instruction stringlengths 15 30k |
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In RSA, some security authorities and/or standards allow $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption.
- [ISO/IEC 9796-2][2] allows $e=3$ (in the context if RSA digital signature).
-... |
In RSA, some security authorities and/or standards allow $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption.
- [ISO/IEC 9796-2][2] allows $e=3$ (in the context if RSA digital signature).
-... |
I have a question regarding the key generation process of methods that are based on the discrete logarithm problem.
This site gives some good insights, but I don't fully grasp it I think: http://www.keylength.com/
For example I know that till lately one should have used 1024 bit group generator and a 160 bit long ... |
In RSA, some security authorities and/or standards allow $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption.
- [ISO/IEC 9796-2][2] allows $e=3$ (in the context of RSA digital signature).
-... |
In RSA, some security authorities and/or standards allow $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption.
- [ISO/IEC 9796-2][2] allows $e=3$ (in the context of RSA digital signature).
-... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption.
- [ISO/IEC 9796-2][2] allows $e=3$ (in the context of RSA di... |
I have a question regarding the key generation process of methods that are based on the discrete logarithm problem.
This site gives some good insights, but I don't fully grasp it I think: http://www.keylength.com/
For example I know that till lately one should have used 1024 bit group modulus and a 160 bit long se... |
I need an implementation of linkable ring signature, a ring signature which allows identifying whether two signatures belong to the same signer. It has important privacy-related applications, like e-voting, but unfortunately there seems to be no public implementation. So I'm going to roll my own.
The simplest method... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 4. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 4. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 3. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 3. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
Client write keys and server write keys are essentially enough to decrypt the data or do we need MAC keys also? |
While studying the RSA algorithm I referred to some books and some sites such as [RSA (wikipedia)](http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Key_generation) and all of them chose **{d,n} as the secret (private) key** and release **{e,n} as the public key** but as **d** and **e** are multiplicative inverse of eac... |
Why RSA uses {d,n} as private key instead of {e,n}? |
We read in literature that verification of a digital signature is slower using DSA then if we would use RSA. Why is this?
The algorithm:
- choose prime number $p$
- choose prime number $q \rightarrow q|(p-1)$
- $g = h^{\frac{p-1}{q}}\mod p$ $(1 < h < (p-1))$ (multiplicative order)
- private key: choose $x... |
Why is verification using DSA slower then vertification with RSA? |
I've seen the elegant way of splitting a key among different people so that only a certain number need to be present to re-compute the key, yet nobody has enough information to re-compute the key on their own. For example, if I want to split $K$ between 4 people, such that any 3 can re-compute the key, I first form a p... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 3. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
If I'm able to prove that any scheme satisfies confidentiality ad unforgeability conditions, will it be a valid signcryption scheme, without explicit signature and encryption parts ? |
I have two devices that need to verify that they both are in possesion of the same secret key. One of the devices is a very limited embedded device that only has AES128 available, no SHA or other hash variants.
My idea is a basic two-way challenge-response scheme:
* Device 1 generates 8 bytes of random data (C1),... |
How to verify a shared secret using only AES? |
Sorry for my dumb question, but it's better to ask dumb question than to do dumb things silently.
I want to encrypt user email in my DB so that if someone stole the DB (and not the key) - he won't be able to restore the email adresses. But I need to be able to find user by email in my DB. And I can't iterate over al... |
We read in literature that verification of a digital signature is slower using DSA than if we used RSA. Why is this?
DSA parameter generation:
- choose prime number $p$
- choose prime number $q$ such that $q \mid (p-1)$
- $g = h^{\frac{p-1}{q}}\mod p$ with $1 < h < (p-1)$ (multiplicative order)
- private ... |
Why is verification using DSA slower than verification with RSA? |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prime cas... |
Do recent announcements about solving the DLP in $GF_{2^{6120}}$ apply to schemes proposed for cryptographic use? |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prime cas... |
Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use? |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prime cas... |
I would like to encrypt some data using a combination of multiple keys. There would be two keys: a client keys that would be generated for each client and a single server/application key used by everyone. The idea is to be able to encrypt/decrypt the data only if we are in possession of both keys. So neither the server... |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical [DLP][2] break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prim... |
In RSA, some security authorities and/or standards allow the public exponent $e=3$, others require or recommend $e>2^{16}$ (or perhaps some other minimum). I gathered the following:
- [PKCS#1][1] allows $e=3$ for both RSA digital signature and encryption (but see 3. below).
- [ISO/IEC 9796-2][2] allows $e=3$ (in th... |
When conducting surveys, an Administrator might send an Enumerator to survey a Respondent. For "sensitive" questions (e.g. about embarrassing behavior), the Respondent may be fine with the truth being revealed to the Administrator but not to the Enumerator.
Is there a way to create a one-way function/process using ... |
You could probably post the Administrator's public key and some random nonce on the questionnaire. The cipher should be easy enough to compute with a calculator. Does running specialized decryption software count as *quick action* on the Enumerator's part? If no then the cipher could be really simple.
Another way to... |
SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations?
I tried to set up [TLS-SRP protocol][1], but it haven't worked for me.
---
[Haaalp! Someone?][1]
[1]: http://superuse... |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical [DLP][2] break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prim... |
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: [Solving a 6120-bit DLP on a Desktop Computer][1] seems to "demonstrate a practical [DLP][2] break in the finite field of $2^{6120}$ elements, using just a single core-month". They credit a 2012 paper by Antoine Joux: [Faster index calculus for the medium prim... |
In the [Handbook of Applied Cryptography][1] in a key sharing algorithm, there is:
Implicit key authentication when one party is assured that no other aside from a specifically identified second party has the possibility to determine the secret key.
Entity authentication when one is corroborated of the identity o... |
I have heard about ciphers that have a block length of 256 megabytes... That is huge.
How well are they understood by the encryption community?
I'm referring to PMC Ciphers.
http://www.ciphers.de/eng/content/Backround-Info/Giant-Block-Size-Polymorphic-Cipher.html
Has anyone used such a cipher in a real world a... |
I've noticed confusing definitions about permutation and substitution, preventing to make the difference.
A permutation changes the order of distincts elements of a set, but this can be writen as a function changing one element by another, exactly as a substitution.
So how can we distinguish exactly these two not... |
I have heard about ciphers that have a block length of 256 megabytes... That is huge.
How well are they understood by the encryption community?
I'm referring to [PMC Ciphers](http://www.ciphers.de/eng/content/Backround-Info/Giant-Block-Size-Polymorphic-Cipher.html).
Has anyone used such a cipher in a real world... |
How well analyzed are giant block length ciphers? |
I've noticed confusing definitions about permutation and substitution, preventing to make the difference.
A permutation changes the order of distincts elements of a set, but this can be writen as a function changing one element by another, exactly as a substitution.
So how can we distinguish exactly these two not... |
RSA vs El Gamal digital signature. Which is more secure? |
Could quantum computers "break" symmetric crypto-systems (e.g. AES)? |
What is a definition of a nonce? |
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))?
If yes, for which other hash functions it will work too? |
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))?
If yes, for which other hash functions it will work too?
Would it work vice versa when A is known? |
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (20 bytes for SHA-1)
If yes, for which other hash functions it will work too?
Would it work vice versa when A is known? |
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1)
If yes, for which other hash functions it will work too?
Would it work vice versa when A is known? |
I am writing an application where data will be AES-128 encrypted with a master secret, and 'trusted' users generate a private secret by encrypting the master secret with a user-passphrase. Data is decrypted by decrypting the private secret to the master secret which in turn decrypts the data.
If a user is deleted, t... |
Does HMAC leak information about the key used? |
Could someone point to results or proofs about the probability of HMAC(k, m1) = HMAC (k, m2), assuming the underlying hash function is SHA-256? Would those probabilities be higher/lower if m1 and m2 are not independent?
Please don't point to birthday attack results. I am only interested in the probability that the ... |
How to test if a number is a primitive root, assuming the modulo is a prime? And if not? |
How to test if a number is a primitive root? |
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1)
If yes, for which other hash functions it will work too?
Would it work vice versa when A is known?
---
*Why do I think it's possible?*
If you take a look on SHA-1 so... |
How to test if a number is a primitive root, assuming the modulus is a prime? And if not?
Is it not enough if the number is relatively prime to the modulus or prime? |
[Discrete logarithms in $\mathbb{F}_{p}$ ][1] share the same asymptotic complexity as integer factorization for general numbers: $L_p[1/3,1.923]$ for general integers, $L_p[1/3,1.587]$ for [special integers][2]. [Discrete logarithms in $\mathbb{F}_{p^n}$][3] have the same asymptotic complexity as factoring special inte... |
How robust is discrete logarithm in $GF(2^n)$? |
Why cryptographic hash functions must be collision-free and is there any methods to evaluate whether a function is not resistant to collision?
Thanks, |
Why crypto hash functions must be collision resistant and how to find resistant? |
Encrypt a file once with 50 characters password or twice with 25 characters? |
After just reading the post http://crypto.stackexchange.com/questions/8479/do-recent-announcements-about-solving-the-dlp-in-gf26120-apply-to-schemes
I was a bit confused. DSA, ElGamal and others are based on the assumtion that DLP is a hard problem to solve. The DLP problem can be defined in different cyclic structu... |
I am writing an application where data will be AES-128 encrypted with a master secret, and 'trusted' users generate a private secret by encrypting the master secret with a user-passphrase. Data is decrypted by decrypting the private secret to the master secret which in turn decrypts the data.
If a user is deleted, t... |
Considering the output of a cryptographic primitive, like an encryption scheme (CBC, ...), a hash function or even the output of any schemes based on number theoretic assumptions, is it reasonable (acceptable) to assume that these outputs are random when prooving the security of a protocol/algorithm which relies on the... |
If a hash function is not **collision-resistant** (there is no such thing as collision-free in [hash](https://en.wikipedia.org/wiki/Hash_function) functions because their output has a fixed length) then an adversary can break the function with little effort. More formally (but still quite informally):
You have a set... |
If a hash function is not **collision-resistant** (there is no such thing as collision-free in [hash](https://en.wikipedia.org/wiki/Hash_function) functions because their output has a fixed length) then an adversary can break the function with little effort. More formally (but still quite informally):
You have a set... |
After just reading the post http://crypto.stackexchange.com/questions/8479/do-recent-announcements-about-solving-the-dlp-in-gf26120-apply-to-schemes
I was a bit confused. DSA, ElGamal and others are based on the assumption that DLP is a hard problem to solve. The DLP problem can be defined in different cyclic struct... |
Recent announcements directly imply that cryptosystems (if any) based on the [DLP][1] problem in the Galois [finite field][2] with $2^n$ elements are no longer secure, at least for those $n$ previously thought to be of cryptographic interest and of the forms enabling the new attacks, as explained [here][3]. [Göloğlu, G... |
Recent announcements directly imply that cryptosystems (if any) based on the [DLP][1] in the Galois [finite field][2] with $2^n$ elements are no longer secure, at least for $n$ big enough that the finite field was previously thought to be of cryptographic interest (e.g. for pairing schemes) and of the forms enabling th... |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
After looking through some papers, I feel qualified to answer my question, for the record.
The scheme works and I've found no evidence that it has been broken. A good review is given in "A survey of ring signature" by L. Wang, which contains a section on linkable signatures.
The technique used in Liu's 2004 paper f... |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
SHA-1's compression function (as well as MD5 and SHA-2) is build from a (custom-made) block cipher in the [Davis-meyer construction][1]. (These are the "invertible operations" you describe in the question.)
The *basic idea* is to use the message block as the key for the cipher to "encrypt" the previous state:
... |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
Why are bitwise rotations used in cryptography? |
In Shannon's landmark paper *Communication Theory of Secrecy Systems*, published in 1949, he discussed two traits of secure ciphers: *confusion* and *diffusion*. Loosely speaking, confusion means that the relationship between the symmetric key and ciphertext should be complex.
Diffusion, on the other hand, focuses ... |
There are techniques for doing online surveys on sensitive subjects. They don't follow the approach you outlined, but here's a sketch of how they work.
Suppose we want to survey people to determine how many people have ever seriously considered suicide (say), but we suspect many people might be unwilling to answer ... |
There are techniques for doing online surveys on sensitive subjects. They don't follow the approach you outlined, but here's a sketch of how they work.
Suppose we want to survey people to determine how many people have ever seriously considered suicide (say), but we suspect many people might be unwilling to answer ... |
As noted in [this answer][1] and [this answer][2] to another question, **permutation** is just a mathematical term for a function $\sigma:X{\rightarrow}X$ that maps a finite set $X$ onto itself, in such way that for each $y \in X$ there exists exactly one $x \in X$ such that $\sigma(x) = y$. This is also equivalent to ... |
I am writing an application, running on a server, where multiple users access data from a database which is AES encrypted with a master secret. The master secret itself is initially randomly generated, and then AES encrypted with a user-secret to yield a 'user-hash'. The master secret is never stored, but the user-hash... |
Recently, there has been [quite][1] a [lot][2] of [news][3] about the [Chinese][4] compromising various US weapons systems and stealing military designs through "cyberwarfare". I am reading the news sources about these attacks, but popular news sites often refer to the technical details as "solving complicated mathemat... |
There are 100 bytes with a CRC16. However I only know the first 50.
I want to change byte 5 from a known value X to another value Y, and fix up the CRC16 to be valid - without knowing bytes 50-100.
This is possible with the TCP checksum, because it's just addition. But CRC16 is a polynomial. Is it still possi... |
Can i modify data "protected" by a CRC16? |
$\DeclareMathOperator{\crc}{crc}$CRC is linear, meaning $\crc(x \oplus y) = \crc(x) \oplus \crc(y)$. This property is fantastic for an attacker.
Let your 100-byte message be called $m$. Now suppose you wish to change the value of the byte $a$ to $a'$. Compute $d = a \oplus a'$. Now, pad $d$ with zeroed bytes so that... |
$\DeclareMathOperator{\crc}{crc}$CRC is linear, meaning $\crc(x \oplus y) = \crc(x) \oplus \crc(y)$. This property is fantastic for an attacker.
Let your 100-byte message be called $m$. Now suppose you wish to change the value of the byte $a$ to $a'$. Compute $d = a \oplus a'$. Now, pad $d$ with zeroed bytes so that... |
$\DeclareMathOperator{\crc}{crc}$CRC is linear, meaning $\crc(x \oplus y) = \crc(x) \oplus \crc(y)$. This property is fantastic for an attacker.
Let your 100-byte message be called $m$. Now suppose you wish to change the value of the byte $a$ to $a'$. Compute $d = a \oplus a'$. Now, pad $d$ with zeroed bytes so that... |
Yes, it is very possible. And quite efficient, too.
$\DeclareMathOperator{\crc}{crc}$CRC is linear, meaning $\crc(x \oplus y) = \crc(x) \oplus \crc(y)$. This property is fantastic for an attacker.
Let your 100-byte message be called $m$. Now suppose you wish to change the value of the byte $a$ to $a'$. Compute $... |
I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if something is encrypted with (1) DES or (2) RC2 (3) RC4 what level security is achieved.
In affect I am asking:
If a adve... |
How insecure in practice? |
I'm debugging an application which communicates between client and server using a SSL/TLS connection, and want to capture and analyze the sent data.
Are the client write keys and server write keys enough to decrypt the data, or do we also need the MAC keys? |
Which keys are necessary to decrypt Application data in a SSL connection? |
As you may know, the Gödel Prize 2013 will be awarded this year (2013) to cryptographers (see this [ACM press release](http://www.acm.org/press-room/news-releases/2013/goedel-prize-13/)). The people awarded are Antoine Joux, the team of Dan Boneh and Matthew K. Franklin.
Can somebody explain their contribution to cr... |
Can somebody explain the major contributions of the tenants of the Gödel Prize 2013? |
[Göloğlu, Granger, McGuire, and Zumbrägel][1] broke the [DLP][2] in the Galois [finite field][3] with $2^n$ elements for $n=6120$, and [Antoine Joux][4] did it for $n=6168$, with modest computing power. These recent announcements directly imply that cryptosystems (if any) based on the DLP in a field with $2^n$ elements... |
I'm quite new to cryptographic systems, and today we discuss about entropy at work. Since entropy is used to ensure the difficulty for an attacker to break in, i was wondering if the more time the enropy stay (without any modifications), the more the system become vulnerable.
Does the concept of entropy is related wit... |
Joux's work is really summarized by [this answer][1] already on Crypto.SE. He discovered a way to generalize Diffie-Hellman to multiple (more than 2) parties. In particular though, he presented a single round protocol for key establishment between 3 parties. Something that until then was thought to be impossible.
Bo... |
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