instruction stringlengths 15 30k |
|---|
What are good combinations of public key algorithms or primitives for long term security? |
Are there functions that satisfy the second-preimage resistance property without satisfying the others (preimage and collision resistance) ?
|
Functions that are only second-preimage resistant? |
The Diffie-Hellman on curve25519 is usually calculated using the base point $(9,…)$ which induces a cyclic subgroup of $G:=\{\infty\}\cup(E(F_{p^2})\cap(F_p\times F_p))$ with index 8, i.e. there is a prime $p_1$ such that $|G|=8p_1$ and the order of $(9,…)$ is $p_1$. An attacker does not have to use a multiple of $(9,…... |
The Diffie-Hellman on curve25519 is usually calculated using the base point $(9,…)$ which induces a cyclic subgroup of $G:=\{\infty\}\cup(E(F_{p^2})\cap(F_p\times F_p))$ with index 8, i.e. there is a prime $p_1$ such that $|G|=8p_1$ and the order of $(9,…)$ is $p_1$. An attacker does not have to use a multiple of $(9,…... |
In AES the forward affine tranformation matrix is defined as:
| 1 0 0 0 1 1 1 1 |
| 1 1 0 0 0 1 1 1 |
| 1 1 1 0 0 0 1 1 |
| 1 1 1 1 0 0 0 1 |
| 1 1 1 1 1 0 0 0 |
| 0 1 1 1 1 1 0 0 |
| 0 0 1 1 1 1 1 0 |
| 0 0 0 1 1 1 1 1 |
and the inverse affine transformation matrix is defin... |
How to calculate inverse affine transform in AES from forward affine transform? |
A client identifies itself as a curve25519 public key. The server wants to verify the client owns the associated private key.
Is there a safe and computationally efficient way of doing so? Which approach could be regarded to be “the most recommendable” from a safety point of view, while keeping it computationally ef... |
Safe and computationally efficient way to verify a curve25519 identity? |
A client identifies itself as a curve25519 public key. The server wants to verify the client owns the associated private key. Is there a safe and computationally efficient way of doing so? Which approach could be regarded to be “the most recommendable” from a safety point of view, while keeping it computationally effic... |
A stream cipher, RSA, or whatever you designate by the expression "discrete logarithm system", are **not** "one-way functions". In particular, asymmetric encryption algorithms and digital signature algorithms provide functionality which is not doable (or not with the same usability) with only the "scrambling" technique... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
Trial divisions before Miller-Rabin checks? |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
Take a [McEliece cryptosystem][1] with public generator matrix $G' = S G P$ where $G$ is a generator of a secret code with known fast decoding (not necessarily a Goppa code over $\mathbb{F}_2$), $S$ is random & non-singular and $P$ is a permutation.
Let's say an attacker Eve has a way to find $G$ from $G'$ but not $... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
I've just watched a video on the [TLS protocol](https://class.coursera.org/crypto-preview/lecture/37) and learnt that it uses unidirectional keys (meaning keys for both sides, from browser to server and from server to browser).
Given that the server uses TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 , how are all those keys s... |
I was thinking of doing symmetric encryption using just hashing and simple XOR encryption. It would work as:
1) Alice and Bob share a symmetric key
2) Alice manages to send an (authenticated) IV to Bob
3) Bob and Alice both combine the IV with the symmetric key and use it to seed a PRNG
4) the output of the PRNG ... |
If an attackers sets out to crack the symmetric key of e.g. AES-CTR, would they prefer to have access to many small cryptotexts or one large cryptotext? I.e. is it more interesting for the attacker to see cryptotexts of many IVs than of a single IV?
Does the answer change if also the plaintexts (many small, possibly... |
Key cracking: Prefer many small texts over one large text? |
Take a [McEliece cryptosystem][1] with public generator matrix $G' = S G P$ where $G$ is a generator of a secret code with known fast decoding (not necessarily a Goppa code over $\mathbb{F}_2$), $S$ is random & non-singular and $P$ is a permutation.
Let's say an attacker Eve has a way to find $G$ from $G'$ but not $... |
What does it mean that a protocol realizes "strong mutual authentication"? And What does it mean that a protocol realizes "weak mutual authentication"? Can you define them formally ?
I have found a definition for "strong mutual authentication" (not formal):
> Strong mutual authentication requires not only mat... |
Apparantly, textbook RSA can be broken if the same plaintext p with gcd(p,n)=1 is encrypted twice with two coprime exponents e and e', but same modulus n. How does this work? If I have $c=p^e mod n$ and $c'=p^{e'} mod n$, how can I calculate p (c, c', e, e', n are provided)?
I don't know what to use the information th... |
There are two main reasons why asymmetric cryptography is practically never used to directly encrypt significant amount of data:
1) Size of cryptogram: symmetric encryption does not increase the size of the cryptogram (asymptotically), but asymmetric encryption does. If we take the example of RSAES-OAEP in [PKCS#1v2... |
Thanks to mikeazo I found another thread with my original question: http://crypto.stackexchange.com/questions/16283/how-to-use-common-modulus-attack
Though I don't understand completely how the answer works (and I am not allowed to post comments yet). I have $e_bs_1+e_cs_2=1$, but one of the $s_i$ is going to be neg... |
Are there functions that satisfy the second-preimage resistance property without satisfying the others (preimage and collision resistance) ?
I'm looking about such functions that compress data (exit the identity function).
|
Are there any cryptographic algorithms or primitives that have been developed and studied that make use of non-commutative or non-associative algebraic structures such as quaternion integers or octonion integers? It seems to me that many of these structures can preserve the things that make them useful to cryptography ... |
Thanks to mikeazo I found another thread with my original question: http://crypto.stackexchange.com/questions/16283/how-to-use-common-modulus-attack
Though I don't understand completely how the answer works (and I am not allowed to post comments yet). I have $e_bs_1+e_cs_2=1$, but one of the $s_i$ is going to be neg... |
I need to decrypt a huge file that I own previously encoded by myself with a RSA public key (it's possible for this step using a symmetric algorithm key). Problem is that I can't load it in my disposable memory for specific embedded architecture reasons.
I need to decrypt it with the private key associated to the id... |
Thanks to mikeazo I found another thread with my original question: http://crypto.stackexchange.com/questions/16283/how-to-use-common-modulus-attack
Though I don't understand completely how the answer works (and I am not allowed to post comments yet). I have $e_bs_1+e_cs_2=1$, but one of the $s_i$ is going to be neg... |
Is it possible to combine SHA1 digest values to get the SHA1 of the concatenated parts ?
I know the "S1" SHA1 of "part 1" and the "S2" SHA1 of the "part 2" and I would like to know the SHA1 of the "part 1" concatenated with "part 2" calculated from "S1" and "S2".
Is it possible ?
|
No.
Most (all?) cryptographic hashes are designed to prevent that kind of relationship. Additionally, SHA1 uses padding and the file size as part of the hash calculation.
The specific reason it is not possible is because the hash is calculated from an initial hash value. This initial value is the same for both S1... |
HMAC does nested hashing in order to prevent [Length Extension Attacks][1].
Given that you use a SHA-3 hash (which is resistant against length extension attacks), would you still need to go through [that][2] procedure in order to produce a secure MAC?
Needless to say a we'd still use a key, which we prepend or ap... |
I'm looking for an algorithm where *n* participants each have a different secret number between [0..x] (and where *x* is known) and where the participants then select another, non-secret, number between [0..x] which *must not* clash with the secret of any participant and which must not reveal any number used by any par... |
Does this crypto algorithm exist? |
I'm looking for an algorithm where *n* participants each have a different secret number between [0..x] (and where *x* is known) and where the participants then select randomly another, non-secret, number between [0..x] which *must not* clash with the secret of any participant and which must not reveal any number used b... |
Is there any known way to construct a length-preserving [all-or-nothing transform](https://en.wikipedia.org/wiki/All-or-nothing_transform)? In other words, a secure all-or-nothing transform where the length of the output is the same as the length of the input.
My thanks to @Ricky Demer for [suggesting this question... |
I'm pretty sure this is a really bad approach (in theory).
But one of my clients is doing this and I was wondering: speaking of practice, how bad it is to perform PBKDF2 (2000 iterations) in this way:
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iteration... |
PBKDF2 - Good or bad approach? |
Well, I'm trying to understand two protocols for mutual authentication. If they are secure or not.
K - Session Key, and it's calculated doing k=H(TimeStamp)
1)
Alice ------ { [TimeStamp]alice }bob , K ----> BOB
<------------ [TimeStamp + 1]bob -------
2)
Alice ------ { [TimeStamp, K]al... |
"1. Should I consider my primary key insecure?"
It depends who you are trying to protect yourself from. AIUI based on the best known cryptanalysis 1024 bit RSA and DSA keys could be cracked by a well-funded attacker (I've seen the math run for RSA, not sure about DSA but AIUI they give similar security at a given key ... |
I am trying to understand two protocols for mutual authentication and if they are secure or not.
$K$ is the session key, and it's calculated $k=H(TimeStamp)$.
Are the following both cases secure? Could they provide mutual authentication?
1. $Alice \rightarrow \{[TimeStamp]alice\}bob,K \rightarrow BOB\\
Ali... |
> 1 . Should I consider my primary key insecure?
It depends who you are trying to protect yourself from. AIUI based on the best known cryptanalysis 1024 bit RSA and DSA keys could be cracked by a well-funded attacker (I've seen the math run for RSA, not sure about DSA but AIUI they give similar security at a given k... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography.
The context is circa pages 145 - 150, and specifically Table 4.4 (p. 148). The table presents (k,t) pairs, where 'k' is the number of bits in the candidate and 't' is the number... |
I'm pretty sure this is a really bad approach (in theory).
But one of my clients is doing this and I was wondering: speaking of practice, how bad it is to perform PBKDF2 (2000 iterations) in this way:
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iteration... |
Signing a document: which algorithm to use? |
This may seem an elementary question about LFSRs, and their link to Markov chains. LFSRs show Markov chain behaviour in that there can be a transition matrix defined over the LFSR, this follows from the very definition of the LFSR. Is there any formal formulation for the LFSR as a Markov chain? |
I am trying to understand two protocols for mutual authentication and if they are secure or not.
$K$ is the session key, and it's calculated $k=H(TimeStamp)$.
Are the following both cases secure? Could they provide mutual authentication?
1. $Alice \rightarrow \{[TimeStamp]alice\}bob,K \rightarrow BOB\\
Ali... |
Say I'm trying to brute force the original plain text of an SHA256 hash, does knowing the RIPEMD160 hash of the same text help? In other words, does providing access to hash values of the same text generated by multiple algorithms decrease security? |
Does knowing multiple hash of the same content make it more likely to generate original plain text? |
I have a question regarding the Fiat-Shamir identification protocol. In this source for example (http://www.cs.rit.edu/~jjk8346/presentation.pdf) it says on pages 9 and 10 that the random commitment r and the private key s have to be smaller than n (the RSA-like Modulus). I am wondering why this has to be. The verifica... |
I'm pretty sure this is a really bad approach (in theory).
But one of my clients is doing this and I was wondering: speaking of practice, how bad it is to perform PBKDF2 (2000 iterations) in this way:
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iteration... |
I have a question regarding the Fiat-Shamir identification protocol. In this source for example (http://www.cs.rit.edu/~jjk8346/presentation.pdf) it says on pages 9 and 10 that the random commitment r and the private key s have to be smaller than n (the RSA-like Modulus). I am wondering why this has to be. The verifica... |
I have a question regarding the Fiat–Shamir identification protocol. In [this source](http://www.cs.rit.edu/~jjk8346/presentation.pdf) (pdf) for example it says on pages 9 and 10 that the random commitment $r$ and the private key $s$ have to be smaller than $n$ (the RSA-like Modulus). I am wondering why this has to be.... |
Fiat–Shamir: why do r and s have to be smaller than n? |
We simply have to trust this party because this scheme requires a trusted dealer (a party that distributes the shares to the secret to the participants).
We can use [verifiable secret sharing](http://en.wikipedia.org/wiki/Verifiable_secret_sharing), that allows the parties to check whether the shares they have obtai... |
We simply have to trust this party because this scheme requires a trusted dealer (a party that distributes the shares to the secret to the participants - this can be you or some other party - but if its you you should trust yourself).
We can use [verifiable secret sharing](http://en.wikipedia.org/wiki/Verifiable_sec... |
Is there a fast algorithm for mapping $n$-bit numbers $s$ (for fixed $n$) into a cyclic subgroup of an elliptic curve (over a finite field) in which the Discrete Logarithm Problem is hard?
By fast, I mean it takes about as long as a point addition (and is much faster than a point scalar multiplication in the ellipti... |
Is there a fast algorithm for mapping $n$-bit numbers $s$ (for fixed $n$) into a cyclic subgroup of an elliptic curve (over a finite field) in which the Discrete Logarithm Problem is hard?
By fast, I mean it takes about as long as a point addition (and is much faster than a point scalar multiplication in the ellipti... |
My implementation of the parallelized Pollard's Rho algorithm is using Jacobian coordinates to avoid the costly inversion operation when performing point addition.
I am wondering if there are any methods to check for distinguished points while in Jacobian form, since switching back to affine coordinates requires an ... |
I have been trying to wrap my head around different definitions of protocol security (stand alone, sequential composition, parallel composition, universal composition) and how the proofs of any of these cases are obtained. However, at current state I find it quite complicated. Can you recommend any good lecture materia... |
I'm pretty sure this is a really bad approach (in theory).
But one of my clients is doing this and I was wondering: speaking of practice, how bad it is to perform PBKDF2 (2000 iterations) in this way:
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iteration... |
I'm pretty sure this is a really bad approach (in theory).
But one of my clients is doing this and I was wondering: speaking of practice, how bad it is to perform PBKDF2 (2000 iterations) in this way:
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iteration... |
Not all elliptic curves are safe to use for cryptography, especially from an ECC safety perspective. The site http://safecurves.cr.yp.to/index.html shows that two tested Brainpool curves, brainpoolP256t1 and brainpoolP384t1, are not ECC security safe even though they are ECDLP safe. Not all the Brainpool curves were ev... |
Is either brainpoolP320r1 or brainpoolP320t1 a SafeCurve? |
I'm in search of the correct definition of a *stateful* authenticated encryption scheme (sAE), and its related security notion. This has been treated several times in the academic literature, however, all the papers I've read contains a discrepancy between how they state the security goal in informal English and their ... |
Flaw in the security definition of *Stateful* Authenticated Encryption? |
I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform [tag:pbkdf-2] in this way (with 2000 iterations)?
a = PBKDF2(x, y)
b = PBKDF2(y, x)
1st param: Password
2nd param: Salt
2000 iterations
`a` is ... |
For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced?
In other words, because none are ever stored by the implementation, can standard username/password rules with a 4-digit PIN be enforced to produce theoretically uncrackable combinat... |
For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced?
In other words, because none are ever stored by the implementation, can standard username/password rules with a 4-digit PIN be enforced to produce theoretically uncrackable combinat... |
For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced?
In other words, because none are ever stored by the implementation, can standard [login authentication guidelines][1] also with a 4-digit PIN be enforced to produce theoretically un... |
For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced?
In other words, because none are ever stored by the implementation, can standard [login authentication guidelines][1] also with a 4-digit PIN be enforced to produce theoretically un... |
> In other words, because none are ever stored by the implementation, can standard login authentication guidelines also with a 4-digit PIN be enforced to produce theoretically uncrackable combinations where the login username & password are substituted for the PBKDF2 password & salt or vice versa, and the PIN is the nu... |
[RFC 5959][1] specifies the encrypted storage of private keys based on PBKDF2-HMAC-SHA-256 and AES encryption (in ECB mode).
Is there a particular reason AES is used, instead of simply XORing the key material with the PBKDF2 output? Is it simply to make storage of long keys faster, because a long PBKDF2 output takes... |
Password-based encrypted key storage? |
I am trying to create a decentralized moderation system for the game Diplomacy, a game for seven players. In each round of a face-to-face game, each player writes their moves on paper then puts it in a box; all moves are read at once. The game was popular as play-by-mail: you mail your moves to a magazine publisher, wh... |
I am trying to create a decentralized moderation system for the game Diplomacy, a game for seven players. In each round of a face-to-face game, each player writes their moves on paper then puts it in a box; all moves are read at once. The game was popular as play-by-mail: you mail your moves to a magazine publisher, wh... |
I have been watching [Christof Paar][1] on his [youtube lectures][2] for most of the day and also googling **alot** also I used bcrypt to store two passwords with salts and I find that I have a few questions.
I am interested in what bcrypt does to the start of the final hash.
$2a$10$
I have two thoughts on... |
I have been watching Christof Paar on his [YouTube lectures](https://www.youtube.com/watch?v=iaH8UG2yMg4) for most of the day and also Googling **a lot**; also I used bcrypt to store two passwords with salts and I find that I have a few questions.
I am interested in what bcrypt does to the start of the final hash.
... |
I have been watching Christof Paar on his [YouTube lectures](https://www.youtube.com/watch?v=iaH8UG2yMg4) also I used bcrypt to store two passwords with salts and I find that I have a few questions.
I am interested in what bcrypt does to the start of the final hash.
$2a$10$
I have two thoughts on this:
... |
I have been watching Christof Paar on his [YouTube lectures](https://www.youtube.com/watch?v=iaH8UG2yMg4) also I used bcrypt to store two passwords with salts and I find that I have a few questions.
I am interested in what bcrypt does to the start of the final hash.
$2a$10$
I have two thoughts on this:
... |
Is HMAC padding the same as bcrypt? |
I would like to know how to calculate the bit-strength of Integer Factorization Cryptography (IFC) such as RSA by using Python. I gathered it is based off the complexity of factorizing the modulus (public key). I want to be able to calculate the bit strength of arbitrary key-lengths of RSA for example, such as 4096 whi... |
I'm implementing SHA 256 in PHP using strings. Where do you truncate in the algorithm?
There are a lot of places where there's binary addition happening so the no. of bits in the W(i) keep increasing, same case with the compression function. So where do I truncate the values?
When I var_dump my array I get this:
... |
Where do I truncate the bits in SHA 256 hash algorithm? |
I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the whole ISO/IEC 9796-2?
I've already had a look on the [paper](https://eprint.iacr.org/2009/203.pdf) but there, only ... |
I'm unsure of how exactly the salt is manipulated by [HMAC][1] in PBKDF2 and the resulting contribution if any to password entropy.
If salts do contribute to entropy, how can total entropy be calculated as a function of password entropy and salt entropy?
[1]: http://en.wikipedia.org/wiki/HMAC#Implementation |
Do PBKDF2 salts contribute to entropy? What is the total if so? |
Do PBKDF2 salts contribute to entropy? If so, how can the combined total be calculated? |
I'm unsure of how exactly the salt is manipulated by [HMAC][1] in PBKDF2 and their potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a decentralized implementation.
If salts do contribute to entropy for this implementation, how can total entropy be cal... |
Could PBKDF2 salts contribute to entropy if passwords & salts are only stored in human memory? |
I'm unsure of how exactly the salt is manipulated by [HMAC][1] in PBKDF2 and their potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a decentralized implementation.
For this implementation, a user would be responsible for generating a "username" as the... |
this node.js module https://www.npmjs.org/package/keypair puts text infront and at the end of each public and private (-----BEGIN RSA PUBLIC KEY-----)
Is this they way they should look or can I remove the text?
var keypair = require('keypair');
var pair = keypair();
console.log(pair);
outputs... |
I'm unsure of how exactly the salt is manipulated by [HMAC][1] in PBKDF2 and their potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a decentralized implementation.
For this implementation, a user would be responsible for generating a "username" as the... |
I'm unsure of how exactly the salt is manipulated by [HMAC][1] in PBKDF2 and their potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a decentralized implementation.
For this implementation, a user would be responsible for generating a "username" as the... |
I'm unsure of how exactly the salt is manipulated by scrypt and its potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a decentralized implementation.
For this implementation, a cryptocurrency login where the salt does not exist in any repository such a... |
Could scrypt salts contribute to entropy if passwords & salts are only stored in human memory? |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.