Questions tagged [symmetric]

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

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Encryption on one AES mode and decrypting on another, where both use HMAC

Let's say there are 2 ciphers, $enc$ and $dec$, where: $enc$ will encrypt the data, and $dec$ will decrypt it. Both $enc$ and $dec$ must be an AES cipher. $enc$ and $dec$ will use the same key $k$ ...
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Mathematical and empirical analysis of AES

Hello everyone and happy new year in advance. I'm doing a work about the analysis of the AES algorithm, and I have some doubts about this. First, I need to do the mathematical analysis of the ...
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Is CTR more secure than CBC?

In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only ...
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Key storage management of session keys and long term keys

In key management, one of the topics is key storage, I want to know where and how these keys(long-term and short-term) are stored? For example I read that android password apps use KeyStore api to ...
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Encryption in SET protocol

I have a rough idea of what is symmetric and asymmetric encryption, but I can't apply the idea to the SET protocol (Secure Electronic Transaction Specification), so how the symmetric and asymmetric ...
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Symmetric Exchange Key Sharing

Question: Suppose that there are 10000 = 10^4 banks and 10 payment card organisations (PCOs). How many secret keys will be needed if each PCO shares a unique secret key with each bank? How many extra ...
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How is the 'Algebraic Degree' calculated in the paper about analysing the white-box AES(Chow et al. 2002) by exploiting internal collisions?

This paper proposed a new attack on the initial white-box AES implementation of Chow et al. In order to determine the good solution, we use the particular structure of the function $S_{0}$. $S^{-1} \...
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What are the fundamental roots of modern symmetric encryption?

In academic pursuits, we often have people (and their ideas) who are considered fundamental to the subject, such as Bayes and probability. In cryptography, it's obvious to see that the Diffie-Hellman ...
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Zero knowledge proof of symmetric keys and encrypted texts resulting in the same text, if the symmetric keys are encrypted with asymmetric ones

Suppose I have: text T, symmetric keys X, Y encrypted text T with symmetric keys X, Y = TX, TY accordingly asymmetric key Z, used to encrypt X, Y to transmit them to a person. Let the encrypted ...
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IND-CCA secure symmetric encryption

Although this question maybe looks silly, I have searched similar questions in this forum and googled it but got no desired answers. IND-CCA security has already been deeply studied in public ...
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Generation of Rijndael S-box [duplicate]

I'm an electrical engineering student and was doing a brief research regarding the round transformations of the AES-128 and came across the Wikipedia article describing the generation of the ...
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What is most secure way for one party to encrypt 4 bytes in less than 40 bytes, which will be publicly available?

I have a project where a user needs to store a U32 encrypted on a blockchain such that they can recover it themselves: the user will always have their key available but may "forget" the U32 ...
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Designing a simple challenge-response symmetric mutual authentication protocol

I am designing a protocol that 2 devices will use to mutually authenticate over an unreliable, unsecure channel. The system must be fast and low-power, so symmetric cryptography is a requirement. I ...
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Is Caesar cipher perfectly secret?

The only time a shift cipher considers to be perfectly secure is when used on a single letter of plaintext and no more. Having that in mind, we can say it is certainly not perfectly secure. Caesar ...
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Help needed for IBM KCV

I found old key letters used in EFT HSMs with TDES keys, parted in two halfs. The check value printed on this letters is called IBM CV and doubled IBM CV. My newer HSM does not support this kind of ...
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Best practice for JWE symmetric key encryption

After the user authenticates with Auth0, the backend issues a JWE with some info about the user. I do not want the user to be able to see the payload, which is why want to encrypt it. Furthermore, ...
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Bruteforcing a symmetric cipher [duplicate]

I don't understand how we could bruteforce a symmetric cipher. Let's take AES with a key size of $128$ as an example. It means that there are $2^{128}$ possible keys, and as many ways to decrypt a ...
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Calculating symmetric key bit strength

16 byte key where each byte is in range 0-255, generated using cryptograhic PRNG will be believed to have 128 bit strength. What would be a bit strength of a key generated using same quality PRNG, ...
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Questions about Symmetric Encryption part of TLS

In TLS, we use DHKE for establishing the session key & then encrypt the actual communication with session key using symmetric encryption. While reading about DHKE, I learnt that you could use the ...
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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 ...
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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 ...
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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 ...
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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 ...
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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}...
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Matrix cipher - symmetric or asymmetric cryptosystem?

Matrix cipher is defined by: a) Encryption: $C = K \times Z$, where $C$ is a cryptogram vector, $Z$ is a message vector and $K$ is encryption matrix (encryption key) b) Decryption: $Z = K^{-1} \times ...
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Proving security of $\Pi' = E_k(E_k(m))$ knowing $\Pi = E_k(m)$ is secure

I recently started studying cryptography but I am not sure I quite understand the concept of proof by reduction. Question I am trying to solve is as follow: Suppose $\Pi$ is a symmetric encryption ...
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Is it safe to use RSA multiple times

Assuming I have multiple symmetric keys on specific machine(more than 10000 probably), can I use the same rsa key to encrypt all of those keys? I'm a bit concerned from a situation where multiple ...
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Symmetric-keys algorithms with different keys for encryption and decryption

The Symmetric-key algorithm article from Wikipedia states: The keys may be identical or there may be a simple transformation to go between the two keys. I am not aware of any symmetric-key ...
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How to choose parameters for Argon2 for password vault

I'm creating a password vault and I'm planning on using Argon2id to derive the master key from the master password. For encryption I'm planning on using XChaCha20 with Poly1305. To be clear: a set of ...
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Is there a cryptographic scheme that achieves both confidentiality and integrity?

Suppose that Alice wants to send a relatively long message M to Bob. Also, suppose that both Alice and Bob have a set of {PK, SK} for public key cryptography. Alice proceeds to encrypt the message M ...
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Symmetric Encryption, meet in the middle attack, effective key length

What is the effective key length of a deterministic encryption scheme, given a meet-in-the-middle attack scenario when you encrypt five times (64 bit keys for each)? . Say the encryption scheme has |...
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OpenSSL supports AES, Camellia, ChaCha. How about Twofish, Threefish, Serpent?

If I understood correctly, some symmetric ciphers such as AES, Camellia, ChaCha are implemented in OpenSSL (along with several older ones) but some other commonly used and proven ciphers such as ...
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Can you have perfect secrecy with countable message/key spaces by dropping countable additivity?

This classic paper by Chor and Kushilevitz shows that if the key space and the message space are both countably infinite, then it is impossible to have a perfectly secure private-key encryption scheme....
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Why should one use a cypher-based message authentication code (CMAC) instead of symmetric encryption and CRC?

What are advantages/disadvantages for using a CMAC that proofs the integrity and authenticity of a message but doesn't encrypt the payload itself? Why should it be used instead of symmetric encrypted ...
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Pipelined architecture for secret key block ciphers

I want to implement a pipelined architecture of AES128; and I couldn't figure out the number of the pipline stages. As I undestand, it is possible to make the piepline stages inside the round, or ...
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Encryption using blinded key

I was wondering whether there are any "blinded" encryption schemas, such as the following: We encrypt message $m$ using $f(k)$, where $f()$ is some blinding function and $c = \text{Enc}(f(k),...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 (...
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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 ...
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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?
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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.

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