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Is there any security issue in using scrypt for Key + IV/nonce generating?
**I mean (for example):**
I have data I want to encrypt using password and AES in EAX mode. I want to use scrypt key derivation function to make a key from entered password. So I will need **salt** for scrypt and **nonce** for EAX. Both v... |
Is there any security issue in using scrypt for Key + IV/nonce generating?
**I mean (for example):**
I have data I want to encrypt using password and AES in EAX mode. I want to use scrypt key derivation function to make a key from entered password. So I will need **salt** for scrypt and **nonce** for EAX. Both v... |
Is there any security issue in using scrypt for Key + IV/nonce generation? In other words, can I safely use only a salt for scrypt and derive the nonce along with the key?
For example:
I have data I want to encrypt using password and AES in EAX mode. I want to use scrypt key derivation function to make a *key* fr... |
I have seen a talk by Rüdiger Weis, where he says that you can combine two symmetric ciphers using XOR. According to him, that has the effect that its sufficient if only one of the ciphers is secure.
How does he do that? **I** have thought of
ciphertext = twofish(message) XOR aes(message)
but I can't see ho... |
I'm working on a secure file storage server. This server allows users to upload and download files based on a "seed". This "seed" is a 128-bit value.
From this 128-bit seed, we run SHA512 to derive a 256-bit key, 128-bit IV and 128-bit file identifier used to find the file on the server. The key and IV are then used... |
Using a truncated hash of a key seems to be a safe way to identify the key (i.e. key fingerprint), but what about truncating a key itself in the case of HMAC-SHA256?
Example:
$ key=`openssl rand 32 -base64`
$ keyId=`echo $key | cut -c 40-43`
$ echo $key
RlBDpvx3pCD/rs2SyeHX0enLOxCP7mEQCB8zvtQhD... |
Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification? |
I'm developing a web app where I wish to use pseudorandom keys for items, perhaps akin to Imgur. I was thinking about how many combinations I need to reduce the chance of someone guessing any random item in the database (by checking the associated URL) to *x*. On the performance side, it would seem to be the same (simi... |
How does the birthday paradox apply to random keys? |
In a typical digital signature scheme in which in order to sign we compute:
1) hash of the message: h(m)
2) resulting hash signed with the private key [h(m)](private key)
If there were a collision on the hash, what an adversary could do?
**Solution (?)**
An adversary can find a different message m2 with... |
In a typical digital signature scheme in which in order to sign we compute:
1. hash of the message: $h(m)$
2. resulting hash signed with the private key $[h(m)](private key)$
If there were a collision on the hash, what an adversary could do?
**Solution (?)**
An adversary can find a different message $m_2$... |
Say we have a public network and lots of peers. Each may need to communicate with another peer.
Would there be any huge security issue to each peer making the the public part of their key openly available across the network?
In this way, any other peer in the system could automatically calculate a secret to ... |
This won't seriously impact the security of the key. HMAC is pretty resilient and changing the last part of the hash won't allow attacks on the a hash such as SHA-256.
Note that you only select 4 characters, of which the last one only encodes 4 bits (as it is at the end). That means you've got a check value the size... |
We implemented a rc4 (ARC4) variant for creating a cryptogaphic stream - question is:
Is this sound?
(I'll give an example for 32 bit variant, though 64 bit/larger is possible)
Algorithm is as follows:
We have an array of integers A (32 bit) and array of 8 bit numbers B.
Perform a round of rc4 to mix the B a... |
RC4 via nonliner mixer -- sound? |
This won't seriously impact the security of the key. HMAC is pretty resilient and changing the last part of the hash won't allow attacks on the a hash such as SHA-256.
Note that you only select 4 characters, of which the last one only encodes 4 bits (as it is at the end). That means you've got a check value the size... |
I know it has been already asked and answered whether [it's possible to generate weak DH parameters][1].
But "recentely" we experienced the [Logjam attack][2], which makes use of the pre-computation capabilities of the GNFS to quickly break many *discrete logarithm problem* (DLP) instances.
Now I know that the ma... |
Is it possible to generate backdoored DH parameters? |
Is there a precise procedure or strategy to follow in order to _prove_ in a **formal** way the (not) collision-resistance of a certain given hash construction? I.e. let $H_1$ and $H_2$ be two hash functions, then define the following construction $H(x) = H_1(x)||H_2(x)$. How could one **formally** prove that such const... |
How to formally prove that a given hash construction is collision resistant or not? |
Some systems, that operate over flaky bearers, need to send signed, encrypted messages that are entirely self contained - i.e. send a single 300 byte UDP rather than have a 10Kb, two-way, certificate conversation over TCP.
Assume the destination has a private key and already knows the source's public key, and the so... |
Is there a standard for public key encrypting and signing short messages? |
Assume I have two data fragments, F1 and F2. I can build sha512 hashes sha512(F1) and sha512(F2), and the hash of the two fragments appended to each other sha512(F1+F2).
My question: Is there any way to combine the two fragment's hashes to compute the hash of their appended version? More precise: Is there an operati... |
> For what kind of "concrete" application should we implement cryptographic algorithms on FPGA? Which secured application require such a huge data processing performance ?
Well, FPGAs are ideal for a wide variety of applications, from high-volume applications to state-of-the-art products.
Imagine you are…
- a ... |
> For what kind of "concrete" application should we implement cryptographic algorithms on FPGA? Which secured application require such a huge data processing performance ?
Well, FPGAs are ideal for a wide variety of applications, from high-volume applications to state-of-the-art products.
Imagine you are…
- a ... |
This page (which won't let me post a comment, sadly!) describes how the origional FHE paper by Craig Gentry describes FHE.
http://windowsontheory.org/2012/05/02/building-the-swiss-army-knife/
(Other references to this stuff can be found on the question: http://crypto.stackexchange.com/questions/27470/are-there-si... |
This page (which won't let me post a comment, sadly!) describes how the origional FHE paper by Craig Gentry describes FHE.
http://windowsontheory.org/2012/05/02/building-the-swiss-army-knife/
(Other references to this stuff can be found on the question: http://crypto.stackexchange.com/questions/27470/are-there-si... |
I'm wondering what the probability of a PRP having numerous keys (say 3 or more) with the same simple idempotent, or near identity, function. For example, does there exist values of $a, b, x_1,$ and $x_2$ where more than two keys, $k$, have the property:
$
AES_k(p) = (x_1 \oplus (a*k) + b) \oplus x_2
$
I can a... |
I'm wondering what the probability of a PRP having numerous keys (say 3 or more) with the same simple idempotent, or near identity, function. For example, does there exist values of $p, a, b, x_1,$ and $x_2$ where more than two keys, $k$, have the property:
$
AES_k(p) = (x_1 \oplus (a*k) + b) \oplus x_2
$
I ca... |
> For what kind of "concrete" application should we implement cryptographic algorithms on FPGA? Which secured application require such a huge data processing performance ?
Well, FPGAs are ideal for a wide variety of applications, from high-volume applications to state-of-the-art products.
Imagine you are…
- a ... |
Assume I have two data fragments: $Frag_1$ and $Frag_2$.
I can build sha512 hashes the usual way with $SHA512(Frag_1)$ and $SHA512(Frag_2)$ and then hash the two fragments appended to each other:
$$SHA512(Frag_1 | Frag_2)$$
My question is, is there any way to combine the hashes of those two fragments so that ... |
[This page](http://windowsontheory.org/2012/05/02/building-the-swiss-army-knife/) (which won't let me post a comment, sadly!) describes how the original FHE paper by Craig Gentry describes FHE.
(Other references to this stuff can be found on [this question](http://crypto.stackexchange.com/questions/27470/are-the... |
> Would there be a minimum ciphertext size that is related to the public key size?
It depends on the algorithms used. An RSA signature, without any bells and whistles, is equal to the key length in size (i.e. 2048 bits for 2048-bit RSA). Likewise raw RSA encryption adds the same. So if you just use both, you add twi... |
Some systems, that operate over flaky bearers, need to send signed, encrypted messages that are entirely self contained - i.e. send a single 300 byte UDP rather than have a 10Kb, two-way, certificate conversation over TCP.
Assume the destination has a private key and already knows the source's public key, and the so... |
> Would there be a minimum ciphertext size that is related to the public key size?
It depends on the algorithms used. An RSA signature, without any bells and whistles, is equal to the key length in size (i.e. 2048 bits for 2048-bit RSA). Likewise raw RSA encryption adds the same. So if you just use both, you add twi... |
I'm trying to use PHP to encrypt files with a public key. I'm using the function [openssl_seal][1] that *"encrypts data by using RC4 with a randomly generated secret key."*
RC4 is considered unsafe so the alternative is to use AES ECB, but it too is generally considered unsafe (AES CBC is sadly not an option).
M... |
I'm trying to use PHP to encrypt files with a public key. I'm using the function [openssl_seal][1] that *"encrypts data by using RC4 with a randomly generated secret key."*
RC4 is considered unsafe so the alternative is to use AES ECB, but it too is generally considered unsafe (AES CBC is sadly not an option).
M... |
When using structured data inside a plaintext (such as gzip headers, xml, etc.) They generate known plaintext which may be useful in cracking the ciphertext. So I had these two ideas on how to make this known structure less useful to attackers while preserving the value to those with valid decryption keys. Firstly if w... |
We implemented a rc4 (ARC4) variant for creating a cryptographic stream - question is:
Is this sound?
(I'll give an example for 32 bit variant, though 64 bit/larger is possible)
Algorithm is as follows:
We have an array of integers A (32 bit) and array of 8 bit numbers B.
Perform a round of rc4 to mix the B ... |
RC4 via nonlinear mixer -- sound? |
Let $H_{1}(x)$, $H_{2}(x)$, ..., $H_{n}(x)$ be a list of $n$ secure one-way hash functions such that for a given input $x$ each $H_{i}(x) \neq H_{j}(x)$ when $i \neq j$. Give one hash function to each of $n$ people. No person should be able to reproduce the output of any other person's hash function.
For any inp... |
Possible to determine equivalence of hash codes from different hashing functions? |
So I was just checking my TLS cipherlist and noticed that there was a 'DSS' / `DSA` / `ECDSA` version of every `RSA` cipher available, except for `DHE-RSA-CHACHA20-POLY1305`.
Why is that? |
Why is there no 'ECDSA' version of 'DHE-RSA-CHACHA20-POLY1305'? |
I would like to be able to "code" images such as [the one seen here on Wikipedia][1].
Is this generally produced with software, or does this require complex programming? Ideally, I would love to be able to batch encrypt images based on settings I pre-defined.
[1]: https://en.wikipedia.org/wiki/Visual_cryptogr... |
How can you produce visual cryptography? |
When using structured data inside a plaintext (such as gzip headers, xml, etc.) they generate known plaintext which may be useful in cracking the ciphertext.
So I had these two ideas on how to make this known structure less useful to attackers while preserving the value to those with valid decryption keys:
First,... |
In SRP-6a, the public key $B$ of the server is normally sent after receiving the public key of the client $A$. Is it okay to send $B$ and $s$ after the client sends its username $I$, but before the client sends $A$? |
Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits).
Also, hash functions that are P-complete have no known parallel algorithm; they must be computed serially which ensures a certain amount of temporal cost in computing them.
Three questions:
1. What is the technic... |
I'm wondering what the probability of a PRP having numerous keys (say 3 or more) with the same simple idempotent, or near identity, function. For example, does there exist values of $p, a, b, x_1,$ and $x_2$ where more than two keys, $k$, have the property:
$
AES_k(p) = (x_1 \oplus (a*k) + b) \oplus x_2
$
I ca... |
I just can't figure out why on earth the $IV$ in Merkle-Damgard **has** to be fixed (that's what the Katz-Lindell book says)? Because even if you choose it randomly from say $\{{0,1}\}^n$ then the resulting construction still remains collision-resistant, or not? |
Why the $IV$ used in Merkle-Damgard has to be fixed to a specific value? |
I'm just learning that US NIST has selected DSA as a digital signature standard. Does the European Union have a similar standard, specifying an algorithm to use when digitally signing messages?
I have been looking this up for some time now, but I fail to find a reasonable answer. |
I recentely asked ["IND-CCA1 RSA padding?"][1] about whether there is a IND-CCA1 secure variant of RSA. The original version of the question also allowed usage of ECC which would allow usage of ElGamal, providing IND-CPA and [somewhat IND-CCA1][2].
Now I have the same setting as in the above question, meaning I need... |
Is there a partially homomorphic quantum secure public key cryptosystem? |
Is there a partially homomorphic quantum secure public key cryptosystem with IND-CCA1 security? |
I am working on a project where I need to implement elliptic curve cryptography, I am struggling from a long time in order to understand the working and the process.
Modular finite field arithmetic, I understood the initial concept, now I am looking at this document from NIST
https://www.nsa.gov/ia/_files/nist-ro... |
I've just noticed that US NIST has accepted DSA as a digital signature standard. Does the European Union have a similar standard, specifying an algorithm to use when digitally signing messages?
I have been looking this up for some time now, but I fail to find a reasonable answer. |
I am working on a project where I need to implement elliptic curve cryptography, I am struggling from a long time in order to understand the working and the process.
Modular finite field arithmetic, I understood the initial concept, now I am looking at this document from NIST
https://www.nsa.gov/ia/_files/nist-ro... |
Is double encryption using AES using different key lengths (128 bit and then 256 bit) vulnerable? |
Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time.
What would be required in terms of entropy and how long would it take? Could it be acheived on a single computer? Would having more computers help?
If the d... |
How feasible would it be to generate 300 million public key pairs in 8 hours? |
Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time.
What would be required in terms of entropy and how long would it take? Could it be acheived on a single computer? How few computers could one get away with?
... |
That sorts of briefly was. DSA, and other algorithms, are approved by [ETSI SR 002 176 V1.1.1 (2003-03) Algorithms and Parameters for Secure Electronic Signatures][1], which is referenced by [CWA 14169:2004 Secure signature-creation devices “EAL 4+”][2], which (in an earlier edition) is referenced by [Commission d... |
That sorts of briefly was. DSA, and other algorithms, are approved by [ETSI SR 002 176 V1.1.1 (2003-03) Algorithms and Parameters for Secure Electronic Signatures][1], which is referenced by [CWA 14169:2004 Secure signature-creation devices “EAL 4+”][2], which (in an earlier edition that it supersedes) is referenc... |
I would also mention that there are many required properties that you want a AKE protocol to satisfy, e.g. authentication, key confirmation, forward secrecy, key freshness, secrecy on the session key.
What you want is allow Alice and Bob to stablish "session keys" for each session of communication. These session key... |
The [Merkle–Damgård hash construction][1] customarily pads the message $M$ to be hashed with a single bit set to 1, a minimal number of bit(s) set to 0, and the representation of the length of the message in binary over some fixed number of bits. The padded message is then formed of a number of blocks $B_i$. The hash i... |
Except if you are picky with updates of references, there is such standard. DSA, RSA, ECDSA-$F_p$, ECDSA-$F_{2^n}$, are approved by [ETSI TS 102 176-1 V2.1.1 (2011-07)][1] (Electronic Signatures and Infrastructures (ESI); Algorithms and Parameters for Secure Electronic Signatures; Part 1: Hash functions ... |
According to the [Barrington's theorem][1], any circuit in NC1 can be converted to a branching program, where the operation is only the composition of permutations. So I wonder whether there is a scheme that can directly encrypt the [two-line notation][2] of permutation, which also enables to do the composition of perm... |
Are there any encryption schemes that enable to permute homomorphically? |
According to the [Barrington's theorem][1], any circuit in NC1 can be converted to a branching program, whose the main operation is the composition of permutations (along with the choosing of permutations according to inputs, which we omit here) . So I wonder whether there is a scheme that can directly encrypt the [two... |
According to the [Barrington's theorem][1], any circuit in NC1 can be converted to a branching program, whose main operation is the composition of permutations (along with the choosing of permutations according to inputs, which we omit here) . So I wonder whether there is a scheme that can directly encrypt the [two-lin... |
Suggested by Ricky Demer in [this post][1], I am reading the paper ["Evaluating Branching Programs on Encrypted Data"][2](TCC 2007), which uses one-round strong OT protocol to implement homomorphic evaluation of branching program (BP) on encrypted data with succinct ciphertext.
As it says on page 6, the natural way ... |
Why an upside down path on the evaluation of branching program on encrypted data? |
Suggested by Ricky Demer in [this post][1], I am reading the paper ["Evaluating Branching Programs on Encrypted Data"][2](TCC 2007), which uses one-round strong OT protocol to implement homomorphic evaluation of branching program (BP) on encrypted data with succinct ciphertext.
As it says on page 6, the natural way ... |
I would also mention that there are many required properties that you want a authenticated key exchange (AKE) protocol to satisfy, e.g. authentication, key confirmation, forward secrecy, key freshness, secrecy on the session key.
What you want is allow Alice and Bob to stablish "session keys" for each session of com... |
Lets say we have a message $m$ that we encrypt with two keys $k_1, k_2$ such that $k_1 \ne k_2$. This will produce two ciphertexts $c_1, c_2$ such that $c_1 = m \oplus k_1, c_2 = m \oplus k_2$.
The attacker managed to get the two ciphertexts and also has the knowledge that both ciphertexts $c_1, c_2$ represent the s... |
I'm looking for an cryptographic algo that allows to encrypt only 8 bit of data for block. Has anyone idea if there is an algo considered secure ? Thanks all |
As usually, we have Alice and Bob.
Suppose Alice wants to send a file F to Bob, ensuring integrity and confidentiality. They share a symmetryc key *Kab* and use AES. (No hash available!).
Alice sends to Bob: *Enc-Kab(F)*
In this simple scheme, are integrity and confidentiality guaranteed?
My answer:
1) C... |
I know that AES 256 bit is far more than enough to secure a file. I just want to know if there are any vulnerabilities or known attacks which can make such this combination less secure "double encryption using AES using different key lengths (first 128 bit and then 256 bit)".
Say, for example, I have a program that... |
As usually, we have Alice and Bob.
Suppose Alice wants to send a file F to Bob, ensuring integrity and confidentiality. They share a symmetryc key *Kab* and use AES. (No hash available!).
Alice sends to Bob: *Enc-Kab(F)*
In this simple scheme, are integrity and confidentiality guaranteed?
My answer:
1) C... |
Does it make sense to have a compression function that uses 64-bit of the message to create an output of 64-bit? |
If data is not multiple of 64 bits, then i Can use padding? I know that it is not secure. But If key is less than 64 bits or more than 64 bits, should I ask user to enter the key again or use padding/truncating?
Any suggestions? |
How can I handle the situation if Key size is less than 64 bits in DES? |
What is the difference between a random oracle and a probabilistic algorithm? |
What is the difference between a random oracle and a probabilistic algorithm? |
I'm just repurposing a question already asked about Cryptolocker for Cryptowall:
"If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use those files to discover the private key?"
There's an answer posted for the case of CryptoLocker, but what about for CryptoWall... |
Knowing pre-encryption data, can we find the private key CryptoWall used? |
I have an OLD work database that seems to have a simple encryption on the PW. I have one users whose pw is `7777` the cipher text is `<<<<` (actual text)
Is it possible to learn any more about the encryption. Ultimately, I'd like to decrypt a few other fields in the DB. I don't know what was used, but it seems very... |
I'm looking for a cryptographic algorithm that allows encrypting only 8 bits of data in a block. Is there any such algorithm that is considered secure?
The reason I'm asking is because I have to encrypt and decrypt the data contained in SPI Flash memory (the BIOS flash), and I need it to be really fast to get the cy... |
In Envelope encryption a symmetric secret key is used to sign the data and then another key is used to encrypt the secret to produce an encrypted secret key. The encrypted messages is packaged with the encrypted secret key and sent to the client/consumer which then decrypted the encrypted secret key to get the secret k... |
Found this report detailing a quantum algorithm for computing isogenies
between supersingular elliptic curves.
http://cacr.uwaterloo.ca/techreports/2014/cacr2014-24.pdf
with the quote "recommendation
to avoid using base curves defined over Fp in De Feo-Jao-Plut type
schemes".
Is it correct then that 'Supers... |
Supersingular Isogeny Key Exchange broken? |
Found this report detailing a quantum algorithm for computing isogenies
between supersingular elliptic curves.
http://cacr.uwaterloo.ca/techreports/2014/cacr2014-24.pdf
with the quote "recommendation
to avoid using base curves defined over Fp in De Feo-Jao-Plut type
schemes".
Is it correct then that 'Supers... |
Found this report detailing a quantum algorithm for computing isogenies
between supersingular elliptic curves.
http://cacr.uwaterloo.ca/techreports/2014/cacr2014-24.pdf
with the quote "recommendation
to avoid using base curves defined over Fp in De Feo-Jao-Plut type
schemes".
Is it correct then that 'Supers... |
Essentially a probabilistic algorithm is simply an algorithm that makes random choices (i.e., takes some random bits). So any algorithm that involves sampling random numbers or the like is a probabilistic algorithm.
A random oracle is a theoretical construct mostly used to analyze cryptographic schemes. It is an ora... |
If the data is not a multiple of 64 bits, then I can use padding. I know that it is not secure. But if the *key* is less than or more than 64 bits, should I ask the user to enter the key again, or should I pad / truncate it?
|
How can I handle the situation if key size is less than 64 bits in DES? |
Although the documents referenced so far are interesting in their own right, the actual relevant (as in "giving a legal value to the signatures") ETSI standard here is [ETSI TS 119 312](http://www.etsi.org/deliver/etsi_ts/119300_119399/119312/01.01.01_60/ts_119312v010101p.pdf).
Note also that the venerable 1999/93/... |
I'm just repurposing [a question already asked about Cryptolocker](http://crypto.stackexchange.com/questions/11254/knowing-pre-encryption-data-can-we-find-the-private-key-cryptolocker-used) for CryptoWall:
> "If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use th... |
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