A white box implementation of the cryptography algorit... |
I had heard that although its easy to implement message digest functions like md5,sha1,sha256 ect in CUDA (or any other GPU platform) it is impossible to implement bcrypt. bcrypt is different from these hash functions, in that blowfish is a block cipher and in order to produce a one way hash a "feed back" is used. I am... |
I had heard that although it's easy to implement message digest functions like MD5, SHA-1, SHA-256 etc. in CUDA (or any other GPU platform), it is impossible to implement bcrypt there.
bcrypt is different from these hash functions, in that Blowfish is a block cipher, and in order to produce a one way hash a "feed b... |
Why can't one implement bcrypt in Cuda? |
Is calculating a hash code for a large file in parallel less secure than doing it sequentially? |
When implementing cryptographic/coding theory algorithms one need to use data like big prime numbers, numbers in Z_n and their inverses, irreducible polynomials in Z_n[x] and so on... While sometimes it is easy to write a simple program to get simple examples of these it's handy to have a list with some non-trivial exa... |
Where can I find useful data for cryptography/coding theory? |
To be honest, there's no good reason why the XOR is needed. My suspicion is that, most likely, the designers included it because they thought, "hey, why not? it can't hurt". But if the designers had left out the XOR, everything would have been just fine.
In particular, if PRF() is a secure pseudorandom function, a... |
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book ([Cryptography Theory And Practice][1] by Douglas Stinson) about it that I'm going through, but it seems to skip something, which is causing my confusion. More likely it's m... |
How does the index of coincidence work in the Kasiki test? |
How can my application make sure the right symmetric key is used for decryption? |
**Situation:**
Several participants contribute encrypted random numbers. These numbers will be used to generate community-agreed random (by simple multiplication).
**Question:**
Is there any way to detect same products values without revealing multipliers? Maybe it is possible to use some homomorphic encryptio... |
Homework? Try using ElGamal encryption. I.e., given an ElGamal ciphertext that encrypts an integer m and your own factor f, try finding a way to generate another ElGamal ciphertext that encrypts f*m. One difficulty is doing this knowing only the public key. Another difficulty is to avoid that an attacker knowing the e... |
Homework? Try using ElGamal encryption. I.e., given an ElGamal ciphertext that encrypts an integer m and your own factor f, try finding a way to generate another ElGamal ciphertext that encrypts f*m. One difficulty is doing this knowing only the public key. Another difficulty is to avoid that an attacker knowing the e... |
What I'll describe works with any homomorphic scheme, whether multiplicative (Elgamal) or additive (Paillier; maybe exponential Elgamal or BGN depending), but I'll describe it with multiplicative.
I assume what you mean is something like this: you have, say, five people. They all generate a random value r_i, and pos... |
What I'll describe works with any homomorphic scheme, whether multiplicative (Elgamal) or additive (Paillier; maybe exponential Elgamal or BGN depending), but I'll describe it with multiplicative.
I assume what you mean is something like this: you have, say, five people. They all generate a random value r_i, and pos... |
Currently, a magnet link containing a 40-digits long SHA-hash value, is assigned to every torrent which is created. Therefore, this hash should be unique to identify a torrent and send the right bytes (packages) to the right people. So therefore, there are 16^40 (1461501637330902918203684832716283019655932542976) possi... |
Is the number of creatable torrents limited? |
In the face of non-quantum attacker, [Keccak](http://keccak.noekeon.org/Keccak-reference-3.0.pdf)[r=1088,c=512] with 512 bits of output provides:
- Collision resistance up to 2<sup>256</sup> operations
- Preimage resistance up to 2<sup>256</sup> operations
- Second preimage resistance up to 2<sup>256</sup> oper... |
What security does Keccak offer against quantum attacks, specifically Grover's algorithm? |
How were the DES S-box values determined? |
What is a white-box implementation?
Does a white-box implementation have specific properties?
|
What is a white-box implementation of a cryptographic algorithm? |
Is there any opensource white-box implementation of AES or DES? |
I have heard that in enterprises it is common that the IT admin have a master passphrase that can unlock any content that an employee encrypts.
It would be temping to think, that the IT admins passphrase is encrypted with the employees passphrase, but then the IT can't change his passphrase.
How does such encrypt... |
How can two difference passphrases unlock the same content? |
How can two different passphrases unlock the same content? |
Another method to the ones described above would be ID-based encryption where a trusted third party, called the Private Key Generator (PKG), generates the corresponding private key based on the user's identity (whether it be domain name or email address).
Given the master public key, any party can compute a public k... |
Recentally, [an attack on AES][1] was discovered which reduces its computationally complexity, by a very slight ammount.
- The first key recovery attack on the full AES-128 with computational
complexity 2^126.1.
- The first key recovery attack on the full AES-192 with computational
complexity 2^189.7.
... |
Are these emerging threats against AES affecting your designs? |
After contacting D-Wave and asking them the implications of their quantum computer against RSA, they responded that they had not cracked RSA for the following reasons:
Short answers:
Q. Is RSA effectively cracked by your quantum computer
A. No.
Q. Should our customers be concerned that companies with quantum ... |
[D-wave systems][1] has released a commercially viable quantum computer. This means; in theory, that all asymmetric encryption algorithms, such as RSA are now useless, due to the speed at which quantum computers can factor. Has RSA been cracked yet? If not; why hasn't it?
<br />Edit: The reason for our company's conc... |
Now that quantum computers have been out for a while, has RSA been cracked? |
[D-wave systems][1] has released a commercially viable quantum computer. This means; in theory, that all asymmetric encryption algorithms, such as RSA are now useless, due to the speed at which quantum computers can factor.
Has RSA been cracked yet? If not; why hasn't it?
The reason for our company's concern i... |
Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my friend to know any element of my set and he don't want me to know his. But we want to know how many elements are in the int... |
How about this idea:
- We'll assume that the integers in the sets are all in the range [2, N] for some agreed-upon N.
(why is the start of the range '2'? Because the below protocol doesn't work with the element 1; if the set has a different range, it is straight-forward to have a public mapping between the val... |
The [Alternating Step Generator][1] (ASG) is a PRNG combining 3 LFSRs. Output of the ASG is the XOR of the output of two clock-gated LFSRs. At each step, a single one of these LFSRs is clocked, according to the output of the control LFSR.
The best (AFAIK) claimed attack on the ASG is [Reduced Complexity Attacks on t... |
Proof that Alternating Step Generator and modifed ASG' have equivalent security? |
Okay, I had a look at your source [[12][1]], e.g. *ON EDIT DISTANCE ATTACK TO ALTERNATING STEP GENERATOR*.
The original ASG defines the key stream Z = {z_i} from three shift registers X = {x_i}, Y = {y_i} and C = {c_i} via these steps:
> 1. Initially, l = 0, t = 1.
> 2. If ct = 1, then l = l + 1;
> 3. Output z_... |
Say some data is to be encrypted using the hash of a password as a key. From the beginning it becomes obvious that one could brute-force the password and get much better results than brute-forcing the actual key. In this scenario, a massive cracking array can recovery relatively strong passwords in a matter of days.
... |
Is public-key cryptography the only option in this scenario? |
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