4
votes
2answers
318 views

Is there a public-key cryptography method that enables public keys to be much smaller than private keys?

Does a public key cryptography method that enables the public key to be orders of magnitude smaller than the private key exist?
4
votes
1answer
144 views

Generating unsigned, bounded random value using signed bounded random values

Use case: I have a random number generator that can generate random numbers in a range that is limited by a number $x$, say $x$ ranges from $2$ to $2^{(n - 1)} - 1$ exclusive. In this case $n$ is $16$,...
4
votes
1answer
179 views

Is there a reason that the N value in scrypt is limited to powers of two?

I have been looking at the scrypt hashing algorithm and am confused as to why the N value, which determines the overall cost, is limited to powers of two. There are ...
4
votes
1answer
175 views

Homomorphic Encryption - Smart Vercauteren Batching

I'm going through Smart and Vercauteren's paper "Fully Homomorphic SIMD operations" and had a question about some notation used in the paper. In section 2 of the above it is stated that for each ...
4
votes
1answer
271 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
225 views

Choice of reduction polynomial in Whirlpool's internal cipher

Whirlpool is an interesting little hash function in the Miyaguchi-Preneel family. In my mind, it's most interesting feature is the design of internal cipher W, where the distinction between key and ...
4
votes
2answers
3k views

ASCII to same-length ASCII encryption?

I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight. The ...
4
votes
1answer
1k 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
607 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
3answers
682 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
779 views

Is CBC mode encryption vulnerable to a reordering attack?

I know that, if CBC-MAC is used in such a way that the tag is the concatenation of all the blocks' outputs (and not just the last one), it's insecure under CPA for the simplest case of 2 blocks CBC-...
4
votes
1answer
260 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
303 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
416 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
2answers
2k views

Difference between salted hash and keyed hashing?

A cryptographic salt is additional input other than message itself for a hash function so that it prevents attacker from launching dictionary attacks . Usually the salt is stored along with the hash ...
4
votes
1answer
651 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
1answer
1k views

Possible ECC backdoor and its impact on Internet traffic

In a recent article, Bruce Schneier suggested that he prefers classic discrete log crypto over ECC because "I no longer trust the constants. I believe the NSA has manipulated them through their ...
4
votes
3answers
295 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
244 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
1answer
228 views

Securely generating passwords based on a secret and a public identifier

I'm trying to create a good scheme for generating passwords in my systems management scripts. What I'd like to do is have a secret key (let's say hello123), which I ...
4
votes
2answers
98 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
1answer
478 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
192 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
284 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
84 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 (id-some-data,...
4
votes
1answer
615 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
824 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
2answers
2k views

Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?

The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
4
votes
3answers
655 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
3k 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
1k 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
239 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
1k views

How to generate a public key from a private ECDSA key?

Having some specific ECDSA curve and a private key, how does one calculate the public key? I am having a hard time finding the algorithm and equations for it.
4
votes
2answers
2k views

Cracking the Beaufort cipher

Is there any easy way to crack a Beaufort cipher? We have a Vigenère table, and are trying to guess the keyword. Any easier way?
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
204 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
96 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
267 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
283 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
364 views

How to properly add ECDSA private keys?

I'm currently working on an application that requires me to add two ECDSA private keys in order to make a new private key. The result has to have the property, that its corresponding public key is the ...
4
votes
1answer
397 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
764 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
408 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
561 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
3k 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
1k 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
2answers
405 views

How is de-synchronisation of HOTP solved?

From RFC 4226 I understand how HOTP generates one-time passwords by incrementing a counter and uses the 'look-ahead' window to try to resynchronise (from this counter), if the user tries a few wrong ...
4
votes
1answer
239 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 $d$ ($d = e^{-1} \mod \varphi(N)$)...

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