# Questions tagged [symmetric]

Symmetric cryptosystems assume two communicating entities share a pre-established secret key.

644 questions
Filter by
Sorted by
Tagged with
25 views

### How to estimate the maximum computational cost bound for Key Derivation Functions (KDFs) before it becomes useless security-wise?

From my understanding of Key Derivation Functions (KDFs), e.g. scrypt, Argon2, etc, we can tune their parameters such that it eventually becomes harder for an attacker to brute force a password-to-key ...
81 views

### Can Key-Encryption Key (KEK) be symmetric?

This from Cryptography course from Coursera: Key wrapping or encapsulation using a KEK can be accomplished using either symmetric or asymmetric cipher For my information KEK solves the key ...
1k views

### What should the nonce value be for client-side encryption?

I am using the following chacha20poly1305 Rust library to encrypt some data in a desktop application. The user provides the key, which never leaves their device, to locally encrypt some data, and then ...
765 views

### How to generate the exact AES key in both client and server side?

I am using AES to create a secure tunnel for transmission of data. As the symmetric key encryption will require the same key to encrypt and decrypt, so we need to generate the exact same key for the ...
65 views

### regarding usage of hashing

I have a question regarding pitfalls of using only encryption. Suppose Bob and Alice want to flip a coin over a network. Alice proposes the following protocol. Alice randomly selects a value X ∈ {0,1}...
28 views

40 views

### Can I use zero-knowledge proofs on pre-image of symmetric encryption?

Let $e_x$ be a symmetric encryption function in regards to key $x$. Let $y_1 = e_1(x_1), y_2 = e_2(x_2)$. My goal is to prove that: $$x_1 = x_2$$ Is there a way of proving this using ZKP? I can't seem ...
3k views

### Which is the simplest cryptographic algorithm which is close to commercial-level security?

An algorithm is simpler than another if It is easier to explain to a noob with basic high-school math knowledge. It is easier to securely self-implement by an intermediate programmer (Yes I know one ...
46 views

### Choosing UWP encryption algorithms

I've just come across the large variety of encryption ciphers available in the UWP WinRT API, both symmetric and asymmetric. I'm trying to figure out which are commonly seen as the most favourable ...
47 views

### Multiple IV CBC

CBC's encryption is not paralelizable but I could divide a 64 block message in 4 16 block parts and encrypt those 4 parts separatly in parallel using a diferent IV for each one. Is this unsecure ? Is ...
39 views

### How to justify the lightweight symmetric PRESENT encryption algorithm is more secure?

My domain is VLSI design, currently, I'm working on PRESENT Lightweight cryptographic algorithm. I want to know how to improve the security of the algorithm rather than increasing bit size? Is there ...
65 views

### Using HMAC with AES modes that do NOT require padding [closed]

I'm trying to use HMAC with AES modes that do not require any sort of padding. Although I am aware that modes like AES-GCM and ...
53 views

### DES decryption of the homomorphic encryption ciphertext

I implemented an application using partial homomorphic encryption for outsourced computations. To get an efficient bandwidth, I am thinking to apply (DES) symmetric algorithm to encrypt the message ...
35 views

### Any gotchas when deriving a symmetric key from two seeds?

Consider a connection protocol where, after jumping through several other hoops, Alice and Bob know each others' public keys; and they now want to do a RSA-handshake-kind-of-thing to come up with a ...
202 views

### Why is a MAC verification algorithm required when we can simply create a new MAC and compare the received one with the one calculated?

The process of verifying integrity through MAC involves two separate algorithms (as mentioned here). On the server side, a signing algorithm runs which calculates ...
35 views

### Looking for a way to enlarge a message so that any modification to the “enlarged” message makes recovering the original message impossible

Let's say we have a message m of small size. I am looking for a system $S$ so that $S(m)$ is arbitrarily large, we can easily compute the inverse $I(S(m)) = m$, and any modification to $S(m)$ makes it ...
69 views

### Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
124 views

### Block cipher modes used in real life

There is a number of block cipher modes, including ECB, CBC, CFB, OFB, CTR and others. After reading "Serious Cryptography. A Practical Introduction to Modern Encryption" by Jean-Philippe ...
51 views

### Is ShiftRows(SubtBytes(x)) = SubtBytes(ShiftRows(x)) the same for the same entry : in AES

Is ShiftRows(SubtBytes(x)) = SubtBytes(ShiftRows(x)) the same for the same entry : in AES It seems like these two are equal, can someone explain in theoretically?
34 views

### Symmetric algorithm effective key length

If we have a symmetric algorithm with key length $m$ bit, and we do a 5 time encryption with it. How much will it be its effective key length.
31 views

### Server distributing/sharing a symmetric key to one or more clients via an established secure connection?

I have a server and a client device that share two separate data channels that each need to have authentication and encryption protections. When a connection is made over data channel 1, it is secured ...
56 views

### Can i XOR an array of bytes with an equal length key securely

If i have say 64 bytes, can i XOR those bytes with another 64 random bytes, and have two new arrays, where both are needed to reconstruct the first? Intuetively i need some symmetric encryption like ...
33 views

### Encrypt encryted message vs DS

In digital signature The encrypted message is signed by the sender private key and verify using sender public key. The encrypted message is encrypted with another public private key pair which the ...
77 views

### Number of keystreams generated in Kreyvium for a single key/IV pair

Kreyvium employs 128-bit key and 128-bit IV. By a single initialization procedure using a key/IV pair, how many keystreams can be generated?
375 views

### Can I use the secret part of a asymmetric encryption keypair as a symmetric encryption key?

Background I'm working on a framework for crypto-based authentication and authorization that is largely inspired by the way Keybase's Teams product works. Keybase uses the same process to generate ...
155 views

### RFC 4493 (AES-CMAC) algorithm with 256 bit key

I apologize for the newbie question. If I were to use a 256-bit key and AES256 (assuming I had the function instead of AES128, the length of the for loops in the functions xor_128, leftshift_bit, ...
24 views

### Are there any known problems performing a One-time pad with 2 keys stored separately - AKA 2 part Symmetric key exchange over TLS

If this is something that already has a name, please tell me to look at that, but I have not been able to find one yet. I am considering this process for storing some data securely. I want to ...
37 views

### Is the password based key exchange secure even if the public key is known to adversary?

I am assuming the answer for part 1 to be a "NO" as the adversary knows the public key he can get the password by offline attack IN part 2 : the answer is "yes" as the public key is freshly generated ...
224 views

### What makes AES look like an ideal cipher?

There are 2128! permutations on 128-bit inputs. AES supports a maximum key length of 256 bits, therefore offers at most 2256 permutations. The total number of 128-bit permutations is much larger than ...
32 views

### Using Diffie Hellman with a shared secret

For a crypto course I need to realize a small software project where a client and a server want to communicate over a unsecured network. They both have the same secret. So I bascially have to secure ...
59 views

### Use Pohlig-Hellman to encrypt large files

I have an application that needs to combine two cascaded (symmetric) encryption keys using the Pohlig-Hellman cipher. For example: The system needs two keys for encryption $c = E_a(E_b(x))$ while ...
97 views

### Weakness in a CBC-like XOR cipher

A simple symmetric encryption algorithm can be written as follows: Input message M and 64 bit key $K$ Divide M into 64 bit size blocks $B_1...B_n$ Get first block $B_1$ and perform bit-wise $\oplus$ ...
84 views

### Which algorithm is the simplest reversible fixed-size length-preserving symmetric “cryptographic” with low probability of collision?

I am not a mathematician/cryptographer, so I could not take much advantage of this other question, and it seems (?) to have more requirements than me (SAC). I say simple, because I need it to be have ...
30 views

### How to measure brute force speed of a computer for a give cipher with given number of keys for second for a given key space

As I understood brute force attack is measured in number of keys which in turns give time required based on speed of computer It is quite interesting find out how effective an arbitrary computer is ...
94 views

### What happens if the first input block is identical to the key in DES?

In Data Encryption Standard (DES), M is the input message and K is the key of 64 bits size. M is divided into n 64 sized blocks (B1,B2,B3...Bn).
119 views

### Proving equivalency of two security definitions of symmetric encryption schemes

how to prove definition 3.8 and 3.9 are equivalence ? picture is from book an introduction to modern cryptography (2nd edition) by j. katz and y. lindell pdf and https://repo.zenk-security.com/...