0
votes
1answer
209 views
File Encryption/Decryption in ECB mode [duplicate]
Possible Duplicate:
Removing Padded Value in Decrypted Message
I tried to encrypt and decrypt a file in ECB mode using AES Algorithm but I encountered one problem during decryption, I don't ...
0
votes
0answers
27 views
SHA-512 hash collisions [duplicate]
Possible Duplicate:
Is SHA-512 bijective when hashing a single 512-bit block?
Is there any guarantee that there are no collisions for all 512-bit input values for SHA-512(Every 512-bit ...
0
votes
1answer
435 views
Removing Padded Value in Decrypted Message
How to remove padded value in Decrypted Message?
I am using AES Algorithm..
ex:
this is the decrypted message..
"abcdefghijklmn "
there is a 2 space in that decrypted message which is equivalent ...
0
votes
2answers
111 views
Do these 2 KSA shortcuts weaken RC4?
Alice securely gives Bob a secret key so they can exchange 10 different messages encrypted with RC4. (Messages will include a counter for uniqueness and a MAC for authentication.) For each message ...
5
votes
1answer
107 views
Proof of work scheme with one and only one correct answer
I need a problem that has one and only one solution, such that the solution is hard to find but easy to verify. I need to be able to generate the problem deterministically from a random seed.
So ...
1
vote
1answer
464 views
How can 3DES encryption use decryption in the middle step?
I have been reading about the 3DES algorithm and I cannot understand one part. In 3DES we do following operation: $$C=E[K_3,D[K_2,E[K_1,P]]].$$
Where $C$ is ciphertext, $P$ is plaintext, $E$ is DES ...
-1
votes
1answer
394 views
How to encrypt a File using AES Algorithm? [closed]
How to encrypt a file using private key in Java.
Adding this question, how to generate the private key for the same.
Before posting I went through some question like How to perform file encryption ...
1
vote
2answers
84 views
How can I protect against the failure of a block or symmetric cipher?
Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of?
Are some combination of ciphers ...
2
votes
2answers
210 views
Is RSA in a ECB-like-mode safe for bulk encryption?
Let's say I would like to communicate with my friend using asymmetric/public-key encryption, e.g. RSA.
(Note: I do realize that in practice this is done through an intermediate symmetric key, but ...
4
votes
3answers
799 views
Are there any simple and yet secure encryption algorithms?
Being very new to C++ and cryptography, I finally managed to implement a version of the Vinegere algorithm. I would like to try something a bit more complicated. I have looked at AES and DES and ...
1
vote
1answer
138 views
Using compression to test encryption
Is the uncompressibility of encrypted data a necessary property for a good cryptographic algorithm?
To make a crude experiment, I encrypted an 8K file with all 'A' and then compressed both the ...
4
votes
2answers
149 views
Is this streamable combination of encryption and MAC secure?
I want to combine encryption and MAC.
For encryption I use AES-256 with CBC and PKCS5Padding.
For MAC I use HmacSHA512.
I use the Encrypt-then-Mac approach (calculate MAC over the ciphertext and ...
6
votes
2answers
175 views
K out of N encryption
A friend just showed me how to combine padlocks to achieve a lock that opens when k out of n people turn their keys.
I was ...
1
vote
1answer
190 views
“Signing” with public key
For this question, the following caveats and assumptions hold:
There exists a 2048-bit RSA key pair used exclusively for signing/verification
The private key is kept completely private
There exists ...
2
votes
1answer
276 views
Replay attack prevention under strict conditions
Say I have a request-response protocol and the task to make it immune to replay attacks. The requirements are as follows:
The defense mechanism cannot rely on the clocks of the parties.
The defense ...
3
votes
1answer
208 views
LFSR dynamic mutation
In normal LFSR, the state is a function of the initial seed, taps positions and time, nothing else. I've seen a modification of LFSR that works like this:
...
2
votes
2answers
314 views
How to get the keyword from a keyword cipher?
I was given a ciphertext and now I am trying to break it via looking for the keyword.
This is a keyword cipher. So:
PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ
If ...
0
votes
1answer
111 views
Decimal to binary question [closed]
This is an easy question, but I can't explain it lol, how would you guys explain it?
There is a procedure for converting a decimal number to binary in the following way: repeatedly divide the number ...
1
vote
1answer
159 views
How to properly add ECDSA private keys?
I'm currently working on an application that requires me to add two ECDSA private keys in order to make a new private key. The result has to have the property, that its corresponding public key is the ...
5
votes
3answers
1k views
In the SHA hash algorithm, why is the message always padded?
In the SHA hash algorithm the message is always padded, even if initially the correct length without padding; the padding is of the form "1" followed by the necessary number of 0s.
Why is it ...
2
votes
2answers
100 views
When to prefer exchanging cryptographic certificates over exchanging only public keys?
Let's think of the following case:
A group of peers want to exchange messages with each other. They use public-key cryptography to sign and encrypt messages. Anyone with any name can join the ...
3
votes
1answer
172 views
Does omitting the first two lines of RC4's pseudorandom generation algorithm weaken the cipher?
A particular educational software program published by a U.S. government agency uses a variant of RC4 to obfuscate its data files (see Stack Overflow question). The variant of RC4 in question is ...
1
vote
1answer
58 views
Cryptographic Algorithm/Protocol needed
I am trying to achieve the following:
Encrypted files are stored on users filesystem. The user uses my client to authenticate against a server. Once he is authenticated successfully he gets a token ...
3
votes
1answer
130 views
Safely use CryptSignAndEncryptMessage?
I am developing an application that sends messages which I want to encrypt and sign. The CryptoApi offers a function called CryptSignAndEncryptMessage.
The description says, what this function ...
5
votes
1answer
321 views
Why are MACs in general deterministic, whereas digital signature constructions are randomized?
The fact is I'm not quite sure if my question statement is true, however all the MAC constructions I know of (e.g. CBC-MAC, CMAC, HMAC) are deterministic, whereas many constructions for digital ...
1
vote
0answers
60 views
Applying multiple hash functions to improve security? [duplicate]
Possible Duplicate:
Guarding against cryptanalytic breakthroughs: combining multiple hash functions
I'm a total newb to cryptography but after reading what I've read about it, I had a ...
4
votes
1answer
224 views
OpenPGP Signature Packet hashed data
RFC 4880 describes the version 4 signature packet, tag 2, as
...
0
votes
1answer
108 views
RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?
Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
9
votes
1answer
185 views
Which MACs can be converted into a secure unkeyed hash function?
It is known that setting the secret key to a fixed, public value does not make MACs like CBC-MAC or GMAC into secure unkeyed cryptographic hash functions that could be used - for instance - for ...
2
votes
3answers
202 views
Algorithm to securely exchange identities
Say four people each have a public/private key pair that they can use to encrypt or sign messages. They have an anonymous way to post messages such that the others can see them. Malicious entities can ...
1
vote
2answers
167 views
Brute force a ciphered message?
I wrote my own cipher to encrypt messages. I would like to test a sample ciphered message to see how strong it is. Are there any tools for such task either in Windows or Linux ?
3
votes
1answer
206 views
Is quantum key distribution safe against MITM attacks too?
i read this recently: http://www.newscientist.com/article/dn12786-quantum-cryptography-to-protect-swiss-election.html
and some parts of this: http://en.wikipedia.org/wiki/Quantum_key_distribution
...
3
votes
1answer
239 views
Do Cryptographic Hashing Algorithms operate only on Integers?
Do all the Cryptographic hashing algorithms operate only on integers (32 bit or 64 bit)? Is there any operation performed on Floating Point Numbers as well?
The reason I ask this is because I read ...
2
votes
1answer
797 views
In which order are the round keys used during AES decryption?
In the Add Round Key step in AES decryption, which part of the expanded key will I XOR first to the result of the SubBytes step?
Is it the 10th round key?
For example, is this the right order?
...
1
vote
3answers
205 views
Does the MixColumns step come before or after AddRoundKey in AES decryption?
I found these images depicting the AES decryption process:
In the first image, the MixColumns step comes before the AddRoundKey step, while in the second image, the AddRoundKey will come before ...
2
votes
1answer
278 views
What is the harm if I publish an encrypted RSA private key publicly?
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 ...
1
vote
2answers
106 views
Standard symbol / notation for “x knows y”, or the inverse
What's the standard way to express "$x$ knows about $y$", or "$x$ has no knowledge of $y$" in cryptographic notation?
Example (PRNG predictor):
$\exists f : P(f(G(k)|_{0..n}) = G(k)|_{n+1}) \geq 0.5 ...
2
votes
1answer
296 views
Linear Feedback Shift Register Taps
Linear feedback shift register tap charts are availale for registers of length 3 to 168. Does anyone have a chart for register lengths from 168 to 256 or beyond? Thank you.
4
votes
5answers
866 views
Galois fields in cryptography
I don't really understand Galois fields, but I've noticed they're used a lot in crypto. I tried to read into them, but quickly got lost in the mess of heiroglyphs and alien terms. I understand they're ...
3
votes
1answer
194 views
Memory-hard operations in work-factor hash functions
I'm playing around with work-factor hash functions, and I'm looking for a memory-hard operation to make it resistant to GPU / parallel hardware attacks. I considered a very large (i.e. 64K) s-box that ...
4
votes
2answers
263 views
After implementing a novel encryption algorithm, how would one go about analyzing its security or get help from others in doing so?
Preface: This question was originally asked on Theoretical Computer Science and later on Computer Science. The kind people on cstheory.SE referred me to this web site. It is being repeated here in an ...
1
vote
1answer
172 views
2
votes
2answers
194 views
How can encryption involve randomness?
If an encryption algorithm is meant to convert a string to another string which can then be decrypted back to the original, how could this process involve any randomness?
Surely it has to be ...
0
votes
0answers
74 views
Is this a secure multiparty protocol?
I am facing the following situation and i am trying to break down the problem into some specific cryptogrphic primitives.
There is a function F that takes as input a bit string and produces a ...
0
votes
1answer
191 views
Why does my implementation of CBC mode only decrypt the first block correctly? [closed]
I have the following code that uses a CBC mode to encrypt a text by dividing it to 3-elements block. But it only works correctly on the first block which is xored with the IV.
...
0
votes
1answer
121 views
ECDSA - point order criterion
i am creating some primitive demostration for ECDSA over small curve ( p < 229). But my implementation have some weird issues. Verify process return false even if the signature is correct. Because ...
2
votes
2answers
118 views
Is the “Signed on date” of a PGP Signature Verified?
I noticed that PGP signatures have a "signed on" field. I was wondering if this is "trustworthy" information and if so how is it accomplished.
For example, I can't see how it could be trusted ...
12
votes
2answers
1k views
Is every output of a hash function possible?
Is every output of a hash function (e.g. SHA1, MD5, etc) guaranteed to be possible, or, conversely, are there any output values that cannot possibly be created from any input? If so, what guarantees ...
6
votes
2answers
251 views
Attacks of the MAC construction $\mathcal{H}(m||k)$ for common hashes $\mathcal{H}$?
Consider a common practically-collision-resistant Merkle–Damgård hash function $\mathcal{H}$ (e.g. SHA-1, RIPEMD-160, SHA-256, SHA-512). We define a Message Authentication Code $\mathcal{C}$
$$(k,m) ...
4
votes
1answer
189 views
Is it secure to use the hash of key as the IV in AES encryption?
I need to store some sensitive data for a program. For each copy of the program, there will be a unique key for encrypting one (and only one) file using AES encryption (OFB). The key will not be ...
