2
votes
2answers
64 views
What does “message schedule” mean in SHA-256?
I am trying to understand the sha-256 algorithm from FIPS 180-2. I understood the padding and parsing of the message string. However after that it states (page 15):
For $i = 1$ to $N$:
{
...
1
vote
3answers
136 views
How Scrypt uses Salsa?
Bcrypt use Blowfish to crypt a derived key from the passphrase, Blowfish is a cryptographic algorithm, but here it is said that:
Note that
Salsa20/8 Core is not a cryptographic hash function ...
1
vote
1answer
112 views
Bcrypt VS Scrypt, Again?
I found this article on SO, but the answer was short, and the subject was closed,
What i don't understand, is:
Which one of the two limits memory usage to avoid custom Hardware to break the password?
...
0
votes
1answer
56 views
Smart Card Basics
I want to implement some of the basic encryption algorithms on smart card, could any body guide me, how to program a smart card, which tools (hardware and software) i should have ,and are these tools ...
3
votes
1answer
95 views
Proofs of security methodologies
I'm looking for course material on the subject of proofs, reductions, and games, as used to prove cryptographic schemes secure. What are the methodologies? What are the preferred ones? In what cases ...
3
votes
0answers
46 views
Why is TLS SRP verifier based on user name?
I don't understand why TLS SRP (or SRP in general) includes the user name in verifier calculation, given that user name is basically public.
From spec RFC 5054 $x$, which is then used to calculate ...
2
votes
2answers
112 views
Is this OTP scheme safe?
I have a message $m_1$ and I want to encrypt it by XORing it with two keys $k_1$ and $k_2$:
$$c_1 = m_1 \oplus k_1 \oplus k_2$$
So far so good.
Now I was wondering if I could create a "fake" result ...
6
votes
1answer
144 views
What does “running in polynomial time” really mean?
I'm currently learning private-key cryptography. I've been able to see that perfect secrecy is achievable if no assumption is made about the computational power of the attacker.
However, perfect ...
3
votes
1answer
76 views
Can substrings of a long string be efficiently authenticated?
Suppose one has a (strong) shared secret key and wishes to authenticate a very long string in a way that will allow the verifier to verify small substrings without reading much of the stored data and ...
3
votes
1answer
43 views
differential and linear cryptanalysis
I have been reading about differential and linear cryptanalysis. They were mainly introduced by Adi Shamir and Biham to show weakness of DES. However, many of articles state that they have been ...
1
vote
2answers
87 views
Does collision resistance stay when extending a hash function to a set domain?
Given a Cryptographic hash function $h$ for element $x$, let's extend it to sets via $H(S)=\prod_{x\in{S}}{h(x)}$. I am asking if the new hash $H$ (in domain of set) is still collision resistant?
To ...
0
votes
0answers
31 views
Is there a Skype plugin that uses TLS and ZRTP [closed]
I'm curious if one can upgrade the security Skype offers to avoid a man in the middle snooping in on the call by both parties using a client side plugin. Does one exist for this purpose?
2
votes
3answers
125 views
Block cipher fixed points
A block cipher is a bijective map from the set of possible plaintexts to the set of ciphertexts, which are the same size and might as well be considered the same thing: $\theta: S\to S$. In this there ...
1
vote
2answers
79 views
Composition of block ciphers and 3DES
There is some intriguing things about DES and 3DES. Now, I know that DES is weak and 3DES was an attempt to construct a more secure block-cipher from a deprecated one.
Having this in mind, what ...
4
votes
1answer
98 views
Why should I use an Initialization Vector (IV) when I have unique keys?
I took a look at this question. My question is not the same.
I've unique keys encrypting (in CBC mode, AES-256) each plaintext, i.e. I do not use a key to encrypt more than one plaintext. Is it ...
1
vote
0answers
122 views
Calculating PGP Symmetrically Encrypted Packet data
I have been trying to create a properly encrypted data packet using the format described in RFC 4880. However, I have been unable to verify any of my outputs due to the lack of examples to draw from ...
-2
votes
2answers
87 views
Is triple des similiar to RSA in that they message size is limited to the key size?
Is triple des similiar to rsa in that the message size you can encrypt is limited (unlike AES)?
Yes you can break the message size into parts and apply it, but I'm not interested in doing that so I ...
1
vote
2answers
57 views
IV Security Clarification
After doing lots of reading on SO and other websites relating to AES cryptography, I am trying to understand the security issues surrounding IV's.
There seems to be a lot of confusion and ...
1
vote
1answer
41 views
When making public key fingerprints - is a sha1 hash still a good idea?
I'm thinking about trying to save some space (and readability) when referencing 2k and 4k public keys (millions of them) by storing the fingerprint in some places instead of the full public key.
...
6
votes
1answer
106 views
Why use $(r,s)$ instead of $(r,s^{-1})$ as DSA signature?
A DSA signature consists of two scalars $(r,s)$.
When signing $s$ is generated as:
$s=k^{-1}(H(m)+xr) \mod q$
The signature is $(r,s)$
When verifying $s$ is only used to compute $w = s^{-1}$. So ...
1
vote
1answer
71 views
How can I split a message in parts of similar size or smaller?
I have a 130-160 characters message that I need to split in say, 3 parts, and be able to reconstruct it by recovering all 3 parts. I also need that these parts are type-able, meaning that they can't ...
2
votes
1answer
72 views
In ECDSA, how many field operations are used for signature verification?
I am wondering about the computational cost of ECDSA signature verification, in term of multiplications in the base field; and, as an aside, in term of (much cheaper) additions. To make things ...
0
votes
0answers
53 views
Will D-Wave's quantum computers ruin classical encryption? [duplicate]
D-Wave has commercially available 512-qbit quantum computers now. A lot of big names are taking it seriously. Google, NASA, and USRA have joined forces to start a quantum AI lab.
How far are we ...
3
votes
1answer
37 views
Distributing blocks with validation and non-dependant list generation
Problem
Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
1
vote
1answer
53 views
How is text converted to a number for RSA?
According to http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Key_generation the key length is the number of bits in n. So how can a message of many megabytes (millions of bits) be modded by a 1024 ...
2
votes
3answers
168 views
If RSA is limited to 117-200 bytes or so, is that a very limited use case?
Am I missing something, or is RSA very very limiting when it comes to ecrypting data when it comes to the actual message size?
I have read that you can only encrypt a message of around 117 to 200 ...
2
votes
0answers
40 views
Which version(s) of SRP are in ISO/IEC 11770-4:2006?
I am on the impression that SRP emerges as the least uncommon and best analyzed protocol for authentication and key agreement based on a short password.
This states that SRP is part of IEC 11770-4, ...
2
votes
2answers
93 views
Are block ciphers used in public key crypto?
I was reading about block ciphers and most articles state they are being used in symmetric key cryptography. Are they also being used in public key cryptography? if not, what alternative pkc use?
...
2
votes
2answers
119 views
HMAC and assumptions on the cryptographic hash
According to Wikipedia, a cryptographic hash function has the following properties:
Pre-image resistance: Given $h$, it's difficult to find any message $m$ such that $h = H(m)$.
Second pre-image ...
1
vote
2answers
40 views
No IV for one off symmetric file encryption
My question is (hopefully, for somebody) a simple one; but my project is holding as I'm not sure.
I read on SO that generating encryption keys without an IV is a bad idea, so is using a constant IV ...
2
votes
1answer
79 views
Encrypt-then-MAC paradigm
I read that the Encrypt-then-MAC paradigm is provably secure.
From what I understand, when using for example AES for encryption and HMAC_SHA256 for MAC generation (and the keys $K_1 \neq K_2$), this ...
-1
votes
0answers
21 views
References on PKI [closed]
I hope this is the right forum. I don't see any PKI specific forum around here. Can somebody recommend some books/references on TLS/PKI? I am starting a project for secure document exchange among ...
-1
votes
0answers
49 views
How to calculate byte length of a hash [closed]
The following :- c4ca4238a0b923820dcc509a6f75849b is an MD5 hash and we know that it is 16 bytes in length.
My question is how do we understand that it is 16 bytes. How the bytes are calculated. ...
2
votes
2answers
116 views
Secure use-cases of block cipher with 64-bit block size
In what cases can we use a weak block cipher like DES ?
More precisely, Are there specific situation in which a weaken block cipher can still be used, for instance for certain types of plaintext ?
1
vote
1answer
65 views
ECC Point Multiplication of Product
I can calculate $Q = a\,b\,G$ in several ways:
$Q = a \, (b \, G)$ or $Q = b \, (a \, G)$. These give the same result, as expected.
But if I do $c = (a \, b) \bmod n$ where $a \, b$ is much greater ...
1
vote
1answer
35 views
Why does the server in S/KEY authentication only store a single password?
I've been reading about the S/KEY One-Time Password system on wikipedia here and was wondering why the server only stores a single password and not the list of one-time passwords like the client does. ...
0
votes
2answers
68 views
A substitution based on a matrix vector product
I choose at random an invertible square matrix A of size 128 in GF(2). I want to use this matrix as a substitution box. Is this a non linear transformation ?
I've seen that substitution boxes are ...
1
vote
2answers
123 views
Is entropy affected by time?
I'm quite new to cryptographic systems, and today we discussed entropy at work. Since entropy is used to ensure the difficulty for an attacker to break in, I was wondering if the more time the high ...
6
votes
1answer
129 views
Can somebody explain the major contributions of the tenants of the Gödel Prize 2013?
As you may know, the Gödel Prize 2013 will be awarded this year to cryptographers (see this ACM press release). The people awarded are Antoine Joux, the team of Dan Boneh and Matthew K. Franklin.
Can ...
1
vote
1answer
88 views
How insecure in practice?
I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
-3
votes
0answers
63 views
Certificateless Cryptography for Wireless Sensor Network [closed]
As we all know that ID-based cryptography has been implemented for wireless sensor networks, can we implement certifficateless cryptography over that? Discuss pros and cons.
7
votes
2answers
345 views
Why are bitwise rotations used in cryptography?
Any understanding I have of cryptography stops right around the cipher level. As such, I'm just curious as to why bit shifts and moreover circular bit shift are so prevalent in cryptography.
0
votes
0answers
48 views
Complex Numbers on Elliptic Curves & Usage in Tate Pairing
I'm working with understanding the internals of the Tate Pairing. I was going through an example of the curve $E: y^2 = x^3 + 3x$ over $\mathbb{F_{11}}$. The author is showing the computation of ...
0
votes
1answer
95 views
Best way to create password manager [closed]
After some searching I wasn't able to find a password manager that fits me (able to sync from my own server, open-source, secure enough and browser auto complete). So, I thought that I will create ...
3
votes
1answer
97 views
Can i modify data “protected” by a CRC16?
There are 100 bytes with a CRC16. However I only know the first 50.
I want to change byte 5 from a known value X to another value Y, and fix up the CRC16 to be valid - without knowing bytes 50-100.
...
2
votes
0answers
105 views
More technical details on the ongoing (alleged) Chinese cyberattacks
Recently, there has been quite a lot of news about the Chinese compromising various US weapons systems and stealing military designs through "cyberwarfare". I am reading the news sources about these ...
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
159 views
What do recent announcements about solving the DLP in $GF(2^{6120})$ mean for RSA
After just reading the post Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use?
I was a bit confused. DSA, ElGamal and others are based on ...
5
votes
4answers
397 views
Encrypt a file once with 50 characters password or twice with 25 characters?
What better Encrypt the file once with 50 characters password or encrypt it twice each time with 25 characters password.
0
votes
3answers
103 views
Why crypto hash functions must be collision resistant and how to find resistant?
Why cryptographic hash functions must be collision-free and is there any methods to evaluate whether a function is not resistant to collision?
Thanks,
