0
votes
2answers
123 views
Reversing SHA1 (don't know the correct term)
Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1)
If yes, for which other hash functions it will work too?
...
0
votes
2answers
103 views
Acceptable assumptions when prooving security
Considering the output of a cryptographic primitive, like an encryption scheme (CBC, ...), a hash function or even the output of any schemes based on number theoretic assumptions, is it reasonable ...
4
votes
1answer
56 views
Linkable ring signature scheme
I need an implementation of linkable ring signature, a ring signature which allows identifying whether two signatures belong to the same signer. It has important privacy-related applications, like ...
-1
votes
0answers
46 views
can we do double encryption of a message without first key?
Lets assume $k_1$, $k_2$ are two keys and there can be any relation between them like $k2 = E(k1) $ that is key $k_2$ is encryption of $k_1$ using some other long term key or any other relation.
...
8
votes
1answer
188 views
Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use?
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: Solving a 6120-bit DLP on a Desktop Computer seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using ...
13
votes
3answers
814 views
How robust is discrete logarithm in $GF(2^n)$?
"Normal" discrete logarithm based cryptosystems (DSA, Diffie-Hellman, ElGamal) work in the finite field of integers modulo a big prime p. However, there exist other finite fields out there, in ...
2
votes
2answers
90 views
How to test if a number is a primitive root?
How to test if a number is a primitive root, assuming the modulus is a prime? And if not?
Is it not enough if the number is relatively prime to the modulus or prime?
-1
votes
0answers
37 views
Attacks on a stream cipher
What attacks are there against stream ciphers?
I found 2:
Bit-flipping attack. Since every input bit mention exactly one output bit, it is possible to change ciphertext bits where the corresponding ...
1
vote
1answer
74 views
Could quantum computers “break” symmetric crypto-systems (e.g. AES)?
These days I'm reading about quantum computing and quantum cryptography which I've found extremely interesting. Well, I also read some blog posts of Bruce Schneier talking about how quantum computers ...
0
votes
0answers
49 views
RSA vs El Gamal digital signature. Which is more secure?
I'm reading about the notions of security concerning digital signatures and I can't understand whether RSA is more secure than El Gamal digital signature. Well, they are both prone to forgery, but I ...
0
votes
0answers
31 views
Hardware implementation of pairing
I would like to design a hardware-based accelerator for a pairing algorithm to make it faster. I know that I need to do arithmetic over a base and an extension field.
Could anyone would suggest which ...
1
vote
0answers
64 views
How well analyzed are giant block length ciphers?
I have heard about ciphers that have a block length of 256 megabytes... That is huge.
How well are they understood by the encryption community?
I'm referring to PMC Ciphers.
Has anyone used such a ...
2
votes
1answer
83 views
Encrypt user email but be able to find user by email
Sorry for my dumb question, but it's better to ask dumb question than to do dumb things silently.
I want to encrypt user email in my DB so that if someone stole the DB (and not the key) - he won't be ...
4
votes
2answers
209 views
Why is SRP not widely used?
SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations?
I tried to ...
1
vote
1answer
69 views
AES encryption with multiple keys
I would like to encrypt some data using a combination of multiple keys. There would be two keys: a client keys that would be generated for each client and a single server/application key used by ...
2
votes
1answer
202 views
Are there any practical implementation of a homomorphic hashing or signature scheme?
A homomorphic hash function is a function $H : A \to B$ between two sets with some algebraic structure $(A, *)$ and $(B, \star)$ such that
$H$ is collision resistant, i.e. it is hard to find $x \neq ...
2
votes
1answer
106 views
Why is verification using DSA slower than verification with RSA?
We read in literature that verification of a digital signature is slower using DSA than if we used RSA. Why is this?
DSA parameter generation:
choose prime number $p$
choose prime number $q$ such ...
1
vote
1answer
88 views
How to verify a shared secret using only AES?
I have two devices that need to verify that they both are in possesion of the same secret key. One of the devices is a very limited embedded device that only has AES128 available, no SHA or other hash ...
-1
votes
1answer
55 views
University for Crypto grad study [closed]
(I thought twice before asking this question and quite reluctant to type as well, but I think this would be helpful).
I am an undergrad student and choose theoretical computer science as my major. ...
0
votes
0answers
30 views
Conditions for proving that a signcryption scheme is secure
If I'm able to prove that any scheme satisfies confidentiality ad unforgeability conditions, will it be a valid signcryption scheme, without explicit signature and encryption parts ?
-1
votes
1answer
57 views
what actually the function for e(g,g)^xy
I doing a project using ABE "Attribute-Based-Encryption" but i didn't understand what actually the function for $e(g,g)^xy$.
Just tell what's the calculation need to perform here. I gone through no of ...
0
votes
1answer
42 views
Size of Parameters in Polynomial Key-Splitting Algorithm
I've seen the elegant way of splitting a key among different people so that only a certain number need to be present to re-compute the key, yet nobody has enough information to re-compute the key on ...
5
votes
3answers
624 views
Recommended skills for a job in cryptology
First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company ...
2
votes
2answers
210 views
Why RSA uses {d,n} as private key instead of {e,n}?
While studying the RSA algorithm I referred to some books and some sites such as RSA (wikipedia) and all of them chose {d,n} as the secret (private) key and release {e,n} as the public key but as d ...
1
vote
1answer
88 views
Key sizes for discrete logarithm based methods
I have a question regarding the key generation process of methods that are based on the discrete logarithm problem.
This site gives some good insights, but I don't fully grasp it I think: ...
-4
votes
0answers
59 views
sir,please suggest me an algorithm or method how can i improve the prediction based encryption method using randomization? [closed]
I am doing research on security for data migration in cloud computing. I have gone through many encryption algorithms to secure data for migration, but I want to create my own algorithm that could be ...
2
votes
1answer
96 views
Isn't the structure of a potential plaintext of a ciphertext generated by a one-time pad dispositive, cryptanalysis-wise?
That is, if I generate every possible result, and analyze the structure against, for example, a dictionary, won't that identify which of the solutions in the domain is most likely the correct one?
I ...
0
votes
0answers
12 views
How do I create a self-signed S/MIME signing certificate with OpenSSL and then sign a file? [migrated]
I would like to create a certificate with OpenSSL and then use it to create an S/MIME format detached signature of a file. Is this something that makes sense in the context of S/MIME? How do I get ...
1
vote
3answers
119 views
Requiring a “supervisor” key pair and a “user” key pair to decrypt multiple-recipient messages
I've been toying with some encryption scenarios recently. One of the hard ones I came across is a multi-party system.
So we have
Bob -- The person who sends the message (and knows it's recipients)
...
0
votes
2answers
102 views
Proper Way to Encrypt Data with Two Keys?
I'm going to develop a system that will have two keys. One supplied and generated by the system that's specific to an individual user and one from the user.
I plan on using AES.
Does it make sense ...
1
vote
0answers
75 views
What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?
I'm working with the affine representations of points of a Koblitz curve.
I've read many papers that show that computing some functions, like $f(P)=3P$ can be computed faster than the standard way. ...
-2
votes
0answers
75 views
Decrypting the Encrypted hex applcation data with encryption keys [closed]
I am having all the keys,
...
-3
votes
0answers
75 views
RSA decryption from ciphertext using private key [closed]
I am sniffing a client side application traffic and I found some encrypted data. I am not able to decrypt it. Information which I have is
Public Key:
...
7
votes
1answer
221 views
Security of pairing-based cryptography over binary fields regarding new attacks
In the last week, the discrete logarithm problem was broken for the binary fields $\mathbb{F}_{2^{(14 \times 127)}}$ and $\mathbb{F}_{2^{(27 \times 73)}}$.
Pairing-based cryptography using binary ...
2
votes
1answer
136 views
Hill-cipher, disordered alphabet
I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model?
In other words, instead of the ...
-2
votes
2answers
71 views
Perfect Secrecy, two Definitions
I'm reading the proof of the implication "Def 2.1 $\Rightarrow$ Def 2.4" in these slides about Adversarial Indistinguishability and Perfectly-Secret Encryption. I have a doubt in the slide 10. Here it ...
0
votes
1answer
128 views
Do I need to keep a 64-bit version number secret?
Assume the following structure:
version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key)
The version starts out ...
1
vote
1answer
125 views
How much data can I encrypt with AES before I need to change the key in CBC mode?
In my cryptography class, the instructor suggested that in order to give the attacker a minimal advantage of $1/2^{32}$, we have to change the key after $2^{48}$ blocks are encrypted.
It seems that ...
3
votes
2answers
104 views
What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
Background: My current server-provider tells me it's no problem to store the passwords in plain-text in the database, saying he has to do so because they use CRAM-MD5 for email authentication. But ...
8
votes
1answer
375 views
Is Wikipedia's table about SHA-2 collisions correct?
I was looking a Wikipedia article on SHA-2, and the "Comparison of SHA functions" table seems to indicate that SHA-2 is less secure than SHA-1.
Is this true, or is the table wrong / misleading?
...
0
votes
0answers
64 views
how many bit flips current computers can carry per second? When brute force is hard?
How many bit flips the fastest current computers can accomplish per time unit? i.e per second. I am trying to find when brute force attacks are considered infeasible. The reason I chose bit flips is ...
-1
votes
1answer
75 views
What key length is required to keep simple keyed “hash” secure?
In a previous question, I described a particular keyed "hash" that mapped a 5-digit input code into a 5-digit output code. It used a 8-bit key which is very insecure - more than 99% of the time, you ...
0
votes
2answers
132 views
Physical Level Encryption
What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
-2
votes
0answers
66 views
One time Pad Adversary
I like know Why $Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = 1/2$, when $\Pi$ is a One Time Pad. I trying:
$$Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = Pr[b'=0|b=0]Pr[b=0] + ...
5
votes
3answers
631 views
What is the recommended replacement for MD5?
Since MD5 is broken for purposes of security, what hash should I be using now for secure applications?
1
vote
1answer
131 views
Are there any hand ciphers not obsoleted by computer cryptanalysis?
Computerized cryptanalysis has obviously made formerly "secure" hand ciphers like Playfair, Four Square, and the Hill Cipher obsolete because they can be defeated in seconds. But is there a hand ...
2
votes
1answer
125 views
Is this algorithm secure?
I recently found this site, proposing a hashing algorithm for passwords.
They describe the following:
pad the password on both sides with SHA1(email) to ...
1
vote
3answers
137 views
Is Base64(SHA1(GUID)) still unique like the original GUID?
Basically what the title is; GUIDs are unique by design. If you run the GUID through SHA1 and then Base64 the hash, will the resulting string have the same guaranteed uniqueness as the GUID, or not?
0
votes
2answers
78 views
Why this k parameter is in unary in adversary PPT algorithm? [duplicate]
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 ...
-4
votes
1answer
65 views
How to calculate cycles per byte [closed]
I have this data:
processor clock frequency: 2,1 ghz
message length: 16 byte
Speed: 4,3 Mbytes/s
how can calculate cycles and cycles per byte?
