instruction stringlengths 15 30k |
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The cipher is an triple key polyalphabetic cipher also known as an Quagmire IV by the ACA. An example would be here: [Quagmire IV example and info (pardon the ads)][1]
I posses the IV key and the PT key. The IV key runs vertically and sets the shifts of the lookup alphabets for the ciphertext. The IV key is the leng... |
Sorry. I can't comment so I have to reply and edit.
Thanks for including the data in the statement of the problem. Does the "plaintext key" correspond with the key "SPEARHEAD" in he Quagmite IV exampe and info link you posted? So what is missing is the key corresponding to "DRUMROLL"? |
Your second question was about programmability. This hasn't been directly addressed yet by [Thomas' answer](http://crypto.stackexchange.com/a/1410) or the comments, so I'll focus on that question only. Unfortunately I don't know of a simple primitive that is secure in the random oracle model that requires programmabili... |
Is there any security concerns with building a CSPRNG using a broken hash function like MD5 or SHA1? If this is a concern, what is the technical reason? What would be a better replacement when efficient is a concern? |
Is there a problem with constructing a CSPRNG using MD5 or SHA1? |
Is there any security concerns with building a CSPRNG using a broken hash function like MD5 or SHA1? The design is such that a CRC-like function is used for mixing entropy and MD5 is used as the output function. If this is a security concern, what is the technical reason? What would be a better replacement when effi... |
I've heard again and again that many crypto systems have been broken in the past for one reason or another and that it is best to use one that has been peer reviewed, etc etc. However, I've yet to see a source (website, book) that gives information about these systems. Is there such a thing? |
How does padding in PMAC work? I have been told two stories: Firstly, I have been told that it works similar to CMAC padding, and secondly, I have been told that it does not need padding.
I find the second story very strange as I think one could make an existential forger quite easily. But if PMAC pads like CMAC, th... |
In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it 2^128 possible keys?) and 2048-bit key size for asymmetric encryption (2^2048 possible keys?).
Why do they differ so greatly? It seems like I am missing a very b... |
why is the recommended key size between symmetric and assymetric encryption differs greatly? |
How can I understand the term RSA key normalization? What exactly is done in the process??
Please explain. |
What is RSA key normalization? |
In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key size for asymmetric encryption ($2^{2048}$ possible keys?).
Why do they differ so greatly? It seems like I am missing ... |
Why does the recommended key size between symmetric and assymetric encryption differ greatly? |
Currently, I am making an app that encrypts text, But how can I check whether if it is secured enough or not? |
How to check the strength of an encryption algorithm? |
Is such a crypto-system available? |
**Definition**
${H_1}^{K_1}(X)$ means data $X$ hashed by keyed hashing algorithm $H_1$ with key $K_1$.
**Short question**
Is $H_1^{K_1}(H_2^{K_2}(X))$ equal to $H_2^{K_2}(H_1^{K_1}(X))$?
Is $H_1^{K_1}(H_1^{K_2}(X))$ equal to $H_1^{K_2}(H_1^{K_1}(X))$?
**Long question**
My web application is storing a... |
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as having been picked from a family of functions, rather from the set of all functions). Are there any other? |
What are alternatives to the random oracle model for modelling hash functions? |
There's the common random string model (where hash functions can be modeled as having been picked from a family of functions using public coins). $\:$ There are also "whatever-tractable random oracles", where adversaries also have an oracle that finds a whatever with respect to the random oracle.
<br>
(Usually 'whate... |
In the context of a new largest (mersenne) prime number being found this week -
The [largest known prime number][1] is now `2^57,885,161 − 1`, and it took 5 years to find it since the last largest prime was found.
But we know that various asymmetric encryption algorithms require ridiculously large primes which ar... |
> Of all the numbers between 0 and $2^{25,964,951}-1$ there are 1,622,441 that are prime.
That sentence is plain wrong. There are about 1,622,411 primes below 25,964,951 (See [Wolfram Alpha](http://www.wolframalpha.com/input/?i=number+of+primes+below+25964951I)). I guess they mixed up $2^{25,964,951}$ with $25,964,9... |
> A Mersenne prime is a prime number that can be written in the form $M_p = 2^n-1$, and they’re extremely rare finds. Of all the numbers between 0 and $2^{25,964,951}-1$ there are 1,622,441 that are prime, but only 42 are Mersenne primes.
The second sentence is wrong.
What they meant to say is that there are 1,62... |
> A Mersenne prime is a prime number that can be written in the form $M_p = 2^n-1$, and they’re extremely rare finds. Of all the numbers between 0 and $2^{25,964,951}-1$ there are 1,622,441 that are prime, but only 42 are Mersenne primes.
The second sentence is wrong.
What they meant to say is that there are 1,62... |
> A Mersenne prime is a prime number that can be written in the form $M_p = 2^n-1$, and they’re extremely rare finds. Of all the numbers between 0 and $2^{25,964,951}-1$ there are 1,622,441 that are prime, but only 42 are Mersenne primes.
The second sentence is wrong.
What they meant to say is that there are 1,62... |
i want to generate random number for example from [1..100].
This algorithm which generates random number should work similarly like ("**Linear congruential generator**").
![enter image description here][1]
[1]: https://i.stack.imgur.com/CgabT.png
Here:
c - increment should be something like 98979817
... |
I can't comment yet and have no solution, but I still wanted to post my own analysis and hope it'll get you a bit further. BTW, the site you linked to with the info about Quagmire IV is mine and yes, sorry about the ads! I haven't updated it in many, many years, so I was surprised to see it pop up :)
The first thing... |
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as having been picked from a family of functions). Are there any other? |
> There's the common random string model (where hash functions can be modeled as having been picked from a family of functions using public coins).
There are also "whatever-tractable random oracles", where adversaries also have an oracle that finds a whatever with respect to the random oracle.
<br>
(Usually 'whate... |
I understand there are specifications for public-key fingerprints that use modern hash algorithms like SHA2. What are they? |
> There's the common random string model (where hash functions can be modeled as having been picked from a family of functions using public coins).
There are also "whatever-tractable random oracles", where adversaries also have an oracle that finds a whatever with respect to the random oracle.
<br>
(Usually 'whate... |
> There's the common random string model (where hash functions can be modeled as having been picked from a family of functions using public coins).
There are also "whatever-tractable random oracles", where adversaries also have an oracle that finds a whatever with respect to the random oracle.
<br>
(Usually 'whate... |
I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need.
Consider the use of AES-128 in CTR mode.
Let _M_ be the set of possible plaintexts, for example _M_ can be all the bytes sequences of a length lesser or equal than a specific integer _n_.
Let _K_ be the... |
I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need.
Consider the use of AES-128 in CTR mode.
Let _M_ be the set of possible plaintexts, for example _M_ can be all the bytes sequences of a length lesser or equal than a specific integer _n_.
Let _K_ be the... |
I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need.
Consider the use of AES-128 in CTR mode.
Let _M_ be the set of possible plaintexts, for example _M_ can be all the bytes sequences of a length lesser or equal than a specific integer _n_.
Let _K_ be the... |
I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need.
Consider the use of AES-128 in CTR mode.
Let _M_ be the set of possible plaintexts, for example _M_ can be all the bytes sequences of a length lesser or equal than a specific integer _n_.
Let _K_ be the... |
Does FIPS 140-2 require specific key sizes, or does it have specific requirements for the data?
In other words, if I encrypt a file, how I can check whether it is FIPS-compliant or not? Does only the key need to be checked, or does the encrypted file have to be checked too? If yes, is it possible to elaborate on how t... |
I have a text file that has been processed by the SNOW steganography tool that uses ICE encryption. However, I do not know the key that would enable me to decrypt and retrieve the message hidden.
What are some ways that are proven to have worked that would help me in retrieving the key? |
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as having been picked from a family of functions). Are there any other?
EDIT: http://cstheory.stackexchange.com/question... |
I have a text file that has been processed by the SNOW steganography tool that uses ICE encryption. However, I do not know the key that would enable me to decrypt and retrieve the message hidden.
What tools are available, that are proven to have worked that would help me in retrieving the key?
Edited: instead of... |
What is 'security margin'? |
I'm trying to implement a cryptographically secured storage site (not Mega, or anything similar) and am trying to prevent the user's password from ever touching the server. The password is used to both log in and generate a PBKDF2 key for AES in Javascript, so the plaintext password should never leave the client machin... |
In this context 'security margin' is a measure for how much better we need to get at analyzing a cipher to break it. Such advances in cryptoanalysis require new ideas of how one might attack a cipher. Thus estimating how strong a cipher is, is hard.
Ultimately we can only tell something is broken, after we've broken... |
I'm trying to implement a cryptographically secured storage site (not Mega, or anything similar) and am trying to prevent the user's password from ever touching the server. The password is used to both log in and generate a PBKDF2 key for AES in Javascript, so the plaintext password should never leave the client machin... |
For example, two people want to know who is the older, without disclosing their age. Is there a secure way to do this without a third party involved?
|
Secure way to compare two secret numbers without disclosing them? |
A problem with your proposed solution is that the digest of the password is now "password equivalent". So, what does hashing it before sending it gain you?
That said, I don't think either of your concerns are concerning (or should be concerning). For the first, [see this][1]. If anything, most passwords will have l... |
In this context 'security margin' is a measure for how much better we need to get at analyzing a cipher to break it. Such advances in cryptoanalysis require new ideas of how one might attack a cipher. Thus estimating how strong a cipher is, is hard.
Ultimately we can only tell something is broken, after we've broken... |
Another recent question on security margin included in its answer the discussion of how many rounds are broken so far. What is the definition of a round? |
What are rounds in the context of ciphers? |
I thought of implementing DES modes of operation as a project...But my guide asked to change or to modify the DES algorithm in such a way to overcome drawbacks of DES...So is there any way to do changes?IF so how?and could you please give me idea on how to bring changes in any of 5 modes of DES.please help me...
Thank... |
Is there a name for the property of a cryptographic algorithm that the operations for encryption and decryption are identical, i.e.
$E_k(x) = D_k(x)$ and accordingly $E_k(E_k(x)) = x$?
An example for this would be most stream ciphers; are there any other, possibly block ciphers, with that property?
It seems li... |
if we believe 256bit keys are secure in AES against any brute force attack, is that possible we use a KDF (convert user's weak entered password in truecrypt into a fixed AES key) with too much round and cycle to make a weak password (with All ASCII printable characters) secure as a true binary 256bit random key ? assum... |
There are two forms of entropy here at work. First there is "uncertainty" entropy from the user password which is typically very low (on the order of 20 to 40 bits for most passwords out there). And then, there's "computational" entropy, which is artificially obtained by forcing an attacker to do work to calculate keys... |
Can we replace xor operation in DES algorithn with some other operations ?If so do it work in both encryption and decryption? |
Can we replace xor operation in DES algorithn with some other operations? |
**Background**:
I am trying to get an understanding of using a hash of a `passphrase` as a `secret`.
Example:
sha256("EasyToRememberPassphrase") -> secret.
I am assuming a properly designed hash function used this way above will yield a `secret` with the same or fairly similar entropy as the input `pass... |
Can the hash of one message be used to make it easier to find the hash of a very similar message? |
I am trying to break a package format. I'm stuck with the index data which contain offsets, file sizes and filenames. The index data are about 1 KB and compressed by zlib (no zlib or gzip wrapper), and then XOR encrypted. I know the key length is 8 bytes. Is it possible to decrypt the data? |
I never ever really understood why in all textbooks I used DH is under "public key cryptography" - as far as I can see it is a method to exchange a key to be used with a symmetric cryptographic algorithm, so it falls very naturally in the area of symmetric key cryptography. So where does DH stand in the split between s... |
Why is Diffie Helmann considered in the context of public key cryptography? |
David Kahn in his book "The Codebreakers" wrote about Jefferson's wheel cipher, saying
that "To this day the Navy uses it" (the book was first published in 1967). Are there any historical accounts of successful cryptanalysis of that cipher? |
Any historical accounts of cryptanalysis of Jefferson's wheel cipher? |
While it seems clear that Public Key Cryptography is NP-Hard, I have never heard the same said about AES.
If it is reducible, what does the reduction look like?
If it is not reducible, why do we assume it is secure?
|
Is AES reducible to an NP-Complete Problem? |
In all textbooks I used the Diffie-Hellman key exchange is under "public key cryptography".
As far as I can see it is a method to exchange a key to be used with a symmetric cryptographic algorithm, so it falls very naturally in the area of symmetric key cryptography.
So where does DH stand in the split between sy... |
Why is Diffie-Hellman considered in the context of public key cryptography? |
Can we replace the XOR operation in the DES algorithm with some other operation? If so, does it work for both encryption and decryption? |
Can we replace the XOR operation in DES with some other operation? |
RSA doesn't provide semantic security when used unmodified, and neither does the commonly used PKCS#1 v.1.5 padding scheme for encryption.
Is this a problem for hybrid cryptosystems at all?
My suspicion is that it isn't, since the ciphertext of the RSA encryption should be a random string used as an encryption ke... |
Is semantic security important in a hybrid cryptosystem? |
Is breaking AES NP-hard? Can the security of AES be reduced to a NP-complete problem?
If it is reducible, what does the reduction look like?
If it is not reducible, why do we assume it is secure?
|
Is AES reducible to an NP-complete problem? |
I am trying to break a packet format. I'm stuck with the index data which contain offsets, file sizes and filenames. The index data are about 1 KB and compressed by zlib (no zlib or gzip wrapper), and then XOR encrypted. In other words, the key is concatenated with itself many times to get a keystream of equal length a... |
As a personal project, I want to implement MD5 on an FPGA, but I have some doubts about the specifics of the implementation.
My first source of how the algorithm is implemented was the RFC 1321, where there is a pseudocode that explains that round 1 will be performed the following way:
/* Round 1. */
/* ... |
I am looking for a secure key diversification function to create individual AES keys for a local smart card deployment. The keys need to be derived from a secret master key and the smart card serial number. Key calculation can happen on the host system.
Is it secure and practical to use `PBKDF2(password=master_key, ... |
As a personal project, I want to implement MD5 on an FPGA, but I have some doubts about the specifics of the implementation.
My first source of how the algorithm is implemented was the RFC 1321, where there is a pseudocode that explains that round 1 will be performed the following way:
/* Round 1. */
/* ... |
For the purpose of key diversification (that is, assigning a unique key per device), you probably can, and should, afford a true `master_key`, that is one with plenty of entropy (like, 128 bits or more random bits).
With that caveat, yes, PBKDF2 is appropriate from a purely cryptographic standpoint, and even, as is,... |
For the purpose of key diversification (that is, assigning a unique key per device), you probably can, and should, afford a true `master_key`, that is one with plenty of entropy (like, 128 bits or more random bits).
With that caveat, yes, PBKDF2 is appropriate from a purely cryptographic standpoint, and even, as is,... |
I am looking for a secure key diversification function to create individual AES keys for a local smart card deployment. The keys need to be derived from a secret master key and the smart card serial number. Key calculation can happen on the host system.
Is it secure and practical to use `PBKDF2(password=master_key, ... |
To spell out what the comments are leading you toward...
This sort of encryption scheme is susceptible to a straight-forward [known-plaintext attack][1].
Every byte of the ciphertext will have been encrypted in the format:
$$C_i = P_i \oplus K_{i\ \bmod{\ len(P)}}$$
where $i$ is the byte index within the c... |
Not a complete answer, but since you mentioned "unmodified RSA" I feel it's relevant.
Something stronger than vanilla RSA is necessary, even if it isn't semantic security.
Example: What if you have a public key exponent of 3 and the symmetric key being encrypted is 16 bytes long? Using raw RSA, $m^e$ would be abo... |
To elaborate on what the comments are leading you toward...
This sort of encryption scheme is susceptible to a straight-forward [known-plaintext attack][1].
Every byte of the ciphertext will have been encrypted in the format:
$$C_i = P_i \oplus K_{i\ \bmod{\ len(P)}}$$
where $i$ is the byte index within th... |
I am trying to break a packet format. The package format simply packs several files into one big file. The file contents are plain. But the index data which contain offsets, file sizes and filenames are encrypted. The index data are about 1 KB and compressed by zlib (the DEFLATE algorithm with no zlib or gzip wrapper),... |
Yes, semantic security (IND-CPA) is important, even for public-key cryptosystems and for hybrid cryptosystems.
Let's focus on hybrid cryptosystems, where a message $m$ is encrypted by picking a random symmetric key $k$, encrypting $m$ under $k$ with a symmetric-key algorithm, and also encrypting $k$ using a public-k... |
RSA doesn't provide semantic security when used unmodified, and neither does the commonly used PKCS#1 v.1.5 padding scheme for encryption.
Is this a problem for hybrid cryptosystems at all?
My suspicion is that it isn't, since the plaintext message of the RSA encryption should be a random string used as an encryp... |
In SRP6a B is calculated in B=kv+ g^b, k=3. What is the purpose of included k, and why must be 3? |
Why SRP6a calculation of B included a multiplier k? |
In [SRP6](http://srp.stanford.edu/design.html) $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why must it be $3$? |
For the purpose of key diversification (that is, assigning a unique key per device), you probably can, and should, afford a true `master_key`, that is one with plenty of entropy (like, 128 bits or more random bits). Edit: that's now stated in the question.
With that caveat, yes, PBKDF2 is appropriate from a purely c... |
For the purpose of key diversification (that is, assigning a unique key per device), you probably can, and should, afford a true `master_key`, that is one with plenty of entropy (like, 128 bits or more random bits). Edit: that's now stated in the question.
With that caveat, yes, PBKDF2 is appropriate from a purely c... |
For the purpose of key diversification (that is, assigning a unique key per device), you probably can, and should, afford a true `master_key`, that is one with plenty of entropy (like, 128 bits or more random bits). Edit: that's now stated in the question.
With that caveat, yes, PBKDF2 is appropriate from a purely c... |
Shannon's idea of diffusion is fundamental to cryptography.
Besides being a descriptive idea, is there any work on measuring or expressing it? Saying something like "System A has more diffusion than B" or "The information in bit x is diffused 1/3 into bit y, 1/3 into bit z, and the remaining third among 11 more bits... |
Shannon's idea of diffusion is fundamental to cryptography.
Besides being a descriptive idea, is there any work on measuring or expressing it? Saying something like "System A has more diffusion than B" or "The information in bit x is diffused 1/3 into bit y, 1/3 into bit z, and the remaining third among 11 more bits... |
In [SRP6](http://srp.stanford.edu/design.html) $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$?
(In SRP 6b, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP 6.) |
Why does the SRP6 calculation of B included a multiplier k = 3? |
First off, many block modes of operation require a message to be padded so that its length is evenly divisible by the block size of the cipher. CBC mode (Cipher Block Chaining), for instance, typically pads a message either with an entire block of zeroes if it happens to be exactly divisible by the block size, or with ... |
There are some complexity-theoretic reasons to believe that cryptography *can't* be based on NP-completeness. For one example, see [this paper by Akavia et al](http://people.csail.mit.edu/akavia/AGGM.pdf). Basically it all boils down to the mismatch between average-case hardness required for cryptography, and worst-cas... |
Ever since the SHA-3 competition, I've been wondering if it is possible to create a hash algorithm that is easier to parallelize. The current algorithms all seem to require building a tree of hashes. This has however rather serious drawbacks:
1. as they requires a tree with certain parameters (such as the size of no... |
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