4
votes
1answer
508 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 ...
4
votes
2answers
474 views

How do I unpack the x and y values from the BITSTRING in a DER ECDSA public key?

In ASN.1, the X and Y values for a 256-bit elliptic curve key are stored as a single 66-byte ASN.1 BITSTRING. Are the values just the first and second half of this bitstring? The private key is an ...
4
votes
1answer
783 views

Can SRP be used with Elliptic Curves?

I'm sure it can, because SRP (secure remote protocol) can be implemented everywhere where Diffie-Hellman works, but I need a proof to put this aspect into Wikipedia. Edit: ok, can it be at least ...
4
votes
1answer
177 views

Which MAC scheme is quantum resistant?

will HMAC survive Grover algorithm ? if not then which MAC scheme provide post-quantum security ?
7
votes
1answer
2k 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 ...
2
votes
2answers
288 views

It is reasonably safe to leave a SSH private key with a 30+ character passphrase public?

I'm curious about exploring uses for a distributing a single RSA private key with a passphrase instead of trying to secure the private key and distribute the public key. With the private key (and ...
3
votes
2answers
735 views

one-time pad key related attack [duplicate]

In one-time pads we always say do not use same key twice to encrypt ASCII messages, but if we use a random key to XOR a random ...
7
votes
1answer
452 views

Is SpookyHash vulnerable to HashDoS?

Aumasson, Bernstein and Bosslet did an excellent job demonstrating fatal weaknesses in MurmurHash and CityHash, but what about SpookyHash? My first uneducated guess is that it would be much harder to ...
8
votes
1answer
335 views

Alice trusts Bob only when Bob trusts Alice

some story first: Alice and Bob both have public/private key pairs. Now Bob wants Alice to sign his public key id. Alice agrees but only when Bob signs the public key id of her. Is this something ...
4
votes
1answer
212 views

How to design a practical and secure MAC scheme?

I am sorry, but I need to introduce some concepts which are not directly related to cryptography to make myself clear, I hope I won't stun you with this ... (I'd rather explain it here than redirect ...
3
votes
1answer
127 views

Potential vulnerability in DH key selection - am I understanding this right?

I'm reading through a DH implementation, and I think I found a potential hole. Public $p$ and $g$ values are properly selected. A candidate secret value $\bar a$ is pseudo-randomly selected such ...
8
votes
1answer
184 views

Solving hard problems in $\mathbb Z_{p}^{*}$ when $\mathbb p$ is close to $\mathbb 2^{n}$

Suppose, for some security parameter $n$ you choose a prime $p$ such that $p = 2^n+c$ for some relatively small $|c| < 2^m << 2^n$. I have seen such primes being called Pseudo-Mersenne Primes ...
0
votes
1answer
584 views

SSTP MSCHAP-V2 Authentication before SSL or after SSL Session

So with the recent news that there's a lovely new tool to crack MSChapV2 packets. So the question I have is on a SSTP Connection is the MSChapv2 handshake encrypted pre SSL setup or post. Obviously ...
1
vote
1answer
163 views

which asymmetric cipher provide highest performance?

to get highest performance Which asymmetric cipher provide fastest encryption/decryption ? ECC or DH ? what key size is recommended today ?
3
votes
1answer
216 views

How to use HMAC for large ciphertexts over TLS

HMAC used to secure chosen cipher-text attacks. if we are encrypting a large file (video) and sending it over TLS for decryption, how server can check MAC for ciphertext when we didn't sent whole of ...
3
votes
2answers
613 views

RSA private key format for Mega

I've been trying to reverse engineer Mega's (mega.co.nz) API calls. And stopped on the step where client needs to decrypt session id with provided RSA key. I can get key data, but I have no idea how ...
13
votes
2answers
446 views

Are safe primes $p=2^k \pm s$ with $s$ small less recommandable than others as a discrete log modulus?

I take the definition of safe prime as: a prime $p$ is safe when $(p-1)/2$ is prime. Safe primes of appropriate size are the standard choice for the modulus of cryptosystems related to the discrete ...
3
votes
2answers
791 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
votes
3answers
3k views

Export from US of crypto software with key-size > 56 bits still needs permission?

Elsewhere someone stated that he couldn't publish his crypto software on the Internet, because US Export Regulations require approval, if the key size is greater than 56 bits. I know that several ...
2
votes
2answers
2k views

Even passwords are vulnerable to hash collision attacks?

As stated in this page large documents hashed using md5 maybe vulnerable to collision attacks. My question is even passwords of 6-30 character are vulnerable to such hash collision attacks? If yes, is ...
1
vote
1answer
200 views

Sensible usecase for restricting special characters in passwords? [closed]

Please See Why Not Allow Special Characters In a Password on Security. Several websites I've come across limit the allowed special characters for a password. My thought was, it should all be ...
1
vote
0answers
102 views

Secure modulus length for Diffie-Hellman [duplicate]

What is secure modulus length for modular exponentiation so that finding discrete log is computationaly impossible?
0
votes
1answer
121 views

reduces the coefficients of a modulo 3 on NTRU

i'm still don't understand about 'reduces the coefficients of a modulo 3' on NTRU tutorial $a = f*e = 3 - 7X - 10X^2 - 11X^3 + 10X^4 + 7X^5 + 6X^6 + 7X^7 + 5X^8 - 3X^9 -7X^{10} \pmod{32}.$ Note ...
2
votes
2answers
276 views

How to efficiently generate a stream of independent, but biased random bits?

Usually, in cryptography, one is interested in debiasing a stream of independent (true) random bits, and several algorithms exist to do this. What about the converse? Let's assume I have a stream of ...
6
votes
2answers
1k views

HRNG for One Time Pad

I have just advanced to the last grade of high school (in Denmark). In this year, we all get to do one big project, where we can build/invent/create whatever we want to "solve a problem". As I study ...
4
votes
3answers
368 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, ...
1
vote
3answers
443 views

File encryption with one keypair?

I'm working on a program that uses an ECC keypair in a (password protected) PKCS12 file (.pfx) to encrypt files. I like this method because I think it will be higher security (using ECDH to negotiate ...
3
votes
1answer
437 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 ...
6
votes
4answers
272 views

Could a very long password theoretically eliminate the need for a slow hash?

Before I provide details, I want to clarify that I am not looking to implement this practically, but I'm only asking to get a better understanding. The way I currently understand it, we use slow ...
2
votes
2answers
128 views

Key Exchange and anonymity issue

If Alice (sender) sends a private message embedded with public key of the Bob(recipient) through onion network, so in this key exchange, does Bob remains anonymous to Alice as Alice knows about the ...
0
votes
1answer
119 views

RSA Certificate Owner and Issuer line meanings?

Apologies if this question is not in the right place. I've recently been looking through some RSA certificates ( specifically, Android apk .rsa files) and I'm having trouble deciphering the one and ...
2
votes
1answer
247 views

How large should a Diffie-Hellman p be if the messages are encrypted?

How large should the prime $p$ and generator $g$ values be in a Diffie-Hellman handshake if the messages are encrypted. If the key that encrypted the Diffie-Hellman messages becomes compromised, ...
0
votes
1answer
254 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 ...
-1
votes
2answers
2k views

How does the rand() function in C work? [closed]

I want to know how rand() works (even when I don't provide any seed how it produces PRNs?) thanks!
3
votes
1answer
1k views

Brute forcing an HMAC

Given current technology such as GPUs and GPU cracking software I was wondering if anyone has an idea on how long it would take to brute force the key used to derive an HMAC?
2
votes
3answers
152 views

How comparable is OFB to a one-time pad?

This is a rather trivial question, I just want to see if I get the concept right. In OFB you generate a pseudorandom stream based on some nonce, and you XOR that with the message to get the ...
35
votes
2answers
5k views

What makes a hash function good for password hashing?

Using a cryptographic hash to store e.g. passwords in a database is considered good practice (as opposed to storing them plaintext), but is subject to attacks on said cryptographic hash, assuming the ...
2
votes
0answers
27 views

Encryption with Deduplication [duplicate]

Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
4
votes
1answer
147 views

Does Linear Cramer-Shoup have pseudo-random ciphertexts?

"Linear Cramer-Shoup" is defined on pages 4 and 5 of $\:$ eprint.iacr.org/2007/074.pdf . Are the ciphertexts in Linear Cramer-Shoup computationally indistinguishable from uniform under a ...
-1
votes
2answers
1k views

Where to store the private key and the public key in a communication protocol

I want to create a simple secured connection protocol over TCP/IP. I just want to connect from my mobile device to a server securely. Firstly I thought to use an SSL connection, but I changed my ...
2
votes
1answer
162 views

Selecting a large NUMS Safe prime

Suppose I want to use the following simple hash function. For a mesage $m$, take some public $a$ and prime $p$ and raise $a^m \bmod p$ (never mind the computational expense of this operation). This ...
3
votes
1answer
321 views

When confusion is applied during encryption?

I know confusion is used in cryptography to make it more difficult to identify any relationship between the ciphertext and the symmetric key. I want to know when the confusion is applied during ...
1
vote
0answers
287 views

computing inverses in truncated polynomial rings manually for NTRU encryption [duplicate]

Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)? As an example from the tutorial: Example. Take $N=7$, $q=11$, $a=3+2X^2-3X^4+X^6$. The ...
7
votes
3answers
683 views

Is this encryption algorithm build from MD5 secure?

I'm being asked to use an encryption algorithm in my code, and besides the fact that I'm sure there will be implementation faults that lead to vulnerabilities, I also have concerns about the algorithm ...
1
vote
0answers
80 views

Can a LIRA system work with cjdns or other decentralized meshnets?

LIRA (Lightweight Incentivized Routing for Anonymity) is a scheme to incentivize participants in Tor to contribute resources, in particular bandwidth. The paper talks about it being used for Tor. Can ...
4
votes
1answer
927 views

BCrypt vs Key Stretching MD5

Ars technica posted an article about the latest in cyber warfare from the stuxnet crew. They key stretched MD5 by iterating it 10,000 times. It seems to be effective at handicapping HashCat's gpu ...
6
votes
2answers
750 views

Can I use a key-derivation-function as the hash function H in SRP?

In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...
0
votes
1answer
265 views

Solving congruences using PARI

I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
3
votes
1answer
383 views

Understanding a Blowfish cryptanalysis

I'm reading a cryptanalysis on Blowfish, and I've come across something that I don't quite get. Let's denote $$\delta = a \oplus a'$$ where a and a' are bytes that cause a collision in some S-box ...
-1
votes
2answers
502 views

Strong encryption done by hand [duplicate]

One of the distinguishing features of a good encryption algorithm, is that it is easy to encrypt, and hard to crack. Are there any that are easy enough for average folk to remember, and calculate by ...

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