instruction stringlengths 15 30k |
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I take your question to mean, how both historically and in the modern age one could construct a pen-and-paper cipher using the Chinese language.
As pointed out in the question, Chinese is a [logographic langauge][1] and therefore has a far greater number of characters than Phonetic systems. Historically this has cau... |
Does the improved version of NTRU — which is described in ["Making NTRU as Secure as Worst-Case Problems over Ideal Lattices" by
Stehlé and Steinfeld](http://users.monash.edu.au/~rste/ProvNTRU_V10a.pdf) — fall under the same patents as the original?
|
Is the "secure-as-worst-case" version of NTRU patented? |
It seems I can't comment on answers because the question is no longer on the Chinese Q&A, but I wanted to support fgrieu's suggestion. Certain web services don't have much care for security, but they want to avoid containing keywords that are blocked by the Chinese Firewall. One I'm familiar with is PIMCloud, a cloud-... |
when it comes to design a new PKI-based key-exchange protocols, why security proof is needed? without it , can we show a protocol's security? Does there exist a PKI-based key-exchange protocol that is secure without security proof? |
why security proof? |
When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed? Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol that is secure without a security proof? |
why security proofs? |
Why not use this secure symmetric key exchange? |
This requires secure commutative encryption and takes 3 rounds (despite being unauthenticated).
What makes you think that "a 'man in the middle' attack will not
<br>
work if the algorithm is not a simple 'xor'ing of plain text and key"?
The part of your post after that statement only describes
<br>
an eavesdr... |
A known-plaintext attack (i.e. knowing a pair of corresponding plaintext and ciphertext) always allows a *brute-force attack* on a cipher:
* Simply try all keys, decrypt the ciphertext and see if it matches the plaintext.
This always works for every cipher, and will give you the matching key. (For very short plai... |
i want a tool that runs on Win7 and can offer automated verification to a protocol under [eCK security model][1]. Does anyone know that? thanks
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pdf |
Does there have automated security protocol verification tool? |
I want a tool that runs on Win7 and can offer automated verification of a protocol in the [eCK security model][1]. Does anyone know such a tool?
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pdf |
Is there an automated security protocol verification tool? |
Previoulsy I had asked this question at http://stackoverflow.com/questions/18235983/can-s-mime-be-still-considered-secure but I feel this forum is topic-wise the right place.
Recently there has been a discussion whether secret service agencies have access to certification authorities. Also before that several CAs we... |
Can S/MIME be still considered secure? |
Interesting discussion here. Is there really much of a difference between numerical ordering and alphabetic sorting? They would appear very similar except the first is base 10 and the other is at a minimum base 26 (a-z), more likely base 36 (a-z and 0-9), and potentially base 62 (a-z, A-Z, and 0-9). Given previous anal... |
I want a tool for automated verification of a protocol in the [eCK security model][1]. Does anyone know such a tool?
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pdf |
Because that requires secure commutative encryption
<br>
and takes 3 rounds (despite being unauthenticated).
What makes you think that "a 'man in the middle' attack will not
<br>
work if the algorithm is not a simple 'xor'ing of plain text and key"?
The part of your post after that statement only describes
<... |
Do I need to worry about "predictability" an an allegedly secure CSPRNG if I am just using it to generate key material from time to time?
Suppose that for some odd reason, I am less trustful today than I was last week of SecGetRandomBytes() in OS X and iOS and of CryptGenRandom() in Windows. If I am using this for o... |
Do I need to worry about "predictability" an an allegedly secure CSPRNG if I am just using it to generate key material from time to time?
Suppose that for some odd reason, I am less trustful today than I was last week of `SecGetRandomBytes()` in OS X and iOS and of `CryptGenRandom()` in Windows. If I am using this f... |
I want a tool that runs on Win7 and can offer automated verification of a protocol in the [eCK security model][1]. Does anyone know such a tool?
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pdf |
I want a tool that (runs on Win7 and) can offer automated verification of a protocol in the eCK security model as described in Microsoft Research's paper ["Stronger Security of Authenticated Key Exchange" ][1].
Does anyone know such a tool?
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pd... |
1. Prove resistance to differential cryptanalysis.
For example this presentation: [Provable security against Impossible Differential Cryptanalysis][1], or this paper: [ ProvableSecurity Against a Differential Attack (1995)][2]
2. Prove resistance to linear cryptanalysis.
For example: [On Measuring Resi... |
I want a tool that for automated verification of a protocol in the eCK security model as described in Microsoft Research's paper ["Stronger Security of Authenticated Key Exchange" ][1].
Does anyone know such a tool?
[1]: http://research.microsoft.com/en-us/um/people/klauter/AKEfinal.pdf |
Do I need to worry about "predictability" an an allegedly secure CSPRNG if I am just using it to generate key material from time to time?
Suppose that for some odd reason, I am less trustful today than I was last week of `SecGetRandomBytes()` in OS X and iOS and of `CryptGenRandom()` in Windows. If I am using this f... |
Suppose Alice and Bob are exchanging messages using S/MIME, protected by certificates that have been issued by either the same CA or by two mutually independent CAs. There exists an adversary Mallory who wants to get the ability to compromise the confidentiality of the communication, or the integrity, or both. We may a... |
When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed? Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol that is secure without a security proof?
And now i'm doing on security proofs. it's a tough thing for me. could anyone w... |
Problems about Security proofs? |
I am attempting to come up with a way of memorizing a seed that could lead to any number of brain wallets for bitcoin. I need multiple wallets because a) I don't want all my eggs in one basket, and b) I want to be able to import small amounts from time to time.
Let's say I came up with a passphrase, and assume it's... |
Here is a protocol for a key exchange:
1. Bob encrypts a message $m$ with his key $K_B$: $m_1 = E_{K_B}(m)$.
2. Bob send the result $m_1$ to you.
2. Alice encrypts my encrypted above message with her own key: $m_2 = E_{K_A}(m_1)$.
3. Alice sends her encrypted message $m_2$ back to Bob.
4. Bob decrypts this messa... |
What are the weaknesses of this message exchange protocol? |
Are you doubting the last paragraph in [my answer to this question][1]? :-)
Yes, any such tampering can always be detected after the fact.
The message I send to you (call it $\mathcal{M}$) depends on what I think is your public key. The message you receive (call it $\mathcal{M}'$) must decrypt with your actual pr... |
If I run the command 'gpg -a -e < input.txt > output.txt' with completely different inputs (e.g. from /dev/urandom), the first 19 characters are always the same. What is this header? Is it identifying in any way?
|
Why are the first few bytes of a gpg encryption always the same? |
Alice and Bob want to communicate using a stream cipher. At the beggining, they create a session key $K_s$ and exchange it via some secure channel (using some asymmetric algorithm). After every message, they want to append a MAC value to verify their identity.
The question is this:
Should I have a *direction* fla... |
Should I use distinct MACs for each user, or should I use a *direction* flag when communicating? |
> 1 - How feasible is it that the chip's manufacturer can predict the output of this PRNG when it passed tests from the people applying the use of this RdRand instruction in kernels?
As nightcracker correctly stated, any strong cryptographic PRNG will produce a stream of numbers that pass statistical tests.
Howev... |
Alice and Bob want to communicate using a stream cipher. At the beggining, they create a session key $K_s$ and exchange it via some secure channel (using some asymmetric algorithm). After every message, they want to append a MAC value to verify their identity.
The question is this:
Should I have a *direction* fla... |
From a recent NY Times article:
> Cryptographers have long suspected that the agency planted
> vulnerabilities in a standard adopted in 2006 by the National
> Institute of Standards and Technology and later by the International
> Organization for Standardization, which has 163 countries as members.
>
> Classif... |
What NIST protocol was allegedly backdoored by NSA in 2006? |
The standard in question was the [*Dual Elliptic Curve Deterministic Random Bit Generator*](http://en.wikipedia.org/wiki/Dual_EC_DRBG) (Dual_EC_DRBG), standardized in [NIST Special Publication 800-90](http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf). In this case, it was not a protocol, but instead a r... |
The standard in question was the [*Dual Elliptic Curve Deterministic Random Bit Generator*](http://en.wikipedia.org/wiki/Dual_EC_DRBG) (Dual_EC_DRBG), standardized in [NIST Special Publication 800-90](http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf). In this case, it was not a protocol, but instead a r... |
Say that you have the Key and the MAC value that was generated from the Key using CBC. Is it possible to generate a message with just the mac and the key? If so, how would you do it?
|
Is it possible to generate a message using the mac and the key? |
If I run the command 'gpg -a -e < input.txt > output.txt' with completely different inputs (e.g. from /dev/urandom), the first 19 characters are always the same. What is this header? Is it identifying in any way?
For example:
-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.4.11 (GNU/Linux)
hQEMA... |
[Recent articles in the media](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-internet-encryption.html?hp&pagewanted=all), based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST ... |
Should we trust the NIST-recommended ECC parameters? |
[Recent articles in the media](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-internet-encryption.html?hp&pagewanted=all), based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST ... |
Most of general purpose multi party computation protocols are highly interactive .
Especially the ones with Shamir's secret scheme , as there is degree reduction step in multiplication that needs parties to interact with each other .
But are there any general purpose non interactive multi party computation protocol... |
Any non interactive multi party computation protocol? |
[Recent articles in the media](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-internet-encryption.html?hp&pagewanted=all), based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST ... |
[Recent articles in the media](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-internet-encryption.html?hp&pagewanted=all), based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST ... |
Suppose Alice and Bob are exchanging messages using S/MIME, protected by certificates that have been issued by either the same CA or by two mutually independent CAs. There exists an adversary Mallory who wants to get the ability to compromise the confidentiality of the communication, or the integrity, or both. We may a... |
as said in the heading I wanted to know how the security of different padding methods, e.g. ANSI X.923, ISO 10126 and PKCS7, is compared to other methods to reach the needed block size, like ciphertext stealing or residual block termination. And what is about the counter mode of operation? I heard that oracle attacks a... |
In the last week, the discrete logarithm problem was broken for the binary fields [$\mathbb{F}_{2^{(14 \times 127)}}$][1] and [$\mathbb{F}_{2^{(27 \times 73)}}$][2].
Pairing-based cryptography using binary fields currently relies on fields such as $\mathbb{F}_{2^{4\times353}}$ (80-bit level of security) and $\mathbb... |
Do I need to worry about "predictability" an an allegedly secure CSPRNG if I am just using it to generate key material from time to time?
Suppose that for some odd reason, I am less trustful today than I was last week of `SecRandomCopyBytes()` in OS X and iOS and of `CryptGenRandom()` in Windows. If I am using this ... |
(That Tor mailing list link appears to be broken at the moment)
Your question is at least partially answered in FIPS 186-3 itself:
http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf
Appendix A describes how to start with a seed and use an iterative process involving SHA-1 until a valid elliptic cu... |
As said in the heading, I want to know how the security of different padding methods, e.g. ANSI X.923, ISO 10126 and PKCS7, is compared to other methods to reach the needed block size, like ciphertext stealing or residual block termination. And what is about the counter mode of operation?
I heard that oracle attack... |
(That Tor mailing list link appears to be broken at the moment)
Your question is at least partially answered in [FIPS 186-3](http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf) itself…
**Appendix A** describes how to start with a seed and use an iterative process involving SHA-1 until a valid ellipti... |
Some (supposedly) cryptographically secure PRNGs have an internal state of only 160 bits or less. When the algorithm is otherwise properly designed, that seems like enough to generate a 128 bit key for e.g. AES.
Can the PRNG also be used for the generation of longer keys, e.g. RSA keys with 1024 bits?
My intuitio... |
(That Tor mailing list link appears to be broken at the moment)
Your question is at least partially answered in [FIPS 186-3](http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf) itself…
**Appendix A** describes how to start with a seed and use an iterative process involving SHA-1 until a valid ellipti... |
Most of general purpose multi party computation protocols are highly interactive .
Especially the ones with Shamir's secret scheme , as there is degree reduction step in multiplication that needs parties to interact with each other .
For example , say a client (trusted dealer) distributes the secret among few serve... |
Most of general purpose multi party computation protocols are highly interactive .
Especially the ones with Shamir's secret scheme , as there is degree reduction step in multiplication that needs parties to interact with each other .
For example , say a client (trusted dealer) distributes the secret among few serve... |
New Applications should still use RSA ? Is it worth going down the ECDH route for protocols? |
Should new applications still use RSA? Is it worth going down the ECDH route for protocols? |
It depends on what you mean by interaction.
Some protocols for secure multiparty computation, e.g. those based on Shamir secret sharings and the GMW protocol, require the servers to communicate a lot during the computation.
In other protocols, such as those based on Yao's garbled circuits (e.g. [Fairplay MP][2]),... |
Most of general purpose multi-party computation protocols are highly interactive.
Especially the ones with Shamir's secret scheme, as there is a degree reduction step in multiplication that needs the parties to interact with each other.
For example, say a client (trusted dealer) distributes the secret among several... |
I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially cause Intel to weaken or create backdoors in their design.
This [petition][1] was posted asking Linus Torvalds to ignore RDRAND and not include it as a source of entropy in `/dev/random/`. You can see Li... |
Could RDRAND (Intel) compromise entropy? |
If the NSA knew a sufficiently large weak class of elliptic curves, it is possible for them to have chosen weak curves and have them standardized.
As far as I can tell, there is no hint about any sufficiently large class of curves being weak.
Regarding choosing the curves: It would have been better if NIST had us... |
I wonder if there exists proofs of security of primitives like hash function (based on block cipher) in the prp model.
I often see proofs in the random oracle model (for hash function based on compression function) and proofs in the ideal cipher model (for hash function based on block cipher).
Is there proofs of... |
Consider a block-cipher $F$ with a $N$-bit block-size and a $M$-bit key-size. That is, if $k$ is a $M$-bit key, $p$ is a $N$-bit block of plain-text and $c$ is a $N$-bit block of cipher-text, then:
$$
F\left(k,p\right) = c
$$
Each plain-text block of $N$ bits must have a 1-to-1 correspondence with a cipher-te... |
Is there a theoretical maximum useful keysize given the block-size? |
I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially be influencing Intel to weaken or create backdoors in their design.
This [petition][1] was posted asking Linus Torvalds to ignore RDRAND and not include it as a source of entropy in `/dev/random/`. You c... |
Given a fixed seed (i.e. no ongoing source on entropy), is there (practically or theoretically) any PRNG algorithm that can generate an infinite sequence of random numbers such that an observer cannot detect that it is a PRNG rather than a genuinely random source ?
All widely adopted cryptographically secure PRNGs s... |
Can a PRNG with a fixed amount of entropy always be detected? |
[Recent articles in the media](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-internet-encryption.html?hp&pagewanted=all), based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- including at least one NIST ... |
Suppose you are given a value $c$. Can you find a prime $p$, an integer $b$, and a point $G$ such that the elliptic curve
$$E: y^2 \equiv x^3 -3x + b \pmod p$$
is cryptographically weak? You need to choose $p,b,G$ so that all of the following restrictions also hold:
1. $p$ has some desired size (say, 256 bit... |
I am learning cryptography at school and I was wondering
1. How are the blocks/streams after decryption synchronized at the receiver to form one long meaningful message?
2. Am I right by saying that stream cipher will incur a LOT more overhead while synchronizing?
Thanks! |
Suppose you are given a value $c$. Can you find a prime $p$ and an integer $b$ such that the elliptic curve
$$E: y^2 \equiv x^3 -3x + b \pmod p$$
is cryptographically weak? You need to choose $p,b$ so that all of the following restrictions also hold:
1. $p$ has some desired size (say, 256 bits)
2. $1 < b ... |
Often in many of the definitions related to Universal hashing, the term "a family of hash functions, say H " is mentioned. What does this 'family' mean exactly? A numerical example is appreciated. Also, what does it mean by choosing a hash function h at random from a hash family H ? |
Many definitions related to universal hashing mention the term "a family of hash functions, say $H$". What does this 'family' mean exactly? A numerical example would be appreciated. Also, what does it mean to choose a hash function h at random from a hash family $H$?
|
The answer to your question will very much depend on implementation details, but you might not be versed enough in cryptographic protocol development to know exactly what to ask, so I'll take a stab at answering this and hopefully my attempt will help you refine the question as needed.
>1. How are the blocks/streams... |
I am learning cryptography at school and I was wondering
1. How are the blocks/streams after decryption synchronized at the receiver to form one long meaningful message?
2. Am I right by saying that stream cipher will incur a LOT more overhead while synchronizing? |
Suppose I have a list of randomly generated uint_8's, uniform over the whole range of uint_8. I write them into a file as raw bytes, no encoding.
Then I reopen the file and interpret the file as packed uint_16's (by pairing up adjacent bytes).
1. Is my reinterpreted stream of uint_16's a uniformly random distrib... |
Every time when i meet the concepts of Perfect forward secrecy(PFS) and weak Perfect forward secrecy(wPFS), i'm ambiguous about them.
**My understanding is that :**
- PFS ensures that if the parties' long-term keys have compromised in the future, then to active adversary $\mathcal{A}$ , he cannot calculate ... |
how to understand PFS and wPFS? |
Suppose I have a list of randomly generated `uint_8`'s, uniform over the whole range of `uint_8`. I write them into a file as raw bytes, no encoding.
Then I reopen the file and interpret the file as packed `uint_16`'s (by pairing up adjacent bytes).
1. Is my reinterpreted stream of `uint_16`'s a uniformly random... |
Given a SSL-enabled web site, the [Qualys SSL tester](https://www.trustworthyinternet.org/ssl-pulse/) will tell what ciphersuite would be negotiated by a bunch of different browsers if they connected to that web site. It will also tell you the list of ciphersuites supported by that server and the list of ciphersuites ... |
Suppose I have a list of randomly generated `uint_8`'s, uniform over the whole range of `uint_8`. I write them into a file as raw bytes, no encoding.
Then I reopen the file and interpret the file as packed `uint_16`'s (by pairing up adjacent bytes).
1. Is my reinterpreted stream of `uint_16`'s a uniformly random... |
Every time when i meet the concepts of PFS (Perfect forward secrecy) and wPFS (weak Perfect forward secrecy), i'm ambiguous about them.
My understanding is that:
- PFS ensures that if the parties' long-term keys have compromised in the future, then to active adversary $\mathcal{A}$ , he cannot calculate the s... |
Can you help me understand PFS and wPFS? |
Every time I encounter the concepts of PFS (perfect forward secrecy) and wPFS (weak perfect forward secrecy), I feel uncertain about them.
My understanding is that:
- PFS ensures that, if the parties' long-term keys have compromised in the future by an active adversary, he cannot calculate the session key.
... |
I wonder if there exists proofs of security of primitives like hash function (based on block cipher) in the PRP model.
I often see proofs in the random oracle model (for hash function based on compression function) and proofs in the ideal cipher model (for hash function based on block cipher).
Is there proofs of... |
This depends on the MAC algorithm.
Two examples:
With HMAC based on a secure hash function, no, there is no known way to construct a message fitting the MAC other than brute-forcing it. (If you want to find a specific message, like when you have a MAC of a message containing a password and some fixed text, brute-... |
Let $b$ be the number of elements in the block cipher's domain. $\:$ Let $n$ be the block cipher's key size.
<br>
If $\:\frac{2^n}{b!}\:$ is negligible, then one can construct an [eTCR (page 4) hash](http://books.google.com/books?id=tbf4quWHW9kC&pg=PA93&lpg=PA93&dq=%22eTCR+hash%22&source=bl&ots=4jW4ZAU2N5&sig=p-jFvTM... |
Let $b$ be the number of elements in the block cipher's domain. $\:$ Let $n$ be the block cipher's key size.
<br>
If $\:\frac{2^n}{b!}\:$ is negligible, then one can construct an [eTCR (page 4) hash](http://books.google.com/books?id=tbf4quWHW9kC&pg=PA93&lpg=PA93&dq=%22eTCR+hash%22&source=bl&ots=4jW4ZAU2N5&sig=p-jFvTM... |
AES is a block ciphers that is consisted from non-linear and linear parts to provide the shannon requirements of confusion and diffusion respectively. The linear parts can for sure be described as a polynomial and more specifically the `SiftRows,MixColumnds,AddRoundKey` parts but what about the non-linear one? |
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