Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.
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5 views
Why this k parameter is in unary in adversary PPT algorithm?
While reading some text on cryptography, I found that algorithm $A$, that the adversary (called Eve by convention) runs to break the cipher message, needs two parameters, candidate message ($y$) and ...
2
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1answer
56 views
Alternatives to HMAC + CBC?
I'm looking at using HMAC + CBC. The combination looks like this:
ciphertext = AES256(text, k1)
data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext
Where:
...
16
votes
1answer
331 views
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 ...
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2answers
79 views
Generate fixed length cipher text from arbitrary length plaintext
Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
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0answers
36 views
How to decipher this morse-like code message? [closed]
I found this little string that looks like Morse Code, but instead of dots (dits) has hearts symbols, I tried to change the hearts for dots, but I was not able to get any redable text.
...
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1answer
68 views
Can someone help with the following hashes? [closed]
Here are a couple of hashes. I feel it should be easy (simple base conversions?) to decode them but I haven't succeeded so far. Can someone help?
...
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1answer
76 views
Security of Salsa20 with some known plaintext?
Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known?
Assume that a different IV and Key are generated before each file is ...
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2answers
200 views
Custom crypto library in C
I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, ...
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0answers
27 views
Decrypting TLS in Wireshark when using DHE_RSA ciphersuites [migrated]
How can I decrypt TLS messages when an ephemeral Diffie-Hellman ciphersuite is used? I am able to expose the premaster secret and master secret from the SSL Client. Using that, how to decrypt the ...
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1answer
81 views
What length should the padding be when encrypting or signing with RSA?
Does it matter what length the padding is? If so - what length should it be?
(Another point: Should it be random?)
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0answers
62 views
RSA Encryption Sckeme [closed]
Can anyone help me with this question?
A and B want to exchange encrypted messages; specifically, B wants to send a message M
written in binary format to A, which needs to be encrypted. They agree on ...
1
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1answer
110 views
Indistinguishability attack example
I want solve the next exercise. The author defined the experiment for the cryptosystem $\Pi$, the adversary $A$ and the security parameter $n$ as follows
$\mathsf{PRIV_{EAV}}(\Pi,A,n)$
The ...
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1answer
97 views
Encrypt a single file, chunk-by-chunk, each chunk using different key (AES)
Encrypt a single file, chunk-by-chunk, each chunk using different key.
I am a security newbie (only took 2 security courses before)
But currently I am using this encryption method for my Android ...
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2answers
55 views
Book Didactic Security Notions [closed]
I want study more about cryptography reading papers, but I have a problems to understand few concepts: security notions, random oracle model, IND-CCA, ... etc. I began study this concepts by internet: ...
3
votes
1answer
136 views
Secure encrypt-then-sign with RSA
I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt.
However, I have encrypted data that I need to sign, to prove the author of ...
1
vote
1answer
67 views
How to compare two datasets „anonymously”?
Ok, I hope this question makes some sense because I am not so sure how to word it any differently… Imagine the following situation:
There are 10 defined colors (blue, orange, yellow etc.)
There are ...
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1answer
40 views
Determine the Identity of Caller [closed]
Let me explain my situation.
I have a provider which is made up of a registration page and a web service. Online vendors (clients) register with the provider by providing details such as username, ...
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1answer
90 views
RSA - Ecrypting the same data with the same public key = same ciphertext?
If an adversary knows my public key and guesses what was my plaintext, can he test for it somehow?
The most obvious way is encrypting the guessed plaintext with my public key and the same parameters ...
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0answers
61 views
Is OAEP reversible?
Given nothing more than some integer $m =$ OAEP($M$), is it possible to recover the original plaintext $M$? In other words, without being given the hash functions or the random string used for ...
3
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1answer
81 views
implementing long term archive encryption
Let's say I want to create private archives for the long term (e.g. more than 30 ). The archives' sizes could be anywhere from 1 GB to 30 GB. As far as I understand I could go down two ways:
The ...
4
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1answer
183 views
repeating-key xor and hamming distance
I read that to break repeating-key xor you can do the following: try a keysize $n$ and compute the hamming distance between the first $n$ bits of the encrypted string and the bits $n+1$ to $2n$ of the ...
3
votes
1answer
109 views
Combining AEAD with RSA
'Hybrid' encryption, where we combine symmetric encryption with public-key cryptography, is pretty 'tried and tested'.
To summarise, we generate a symmetric key and encrypt it using RSA. We would ...
2
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2answers
101 views
Keys required for cryptography
I am reading an article on cryptography at following location:
http://www.entrust.com/resources/pdf/cryptointro.pdf
Historically, encryption systems used what is known as symmetric cryptography. ...
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0answers
25 views
Create groups of keys [closed]
I looking for a solution to encrypt, sign documents or email a key group and send to one customers. The group of keys are had already created user keys and I would like to use them.
Is not an option ...
5
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2answers
127 views
Security of tokenization of plain text conversations - cryptanalysis
I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
3
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2answers
68 views
GPG and PAR2 error correction data from the plain archive, will it compromise security?
I have the following scenario:
Archives compressed with 7z, hundreds of MiB in size
GPG to encrypt the archives (binary, without ASCII armor)
PAR2 to create error correction data
Question
1. ...
2
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3answers
129 views
Is there a way to use Shamir Secret Sharing with updatable data?
I want to divide a system that maintains these properties, based on Shamir's Secret Sharing:
A secret key is split up to N pieces, where T of them are enough to reconstruct the key.
The original key ...
2
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0answers
65 views
How can I prove that this encryption scheme from a random oracle is secure?
I am reading this example:
A random oracle is an ideal object.
What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
2
votes
2answers
146 views
Assymetric password encryption - Viable? Which algorithm?
We have an application that requires cleartext passwords for user authentication because of the authentication mechanism in use (RADIUS/CHAP), which unfortunately we cannot change. Since we don't want ...
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2answers
66 views
ElGamal: Generation of “g” value?
I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of ElGamal signatures:
$p$ = safe prime
$q = (p-1)/2$
$g$ = an ...
2
votes
1answer
73 views
Why unit vectors should be encrypted bit per bit in that case?
At this work at section $2.2$ concerning a possible application for the BGN cryposystem the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the ...
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1answer
89 views
ECKS-PS algorithm: searching in encrypted data; bilinear maps
I have found an encryption algorithm named ECKS-PS (published in the paper Efficient conjunctive keyword search on encrypted data storage system) that allows an user to search in encrypted data. All ...
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0answers
19 views
ECKS-PS algorithm: searching in encrypted data; bilinear maps [duplicate]
I have found an encryption algorithm named ECKS-PS (published in a paper named 'efficient conjunctive keyword search on encrypted data storage system', written by Jin Wook Byun, Dong Hoon Lee, and ...
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1answer
71 views
Ciphers in CBC mode reveal place of change in plaintext
Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block. Suppose one plaintext is encrypted using CBC, and then one bit of it is changed, ...
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1answer
178 views
Multi layer encryption with ECB mode [closed]
if i use the 2 of the same key with 2 of the same algoritm when encrypting in ECB like when i have 2 blocks of the same color and i encrypt the 2 blocks with the same color the cipher text should
not ...
2
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1answer
53 views
Why constrain the message lengths in indistinguishability in the presence of an eavesdropper?
I need your help with a very basic concept in cryptography which I can't understand/prove on my own.
I'm trying to prove and understand why, under "indistinguishability in the presence
of an ...
2
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2answers
131 views
How can mega store my login details and still be secure?
I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works:
Upon first signing up for an account you make a ...
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vote
1answer
90 views
What's the difference between Trapdoor Functions and Encryption Functions?
From Wikipedia:
A trapdoor function is a function that is easy to compute in one
direction, yet believed to be difficult to compute in the opposite
direction (finding its inverse) without ...
5
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1answer
97 views
Using encryption schemes for identification
I've been researching how to implement a post-quantum SSL-like connection authentication, especially correct identification&authentization of the server/client. Because good post-quantum digital ...
4
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1answer
98 views
Client and server using same SSL certificate - any issues?
I'm working on software where multiple components will communicate with each other using SSL.
There would be one central component acting as a server, which would also require the clients to present ...
2
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1answer
207 views
Is AES-256 a post-quantum secure cipher or not?
We know Grover's algorithm speedup brute-force attacks two time faster in block ciphers (e.g brute-forcing 128 bit keys take $2^{64}$ operations not $2^{128}$).
That explains why we are using 256 bit ...
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vote
2answers
74 views
Can two rc4 encoded messages be XORed and decrypted if encrypted with the same key?
If I have the following:
E1 = RC4(M1, K);
E2 = RC4(M2, K);
If two different messages M1 and M2 are encrypted with the same key, K, can the key be recovered by ...
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1answer
78 views
In which disciplinary kind can Cryptography be put?
Is it a multidisciplinary? an interdisciplinary? a cross-disciplinary? or a trans-disciplinary?
what are the basis put to describe each kind?
I mean how can we infer by which disciplinary field we can ...
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2answers
121 views
Security of Deterministic Encryption Scheme
A deterministic encryption scheme is a cryptosystem which always produces the same ciphertext for a given plaintext and key, even over separate executions of the encryption algorithm.
Although we ...
4
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3answers
200 views
Comparison: complexity measures vs. security
Assume that you want to compare several cryptographic primitives (say, encryption schemes), and choose one. You need to consider several complexity measures, such as the key length, encryption time, ...
2
votes
1answer
113 views
How to compute the dot product on encrypted values?
Is there a practical homomorphic encryption scheme that can give reasonable execution time results in computing a dot product:
$$a_1*b_1 + a_2*b_2 +a_3*b_3 +\ldots+ a_n*b_n$$
I imagine the scheme will ...
2
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1answer
104 views
Cracking an RSA with no padding and very small e
I have a project wherein i have to crack a given cipher text encrypted using RSA and have been given N and e. Can someone suggest an RSA attack using a very small exponent e(here e=3) and no padding?
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1answer
71 views
Encrypting and Decrypting a 19-digits long BigInteger
How can I take a maximum 19-digits long BigInteger and encrypt it with the following rules:
The result must be based on digits and lower-case English letters ...
6
votes
1answer
151 views
How would one crack a weak but unknown encryption protocol?
I asked a question on security.stackexchange, but was told it would be a better fit here:
http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol
...
20
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5answers
6k views
Is Convergent Encryption really secure?
Recently a company called Bitcasa demonstrated a product of cloud storage. they indicated that they would use "Convergent Encryption" to secure your data and de-duplicate, essentially one copy of the ...
