Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [one-time-pad]

A cipher which uses a different encryption key every time, as long as the message. The key is XOR'ed with the message to render the cipher text which can then be XOR'ed with the same key to get the plain text.

A cipher which uses a different randomly-generated, pre-shared key stream of the same size as the message. Commonly the plaintext is XOR-ed with the key stream to generate the ciphertext. Similarly XORing the ciphertext generates the plaintext.

Modular addition / subtraction may be used instead of the XOR operation. As long as the key stream is perfectly random, the OTP is considered provable secure; in practice the stream is never perfectly random.

Another issue with the one-time-pad is that the size of the key stream must have at least the same size as the message. This makes it impractical for many use cases.

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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 original file are identical. Of course nothing can…
Dreamspace President
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Are one time pads still used, perhaps for military or diplomatic purposes?

The ME-600 key generator was developed in the early 1990s for generating truly random one time key streams. That's not exactly World War 1 or 2. I don't know how long it was used, or whether it still is. Now with quantum computing on the horizon,…
Paul Uszak
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One Time Pads and "Bit Flip" Attacks

One Time Pads and Vulnerability to "Bit-Flip" Attacks: I've seen it in this group, and apparently there are a (small) number of voices on the 'net opining that those relying on OTP are essentially "amateurs" (or otherwise oblivious) to the…
F1Linux
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Why is mod calculation necessary in a one time pad encryption?

Considering the English alphabets to be encrypted why is the computation of mod 26 necessary after adding the pad to plain text. Is it just that it adds to another level of encryption or is it used so that two letters may end up with the same symbol…
GunJack
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Can we use numbers as a pad in the Vernam cipher - why or why not?

I was playing with the Vernam cipher on some online converter. But when I tried to encrypt my message string with numbers, it remained unchanged. Moreover, it was ignoring numbers and was encrypting as some alphabet appears in the key. So, can…
Mashhood
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Perfectly secret variable one-time pad

Consider a variable one-time pad, that is, $\mathcal{M}:=\{0,1\}^{\leq \ell}$ is the set of plain text. Now, this scheme is not perfectly secret, since you can take two plain text of different size, say $|m_1| = 1, |m_2| = 2$ and considering a…
Lug322d
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Can I securely refill a one time pad over the same connection?

If you have a channel where you are communicating using a one time key, is it possible to receive additional key over that same connection without compromising security? Naively sending it through the same encrypted channel would of course consume…
Filip Haglund
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Compute OTP key if set of plain texts and its set of cipher texts are known

Given a set of plain texts $P \subseteq \{0, 1\}^n$. Assume we know the corresponding set of cipher texts $C \subseteq \{0, 1\}^n$ produced by applying one-time pad with an unknown key $k \in \{0, 1\}^n$. Question: How to compute $k$, based on $P$…
curiouscupcake
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One time pad - how is the difference in length between the plain text & the OTP handled?

Since OTP have to be agreed upon in advance, they may be longer than the plaintext. So in this case, how is the encryption done? Is the OTP truncated to the same length of the plaintext before encrypting or is some kind of padding used - how does it…
user93353
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Viability of using One-Time-Pad + HMAC in low-volume IoT communications

In the Internet-of-Things world there are certain applications that produce very low volume communications. For example reading a water meter once every hour comes to mind. If the reading could be encoded as a 32 bit unsigned integer and adding a 24…
Markus Juenemann
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One-time-pad encryption

As we know, intercepted ciphertext created by a one-time pad only reveals the length of the message. That is the only information the attacker can get since this ciphertext is unbreakable without the key. I understand that for a file 1GB in size we…
user42581
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What are the correct order of operations for One Time Pad Cipher?

According to Wikipedia the One Time Pad Cipher is unbreakable. On the Wikipedia page it explains how to perform this simple encryption process by hand. For the encryption it adds (+) the message and the key and then modulo by 26. For the…
J. Doe
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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 faster way. What I want to do: I have 2 encrypted…
Neph
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Implementing a one-time pad without binary?

I found a program which takes a purely alphabetical message, converts the letters to their ASCII values and combines them with the ASCII values of an alphabetical key (wrapping around when it gets to Z). (The key being used is fully random and is…
Caleb Paul
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Can you use repeating numbers like $\pi$, and $e$, as the Key to OTP ciphers?

Since $\pi$ and other numbers repeat could you use them as a OPT key. Ex: a 5 character message is sent and the first 5 digits of $\pi$ are used. after that the next $X$ number of digits are used and so on. from what I understand of Cryptography…
Tyler G
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