instruction stringlengths 15 30k |
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So I was watching a popular series tonight (Person Of Interest) when suddenly during a frame change I noticed a very quick blue screen with writing.
At the time I never thought anything of it as it was to quick, it was embedded within a one second interval gap at 20:50 to 20:51.
I tried using my media player ... |
Encrypted Message in popular TV Show? |
ASCII Message in TV show? |
Is signing a hash instead of the full data considered secure? |
There is no meaningful distinction between these two things. Consider this scheme:
1. Hash the object.
1. Sign the hash.
Now, does this scheme sign the hash or the full object? Step 2 signs the hash. But the *scheme* signs the full object. So which is it?
|
For the purpose of key diversification (that is, assigning a unique key per device), a true `master_key` is customary; that is, one with plenty of entropy (like, 128 bits or more random bits). Edit: that's now stated in the question.
With that caveat, **yes, `PBKDF2(password=master_key, salt=serial_number, rounds=10... |
For the purpose of key diversification (that is, assigning a unique key per device), a true `master_key` is customary; that is, one with plenty of entropy (like, 128 bits or more random bits). Edit: that's now stated in the question.
With that caveat, **yes, `PBKDF2(password=master_key, salt=serial_number, rounds=10... |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
Selective format-compliant JPEG encryption? |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
I am trying to break a packet format. The packet format simply packs several files into one big file. The file contents are plain. But the index data which contain offsets, file sizes and filenames are encrypted. The index data are about 1 KB and compressed by zlib (the DEFLATE algorithm with no zlib or gzip wrapper), ... |
I came across some code in our project that encrypts usernames (limited to 50 chars, most are less than 10) using the following parameters:
IV size is 16 bytes
Key size is 32 bytes
Algorithm is CBC-AES (256bits)
Is there a security issue because of these parameters? Why would you use CBC and not ECB with a ... |
I came across some code in our project that encrypts usernames (limited to 50 chars, most are less than 10) using the following parameters:
IV size is 16 bytes
Key size is 32 bytes
Algorithm is CBC-AES (256bits)
Is there a security issue because of these parameters? Why would you use CBC and not ECB with a ... |
If I have a string encoded with AES CBC with PKCS#5 padding, how can one possibly decrypt/crack it? What are the approaches that one can take to break its security? |
How to break AES CBC with PKCS#5 padding? |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
Among other sources, [this wikipedia entry][1] states that triple DES using three seperate keys (k1, k2, k3) is vulnerable to meet-in-the-middle-attacks, while triple DES using only two keys (k1, k2, k1) is not.
Why is this attack possible if all the keys are different, but not if the first and the third are the sam... |
Why is triple-DES using three different keys vulnerable to a meet-in-the-middle-attack? |
There is a side channel attack on tamper-resistant USB cryptographic tokens using padding-oracle, described by Bardou, Focardi, Kawamoto, Simionato, Steel and Tsay, titled "Efficient padding oracle attacks on cryptographic hardware" (INRIA; CRYPTO 2012, LNCS Volume 7417, 2012, pp 608-625), [full paper](http://hal.inria... |
There is a side channel attack on tamper-resistant USB cryptographic tokens using padding-oracle, described by Bardou, Focardi, Kawamoto, Simionato, Steel and Tsay, titled "Efficient padding oracle attacks on cryptographic hardware" (INRIA; CRYPTO 2012, LNCS Volume 7417, 2012, pp 608-625), [full paper](http://hal.inria... |
There is a side channel attack on tamper-resistant USB cryptographic tokens using padding-oracle, described by Bardou, Focardi, Kawamoto, Simionato, Steel and Tsay, titled "Efficient padding oracle attacks on cryptographic hardware" (INRIA; CRYPTO 2012, LNCS Volume 7417, 2012, pp 608-625), [full paper](http://hal.inria... |
There is a side channel attack on tamper-resistant USB cryptographic tokens using padding-oracle, described by Bardou, Focardi, Kawamoto, Simionato, Steel and Tsay, titled "Efficient padding oracle attacks on cryptographic hardware" (INRIA; CRYPTO 2012, LNCS Volume 7417, 2012, pp 608-625), [full paper](http://hal.inria... |
Searching for "small blocksize cipher" finds a number of discussions on the topic, mostly refering to FPE.
[This one](http://crypto.stackexchange.com/questions/504/can-you-create-a-strong-blockcipher-with-small-blocksize-given-a-strong-blockci/) in particular suggests using AES as the round function of a Feistel net... |
This will probably be OK. It does have some non-trivial side effects/caveats:
* The effective key length is reduced to 86 bits. Only the low 22 bits of each of the 4 key words will matter, so only 88 bits of the key material are relevant. Then, there are known equivalent-key properties of TEA that further reduce ... |
I am new to crypto and trying to understand why it would be insecure to use AES to encrypt a key with the same key.
Basically, something like this:
encrypt(key, key)
What happens when both key and message are the same (128bits).
The obvious question would be why I would want to do that. If I have a secure cha... |
There is no point to this. It would be like having two keys for a locked chest and then locking one of them in the chest. The only way to get the key out is by using the other key. You already have the key so why do you need the one in the chest? You can just make copies of the key without needing to go into the ch... |
I'm taking the question as: given some cryptosystem using AES-128 with some random secret key $K$, what are the benefit and drawback of computing and making public $\hat K=\operatorname{AES}_K(K)$?
**Benefit**: a legitimate holder of $K$ could do the same with the $K'$ he holds and believes is $K$, and compare $\ope... |
I'm taking the question as: given some cryptosystem using AES-128 with some random secret key $K$, what are the benefit and drawback of computing and making public $\hat K=\operatorname{AES}_K(K)$?
**Benefit**: a legitimate holder of $K$ could do the same with the $K'$ he holds and believes is $K$, and compare $\ope... |
I'm looking at using [Scrypt](http://en.wikipedia.org/wiki/Scrypt) as a KDF. Assume the following:
- the input will always be high-entropy random bytes generated by a CSPRNG
- the length of the input can vary from between 8 to 32 bytes
- the input-bytes are never re-used for generating another key
- the salt is ... |
Searching for "small blocksize cipher" finds a number of discussions on the topic, mostly refering to FPE.
[This one](http://crypto.stackexchange.com/questions/504/can-you-create-a-strong-blockcipher-with-small-blocksize-given-a-strong-blockci/) in particular suggests using AES as the round function of a Feistel net... |
Sorry about the horrible title, didn't now what to say.
I'm trying to avoid having to send an IV with every message purely to keep packet sizes down, so I thought of a method to establish a "IV Pool".
This is how I thought it should be:
**Client** ---- *Handshake* ---> **Server**
**Server** ---- *Handshake*... |
I'm taking the question as: given some cryptosystem using AES-128 with some random secret key $K$, what are the benefit and drawback of computing and making public $\hat K=\operatorname{AES}_K(K)$?
**Benefit**: a legitimate holder of $K$ could do the same calculation with the $K'$ he holds and believes is $K$, and c... |
In the public-key system RSA scheme, each user holds a public key, e, and a private key, d. Suppose that Bob gives his private key to other users. Rather than generating a new modulus, Bob decides to generate a new public and a new private key.
Is this safe for Bob? |
Is this message secure in RSA algorithm? |
In the public-key system RSA scheme, each user holds beyond a public modulus $m$ a public exponent, $e$, and a private exponent, $d$.
Suppose that Bob gives his private exponent to other users. Rather than generating a new modulus, Bob decides to generate just a new public and a new private exponent $e'$ and $d'$.
... |
Is sharing the modulus for multiple RSA key pairs secure? |
Is it possible to generate signature only from Public key. See example below where i have valid signature but what if I change hash ? Is then any way to do this?
Public key(160 bytes):
0024000004800000940000000602000000240000525341310004000001000100B7373AAC1521A3EF2F5C72DFD3D3F715C56810F2A222AD9179D9DEE099389B7A67... |
So, as an exercise to greater understand some things about cryptography, I decided to try and implement GOST 28147-89, which uses eight 4x4 S-Boxes. I can grasp the concept of putting 4 bits through the S-Box and getting four out, but how would one reverse this?
Furthermore, how would one reverse uneven S-Boxes, suc... |
How can an S-Box be reversed? |
when you try connect SSH you see a signature which is short but i herd i even stronger than sha256. it must be perhaps because of more more rounds. is there any hash function or a method on current hash functions that use more more rounds or something like that to prevent collision attacks and provide a very strong ha... |
what kind of hash function can provide a short hash and be collision resistant? |
When you try to connect via SSH, you see a signature which is short but I heard it is even stronger than sha256. It is perhaps stronger because it uses more rounds. Is there a hash function or a method on current hash functions that use more rounds or something like that to somehow prevent collision attacks and provide... |
Sending a big block of data to be then used as initialization vectors is secure (assuming it is transferred encrypted and authenticated), but kind of defeats the purpose of "keeping the message size down".
The requirements for an initialization vector depend on the mode of operation, not on the underlying cipher (... |
I posted this in a reply to http://crypto.stackexchange.com/questions/494/what-is-the-post-quantum-cryptography-alternative-to-diffie-hellman/ but since it's actually another question, it was deleted.
Has anyone come across any implementations of Ntru TLS? I'm working a project for uni that does quantum secure encr... |
Suppose that we have a sequence of $N$ digits that is produced by a Linear Feedback Shift Register ([LFSR][1]) of length $L$. A very important tool in cryptanalysis of stream ciphers (among many other things) is the [Berlekamp-Massey algorithm][2]; if $2L\leq N$, this algorithm will produce the *unique* LFSR that gener... |
The Berlekamp-Massey algorithm find the _shortest_ LFSR that can produce the given sequence.
Formally, if the sequence has $n$ elements $S_0, S_1, \ldots, S_{n-1}$, then the
algorithm finds $\lambda_1, \lambda_2, \ldots, \lambda_t$ such that for
$i = t, t+1, \ldots, {n-1}$, the following equation holds:
$$
S_{i}... |
I'm taking the question as: given some cryptosystem using AES-128 with some random secret key $K$, what are benefits and drawbacks of computing and making public $\hat K=\operatorname{AES}_K(K)$?
**Benefit - $\hat K$ can be used as a KCV**: A legitimate holder of $K$ could do the same calculation with the $K'$ he ho... |
The Berlekamp-Massey algorithm find the _shortest_ LFSR that can produce the given sequence.
Formally, if the sequence has $n$ elements $S_0, S_1, \ldots, S_{n-1}$, then the
algorithm finds $\lambda_1, \lambda_2, \ldots, \lambda_t$ such that for
$i = t, t+1, \ldots, {n-1}$, the following equation holds:
$$
S_{i}... |
I take the question as: how short can be a cryptogram used to verify integrity of some data, in the common situation where
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the crypto... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
Suppose that we have a sequence of $N$ digits which is produced by a Linear Feedback Shift Register ([LFSR][1]) and the shortest such LFSR is of length $L$. A very important tool in cryptanalysis of stream ciphers (among many other things) is the [Berlekamp-Massey algorithm][2]; if $2L\leq N$, this algorithm will produ... |
Does encrypt time less than decrypt time in RSA cryptograohy? |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
I take the question as: how short can a cryptogram be when used to verify integrity of some data, in the common situation where:
1. we trust the party that computes the cryptogram from the original data;
2. an adversary knows everything we or the trusted party knows;
3. we trust the channel by which we obtain the ... |
What are unified addition and differential addition in elliptic curve point arithmetic? |
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping the rest unaltered. The aim would be, for instance, being able to publish a picture on any given social network, making t... |
I have genereted two equal session keys on client and server successfully. But I couldn't understand how each other should validate that they have same session keys.
On the client I generated a SHA1 hash with equation p = SHA1(A | B | S) where A and B are public keys of client and server and S is the SHA1 hash of th... |
Unified addition means that the formula you use for adding two points doesn't depend on whether they are equal. Simplifying [point addition in the Weierstrass form](http://en.wikipedia.org/wiki/Elliptic_curve#The_group_law) somewhat $s=(y_A-y_b)/(x_A-x_b)$ when $A\neq B$ - this is "Adding". Otherwise $s={3x_A^2-p}/{2y_... |
Unified addition means that the formula you use for adding two points doesn't depend on whether they are equal. Simplifying [point addition in the Weierstrass form](http://en.wikipedia.org/wiki/Elliptic_curve#The_group_law) somewhat $s=(y_A-y_b)/(x_A-x_b)$ when $A\neq B$ - this is "Adding". Otherwise $s=(3x_A^2-p)/{2y_... |
I'm not a Cryptography expert, but i've seen this topic sometimes on the Web: Master decrypt keys.
Most of the people said that "Master decrypt key" does not exist.
This makes sense if you developed your own Cryptography software.
But if a company releases a cryptography software, where the user must enter the... |
Master keys for decrypting? |
I'm working on a program that uses an ECC keypair in a (password protected) PKCS12 file (.pfx) to encrypt files. I like this method because I think it will be higher security (using ECDH to negotiate the key) and more easy to use (one PIN for all files). How I'm going about this is by using the public and private keys ... |
File encryption with one keypair? |
This is giving me a brain ache now... If I have AES-128, block is 128 bit, then every plaintext (128-bit) can be encrypted to some ciphertext that is also 128-bit. This is the block size. But: 128-bit block can have 2^128 different values. So if I have 128-bit key - then it seems to be natural to have every different k... |
I am designing an implementation of RSA . I recorded computation times in Java by using `System.currentTimeMillis()`. It returned an encryption time of 0.05 ms and decryption time of 0.55 ms, or a ratio of 1:11.
This seems like a large difference. Is it supposed to be this way?
//here my key has 256 bits
... |
Is RSA encryption significantly faster than decryption? |
> So if I have 128-bit key - then it seems to be natural to have every
> different key produce different ciphertext for a given plaintext - p1.
That is not so. AES is a keyed permutation of a 128-bit block, that is, each different key produces a unique permutation. But the key space is *not* a permutation on the ou... |
> So if I have 128-bit key - then it seems to be natural to have every
> different key produce different ciphertext for a given plaintext - p1.
That is not so. AES is a keyed permutation of a 128-bit block, that is, each different key produces a unique permutation. But the key space is *not* a permutation on the ou... |
This is giving me a brain ache now... If I have AES-128, block is 128 bit, then every plaintext (128-bit) can be encrypted to some ciphertext that is also 128-bit. This is the block size. But: 128-bit block can have 2^128 different values. So if I have 128-bit key - then it seems to be natural to have every different k... |
In the definition below, what exactly does it mean for the adversary (not even sure that's the correct term?) to equal one? (I wasn't quite able to format the math as desired, but hopefully it's close enough)
$$
Pr_K[A^{F_k(.)} = 1]
$$
[Source](http://www.csc.kth.se/utbildning/kth/kurser/DD2448/krypto13/handou... |
In the definition below, what exactly does it mean for the adversary (not even sure that's the correct term?) to equal one?
$$
\underset{K}{Pr} \left [A^{F_k(\cdot)} = 1 \right ]
$$
[Source](http://www.csc.kth.se/utbildning/kth/kurser/DD2448/krypto13/handouts/lec03.pdf) (Page 22/35?) or [Imgur Link](http://i.i... |
Consider the Blum-Goldwasser encryption scheme as described on [Wikipedia][1]. I was told that it was not IND-CCA-2 secure.
I heard there was malleabilty, probably it has to do with XOR-ing. But I do not see the point. As stated in the Wikipedia article, in step 2 of the encryption, we choose a random element. So wh... |
Why is Blum-Goldwasser not IND-CCA-2 secure? |
Apologies if this question is not in the right place.
I've recently been looking through some RSA certificates ( specifically, Android apk .rsa files) and I'm having trouble deciphering the one and two letter combinations in the Owner/Issuer lines.
ex: CN, OU, O, L, ST, C
L, ST, and C are Location, State and ... |
RSA Certificate Owner and Issuer line meanings? |
I have a fairly simple Python program using PyCrypto to use AES+CBC to encrypt a stream of input. In order to adhere to the 16-byte input size multiple, I've implemented PKCS#7 by hand. (While I know implementing cryptographic methods by hand is generally a bad idea, padding 1-16 bytes of data isn't exactly the hardest... |
Implementing PKCS#7 Padding on a Stream of Unknown Length? |
I'm encrypting a file using AES-256 in CBC mode. I'm padding to the 16-byte input multiple by using the PKCS#7 limit. The problem I'm currently having is that if I'm transferring or reading the encrypted file over a socket, I won't know when the encrypted file has been finished, as I'm reading it in chunks. Because of ... |
Is storing original file size in an encrypted file header a bad idea? |
> So if I have 128-bit key - then it seems to be natural to have every
> different key produce different ciphertext for a given plaintext - p1.
That is not so. AES is a keyed permutation of a 128-bit block, that is, each different key produces a unique permutation. But the key space is *not* a permutation on the ou... |
I'm encrypting a file using AES-256 in CBC mode. I'm padding to the 16-byte input multiple by using the PKCS#7 limit. The problem I'm currently having is that if I'm transferring or reading the encrypted file over a socket, I won't know when the encrypted file has been finished, as I'm reading it in chunks. Because of ... |
browser vendors in TLS protocol for RSA certificates use ASN.1 encoding. while RSA public keys are just a number why we need encode them to something else that might make security problem for us ? |
Answer's plan:
- re-stating the problem;
- explaining its conventional solution, using a hash published in hexadecimal, usually of 32 to 64 characters;
- explaining a better (perhaps novel) solution, combining two established cryptographic primitive (a hash and a function originally designed for [Password Based Ke... |
Answer's plan:
- re-stating the problem;
- explaining its conventional solution, using a hash published in hexadecimal, usually of 32 to 64 characters;
- explaining a better (perhaps novel) solution, combining two established cryptographic primitives (a hash and a function originally designed for [Password Based K... |
Think about this, say my public key is
<code>9821347676528476512348612390874073765227653408545634205496835</code> (note this is not a valid public key, just randomish typing).
What does that mean? Big or little endian? Hex or decimal? Specifically for RSA, where is $e$, where is $N$? What is this public key autho... |
After reading some excellent papers on [SipHash][1], I understood that good non-cryptographic hashes such as [MurmurHash][2] and [CityHash][3] are not secure for [MAC][4] usage, due to a certain type of DDos attack becoming possible, thanks to a combination of Hash-table degeneracy into a list and predictable collision... |
After reading some excellent papers on [SipHash][1], I understood that good non-cryptographic hashes such as [MurmurHash][2] and [CityHash][3] are not secure for Internet usage, due to a certain type of DDos attack becoming possible, thanks to a combination of Hash-table degeneracy into a list and predictable collision... |
Is there a way to analyse xxHash and tell, either by human analysis, or with an automated tool, that this hash function is or is not cryptographic? |
Well, first of all, you need to be clear about the meanings of various cryptographical primitives.
- Cryptographic hash function; this is a function that takes an input string, and generates a hash. The idea is that we don't know how to create two input strings with the same hash, and so the hash can be used as a ... |
I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to validate whether the passphrase was correct or not and, in turn, whether I'm decrypting things successfully.
One idea whi... |
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