# All Questions

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### Sign & Encrypt vs. Encrypt & Sign - What does gpg do? [migrated]

I've already read the discussion Should we sign-then-encrypt, or encrypt-then-sign? and the paper Defective Sign & Encrypt in S/MIME, PKCS#7, MOSS, PEM, PGP, and XML. My question has to do with ...
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### Storing sensitive information for a short time, how should I encrypt it or do I even need too? [migrated]

So I will be accepting some sensitive information via a html form, I will be using PHP to store the information. All this has been set up, tested etc. The form works in 4 "steps", each step is its own ...
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### Secure “table-look-up” operation

I am thinking about this problem: The server has a two-column table $T=\{c_1,c_2\}$. A user has a query $q$ that is sent to server. The server find an item $x$ in the first column satisfying $x=q$ ...
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I have to show that the following construction of $q$ allows to factorize $N$ $p \in \mathbb{P}$ $q = \left[p * [(p - 1)^{-1} \mod e]\right] \mod e$ $k=1$ while $q \not \in \mathbb{P}$: $q = q ... 2answers 108 views ### Do we have to consider the cryptographic properties of the decryption, if we're only using the encryption? Treyfer for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption. Do we have to consider the (bad) cryptographic ... 0answers 32 views ### ElGamal Signatures I know various applications of RSA signatures. I wonder, is there any real-world applications of ElGamal signatures and encryption? 2answers 52 views ### Elliptical curve cryptography Determine if a public key point y is negative or positive, odd or even? Take a Elliptical curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Example Private key 1 -> (x, ... 2answers 82 views ### Must root certificates be self signed? Root certificates are normally self-signed. What is the reason behind that convention? I mean, one must trust the root certificate in a non cryptographic way anyhow. 0answers 31 views ### Anonymous off-line digital cash scheme [closed] I'm looking for a conceptual method to implement anonymous offline digital cash scheme. We can use blind digital signing by the bank to retain the anonymity between bank and customer. Using revocable ... 0answers 25 views ### Range-Bounded Commitment fails when implemented? [migrated] For part of my thesis I must implement (in Java) a Chan, Frankel, Tsiounis range-bounded commitment protocol as quoted in Boudot's paper Efficient Proofs that a Committed Number Lies in an Interval ... 1answer 97 views ### How does the Efficient Fully Homomorphic Encryption from (Standard) LWE work? I am interesting to learn the low level implementation of Efficient Fully Homomorphic Encryption from (Standard) LWE and I am wondering if anyone can answer the following questions: Does the BV ... 0answers 51 views ### Is there specific name for simple XOR with ADD/SUB encoding? Several years ago a group of malware authors began using code like this: for (j = 0; j < length; j++) ptr[j] = (ptr[j] ^ VALUEA) - VALUEB; for encoding, and ... 2answers 47 views ### Are Anonymity and Authentication possible together? Anonymity and authentication look to be seemingly contradictory but are both possible together ? I tried reading couple of papers but could not get the big picture. So what are the major approaches ... 1answer 69 views ### Shared modulus attack on RSA Consider a scenario in which a group of people use a common modulus$n$in the textbook RSA crypto system, where$n=pq$,$p$and$q$are large distinct prime numbers. Is there any chance for an ... 2answers 81 views ### Safe curves in Weierstrass form? I would like to implement a protocol using elliptic curves. I'm thinking of using MIRACL so using curves in their Weierstrass form is preferable as it they are supported by this framework. I don't ... 0answers 24 views ### Batch ElGamal Scheme I know about ElGamal scheme and its key generation, encryption, and decryption methods. I'm not sure about what is meant by batch ElGamal. Can someone please clarify it. How it differs from ElGamal ... 1answer 39 views ### converting finite field elements to octet strings I need to convert elements of the finite field$GF(p^k)$, where$p$is an odd prime, to octet strings. To be more precise, I want to include elliptic curve points over$GF(p^2)$in a Subject Public ... 1answer 87 views ### Define “cryptographer” I often encounter the phrase "I am not a cryptographer". Is there a generally accepted definition for who is a cryptographer? What qualifications would be expected? For instance, should that person ... 2answers 71 views ### Is reverse NTRU still secure? I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only ... 2answers 66 views ### If I compute the SHA-1 of all possible 40 digits hexadecimal strings, will I get all possible sha1 hashes? [duplicate] Wikipedia says sha1 produces a 160-bit (20-byte) hash value. So if I compute the SHA-1 of all possible SHA-1 values, which as far as I understand is at current time impossible both to calculate and ... 0answers 32 views ### research on Encryption for master [closed] I'm tring to choose an way for an Encryption mothod for my research? So,I want to choose one-layer encryption or multilayer encryption,and I want it to be easy to applicable. when I search about it, ... 1answer 48 views ### Is this scheme to derive multiple keys secure? I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also: Neither private ... 2answers 37 views ### Why is (gy, gx) signed in STS (station-to-station)? My question relates to the station-to-station protocol as described in https://en.wikipedia.org/wiki/Station-to-Station_protocol [1] and http://cacr.uwaterloo.ca/hac/ [2] p 519. ... 1answer 37 views ### Digital signatures using a partially public key I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices. To ... 0answers 27 views ### Blowfish and DES small block size and maximum message size Would the following affect the maximum message size limititaion of Blowfish and DES due their small 64 bit block size? Let's take Blowfish for example. You take a 256 bit Blowfish key, quickly ... 2answers 39 views ### Is there a standard format for compact 56-bit DES keys? DES keys are traditionally stored as 8-byte blobs, with only the high 7 bits of each byte being meaningful to the algorithm; the low bit of each byte is set so that the population count of the byte is ... 1answer 43 views ### Help defining a shift cipher mathematically For an assignment question, I am trying to prove formally that double encryption with two keys by the shift-cipher encryption function results in a shift cipher as well. If the Shift-cipher encryption ... 0answers 3 views ### Veracrypt Hash Algorithms Missing [migrated] I was going to encrypt my system drive with Veracrypt 1.14 and when choosing the Hash Alghorithm, I noticed there were only these two available despite cipher chosen: SHA-256 RIPMED-160 So ... 0answers 2 views ### Avoiding MITM forwarding packets [migrated] Suppose a sender and a receiver communicate over wireless. Is there a way to prevent packets sent and received are not being repeated/forwarded by a MITM? That is, when the agents are out of range and ... 1answer 24 views ### What is the significance of the Period of a Steam Cipher [duplicate] If we only know the period of a Stream Cipher, let's say 150-200 bit in length, how can we use this information to attack a stream cipher? Taking a look at this link, What is the period of a cipher? ... 0answers 22 views ### Are there any existing ASN.1 structures for transferring symmetric keys? Is there any reasonable ASN.1 standard to encode symmetric keys? I found PSKC, but it seems extremely heavy, and I can't quite find any library (e.g. bouncycastle) that would simplify using it. If ... 0answers 29 views ### Secure and unlinkable identifiers Let's say we have Alice and Bob sharing a symmetric key$k$. Alice wants to leave a number of messages for Bob on an untrusted server (honest-but-curious model) that is also used by many other people ... 2answers 249 views ### Secure method for encrypting 32 byte private keys I am using 32 byte EC private keys on the client side of a web application. These keys should be securely stored on a server database. The keys should be encrypted (AES) before being sent to the ... 1answer 31 views ### Number generation for Fujisaki-Okamoto commitment scheme parameters I need to implement the Fujisaki-Okamoto commitment scheme for a project such that I can demonstrate performance of various zero-knowledge proofs in relation to one another, for example Boudot's ... 0answers 60 views ### Bobcat hash, trying to find a 48-bit hash collision for x I am trying to find a collision with the Bobcat hash of the 48-bit hash. I am a beginner coder so please point out any flaws in my modification of the bobcat program. It does find a truncated 12-bit ... 1answer 30 views ### Avoiding replay attack on certified announcements Suppose two agents A and B share a common secret and A makes a regular unique 16-byte ... 0answers 26 views ### why game based security definiton is used for ID CCA? [duplicate] I have read many cryptographic encryption. In almost all schemes, security is defined with game based and simulation based definition. Can anybody give me the exact concept behind this game based ... 1answer 115 views ### When did Kerckhoffs's principle become fully accepted in design and practice of modern ciphers? Kerckhoffs's principle is named after a publication over 130 years old. Yet it is still something that is commonly misunderstood and challenged by newcomers to cryptography. This question from Open ... 1answer 42 views ### Use of q-ary lattices in developing cryptosystems Why q-ary lattices are used to most cryptosystems rather than lattices. In most of the papers q-ary lattices are used. Is there any advantage? and Given $$B=(v_1,v_2,v_3,.....v_n)$$ is the basis, ... 2answers 69 views ### Homomorphic Encryption vs. Garbled circuits I'm currently trying to understand all the differences between homomorphic encryption and garbeled circuits. As I understood the use of homomorphic encryption hides either the data or the computation ... 1answer 61 views ### Why not use OAEP for signatures? There seems to be a distinct lack of implementations of RSA signatures using OAEP to pad the digest. Other than the old, funky, padding schemes, it's PSS all the way. PSS seems to have the whiff of ... 3answers 74 views ### How is a public/private key pair generated from a Diffe-Hellman key exchange? I very well understand the DH key exchange. But what is the public key and private key at the end of the exchange. For example: Alice and Bob agree to use a modulus$p = 23$and base$g = 5$(which ... 0answers 50 views ### Elliptic curve point addition with$Z_1 = Z_2 = 1$Elliptic curve point addition and point doubling operations using Projective and Jacobian coordinates require fewer field multiplication operations when considering$Z$coordinates of input points ... 1answer 39 views ### Sextic twist maps to q Eigenspace of Frobenius Let$E(p)$be a Barretto-Naehrig elliptic curve with r-torsion and embedding degree 12 and$E'$a sextic twist with homomorphism$\psi$. How to show, that$E'$has a unique r-torsion group$\psi$... 1answer 42 views ### Is succinct verification of an arbitrary data transformation theoretically possible? Is it feasible? How? Given input string S, and transformation (i.e. computer program) T, is it possible to provide a succinct proof that another binary string S' is identical to the output T(S)? By "succinct", I ... 1answer 137 views ### How can AES + cycle walking be used as an FPE? I'm a bit confused after reading several articles that seem to provide conflicting information. Basically I was wondering if AES by itself can be used as an FPE? And if so is this something ... 1answer 49 views ### Practical benefit of using a KDF? I see that KDFs should be used in systems that rely on PSKs, but what practical benefit does it provide? For instance, suppose the system relies on a shared secret for AES encryption and decryption. ... 1answer 91 views ### Encrypt a message with hash function, shared symmetric key, but no cipher I am very new to Crypto and need some clarification or input. The question is: Suppose that Alice wants to encrypt a message for Bob, where the message consists of three plaintext blocks,$P_0$, ... 2answers 79 views ### How does DSA provide non-repudiation in proving a document was properly displayed (not altered or displayed incorrectly)? I am building an iOS app that allows the user to sign a document served to them by a web server. So that page of the app simply has a document in the top pane, and at the bottom pane, a place to sign ... 1answer 25 views ### Lower bound of key space size with relaxed perfect secrecy My apologies, I'm quite new to cryptography. If we relax the definition of perfect secrecy such that for cyphertext$c$, messages$m_0$and$m_1$, and constant$E$:$P[c|m_0] \le E * P[c|m_1]\$ ...

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