# All Questions

2answers
108 views

### Determining average number of hash calls to get a hash that begins with X

I have been attempting to find an answer to a self-study question: If I have a hash algorithm that outputs 256 binary bits, on average, how many times would I have to call the hash function so ...
2answers
233 views

### Reusing message in One Time Pad

One of the main rules of the OTP is, that a key should never ever be reused. But if we use some commutative operation (XOR for example) for generating the cipher text, then I don't see any difference ...
1answer
146 views

### Roots of polynomial in Shamir secret sharing

I need to know whether one can obtain any roots of the polynomial in Shamir secret sharing if he possesses less than threshold shares. For instance in (t,n) if he has t-1 shares can he obtain any ...
1answer
78 views

### stream cipher computation cost [closed]

With AES-CTR the computation time to encrypt a message of lengh $n$ blocks is $n$ computations of the block cipher. What is the running time to encrypt a message of $n$ bits using a stream cipher, ...
1answer
47 views

### Group Dependent Language

The text below has been taken from the below paper Groth-Sahai Paper. The relevant part is highlighted in red. What does this group-dependent language mean in this context? From the definition of a ...
2answers
204 views

### Strategy to crack a presumed substitution cipher

The ciphertext given is: ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae I've done ...
0answers
81 views

### Montgomery Multiplication in FPGA explanation

I'm trying to implement an RSA module in a FPGA. I choose to use Montgomery multiplication. I've found a document where the Montgomery Multiplication is pretty clear. I don't understand only a step. ...
0answers
64 views

### Don't Understand these Parameters

I don't understand section 3 of the paper Fully Homomorphic Encryption over the Integers. How can one calculate these paramters and make these equations in pictures into code?
0answers
131 views

### What is the (uncompressed) x,y-representation of a curve point on the P-256 NIST elliptic curve?

I am trying to understand the FIDO U2F Raw Message Format, especially the format in which a user public key should be provided. The documentation says the following: A user public key [65 bytes]. ...
2answers
358 views

### Key management for military GPS receivers

I wonder what encryption scheme is used in high-precision encrypted GPS streams (the so-called “P(Y) code”). If there's a master key needed, then it has to be in every device. Yet the master key ...
0answers
34 views

### impersonating attack against a protocol

recently I'm reading Efficient eCK-secure Authenticated Key Exchange Protocols in the Standard Model, and I sense that the scheme in the following(the reader can refer to the paper for details) is ...
2answers
129 views

### What is “msg = group.random(GT)” in Charm encryption schemes?

In many encryption schemes in Charm the random group message is used instead of a text-message: msg = group.random(GT) For example, in CP-ABE scheme, random ...
1answer
177 views

### what is the difference between IBE and ABE schemes

Can somebody explain in simple words. real life example light help and limitations of these schemes etc.
1answer
843 views

### SHA1 no longer considered secure for SSL Certificates — what about Cipher Suites?

Many browsers and Internet companies have recently claimed that SSL Certificates with a signature algorithm of SHA1 will imminently no longer be considered secure. Most notably, Google and Google ...
1answer
55 views

### Deprecation of RSA-SHA-1 in DKIM keys?

I recently noticed that OpenDKIM on my mail server is objecting to DKIM signatures from a client, saying their key is insecure. It may be that that's due to lack of secure DNS (confirmation anyone?) ...
2answers
210 views

### How do disk encryption programs solve the “IV problem”?

I was reading a paper on the "elephant diffuser" used in BitLocker and it got me wondering how other systems (e.g. TrueCrypt before it shutdown) solved the problem the elephant diffuser was meant to ...
1answer
85 views

### Basic question about design of program with data encryption

I need to store encrypted files on a hard disk. The actual code side is not important for me now (I plan to use C# and AES-GCM encryption from Bouncy Castle library, please tell me if you think that's ...
0answers
20 views

### Ability to locate free sectors on an encrypted volume

I am trying to understand, generally how could this be a security issue ? Assuming the volume's backing media has this weakness (lets say an NTFS sparse file based TrueCrypt container) what could the ...
0answers
78 views

### Problem understanding the construction of block cipher distinguishers

I know a block cipher distinguisher is an algorithm which can predict with high probability whether a system is a random permutation or a block cipher by asking a few queries to the system. My ...
1answer
98 views

In the paper Fully Homomorphic Encryption over the Integers in the introduction: How do I calculate $r$ and $q$ of this equation in the picture? $r \approx 2^{\sqrt{\eta}}$ and $q \approx ... 1answer 164 views ### Fully Homomorphic Encryption over the Integers - perform an operation on an encrypted data In Fully Homomorphic Encryption scheme represented here Fully Homomorphic Encryption over the Integers In the Evaluate process (see section “3.1 The Construction” of the paper): $$Evaluate(pk, C, c1, ... 1answer 137 views ### Is this modified Schnorr signature scheme secure? Signing Let y = g^x, which is your public/private keypair. Let r = g^v, for random v Let c = H(M) Let z = (v + cx) mod q The signature is the pair (r,z) Verifying g^z = ry^c mod p We further ... 0answers 45 views ### Need: Fast bulk signature verification followed by fast non-interactive multisignature aggregation Q: Is there an efficient way to batch-verify signatures (e.g. some may be incorrect) and then non-interactively aggregate the correct ones into a multisignature (they are of the same message) such ... 1answer 350 views ### What weaknesses in Hash_DRBG did NIST find and fix? Matthew Green states in the Practical Kleptography presentation (video, at about 12:15) that Hash_DRBG (from SP800-90A) as originally proposed by NSA had potentially exploitable flaws or bugs and that ... 0answers 80 views ### Protocol for establishing physical ownership of a connected/IoT device? If I'm connected to a device e.g. using BLE are there rules/protocols for establishing that I'm also in physical possession of that device (at least for the first time I connect to it)? Crypto is in ... 1answer 207 views ### Generation of N bit prime numbers -> what is the actual range? Short version: When generating a prime number of N bits, should I draw random numbers from the range [0 , 2^n], or [2^{(n-1)} , 2^n]? Context: I'm trying to implement a toy-version of RSA as a ... 1answer 181 views ### Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity? Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity? My reasoning is that the attacker doesn't know all the plaintext, so by having a hash, the ... 0answers 58 views ### Forward pseudorandom permutation [closed] Please consider the following scenario: The user A and B use their keys, K1 and K2 respectively. Each client have a vector of elements. Each client separately permutes his vector using his key and ... 2answers 237 views ### Random vs. Fixed Paddings Is there any consensus (i.e. are there any research results) on the benefits and drawbacks of various padding schemes? Generally there seem to be two kinds of them: random paddings, like ISO10126 ... 1answer 209 views ### Bouncy Castle elliptic curve from explicit parameters (E-521) I'd like to use a curve that's not included in the Bouncy Castle EC named curves spec, specifically E-521. According to the BC javadocs, you need a few values in order to do this: q, a, and b for the ... 0answers 33 views ### Perform general computation using a crypto algorithm as a building block I have a somewhat special question. In our software we use a existing dongle which got cracked by our customers. The protection offered by the dongle isn't very sophisticated. For the moment I can't ... 1answer 67 views ### Is elliptic curve point multiplication semantically secure? Is elliptic curve point multiplication semantically secure? I'd like to know if there are some sets of elliptic curve parameters (e.g. NIST curves) that are proved to be semantically secure or that ... 1answer 1k views ### Why do the elliptic curves recommended by NIST use 521 bits rather than 512? Wikipedia says in reference to the elliptic curves officially recommended by NIST in FIPS 186-3: Five prime fields for certain primes p of sizes 192, 224, 256, 384, and 521 bits. For each of the ... 1answer 126 views ### Security properties and Cryptography objectives applied in algorithms We all know there are five properties of Security. They are: Confidentiality Availability Authorization Integrity and Provenance As Security and Cryptography are co-related these properties ... 0answers 57 views ### exchanging private key between service and iPhone app - digital signing I need to do digital signing of my request data which will be sent to the server. My server sends distinct private keys to her clients after authentication and expects all responses to be digitally ... 1answer 230 views ### AES-128 with weak key Doing malware research (simple crypto locker) I found out that it uses AES-128 with weak key - every one of the sixteen bytes is represented by (a-z,A-Z,0-9). Thus simple brute-force attack should ... 0answers 34 views ### Plain cascade and Xor cascade I have seen in few places (mostly papers) talking about plain cascade and XOR cascade. I know what is cascade cipher is but I am not clear about what these are. Can anyone help to understand using ... 0answers 35 views ### Plaintext-aware encryption for symmetric schemes? The notion of plaintext-awareness is well-known for asymmetric encryption, but the notion seems to make sense for symmetric encryption as well. Is this a known concept? 1answer 162 views ### Modes of operation for Public Key Encryption schemes Symmetric key encryption schemes have well defined modes of operations for achieving deterministic (ECB) or Randomized (CBC, OFB, CTR ) etc. and other applications of the same. But are they defined ... 2answers 186 views ### Ways to make a “doomsday” cryptocurrency which becomes untradable As a social experiment (not a money-making scheme), I'm interested in developing a crazy cryptocurrency which, by its very design, will become worthless and untradable after a certain point. Ideally, ... 1answer 308 views ### Why is 224 bit ecdsa faster than 192 bit ecdsa? I ran several benchmarks using openssl on 2 different computers and I got a surprising result. for the Nist 192 bit curve the benchmark result is ... 1answer 59 views ### How can i calculate prime of Elliptic Curve? In many articles i have found directly the calculation of prime elliptic curve. How can i calculate this prime p ? For example if I consider NIST P-256, p = 2^{256}-2^{224}+2^{192}+2^{96}-1. Why ... 0answers 77 views ### Does Ciphertext policy ABE support search operation on encrypted data Basically CP-ABE (or attribute based encryption) allows end-users to encrypt the data with desired access control structure. I was investigating the how to do keyword-search on encrypted data given ... 3answers 2k views ### Diffie-Hellman and man-in-the-middle attacks See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob ... 1answer 85 views ### Is there any definition for “generic attack” in context of cryptography or more specific “hash functions”? I'm searching a definition of "generic attack" in context of cryptography or more specific in context of "hash functions". I searched some books and the web but I did not found any definition for it ... 0answers 90 views ### Is it possible (how difficult) to find MORE than one valid RSA signature? Is it possible (how difficult) to find more than one valid RSA signatures for a given message m (after padded) and a public key ... 1answer 81 views ### Authenticating Very Short (Sub-Block) Data If I'm encrypting very short/small data - like an int or a long (32 or 64 bits), does it make any sense to authenticate the ciphertext, when using an "online" mode of operation (like EAX)? ... 0answers 177 views ### VKO GOST R 34.10-2001 (described in RFC4357), Key Agreement Algorithm. Looking for its implementation/detailed description/examples VKO GOST R 34.10-2001 was described in RFC4357 Page 7 But the description is very poor. Here it is: This algorithm creates a key encryption key (KEK) using 64 bit UKM, the sender's private key, ... 3answers 479 views ### Security proofs for CBC mode I'm looking for different approaches to proofs for the security of CBC mode encryption. What are the best sources of information about this subject? 1answer 164 views ### Point addition equation in projective co ordinates How can I get point addition equation for elliptic curves in projective co ordinate system? Can I get it by changing$$ x = X/Z $$and$$ y =Y/Z$\$ in the equation for affine co ordinates' group law? ...

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