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

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Encryting data with password for local storage using libsodium

I want to encrypt data that is stored on the hard disk using a user-entered password. For this I look into the sodium docs and all I can find for symmetric encryption is authenticated encryption. ...
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19 views

Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
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2answers
1k views

ASCII to same-length ASCII encryption?

I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight. The ...
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2answers
165 views

Game with symmetric key

Alice and Bob are playing Rock-paper-scissors. Alice chooses $a \leftarrow\{stone, paper, scissors\}$ and a nonce $R_A$ used as symmetric key for encryption $$A → B : A, R_A(a)$$ Bob chooses $b ...
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4answers
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Found a way to crack AES-128, what now?

I have just found a way to crack AES-128 in a reasonable time (1-2 days). How do I publish and prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they ...
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1answer
29 views

Key derivation design to avoid key leaks

I have the first function that generates keys from AES decryption (128-bit key). It takes seed as input: ...
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1answer
59 views

Special case of format-preserving encryption

Is there encryption algorithm with the following properties? We always have plaintext in natural language, and the produced ciphertext is also in natural language.
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1answer
59 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
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1answer
369 views

AES file encryption with PBKDF2. Safe parameters?

I'm developing an application that will use public key authentication to contact some webservice. So the user has his keypair on his computer, and I want that file to be encrypted using AES with a key ...
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110 views

DH and PKI for KeyExchange

My question is fairly simple. I have more than two nodes which needs to communicate very efficiently from computational point of view. One of the nodes can become a coordinator between the nodes. ...
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1answer
106 views

Are there any quantum-resistant symmetric encryption schemes?

It seems that quite a few currently available encryption schemes will possibly be broken by quantum computing. Are there any symmetric encryption schemes that will remain unbroken (either because of ...
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57 views

S-Boxes and SP-Network

I work on an exercise and I have to study functions as : $ f : \mathbb{F}_q \rightarrow \mathbb{F}_q$ with $q = 2^n$ which can define a S-Box for SP-Networks. There is a question that I can't answer ...
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38 views

Determine encryption method with input and output

A website stores username and password in a session cookie. In the cookie the password is "encrypted" or modified in some way. Given that the "encrypted" version is always the same, I do not believe ...
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88 views

Super-simple encryption of short strings

I want to anonymise the initials of experiment participants by giving each a pseudonymic set of initials, by encrypting their true initials. Their initials are only two or three letters in length. ...
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1answer
605 views

Why does applying 56-bit DES twice only give 57 bits of security? [duplicate]

Given two 56-bit keys, $k_1$ and $k_2$, why does $E_{k_1}(E_{k_2}(M))$ only give 57 bits of security? So basically I'm unsure why it only gives 57 bits of security; I understand that one key will ...
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1answer
45 views

Are keys generated by the user or block cipher algorithms themselves? [closed]

We know block cipher algorithms. In the block cipher algorithms, Key Scheduling is the one crucial part. I see that in some simulation programs of the AES,DES,TripleDES encryption algorithms. In ...
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1answer
88 views

OTP - Why not reuse key? EDITED! [duplicate]

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! This might sound really dumb but why is it bad/insecure too use the same key twice on One-time-pad? Question: Why and how does using ...
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1answer
56 views

OTP - Reuse key BUT add IV, is it secure enough?

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
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3answers
92 views

Is the keystream transmitted with the ciphertext when a stream cipher is used?

When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the ...
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3answers
601 views

How can mega store my login details and still be secure?

I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works: Upon first signing up for an account you make a ...
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3answers
975 views

Why does the recommended key size between symmetric and asymmetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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1answer
159 views

What is this cryptosystem called?

From a paper Outsourcing Large Matrix Inversion Computation to A Public Cloud (IEEE Transactions on Cloud Computing, Vol. 1, N°1, 2013; alternate source requiring registration; preprint), I got to ...
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1answer
217 views

What is the most light-weight symmetric cipher thats still usefull?

I need a very light encryption scheme which costs almost no performance during encryption (while decryption may be slow). I found 5 algorithms: RC4, DES, LED, PRESENT, and Piccolo. But how do I ...
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2answers
130 views

Reusing a one-time pad?

I have an embedded device. It produces larges files (200 MB). I want the device to encrypt the file before writing to disk, so I gave them all a 16-byte random key. How can I transform the large ...
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45 views

Encryption with a known plaintext

I'm building an application where users can be a part of groups, and can obtain and distribute URLs from the group page that allow anyone who clicks on them to join said group. Groups should not ...
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40 views

how to integrate 2-3 algorithms to encrypt large data fastly and securely insted using AES? [closed]

I am thinking to build an encryption algorithm which take less time when encrypt large data such as video,mp3 and which has security credential.
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133 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
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1answer
84 views

What would a backdoor in symmetric key cipher look like? [duplicate]

Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but ...
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1answer
207 views

Is CAST5 still a secure algorithm to use?

I just installed GnuPG for Windows. The documentation says the default symmetric cipher is CAST5. In PGP also, default cipher was CAST5. Is CAST5 secure to use? Any known attacks reported on this ...
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1answer
157 views

Symmetric mutual authentication with client using a derived secret

I'm attempting to find a client/server authentication protocol that allows the client and server to authenticate each other when the client doesn't know the server secret but does have a sensitive key ...
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216 views

Is symmetric encryption no longer necessary?

Here is it: Symmetric encryption is no longer necessary, because all security services can be implemented with public-key cryptography. Moreover, in public key cryptography the operations for ...
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1answer
62 views

Generating cyclic group for Ciphertext-Policy Attribute-Based Encryption [closed]

I am doing Project under the topic CP-ABE.I need to generate a symmetric bilinear group Go of prime order p and with generator g...Then how to choose random elements from Zp....kindly anyone help ...
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94 views

Updating the secret key used for HMAC

I am designing a distributed system, composed by a set of physically distributed embedded devices (8 bit cores with less than 1 KB of RAM). The devices need to be able to authenticate the originator ...
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125 views

Comparison among algorithm based on key length

Some months ago I found in some paper that we cannot compare symmetric algorithm with asymmetric algorithm based on the key length and more important we cannot compare asymmetric algorithm using only ...
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2answers
129 views

Combining a keystream generator with a block cipher

I understand that: A stream cipher's security is diluted if the same key is used more than once. This is fixed by using an additional initialization vector in the keystream's computation. A block ...
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1answer
42 views

Can one deduce the symmetric key size used to encrypt a given a piece of ciphertext?

Assume an attacker captures a piece of ciphertext encrypted with a symmetric key. He knows all the details of the algorithm used to encrypt except for the size of the key used in this case. Can he ...
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1answer
122 views

Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
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78 views

Analyzing security flaws of cipher

I know using homebrew encryption can be very dangerous as it is very likely to have many flaws in its design. The following concept is just for learning purpose in case anybody is getting red flags ...
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107 views

Is my method symmetric encryption?

To obfuscate data I made up this method on the spot without planning since the goal wasn't real encryption. At first I though this cannot be real encryption but after revisiting the code and reading ...
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1answer
196 views

efficient authentication with broadcast encryption?

(I am not a crypto expert, so I apologize if the terminology I use is incorrect.) Suppose I have the following simple broadcast encryption scheme for securely sending content to $n$ authorized ...
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1answer
156 views

Using modulus in one time pad?

I would like to know what is the real purpose of using a modulus in the equivalent of a Vernam cipher: Data $d$, large number $M$. Assume the key length is $\lambda$ bits. Then $M$ could be ...
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540 views

Implement deniable encryption with AES/RSA

I'm on a crypto app using OpenSSL (I'm more an implementer/cryptographer than a cryptologist), mainly as a hobby, for now. My app will be able to encrypt a file (not a container) with symmetric or ...
2
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0answers
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Which gives better deterministic encryption SIV or Plain ECB mode?

Lets say , if we encrypt a plain text message $msg$ with key $key$ in below two ways. Which is the below would give better deterministic encryption and why ? AES-ECB($key$ , $msg$) SIV($key$, NIL , ...
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Memory requirement in light weight block ciphers cryptanalysis

If we have a light weight block cipher where the block length is different than the key length. Let's say the block has a length of 64 bits while the key is 80 bits. For an attack to be successful, ...
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3answers
248 views

Difference between Symmetric and Asymmetric. Is this answer correct, based on a written test?

I asked the following question on a final exam: Symmetric Ciphers (e.g. AES, DES, Blowfish) use up to 256 bit on the best case, which are considered strong against brute-force attacks. On ...
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3answers
119 views

Using the same symmetric key in both directions?

A simple symmetric encryption scheme uses the same key, derived from a password, for both directions of the communication. Is this bad practice, and if so what should be done about it? Is it 'good ...
3
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0answers
70 views

Using machine-learning techniques for data-dependent operations in ciphers

From 'Methods of Symmetric Cryptanalysis' by Dmitry Khovratovich, The data-dependent operations are one of the most controversial design concepts. We say that an operation is data-dependent, if it ...
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1answer
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Repeating something encrypted and non-encrypted?

If one wants to keep the receiver's name non encrypted, but it also appears in the encrypted message - will it leak information? (other than the receiver's name, of course.) Let's assume a "bad" case ...
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2answers
146 views

suitable programming language for cryptography algorithms [closed]

I know as programming languages C and java , and I know that java is slow so for this reason it is not suitable for cryptography applications espacially low level programming (manipulating bits) , so ...
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1answer
64 views

block cipher algorithms with variable block lengths

Rijndael supports block lengths of 128, 192 and 256. AES does not but Rijndael does. What other algorithms support variable block lengths? Or is Rijndael unique in that regard?