1
vote
0answers
10 views

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 ...
0
votes
0answers
13 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 ...
10
votes
1answer
49 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: ...
8
votes
1answer
62 views

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, ...
1
vote
0answers
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?
0
votes
0answers
37 views

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 ...
0
votes
0answers
28 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 ...
2
votes
1answer
74 views

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 ...
2
votes
0answers
80 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 ...
3
votes
2answers
43 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 ...
5
votes
0answers
106 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 ...
1
vote
2answers
107 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 ...
2
votes
2answers
135 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 ...
-3
votes
0answers
39 views

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

54c2c00ddf08dd17d5337c9f082797850b720a7be88bb6dfa646eb07740748c8ca08d6a910b4c1e5e73d84f0651c75718e80ec760ba356b2ea41b95e480127130afebd1bb27e019abb868a21a2ff9231807fa88c23fe3e0e3ff76d88f9949b0493592046 ...
3
votes
1answer
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 ...
3
votes
2answers
49 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 ...
1
vote
1answer
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 ...
1
vote
1answer
40 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 ...
2
votes
1answer
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 - ...
1
vote
0answers
40 views

Concepts for realization in applied cryptography [closed]

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 ...
5
votes
1answer
63 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 ...
0
votes
1answer
58 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 ...
4
votes
2answers
215 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 ...
2
votes
1answer
30 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 ...
3
votes
2answers
942 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 ...
7
votes
2answers
172 views

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: ...
1
vote
1answer
111 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 ...
1
vote
0answers
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 ...
1
vote
0answers
14 views

Is there any equivalent to the apache xml security library for JSON? [closed]

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)
0
votes
0answers
32 views

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} ...
2
votes
1answer
551 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. "." ...
0
votes
0answers
44 views

Are there any cryptosystems that use multiple keys to perform encryption instead of one or two? [closed]

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)?
4
votes
1answer
45 views

Hitting a counter example in homomorphic encryption over the integers

The paper Fully Homomorphic Encryption over the Integers talks about a super simple symmetric key implementation on page 1 and 2. It says that to generate a key, you pick a random odd number between ...
2
votes
1answer
30 views

RSA - PKCS#1 padding - overall correction of algorithm

From PKCS#1, page 24: After we create the EM byte string and convert it to an integer, we then encrypt that integer with RSAEP (page 10) to get the ciphertext (as an integer). My question arrives ...
2
votes
1answer
18 views

Exchanging keys via third party

In many symmetric key ciphers sender and receiver have to exchange a single key. They may also do it through 3rd party who distributes it to both of them. since 3rd party can read all messages ...
8
votes
1answer
342 views

Does Curve25519 only provide 112 bit security?

In a recent mail on the IETF CFRG mailing list it was claimed that: The (currently missing) security considerations (or somewhere) should describe why Curve25519 is ok when used in contexts where ...
1
vote
1answer
27 views

One time pad- XORing or substitution

I have come across 2 versions of otp while reading it and want to confirm it. they have taken a plain text consisting of alphabets where they are shifted and replaced by alphabets itself. XORing of ...
3
votes
0answers
32 views

Size of encrypted AES CEK in CMS block

When I run openssl cms -encrypt -aes256 -in sample.der -out wrapped.der -outform DER -recip ecc.crt -keyopt ecdh_kdf_md:sha512 the part of the CMS output which ...
1
vote
0answers
36 views

CPA-security proof of “l-padded RSA” encryption scheme

The 10.9 exercise from the Katz-Lindell textbook creates a lot of confusion, let me state it here. Consider the following experiment for an algorithm $A$ and a function $l$ with $l(n) \leq 2n-2$ for ...
1
vote
0answers
10 views

Encipher the following plaintext message using the Vignere method using the key K = [4,2,3] [closed]

Encipher the following plaintext message, Exotic, using the Vignere method using the key K = [4,2,3] Can anyone help me get the ...
2
votes
2answers
44 views

Privacy and Integrity in Public Cryptography

I'm trying to figure out which is the best way to get privacy and integrity together in public cryptography. Alice needs to send multiple files $f$ (may be big) to Bob. I've thought: Alice computes ...
3
votes
2answers
60 views

A periodic PRNG based on hash function?

I need a PRNG which provides 128 bytes numbers. Let's say that given a symmetric key $K$ and an internal state $s$ I use the PRF HMAC-SHA512 this way: The output is PRNG($K, s$) = ...
5
votes
1answer
213 views

Can iterated hashing be used to mitigate collision and preimage weaknesses?

How much security does double hashing add regarding collisions and preimages? Is it helpful to iterate a hash function even more times than two? For example, can MD5 be fixed (in practice) by ...
6
votes
1answer
111 views

What was the NSA's reasoning for making their bitwise combination functions in SHA-1 the way they did?

I know that these functions are there to actually make the program work. What I want to know is why they made the functions one way but not another. For example, why did they pick F1(B, C, D) = (B ...
4
votes
2answers
87 views

Randomness in Public Key Encryption

For a scheme to be at least CPA secure, one has to randomize the scheme. In case of a secret key encryption scheme, the used randomness will typically become part of the cipher text as in the case of ...
3
votes
0answers
24 views

Safe generation of $k$ points on a curve such that the mutual discrete logs are hard?

I have a multiplicative group $G$ of prime order $p$ implemented using a twisted Edwards curve (similar to Ed25519). I want to compute a set of $k$ distinct points $P_1,...,P_k$ that generate $G$, ...
1
vote
1answer
62 views

Inverse public-key encryption

I'm in the need of an inverse public-key encryption method where you encrypt with the private key and decrypt with the public key. In other words an asymetric encryption where you can't generate the ...
1
vote
0answers
36 views

Ciphertext size of any CPA-secure public-key encryption scheme

I know that, for any CPA-secure public-key encryption scheme, the size of the ciphertext after encrypting a single bit is superlogarithmic in the security parameter. That is, for $(pk,sk) \leftarrow ...
4
votes
4answers
63 views

Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?

Imagine we have $t-1$ shares in $(t,n)$ shamir secret sharing. So at least $t$ shares are needed. Question: Why cannot we use $t-1$ shares to find a root of the polynomial and then recover the ...
2
votes
1answer
41 views

Symmetric key in homomorphic encryption over the integers

Much like this question: Public key in fully homomorphic encryption over the integers I am also reading I'm reading Fully Homomorphic Encryption over the Integers, but I'm working on implementing the ...

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