# All Questions

231 views

### What is a generator?

I am trying to read up on the math behind DH and ran into the word generator used a lot. I am not sure what it means. Can someone explain? I see this question where the OP talks about g as the ...
44 views

### space complexity of quantum collision search

Is there a known way to reduce the space complexity of quantum collision search beyond what is offered by the built-in time-space tradeoff, while keeping the time complexity significantly below what ...
126 views

### Associative standard cryptographic hash function

I am looking for a standard hash function which satisfies the following property: A hash function $H(a,b) = F(h(a),h(b))$ with $h$ (within $F$) any standard cryptographic hash function and $F$ an ...
408 views

### Shamir's secret sharing scheme - type of channels

For information theoretic security in Shamir's [m,m] secret sharing scheme, do i need both authentic and confidential channels? Another related query is ;is it true that if the channels are only ...
95 views

### Low level explanation of how a message is sent via RSA

I understand that RSA encryption uses this formula: C = M^e (mod N) public key is e and N N is pq - p and q are private key. mod N makes above function one-way ...
344 views

### Is TEA considered secure?

Wikipedia claims that the best attack on the surprisingly simple TEA block cipher, that isn't a related-key attack, has a time complexity of $2^{121.5}$. So despite how unsophisticated the cipher ...
238 views

154 views

### RSA, finding p,q [duplicate]

If the public key $(e,n)$ and the private key $(d,n)$ are known, what is the easiest way to find the primes $p$ and $q$? When $n$ and $\phi(n)$ are given this is easy to solve. But I can't manage it ...
157 views

### Hash collision resistance of $\mathcal H^\prime(m) = \mathcal H(\mathcal H(m)|m)$

So far as I can find, every method better at producing hash collisions in cryptographic hashes than generic collision search involves finding some metric for the distance between two messages' hashes ...
74 views

### The advantages of Merkle Signature and One time Signature

In Merkle Signature, it also requires one-time signature to be used once for a message. The signature in Merkle scheme is even longer compared to Lamport one time signature. The verifier also has more ...
138 views

### Is it necessary to generate a private key for each encryption process?

I read about Asymmetric key cryptography like EG-ECC , RSA, ECDH. I understand the concept of mathematics to these algorithms. But I have wondered about the public key for sender and private key for ...
79 views

### Key exchange if forward secrecy is not an issue

Let's say that we have a cryptosystem where Forward Secrecy and Man-In-The-Middle attacks are not an issue, purely hypothetically. Would it be correct for a key exchange with any given public-key ...
100 views

### Encrypt HDD with keyfile and password and allow backing up the keyfile with secret sharing

I want to: Encrypt my whole HDD with a keyfile and a password (meaning that both are required to decrypt it), Be able to back up pieces of the keyfile in several distant locations using Secret ...
71 views

### How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
104 views

### DH key exchange with only one end authenticated

We know there is a man in the middle vulnerability with unauthenticated DH key establishment. And the way to negate that is to use authenticate the keys used. But what if I only verify the signature ...
188 views

### Why is ElGamalEngine in bouncy castle restricting input data to be less than the length of the group parameter p?

I am currently using the ElGamalEngine of bouncy castle to implement exponential ElGamal for the purpose of making ElGamal additively homomorphic. To do this i raise the message to be encrypted to the ...
99 views

### FHE over the integers - Is that paper's scheme known to be insecure against quantum adversaries?

I was reading the paper Fully Homomorphic Encryption over the Integers, and started wondering if there is a known quantum attack on their main scheme, because There is an efficient quantum attack ...
147 views

### How to retrieve the plaintext of a substitution ciphertext?

So the other day, I was piqued by a ciphertext that was trivially encoded through substitution. Solvable only because we can use our eyes to determine word boundary word detection, etc. Trawling the ...
43 views

### Computational Diffie-Hellman problem over the group of quadratic residues

Suppose that $N=pq$ where $p$ and $q$ are safe primes. $\mathbb{QR}_N$ is the group of quadratic residues which is a cyclic group with order $\frac{\phi(N)}{4}$. Let $g$ be the generator of ...
401 views

### Cryptographically secure keyed rolling hash function

I could not find any mention on the Internet of a proven/known cryptographically secure keyed rolling hash function (ie rolling MAC). Has the question been studied, is it possible to build one ? By ...
143 views

### Point addition and doubling in Ed25519 (ref10)?

I just migrated CodesInChaos' C# port of Ed25519(ref10) to Java, and everything works fine. (I.e. I get the same results for key generation, signature and verification.) Now, I would like to do a ...
66 views

### Symmetry between a public and a private key

I know that the private and public key in assymetric cryptography are different and the public is used for encryption while the private for decryption. My question is if they are symmetrical to each ...
152 views

### Number of keys when using symmetric and asymmetric encryption?

Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ...
63 views

### On modeling a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$

How can one model a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$? (Assume $\mathbb{G}_1$ and $\mathbb{G}_2$ to be additive and multiplicative groups of prime order ...
102 views

### Computing youngest person among 3 while keeping ages private

I already found a protocol to find out who is richer (older) between two parties, but Is there any protocol to find the youngest person among 3 parties, without revealing actual ages?
59 views

### Can N, q be shared for multiple users when using SRP-6A

Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system? I know that q MUST be a Sophie Germain prime and N a safe prime, but can they ...
104 views

### Size of p in ElGamal cryptosystem?

In the ElGamal cryptosystem, I was wondering whether the $m$ (message) should be less than $p$ (large prime). Because on decryption, we are getting $m \bmod p$. For $m \bmod p$ to be equal to $m$, ...