1
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1answer
147 views

Do I need two keys for AES CBC and HMAC or can I use the same key for both operations?

I am setting up a Python program to encipher messages on the following basis: -from my password, generate 32-byte key from SHA256(password) -generate a 16-byte IV from a PRNG -measure the length of ...
1
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1answer
97 views

Can we parallelize the Feistel Networks?

Classic Feistel Networks and various types of FN's are sequential in nature. [1]has a good overview of different types. But is there a way we can do Feistel Networks in parallel and achieve good ...
1
vote
1answer
158 views

Which homomorphic encryption scheme has the same size of plaintext space and ciphertext space?

I want to pre-compute the result for all possible ciphertext of a homomorphic encryption. Is it acheivable? Is there a fully homomorphic encryption scheme that has the same size of plaintext space ...
1
vote
1answer
86 views

Is it possible to deduce the IV from CBC ciphered data, without knowing the key?

The question came up here, which left me thinking: Is it possible to deduce the IV from CBC ciphered data, without knowing the key? And if not, why is it considered a bad idea to create an IV by, for ...
1
vote
1answer
99 views

Perl DES PCBC as protection against decryption/crypt analysis

Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties? If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the ...
1
vote
1answer
55 views

Can CBC encryption have separate keys for separate blocks of plain text?

Can we have separate key for separate blocks which we get while operating a plain text message using CBC encryption model? If yes, what are it's advantage? Please enlighten me.
1
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1answer
187 views

Why does Fortuna RNG use double SHA-256?

In the paper for Fortuna the authors say that you can use any good digest algorithm (obviously as long as its output is 256 bit) and then they recommend double SHA-256. Why? What's the benefit? What ...
1
vote
1answer
71 views

Near preimages, applicable to Bitcoin?

Bitcoin mining relies on generating a smaller hash than the so-called target (a function of the so-called difficultly), thus is vulnerable to a truncated preimage attack (you just need to obtain a ...
1
vote
1answer
154 views

What is difference among eavesdropper attack, multiple message attack and CPA attack?

What is/are difference(s) among eavesdropper attack, multiple message attack and CPA attack in context of symmetric key encryption? I only know that in eavesdropper attack there is an adversary ...
1
vote
1answer
100 views

how to use salt to sign a message and how is it effective? [duplicate]

I've had an assignment to sign a file using hash and salt, so I read about salt and I got why it's important when it comes to password, but not to sign messages. How do I sign something using salt? ...
1
vote
1answer
2k views

CryptoJS.AES result always has same first few bytes?

When using this very minimal CryptoJS AES example: ...
1
vote
1answer
736 views

Difference between known-plaintext attack and forward search attack

I am looking at the different attacks on RSA. I came across known-plaintext attack where the public key can be used to encrypt all possible messages until it finds a match on the sent encrypted ...
1
vote
1answer
253 views

What is the best way to share a shared secret key over HTTPS to be used for HMAC authentication?

I am writing an application in Java that will be using SHA-1 HMAC message authentication. From what I understand, a connection over HTTPS is considered secure enough to share a secret key in plain ...
1
vote
1answer
363 views

Right usage of PBKDF2 and login system questions

I'm developing the login part of my application and I was asking myself how to do it right. My application stores some users' data server-side that must be inaccessible from us, so all the content ...
1
vote
1answer
74 views

Secure Broadcast Channel

I've read a paper that says that one of the "assumptions" that it makes is secure broadcast. Why is this an assumption? Can't a broadcast channel be built with simple primitives--i.e. encrypt and sign ...
1
vote
1answer
165 views

Designing a secure IM protocol

I haven't been programming much lately, so I figured I would make an encrypted instant-messaging program (read: Skype clone) with groups to hone my skills. That's not important though, I can do that. ...
1
vote
1answer
211 views

What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
1
vote
1answer
161 views

Compared to GCM or XTS modes, how secure is H xor R1, E (R2, R1, Message) for confidentiality and integrity?

Let R1 and R2 be (32 byte) random values, and let a H = Hash (R1, R2, Message) be of the same length as each R value. Provided E (R2, R1, Message) is operating in some chaining mode, are there any ...
1
vote
2answers
84 views

Shamir's ID based signatures - Notation issues

I am currently implementing Shamir's ID Based signature scheme as defined in the original paper. The sign and verify operation are defined as follows: Sign: $s = g * r^{f(t,m)} (\mod n)$ ...
1
vote
1answer
93 views

OTP sequence uniqueness

Is it possible to use Time-based One Time Password (TOTP) algorithms to generate tokens from multiple channels (where a channel is defined as a "user" using a certain shared key $K_c$ for channel ...
1
vote
1answer
270 views

Hash functions with or without secret key

The classical definition of hash functions (found in books) are OK, but when studying a little more there is a lot of notions that seem ambiguous (contradictory) to me : Sometimes we have hash ...
1
vote
1answer
107 views

How unsafe is to share parts of a password

The best way to ask this question and have a concrete answer is to set a very specific example. This is the example I would be interested in reading an answer to: Consider that my friend Alice has ...
1
vote
1answer
278 views

crypto design with AES256 MODE OFB

I have the following APP Design key store (contains 1:n user payload as 1:n key store entries) key store salt (is used to extend to key store password to 256 bits, stored in clear text) key store ...
1
vote
2answers
325 views

How can I simulate and measure brute force hacking using RSA?

I want to implement brute force hacking using RSA. How can I simulate and measure time duration? What software (or software-based simulator) would be needed?
1
vote
1answer
90 views

Hashing a uuidv4 + time to create a unique id

First, I am no crypto expert although I am doing the MOOC. I have an item which has as id: uuidv4 When I create this item: I create a new uuidv4 check if it already exists and if not, I store it ...
1
vote
1answer
388 views

Encrypting a payload for transmission over HTTP. AES256 with PBKDF2

I've done some reading about implementing AES256 and deriving a key from a password. If I understand correctly: I want to generate a new salt (for the key) and a new IV (for the encrypted message) ...
1
vote
2answers
569 views

Securely send public key from client to server in RSA?

I have a client and a server communicating with messages encrypted using RSA. Initially, the client knows server's public key, but the server does not know the client's public key. Is it possible to ...
1
vote
1answer
168 views

Public-Key Deterministic Encryption : Why does not provide perfect security?

I've got a question about an assignment . The question is "Why a Public-Key Deterministic Encryption Algorithm does not provide perfect security ?" . I suppose it means according to Shannon . Any ...
1
vote
1answer
104 views

Cracking Stream Cipher

I need to crack a stream cipher. I have a set of plain text and encrypted text pairs. The hint to the question asks me to use entropy analysis and look at the hex dump of the encrypted text. However, ...
1
vote
1answer
214 views

Insecurity in Needham and Schroeder protocol?

I've been studying specifically the authentication algorithm Needham and Shroeder, and understand the idea in general of the message exchange. But, researching on the subject, I found a question that ...
1
vote
1answer
39 views

Logarithm in Private Set Intersection

Is the logarithm in the private set intersection protocol mentioned in Section 3.4, Step 5 of http://www.ece.umd.edu/~danadach/MyPapers/set-int.pdf, a base 10 or 2? How do we find this out?
1
vote
1answer
82 views

Authentication and deniability

I have the following problem: Alice wants to send Bob a message such that Bob knows it is from Alice but at the same time he cannot prove that Alice send him this message. The solution I came up ...
1
vote
1answer
83 views

What is the padding scheme for the original Tiger hash?

The specification doesn't seem to indicate how to pad messages to the requisite 512-bit boundary. What is the padding scheme for the original Tiger hash?
1
vote
1answer
122 views

Method to calculating e in RSA

For simplicity I choose two small primes for p and q. p=3 q=11 n=33 Φ(n)=20 Now we need ...
1
vote
1answer
103 views

Cryptography: Oblivious Transfer with at most one transfer?

I am trying find a transfer method for this problem. Suppose Alice and Bob both has access to a function $\text{F}$ with two parameters. $\text{F}(x,y)$ randomly returns $p$ to alice and $q$ to Bob ...
1
vote
1answer
2k views

How can i predict the next number of a long sequence of seemingly random numbers? [closed]

How can I accurately predict the next random number between 1 and 999, given past results. I have no knowledge of the PRNG or algorithm used. How can I predict the next number of a long sequence of ...
1
vote
1answer
127 views

Hashing entropy generator output with SHA256

I'm using SHA256 to hash the output of an entropy generator to generate random numbers. Is it generally better to treat the output of the entropy generator as single messages and hash each of those ...
1
vote
1answer
152 views

Is Bitmessage a Mix network?

I've read the Bitmessage whitepaper and I found it rather lacking on the details, but it promises anonymous routing. Can it be considered a variation on mix-networks, where each peer acts as a ...
1
vote
1answer
2k views

What is the difference between SHA256WITHRSA and SHA256WITHRSAENCRYPTION digest algorithms?

I installed djigzo on my android phone and I want to use it for smime mail. I don't know the difference between choosing SHA256WITHRSA and ...
1
vote
1answer
210 views

Generate keys with k3d3 / ed25519-java

I'm trying to use a java implementation of ed25519. In the code, I can't find any functions that generate keys. My experience with cryptography is limited to about three weeks of asking questions on ...
1
vote
1answer
500 views

If G is a secure PRG and G' is a function of G, is G' secure?

For example: for secure PRG G if I have a G' s.t. G'(k) = G(k)||0, is ...
1
vote
1answer
477 views

Using HMAC-SHA256 with short passwords and sliced outputs for short-lived secure hashing

I don't have much background in cryptography, so forgive me if I'm using the wrong mathematical terms to explain my needs. Following this question, I learned that taking a random secret 16-bytes ...
1
vote
1answer
96 views

Why is the security of block cipher not a function of key and tweak?

The proofs and security of block ciphers constructed especially of Luby Rackoff Constructions and Feistel Networks is based on the number of queries and round functions. The security measure is always ...
1
vote
1answer
1k views

Is Curve25519-java secure?

I have only about 2 weeks of cryptography experience mostly in the form of questions on bitcoin.se. Is Curve25519-java up to date with current Curve25519 standards? Is Curve25519 itself secure? ...
1
vote
1answer
180 views

How to prove that a ciphertext is encrypting multiplication of two values?

Zero-knowledge proofs with soundness, completness and zero-knowledge enable a prover to convince a verifier that a witness validates successfully a predicate without giving any information about the ...
1
vote
1answer
91 views

Can I use the cipher text ouput of only one DES rotation as plaintext to check validity?

I have made a python code for one DES rotation. Can I use the resulting cipher text as a plain text for the same rotation with the same key? I think the answer is no, I can't do so. But I need to be ...
1
vote
1answer
110 views

Which data to share in CTR mode?

Suppose I've got two clients $A$ and $B$. Client $A$ encrypts data in CTR (Counter) mode to get a ciphertext. What information will client $B$ have to receive from $A$ to decrypt the ciphertext? Just ...
1
vote
1answer
123 views

Would this prevent FNV1a 32 bit hash collision?

I am considering the FNV1a 32 bit hash as part of a simple software security and authentication system. I am aware that FNV1a is NOT ideal but it may suit my needs. I am aware that FNV1a has rather ...
1
vote
1answer
184 views

What is “serial concatenation”? [closed]

I have a third-party point-of-sale API (Speedflow Pay-N-Get) that I am trying to communicate with over HTTP, but I have a problem with it. In a nutshell, a request is encrypted using RSA, and the ...
1
vote
1answer
107 views

Does it make sense to stretch non-keys?

I was thinking about stretching salt. Key-stretching is good against brute force guessing and assumes your system isn't compromised. Salting a one-way makes it so you have to compute * n for each ...

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