Linked Questions

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2answers
562 views

Decrypting ciphertext that is missing a block

In the AES encryption, suppose that the key is known. The ciphertext is also known except for a block of the same size as the key. For example, the adversary knows $k, c_0, c_1, \dots, c_{n - 1}$; ...
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3answers
2k views

Key length requirement in a simple XOR implementation

I don't have much previous experience at all with cryptography, this is pretty much the first time I've tried anything similar. I'm trying to implement an extremely simple XOR encryption system in ...
3
votes
2answers
314 views

Decrypting two XORed compressed messages?

If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we ...
1
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1answer
722 views

What does it mean when two encrypted files, encrypted with the same method but with different keys, when xor'd together, produce a repeating pattern?

Let's say I have fileA and fileB, both encrypted somehow, but in the same method with different keys. If I xor them together, they will make a repeating pattern of 32 bytes length. What does that say ...
2
votes
1answer
1k views

problem with “one time pad” [closed]

I am a french student and I read the post on the forums (How does one attack a two-time pad (i.e. one time pad with key reuse)?). I need your help if possible. I 'm 11 encrypted messages , all ...
1
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3answers
296 views

What are the vulnerabilities of this OTP-like system?

I've read that a OTP is only perfectly secure if the key is perfectly random, and the pad is never reused. If you encrypt documents using two keys, where one is random but stays constant for some ...
3
votes
3answers
752 views

What are some real world examples where one time pad encryption is used or can be used?

I understood that One-Time Pad (OTP) encryption ensures perfect secrecy. However, I couldn't find any real-world examples where the OTP is used. Also, which are some real-world examples where it won'...
0
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1answer
640 views

File using same key on XOR cipher. Using CBC [closed]

I have some files that are encrypted using an unknown key and it's using the CBC method to encrypt the files. When I XOR two files together the first two bytes are always the same, but different for ...
1
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2answers
496 views

Little problem with Vernam Cipher

We have got a task with the following content: Given is a language with 3 letters: A, B, C. The binary expression is: A = 000, B = 1111 and C = 0011 Two ...
1
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1answer
295 views

How to attack a two time pad if the plain text is randomized?

As an extension to this quesiton, or this one how would you go about attacking a re used pad if the plaintext was randomized before being encrypted? ...
3
votes
0answers
771 views

One-Time-Pad with key-reuse: Faster way of decrypting?

I know there are already of few questions about this and I'm working with the advices that were given but I still doubt my approach is the fastest, so I'd really appreciate if you helped me find a ...
1
vote
2answers
202 views

Modification of vigenere cipher cryptographically secure?

After looking for ages online for a python implementation of the Vigenere cipher, and finding few, I decided to implement it myself. After ironing out all of the flaws, it's now a working (and secure) ...
1
vote
1answer
400 views

Analyzing/Breaking a strange One-Time-Pad

In my assignment there is a bonus question: It asks me to decrypt a file which has been encrypted using an One-Time-Pad. But the ciphertext seems to contain english word fragments and other parts ...
2
votes
3answers
607 views

Does ChaCha20 counter actually increment through iterations?

RFC defines: state = constants | key | counter | nonce Suggested on multiple places is to set counter to 0 or 1. It is still ...
1
vote
2answers
338 views

How to know the difference between two ciphertexts without key stream in stream ciphers [duplicate]

If I have two cipher texts lets say $C_1$ and $C_2$ of the same length encrypted through stream cipher technique using the same keystream. Let's say they are: $$C_1: \texttt{96 C6 A1 08 E7 F2 33 3B ...

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