Linked Questions

-4 votes
1 answer
4k views

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

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 a key twice make it insecure. (in One-time-pad). EDIT: I have ...
Alvin's user avatar
  • 55
0 votes
0 answers
2k views

Stream Cipher : Never use stream cipher key more than once [duplicate]

Possible Duplicate: Taking advantage of one-time pad key reuse? How does one attack a two-time pad (i.e. one time pad with key reuse)? Denote C is cipher text, m is message, and PRG(k) is a ...
hqt's user avatar
  • 109
1 vote
2 answers
1k 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 ...
Tahir's user avatar
  • 33
0 votes
1 answer
202 views

Why do we need to use PRGs to generate random numbers for a one-time-pad? [duplicate]

I'm looking at the following idea for using a symmetric key to encrypt multiple messages (back & forth communication between Alice & Bob). It can be summarized as follows: Both sides agree ...
Foobar's user avatar
  • 247
1 vote
0 answers
308 views

Decrypt a message which is encrypted using XOR? [duplicate]

This is a puzzle asked in a contest. Given that encryption , decryption happens as per following rule/code: ...
john's user avatar
  • 111
0 votes
0 answers
237 views

RC4 using a key without nonce's or IV's [duplicate]

I'm researching RC4 and I am trying to recreate a condition where RC4 is crackable. However I can't quite find the article/resource I need to find the weakness for an implementation like this (python):...
Don's user avatar
  • 101
1 vote
0 answers
202 views

ChaCha20 - How confidentiality is lost if reusing nonce? [duplicate]

I read that (key, nonce) pair should be used only once for encryption of a message. My question is how confidentiality can be lost if two peers using a shared key use same (key, nonce) pair to encrypt ...
Manjeet's user avatar
  • 11
1 vote
0 answers
144 views

How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
firehorse's user avatar
77 votes
3 answers
90k views

How does one attack a two-time pad (i.e. one time pad with key reuse)?

My question might appear the same as the question Taking advantage of one-time pad key reuse?, but actually I did read all the answers and none of them helped me with the details I need. I am new to ...
Samer Makary's user avatar
19 votes
9 answers
6k views

Is one-time pad encryption vulnerable when near identical data is sent many times with different OTP?

Let's assume a text file that grows at its very end but is otherwise not edited. We now have 100 transmissions of this, but OTP-encrypted (different OTP each time, of course). The first 50% of the ...
Dreamspace President's user avatar
13 votes
5 answers
4k views

What is wrong with XOR encryption with secure PRNG?

Suppose I want to encrypt a message with a password. Couldn't I just XOR the bytes with bytes from a cryptographically secure pseudorandom number generator (CSPRNG) with seed being the password, or a ...
newb's user avatar
  • 141
20 votes
1 answer
24k views

Why must IV/key-pairs not be reused in CTR mode?

Many sources mention that IVs must not be reused with the same key in CTR mode, for encrypting 2 different pieces of data, because that totally destroys security - but I haven't found an explanation ...
Dexter's user avatar
  • 647
13 votes
6 answers
9k views

Which cryptography technique does not increase the size of the plain data?

I want to encrypt some data(text/voice/video) but it is essential that the size of the cipher data remains the same as the plain data. Which techniques can I use, and how secure are these techniques ...
Jay's user avatar
  • 369
8 votes
3 answers
3k views

What should the nonce value be for client-side encryption?

I am using the following chacha20poly1305 Rust library to encrypt some data in a desktop application. The user provides the key, which never leaves their device, to locally encrypt some data, and then ...
Rima Salloum's user avatar
1 vote
3 answers
2k views

Does knowing common prefixes help crack blowfish?

I have strings that are if the form: {static data}{changing data} The beginning static data part is around 20 characters and is common to all strings. The last ...
ICR's user avatar
  • 157

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