# All Questions

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### Using password-based encryption as a hashing scheme

Classic scheme: Given password and hashing algorithm Generate salt Calculate ...
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I have a scheme and I don't know that this scheme is semantic security or not. Secret keys $\{s_1,s_2, x_1,x_2\}$ and public parameter $p$ (large prime number). Encryption E(m): $C_1 = s_1m + x_1k ... 1answer 198 views ### What is the complexity for attacking 3DES in linear or differential cryptanalysis? I know that 3DES is NOT vulnerable to DC , LC . But is it because the attacks requires too many input\output pairs ? Or because it's impossible ? (i.e requires more than 2^64 pair ) 0answers 20 views ### RSA: If I sign the same digest with same key twice, will the signatures be identical? [duplicate] If I don't have public keys to verify the signature, can I use this to discover that two signing services are using the same key? Can you send a reference? 2answers 127 views ### Inner product with homomorphic encryption I want to do a very simple thing: Given two vectors, I want to encrypt them and do some calculation, then decrypt the result and get the inner product between both vectors. I want to do this as fast ... 2answers 270 views ### Is standardizing a modified AES a good idea? "Recently" the Ukraine standardized a new block cipher Kalyna, which according to the abstract of"A New Encryption Standard of Ukraine: The Kalyna Block Cipher" by Oliynykov et al. (warning: the paper ... 1answer 151 views ### What is a man-in-the-middle attack (for instance in Diffie-Hellman)? I'm new to cryptography and I just started learning about the Diffie-Hellman key agreement. I read that this system is vulnerable to a man-in-the-middle attack when used alone. What kind of attack is ... 2answers 759 views ### I hashed my bag and in it I put… “Is there a hash for unordered items?” (By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I packed my bag and in it I put a shovel (hashed to ... 1answer 112 views ### Pseudo Random Function The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function. i.e. The key-ed function family$\{F_k\}$is PRF ... 1answer 502 views ### Suggestion : CRC vs SHA1 I need some suggestions about the use of the CRC in my application. I need to be sure about the BIOS run by the CPU. I have a FPGA between the BIOS flash and the CPU that sniff every read performed by ... 1answer 48 views ### Why should the input value on a DPA attack be non-constant? I actually was wondering if anyone could help me out with the following problem: Let's assume we are attacking the first SubBytes() operation on AES with the help ... 1answer 217 views ### How often does RSA-OAEP have a leading zero? We are working with a third party vendor who is very tight lipped about their security protocols, and one of our customers who used this vendor's products is claiming that approximately one in every ... 3answers 103 views ### Is this client-side password hash scheme secure? I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of ... 2answers 130 views ### Does authenticated encryption add any protection to a signed digital envelope? The general scenario of hybrid encryption is to use public key cryptography for the exchange of a one time session key that can be used for the encryption of the plaintext with a symmetric encryption ... 5answers 3k views ### “123456” and “password” as crack standards I know that when we encrypt, we use standard encryption technologies and to store data it's often stored as a hash. By encrypting a common password, for example "password" using ... 1answer 126 views ### Where is SRP-Z from? The Stanford license for SRP says: Broader use of the SRP authentication technology, such as variants incorporating the use of an explicit server secret (SRP-Z), may require a license; Yet ... 0answers 50 views ### Fast mental encryption algorithm? [duplicate] Are there any algorithms that exist to encode messages written with pen and paper such that the messages can be encrypted/decrypted mentally? For example, Bob thinks of the text "This is my ... 1answer 130 views ### Proving membership of a group without revealing identity I have an interesting problem for which I've failed, so far, to find an elegant solution. Imagine that a user needs to repeatedly prove to public observers that they are a member of a trusted set ... 1answer 135 views ### Simulation aborted because the adversary doesn't use the random oracle I'm trying to construct a proof for an encryption scheme in the Random Oracle model. This encryption scheme is like a PKE scheme but with an additional function that kind of "alters" ciphertexts ... 1answer 202 views ### EdDSA Signature Algorithm - hash of secret key Why does EdDSA use the (SHA512) hash of the secret key as the exponent for the public key rather than using the secret key value directly? This seems inefficient and I can't see how it adds any extra ... 3answers 292 views ### Source for PKCS#11 Header Files Is there a known authoritative source for the ANSI C header files for PKCS#11 Cryptoki? Specifically, I am having trouble locating pkcs11.h, pkcs11t.h, and pkcs11f.h for v2.30 and v2.40. Are there ... 1answer 86 views ### Ideas for non duplicate cryptographically secure numbers My Boss asked me this today. I am not a math major. He needs to generate 50 billion non-sequential non-duplicate (no collisions) cryptographically secure random numbers. I work in GO. Any ideas? 1answer 68 views ### RSA function over$Z_t^{*}$where$t$is prime RSA function is defined over$Z_N^{*}$where$N=pq$with$p,q$primes. A public key is a pair$(N,e)$and a private key is$(N,d)$where$d=e^{-1} \mod \phi(N)$. Assume that RSA function is defined ... 1answer 102 views ### ElGamal scheme attack when one message is known and ciphertexts are intercepted Let$G$be a finite cyclic group of order$p$and let$pk = (g, h=g^a)$and$sk=(g,a)$be Bob's ElGamal public/secret key pair in$G$. To encrypt a message$m$, a random number$r$is selected and a ... 0answers 105 views ### What happens if no final subtraction is done in Montgomery multiplication? I'm doing Montgomery arithmetic modulo$N = 2^{255}-19$for the Curve25519, picking$R = 2^{256}$for Montgomery. After multiplying two numbers$0 \leq A,B < N$in the Montgomery representation ... 1answer 120 views ### Double the key in block cipher - which approach is better? Assume than you have a block cipher$E(k,m)$for which the only attack exists has complexity of$2^{64}$. You consider to double the key size by either:$E'_1(k_1,k_2) := k_1 \oplus E(k_2,m)$... 1answer 522 views ### TLS encryption with a self-signed PKI and Python’s asyncio module I want to enable TLS encryption with a custom / self-signed PKI for a self-contained distributed system built with Python 3’s asyncio. I’ve read Python’s ssl docs as well as several tutorials: ... 1answer 218 views ### Extracting a WinRAR password If I have an original file and a WinRAR password protected .rar file containing that file, than can I extract the password? 1answer 51 views ### Forgery attack on OCB When using same nonce in OCB mode of authenticated encryption, how forgery attack can be done? 0answers 36 views ### Establish authentication I have designed a basic authentication scheme where two nodes will mutually authenticate that other holds a shared secret. I have very limited RAM/ROM (its on uC) and bandwidth. Here it goes: ... 2answers 172 views ### HMAC-SHA1( secret key ) with header of a transmitted file Given: an AES-128 secret key (ASecKey) encrypts a file (CBC mode). (Assume good random) Is is insecure to append (include) an HMAC-SHA1 of ASecKey to file? Purpose: The receiver can then quickly ... 1answer 264 views ### What is a “lattice” in cryptography? There are some questions here concerning lattice-based cryptography and this kind of cryptography seems to be especially useful if quantum computers are assumed to exist. When reading such questions ... 1answer 57 views ### Security of MSS I have started reading about the Merkle Signature Scheme. I am a little confused about why it is believed to be secure against quantum attacks, couldn't the hash function be attacked? What would make ... 1answer 68 views ### Block Ciphers - Standardize plain text I need to use AES-128 to encrypt a plain text about 720 bits. Is it correct to say that – in this case – the plain text will be divided in 5 blocks of 128, the result will be equal 640 bits, and the ... 1answer 148 views ### Can I use HKDF to improve security of HMAC used with weak hash function? I am writing a framework which encrypts/decrypts files (or streams, in general) with symmetric key using block cipher (for example, AES). To authenticate encrypted file, I use HMAC, which is ... 0answers 71 views ### RSA Signature Forgery We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one ... 1answer 86 views ### Logjam-style attack on Factoring? We're all aware of the Logjam attack, which is known as "FREAK on discrete logarithms". The attack works by doing a large pre-computation step, which needs only to be done once per field and then ... 2answers 63 views ### Getting the encryption/has algorithm used for modem configuration file [closed] Hello guys I have backed up my modem configuration file and found the username and password is in clear text; the files shows the username and the password is : ... 2answers 136 views ### Do all attacks against PKCS1 v1.5 encryption require an oracle As far as I know, all attacks against RSA PKCS1 v1.5 require an oracle; is that true? Or are there any other attacks against it which are able to break it without an oracle? Background: I need to ... 0answers 29 views ### HMAC for encrypted authentication token: recommended iteration number [duplicate] In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance ... 1answer 216 views ### How can a lattice attack be applied to ECDSA signatures? The aim is to check if it is possible to break the ECDSA cryptosystem under the following criteria. Suppose that each ECDSA signature is generated by using the GLV method for point multiplication ... 1answer 243 views ### Derive cipher IV and cipher Key using PBKDF2 with random salt? It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ... 3answers 258 views ### Establishing encryption key using shared secret I need to establish some security on a network of 8 bit microcontrollers. very limited RAM, CPU and packet sizes. I have zeroed in on a shared secret based scheme. Setting up shared secret is out of ... 0answers 35 views ### El-Gamal and Lines on Planes I've been thinking about a geometric picture for El-Gamal. The idea is to understand the set$\{(my^{x},g^x) \mid x \in Z_p\}$(the set of encryption of$m$for fixed$g$and$y$) by taking the ... 1answer 76 views ### Is algorithm with more than$2^{word size}\$ words secure? [closed]

Let's say we have a feistel cipher or feistel pseudo-random permutation with 8-bit function (S-box) similar to Treyfer, but with much bigger block size like 16MB. Here is example of such pseudo-random ...
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### Why is the public/private key length used in libsodium so much shorter than needed for RSA [duplicate]

Reading the libsodium source I see that is uses a key length of 32 bytes (256 bit) for private/public key encryption. For RSA private/public key encryption a key length of 2048 (or 4095) bit is ...
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### Dan Boneh's Cryptography lecture - problem with 802.11b

I am going through Dan Boneh's Cyprography lectures on Coursera. In Lecture 6 https://class.coursera.org/crypto-010/lecture/6 At 7:30 minutes, he discusses the problems with 802.11b design. I ...
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### AES and Homomorphic Encryption

Is it possible to do the following? Input would be to generate a new AES key, encrypt the private data with that key, encrypt the AES key with the FHE key, and send the FHE-encrypted AES key along ...