# All Questions

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### What are Cryptographic Multi-linear Maps?

I've encountered this term many times in the fields of Fully-Homomorphic Encryption and Obfuscation. I want to learn those subject and Cryptographic Linear Maps seems to be an obstacle in the way. ...
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### ECDSA vs RSA: Performance on Android platform and surprising results

For our privacy-preserving protocol, an encrypted channel is established. In order to protect our system from man-in-the-middle attacks, signature-based approach is used. After we've implemented it ...
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### What constitutes a “description of B” for probabilistic encryption as defined in Cryptology 6.3.4?

On page 21 of the Rivest's Cryptology chapter, he defines a trapdoor predicate as a boolean function for which it is easy to choose an x such that ...
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### Special random distribution algorithm

I am implementing ring signatures as a part of an authorization system. Since the number of users could get high enough to make computation on end-user devices infeasible, I am thinking of ...
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### Are hash functions chaotic?

I'm looking into "bitcoin like" mining processes. Say a security process uses a hash of data as proof that the data was known at some point in time. From what I understand, hash functions are ...
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### How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for ...
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### RSA Key Blinding

I was looking the answer to the following question (Timing attack on modular exponentiation), discussing the Private Key Blinding as a countermeasure for timing attacks. Therefore I'm asking if ...
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### Initialize the eight working variables SHA256

I have a little confusion in understanding explanation of SHA256 by FIPS a, b, c, d, e, f, g, h are being initialized as (this is what i don't understand) 2 . ...
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### 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 ...
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### Performance analysis of roaming authentication protocol using pbc library

Recently, I have surveyed a few research papers related to roaming authentication protocol for wireless networks. For example: “Efficient Privacy-Preserving Authentication in Wireless Mobile Networks” ...
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### Is TLS_RSA_WITH_RC4_128_SHA still a secure cipher to use? [duplicate]

I have read numerous times that the RC4 cipher itself is considered broken in TLS. Still many websites are using the TLS_RSA_WITH_RC4_128_SHA configuration even to date. Now, I know that sometimes ...
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### How can the key size be calculated [closed]

If the decrypting key is 448, then what is the key size? Suppose I am encrypting a plain text with a key by choosing some random numbers between ...
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### Does the secret key used in AES have to prime?

I’ve looked around this site and the web quite a bit, but can’t find a definitive answer on whether or not the secret key $k$ used in the AES crypto-system has to be a prime number? Or can you just ...
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Is it possible to figure out what $arg1 is if I know both$arg2 and $arg3 in addition to ... 1answer 162 views ### RSA, finding p,q [duplicate] If the public key$(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)$are given this is easy to solve. But I can't manage it ... 1answer 165 views ### Hash collision resistance of$\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 ... 0answers 95 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 ... 2answers 149 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 ... 1answer 83 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 ... 1answer 110 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 ... 0answers 72 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 ... 1answer 114 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 ... 2answers 312 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 ... 0answers 109 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 ... 2answers 196 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 ... 1answer 45 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$be the generator of ... 1answer 493 views ### Cryptographically secure keyed rolling hash function I could not find any mention on the Internet of a proven/known cryptographically secure keyed rolling hash function (ie rolling MAC). Has the question been studied, is it possible to build one ? By ... 2answers 172 views ### Point addition and doubling in Ed25519 (ref10)? I just migrated CodesInChaos' C# port of Ed25519(ref10) to Java, and everything works fine. (I.e. I get the same results for key generation, signature and verification.) Now, I would like to do a ... 1answer 73 views ### Symmetry between a public and a private key I know that the private and public key in assymetric cryptography are different and the public is used for encryption while the private for decryption. My question is if they are symmetrical to each ... 2answers 428 views ### Number of keys when using symmetric and asymmetric encryption? Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ... 1answer 69 views ### On modeling a random oracle hash function which maps$\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 $to be additive and multiplicative groups of prime order ... 1answer 110 views ### Computing youngest person among 3 while keeping ages private I already found a protocol to find out who is richer (older) between two parties, but Is there any protocol to find the youngest person among 3 parties, without revealing actual ages? 1answer 72 views ### Can N, q be shared for multiple users when using SRP-6A Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system? I know that q MUST be a Sophie Germain prime and N a safe prime, but can they ... 2answers 118 views ### Size of p in ElGamal cryptosystem? In the ElGamal cryptosystem, I was wondering whether the$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$, ... 0answers 97 views ### Decrypt a public encrypted message and Sign a signature, how the math is different? As I understand, when you want to send a confidential message to someone, you encrypt the message with his public key. And he use his private key to decrypt the message. At the same time, one can use ... 2answers 70 views ### Building cryptographic primitives using additive maps? Suppose we have a one-way function F(x) that exhibits the property F(a + b) = F(a) + F(b). Such a function could be used as a cryptographic primitive, no? 1answer 125 views ### Group Signature Scheme without Opening but with Revocation After reading many papers about group signature schemes, I saw that basically all of them employ the possibility of "signature opening": The Group Manager (GM) can identify any signature made by his ... 1answer 114 views ### Shamir's Secret Sharing of modular inverse Given a secret$K \bmod q$which is shared among entities$E_1,…,E_n$using polynomial Shamir's Secret Sharing, how can the inverse of$k$be shared without revealing$k$and$k^{-1}$? 0answers 73 views ### Cryptodefense ransom use RSA-2048. Any chance with known plaintext attack? [duplicate] The "new" kind of ransomware invade your computer and crypt all your files using the RSA-2048. Personally, I have been victim of cryptodefense: 40000 files encrypted... I'm not going to pay anything ... 1answer 152 views ### Predicting Google Authenticator OTP Codes [closed] I use Google Authenticator to generate OTP codes for logging in. As you know, the numbers change every 30 seconds or so, and (AFAIK) use an RSA key to generate those numbers. If someone were to ... 1answer 192 views ### When is it safe to not use authenticated encryption? I have read the post Why should I use Authenticated Encryption instead of just encryption? When is it safe to not use authenticated encryption? I assumed hard drive volume encryption or per file ... 1answer 226 views ### In the STS Authentication Protocol, why are the signatures encrypted? From Wikipedia: (1) Alice → Bob : g^x (2) Alice ← Bob : g^y, E_K(S_B(g^y, g^x)) (3) Alice → Bob : E_K(S_A(g^x, g^y)) I know there should be something I'm ... 1answer 210 views ### ECC partially blind signature scheme verification Continued from Is there a flaw in this ECC blind signature scheme? The problem I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made ... 0answers 59 views ### Is container format relevant to security of encrypted message inside? Still trying to design a fully binary cryptography container format for my mobile app, I am here asking if container is ever relevant. Thanks to Apple, I cannot use GPG directly because I can neither ... 1answer 320 views ### Is knowing the private key of RSA equivalent to the factorization of$N$? Given the RSA modulus$N$the fastest method to factor it is of sub-exponent order. But, now if I know the private key$d$of RSA, does that mean I can factor$N$efficiently?. It intuitively seems ... 1answer 184 views ### RSA Proof - Is Z(n) closed under multiplication In RSA proof it can be proved that$\mathbb{Z}^*_n$is closed under multiplication. Can it be also proved that$\mathbb{Z}_n$is closed under multiplication? If yes, then how? 0answers 32 views ### Bit strength of combining hash functions? [duplicate] Suppose there are hash functions H1 and H2 with bit strength of H1 and H2 is n1 and n2. A new good hash function is generated by combining H1 and H2. What will be the bit strength of these combined ... 0answers 175 views ### Is G is a secure PRG? Is the following function is secure PRG? Given F is a secure PRG and k is choosen random from key space K.$G(x) = F(k,x) \oplus F(k,x \oplus 1^s)$My solution -$x \oplus 1^s = x'\$ so G(x) ...
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Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
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### RSA and ECDSA performances

Signature algorithms with elliptic curves have small output sizes compared to RSA for the same level of security. What about the processing time to generate a signature ? I've seen figures giving ...

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