Questions tagged [symmetric]
Symmetric cryptosystems assume two communicating entities share a pre-established secret key.
2
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1answer
91 views
Explaining Chaotic Cryptography
I will venture myself into studying chaotic cryptography. However, I find it hard to explain what chaotic cryptography entails to those that have some knowledge of cryptography. Neither can I explain ...
0
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1answer
41 views
Format of hybrid crypto envelope structure?
From posts including the accepted answer to
How to encrypt file with RSA and AES that anyone with RSA key can decrypt them?
hybrid crypto (AKA envelope encryption) a GPG-encrypted file has an ...
0
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1answer
41 views
Send content to owner of gpg public key, nested content symmetric encryption
If I want to encrypt a text content file using a symmetric algorithm like AES,
is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key ...
0
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1answer
46 views
PRGs exist if computationally secret encryption schemes exist
I have understood the "equivalences" between PRP, PRF and PRG. Now, I just read an statement in my lecture notes that made me think that there has to be a conversion between PRG and computationally ...
-3
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1answer
48 views
One-time pad question (Old ciphers) [closed]
The plaintext SECRETIVE is encrypted using One Time Pad with key DDDDDDDDD. Which of the following is TRUE?
The ciphertext will be the same as using Caesar cipher with key of 4
The ciphertext is the ...
2
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1answer
287 views
Security of AES after key expansion 4-MB with ECB and CBC
My question is,
how does the security depend or change if I encrypt with AES-128 in total 4-MB of Data?
With Electronic Code Book Mode and
Cipher Block Chaining Mode ?
Does an adversary still ...
2
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1answer
63 views
Detect MITM with hashed session-key — Is my protocol secure?
I have the following setup:
An app ("client") wants to communicate securely with a device I created ("server").
The client has the public key of the server (and a hashed password) preinstalled.
I use ...
1
vote
1answer
39 views
Can a message be encrypted with BOTH mono-alpha and poly-alpha ciphers?
For my class assignment, I was given this text;
Qpuvu vo vv stazpuykzh Hhycmlmv asb. Ad dhyaqva wh uyo uzb jpwww Avlw.
Tkpjllfdmbp zoatz vzjavfvna ZLHqh. Amva luy yyvlz yu bhk zua zlhvvalaz
yow ...
3
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1answer
61 views
Change a secret key in an embedded device
There is a device that uses a secret key Sk to encrypt data.
Assume this Sk is compromised.
Could the following scheme be considered safe, in case we want to change the compromised Sk:
We store some ...
5
votes
1answer
91 views
Combining known attacks and quantum cryptanalysis
I'm regularly reading that AES-256 is secure against quantum computers because Grover's algorithm will only halve the key strength (i.e. "only" require $\sqrt{2^l} = 2^{l/2}$ operations instead of the ...
4
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3answers
393 views
In what cases might PRESENT be implemented as encryption-only?
In the paper, under section 4.1 Goals and environment of use we read:
In applications that demand the most efficient use of space, the block cipher will often only be implemented as encryption-only.
...
0
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1answer
50 views
Does repeated xoring of the (same) key K lower the entropy of K?
If a symmetric encryption key $K$ has been generated by some recommended (NIST for example) RBG then we should have a key with high entropy.
But if we xor other bit-strings (e.g. IVs, other keys, etc....
4
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0answers
102 views
Why are matrices so common in symmetric encryption?
Matrices have been used in symmetric ciphers since the Hill Cipher (before?) all the way up to modern ciphers such as Twofish and AES.
I understand matrices can be invertible, therefore making them ...
4
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0answers
66 views
Patent Status & Usability of AE Modes [closed]
Post Structure:
Sources Cited
Question & Details
Before You Answer
Useful Info From Comments
Sources Cited:
https://blog.cryptographyengineering.com/2012/05/19/how-to-choose-authenticated-...
1
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0answers
89 views
CPA-secure private-key encryption scheme that is unforgeable but is not CCA-secure
This is exercise with 4.26 in Katz and Lindell's introduction to cryptography 2nd ed.
The question is: Show a CPA-secure private-key encryption scheme that is unforgeable but is not CCA-secure.
...
2
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2answers
341 views
Is there a symmetric cipher that is explicitly designed to be slow?
I am trying to find a symmetric cipher that is explicitly designed to be slow. I realize that this is generally not desirable, but I'd like many cycles and lots of electronic action. I could modify ...
1
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3answers
118 views
Could ANY cipher serve as the foundation for a public key cryptosystem?
My reasoning goes like this:
In principle, any trapdoor function can serve as the foundation for
an asymmetric encryption scheme.
All ciphers are trapdoor functions, since it's easier to encrypt ...
0
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1answer
45 views
Hash ratchets with truncating hash function
I'm working on a forward secret messaging system that relies on hash ratchet. I'm using BLAKE2b as the one-way function, which by default produces 512-bit digests. These digests are truncated by my ...
2
votes
2answers
171 views
Decrypt Base64 Encoded Monoalphabetic Cipher
I'm attempting to decrypt a body of ciphertext which has been encrypted using a monoalphabetic cipher. The trouble I'm having is that the plaintext was base64 encoded before being encrypted. In this ...
0
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1answer
78 views
Oblivious Encryption: Oblivious Transfer Based Encryption
I’m aware of a couple of OT protocols, most of which use Public Key Cryptography, Key Establishment (or similar constructs) as the base. I don’t really have specific knowledge on other OT protocols, ...
5
votes
1answer
132 views
Why do block ciphers use key schedules instead of round constants? (Even-Mansour)
Let's take AES as an example. What would be wrong with just having a 256 bit key that you XOR into your input and then XOR into your output? No key expansion at all.
I believe it's even known as the ...
8
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0answers
137 views
What was the BassOmatic cipher, and what made it so weak?
According to Wikipedia, this homebrew cipher was originally used in PGP, before Phil Zimmermann replaced it with IDEA. Supposedly, insecurities in the algorithm were pointed out to him, leading to ...
1
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0answers
67 views
Multi-Party Offline Key Exchange Using Public and Private Keys
I hope the title already explains the problem I have in mind; but let me lay out some more details.
Given public-private key pairs $P_A, P_B, P_C, ... P_Z$, (first $3$ of which are owned by our usual ...
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1answer
71 views
Non-derivable public key asymmetrical encryption? [duplicate]
The need we have is to pass encrypted messages but such that the encryption key can't be generated from the decryption key.
This rhymes with vanilla asymmetrical crypto, but in every schema I've seen,...
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vote
2answers
106 views
How is a ciphertext encrypted using random numbers decrypted using a symmetric key algorithm
We use true random number generators as a source of keys for encryption. What I can not wrap my head around is: How is this cipher text decrypted in case of symmetric key algorithm as we need the same ...
2
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0answers
18 views
Symmetric encryption with partial knowledge of key
While reading Laurent Bussard's thesis, Section 4.5.1, p91 (p119 of the pdf) I wondered about the following paragraph (emphasis mine):
the prover first picks a random symmetric key $k \in_R \{0, 1\}...
1
vote
1answer
55 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
votes
2answers
175 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 ...
1
vote
1answer
50 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
votes
0answers
54 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 ...
1
vote
3answers
554 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 ...
0
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2answers
50 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
127 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 ...
-1
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2answers
123 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 ...
0
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1answer
46 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
75 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 ...
10
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1answer
997 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 ...
0
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1answer
46 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
128 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 ...
0
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3answers
83 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
votes
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 ...
2
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2answers
114 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}, ...
2
votes
1answer
27 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 ...
1
vote
1answer
106 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 = ...
0
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4answers
2k 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
641 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
49 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
78 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 ...
10
votes
3answers
696 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
92 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 ...
