Questions tagged [decryption]

In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Only authorized parties can decipher a ciphertext back to plaintext and access the original information.

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Decrypt the same ciphertext to multiple messages of my choice if I can use any key I want to decrypt

In a modern secure encryption scheme, is it possible(both theoretically and practically) to encrypt a message using a key to get the following ciphertext c = Enc(M1,k1) and later find another key so ...
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Bitslice DES decryption

I would like to implement fast DES decryption using Bitslice technique. Without bitslice DES technique, I have already done decrpytion in this source code by changing the for loop from 15 to 0. In ...
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Subexponential algorithms that apply only one of factoring and discrete logarithm?

Shor (quantum polynomial), Number Field Sieve (subexponential), Pollard rho (square root) all have both factoring and discrete logarithm over $\mathbb F_p^*$ variants. What are the subexponential ...
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Is there a way to find the two generator polynomials of a JPL sequence?

I am decoding a binary sequence that was detected as an unpractically long LFSR by the Berlekamp-Massey algorithm. First of all, the generated sequence is far longer than it needs to be and since it ...
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83 views

Using Viterbi algorithm to decrypt Vernam cipher

I'm reading a book on cryptography and it mentions the Viterbi algorithm being used to decrypt Vernam cipher if the same key is used multiple times. According to the book the Viterbi algorithm takes ...
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69 views

Encryption of data with multiple possible decryption keys

I'm new to the Cryptography Stack Exchange, so my question might be very naive. What encryption algorithms are out there that will allow different decryption keys to decrypt the same piece of ...
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28 views

decryption in IDEA if the encryption was made without the output transformation

I'm implementing IDEA encryption and decryption and I'm trying to implement it in different variants(e.g if we didn't do the output transformation or if we don't do full 8-round encryption). I got the ...
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Where exactly do you add the zeroes to a URL in a padding oracle attack? Also, how would you decrypt a file this way?

I have been studying various crypto attacks, and one of the attacks that I have recently studied was the padding oracle attack. Now, I mostly understand it, but there is one aspect of the padding ...
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113 views

How can I decrypt AES-256 GCM with key with a IV that is missing?

I want to decrypt a file that has been encrypted using AES-256 in GCM mode in libressl. I have the key but I don't have the IV, is there any way I can still decrypt?
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How to decrypt raw TLS bytes?

Is there any tool / way to decrypt raw bytes of a TLS 1.2 session, when the master key is known, even if forward secrecy is used? The closest I found is this. I know its possible using Wireshark, but ...
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How to break a vigenere cipher with a period of 2, and knowing a part of the plaintext

the encrypt code is "ARJHNRIUCGQHPFGQFHTXPDEHTLNOC", and the part that i ​know of the plaintext is "DERUNA". The key is period of 2, so the key are 2 letters. Each letter of the ...
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Is there a possibility to apply Moni Naor and Adi Shamir's "visual cryptography" on text ( paragraph)?

[Instead of two images I want to consider two paragraphs(text) when combined should give me a secret message] In their algorithm, the image has been split into two component images. Each component ...
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What cipher requires the full message to solve

I am working on a scavenger hunt and wanted to encode a clue in a cipher that requires the full message to decipher. My goal in this is to prevent players from predicting the result before obtaining ...
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108 views

Conditional decryption

Is it possible for one party to encrypt some data and have another party (unknown to the first party) view that original data if a certain condition is met? I cannot find any information about this ...
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61 views

CCA Security/Decryption of PRF scheme

Let $F : \{0,1\}^n \times \{0,1\}^n \rightarrow \{0,1\}^n $ be a PRF. And let the encryption function be $Enc{_k}(m) = r\mathbin\| (F{_k}(m\bigoplus r)$ , r being a random value. Im trying to proof ...
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What is the exact algorithm for encryption and decryption with hummingbird-1 cryptography?

I have really googled the entire internet but could not find a clear algorithm for hummingbird-1 cryptography.The problem emerges in the decryption module: What is the initial value of state register ...
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103 views

Decryption of Vigenère cipher by hand using Kasiski method

My task is to decrypt the following message, which was encrypted with a Vigenère cipher of length 4: ...
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97 views

How to decrypt a combination of transposition and substitution cipher text

I'm having problems decrypting a cipher text that has an transposition cipher applied to it but also a substitution cipher. I don't know in which order they were applied. Does anyone know what steps I ...
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166 views

Decryption of RSA with e that has no inverse

I'm studying the RSA protocol and I was wondering if there was any way of decrypting a message if the $e$ doesn't have an inverse $\mod (p-1)(q-1)$. Usually, you have to choose a value of $e$ that is ...
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How do I progress with cracking this monoalphabetic substitution cipher that ignores natural word divisions?

Having some trouble cracking this cipher (this is part of a homework assignment for a cryptology class) I've looked at letter frequencies but I'm not sure what else there is to help me. Given the ...
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Decrypt a ciphertext knowing of a pattern of key repetition

I have two ciphertexts (I do not know which encryption algorithm was used to create them) which both starts with the same 3-characters long word. This led me to believe that the same key was used for ...
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Fast key exchange algorithm in hardware with small key size

Which asymmetric algorithm will be best only for key exchange to set up communication using symmetric cryptographic algorithm. Comparison should be in term of speed, key length and their hardware ...
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My fernet key "expired" what now?

6 months ago i created a bot that basically stored every users data in json format in different text files and i had a fernet key. I basically didn't touched it for like 2 months now, because it's a ...
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How can I go about decrypting some files that were most likely encrypted using android's file-based encryption?

I am looking to try and decrypt some files from a phone that I no longer have. I've tried to provide some background information here for context purposes. The files in question were backed up from ...
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Am I Doing RSA Correctly?

I am trying to figure out how to complete RSA manually. I am trying to encode a simple block message (Mi). I used CrypTool to determine the encryption. When I "manually" computed the ...
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60 views

Can you obtain private key d and compute plaintext from El-Gamal?

Given an Elgamal encryption scheme with public parameters $k_{pub}=(p,\alpha,\beta)$ and an unknown private key $k_{pr}=d$. Due to an erroneous implementation of the random number generator of the ...
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35 views

Add setup to GPG symmetric

I use GPG symmetric, to encrypt text file. Is it possible to use GPG symmetric, to encrypt a text file, and at the same time, add additional setting to the encrypted file, to give us 2 conditions: ...
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25 views

Using same key pairs in several different encryption tools and version

can we use the same key pairs created by an encryption tool, for encryption decryption, in another encryption tool ? for ex, created by hypercrypt, but being used in cryptermite, or maybe within the ...
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Can I map 2 plaintext letters to 1 ciphertext letter?

Plaintext: "abcd" where P1,P2,P3,P4 map to each corresponding letter. And C is the ciphertext where C1,C2,C3,C4 map to each corresponding letter. Keys = (x,y,z) Can I use the following ...
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How is the second digram a legal mapping? (Playfair Cipher)

So this is a partly completed key I have: _ R _ _ _ _ T _ _ _ _ _ H _ _ _ _ L _ _ _ P _ _ W And this is my plaintext/ciphertext: ...
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Looking for encryption function given decryption function (2048-bit ciphertext and key, addition and subtraction operations)

I have a decryption algorithm for 256-byte (2048-bit) blocks and want to find the matching encryption algorithm. What I know about the algorithm and have: 256-byte ciphertext (I have multiple ...
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Suitable hybrid encryption approach?

I need help for my bachelor thesis. I have a general question regarding hybrid encryption in different ransomware. The hybrid encryption often uses symmetric and asymmetric encryption techniques. ...
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CP-ABE (partially hidden access structure)

Anyone aware of the implementation of paper "Lai, Junzuo, Robert H. Deng, and Yingjiu Li. 'Expressive CP-ABE with partially hidden access structures.' 2012" specially in python or Charm ...
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How do I invert the final round S Boxes during linear cryptanalysis

I'm using Howard Hey's tutorial on linear cryptanalysis, however I don't understand the final stages. I understand using exhaustive partial subkeys to turn the ciphertext into the final round output, ...
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27 views

Decrypting iPhone Backup

Are key bag keys rotated between backups? Or if I have keys from an old backup, am I able to use then with a later backup? Short of it, have a friend w/ an incomplete backup and attempting to leverage ...
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59 views

Cracking Viginere Ciphers using same-length key used twice

Assuming I had two ciphertexts which were encrypted using the same key that has the same length with the ciphertexts. (However the keys didn't have any repetitions or features that would assist in ...
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33 views

Advice on software to be used

I have the following problem: I have a series of numbers (6, 9, 6, 2, 6, 3, 4, 7, 3, 5, 4, 3, 2, 5, 8, 6, 2, 6, 3, 4, 5, 8, 7, 8, 2, 7, 7, 4, 8, 3, 3, 2, 8, 8, 4, 3, 2, 4, 7, 7, 6, etc.), each number ...
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How to perform a known plaintext attack?

I have got the following documents: (1) The plaintext (2) The ciphertext (3) The python program used to encrypt/decrypt the text My goal is to find the key that was used to encrypt the plaintext into ...
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Can I and How Decrypt this Online

Although I had a security course in school a long time ago, I am effectively new to cryptography. I have an encrypted text, the encryption key of 44 characters, the encryption method, (Fernet, which ...
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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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38 views

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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Identify the value of the plaintext from a noised expression

Having the following instructions: Using Paillier encryption to encrypt $m$. So, we get $Enc(m)$ Multiply $Enc(m)$ and $A$ to Get $C$. So, $C = Enc(m).A $ Decrypt $C$ using Paillier Decryption ...
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Confused in selecting the encryption method for mobile number and email encryption

I'm new in cryptography and I'm developing a mobile app that gets user_name, E-mail ID, and ...
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What measures can I do to prevent decryption of encrypted data?

This is entirely hypothetical, I'm working on securing some data and I want to make sure we do this properly. If I have a list of information which is encrypted (say, using a 256 bit encryption key) ...
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Unable to determine plaintext from ciphertext

Given the letter-number cipher: a=00, b=01, c=02, etc., encrypt the word 'hi' and decrypt its ciphertext using RSA. The public key is (5,35) and the private key is (29,35). I know that 'hi' is ...
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Finding a dataset to benchmark cryptographic algorithms

I’m planning to compare cryptographic algorithms in terms of encryption/decryption time, memory used etc. and for that I’m in need of a standard dataset consisting of plaintexts of different bit sizes ...
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Three Pass Protocol Question!

Alice and Bob have agreed to use the Three Pass Protocol. p=1009 Alice chooses the encryption exponent e_A = 101 Bob chooses the encryption exponent e_B = 209 Now Alice and Bob send three ...
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I know my passphrase. I don't remember specifically how I entered it

First if this is the wrong place to post this please forgive me. I know my passphrase. I don't remember specifically how I entered it. ex. If the phrase is "The house at the end is blue and white. I ...
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How to recover deleted-recovered windows efs-encrypted files?

I'd some EFS-encrypted files on a HDD which were deleted unintentionally. I used a data recovery software to restore them, but afterward, windows does not recognize those recovered files as encrypted ...
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How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...