2
votes
4answers
2k views

Is my pseudo-random initialization vector secure?

How can I know if I am generating a secure pseudorandom initialization vector? Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
1
vote
1answer
552 views

Recommended Books for Cryptography : Theory and Implementation [closed]

It is a great idea if experts in Cryptography from mathematicians to security engineers introduce books and textbooks which they think is helpful or instructive for all people interested in the ...
5
votes
1answer
4k views

Common modulus attack on RSA when the 2 public exponents differ by a single bit

This is an exam question an i have no idea how to recover the message m. John wants to send an encrypted message to mary who has a pair of RSA keys, However, John does not know Mary's public key and ...
5
votes
4answers
826 views

What is the actual difference between security through obscurity and true encryption?

In an abstract sense, aren't both the same? Don't their definitions boil down to the following? security through obscurity: trying to make sure some information cannot be obtained without knowing ...
2
votes
2answers
316 views

The security of data traffic over both SSTP & SSL

Suppose you're connected to a VPN server via an SSTP VPN, and then you're trying to sign in to your webmail account that is already secured with an SSL certificate, e.g. hushmail.com. However, it ...
1
vote
1answer
339 views

Digital Certificate Chain Verification

Does a certificate contain the complete chain of all certificates up to the trusted root certificate, or does the program that verifies certificates have to fetch each parent certificate individually ...
4
votes
2answers
476 views

Is any decent RNG acceptable as a stream cipher?

I have a function f(x,n) that takes a 128-bit key x, and generates n bytes of pseudo-random data. I've tested the output bytes this function for various keys with the NIST RNG testing suite (NIST ...
3
votes
3answers
309 views

Is a continuous stream of encrypted data embedded in garbage more or less secure than only encrypting the data?

Consider a communication channel that needs to be secure (Encryption can not use full "volume" encryption, since future messages are not known). Would it be better to only transmit encrypted ...
0
votes
1answer
293 views

Polynomial for secure communication

Can we use a polynomial $P(x)$ to securely communicate ? For example Alice & Bob agree on a degree of a polynomial. The value $x$ & the coeficients are generated from a seed using a hash ...
3
votes
3answers
297 views

Existing works on pre-computing ElGamal ephermal keys

I was playing around with a problem in e-voting schemes that use additive homomorphic encryption to tally votes, namely that at the end of the day somebody (or somebodies, if the secret material has ...
1
vote
1answer
131 views

MD5 pre-fixing with an unkown postfix

Is the MD5 prefixing attack still valuable to an attacker if he doesn't know the postfix of the string? For instance, what if the following sanity check was being used: ...
3
votes
1answer
1k views

AES CCM vs CCMP

Are the terms AES CCM and AES CCMP are equivalent, or is there any technical differences between the two?
5
votes
2answers
773 views

Cryptographic GUID?

I need a GUID. Really just any number that is likely to be unique. However I prefer not to leak time and other things as a GUID may leak. What should i use as a cryptographic replacement? I was ...
7
votes
1answer
562 views

Why does SRP-6a use k = H(N, g) instead of the k = 3 in SRP-6?

I've been reading up on the Secure Remote Pasword protocol (SRP). There are a couple different versions of the protocol (the original published version being designated SRP-3, with two subsequent ...
5
votes
2answers
289 views

Do MD5's weaknesses affect Oplop?

Oplop is an algorithm that generates account-specific passwords from a master password and user-chosen nickname (typically username@domain). From the website: Concatenate the master password with ...
5
votes
2answers
2k views

Why can't the IV be predictable when its said it doesn't need to be a secret?

I heard multiple times not to reuse the same IV and IV should be random but doesn't need to be secret. I also heard if the IV is something like sequential numbers or something predictable I should ...
1
vote
2answers
240 views

Is stretching hash several times basically the same as bcrypt?

As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
1
vote
1answer
63 views

Design question for a service that signs messages on behalf of a user

I'm working on a messaging service that lets users author messages and have them signed with an RSA key. The key is used for identity purposes only and can be revoked, so compromising the private key ...
4
votes
2answers
4k views

Secure private key storage

I'm developing application in Java that has to store RSA keys in software for foreseeable future (that is, at least 10 years). The two most common standards of storing private keys are PKCS12 and JKS ...
2
votes
1answer
191 views

How many different keystreams can I produce with AES in Counter Mode?

I'm using a 64-bit nonce (incremented between the streams) and a 64-bit counter (incremented within a stream) for AES in CTR mode. How many different key streams can I produce with this setup?
2
votes
1answer
219 views

How is the EAX-mode used in EAP-PSK (RFC 4764)?

According to the specification of RFC 4764, contents in EAP's third message and fourth message are required to be encrypted by AES-128 in EAX mode (also called protected channel). In RFC 4764, the ...
7
votes
1answer
158 views

How to turn adversary against encryption of zeroes into adversary against random bits?

I recently read the article Nonce-Based Symmetric Encryption by Rogaway, where he presents two different notions of indistinguishability, which he calls ind$ and ind, respectively. Here's the ...
-2
votes
1answer
161 views

Why is 2 the inverse of 10?

I have one question about the ECDSA signature scheme. When Bob wants to send a message to Alice that is to be signed she makes following things (with for example $A = (5,1)$, $d=7$, $q=19$). ...
9
votes
1answer
475 views

Why x00 is usually avoided in salt?

In .NET Framework, there is a cryptographic Random Number Generator (RNG) provider which enables to generate a cryptographically strong sequence of random bytes. This provider contain, among others, ...
0
votes
1answer
89 views

inverse of 985 mod(φ60131)

Alright Ive been working on this one for a while I found φ(60131) to be 97294 ½(60131+60131(5)^.5) = 97294 then I worked through the GCD ...
4
votes
3answers
2k views

Which of these 3 AES 128 symmetric encrypt/decrypt routines is most secure?

I am developing a symmetric en-/decryption routine written in c# for a database containing user-specific, sensitive information. I have narrowed down the implementation to 3 different approaches, ...
2
votes
1answer
271 views

Aes encryption -The relevance of static matrix in mixcolumns operation

Can someone explain to me the relevance of the static matrix used for the mixcolumns operation in aes encryption.i.e the relevance of why the byte is multiplied by 2 + next byte multiplied by 3 + next ...
1
vote
3answers
145 views

MISTY1 Implementation error

I am trying to implement MISTY1. It's RFC, RFC2994, contains psuedocode that I basically copy and pasted into Code::Blocks. However, I managed to mess that up somehow. After 2 days, I still have not ...
1
vote
1answer
809 views

How to jusify {e,n} is a valid RSA public key?

I have a two set of key {36,77} and {50,117}, How can validate if it is a valid RSA public keys? Is there any simple method?
5
votes
3answers
3k views

Do I have to recompute all hashes if I change the work factor in bcrypt?

The well-known article about why we should use bcrypt for hashing passwords mentions the work factor - some parameter to the algorithm that determines how long one hashing should be in terms of number ...
3
votes
1answer
225 views

Encrypt array of int for individual retrieval

I have limited exposure to cryptographic terminology, so please bear with me. My end goal is to encrypt integer IDs, before transmitting them to a web client in a list of search results, in a way ...
3
votes
1answer
195 views

What are the dangers of predictable (repeated) plaintext structures?

When using a "good", modern cipher (specifically one that provides ciphertext indistinguishability), is it a problem at all if there is some well-known structure in all plaintexts? For example, ...
6
votes
1answer
438 views

Does TLS use RC4-drop[n]?

According to many sources, the first few (n) bytes of the RC4 keystream are strongly biased, and therefore should be discarded before using the keystream to encrypt anything; this precaution is ...
12
votes
3answers
763 views

What is the best way to put a backdoor in an encryption system?

How can you put a backdoor into an encryption algorithm? Are there any techniques that can be used to reduce the time it takes to break a key? I am looking for practical examples encryption schemes ...
6
votes
3answers
313 views

Can nesting different ciphers with different keys ever decrease security?

Very related to this question but not addressed there. Does the following construction risk introducing any vulnerabilities that render it less secure than using either of its individual components ...
1
vote
1answer
315 views

Are there any multiparty homomorphic encryption schemes?

Are there any multiparty homomorphic encryption schemes ? Most of the literature is about two party schemes . Is there any generalization made for n party ?
5
votes
2answers
732 views

Adaptive Hash Functions: How to tell how many iterations were used?

If an adaptive hash function like bcrypt or PBKDF2 is used in hashing passwords, the number of iterations used in the hashing process can be configured. For a penetration tester or a malicious ...
2
votes
0answers
295 views

How to properly format a PGP Message Block?

As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
4
votes
1answer
948 views

How to securely use Elgamal encryption in libgcrypt?

How secure is libgcrypt's Elgamal implementation of encryption (how different it is from textbook Elgamal), and how can I tweak padding and other preprocessing actions? For example, I know that usign ...
3
votes
2answers
294 views

Is just a bit of random, “fully random”?

I understand that hashing a datetime is a pseudo-random number, and not good in a security context. But what about hashing a datetime plus a truly-random but constant string (just a string that an ...
1
vote
1answer
2k views

AES GCM symmetric encryption of data at rest in c#, ciphertext much longer than plaintext

I've written encryption/decryption routines using AES GCM. Code can be found here. I recently realized that the cipher text is longer than I believe it should be. It should add the tag and IV onto ...
-3
votes
1answer
919 views

128-bit Pseudorandom number Generator

Is there any 128-bit pseudorandom number generator available? I tried the Blum Blum Shub Generator, but I can't produce a 128-bit pseudo-random number. Maybe before I produce a 128-bit pseudorandom ...
2
votes
0answers
370 views

Diffie hellman key exchange on elliptic curve over an extension field [closed]

I am attempting to do a final semester project where I implement Diffie-Hellman key exchange on an elliptic curve over an extension field (2^256). Can anybody help me to generate the extension field ...
2
votes
1answer
481 views

Poor man's SSL - is this method as safe as SSL/TLS?

I need to send data between two applications. I've got requirement that says that data should be transmitted using secure protocol such as SSL/TLS. Data is sent using TCP sockets and I don't have ...
2
votes
1answer
830 views

Can we trust digital signatures?

Consider that Alice wants to send a digitally signed message to Bob. Mallory might be able to publish his public key under Alice's name and then impersonate Alice to send a message with an apparently ...
1
vote
1answer
668 views

Deniability of OTR messaging

I've been looking at the off-the-record messaging protocol, and there is something about its deniability property that seems strange to me. Consider the following scenario: In the course of an ...
0
votes
3answers
229 views

Is there a way to break this encryption?

I was wondering about making up a simple system to encrypt a file: ...
2
votes
3answers
859 views

Encryption vs. decryption of same plaintext

Does the same encryption algorithm given the same plaintext always produces the same ciphertext? Does this cause any security flaws?
5
votes
3answers
1k views

RS Erasure Coding and Shamir's Secret Sharing

So I was trying to understand the basic difference between erasure coding and secret sharing, and I found this paper (that you can find here or here). For what I understand, it states that Shamir's ...

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