All Questions

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OpenSSL ECDH key exchang mechanism

I am using FIPS based OpenSSL module for encryption of sensitive data for my desktop socket server and client applications. I am using ECDH for key agreement.The keys public and private pair is ...
4 views

Confusion regarding computing Multiplicative Inverse Modulo P?

May be a silly doubt, please rectify my confusion regarding below problem: If g=2; p=11; a=6; and x=9; A = g^a mod p = 2^6 mod 11 = 9; X = g^x mod p = 2^9 mod 11 = 6; C = A^x mod p = 9^9 mod 11 = ...
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Starting point on Fully Homomorphic Encryption and Proxy Re-encryption

I am new in this field. Can some one tell me where should I start for FHE and PRE reading ? Any papers where I can find Basic information on FHE and PRE ? Thank You in advance.
8 views

Deriving message from signature (RSA)

Usually signatures are used for verification, and this requires that you pass both the message and the signature. I was wondering; if the message holds to a certain format (for example, valid json ...
11 views

AES decryption vs encryption

Let's consider the CTR mode. For a faster encryption/decryption, is it preferable to use the decryption operation of AES, or its encryption ?
10 views

Anonymous messaging using blind signatures

I want to implement a message relay server that knows nothing about who has sent a message but at the same time maintains a message quota per user. While searching for ways to do that on the internet ...
23 views

Why Curve25519 for encryption but Ed25519 for signatures?

NaCl and libsodium libraries use Curve25519 for authenticated encryption (actually for sharing a key which is used for encryption) and Ed25519 for signatures. What is the purpose of using different ...
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Assuring Client is Authorized to use JSON Web Token

JSON Web Tokens ( JWT ) are server-signed objects that the issuing server uses to identify a user, track session data and authorize requests. The fact that JWT are server-signed gives assurance that ...
7 views

How do I encrypt a PGP message through java's crypto extension? [migrated]

Currently I'm using bouncy castle's libraries for the actual work and have found an example at sloanseaman.com that (after a little tweaking) works with v1.52. I've also got a working example from ...
41 views

What is the impact of a server not fully verifying the data in the Client Finished packet of a TLS connection?

F5 BIG-IP devices suffer from a vulnerability in which not all bytes of the Finished packet in a TLS connection are validated. The sort-of technical description can be found here. F5 don't consider it ...
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Test for randomness

Suppose I have a data set provided by PRNG in a matrix form with 400,000 rows and 20 columns. Each row consists 20 unique integer values from 1 to 80. I need to check the goodness of the PRNG. For ...
138 views

Using a hash (like SHA-256) vs AES as the source for pseudo-random values in Feistel network?

This question is in relation to Wikipedia article on Format Preserving Encryption It says the following It is also possible to make a FPE algorithm using a Feistel network. A Feistel network ...
27 views

Attribute Based Encryption [duplicate]

Could someone explain the main differences between Key Policy Attribute Based Encryption (KP-ABE) and Ciphertext Policy Attribute Based Encryption using an example? I know that KP-ABE depends on the ...
48 views

POODLE attack on TLS 1.2

The POODLE attack uses the way block ciphers in CBC mode are decrypted in combination with the packet's padding to determine some byte's value. From what I understand, even TLS 1.1 can be vulnerable ...
20 views

Hash-values's length in identification schemes

I am trying to understand the impact of applying a hash function in an identification scheme. It makes reference to the publication "On the length of cryptographic hash-values used in identification ...
37 views

Whar are the differences between curve NIST P-521 and Edwards E-521 for signature?

I implemented and used the P-521 curve for ECDSA. Signatures are 132 bytes long. It seems that Edwards E-521 is safer but I did not investigated very deeper. What is its signature length ? How is it ...
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End-to-End (Point-to-Point?) Email encryption [migrated]

I'm looking into providing security for the email server I recently deployed, however the subject matter is a touch more complex than I anticipated and I would appreciate confirmation or correction of ...
10 views

How do I create a PKCS#7 or CMS enveloped signature in python? [on hold]

There doesn't appear to be PKCS#7 or CMS support in pyCrypto. Ideally, there will be a call that will create return an enveloped signature given a signer certificate, an RSA private key and a payload ...
41 views

What are the roles of the simulator in simulation based proofs

I'm trying to better understand simulation based proofs in the UC model - but the guidelines to construct a simulator confuse me. To my understanding, the simulator is activated in two ways: ...
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Edwards / Montgomery ECC with Weierstrass Implementation?

So let's assume I want to perform Ed448 or Ed25519 digital signatures or want to perform a DH key-exchange. Assume further that those curves (Curve448 or Curve25519) are required. But the problem is, ...
24 views

Open source code about the basic Quisquater-Piret DFA of AES-128 [on hold]

Where can i find open source code about the basic Quisquater-Piret DFA of AES-128? Are there any websites sharing the code about such physical attacks?
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Can a block cipher encrypt the message to itself (plaintext equal to ciphertext) [duplicate]

The result of the cipher should be indistinguishable from random, but can it happen that cipher produces the ciphertext that is equal to the plaintext as it also lies in the corresponding space? I ...
27 views

In HMAC-MD5 Implementation, why “i_key_pad” and “o_key_pad” if They Are Public and Constant? [duplicate]

Please Consider: English is My Second Language This Wikipedia article on HMACs shows a part of a HMAC-MD5 implementation making use of i_key_pad and ...
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Is there really any way to nullify or avoid MITM attacks?

The question pretty much sums it up. Is there any way to make an attacker who is successfully performing an MITM attack to actually not be able to read or change the messages? Assuming there is no ...
76 views

How to break this PRNG encryption scheme? [on hold]

Suppose we have the following symmetric algorithm: key = random bits G = PRNG(seed: key) input = [0,1,1,0,1,0,0,0, 0,1,1,0,1,0,0,1] // "hi" in ascii The key can ...
40 views

Chosen plain text and chosen ciphertext definitions clarification

I am trying to understand a concept of CPA and CCA attack and I cannot get one thing from the definition. If an attacker can execute a CPA attack for something like Send 100 dollars to attacker that ...
80 views

Using same modulus for RSA

I know that there exist some attack when using same modulus. Can two different pairs of RSA key have the same modulus? RSA cracking: The same message is sent to two different people problem But ...
104 views

What are the required security properties for salts?

I was recently thinking about password hashing (maybe caused by the PHC progression). I started to think a little more about it and got stuck at this question: What security properties do ...
129 views

Is it okay to include relative time for true random number generation?

Similar questions have been asked regarding use of time in true random number generation, but I'd like to consider using time as just one source of entropy, complementing others. True random number ...
35 views

what´s this is???? What it says here ? And how you could change it, or edit it? [on hold]

54c2c00ddf08dd17d5337c9f082797850b720a7be88bb6dfa646eb07740748c8ca08d6a910b4c1e5e73d84f0651c75718e80ec760ba356b2ea41b95e480127130afebd1bb27e019abb868a21a2ff9231807fa88c23fe3e0e3ff76d88f9949b0493592046 ...
25 views

Given occasional LFSR samples can the next sample be computed?

Suppose I have access to an LFSR generator output used in a radio communications system, with the LFSR being used to authenticate devices. The system cycles an internal unknown length LFSR (greater ...
45 views

How strong can multiple encryption be?

Suppose I encrypted a homophonic substitution cipher at the level of syllables, trigrams, digraphs, and individual letter with a Vigenere cipher using the keyword cryptography. I would then encrypt ...
21 views

TLS Handshake : Server authentication or only Server ‘s Certificate authentication?

I have some difficulty understanding the way in which the Server is really authenticated by Client in TLS handshake (in case of using RSA key exchange). When Client receives Server ‘s Certificate and ...
39 views

Authenticating with a document

Hope you're having a nice day. I need to implement an authentication system between a "document" (it's not exactly a document, but an object without any computing capacity, only able to store ...
35 views

Is there a practical security difference between OTP with letters and OTP with numbers?

Is there a practical security difference between OTP with letters and OTP with numbers? If, for instance, I encrypt a letter message, using Tabula Recta, with a random letter key THISI SATES TXAAA - ...
39 views

Concepts for realization in applied cryptography [on hold]

I'm a computer science student (not a mathematican) and I'm gonna to write a master degree diploma on applied cryptography. Specifically, I'd like to create a realization of some cryptographic stuff ...
59 views

Where is CFB-MAC defined?

I can find a couple of descriptions of using CFB mode to create a MAC, but cannot find any standard or papers analyzing its security bounds. Is there a standard for CFB-MAC? Where can I find an ...
57 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...
208 views

Is Curve25519 vulnerable to private key exposure in the case of a bad RNG?

I'm really excited by what I've learned of advancements in elliptic-curve cryptography. Curve25519 seems to be a great choice at this point in time, but if I recall correctly, some elliptic curve ...
29 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
927 views

Generate RSA-2048 private key for a VERY fast decryption (don't care if it will be unsecure)

Given public standard RSA exponent e = 65537, is there any (d, n) pairs so that RSA decryption becomes a trivial operation? The modulus n must be no less than 2048-bit. The goal is to get a real ...
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+100

Key Size for Symmetric Homomorphic Encryption Over the Integers

In the paper Fully Homomorphic Encryption over the Integers, it mentions a symmetric key scheme on page 1 and 2. Key Generation: Pick a random odd number $p \epsilon [2^{N-1},2^N)$ Encrypt A Bit m: ...
105 views

Proving an encrypted message contains (but does not 100% consist of) a plain-text message?

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then concatenate X and Y, into Z. I encrypt Z, into "encrypt(Z,u) = Q". r is ...
19 views

Proving an encrypted message contains (but does not 100% consist of) a plain-text message? [duplicate]

I have keypair (u,r), and two pieces of data, X and Y. I reveal X publicly but keep Y secret. Y has high entropy. I then combine X and Y, into c(X,Y) = Z. I encrypt Z, into "encrypt(Z,u) = Q". r ...
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Is there any equivalent to the apache xml security library for JSON? [on hold]

I'm talking about org.apache.xml.security(santurio) Is there any equivalent library that works with JSON and provides the same set of features? (mostly AES-128 with KEK support)
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In DGHV FHE, why noise $r$ can be in $(-2^{\rho'}, 0)$?

"Fully Homomorphic Encryption over the Integer" described a simple FHE scheme based on the GACD assumption. Its encryption function (on page 6) has the form \$c \leftarrow (m + 2r + 2*\sum_{i \in S} ...
542 views

Are there ANY text strings that will generate the same SHA-512 Hash output? [duplicate]

Are there ANY text strings that will generate the same SHA-512 Hash output? Please provide an example, and how you came to that conclusion. I've tried thousands of variations, including ".." vs. "." ...
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Are there any cryptosystems that use multiple keys to perform encryption instead of one or two? [on hold]

Are there any cryptosystem that uses multiple keys (3 or more) to perform encryption rather than one (symmetric-key cryptography) or two (RSA, public-key cryptography, etc)?