instruction stringlengths 15 30k |
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I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I just send a password in plaintext between the two processes and the host process just performs a string comparison with it... |
I don't think they have implemented homomorphic encryption at all. They have just implemented regular AES encryption (they have a FIPS 197 certificate for their AES), but in what appears to be a very insecure way. Why would they choose to do that? Because they had no choice. Here's what I mean:
The challenge for cl... |
Suppose there is a message that is encrypted with AES-128-CBC. The message is as follows, new lines are used to delimit the 16 byte boundary for each block:
Wire funds from:
Alice to Bob in
the amount of $
1
Because this message is encrypted using CBC mode, any modification of the first blo... |
Under what circumstances is a decryption routine able to tell that the padding of a message is invalid? If a cipher text block where to be randomly modified, what is the probability that the padding would be correct? How does the type of padding influence the detectability of cipher text that has been tampered with? |
How is block cipher padding verified for consistancy? |
First of all, you stated:
Because this message is encrypted using CBC mode, any modification of the first block of
cipher text would propagate throughout the message.
Actually, that's not true. Here's the CBC mode operation in the decryption direction:
![CBC mode decryption][1]
([Public domain ima... |
Our industry (area of cheap networked devices) has a standard that defines the usage of keys for both authentication and encryption using EAX mode of AES. This standard does not define key management, and someone wants to change this key material in devices using the RFC 3394 key wrap algorithm. For that they want to u... |
Suppose I have to use 64-bit keys for encryption (e.g. to comply with export restrictions). For this question, assume this key is truly random, and the encryption algorithm is Blowfish.
Blowfish key schedule expands this 8-byte key into 4168 bytes of state (P-array and S-boxes). Will it slow down bruteforce attacks ... |
Can iterated key expansion in Blowfish slow down bruteforce attacks on small key sizes? |
Suppose we have a state of block cipher initialized with some key unknown to us, that is, we have the state after running key schedule, but we have no access to actual key or subkeys, all we can do is encrypt and decrypt data with this state. How to safely derive an HMAC key for it that we can use to authenticate data ... |
What are the safe ways to derive HMAC key from block cipher? |
Suppose we have a state of block cipher initialized with some key unknown to us, that is, we have the state after running key schedule, but we have no access to actual key or subkeys, all we can do is encrypt and decrypt data with this state. How to safely derive an HMAC key from it that we can use to authenticate data... |
Suppose I have to use 64-bit keys for encryption (e.g. to comply with export restrictions). For this question, assume this key is truly random, and the encryption algorithm is Blowfish.
Blowfish key schedule expands this 8-byte key into 4168 bytes of state (P-array and S-boxes). Will it slow down bruteforce attacks ... |
What are the safe ways to derive HMAC key using block cipher? |
Suppose there is a message that is encrypted with AES-128-CBC. The message is as follows, new lines are used to delimit the 16 byte boundary for each block:
Wire funds from:
Alice to Bob in
the amount of $
1
Because this message is encrypted using CBC mode, any modification of the first blo... |
First of all, you stated:
> Because this message is encrypted using CBC mode, any modification of
> the first block of cipher text would propagate throughout the message.
Actually, that's not true. Here's the CBC mode operation in the decryption direction:
![CBC mode decryption][1]
([Public domain image f... |
> **Possible Duplicate:**
> [Security considerations for partially shared password databases](http://crypto.stackexchange.com/questions/3639/security-considerations-for-partially-shared-password-databases)
<!-- End of automatically inserted text -->
Programs like KeyPass and 1Password store password database file... |
How secure would a hash function be which AES-encrypts the message with a well-known password (say the first 128 bits of pi) using cipher-block-chaining and then XORs all the encrypted blocks together? (in the case where the message is only 16 bytes, you can append an extra zero block to the message) |
How secure would a hash function be which appends an extra block of 16 zeroed out bytes to the end of the message and then AES-encrypts it with a well-known password (say the first 128 bits of pi) using cipher-block-chaining and then XORs all the encrypted blocks together?
|
Why pairing based crypto is being widely used in some special crypto primitives as ID based crypto and variations of standard signatures? I mean taking as deep as possible what makes it suitable for that schemes while other schemes do not feet? |
Why pairing based crypto is suitable for some particular cryptographic primitives? |
It won't compress because data that is encrypted with AES becomes pseudo-random-like and thus as close to maximum entropy as possible. As you pointed out, the clear text input is low entropy.
Additionally, entropy can be used as a way to detect clear text (given the clear text isn't pseudo-random itself). The outp... |
I need to encrypt a file, distribute it over an insecure channel, and decrypt it later. Using a symmetric-key algorithm. Here's what I intend to do:
Get a password P from the user. Generate a 16-byte random salt S. Derive a key K1 = PBKDF2(HMAC-SHA1, P, S, iter=2000, bits=256). Divide the data into blocks of 1024 by... |
Is this a good way to encrypt a file? |
I need to encrypt a file, distribute it over an insecure channel, and decrypt it later. Using a symmetric-key algorithm. Here's what I intend to do:
Get a password P from the user. Generate a 16-byte random salt S. Derive a key K1 = PBKDF2(HMAC-SHA1, P, S, iter=2000, bits=256). Divide the data into blocks of 1024 by... |
Assuming I had to distribute salt+ciphertext together over an insecure channel, isn't it better to store the salt encrypted?
By encrypted I mean with a block cipher and with key and IV derived from the same passphrase used to encrypt the original text.
I've been told that leaving salt unencrypted is the way to go... |
Why not encrypt salt? |
how can Alice, Bob, and Charlie share a common secret key using Diffie-Hellan key exchange protocol?
a=3, b=4, c=5
g= 2
p=5 |
How can Alice, Bob, and Charlie share a common secret key using an extended version of the Diffie-Hellman key exchange protocol?
a=3, b=4, c=5
g=2
p=5 |
How can the Diffie-Hellman key exchange be extended to three parties? |
Should I use a different salt for each password?
In my system, there are no user names, only passwords. When a user logins in, he types in one or more passwords and the server compares the results of the password(s) hashed many times (PBKDF2) for authentication. Each password might unlock some subset of functions.... |
Do I have to have a different salt for each password? |
> "In my system, there are no user names, only passwords."
This is the real problem. Using the same value for both identification and authorization is usually a bad idea, for several reasons:
* Two accounts cannot have the same password.
* An on-line attacker needs only a single query to determine if _any_ pass... |
> **Possible Duplicate:**
> [Can one generalize the Diffie-Hellman key exchange to three or more parties?](http://crypto.stackexchange.com/questions/1025/can-one-generalize-the-diffie-hellman-key-exchange-to-three-or-more-parties)
<!-- End of automatically inserted text -->
How can Alice, Bob, and Charlie share a... |
Are there are a known pair of distinct bit strings such that SHA1(A) == SHA1(B)?
If the answer is no than how can SHA1 be considered broken?
|
No SHA-1 Collision? Yet SHA1 is broken? |
I came up with a truly new method of applying modulo-2-addition encryption function in stream ciphers which is inspired by a mechanism used to prove a mathematical theorem. How can I determine whether my method is cryptographically correct and considerable? If so, how can I officially submit or formally register it in ... |
Is there an algorithm that can be used to verify the contents of a cyphertext, but not the order of the elements?
I am thinking that a deck of cards could be shuffled, and it must be verifiable that the deck contains all cards, but not to know what order they are in.
Any ideas how to approach this problem? |
It is not clear what you are asking.
Maybe you are asking the following. You have a set of 52 ciphertexts, each of which is allegedly the encryption of a different card, and you want to check that these are an encryption of some permutation of the 52 possible cards (i.e., no card appears twice, every card appears a... |
I want to encrypt a small amount (few kilobytes) of data and be fairly confident it will be secure against brute force decryption for at least a a few decades (or more). I am flexible on the amount of time it takes (even a minute is reasonable) to encrypt as this will run on the client machine, and not on a server.
... |
How to encrypt data and know it will be secure for at least a few decades? |
I realise this isn't a 'yes or no' question, and I apologise for asking something that could be seen as a discussion thread, but I had to ask.
I'm currently doing an EPQ in CS (specifically how QC will change Cryptography). I'm trying to gather up topics to cover, and so far I've scribbled down -
Effects -
1. ... |
How will Cryptography be changed by Quantum Computing? |
I want to encrypt a small amount (few kilobytes) of data and be fairly confident it will be secure against brute force decryption *and advances in cryptanalysis* for at least a a few decades (or more). I am flexible on the amount of time it takes (even a minute is reasonable) to encrypt as this will run on the client m... |
> Is this a good idea?
Not really.
It is rare to find attacks against vetted designs that allow a complete break with a tiny amount of cipher-text.
Assuming you plan to have a unique key (which isn't used anywhere else) for just this few kilobytes of plaintext, it's very unlikely any cryptographic attack could... |
> Is this a good idea?
Not really.
It is rare to find attacks against vetted designs that allow a complete break with a tiny amount of cipher-text.
Assuming you plan to have a unique key (which isn't used anywhere else) for just this few kilobytes of plaintext, it's very unlikely any cryptographic attack could... |
Are there advantages to using [TOTP][1] over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
[1]: http://tools.ietf.org/html/rfc6238 |
Could a variable participant lottery system cryptographically prove that they have zero knowledge of the outcome of a draw?
Participants do not choose numbers in this lottery and winning numbers are not drawn. Instead, they simply enrol with a wager. Winners are selected by taking all wagers and building an array of... |
Could a variable participant lottery system cryptographically prove that they have zero knowledge of the outcome of a draw?
Participants do not choose numbers in this lottery and winning numbers are not drawn. Instead, they simply enrol with a wager. Winners are selected by taking all wagers and building an array of... |
Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission
The question was stated as this :
> What could a hacker do while provided with the SSH server private key
> and a MitM position specifically when the client is authenticated with a
> public key (server ... |
[Porticor][1] has an interesting file encryption offering for encrypting and decrypting files in an MySQL database quickly.
They are an Amazon AWS (Amazon Web Service) Partner Network technology partner and their product is available in the AWS Marketplace.
It seems similar to Gazzang's zNcrypt.
Porticor has b... |
Is Porticor's "homomorphic" key encryption something that can really be done or is it just marketing hype? |
I am unsure of how a padding oracle attacks work. What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines.
Can anyone explain this? |
I am unsure of how a padding oracle attack works.
What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines.
Can anyone explain this? |
How does a padding oracle attack work? |
As I understand it, you're asking for a protocol where every player contributes some "entropy" to the overall random mechanism, so they can be assured that nobody else gamed the system. But in such a system you would assume that every player has the opportunity to select a value giving them the best chance of winnin... |
Why RC4 used 24-bits constant value + 40 bits random values to generate key? |
This is an idea I had for cipher that I thought might reduce to a known hard problem. It is efficient (compared to something like BBS) in terms of time but not in terms of space.
Here's the algorithm:
1. Produce 128 real random streams equal in length to the plain-text.
2. Let each bit of the 128-bit streams ... |
This is an idea I had for cipher that I thought might reduce to a known hard problem. It is efficient (compared to something like BBS) in terms of time but not in terms of space.
Here's the algorithm:
1. Produce 128 real random streams equal in length to the plain-text.
2. Let each bit of the 128-bit streams ... |
Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission
The question was stated as this :
> What could a hacker do while provided with the SSH server private key
> and a MitM position specifically when the client is authenticated with a
> public key (server ... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
Why is the salt used only once in PBKDF2, while the password is used often? |
This is an idea I had for cipher that I thought might reduce to a known hard problem. It is efficient (compared to something like BBS) in terms of time but not in terms of space.
Here's the algorithm:
1. Produce 128 real random streams equal in length to the plain-text. (These do not need to be secret, they can... |
Is TOTP or a timestamp encryption a better timestamp-based authentication token system? |
It's not really PBKDF2 that uses the key twice. PBKDF2 uses HMAC, and HMAC happens to work by using the key twice.
More specifically, PBKDF2 is actually a general construction [that uses][2] a cryptographic [Pseudo-Random Function][6] (PRF) to do some of the internal work. The PRF used here is keyed [HMAC][1]. The H... |
What are well respected [Cryptographic Timestamping](https://en.wikipedia.org/wiki/Trusted_timestamping) authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), hybrid ?
Is there any good resource (better than googling, what does... |
What are well respected [Cryptographic Timestamping](https://en.wikipedia.org/wiki/Trusted_timestamping) authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), hybrid ?
Is there any good resource (better than googling, what does... |
What are well respected [Cryptographic Timestamping](https://en.wikipedia.org/wiki/Trusted_timestamping) authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), hybrid ?
Is there any good resource (better than googling, what does... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
Does anyone know how to do a Diffie-Hellman or [ECDH][1] key exchange with more than two parties?
I know how to do a key exchange between 2 parties, but I need to be able to have a key agreement between 3 or more parties.
[1]: http://en.wikipedia.org/wiki/Elliptic_curve_Diffie%E2%80%93Hellman |
In practice, I don't think it is *necessary* to use the password in every iteration. As far as I know, I think the construction would still be secure (in practice) if you used the salt and password only in the input to the first iteration, and then just repeatedly hashed the result many times without feeding in the pa... |
**Summary: I don't know of any good reason why it has to be this way.** In practice, I don't think it is *necessary* to inject the password into every iteration. As far as I know, I think the construction would still be secure (in practice) if you used the salt and password only in the input to the first iteration, an... |
**Summary.** This scheme is insecure. It can be cryptanalyzed using standard methods from the cryptanalytic literature. It also has poor performance.
**Your algorithm.** To summarize your scheme, in your algorithm a message $m \in GF(2)$ is encrypted by picking a random quadratic polynomial $p(x_1,\dots,x_{128})$ ... |
**Summary.** This scheme is insecure. It can be cryptanalyzed using standard methods from the cryptanalytic literature. It also has poor performance.
**Your algorithm.** To summarize your scheme, in your algorithm a one-bit message $m \in GF(2)$ is encrypted by picking a random quadratic polynomial $p(x_1,\dots,x_... |
> What are the disadvantages of using random s-boxes?
This relates to the "why" behind some of the rules for s-boxes. AES, for example, requires an invertible s-box. A random s-box will not necessarily be invertible. In an s-box we also want non-linearity to thwart linear and differential cryptanalysis. This might n... |
The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But if that's the case, why does it play such a minor role?
I'll let the equations speak for themselves, starting with HM... |
First off, you are still missing some information. What encryption mode will you be using? What key are you using for the HMAC?
That said, my answer is no. This isn't a good way. The reason being is that unless you are a professional cryptographer, you shouldn't design your own cryptographic protocols/methods. There... |
Systems like ssh, for example, often encrypt a user's private key using a password, so that is not new. The fact that they are published on a web server that technically anyone could access is a little different. But, if the password is strong, brute force and dictionary attacks would be impossible. So the system seems... |
i am implementing a timing attack on RSA for school and i need to generate two sets of messages Y and Z for which holds:
(Y^d mod N) * Y < N and (Z^d mod N) * Z > Z
where d and N are known. How can i efficiently find solutions for Y and Z?
I have tried using a random function but it takes too long to comp... |
i am implementing a timing attack on RSA for school and i need to generate two sets of messages Y and Z for which holds:
(Y^d mod N) * Y < N and (Z^d mod N) * Z > N
where d and N are known. How can i efficiently find solutions for Y and Z?
I have tried using a random function but it takes too long to comp... |
I am implementing a timing attack on RSA for school and I need to generate two sets of messages $Y$ and $Z$ for which holds:
$ (Y^d \mod N) \cdot Y < N $ and
$ (Z^d \mod N) \cdot Z > N $
where $d$ and $N$ are known. How can I efficiently find solutions for $Y$ and $Z$?
I have tried using a random function... |
Say you have a picture with 1 megapixels taken at random and with 2^24 possible colours per pixel (RGB-24). That image would be unique and the possible combinations (2^24)^(10^6) immense.
However when taking a picture in the real world, say of a clear sky, there will be a lot of repetition.
The question is: woul... |
Do pictures generate a random output? Cryptography |
I would like to know how to store a sensitive file; a credential of sorts. I want to password-protect it, obviously. It would be appropriate - in my application - to prompt the user for the password each run. There are proper apps - like SSH - that password-protect private keys and so on, and that's the model and be... |
Say you have a picture with 1 megapixels taken at random and with $2^{24}$ possible colours per pixel (RGB-24). That image would be unique and the possible combinations $(2^{24})^{10^6}$ immense.
However when taking a picture in the real world, say of a clear sky, there will be a lot of repetition.
The question ... |
Are picture files "random enough" to be usable as a one-time pad? |
**What is the harm if I publish an encrypted RSA private key publicly?** Or in this case, what is the harm if I publish many thousands or millions of them?
Assuming that the private key is encrypted with a typical user password, the passphrase is some combination of password + user ID (which is not necessarily user... |
For example, Is possible to combine (Concatenate or Chain or XOR) Skein SHA-3 candidate with Grostl SHA-3 candidate to increase security?
Note: I just want more secure output and CPU cycles does not matter |
Can I combine two of SHA-3 candidates cryptography hash functions and obtain more secure Algorithm? |
I'm encrypting some files using AES.
I'm also using file's digest (SHA-1) to check that data is decrypted correctly.
Is it safe to use this digest as AES's IV and store it in the header of file?
Or it has security issue?
Thanks |
Is it safe to use file's hash as IV? |
I'm encrypting some files using AES in CBC mode.
I'm also using file's digest (SHA-1) to check that data is decrypted correctly (so i need to store it with file).
Is it safe to use this digest as AES's IV and store it in the header of file?
Or it has security issue?
Thanks |
You obviously use [semantic security](http://en.wikipedia.org/wiki/Semantic_security) when you use deterministic encryption.
You end up with something similar to convergent encryption, which has a few issues. Check the question [Is Convergent Encryption really secure?](http://crypto.stackexchange.com/questions/729/i... |
You obviously use [semantic security](http://en.wikipedia.org/wiki/Semantic_security) when you use deterministic encryption. This means an attacker can tell if two files are identical. publishing the unencrypted hash also leaks which file you encrypted, if the attacker knows the hash from elsewhere.
You end up with ... |
You obviously lose [semantic security](http://en.wikipedia.org/wiki/Semantic_security) when you use deterministic encryption. This means an attacker can tell if two files are identical. publishing the unencrypted hash also leaks which file you encrypted, if the attacker knows the hash from elsewhere.
You end up with... |
i am having problems understanding how CBC works! I know that it is a chain and the IV is XORed with the PT but then what? I mean we encrypt it with key k and the result is the CT which we use for the next chain-XOR but my question is HOW the encryption works? For example in Stream ciphers i just had to XOR the K with ... |
Programs like KeyPass and 1Password store password database files encrypted by a single password. If someone knows the protecting password ("Vault Key"), they can read the entire database ("secrets").
Being part of a family, I sometimes share passwords with my wife and others for bank accounts or Netflix which we ma... |
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