instruction stringlengths 15 30k |
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Theorem 1 of <http://www.researchgate.net/publication/221010790_Implicit_Factoring_with_Shared_Most_Significant_and_Middle_Bits?ev=pub_cit_inc>["Implicit Factoring with Shared Most Significant and Middle_Bits"] by Jean-Charles Faugère, Raphaël Marinier, Guénaël Renault from 2010 deals with factoring products of two pri... |
Theorem 1 of ["Implicit Factoring with Shared Most Significant and Middle_Bits"](http://www.researchgate.net/publication/221010790_Implicit_Factoring_with_Shared_Most_Significant_and_Middle_Bits?ev=pub_cit_inc) by Jean-Charles Faugère, Raphaël Marinier, Guénaël Renault from 2010 deals with factoring products of two pri... |
Diving into the history and evolution of the Message-Digest algorithm by Ronald Rivest, I have been able to track back papers from MD6 down to MD2. Yet, somehow I can not seem to be able to find any papers, specifications or even the slightest indications of MD1.
As the numbering (MD2, MD4, MD5, MD6) seems to be a c... |
Is the first version of the Message-Digest algorithm by Ronald Rivest publically available? |
Your assumption is flawed, you are thinking the IV used for encryption and decryption are different, and that the decrypt IV is an output from the cipher. It is only an input, and it is the same for both operations. Therefore it does not leak any information about the key or the plaintext.
> Is using the IV in such ... |
CTR mode turns a block cipher into a synchronizable/seekable stream cipher. The IV in this case is a nonce (number used once), and in general practice for a 128-bit block cipher is 96-bits (12 bytes), leaving 32-bits (4 bytes) for the block counter.
> How insecure is this?
Not at all, given the following VERY imp... |
I'm playing around with a package that does Elliptic Curve Cryptography from here:-
http://jecc.sourceforge.net/
Every time I encrypt a value it produced a different result (same private key). However I'm always able to decrypt this result with the related public key. For a 1 byte result the the resulting data is... |
I tried out the paper/pencil explanation @ http://sergematovic.tripod.com/rsa1.html, and it seemed to make sense just fine until I came to decryption. Here is what I worked out:
Key Creation:
=============
Choose two different prime numbers _p_ and _k_:
p = 23
k = 29
Find _n_ by calculating `p * q... |
(Originally posted to SOF, but I got no answers)
I am designing a small application for use inside my company. My application needs to connect to a third party website on behalf of my application user. I would like to safely store the user's credentials for the third party site in my database. Obviously, storing the... |
I read that hash chaining can be used to prevent hash collisions, while the chosen prefix attack allows hash collisions for algorithms like MD5.
How are they related? Does hash chaining prevent the chosen prefix attack? |
What is the exact difference between the `CKM_RSA_PKCS` and `CKM_RSA_X_509` mechanisms in the PKCS#11 v2.20 specification (Please explain with an example)?
|
Your scheme lacks any authenticated.
I recommend you use authenticated encryption.
Yes, this will require additional storage.
It's necessary.
ECB mode is not recommended.
To expire a key and introduce a new one, why don't you just decrypt all of the current stuff under the previous key and re-encrypt under the... |
To begin with, I see four potential problems with your key file.
1. The work factor (8) is probably too low. If we presume you pick your pass phrase by selecting $c$ words at random from a list of $2^{13}$ distinct words (e.g. [correct horse battery staple][1]) you get a pass phrase with $13c$ bits of entropy. (AF... |
To begin with, I see four potential problems with your key file.
1. The work factor (8) is probably too low. If we presume you pick your pass phrase by selecting $c$ words at random from a list of $2^{13}$ distinct words (e.g. [correct horse battery staple][1]) you get a pass phrase with $13c$ bits of entropy. (AF... |
I've written extensively about how to solve this problem, over on the IT Security Stack Exchange site. Let me point you to my answers over there:
* [What is the best way to securely keep clear passwords?](http://security.stackexchange.com/a/17785/971)
* [How can I create a service that automatically logs onto a ... |
You should consider using an authenticated encryption ([AEAD](http://en.wikipedia.org/wiki/AEAD_block_cipher_modes_of_operation)) mode. As @d-w says, and as the name implies, it will detect malicious manipulations of the cipher text stored in the DB with high probability.
On top of that:
1. you will also detect a... |
You should consider using an authenticated encryption ([AEAD](http://en.wikipedia.org/wiki/AEAD_block_cipher_modes_of_operation)) mode. As @d-w says, and as the name implies, it will detect malicious manipulations of the cipher text stored in the DB with high probability.
On top of that:
1. you will also detect a... |
Can we use the Symmetric-Key algorithms without an initialization vector ?
I am making an app where both the sender and receiver shares a key and there is no way for creating an initialization vector for each encryption. So I was thinking about setting initialization vector to `NULL` while encrypting. Is it allowed th... |
You should consider using an authenticated encryption ([AEAD](http://en.wikipedia.org/wiki/AEAD_block_cipher_modes_of_operation)) mode. As @d-w says, and as the name implies, it will detect malicious manipulations of the cipher text stored in the DB with high probability.
On top of that:
1. you will also detect a... |
Can we use symmetric-key algorithms without an initialization vector?
<br>
I am making an app where both the sender and receiver share a key and there is no way to create an initialization vector for each encryption. So I was thinking about setting the initialization vector to `NULL` while encrypting. Am I allowed to... |
Assume the case, that two participants have agreed on a key $K=g^{ab} \mod p$ via Diffie Hellman. I have the need to change the key every now and then. The first idea I had was to simply initiate a new agreement, so both chose another exponent, so the new key would be $K'=g^{a'b'}\mod p$.
I wonder if it would be al... |
I am trying to do some elliptic curve calculations by hand, just to refresh myself on how the system works. I calculated some points and did some operations by hand. I am trying to double check my work with some web calculators, but I have tried several different calculators and each gives me a different result...
I... |
Where can I double check my elliptic curve results? |
I am trying to do some elliptic curve calculations by hand, just to refresh myself on how the system works. I calculated some points and did some operations by hand. I am trying to double check my work with some web calculators, but I have tried several different calculators and each gives me a different result...
I... |
There are a bunch of issues involved with this question; the bottom line is that it while it wouldn't be a bad approach from a cryptographical standpoint, it appears to be more costly than the standard approach.
Let us first examine the number theory issues: the first question to ask is "does $g$ generate a large pr... |
Assume the case, that two participants have agreed on a key $K=g^{ab} \mod p$ via Diffie Hellman. I have the need to change the key every now and then. The first idea I had was to simply initiate a new agreement, so both chose another exponent, so the new key would be $K'=g^{a'b'}\mod p$.
I wonder if it would be al... |
Probably not safely and in the way you mean. The NULL IV is completely unsafe.
There are deterministic encryption schemes used for things like searchable encryption, de duplication/convergent cryptography, and key wrapping. They leak a lot of data about the underlying file you are encrypting. In general, they are n... |
If you _really_ can't use an IV (why?), then just about the best thing you can do is use something like [SIV mode (RFC 5297)](http://tools.ietf.org/html/rfc5297). SIV is a "maximally misuse-resistant" [authenticated encryption mode](http://en.wikipedia.org/wiki/Authenticated_encryption) which provides the following ch... |
I understand the the texts within the Voynich Manuscript are of an unknown language, and yet cryptographers are still working on it and still trying to decipher it. Does that mean that it is possible to crack any piece of writing even if it's in a language you don't know, and assuming you have no access to any tools th... |
Is it possible to translate a piece of language into your own without knowing the language? |
Can we use symmetric-key algorithms without an initialization vector?
I am making an app where both the sender and receiver share a key and there is no way to create an initialization vector for each encryption. So I was thinking about setting the initialization vector to `NULL` while encrypting. Am I allowed to set... |
I'm working on a little personal project where security is very important, and I've thought for a while about the best way to do this. Now I am looking for a little outside help on good practices. The goal is to store personal text data on a server (like wifi passwords, etc) and be obtained through a password. I wanted... |
What's wrong with my security model - or how can it be attacked? |
all examples of one way function I see till now are closely related to the assumption that $NP\neq P $ (or even weaker one such as $UP\neq P$), but why not considering the theorem $P\neq EXP$ ? in particular why not building functions that in one way are in the class $FP$ and the inverse function computable in $FEXP$(t... |
Collusion is a concern but unlikely in very large ad-hoc ring networks where each ring is a one-shot random walk of a suitably large and mostly trustworthy membership pool. Collision and congestion are problems though; read below.
If the opponent(s) can determine where the message or the key to decipher the message ... |
Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately [180,000 currently used][1] words in the English language.
# The protocol
1. Bob creates a random private key of 512 bits in length e.g. `2fba5541fda58c643524cb62... |
I've been familiarizing myself with the basics of PGP. If I understand correctly, PGP symmetrically encrypts the data of interest using a random single-use key, then encrypts the encrypted data and its symmetric key using the public key of the intended recipient.
What benefit does the inner layer of symmetric key en... |
Why the symmetric key layer in PGP? |
The random number generation routine must have supreme randomness, special care should be taken to ensure this. The larger concern is the decryption of the keyfile should in no way reveal the key to even authorized users. The password entropy concerns have been well voiced. Depending on the frequency of key changes, yo... |
Using RSA public key (n,e) the encryption of a message is
c= (m^e) mod n
and the corresponding message is decrypted as
m = (c^d) mod n
How the RSAES-OAEP algorithm specified in PKSC#1 v2.1 differs from the above basic method ? |
Using RSA public key (n,e) the encryption of a message is
c= (m^e) mod n
and the corresponding message is decrypted as
m = (c^d) mod n
How does the RSAES-OAEP algorithm specified in PKSC#1 v2.1 differ from the above basic method? |
Using RSA public key (n,e) the encryption of a message is
c= (m^e) mod n
and the corresponding message is decrypted as
m = (c^d) mod n
How does the RSAES-OAEP algorithm specified in PKSC#1 v2.1 differ from the above basic method?
Is it possible to decrypt a text encrypted using RSA PCKS1 v2.1 R... |
> "Frequency analysis of the output might help determine simple words in
> the ciphertext such as 'the' etc if that word is repeated and sent
> multiple times. This isn't necessarily a problem as it's only a simple
> word and doesn't convey much meaning to the message".
If the word "the" doesn't convey much meani... |
This is a type of code book security. Code books can be very strong or very weak depending on operational security.
If you never reuse a code book word *even in a single message* and the code words are genuinely random - this approach could work.
Of course if you can't reuse code words and need perhaps 40 insta... |
Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately [180,000 currently used][1] words in the English language.
# The protocol
1. Bob creates a random private key of 512 bits in length e.g. `2fba5541fda58c643524cb62... |
KEM/DEM hybrid encryption has another advantage. It enables a very efficient multi-recipient encryption. The payload is encrypted and transmitted only one time.
Haven't you wondered yet why you are able to decrypt and read your own message although it was encrypted with the recipient's public key? Normally PGP encry... |
I am studying LogSpace Merkle Tree Traversal algorithm in [this book][1]. In the [pag. 58] I don't understand the Table 1. My question is Why within of the $2^h$ rounds for $NEED_h$ exist only one $TAIL$, if tail in the page 42 is defined than intermediate nodes in $STACK_h$?
![enter image description here][2]
Defin... |
I am studying LogSpace Merkle Tree Traversal algorithm in [this book][1]. In the [pag. 58] I don't understand the Table 1. My question is Why within of the $2^h$ rounds for $NEED_h$ exist only one $TAIL$, if tail in the page 42 is defined than intermediate nodes in $STACK_h$?
![enter image description here][2]
$STAC... |
Directly applying the RSA-function to a message is **not secure** in real life. The function leaks all kinds of information about the underlying plaintext and is particularly vulnerable to active attacks (where the attacker might be able to learn something about some related message also encrypted under RSA, and use th... |
Directly applying the RSA-function to a message is **not secure** in real life. The function leaks all kinds of information about the underlying plaintext and [is particularly vulnerable to active attacks](http://security.stackexchange.com/a/32076/18527) (where the attacker might be able to learn something about some r... |
Directly applying the RSA-function to a message is **not secure** in real life. The function leaks all kinds of information about the underlying plaintext and [is particularly vulnerable to active attacks](http://security.stackexchange.com/a/32076/18527) (where the attacker might be able to learn something about some r... |
I was reading up on PBKDF2 and noted the following:
DK = PBKDF2(PRF, Password, Salt, c, dkLen)
PRF is a keyed HMAC, but I can't seem to find out what they use as key for the HMAC? |
PBKDF2 uses HMAC-SHA1 to generate keys, but what is the key for the HMAC? |
Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately [180,000 currently used][1] words in the English language.
# The protocol
1. Bob creates a random private key of 512 bits in length e.g. `2fba5541fda58c643524cb62... |
I am trying to design MiTM protected key exchange algorithm.
For instance I am using RSA asymmetric keys.
Alice and Bob respectively have each their own pair of keys. And they should be able to exchange public keys. In real life implementation there would be a relay 3rd party which should only allow Alice and Bob e... |
All examples of [one-way functions][1] I have see till now are closely related to the assumption that $NP\neq P $ (or even weaker ones, such as $UP\neq P$), but why not considering the theorem $P\neq EXP$?
In particular, why not building functions that in one way are in the class $FP$ and the inverse function compu... |
Directly applying the RSA-function to a message is **not secure** in real life. The function leaks all kinds of information about the underlying plaintext and [is particularly vulnerable to active attacks](http://security.stackexchange.com/a/32076/18527) (where the attacker might be able to learn something about some r... |
I don't understand what an active s-box is.
(in reference of designcriteria 8 of the DES)
Because e.g. by the DES all 8 s-boxes are used every round.
But this is not was active means.
So my question. What is an active S-Box and what it means when a s-box is active or when two or three s-boxes are active?
Tha... |
Directly applying the RSA-function to a message is **not secure** in real life. The function leaks all kinds of information about the underlying plaintext and [is particularly vulnerable to active attacks](http://security.stackexchange.com/a/32076/18527) (where the attacker might be able to learn something about some r... |
So let's say you had infinite time and energy. You have a hashed string of some sort. Because you have infinite time and energy, you can produce a collision(or the original value) easily enough. But, there is a problem. The hashed string was hashed an unknown amount of times. (ie, it may have been produced by `sha256(s... |
Will rehashing an SHA256 hash continually, eventually produce every possible value? |
> Is it possible that hashing "foobar" recursively an infinite amount of times will eventually yield any arbitrary hash value?
I very much doubt it. A simple demonstration of this logic can be done through the birthday paradox. Suppose we log each successive recursive SHA-256 on "foobar" in a table. We can ask ourse... |
> Is it possible that hashing "foobar" recursively an infinite amount of times will eventually yield any arbitrary hash value?
I very much doubt it. A simple demonstration of this logic can be done through the birthday paradox. Suppose we log each successive recursive SHA-256 on "foobar" in a table. We can ask ourse... |
> Is it possible that hashing "foobar" recursively an infinite amount of times will eventually yield any arbitrary hash value?
I very much doubt it. A simple demonstration of this logic can be done through the birthday paradox. Suppose we log each successive recursive SHA-256 on "foobar" in a table. We can ask ourse... |
I want to sync blobs over the network and the most frequent change will be appending to blob. To minimize data amount sent I would prefer to encrypt appended data, send it over the network, append to encrypted blob and then decrypt whole blob at once when needed. Changes are very frequent and small, so storing each cha... |
Can GCM be used in incremental mode? |
I don't see any obvious way to do this without violating the security of GCM; at least, if you are at all concerned with an evesdropper (and if you're not, why are you encrypting at all?)
Here is a distallation of your requirements: you want to have the sender send the ciphertext (including nonce, ciphertext and tag... |
I don't see any obvious way to do this without violating the security of GCM; at least, if you are at all concerned with an evesdropper (and if you're not, why are you encrypting at all?)
Here is a distallation of your requirements: you want to have the sender send the ciphertext (including nonce, ciphertext and tag... |
I don't understand what an active s-box is (in reference of design criteria 8 of the DES).
Because (e.g.) according to DES, all 8 s-boxes are used every round. But this is not was active means.
So my question: What is an active S-Box, and what does it mean when a s-box is active (or when two or three s-boxes are... |
What is an active S-Box? |
I don't understand what an active s-box is (in reference of design criteria 8 of the DES).
Because according to DES, all 8 s-boxes are used every round. But this is not what active means.
So my question: What is an active S-Box, and what does it mean when an s-box is active (or when two or three s-boxes are acti... |
If you want to deliberately leak information, so that specific entities can factor N, but it is generally secure, because this is what I can understand from your next post the you have to look into SETUPs (Secretly Embedded Trapdoor with Universal Protection). The original work is from Young & Yung see this: http://dl.... |
The recent revelations that airport staff can detain travellers in an interrogation room and force them to give over passwords to encrypted-HDD laptops under threat of jail time has made me think about some sort of dual password encryption/decryption mechanism.
For example:
- Password 1 decrypts all the data as ... |
Is there an encryption/decryption algorithm that can give two different outputs? |
Recent news articles have suggested that the NSA may be involved in trying to influence the cryptography in public standards or commercially deployed software, to enable the NSA to decrypt the encrypted traffic. See, e.g., [this article in the New York Times](https://www.nytimes.com/2013/09/06/us/nsa-foils-much-intern... |
Who uses Dual_EC_DRBG? |
Frankly, I'd be surprised if anyone did use it. Even before the potential backdoor was discovered back in 2007, the Dual_EC_DRBG was known to be _much_ slower and slightly more biased than all the other random number generators in NIST SP 800-90. To quote [Bruce Schneier](http://www.schneier.com/blog/archives/2007/11... |
Threshold decryption of public key encryption scheme allows the decryption key to be distributed among trustees . then to decrypt the cipher text it requires at least threshold t trustees to run the decryption protocol in order to get the plain text.
Now most of the literature is either based on generic multiparty c... |
Threshold decryption of public key encryption schemes allows the decryption key to be distributed among trustees. Then, to decrypt the cipher text it requires at least threshold t trustees to run the decryption protocol in order to get the plain text.
Now most of the literature is either based on generic multiparty ... |
Are there any proofs that cryptographic functions on an elliptic curve are any more difficult than the analogues over modulo arithmetic?
While at present, ECC appears to be more difficult, as it is not as advanced as research into RSA etc., it seems to me there should be no reason why ECC is much stronger than, say,... |
Is javascript RSA signing safe? |
Can anyone explain (or point to a reference) what is a hybrid argument in a security proof, and when it's convenient or preferable to use it? |
What is it meant by a "hybrid argument"? |
Can anyone explain (or point to a reference) what is a hybrid argument in a security proof, and when it's convenient or preferable to use it?
Among some of the places where I've seen it mentioned, there is [this paper](http://link.springer.com/chapter/10.1007%2F978-3-642-19571-6_16). The term *standard hybrid argume... |
Can anyone explain (or point to a reference) what is a hybrid argument in a security proof, and when it's convenient or preferable to use it?
Among some of the places where I've seen it mentioned, there is the paper [Boneh, Sahai, Waters - Functional Encryption: Definitions and Challenges](http://link.springer.com/c... |
uWhat is it meant by a "hybrid argument"? |
What is it meant by a "hybrid argument"? |
There are very few non-trivial proven lower bounds in computational complexity, and none whatsoever in cryptography, as far as I know.
Almost all results are of the form "If X is infeasible, then so is Y." For example, "If AES is a secure pseudo-random function, then so is CBC-AES given parameters such-and-such."
... |
What key exchange do OpenSSL and CryptoAPI prefer by default? |
This week's revelations put this question (and its answers) into an entirely new light.
This Schneier editorial is pretty good:
http://www.theguardian.com/world/2013/sep/05/nsa-how-to-remain-secure-surveillance
The NYT has a graphic summarizing the revealed NSA capabilities thus far:
http://www.nytimes.com/... |
This week's revelations put this question (and its answers) into an entirely new light.
This Schneier editorial is pretty good:
http://www.theguardian.com/world/2013/sep/05/nsa-how-to-remain-secure-surveillance
The NYT has a graphic summarizing the revealed NSA capabilities thus far:
http://www.nytimes.com/... |
I am the designer of the random number generator that is behind the Intel RdRand instruction.
>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?
It isn't. We cannot. It passes the test... |
Does the improved version of NTRU described in the following paper fall under the same patents as the original?
Stehlé and Steinfeld, "Making NTRU as Secure as Worst-Case Problems over Ideal Lattices".
http://users.monash.edu.au/~rste/ProvNTRU_V10a.pdf |
Is the secure-as-worst-case version of NTRU still patented? |
Is it possible to reconstruct the previous output bits of a stream cipher, e.g. RC4, when only the current state is known, or is that computationally hard, or even impossible (due to ambiguous preceding states)?
For Salsa, it's obviously possible, since that even allows for random access.
Is there a formal name f... |
Can stream ciphers (usually) be "run backwards"? |
Imagine I am a software developer. I want a block cipher, and I have the choice of using AES or Camellia. Which should I use? Which makes more sense from a technical perspective, and why? I need to select the preference order for TLS ciphersuites: should I put the AES ciphersuites above or below the ciphersuites?
... |
Camellia or AES - which should I use? |
I see a lot of Q/A where persons are trying to generate a specific key pair using static data such as a password. Now say we use a known PRNG (dangerous assumption), seeded with a the data as a static seed, would this always generate the same key pair?
I presume it would generate the same key pair if you would use t... |
I see a lot of Q/A where persons are trying to generate a specific key pair using static data such as a password. Now say we use a known PRNG (dangerous assumption), seeded with a the data as a static seed, would this always generate the same key pair?
I presume it would generate the same key pair if you would use t... |
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