instruction stringlengths 15 30k |
|---|
Diffie-Hellman: *assumed* largest prime factor of order of $g$? |
I have two secret values L1, L2, and two Pedersen commitments C1 = C(L1), C2=C(L2). The commitments C1, C2 are public. Given a challenge c, I want to output d = c*L1+L2 and prove in zero-knowledge that d is formed correctly. What should the zero-knowledge proof look like? |
> I've read in several places that somehow the largest prime factor $q$ of $|g|$ (order of $g$) is assumed to be large enough without actually knowing $q$. How do they do that?
Actually, both references talk about the behavior of the TLS client when negotiating a DHE-based ciphersuite. The server proposes $p$ and $... |
When an embedded device needs asymmetric crypto to _encrypt_, (e.g. measurements it makes) or _check authenticity_ (e.g. of commands or firmware updates it receives), there is no need for a private key or key generation in the device, and nothing beats [RSA][1] and [Rabin][2] on simplicity and speed (for RSA: with $e=3... |
Is there an encryption scheme that provides efficient homomorphic OR operations at the ciphertext space? Of course any fully homomorphic encryption can be used but I do not require or want additional homomorphic operations. |
ANSI x.923 padding and the padding used within PKCS#7 are functionally equivalent. The last byte of the padding stream is the length of the padding stream. The difference is the value of the other bytes, which are all 0x00 in ANSI, and all the identical to the last byte in PKCS#7.
f4 93 d6.00 00 00 00 00 00 00 0... |
When I sign a message (which has potentialy low entropy) using a private key and i send it without the original message, can the original message be retrieved from the Signaturen?
I want to prove over an unsecure channel that i know a secret password without revealing it.
Could a man in the middle who does not know t... |
Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round).
The advantage of heterogeneous UFNs is, that its internal properties change each round, making it more difficult to find specific characteristics which pro... |
> When I sign a message (which has potentialy low entropy) using a
> private key and i send it without the original message, can the
> original message be retrieved from the Signaturen?
It depends. If you use a signature scheme with appendix it will be impossible to recover the message using other ways than brute-... |
When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)?
I want to prove – over an unsecure channel – that I know a secret password without revealing it.
Could a man-in-the-middle (who does... |
Can the original message be retrieved from a public/private key signature? |
> When I sign a message (which has potentialy low entropy) using a
> private key and i send it without the original message, can the
> original message be retrieved from the Signaturen?
It depends.<br>
If you use a signature scheme with appendix it will be impossible to recover the message using other ways than b... |
I read that the S-boxes introduce the much needed nonlinear behavior to DES. Can someone give me a lay mans explanation of why the effect of the S-boxes is said to be non-linear? |
I've been searching (unsuccessfully) online for a high-level overview of how LUKS/cryptsetup disk encryption works. I am reading through the cryptsetup source code to try to understand what is going on "under the hood", but my limited knowledge of C and crypto code in particular is making it difficult to really underst... |
I've been searching (unsuccessfully) online for a high-level overview of how LUKS/cryptsetup disk encryption works. I am reading through the cryptsetup source code to try to understand what is going on "under the hood", but my limited knowledge of C (and crypto code in particular) is making it difficult to understand h... |
I'm working on a P2P communications and chat framework, and am looking for a quantum-secure asymmetric key exchange algorithm which I can use to perform a key exchange of an AES-256 bit key. This is an open-source project which will be licensed under GPL-3.0, and I have considered using NTRU. However; I have discovered... |
I have two secret values $L_1$, $L_2$, and two Pedersen commitments $C_1 = C(L_1)$, $C_2=C(L_2)$. The commitments $C_1$, $C_2$ are public. Given a challenge $c$, I want to output $d = c*L_1+L_2$ and prove in zero-knowledge that $d$ is formed correctly. What should the zero-knowledge proof look like? |
I have a question , if I have the key, the ciphertext and text that are encrypted , then how can you guess Initialisation Vector ?
I searched but did not find the answer to my question
Thank you in advance |
If I have the key, the ciphertext under AES-CBC and the plaintext, then how can I guess the initialisation vector?
|
> When I sign a message (which has potentialy low entropy) using a
> private key and i send it without the original message, can the
> original message be retrieved from the Signaturen?
It depends.<br>
If you use a signature scheme with appendix it will be impossible to recover the message using other ways than b... |
I've been searching (unsuccessfully) online for a high-level overview of how LUKS/cryptsetup disk encryption works. I am reading through the cryptsetup source code to try to understand what is going on "under the hood", but my limited knowledge of C (and crypto code in particular) is making it difficult to understand h... |
I've read in several places:
- http://crypto.stackexchange.com/questions/10494/some-of-my-confusions-about-ddh-assumption - comment by Thomas Pornin on his own post
- [Is there a key length definition for DH or DHE?][1] - the answer by Tom Leek
that somehow the largest prime factor $q$ of $|g|$ (order of $g$... |
> My question is how many more rounds would they have to use to keep this security margin on AES (other then adding a hash to AES 256 key schedule)?
When AES was standardized, the [best known attack][1] (pdf, page 19) in terms of rounds broken was a related key attack that broke 9/14 rounds of AES-256. The best atta... |
In his blog [Schneier discusses][1] that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of related subkey attack".
My question is how many more rounds would they have to use to keep this security margin on AES... |
What is the currently most efficient (interactive) zero knowledge proof/argument for the subset sum problem?
The most recent relevant paper I have found is https://eprint.iacr.org/2012/548.pdf, but it considers NIZKs and is quite involved.
I assume there are more efficient interactive protocols? |
I'm wondering why we use encrypt-decrypt-encrypt (EDE) sequence in 3DES (also known as DES-EDE, TDES or TDEA) with three keys instead of three times encryption (EEE) with three different keys?
|
Assume a hash function $H:\left\{0,1\right\}^*\to G$ where $G$ is a group and assume that finding an inverse in $G$ is easy.
How can a preimage efficiently be found using the fact that $H(M_1\cdot M_2)=H(M_1)\cdot H(M_2)$?
I've tried playing around with the group properties but I haven't gotten very far. Any dire... |
If the hash of the multiplication is equal to the multiplication of the hash, how can this be used to leverage an attack? |
Assume a hash function $H:\left\{0,1\right\}^*\to G$ where $G$ is a group and assume that finding an inverse in $G$ is easy.
How can a preimage efficiently be found using the fact that $H(M_1\cdot M_2)=H(M_1)\cdot H(M_2)$ for $M_1,M_2\neq0$?
I've tried playing around with the group properties but I haven't gotten... |
Signal vs Telegram in terms of protocols? |
I'm working on a P2P communications and chat framework, and am looking for a quantum-secure asymmetric key exchange algorithm which I can use to perform a key exchange of an AES-256 bit key. This is an open-source project which will be licensed under GPL-3.0, and I have considered using NTRU. However; I have discovered... |
Based on my skimming over [FIPS 180-4][1] it looks like the only difference between SHA512 and SHA512/256 is the initial hash value and the fact that the final output is truncated to 256 bits.
My question is... if you have a library that does sha512 can you transform that to sha512/256? Like maybe there could be so... |
transforming sha512 into sha512/256? |
Is that additive-homomorphic scheme secure? |
Is that simple additive homomorphic scheme secure? |
I'm working on a P2P communications and chat framework, and am looking for a quantum-secure asymmetric key exchange algorithm which I can use to perform a key exchange of an AES-256 bit key. This is an open-source project which will be licensed under GPL-3.0, and I have considered using NTRU. However; I have discovered... |
Based on my skimming over [FIPS 180-4][1] it looks like the only difference between SHA-512 and SHA-512/256 is the initial hash value and the fact that the final output is truncated to 256 bits.
My question is: if you have a library that does SHA-512 can you transform that to SHA-512/256?
Like maybe there could ... |
Transforming SHA-512 into SHA-512/256? |
The definition of Paillier Cryptosystem says that it is a probabilistic asymmetric key algorithm for public key cryptography. Can some body explain why it is called "*probabilistic*"? |
Why is Paillier Cryptosystem called probabilistic? |
I am currently looking into RSA and have some questions. I am interested in theoretical answers, assuming there is infinite time for decryption.
Is it necessary to work out the private-key exponent for decryption? Are there no alternative options?
Can a message encrypted using RSA be decrypted using only the pu... |
I am currently looking into RSA and have some questions. I am interested in theoretical answers, assuming there is infinite time for decryption.
1. Is it necessary to work out the private-key exponent for decryption? Are there no alternative options?
2. Can a message encrypted using RSA be decrypted using only th... |
I am running FindBugs with findsecbugs plugin to scan java code for security issues. I am getting "Cipher With No Integrity" error for a Cipher function implemented with "PBEWithMD5AndDES". The legend says "The ciphertext produced is susceptible to alteration by an adversary. This mean that the cipher provides no way t... |
PBEWithMD5AndDES Cipher does not check for integrity first? |
In [PKCS1's Probabilistic Signature Mode][1] you have the Hash and the MGF Hash. Both appear to be, by default, sha1, with the OpenSSL CLI client, however, I can change it to sha256 with the following:
openssl dgst -sha256 -sigopt rsa_padding_mode:pss -sigopt rsa_pss_saltlen:-1 -out signature.txt -sign privateke... |
I am running FindBugs with findsecbugs plugin to scan java code for security issues. I am getting "Cipher With No Integrity" error for a Cipher function implemented with "PBEWithMD5AndDES". The legend says "The ciphertext produced is susceptible to alteration by an adversary. This mean that the cipher provides no way t... |
Let's take this PHP code. We use libsodium and libsodium-php.
You have `$text`, `$senderPrivateKey`, `$recipientPublicKey` and a `$nonce`. The latter was obviously created like this by just using Sodium:
$nonce = \Sodium\randombytes_buf($size);
Now this is the code which adds PKCS#7 padding:
/* determ... |
Is PKCS#7 padding generated with a pseudo-random-number generator okay? |
> I am interested in theoretical answers, assuming there is infinite time for decryption.
We call such an attacker a 'computationally unbounded adversary'
> 1. Is it necessary to work out the private-key exponent for decryption? Are there no alternative options?
One approach that a computationally unbounded a... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in their public... |
How do I get the equivalent strength of an ECC key? |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in their public... |
I want to implement this credential system (https://eprint.iacr.org/2012/298.pdf). The implementation would involve some zero-knowledge proof and some exponentiation. What is the best library/implementation for me to start with? For some basic group computations like $g^x$, do people usually just come up with their own... |
What are some de facto libraries that people use to implement and evaluate cryptography protocols? |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in their public... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
Signature algorithms with elliptic curves have smaller output sizes compared to RSA for the same level of security.
What about the processing time to generate a signature ?
I've seen figures giving the advantage to RSA. That seems curious.
Leaving aside the implementation aspects, what could justify (in terms ... |
How do RSA and ECDSA differ in signing performance? |
Let's take this PHP code. We use libsodium and libsodium-php.
You have `$text`, `$senderPrivateKey`, `$recipientPublicKey` and a `$nonce`. The latter was obviously created like this by just using Sodium:
$nonce = \Sodium\randombytes_buf($size);
Now this is the code which adds PKCS#7 padding:
/* determ... |
I want to implement this credential system (https://eprint.iacr.org/2012/298.pdf). The implementation would involve some zero-knowledge proof and some exponentiation. What are some of the possible library/implementation for me to start with? For some basic group computations like $g^x$, do people usually just come up w... |
What libraries do people use to implement and evaluate cryptography protocols? |
I want to implement this credential system: [“Anonymous Credentials Light”](https://eprint.iacr.org/2012/298.pdf) (PDF). The implementation would involve some zero-knowledge proof and some exponentiation.
For some basic group computations like $g^x$, do people usually just come up with their own implementation or i... |
Can Elgamal be secure in $\bmod {n^2}$? Meaning instead of using a prime order group to use a group where DCR assumption holds? |
Symmetric encryption algorithms with large IVs and authentication? |
The previous answer has the correct formula for estimating the security level of prime field elliptic curves. However, the table seems to just list the closest Koblitz curve sizes used, as Richie Frame points out.
If you computed the actual security strength of the curves in question, you would not end up with exact... |
I have a 128-bit input-block and the corresponding cipher-block given.
Additionally I have the **last** round-key given.
Is it now possible to get (calculate) the associated cipher-key? I already implemented the normal key-schedule with the rcon to generate the round-keys out of a cipher-key (like on wikipedia: http... |
I'm just trying to wrap my mind around the decision to select the 128-bit Rijndael as the AES cipher, even with 192-bit and 256-bit keys. Even with a 256-bit key, you only get 2^128 possible outputs per 128-bit block, thus kind of rendering the larger key size meaningless (not to mention the weaker key schedules).
W... |
AES - What is the advantage of a 256-bit key with a 128-bit block cipher? |
I've stuck in the above problem:
Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key (e, n), Alice send the ciphertext c to Bob through RSA encryption. Now, Eve can read the ciphertext c, how can Eve decrypt the ciphertext and read plaintext m?
Thank you in advance!! |
RSA Attack, known public key and ciphertext. Can decrypt the message m? |
I've stuck in the above problem:
Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key (217,7), Alice send the ciphertext c=53 to Bob through RSA encryption. Now, Eve can read the ciphertext c, how can Eve decrypt the ciphertext and read plaintext m?
Thank you in advance!! |
I can't comment yet. But this have been already asked. Some examples of answers :
http://crypto.stackexchange.com/questions/31427/theoretical-decryption-of-rsa
http://crypto.stackexchange.com/questions/31433/how-to-decrypt-a-rsa-encrypted-text-file-when-only-public-key-is-known
-------------------------------... |
I'm stuck with this problem: Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key $(217,7)$, Alice send the ciphertext $c=53$ to Bob through RSA encryption. Now, Eve can read the ciphertext $c$, how can Eve decrypt the ciphertext and read plaintext $m$?
|
I can't comment yet. But this have been already asked. Some examples of answers :
http://crypto.stackexchange.com/questions/31427/theoretical-decryption-of-rsa
http://crypto.stackexchange.com/questions/31433/how-to-decrypt-a-rsa-encrypted-text-file-when-only-public-key-is-known
-------------------------------... |
Some examples of answers to similar questions:
- http://crypto.stackexchange.com/questions/31427/theoretical-decryption-of-rsa
- http://crypto.stackexchange.com/questions/31433/how-to-decrypt-a-rsa-encrypted-text-file-when-only-public-key-is-known
**Hint:** $N = 217 =\ ?\ \times\ ?$
In the public key, $e... |
Some examples of answers to similar questions:
- http://crypto.stackexchange.com/questions/31427/theoretical-decryption-of-rsa
- http://crypto.stackexchange.com/questions/31433/how-to-decrypt-a-rsa-encrypted-text-file-when-only-public-key-is-known
**Hint:** $N = 217 =\ ?\ \times\ ?$
In the public key, $e... |
The first remark is that the cryptosystems are used with independent keys. This is important, otherwise it is usually very hard to prove anything.
### The simple solution ###
Now, the simple solution is, as is mentioned in the comment and the linked question, is to *secret-share* your message into two shares and en... |
I know [how to calculate the comparable symmetric strength of an RSA modulus](https://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size): calculate the running time for a field sieve. This is how [NIST gives approximate symmetric sizes for asymmetric algos in their publi... |
So I generated 2 1024 bit prime numbers, I generated N and got a 2048 bit number, does that make my encryption 2048 bit or 1024 bit? |
How do I classify my RSA encryption strength? |
I'm trying to contrast key rotation requirements for asymmetric and symmetric ciphers.
In the case of symmetric ciphers, we have the results such as the so called "CBC Theorem" (stated on pg. 24 of https://crypto.stanford.edu/~dabo/cs255/lectures/PRP-PRF.pdf)
The CBC Theorem states that for a "q - query" CPA attac... |
I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I;ve seen many sample of keys with variable length from 32 characters to 96 characters. what are the ironclad rule for this key?
Thanks |
I'm currently working on a proposal for some secure complete system and one of the things currently lacking is the database security.<br>
However I don't want to roll my own crypto there and thereby need a secure, somewhat reviewed / standard way to cryptographically secure the databases.
I had a look at CryptDB for ... |
What is the best current way to cryptographically secure databases? |
I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters.
What is the rule for this key size? |
What size should the HMAC key be with SHA-256? |
I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters.
What is the ironclad rule for this key size? |
How to find 64 collisions for a hash value? |
I'm currently working on a proposal for some secure complete system and one of the things currently lacking is the database security.<br>
However I don't want to roll my own crypto there and thereby need a secure, somewhat reviewed / standard way to cryptographically secure the databases.
I had a look at CryptDB for ... |
With the upcoming sunsetting of SHA-1 by browsers I was checking signature algorithms for sites I visit. BTW I'm using Firefox 43.0.2 on Windows.
I noticed something interesting when I visited the site Origin Energy site. https //online.originenergy.com.au.
The site's (leaf) certificate uses the SHA-2/SHA-256 sig... |
I have been reviewing the documentation for SHA256 and I believe the last two words (64 bits) for each chunk are not used in creating the message schedule.
From Wikipedia...
Extend the first 16 words into the remaining 48 words w[16..63] of the message schedule array:
for i from 16 to 63
s0 := (w[... |
The first remark is that the cryptosystems are used with independent keys. This is important, otherwise it is usually very hard to prove anything.
### The simple solution ###
Now, the simple solution is, as is mentioned in the comment and the linked question, is to *secret-share* your message into two shares and en... |
With the upcoming sunsetting of SHA-1 by browsers I was checking signature algorithms for sites I visit. I'm using Firefox 43.0.2 on Windows.
I noticed something interesting when I visited the site [Origin Energy site][1]: https://online.originenergy.com.au.
The site's (leaf) certificate uses the SHA-2/SHA-256 si... |
> Are the Certificate Signature Algorithm and signature algorithm in the
> negotiated connection cipher suite used for different purposes?
**Yes they are.**<br>
The hash negotiated in the cipher suite is completely irrelevant to the certificate. The verification of the certificate and the signatures in the TLS han... |
> Are the Certificate Signature Algorithm and signature algorithm in the
> negotiated connection cipher suite used for different purposes?
**Yes they are.**<br>
The hash negotiated in the cipher suite is completely irrelevant to the certificate. The verification of the certificate and the signatures in the TLS han... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.