Questions tagged [symmetric]

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

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How Secure Is This One-Way Function (Key Schedule)

While thinking about cryptography and how to "derive a key schedule" (like in AES), I thought of an algorithm that I can't figure out how to reverse (which is good). It's very simple and ...
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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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How can AES 256 be implemented in C?

I want to implement AES 256 encryption in a program written in C (using OpenSSL, which I have installed) which would accept a string or a .txt file from the user and encrypt it with a hash of a user ...
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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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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $\oplus$ ...
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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 ...
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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 ...
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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).
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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/...
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Why isn't data encrypted with mutiple ciphers?

Why isn't data encrypted with multiple uncompromised (so far) ciphers? Feel free to answer for a single private key for both and separate private keys. For example, encrypting data with TwoFish and ...
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Concrete Example of AND Gate Using Garbled Circuit

Most of the resources online like the wiki presents the beautiful idea of Garbled circuit in a rather unnecessarily abstract manner. This is the screenshot of Wiki's protocol: What would be an ...
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Why can a symmetric encryption algorithm be considered a pseudo-random number generation algorithm?

I have a question from my teacher: "Why can a symmetric encryption algorithm be considered a pseudo-random number generation algorithm? Can anyone explain it to me? And sorry if my english is not ...
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Testing speed of symmetric vs asymmetric encryption and decryption using gpg

I'm aware that symmetric is faster than asymmetric. I want to test this, but my (obviously incorrect) tests show the reverse. Symmetric test: ...
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Encrypt symmetric session key with asymmetric or symmetric master key?

Every day, I must backup my server's files, encrypt the backup, and upload it to untrusted cloud storage (dropbox, s3, etc.) I've spent time on security.stackexchange where I discovered the typical ...
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Which is the best algorithm for large scale file encryption other than AES?

I've been looking for a fast, powerful and robust algorithm for encrypting large files with authentication . I would like to implement the algorithm on my own without using third party software. I've ...
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Encryption with 2 symmetric keys and decryption with one key

Here is my use case: I need to keep encrypted data in Hadoop. The data is encrypted with symmetric key that is being changed every half a year. When data is retrieved it should be decrypted. Lets ...
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Symmetric versus asymmetric self encryption

I can encrypt my files with a symmetric encryption algorithm like AES, or with an asymmetric encryption algorithm like RSA or ECC (I encrypt my files with my own public key). No communication is ...
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Research Question (Part 2): new symmetric key cryptosystem

A few weeks ago I asked about a new symmetric cryptosystem discovered as consequence of some new mathematics work (link here). As per suggestion of commenters, I spoke with a cryptography professor, a ...
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Estimating the probability of success of a Turing-Welchman attack on an enigma machine as a function of the length of the crib (known plaintext)?

Could anyone please tell me how to to Estimate the probability of success of a Turing-Welchman attack as a function of the length of a crib (known plaintext)?? for example we have the : plain text=...
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Comparison of end-to-end encryption and TLS

I am writing a comparison paper about security of electronic communication and I want to compare end-to-end encryption and TLS by giving two examples such as Whatsapp and Facebook Messenger. However, ...
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Another cut-and-paste attack on CBC mode

I am trying to see specific cases of attacks in the CBC mode, in particular, I am investigating some attacks such as Example of a cut-and-paste attack on CBC. Here I have posted something similar and ...
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Are the signcryption and the authenticated encryption same?

The signcryption and the authenticated encryption are both the combine of encryption and authentication with three natural composition (i.e., EtS, StE, E&S). I am not sure that if they are the ...
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Can symmetric crypto system with counteably infinite message space be perfectly secret?

lets say we have a countable message space for example set of natural numbers then can we have a cryptography system that information-theoretically (Shannon or other equivalence definition) be ...
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Research question: usefulness of newly discovered symmetric key cryptosystem

both myself and my collaborators are pure mathematicians with only tangential experience in the study of cryptographic systems, so if this question is unclear or does not belong here, please do let me ...
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Decrypting data on client side for use inside program

So I am developing a python program and encrypting the trained machine learning models which need to be decrypted when loading them on client side. My program will deployed on the client's machine ...
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Why encrypt symmetric keys first with RSA and then the private-key with a PW?

In for example the Microsoft Encrypting File System, the SYM-Key is first encrypted with a RSA-Pub-key and its corresponding private-key is then encrypted using a users password. Why not encrypt the ...
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Is the encryption more secure if we apply Pohlig-Hellman cipher twice with different keys but with the same modulus?

To encrypt a message $M$, we compute $C=M^k \bmod p$ and to decrypt a Cipher-text we compute $M=C^{k^{−1} \bmod (p−1)} \bmod p$ But if we use Pohlig Hellman twice like $C_1=M^k \bmod p$, and then $...
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Can a message and one time pad each encrypted with separate ciphers be weaker than the stronger of either cipher?

Assume you have: A truly random one time pad, $P$ A plain text message, $M$ Two symmetric ciphers, $C_S$ and $C_W$, where $C_S$ is always more secure than $C_W$ Assume the keys have already been ...
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I have a new cryptography algorithm, what should I do?

I created a new, unknown symmetric encryption algorithm. It looks like it's very fast and can be useful. I'm kind of independent researcher, hobbyist. Since years I'm interesting in Collatz problem ...

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