Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
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1answer
30 views
Trivial Broadcast Encryption Scheme for video conferencing how well does it handle users joining or leaving a call?
Consider the trivial Broadcast Encryption Scheme for video conferencing, where each user shares a long-lived key with the broadcaster, and the session key used to encrypt a multicast message (or ...
2
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2answers
67 views
Encryption using static AES256 symmetric key vs ephemeral session key
For a hackathon I am designing an information exchange system for healthcare. Healthcare data is stored on unsecured systems. I want to assure confidentiality, integrity and authenticity of this data ...
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1answer
29 views
Using AWS KMS to manage secret keys
For my use case, I need to maintain a secret key with the client to generate and verify HMAC for requests.
We can have multiple clients and we can not make assumptions such as a client's server will ...
2
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0answers
48 views
Sharing salt for deterministic symmetric key derivation
I have a requirement to generate and share unique symmetric keys for a large numbers of small data objects.
In many cases the storage and retrieval of the key for each object will be a significant ...
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3answers
531 views
Understanding MACs and why cleartext is sent over
Assume both Alice and Bob have a symmetrical key, let's call it $k$.
They agree on a cryptographic hash function, let's call it $\mathsf{HASH}$.
Now Alice wants to send an authenticated message.
She ...
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2answers
44 views
question on encryption of multiple distinct messages
When I study symmetric encryption, it is quite straightforward to understand the following: in the presence of eavesdropper, simply using a PRG $G(k)$ and XORing multiple messages won't provide ...
2
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1answer
44 views
Can non-repudiation be ensured without public-key cryptography?
Message authentication is ensured by using HMAC, which can be thought of as a symmetric-key construction.
Source authentication in multicast communications can be guaranteed using TESLA, which is ...
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2answers
54 views
What is the use of Byte-Substitution,Shiftrows,MixColumn steps in AES, if 128 bit key is known for decryption?
I have just started learning AES algorithm.
S-Box is using Galois Fields $\text{GF}(2^8)$ math behind its computation and Shiftrows & MixColumn steps also doing some math at both encryption and ...
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1answer
39 views
Which symmetric algorithm should I use for storing files in untrusted servers?
I have gigabites of files, which I have to backup. I have some servers for storing this files. But these servers are untrusted. So I need to encrypt files, then backup files. When my PC breaks down, ...
0
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1answer
69 views
Is this method of speeding up a symmetrical algorithm secure? (AES output joining)
I was trying to find out a way of speeding up a given symmetrical algorithm the reason and programing launguage in this case are unimportant. I have came up with the following thing:
Divide data into ...
9
votes
1answer
832 views
After ECDH with Curve25519, is it pointless to use anything stronger than AES128?
Is the following reasoning correct:
After ECDH with Curve25519, the resulting shared secret will be an EC public key with a bit strength of 128 bits.
This public key would then be hashed (let's say ...
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1answer
41 views
How to be sure to retrieve the good key when brute-forcing a cipher?
Imagine the case of the one-time pad. It is proved to be secure because the key could be everything. We have no guarantee that this key or that key was the one used while encrypting our data. ...
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1answer
41 views
What is the advantage of a symmetric encryption system over an asymmetric encryption system?
What are the reasons why somebody would choose a symmetric system over an asymmetric system considering its disadvantage such as a key management and a key transmission?
Some people say a symmetric ...
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3answers
71 views
Can someone steal the key between 2 clients which are using Symmetric Encryption?
Can someone which is not authorized be able to listen between the conversation of 2 clients and catch the key? Because if I understood correctly one client needs to send the key through a channel so ...
3
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1answer
108 views
Simple Electromagnetic Analysis vs symmetric cryptography
I've asked this question here and was advised to post this question on this forum in hopes of an answer.
I'm currently taking a security class and i came into this issue when writing a report about ...
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1answer
53 views
Can the key-generation algorithm always be uniform?
Assume that the encryption uses $n$-bit keys to encrypt $l(n)$-length messages.
If a symmetric key encryption scheme is defined as $\Pi_{1} = ( \mathrm{Enc}, \mathrm{Dec} )$, then for every $x_{0}, ...
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1answer
24 views
Secure scheme to share symmetric key using asymmetric keys and certificates with N parties
I need to distribute symmetric AES key into number of end points which will use it to decrypt data. The AES key will be the same on all end points, it is not possible to generate unique on every end ...
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1answer
94 views
Why is this authentication protocol with a nonce and tree parties not secure?
Why is the following authentication service not secure?
C⟶S: $I_C$
S⟶C: $N$
C⟶S: $E(K_{C,A}, N)$
S⟶A: $E(K_{S,A}, \{I_C, E(K_{C,A}, N)\})$
A⟶S: $E(K_{S,A}, N)$
where:
C = client
S = server
A = ...
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4answers
230 views
Can I find the encryption key if I know the plain text and the encrypted text (DES and AES)?
If I have the plain text and its output after encryption with a key K1, is it algorithmically feasible to find K1?
I am specifically interested in the cases of DES and AES encryption algorithms.
3
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2answers
636 views
Should text be hashed before being used as an encryption key?
Let's say I have an API that provides an encryption wrapper around another API. I give the consuming programmer the option of either passing a string or byte array as an encryption key.
The byte ...
0
votes
1answer
48 views
Is the private key of a private/public key pair also a symmetric key?
I think I've got a fairly good (practical, not mathematical) understanding of symmetric versus asymmetric cryptorgraphy, so the difference between those is not the question.
In a local discussion ...
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2answers
53 views
Is HMAC a suitable substitute for HKDF?
My PHP version does not include the hash_hkdf() function, and upgrading versions is not worth the trouble for my project (which is for personal pleasure, not for ...
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3answers
653 views
Symmetric cipher key size vs number of rounds. Longer key = more secure cipher?
I would have questions related to discussion under this article.
Bruce Schneier answered questions regarding key size vs number or rounds:
Why do you need more rounds with longer keys? And how did ...
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1answer
42 views
Is there any symmetric encryption algorithm cannot guess the key when encryption and decryption value are known?
I want symmetric encryption algorithms that cannot have their keys recovered when given plaintext and ciphertext. I tried XOR cipher algorithm, but when I've obtained ciphertext and plaintext, the key ...
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2answers
107 views
How can we encrypt a file to be just readable (and not writable) after decryption?
Is it possible to encrypt a file (e.g., a text document) such that when a user decrypts it, he/she be able to just read the file and not be able to change the content of the file?
I mean, the result ...
1
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1answer
87 views
What is the advantage of CFB over OFB?
I was wondering if CFB can be better than OFB in any ways. I would like to know in what cases one would use CFB over OFB.
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1answer
36 views
Looking for a specific cryptosystem (encryption two times with two different keys and then decryption with another different key )
I am looking for a specific cryptosystem with the following properties:
Suppose a User (Say $User_1$) encrypts a message $M$ with the key $K_1$ (the resulted ciphertext is $C_1$). Another user, say $...
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2answers
759 views
How can I share a number with an opponent?
Let's say I have a message (eg: Hello, world!) and I want to encrypt this message using symmetric encryption (AES-256). I am using a list of keys, where I randomly ...
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0answers
158 views
The right way to encrypt sensitive data with an user password
I am developing something like 1Password and I want to be sure that method that I use is secure. Main idea of the app is storing user passwords, and is protected with a global master password. Main ...
0
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0answers
30 views
Decrypt the encrypted message with similar symmetric key
Machine A generates a fingerprint and uses it as a symmetric key to encrypt the message. After that, the encrypted message is sent to Machine B without sending the symmetric key. In machine B, it can ...
1
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1answer
74 views
Deterministic symmetric indistinguishable encryption
Are there any block-cipher modes (or symmetric encryption schemes in general) that are fully-deterministic, meaning same inputs lead to the same outputs (like for all modes with constant IV) and ...
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4answers
2k views
Is using the same IV in AES similar to not using an IV in the first place?
So if I understand how an IV works with AES, I'm supposed to generate a different IV for every message because using only a key, I will get the same encryption if the message was encrypted twice (...
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2answers
120 views
Broadcast encryption not using symmetric keys
Is there a common scheme for a broadcast style encryption that doesn't involve and exchange of a common key? I'm aware that traditionally what would be done is there would be a common symmetrical key ...
1
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1answer
47 views
Is symmetric encryption with a key containing the userId passes as authentication?
The scenario:
There is a web application where ownership check is time expensive so during the development all users were able to access all other user's objects (let's say apples) by changing the ...
3
votes
0answers
76 views
Safely using ciphers that take small key sizes
Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and $P = D_{k_1}(D_{k_2}(D_{k_3}(...
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1answer
70 views
What does GHASH really do?
I try to understand the GCM-MODE used in TLS.
The problem I have had is described below.
1:textbook describes how GHASH works:
2:
I get some debuginfo from openssl code that contain enc_key(32 bytes)...
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0answers
46 views
$c = d \oplus (f(d)\parallel p)$, solve for $d$ and $p$, how many solutions could you find?
$d$ is $2n$-bit and truly random, $f(d)$ and $p$ are $n$-bit, $f:\{0,1\}^*\to\{0,1\}^n$ is a digital signature with a public-private key pair, and $p$ is that public key. For a value $c = d \oplus (f(...
5
votes
1answer
780 views
What is the main limitation of DES?
I know this question seems too general, not specific. Our professor asked this question today, and I have no idea how to answer it.
Maybe it's the key size, maybe another thing? Any idea?
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1answer
65 views
Are sufficiently large key sizes enough to deter quantum attacks for symmetric key ciphers? [duplicate]
Are sufficiently large key sizes enough to deter quantum attacks for symmetric key ciphers such as AES?
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0answers
21 views
Alternative Hard Problem to Prime Factorization? [duplicate]
Suppose in the future someone conjures a technique to (arbitrarily) quickly find the prime factors of arbitrarily large numbers, thus undermining the computational security of (as far as I am aware) ...
3
votes
3answers
63 views
Establish more secure symmetric crypto system given A and B have small initial secret
Alice and Bob have a secret number X that is known only to them. However, the number is only 14 bits, and Trudy knows they share such a secret and can intercept messages between them. Instead of using ...
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0answers
40 views
A cipher scheme using symmetric and asymmetric cryptography, possible collisions?
A public-key p is signed with a one-way function f, resulting in signature s. The signature s is then symmetrically encrypted with vernam cipher, modulo-2 addition, using the public key p as the ...
3
votes
1answer
902 views
If a key is used to encrypt that same key, is the computational cost to brute force it decreased?
If a key d is used to encrypt a message m that is identical to the key d, resulting in a cipher c
c = encrypt(m, d) = encrypt(d, d)
is the computational cost to brute force d lower than if the key d ...
4
votes
2answers
93 views
What is the computational cost of guessing symmetric keys for two ciphers that decrypt to the same input?
A message m is encrypted with two symmetric keys, resulting in two ciphers c,
c1 = encrypt(m, key1)
c2 = encrypt(m, key2)
What is the computational cost of guessing symmetric keys for both ciphers ...
2
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1answer
63 views
Role of session identifier in Otway-Rees protocol
According to Wikipedia, Otway-Ress protocol is as follow:
The protocol can be specified as follows in security protocol notation, where Alice is authenticating herself to Bob using a server S (M is ...
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2answers
157 views
XOR and cipher stream
I am new to cryptography and I am very confused. In fact, I am so confused that I have trouble providing a suitable title for my thread...
I know that a Substitution Cipher is designed to substitute ...
0
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1answer
67 views
How to solve rubix-cube like symmetric encryption
So for a project at University I wrote a symmetric encryption system that was very similar to how a rubix cube would work. I had each byte of my data mapped to a element in a grid, with 6 grids in ...
3
votes
2answers
124 views
Apply visual cryptography to a video stream?
I read that there are different ways to apply visual cryptography. One is to generate two images that when overlapped provide the original image. The main issue of using this approach with a video is ...
0
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1answer
156 views
Best method to achieve authenticated encryption with openssl
Problem
I want to send a plaintext document between from myself to someone else over an untrusted link. I want to firstly stop third parties from reading the document, I want the receiver to be able ...
0
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1answer
179 views
Which cipher to use with openssl for shortest output?
I'd like to encrypt my 12-24 words seed for my bitcoin wallet with openssl command line tool to be able to have it with me on paper without the risk that somebody could use it
Which cipher should I ...
