# 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 ...
105 views

### 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 ...
79 views

### 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 ...
53 views

### 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 ...
90 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 ...
1 vote
52 views

### How to decode "SELF-SHIFT" cipher?

I try to use the function $$C_i=E(M_{2i}, M_{2i+1}) = (M_{2i} + M_{2i+1})\bmod 26.$$ to encode English text. For example, Plaintext: The quick brown fox jumps over the lazy dog. Regrouped Text: TH EQ ...
1 vote
71 views

### What is the best way to save ChaCha20 Nonce in Cipher-Image BMP file?

I have a question about ChaCha20. As far as I know ChaCha20 is a cipher algorithm that uses 4 inputs: Key (secret) Constant (not secret) Block Number/Counter (keystream block number) Nonce (random ...
1 vote
78 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 ...
1 vote
34 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 ...
1 vote
41 views

### 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 ...
1 vote
305 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?
1 vote
64 views

### 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 ...
1 vote
100 views

### 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 ...
1 vote
77 views

### 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 ...
1 vote
37 views

### 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 ...
1 vote
166 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 ...
1 vote
81 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 ...
1 vote
53 views

### 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 ...
1 vote
164 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: ...
1 vote
103 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 ...
1 vote
247 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 ...
48 views

### Discrete Logarithm Based algorithm

The private (secret) key in DL (discrete logarithm) based algorithms is uniformly selected from the group Zq*. This private key is then used to compute the public key. Could the opposite be done, for ...
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### RSA / AES issue : Decryption

I perform the following commands because I need to decrypt a file -encryption key file- (which is longer than module): cat key.enc | base64 -d > encryptedrawfile.txt openssl rsautl -decrypt -inkey ...
36 views

### calculate a tag of CBC-MAC

with a block cipher having a 256-bit key and 128-bit block length to MAC a 1024-bit message. How many evaluations of the block cipher will be performed to calculate the tag? [Assume there is no ...
62 views

### RSA: decrypting short message with a different public key

I am having a hard time understanding what I have come across using RSA-textbook. So I have: e = 3 as an exponent a VERY long public key N of 1991 bits (clearly useless trying to factor) a very short ...
34 views

### Decrypting a polyalphabetic cipher

I'm currently trying to crack a ciphertext with three rotating substitution ciphers. I've tried dividing the cipher up into three parts and do text frequency analysis since I know the language but no ... 22 views

### Are there any schemes for support time-limited decryption that are not based on P2P or TTP models?

Time-lock encryption is a method to encrypt a message such that it can only be decrypted after a certain deadline has passed. This sounds like time-lock decryption. I was wondering if the inverse with ...
64 views

### RSA: is it possible for the cube root attack to fail even if e=3?

I've came across an example where the e value is three but no matter what tool/script I try, I can't decrypt it. I'm wondering if the ciphertext and n is super super large, is it possible to crack it ...
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### Don't know how to approach this problem, or where to start. Finding an adversary to a hiding and binding game

I have this problem: I also have the python version of this problem here: ...
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### Teaching AI a cryptogram and asking it to solve a similar cryptogram on its own

Say that 1 cipher and another are known to hold some form of correlation. Would it be possible to teach an AI one language through the training of a model and allow it to make make predictions on ...
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### Example of exchanging information

I am searching for a simle model that can simulate the following procedure. Suppose that $i$ and $j$ are two agents that each one obtains her state dependets signal $s_i(\omega)$ and $s_j(\omega)$. ...
118 views

### Vigenere Decryption with key length

I have a question. If I have 2 ciphertexts given and the same key has been used on both. They key lenght is the same as the plaintext and cipherrtext length. How do I decrypt them and find the key. So ...
50 views

### 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 ...
82 views

### 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 ...
37 views

### 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 ...
32 views

### 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 ...
88 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 ...
42 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: ...
56 views

### 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 ...
68 views

### 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. ...
323 views

### 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 ...
87 views

### 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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### 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) ...
42 views

### 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 ...