20
votes
3answers
19k views

How can I use SSL/TLS with Perfect Forward Secrecy?

I'm new to the field of cryptography, but I want to make the web a better web by setting up the sites that I host with Perfect Forward Secrecy. I have a list of questions regarding the setup of ...
3
votes
1answer
143 views

ZIP 2.0 encryption bruteforce attack

I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password. The password was written on a paper slip, but I remember that it consisted of 30+ ...
1
vote
0answers
82 views

To prove $r_2$ is a uniformly at random value in $Z_n$, where $r_2=r_1 . m$

$m$ is arbitrary value in $Z_n$, where n is RSA modulo. Then we do: $r_2=r_1 . m (modn)$, where $r_1$ is a random value such that $r_1\in Z^*_n$. ** Question(1): is $r_2$ a uniformly at random ...
1
vote
0answers
45 views

Crypto Libraries with Pairing Based Functions for Academic and Educational Use? [on hold]

I am aware of some crypto libraries containing functions and tools for pairing based cryptography. However, I want to have a more extensive list of them. My ultimate purpose is to implement some of ...
0
votes
0answers
101 views

becoming a cryptographer after math studies [duplicate]

After studying philosophy and being a philosophy teacher, I took back studies 4 years ago and I did a bachelor in maths. I'm in maths grad school now (I'm 32), and I would like to work in ...
1
vote
0answers
59 views

Which mathematical operations does secp256k1 point multiplication use?

To convert a bitcoin private key to a public key, the secp256k1 point multiplication math is used. Could I – theoretically – convert a private key to a public key just using the four arithmetic ...
0
votes
0answers
17 views

Verify signed file using GPG by passing in signature hosted online rather than stored locally (i.e. in keyring)? [migrated]

Is it possible to pass the URL of a GnuPG signature when executing a verify query against a signed file? For example, instead of: gpg --verify file.txt Is there ...
2
votes
1answer
205 views

The security of an encrypt-and-MAC

I would like to know what is the security of an encrypt-and-MAC with different keys for each transaction For example: the one-time-pad with $k_1$ and the HMAC with $k_2$ $$C = M \oplus k_1\\ MAC = ...
0
votes
1answer
40 views

Detect desynchronization in HOTP authentication [duplicate]

In HOTP authentication, is there a way for a system to detect that the token has been desynchronized? If so how does it know that the OTP was generated from a desynchronized (but valid) token and is ...
1
vote
1answer
74 views

Protection of Elliptic Curve Implementations against side-channel attacks [on hold]

Recent fast elliptic curve implementations, for example a presentation at Eurocrypt 2014 (earlier presentation slides, the paper) talks about protection against only timing attacks. Why only timing ...
2
votes
1answer
72 views

Implementation of garbled circuits using RSA

I was just reading these notes on garbled (Yao) circuits and I just stuck trying to figure out how an implementation of Table 1 would work using RSA encryption. In RSA the public key is (n,e). So for ...
1
vote
2answers
90 views

Is it just as difficult to find a desired output in a hash digest, for MSB vs LSB?

This question comes to mind after seeing "custom" Bitcoin addresses with some special string at the beginning of the address. They are generated in the same way Bitcoins are "mined", continually ...
0
votes
0answers
26 views

Arranging Vigenere Cipher into columns [migrated]

As I understand if you arrange a Vigenere cipher into columns you can use the Index Of Coincidence to find out the key length. I'm struggling to write an Algorithm that would take a piece of text and ...
0
votes
1answer
49 views

Security of chameleon hash functions

With the knowledge of the trapdoor, we are able to compute the same digest for differents messages. I've read that given two messages $m$, $m'$ and two numbers $r$, $r'$ such that ...
1
vote
1answer
59 views

problem with “one time pad” [closed]

I am a french student and I read the post on the forums (How does one attack a two-time pad (i.e. one time pad with key reuse)?). I need your help if possible. I 'm 11 encrypted messages , all ...
1
vote
0answers
47 views

Does the transposition cipher have a network application?

So I'm reading a chapter in my networking book and it talks about substitution and transposition ciphers (Transposition Cipher Wikipedia). I know that most network security uses public key or ...
4
votes
1answer
60 views

Can we run a probabilistic function on ciphertext with Functional Encryption (or Attribute Based Encryption)?

In the definition of functional encryption ($FE$): $FE.Setup(1^k)$ takes as input the security parameter $1^k$ and outputs a master public key $fmpk$ and a master secret key $fmsk$. $FE.KeyGen(fmsk, ...
2
votes
1answer
109 views

SHA-1 collision resistance

I'm researching on the SHA-1 algorithm and looking for reasons why it has fallen prey to differential cryptanalysis. I have read the research papers by Merc Stevens and Wang both of which describe how ...
-1
votes
0answers
65 views

Decryption of .png and .jpg files [closed]

I'm trying to modify graphic assets of the software I'm using (for aesthetic puroposess, I guess it's hard to do something harmful with graphic assets) but developer encrypted them. I'm not sure why ...
-1
votes
0answers
45 views

How do you perform frequency analysis to break Vigenere cipher programmatically?

I am trying to write a program to which when provided a ciphertext(maxlength - 200) and a key length(maxlength - 40), gives a plaintext as output from a possible set of plaintexts. By possible set of ...
0
votes
1answer
32 views

MD5 update functions

In the hashlib module in python is a function called m.update() where m is a ...
0
votes
1answer
102 views

Encrypting twice with different modes?

I was using a SOCKS5 proxy today (tunneled through SSH) and I began to wonder what the effect of encrypting twice (TLS over encrypted SOCKS5 in this case) would have on the security of the transmitted ...
1
vote
1answer
62 views

Why can't garbled circuits be reused?

There are a bunch of papers do research on resizable garbled circuits. But I wonder why garbled circuits cannot be reused? For example, the constructor constructs a garbled circuit of "AND" like ...
7
votes
1answer
284 views

What is the history of recommended RSA key sizes?

One can find up to date recommended key sizes for RSA at http://csrc.nist.gov/publications/nistpubs/800-131A/sp800-131A.pdf for example. In short it suggests a key size of at least 2048 bits. Is it ...
-1
votes
1answer
48 views

Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312

Prove that the affine cipher over Z26 has perfect secrecy if every key is used with equal probability of 1/312. Just some guidance/help with this problem would be greatly appreciated not sure how to ...
16
votes
1answer
404 views

How secure would HMAC-SHA3 be?

It would be possible to implement the HMAC construction with (draft) SHA-3, leading to HMAC-SHA3-224, HMAC-SHA3-256, HMAC-SHA3-384, HMAC-SHA3-512 (the last 3 digits are the output size $\ell$, where ...
0
votes
2answers
79 views

Database row level encryption scheme

I am wanting to secure some highly sensitive data in a database. This would mean that the data needs to be encrypted and remain secure for 100 years if it were to fall into adversary hands. I also ...
2
votes
3answers
95 views

Is it true the longer the key length is the more secure the encryption?

Then why don't we use xxxxxxx bits encryption? what stopping us from using a very lengthy key? I am referring to the encryption we use with SSL
0
votes
0answers
60 views

How can I break this cipher? [closed]

I am currently trying to break: +VZ7ZVcKPavGh4iGArNy and +VZyY1sBOazFh4COBrB2 I have a known plaintext that is: 378734493671000 which encrypts to: +VZyZlAHP6HAgoaPBrBz Is anyone able to explain how ...
0
votes
1answer
77 views

Cryptography system that limits the length of the encypted message

I have two devices which communicate via sms. This communication should now be encrypted. The devices can only send messages with the lenght of 160 characters. So i am looking for an encryption ...
0
votes
0answers
53 views

initiate the elliptic curve

when we consider a curve in a prime field for example Weierstrass form and want to initiate it in Miracl,we should give these inputs for initiate curve: ebrick_init(&binst,x,y,a,b,n,window,nb) ...
0
votes
3answers
109 views

Elliptic curve parameters

What's the meaning of 160 bit Curve in Elliptic curve ? or 192 or 224 or 256 and etc. And What is the standard for selecting this number of bit ? why they don't say 100 bit curve?
0
votes
0answers
54 views

Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack

While reading a literature on signature schemes, I came across the concept of Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack. Can anyone point me to the paper ...
0
votes
1answer
57 views

I need to know number of encryption/decryption operations?

If i want to break quadruple DES (say EDED), what is complexity? Like for EDE, it is O(2^112).
0
votes
1answer
38 views

HMAC_DRBG Generate Process: requesting N bytes at once different from requesting N bytes in total?

Am I correct in assuming that HMAC_DRBG would return different results if I, e.g. first request 4 bytes followed by a request of another 4 bytes instead of asking for 8 bytes at once? It seems that ...
0
votes
1answer
31 views
1
vote
1answer
45 views

Chess Grandmaster Problem and “Valid” Attacks on Zero-Knowledge Proofs of Identity

A long question here, but I really want to motivate why I'm confused. Consider the following attack on the Schnorr Identification Scheme. Alice chooses a random $k$, computes $\gamma = \alpha^k ...
1
vote
1answer
140 views

Compare two approaches for cracking RSA key

I came across these questions while studying for a crypto course, does anyone have any ideas on how to answer these? (a) Random prime numbers of size 1536 bits are chosen to generate an RSA modulus ...
1
vote
2answers
107 views

Are LFSRs enough for this?

Consider the following experiment: Let there be a machine which runs (ie. continually clocks) an LFSR of size (ie. number of bits) $b$, having a button that, when pressed, extracts the next $t$ ...
7
votes
2answers
866 views

How to better generate large primes: sieving and then random picking or random picking and then checking?

I'm writing an RSA algorithm, and am wondering what is the best and/or usual way to choose the initial prime numbers (p and q). I know of two methods to achieve this, one based on a prime number ...
5
votes
2answers
123 views

Shannon confusion and diffusion concept

I read the document(not the whole document) from Shannon where he speaks about the concepts of confusion and diffusion. I read in many places(not in the document but around the internet) that ...
7
votes
1answer
100 views

Implementation and Testing of SRP-6a

I have been wracking my brain trying to develop a functioning implementation of SRP-6a in Python to use with a 3rd-party API that claims to use SRP-6a with $N=$ 2048-bit prime and generator of $2$. ...
1
vote
1answer
1k views

How does TLS_FALLBACK_SCSV help?

After reading through https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-0, I could understand that this option is recommened for use when one has legacy SSL Servers which only support SSLv3. ...
0
votes
1answer
38 views

Does the following linear equation hold in bilinear pairings:

Does the following hold in bilinear pairings: $$e(g^{a_1x_1}g^{a_2x_2},g^{c_1}g^{c_2})=e(g^{x_1+x_2},g^{a_1a_2(c_1+c_2)})$$
1
vote
2answers
87 views

Comparing Files: Is it better to use multiple hash algorithms or just one?

I'm looking to compare (for byte-for-byte equality) two binary files. I already have the process down: Check for existence etc. Compare file lengths Use a hash or CRC of a sort (right now I use ...
0
votes
2answers
96 views

AES: Guess Password using the unencrypted text?

I am using the same password for some encrypted files currently (I know this is bad practice, though), and I wonder whether an attacker could decrypt if one decrypted file fell into his hands.
1
vote
0answers
74 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
2
votes
1answer
67 views

Encrypted read-only message queue

I'm creating a prototype for a messaging queue with some custom logic (can't re-use any existing solution). One requirement is to have all messages encrypted. There are three classes of nodes ...
2
votes
1answer
43 views

Use of ElGamal encryption for signature generation

If RSA (textbook RSA that is) generates a digital signature by using the sender's private key, couldn't any cryptosystem (the only two that come to mind are RSA and ElGamal) capable of asymmetric ...
-1
votes
0answers
31 views

Side channel vulnerabilities in SW RSA implementations? [closed]

I would like to know a list of practical side channel attacks with references. These attacks should work on SW implementations and I do not consider attacks that require physical access such as power ...

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