4
votes
1answer
226 views

McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
4
votes
2answers
508 views

Perfect Forward Secrecy with Pre-shared Key

I've recently been looking at how to do perfect forward secrecy on a unidirectional connection (server can only push messages to client, client cannot respond). What I've come up with is the idea of ...
4
votes
1answer
946 views

Java's SecureRandom & plaintext attack?

Java's SecureRandom is meant to be cryptographically secure, and I know part of that means that the output should not be usable to predict further output. Though, ...
4
votes
1answer
488 views

Why use Needham-Schroeder if we have Diffie-Hellman?

If we want to establish secret symmetric key between two entities, why use Needham-Schroeder if we have Diffie-Hellman? With DH we don't need to have any trusted party, so what's the point of NS?
4
votes
2answers
459 views

Can an RSA public key be generated without ever knowing the factors? [duplicate]

Context: http://blog.cryptographyengineering.com/2013/12/a-few-more-notes-on-nsa-random-number.html Assume I wanted to use RSA as the basis for a hash function or DRBG. Also assume that my construct ...
4
votes
1answer
2k views

What are the advantages of CBC over ECB?

From this question I understand that, for a block cipher, using CBC is better than ECB. It seems that if one only has part of the cipher text, then decryption is difficult because the decryption ...
4
votes
3answers
384 views

Why use a timestamp and how can someone know it's the correct one?

Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message ...
4
votes
1answer
230 views

Why does CBC-MAC need prefix-free inputs to be a good PRF?

In the FFX spec, there is a note about using CMAC as the round function. Security notes. The round function F is constructed in such a way that the set of inputs on which the CBC-MAC is ...
4
votes
2answers
265 views

How to Distribute the Shares using Secret Sharing for arbitrary Monotone Access Structures

Consider 4 people, $A$,$B$,$C$,$D$, & a secret $s\in\{0,1\}^k$. Construct a scheme which enables the following subsets of people to retrieve the secret $\{A,B\}$, $\{A,C\}$, $\{B,C,D\}$. I know ...
4
votes
2answers
391 views

Decrypting without using the private key

Let $g$ be a generator of a multiplicative group $G$ of order $q$, $x$ be a private key, and $h=g^x$ be a public key of an exponential ElGamal cryptosystem. Given a ciphertext $c$ produced as the ...
4
votes
1answer
462 views

some of my confusions about DDH assumption

The wiki defines the decisional Diffie–Hellman assumption as follows: Decisional Diffie–Hellman assumption Consider a (multiplicative) cyclic group $G$ of order $q$, and with generator $g$. The DDH ...
4
votes
3answers
272 views

Can padding length, and thus plaintext length, be considered public information when using aes-cbc?

Right now I'm using a simple padding system that takes the plaintext, hashes it with SHA512, and appends $x$ bytes of the hash as padding where $x$ is the delta between the plaintext and nearest ...
4
votes
1answer
240 views

Swapping Key and IV in AES? Safe?

I have an application where I want to be able to send an encrypted file, and then mete out "keys" that allow the receipient to decrypt the file from a certain point to the end of the file. Actually, ...
4
votes
2answers
97 views

Is it possible to insert a key derivation function when using EAX?

I am currently investigating use of EAX mode for a dedicated application and following useful clarifications received from my previous post , to consider according to my applicable input security ...
4
votes
2answers
720 views

Winternitz One-Time Signature

I am reading the page 38 in this "Post Quantum Cryptography" book (Equations 8 and 9). My question is, why to compute the verification key $Y$, $f$ is applied $2^w-1$ times? Are there any security ...
4
votes
1answer
428 views

How does partial key escrow work?

It is being speculated that one of the ways that NSA leaker Edward Snowden may have created his "insurance policy" – distributing sensitive documents to various individuals with instructions to ...
4
votes
1answer
184 views

Does EAX use the same keys for encryption and authentication?

I am actually checking use of EAX AEAD mode, and following EAX spec review (scheme definition for my part), my question is: what about the derivation of the authentication and encryption keys? In the ...
4
votes
1answer
267 views

How to pad messages with large amount of padding

I'm playing around with an application for secure email-like communication and I want to perform length hiding padding on the plaintext messages so they always have a consistent size before encrypting ...
4
votes
1answer
83 views

“proof of access” schemes

What is the state of the art way when implementing a scheme challenging a party to prove they have access to certain data? What I'm looking for something along the lines of Give them ...
4
votes
1answer
524 views

Alternatives to HMAC + CBC?

I'm looking at using HMAC + CBC. The combination looks like this: ciphertext = AES256(text, k1) data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext Where: ...
4
votes
1answer
750 views

Recommended way of adding a pepper/secret key to password before hashing?

There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
4
votes
1answer
389 views

Is it possible to determine the group order by knowing the “public” and “private” key exponents in an RSA group?

I have an RSA group with modulus $n = p \cdot q$, two safe primes $p=2p'+1$ and $q=2q'+1$ and the "public" and "private" key exponents $d$ and $e$. $\phi(n) = 4p'q'$ is the order of the RSA group. If ...
4
votes
3answers
536 views

Is there a way to use Shamir Secret Sharing with updatable data?

I want to divide a system that maintains these properties, based on Shamir's Secret Sharing: A secret key is split up to N pieces, where T of them are enough to reconstruct the key. The original key ...
4
votes
2answers
2k views

What data is saved in RSA private key?

What data is saved in RSA private key in openssl? How to view it? Wikpedia says these variables are saved.
4
votes
1answer
910 views

Visualization of cryptography

I think CrypTool is great software. And what I find most useful in it is visualization of algorithms such as Caesar, Vigenere, AES, DES. And my question is: does anyone know other tools which are ...
4
votes
1answer
221 views

Future-Proof Versioning and Validation

I am working on a library (using standard primitives: AES256 CTR; HMAC with SHA256; PBKDF2 with SHA256, 128 bit salt, and 10000 rounds) to encrypt and decrypt data, given a password. The encrypted ...
4
votes
1answer
491 views

Why are protocols often proven secure under the random oracle model instead of a hash assumption?

Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle? I mean, is it possible to devise a protocol $P$ using a function $H$, and ...
4
votes
1answer
4k views

Why, or when, to use an Initialization Vector?

i'm trying to figure out when an Intialization Vector (IV) should be used. There are anecdotal reports that WEP was broken because of weak IV's. It's also claimed that if two pieces of plaintext are ...
4
votes
1answer
195 views

What authentication techniques can be used by QKD Systems?

As it is well known that QKD systems are prone to simple MITM attacks… what authentication techniques are being used in QKD to prevent those attacks in practice?
4
votes
1answer
95 views

Dimension of Encryption of a linearly dependent set of plaintexts

Suppose I have an encryption scheme of the form $ E(P)=C $ where $P$ is the plaintext and belongs in $\{0,1\}^N$, $C$ the ciphertext which belongs to $\{0,1\}^M$ and the encryption is performed under ...
4
votes
1answer
246 views

Why are there $ signs in my passwd file?

I am trying to get access to my eReader and I managed to get the passwd file. ...
4
votes
2answers
254 views

How can the Schmidt–Samoa cryptosystem uniquely decrypt large messages?

Suppose I choose $p=7$ and $q=11$. This gives a public key of $p^2·q = 539$. However, decryption occurs using a modulus of $p·q=77$. If a person chooses to encrypt $500$ using my public key, how ...
4
votes
3answers
1k views

Hash function in PBKDF2

From this excellent answer I learned (correct me if I am wrong) that when writing a block cipher with say key size 128 bit, one has to pad the password given (variable size) so that it becomes exactly ...
4
votes
1answer
366 views

Is it secure to use the hash of key as the IV in AES encryption?

I need to store some sensitive data for a program. For each copy of the program, there will be a unique key for encrypting one (and only one) file using AES encryption (OFB). The key will not be ...
4
votes
1answer
681 views

Is XOR in a CBC-like mode secure?

Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively. The first byte of ciphertext is computed like this: $C_{1} = K_{1} \oplus P_{1}$ ...
4
votes
1answer
398 views

How was the complexity of the Biclique Attack calculated?

The abstract of the Biclique Attack paper claims: The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$. What does $2^{126.1}$ mean in this context? And ...
4
votes
1answer
190 views

DIfferent inner and outer hash functions for NIST Recommended HMAC?

The NIST recommended HMAC uses $$\operatorname{HMAC}_k(text) = H_\mathrm{out}( (k \oplus \mathrm{opad}) \operatorname\| H_\mathrm{in}((k \oplus \mathrm{ipad}) \operatorname\| text) )$$ Is it ...
4
votes
1answer
546 views

How is BCrypt secure when it uses a static dataset for blowfish hashing?

I'm planning on using this Javascript BCrypt implementation, but as you can see in the code, it uses a 4KB precalculated dataset for the P and ...
4
votes
1answer
2k views

What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
4
votes
1answer
2k views

How does PBKDF1 work?

I need some basic guideline on Password Based Key Derivation Function. PBKDF1 generates a key from password and salt using Hashing algorithm (like SHA1, SHA256, MD5). What is the step behind this?
4
votes
2answers
951 views

How to construct encrypted functions (with either public or private data)?

Homomorphic encryption is often touted for its ability to Compute on encrypted data with public functions Compute an encrypted function on public (or private) data I feel I have a good grasp of #1 ...
4
votes
1answer
233 views

What is the property of RSA where N=e?

In RSA, suppose we know that $e=N$ and we are given the value of $e$. ($N = p\cdot q$ for some large primes $p$ and $q$; $\gcd(e, \varphi(N) = 1)$ Can we calculate $d$ ($d = e^{-1} \mod ...
4
votes
1answer
1k views

How does a key wrapping like RFC 3394 secure my cryptographic keys?

So I'm messing around in the BouncyCastle library with the RFC 3394 AES Key Wrap engine and I'm trying to understand the benefit of it. The problem I'm running into is how to store keys securely on a ...
4
votes
1answer
194 views

Does anyone have a KAT for 3DES KO-2?

Does any one have, or can refer to a Known-Answer-Test (KAT) for Triple DES Keying Option 2? (Keying Option 2 means $C = DES_{k_1}(DES^{-1}_{k_2}(DES_{k_1}(P)))$ for encryption and $P = ...
4
votes
1answer
27 views

Can the backdoor in Dual_EC_DRBG be used to create a public key stream cipher?

Dual_EC_DRBG has the property that if $Q = e\cdot P$, someone who knows $e$ can break the PRNG. This seems to lead to a public-key stream cipher: Alice chooses a random $P, e$, where $P$ is a ...
4
votes
1answer
195 views

Any stream cipher with avalanche effect?

As far as I know, all stream ciphers work by generating a stream of pseudo random bytes, and XOR it with the plain text to get the cipher text. It has the property that one bit change in the cipher ...
4
votes
1answer
101 views

Security of encrypting many short values with AES in GCM mode

We intend to encrypt certain values in a database which holds personal information such as addresses so as to prevent data leakage should the database be compromised. The intention is that each field ...
4
votes
1answer
103 views

Understanding ransomware – What makes plain-text-attacks or brute-forcing so hard?

Say I have four files. Two are completely unencrypted, while the other two are the exact same files other than that they have been encrypted with (apparently) the same public key (via a ransomware ...
4
votes
1answer
119 views

Is finding collisions in a part-hash not often enough a bad problem?

My situation: I've been working now for a couple of months on my own unique hash function, I've changed it many times and had two main versions but I won't bore anyone with the details of my work; at ...
4
votes
1answer
24 views

What is PCT_SSL_CIPHER_TYPE_1ST_HALF?

I'm writing a tool to do security posture assessments of SSL/TLS services, and ran into an interesting result. I ran through all defined cipher suites to test which could be negotiated (like sslscan ...

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