0
votes
0answers
15 views

Computing the redundancy of language for a Vigenère cipher with m=5

Redundancy of L = 1- Entropy of L/ log base 2 {P} The Redundancy of L is given by 1 minus the Entropy of L divided by log base 2 of the Cardinality of the Plaintext space. Could someone advise me how ...
1
vote
1answer
51 views

Where is defined the fact of having a “learning” and “challenge” phase in cryptography proofs?

I've read Bellare and Rogaway 2004 and Shoup 2004 about game-based cryptography proofs, but I lack precisions about how should be built the "learning" and "challenge" phases, since my games will ...
8
votes
2answers
156 views

How Secure is a Pronounceable Password? In means of entropy

There are some strong studies which support the use of pronounceable passwords and multiple tools which provide generation of such passwords. According to this question the entropy of a password ...
0
votes
1answer
61 views

Prepending random data to encrypted file

If random data is prepended to a file encrypted with GNUPG's symmetric encryption, how may an attacker find out if the input file is deliberately corrupted or the passphrase is wrong? If it is not ...
0
votes
1answer
69 views

Proof that counter mode of operation and CBC mode are CPA secure when pseudorandom permutations?

I know counter mode can be CPA secure, when used with block ciphers modeled as random permutations. If we use pseudo-random permutations, is it still CPA secure? Is there a proof? How about CBC ...
0
votes
1answer
56 views

Encrypt a file for random access but only after an initial read of the whole file

I'm symmetrically encrypting a file (using a random salt and a user supplied password with PKCS5S2, i.e., nothing special) and I need to be able to access it randomly. Therefore I'm using a stream ...
1
vote
2answers
88 views

Does google's Crypto.JS AES encryption use PBKDF2 as default?

Does google's Crypto.JS AES encryption use PBKDF2 as default? Some references, but I can't figure out the answer myself: https://code.google.com/p/crypto-js/#The_Cipher_Algorithms ...
1
vote
0answers
88 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 ...
3
votes
2answers
250 views

Small Prime Difference in RSA

In RSA, the $p$ and $q$ should be randomly generated, and they are the same size. The difference between $p$ and $q$ should not be small. Suppose that $u=|p-q|<20$ and $p \times q ...
1
vote
1answer
87 views

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

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 ...
3
votes
2answers
133 views

Does a stream cipher require a KDF when it's key is variable length?

RC4 has a variable length key. Is it still necessary to use a key derivation function, such as PBKDF2, to initialize it? Would using a single character password weaken it's output when compared to a ...
0
votes
1answer
66 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 ...
3
votes
1answer
190 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+ ...
4
votes
1answer
64 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, ...
1
vote
1answer
72 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
55 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 ...
1
vote
1answer
68 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 ...
2
votes
1answer
82 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 ...
3
votes
1answer
105 views

What does “learnable with oracle queries” mean?

I came across the following quotes in reading papers on obfuscation (1, ibid, and 2): The next result follows from the fact that point functions are not exactly learnable (since a uniformly chosen ...
0
votes
1answer
41 views

MD5 update functions

In the hashlib module in python is a function called m.update() where m is a ...
0
votes
0answers
59 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
0answers
77 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
50 views

blowfish ecb with openssl doesn't give the expected result

I do the following via the Linux CLI: ...
0
votes
1answer
46 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 ...
-1
votes
1answer
60 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 ...
1
vote
1answer
63 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 ...
0
votes
1answer
112 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 ...
0
votes
1answer
66 views

I need to know number of encryption/decryption operations? [closed]

If i want to break quadruple DES (say EDED), what is complexity? Like for EDE, it is O(2^112).
5
votes
2answers
194 views

How do you test randomness?

Suppose I receive a list of 1 million coinflips, and I want to know how likely it is that the list was randomly generated. My first thought would be to count the number of heads and tails, which ...
1
vote
1answer
3k 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. ...
1
vote
1answer
168 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 ...
0
votes
1answer
83 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 ...
1
vote
2answers
93 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
1answer
23 views

CSPRNG's (ELI5) What's the purpose of multiple seeds/ regenerating sources of entropy (i.e. /dev/random)?

Why is there a need to generate more than one high entropy seed? It would seem like if the original source of entropy is high quality, than some 512 bits should be more than enough to seed a CSPRNG ...
1
vote
2answers
122 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 ...
2
votes
1answer
65 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 ...
7
votes
1answer
316 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 ...
0
votes
1answer
47 views

Does the following linear equation hold in bilinear pairings:

Does the following hold in bilinear pairings: $$e(g^{a_1x_1}g^{a_2x_2},g^{c_1}g^{c_2})=e(g^{x_1+x_2},g^{a_1a_2(c_1+c_2)})$$
0
votes
2answers
106 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.
0
votes
3answers
120 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?
2
votes
1answer
79 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 ...
-1
votes
2answers
74 views

Output of a Feistel network with all “0” round function

What is the output of an r-round Feistel network when the input is $(L_0, R_0)$ and each round function outputs all 0s, regardless of the input?
1
vote
0answers
78 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 ...
1
vote
1answer
64 views

How to encrypt letters less than block n using Hill Cipher

I am learning about Hill Cipher and know that it is a block cipher where each block of n letters (considered as an $n$-component vector) is multiplied by an invertible $n \times n$ matrix, again ...
0
votes
0answers
57 views

Need help solving a shift cipher problem?

A three letter alphabet {a, b, c} has probabilities p(a) = .5 and p(b) = p(c) = .25. A shift cipher is applied to pairs of letters. More precisely: plaintexts consist of two-letter sequences of ...
2
votes
3answers
118 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
2
votes
0answers
64 views

Is it safe to derive a password from a signature provided by ssh-agent?

I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of ...
0
votes
1answer
81 views

Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
1
vote
1answer
69 views

Can Diffie-Hellman be scaled up or force-multiplied?

I'm not too familiar with the math involved with the exchange of keys, I've read it over several times, but math isn't my strong point. My understanding is that smart people are hard at work to ...
1
vote
2answers
122 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 $t$ ...

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