instruction stringlengths 15 30k |
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Fully homomorphic encryption can compute any function. Therefore, if a computer can perform a task on plaintexts, then fully homomorphic encryption could theoretically be used to perform that exact same task on ciphertexts.
It seems like your doubt stems from an equality check. From your example, you seem to believe... |
Fully homomorphic encryption can **theoretically**<sup>1</sup> compute any function. Therefore, if a computer can perform a task on plaintexts, then fully homomorphic encryption could theoretically be used to perform that exact same task on ciphertexts.
It seems like your doubt stems from an equality check. From you... |
Right now I'm using a simple padding system that takes the plaintext, hashes it with sha512, and appends x bytes of the hash as padding where x is the delta between the plaintext and nearest blocksize multiple.
Is this considered a secure method of padding the message? I am also authenticating the encrypted data usi... |
Can padding length, and thus plaintext length, be considered public information when using aes-cbc? |
This is how the Pedersen commitment seems to work:
Let $p$ and $q$ be large primes such that $q \mid (p-1)$, let $g$ be a generator of the order-$q$ subgroup of $Z_p^{\star}$. Let $a$ be a random secret from $Z_q$, and $h=g^a \bmod p$.
The values $p$, $q$, $g$ and $h$ are public, while $a$ is secret.
To **comm... |
Is there any research about cryptography on nondeterministic Turing machines? |
I read a wiki page about [Camellia cipher][1] and know that it is a block cipher that can use 128-bit, 192-bit or 256-bit keys. But I cant find any information about if its a symmetric cipher (uses one key for both encryption and decryption) or asymmetric cipher (uses different key for encryption and different key for ... |
Camellia cipher - is it symmetric or asymmetric cipher? |
I am just wondering what is the most common, or most used, block cipher mode used that goes with CTS?
Is it *“ECB”* or *“CBC”*? |
PGP/GPG can used to sign text, others use public key to verify them. So one could say, that these cryptographic algorithms deal with space.
Are there any algorithms that can deal with time? E.g. I sign a document at `2011-12-31 23:59:59`, others can verify this document is really, truly signed at `2011-12-31 23:59:5... |
PGP/GPG can used to sign text, others use public key to verify them. So one could say, that these cryptographic algorithms deal with space.
Are there any algorithms that can deal with time? E.g. I sign a document at `2011-12-31 23:59:59`, others can verify this document is really, truly signed at `2011-12-31 23:59:5... |
Let me know a **cryptographic symmetric stream cipher system** with only two functions say `S()` and `P()` and it should satisfy the following conditions:
1. There will be two independent computers say M1 and M2 (no connection exists between them) and only one function should be stored in a machine. For example: Fun... |
Let me know a **cryptographic symmetric stream cipher system** with only two functions say `S()` and `P()` and it should satisfy the following conditions:
1. There will be two independent computers say M1 and M2 (no connection exists between them) and only one function should be stored in a machine.
For example... |
Actually, that wikipedia article you mention in your question already answers your question:
> It is moderately common for companies and sometimes even standards bodies as in the case of the CSS encryption on DVDs – to keep the inner workings of a system secret. Some argue this "security by obscurity" makes the pro... |
From what I've been reading, Keccak's round function is reversible. That's pretty obvious for the *rho*, *pi* and *iota* transforms. For *chi* to be reversible, `x`'s range has to be odd — but that's alright since Keccak's `x` has a range of `5`. Yet, what criteria make the theta step reversible?
Checking some small... |
What criteria make the theta step of Keccak's round function reversible? |
From what I've been reading, Keccak's round function is reversible. That's pretty obvious for the *rho*, *pi* and *iota* transforms. For *chi* to be reversible, `x`'s range has to be odd — but that's alright since Keccak's `x` has a range of `5`. Yet, **what criteria make the *theta* step reversible?**
Checking some... |
From what I've been reading, Keccak's round function is reversible. That's pretty obvious for the $\rho$, $\pi$ and $\iota$ transforms. For $\chi$ to be reversible, $x$'s range has to be odd — but that's alright since Keccak's $x$ has a range of `5`. Yet, **what criteria make the *theta* step reversible?**
Checking ... |
What I am picturing is something like this:
Block A: `Hello, how are you today?`
Block B: `The weather reminds me of summer.`
I encode this, giving me two keys and a resulting encrypted block e.g.
AP: `2da93742a7340ad12372aff`
BP: `023cd97d40293d7c4027947`
DATA: `ksdjhfksdjhf0wddfg74059r7sdhdkfh`
W... |
Let's say that Alice and Bob complete a key exchange and then Alice uses that key (k1) to encrypt a 256-bit key (kaes1) and sends it to Bob.
From there, Alice and Bob exchange a lot of messages back and forth, using AES-256 to symmetrically encrypt the data with the key kaes1.
Then, Charlie comes along and wants ... |
What security flaw exists, if any, in the solution of this non-encrypted authentication scenario?
An unencrypted message passes one-way from computer A to B. Its transmission is viewable by the public. The message does **not** need to be kept secret. Both A & B have already securely exchanged any needed keys. A ... |
What security flaw exists in MAC authentication scenario? |
What security flaw exists (if any) in the solution of this non-encrypted authentication scenario?
An unencrypted message passes one-way from computer *A* to *B*. Its transmission is viewable by the public. The message does **not** need to be kept secret. Both *A* & *B* have already securely exchanged any needed keys... |
What security flaw exists (if any) in the solution of this non-encrypted authentication scenario?
An unencrypted message passes one-way from computer *A* to *B*. Its transmission is viewable by the public. The message does **not** need to be kept secret. Both *A* & *B* have already securely exchanged any needed keys... |
What I am picturing is something like this:
Block A: *"Hello, how are you today?"*
Block B: *"The weather reminds me of summer."*
I encode this, giving me two keys and a resulting encrypted block e.g.
AP: 2da93742a7340ad12372aff
BP: 023cd97d40293d7c4027947
DATA: ksdjhfksdjhf0wddfg74059r7sdhdkf... |
Let's say that Alice and Bob complete a key exchange and then Alice uses that key `k1` to encrypt a 256-bit key `kaes1` and sends it to Bob. From there, Alice and Bob exchange a lot of messages back and forth, using AES-256 to symmetrically encrypt the data with the key `kaes1`.
Then, Charlie comes along and wants t... |
You basically ask the following question: Is there a weakness anywhere if I encrypt the same message independently with 2 different keys? To answer this, please consider the following:<br><br>
1. The cipher text coming from a perfect encryption algorithm is indistinguishable from random data. <br>
2. Practical encry... |
Fully homomorphic encryption can **theoretically**<sup>1</sup> compute any function. Therefore, if a computer can perform a task on plaintexts, then fully homomorphic encryption could theoretically be used to perform that exact same task on ciphertexts.
It seems like your doubt stems from an equality check. From you... |
What security flaw exists (if any) in the solution of this non-encrypted authentication scenario?
An unencrypted message passes one-way from computer *A* to *B*. Its transmission is viewable by the public. The message does **not** need to be kept secret. Both *A* & *B* have already securely exchanged any needed keys... |
You basically ask the following question: Is there a weakness anywhere if I encrypt the same message independently with 2 different keys? To answer this, please consider the following:
1. The cipher text coming from a perfect encryption algorithm is indistinguishable from random data.
2. Practical encryption algor... |
I was reading http://crypto.stackexchange.com/questions/3645/how-is-ciphercloud-doing-homomorphic-encryption and was wondering:
Is there a technically feasible way for companies like CipherCloud to use homomorphic encryption (HE) while preserving full functionality in a third party SaaS app (e.g. Salesforce)? Furthe... |
>Is there a technically feasible way for companies like CipherCloud to use homomorphic encryption (HE) while preserving full functionality in a third party SaaS app (e.g. Salesforce)?
Fully homomorphic encryption can **theoretically**<sup>1</sup> compute any function. Therefore, if a computer can perform a task on ... |
The Schnorr protocol is a 3-steps proof of knowledge of a discrete logarithm, whose interactive version works as follows.
Let $p$ and $q$ be two public primes, such that $q \; | \; (p-1)$, and let $G$ be a cyclic group of order $q$, having generator $g$. The prover $P$ wants to prove knowledge of $x=\log_g(y)$ to a... |
Could this be a valid variation of the Schnorr protocol? |
A friend shared with me the following link: [Encryption is less secure than we thought][1]
I'm not a security expert and could understand great part the article, except the section about noise, but what I haven't figured out is the impact of that research in real life.
What does it mean for mortals, in practice?
... |
MIT says: mathematical theory behind encryption is wrong. What are the consequences? |
>Is there a technically feasible way for companies like CipherCloud to use homomorphic encryption (HE) while preserving full functionality in a third party SaaS app (e.g. Salesforce)?
Fully homomorphic encryption can **theoretically**<sup>1</sup> compute any function. Therefore, if a computer can perform a task on ... |
The Schnorr protocol is a 3-steps proof of knowledge of a discrete logarithm, whose interactive version works as follows.
Let $p$ and $q$ be two public primes, such that $q \mid (p-1)$, and let $G$ be a cyclic group of order $q$, having generator $g$. The prover $P$ wants to prove knowledge of $x=\log_g(y)$ to a ve... |
The Schnorr protocol is a 3-steps proof of knowledge of a discrete logarithm, whose interactive version works as follows.
Let $p$ and $q$ be two public primes, such that $q \mid (p-1)$, and let $G$ be a cyclic subgroup of $\mathbb Z^\times_p$ of order $q$ (i.e. a [Schnorr group](http://en.wikipedia.org/wiki/Schnorr... |
I have a ciphertext encoded with One Time Pad. I do not know the key. How can I find the possible keys which when decoded, will result in a meaningful plain text? |
As noted by Perseids in a comment to [this answer][1], the formula $s = r + c + x$ would allow an adversary (who has completed the protocol once in the role as verifier with $P$ and already got one valid triplet $t_1,c_1,s_1$) to compute responses to any arbitrary challenge, simply using the formulas $t_2 = t_1$, $s_2 ... |
As noted by Perseids in a comment to [this answer][1], the formula $s = r + c + x$ would allow an adversary (who has completed the protocol once in the role as verifier with $P$ and already got one valid triplet $t_1,c_1,s_1$) to compute responses to any arbitrary challenge, simply using the formulas $t_2 = t_1$, $s_2 ... |
I am about to go study for my masters in machine learning, data mining and high performance computing, but have recently become very interested in cryptography after taking Dan Boneh's Cryptography course on coursera.com.
I was wondering if there are any practical applications for machine learning in cryptography? ... |
Any practical uses of machine learning for cryptography? |
Does there exist a voting scheme where voters cast private encrypted votes that automatically become public only AFTER the threshold number of votes is cast? Ie this needs to be done without a central authority that is trusted to hold keys.
I dont need it to be receipt-free, I just want it to be authority free and ... |
I am currently doing some research on universally verifiable mixnets, but it seems to me that there are too few papers about them after 2006 or so and most of them come from the team of Douglas Winkstrom.
Is this correct?
Can anybody point me to current references about mixnets and their use in voting protocols?
|
Can we use a threshold scheme to construct a (yes/no)-election protocol, such that every voter can give a positive or negative vote or he can abstain, and such that only the result of the election is revealed, but the number of positives, negatives and abstains stays secret?
Are there some ways to do this without a ... |
How to construct a yes/no election protocol, such that only the result is revealed? |
> Bob and Alice each have a bit string they want to keep private. They each want to know what the bitwise AND of their two strings would be without telling the other or anyone else listening to their exchange their actual bit strings... how can they do this? Keep in mind that even once they both hold the AND of their t... |
Does there exist a voting scheme where voters cast private encrypted votes that automatically become public only ***after*** the threshold number of votes is cast?
It needs to be done without a central authority that is trusted to hold keys. I don't need it to be receipt-free, I just want it to be authority free and... |
I am trying to look into a relation between the following three problems which are widely used to build public crypto systems
-Discrete log
-Elliptic Curve Discrete log
-Integer Factorization
The type of questions I am trying to answer is, can one of these problems be reduced to another? such that, an efficient s... |
Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext? |
I am making the following assumptions regarding your requirements:
1. The number of participants is low enough, for it to be feasible for each participant to open a reliable, authenticated and confidential communication channel to each other participant.
2. The vote of each individual participant is only meant ... |
A meet-in-the-middle (! NOT man-in-the-middle !) attack on textbook-RSA was presented to me. The only requirements for it was that the attacker gets the output of RSA and the public key, and that the message be the product of 2 numbers of the same magnitude, which apparently happens with 20% probability. (ie: only eave... |
Textbook-RSA meet-in-the-middle attack against other RSA based schemes? |
A *“meet-in-the-middle”* (**not** *“man-in-the-middle”*!) attack on textbook-RSA was presented to me. The only requirements for it was that the attacker gets the output of RSA and the public key, and that the message be the product of 2 numbers of the same magnitude, which apparently happens with 20% probability. (ie: ... |
You can probably prove the security against your game from the security in the IND-ID-CCA game of Boneh and Franklin (see http://courses.cs.vt.edu/cs6204/Privacy-Security/Papers/Crypto/IBE-Weil-Pairing.pdf). The idea is to create an adversary $\mathcal{B}$ against IND-ID-CCA from your adversary $\mathcal{A}$. Essential... |
You can probably prove the security against your game from the security in the IND-ID-CCA game of Boneh and Franklin (see http://courses.cs.vt.edu/cs6204/Privacy-Security/Papers/Crypto/IBE-Weil-Pairing.pdf). The idea is to create an adversary $\mathcal{B}$ against IND-ID-CCA from your adversary $\mathcal{A}$. Essential... |
I was checking the RFC's after wondering for some time. In RFC 4226 (HTOP), it states on the appendix:
> A simple enhancement in terms of security would be to extract more
> digits from the HMAC-SHA-1 value.
>
> For instance, calculating the HOTP value modulo 10^8 to build an 8-
> digit HOTP value would reduce ... |
Why are HOTP and TOTP implementations all using 6 digits and not more? |
A *“meet-in-the-middle”* (**not** *“man-in-the-middle”*!) attack on textbook-RSA was presented to me. The only requirements for it was that the attacker gets the output of RSA and the public key, and that the message be the product of 2 numbers of the same magnitude, which apparently happens with 20% probability. (ie: ... |
Why stop at 8 digits? 10 digits will be even more secure. Or 12. The output of the HOTP algorithm is 160 bits so you could go all the way to about 48 digits.
Bottom line: 6 digits is secure **enough** for most applications and that is all that counts. Any more is inconvenient for the user and slightly more expensive... |
Suppose one has an ideal block cipher
<br>
$E \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \: \to \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \;\;\;$ and $\;\;\; D \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.0... |
Is there a security proof for the Triple-DES construction in the ideal cipher model? |
I was checking the RFC's after wondering for some time. In [RFC 4226 - HOTP: An HMAC-Based One-Time Password Algorithm](http://tools.ietf.org/html/rfc4226), it states on the appendix:
> A simple enhancement in terms of security would be to extract more
> digits from the HMAC-SHA-1 value.
>
> For instance, calcul... |
I'd like to generate a private elliptic curve key from user input like pass phrase. Is the best way to do this with a key derivation function like PBKDF2? Is there a better way? |
Generate Elliptic Curve Private Key from User Passphrase? |
Suppose one has an ideal block cipher
$E \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \: \to \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \;\;\;$ and $\;\;\; D \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in... |
Suppose one has an ideal block cipher
$E \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \: \to \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^w \;\;\;$ and $\;\;\; D \: : \: \{0,\hspace{-0.04 in}1\hspace{-0.03 in}\}^k \times \{0,\hspace{-0.04 in}1\hspace{-0.03 in... |
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 ... |
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 qu... |
OMAC/CMAC only specifies constants for 64-bit (0x1B) and 128-bit (0x87) block size. I would like to know how to get constants for other block sizes.
http://en.wikipedia.org/wiki/CMAC says it "is the non-leading coefficients of the lexicographically first irreducible degree-b binary polynomial with the minimal number... |
In the [Rabin cryptosystem](http://en.wikipedia.org/wiki/Rabin_cryptosystem), decrypting a message can produce four different outputs, of which only one is the correct plaintext. How can one know which of the outputs is the correct one? |
Well, whether there's a better way depends on what you mean by 'better'; that is, what are you actual requirements? On the other hand, depending on what you are doing with the EC key, it may be that the overall design your assuming (map a passphrase to an EC private key) is itself unsuitable (and the actual function y... |
OMAC/CMAC only specifies constants for 64-bit `(0x1B)` and 128-bit `(0x87)` block size. I would like to know how to get constants for other block sizes.
http://en.wikipedia.org/wiki/CMAC says it *"is the non-leading coefficients of the lexicographically first irreducible degree-b binary polynomial with the minimal n... |
All of the SHA-3 finalists discussed speed and efficiency of a hardware implementation of their algorithms. How relevant are such details?
I'm curious about who commercializes hardware that implements specific hashing algorithms, and who uses them. In what situations is this worth a dedicated chip, vs. just running ... |
How relevant are hardware implementations of crypto algorithms? |
For AES CBC i would suggest you stick to the standards.
The [PKCS7][1] padding scheme is pretty easy to implement and has been tested extensively now that its been out in the public for a while. I had implemented PKCS7 padding for my AES CBC cipher a few weeks ago and you can see the code [here][2] if it helps.
... |
Have you considered [Stream Ciphers][1]? They seem better suited for your problem.
[1]: http://en.wikipedia.org/wiki/Stream_cipher |
I'd like to generate a private elliptic curve key from user input like pass phrase. Is the best way to do this with a key derivation function like PBKDF2? Is there a better way?
**Edit (based upon @poncho's questions)**
To be specific, this is for a Bitcoin ECC private key. It seems to me that if a user picks a p... |
Assume for the sake of the question that I have two variable-length bit strings, each with 128 bit cryptographic randomness, and I want to extract two 128 bit keys via HKDF-SHA256.
Which alternative is better (if any), and why?
1. Use a single HKDF-extract on the concatenation of the two strings, and two HKDF-exp... |
Is CBC with [Ciphertext Stealing](https://en.wikipedia.org/wiki/Ciphertext_stealing) (CTS) considerably weaker than CBC with padding such as PKCS7?
I would imagine the most common situation where CTS is necessary would be due to some size constraint of an existing system, and redesign of the system is inconvenient. ... |
I created my PGP key in 2000. I’ve revoked the older, weaker subkeys in favor of a 4096-bit RSA one, but the primary key is 1024-bit DSA. I read [on Wikipedia](https://en.wikipedia.org/wiki/Digital_Signature_Algorithm#Parameter_generation) that “[NIST 800-57](http://csrc.nist.gov/publications/nistpubs/800-57/sp800-57-P... |
Is a 1024-bit DSA key considered safe? |
**Summary.** The short answer is: Cryptography would be insecure. Any encryption you can do with a non-deterministic algorithm, can be broken (in approximately the same running time) by another non-deterministic algorithm.
Non-determinism is *extremely* powerful. If you give everyone access to non-determinism, the... |
**Summary.** The short answer is: Cryptography would be insecure. Any encryption you can do with a non-deterministic algorithm, can be broken (in approximately the same running time) by another non-deterministic algorithm.
Non-determinism is *extremely* powerful. If you give everyone access to non-determinism, the... |
**Summary.** The short answer is: Cryptography would be insecure. Any encryption you can do with a non-deterministic algorithm, can be broken (in approximately the same running time) by another non-deterministic algorithm.
Non-determinism is *extremely* powerful. If you give everyone access to non-determinism, the... |
I created my PGP key in 2000. I’ve revoked the older, weaker sub-keys in favor of a 4096-bit RSA one, but the primary key is 1024-bit DSA. I read [on Wikipedia](https://en.wikipedia.org/wiki/Digital_Signature_Algorithm#Parameter_generation) that…
> [NIST 800-57](http://csrc.nist.gov/publications/nistpubs/800-57/sp8... |
Is CBC with [Ciphertext Stealing](https://en.wikipedia.org/wiki/Ciphertext_stealing) (CTS) considerably weaker than CBC with padding such as PKCS7?
I would imagine the most common situation where CTS is necessary would be due to some size constraint of an existing system, and redesign of the system is inconvenient. ... |
How could the following scheme be made more resilient to attacks capable of utilizing massive amounts of resources?
*Assume all random values are cryptographically secure.
Key derivation: scrypt using a random 16 byte nonce. The work factor is 1048576 which takes a GB of memory and ~3 seconds to compute on a 2500... |
How resilient to attackers with extreme resources available is this encryption method? |
How could the following scheme be made more resilient to attacks capable of utilizing massive amounts of resources?
*Assume all random values are cryptographically secure.*
**Key derivation:** scrypt using a random 16 byte nonce. The work factor is 1048576 which takes a GB of memory and ~3 seconds to compute on a... |
**Summary.** The short answer is: Cryptography would be insecure. Any encryption you can do with a non-deterministic algorithm, can be broken (in approximately the same running time) by another non-deterministic algorithm.
Non-determinism is *extremely* powerful. If you give everyone access to non-determinism, the... |
In a hypothetical discussion we ended up with a concrete question I'd like to find the answer to:
If you try to brute force an RSA encryption, but the original vale which was encrypted was just random binary data, can you ever be sure you found the correct key? In other words: What are the success criteria for RSA b... |
Brute force attack on RSA - success criteria? |
All looks pretty secure except for your auth key derivation. You should use a better key derivation method like [HKDF][1] instead of just SHA-512.
I don't think your random nonce is doing anything in this scenario - an attacker who wants to brute-force a weak password wouldn't be slowed down by a nonce transmitted i... |
All looks pretty secure except for your auth key derivation. You should use a better key derivation method like [HKDF][1] instead of just SHA-512.
I don't think your random nonce is doing anything in this scenario - an attacker who wants to brute-force a weak password wouldn't be slowed down by a nonce transmitted i... |
Well, typically for RSA, we have the public key. That makes the verification process easy:
- If you're trying to guess the private key (factoring or equivilent), that's easy; you just verify the factorization; "does the two primes we get, multiplied together, give us the modulus in the public key?"
- If you're t... |
All looks pretty secure except for your auth key derivation. You should use a better key derivation method like [HKDF][1] instead of just SHA-512.
I don't think your random nonce is doing anything in this scenario - an attacker who wants to brute-force a weak password wouldn't be slowed down by a nonce transmitted i... |
I'm trying to understand the math outlined in [this paper](http://www.withouthat.org/~sid/me/wp-content/uploads/2008/09/document.pdf) on a RSA signature forgery attack. I understand it except for one aspect of how the cube root (that makes the forged signature) is computed.
On page 8, it's shown that this expression... |
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