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.

270 questions
751 views

### Is the Vernam (One Time Pad) cipher useful? [duplicate]

By profession I’m a programmer. I don’t know a lot about how cryptographic algorithms are implemented, or even where I’d start, and I don’t know about cryptanalysis, but as I work in Blockchain ...
1k views

### Non-malleability of One Time Pad Encryption

Can anyone explain to me what the following means in relation to one time pad security? It's from the book 'Serious Cryptography: A Practical Introduction' and my logic knowledge seems to have lost ...
172 views

### Can I use a key twice if the message is longer than the key in one-time pad?

I have a key for a one-time pad. Its length is 512, and I have a message to encrypt whose length is 600. Can I reuse the first 88 chars of the key to encrypt the end of the message? The key is still ...
2k views

### Can one claim that AES has perfect secrecy for a key size and message size of 128 bits?

While looking at this question I discovered the following here (question 5), and wanted to ask it as a separate question. Alice knows that she will want to send a single 128-bit message to Bob ...
264 views

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 ...
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### One Time Pad change by third party?

I was reading about how a one time pad output can be changed by a third party without the receiving person realising. Surely the output at the other end would be garbage? Also, could you not ...
243 views

### Can OTP be used with RSA

Considering that a PKI has already been established, why can't we use RSA to send the One Time Pad instead of using AES? It makes sense to me since: A trusts the CA which is providing the identity ...
369 views

### Given a list of ciphertexts, how to identify the ones that used the same key for encryption

I'll start off by saying I am not looking for solutions here, just suggestions on how to proceed. I am given a short list of ciphertexts (20something) and I know that one of the ciphertexts has been ...
432 views

### Can I generate OTP secrets by using a hash?

Since I learned about one time pads in last security lecture, I'm quite fascinated how easy the concept is, but how it still is absolutely safe. Learning from implementing a multi time pad attack, ...
719 views

### Why in one time pad must the key distribution to be truly random

One time pad required a truly random key. Why canwt it be a psudo-random key? For example, if the key distribution is that for each bit the probability to get 1 is 0.6 and the probability to get 0 is ...
121 views

### is the perfect secrecy of one time pad dependent on the xor randomness preserving property?

Is the perfect secrecy of the one time pad dependent upon the xor "randomness preserving" property (xoring a uniformly random string with any string yields a uniformly random string)? I have seen ...
224 views

### Including the next random One Time Pad as part of the encoded message?

I've tried to do something very simple here, which is to encrypt a message with a one-time-pad (OTP) and include the next OTP as part of that same encrypted message. i.e. The first message consists of ...
262 views

### Transferring Encrypted One-time pad over the internet

I was working with one-time pad, and as I understand , for one time pad to be 100% secure a key shouldn't be repeated. So assuming Alice and Bob have to exchange messages over the network secured over ...
272 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 ...
123 views

### Stuck on finding M2 knowing M1 in One Time Pad

Lets say I have a plaintext M1 and a plaintext M2, I know both the ciphers C1 and C2 from these M1 and M2. But from M1 I also know a piece of M1 or maybe even the whole text. And I also know C1 XOR C2 ...
325 views

### Is a one-time pad secure if the encryption method is not?

(The following situation is hypothetical.) I need to communicate something securely and I have decided to use one-time pads. I am going to be using human genes as the source of the OTP data (this is ...
217 views

### Generating OTP using Digital Dead Drop

I've had a thought and I'm wondering if this would be a useful way to devise and distribute a one-time pad. It relies on a digital dead drop and a hash function. The digital dead drop could take a ...
233 views

### One way communication with forward secrecy?

Is it possible to achieve forward secrecy using a one way communication channel with pre-shared secret? I have a setup where I need to send some information across a unsafe channel between server A ...
223 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 ...
221 views

### Is creating an OTP of a key to some data a secure secret sharing scheme?

Suppose I have some data that has been encrypted with a known, secure algorithm and a key k. I want to distribute "pieces" of the key to n of my colleagues, and only be able to access the data when ...
131 views

### Multi-Embedded Xor for Perfect OTP

I am looking for a perfect OTP design, so let's see if this design is good. There are 2 issues when it comes to a good OTP system, the key and the plaintext, we will use XOR as cypher: If the ...
228 views

### 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 ...
218 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? ...
802 views

### Is Poly1305 an information-theoretically secure MAC?

I have heard some people say that the Poly1305 authenticator is a "nuclear" MAC i.e. it is information-theoretically secure. After reading the paper I see it is based on the Wegman-Carter MAC which is ...
78 views

### Perfect Deniability of a MAC Protocol

I proposed an idea of Perfect Deniability of a MAC I tried to come up with a protocol that satisfies those security requirements as well as the normal security requirements of a MAC One-Time MAC ...
207 views

### Perfect Deniability of a MAC

Overview One feature that is often underlooked of the One-Time Pad is its perfect deniability. i.e. If Alice sends a message to Bob that is seen by Eve then if Eve later goes to Alice with the ...
13k views

### Are one-time pads crackable in theory?

I've been taught that one-time pads are the only perfect encryption, since the only way to recover the message is by knowing the key. For example, for a target bitstring of 100 bits, I cannot scan ...
164 views

### Attacks on Biased OTP

I know that a perfectly random unbiased and not reused OTP cipher is perfect. An OTP under cryptanalysis has a very strong bias (up to 30 % of symbols are represented by 5 out of 255 possible symbols) ...
614 views

### Does humanly verifiable one time pad authentication exist?

Firstly some predicates:- Sufficient hardware generated one time pad key material. No pad reuse. Messages of 160 characters length (think Twitter). 28 characters only in use (A-Z, space and full stop ...
525 views

### How to Encrypt WAV file using One-time Pad Algorithm

I am confused about what parameters that I must encrypt on a WAV file. If the file is text, it's only required to convert the character to ASCII code; if picture, just encrypt the pixel. What is ...
146 views

### Hiding the metadata of a one time pad message by encrypting the next key

here is an idea that I feel has some big flaw I can't put my finger on. The scenario is: Alice will go overseas for 5 days and will hopefully retrieve some information and send it back to Bob. She ...
707 views

### How to decrypt a code with a given OTP key practically [closed]

For practicing purposes I obtained some cipher and an OTP key. Now my task is to decrypt the cipher using this key. Both files are .bin files and when I open them with TextEdit there are a huge ...
195 views

### How could consumer level OTP + QKD over the internet ever be practical?

Please note, I am in no way questioning the future usefulness of quantum key distribution (QKD) in certain applications. I have no doubt it will prove useful for large banks, and in certain military ...
338 views

### Using One Time Pad and RSA compared to using only One-time Pad

Here I implemented One Time Pad first for only one time and then I used RSA algorithm to encrypt the message. For RSA algorithm, I pick p = 2143 and q = 3257 value which does not share any common ...
515 views

### One Time Pad Alphabet Size

I am building a simple one time pad system using a low-power microcontroller to XOR a stored key with an input string, and vice versa. Due to several internal factors, it's very preferable for the ...
93 views

### Is this cryptographically secure?

If I securely (manually) give/put two computer (Alice and Bob) a secret key, they can securely communicate to each other (?) Alice encrypt a message (maxlength = secret key length) and send it to Bob,...
74 views

### Decrypt Messages With Reused Pad [duplicate]

I have 2 messages which have been encrypted using the same pad. I know that if i xor these 2 messages together the key falls out. I am confused in how to figure out what the 2 messages are from the ...
119 views

### 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 coonection without compromising security? Naively sending it through ...
117 views

I had to decrypt two book passages from different books which had both been encrypted using the same one-time-pad, and automate the process at that. I've found a few explanations of how this could be ...
154 views

### Is there a name for encrypting a decimal number using a one time pad?

I asked a question somewhere else on stack exchange and had to put something like "using the numerical one time pad the user can create their encrypted message by hand". Is there a better way of ...
100 views

### How to detect if n long messages have encrypted with the same one-time pad?

I have a slight idea on what the attack would be. But my question is: how would one detect if n long messages (n>5) have been encrypted with the same one time pad, K?
58 views

### What to do with this specific scenario of a key reuse [duplicate]

I am brand new to the world of cryptogrophy. I am trying to decrypt a many-time-pad. I understand the methodology of using the XOR to get the messages. C1 XOR C2 = M1 XOR M2 Now my question lies in ...
898 views

### Would using a one-time pad multiple times with some conditions be safe?

I understand why |one-time pad|=|message| using a normal one-time pad, but I don't understand why for perfect secrecy it must alway be that |key|>|all messages exchanged|. What if, for example, I had ...
561 views

### Does one time pad randomness help brute force attacks?

I understand that attempting to brute force the decryption of a message coded with a one time pad results in generating every possible message. The Wikipedia example is that decoding "EQNVZ" with key ...
693 views

### Why is pseudorandom OTP (P-OTP) IND-CPA insecure

My lecture notes state that P-OTP is IND-COA but not IND-CPA insecure. I understand IND-COA secure, assuming PRG is secure, as that is the whole point of a OTP, but why is it IND-CPA insecure? Surely, ...
2k views

I hope, as we know intercepted ciphertext created by One-time pad encryption tells only length of the message, and that is only information attacker can get since this ciphertext its unbreakable to ...
104 views

### Split encryption into two steps

Are there two step encryption systems that - given the same plain text - support choosing two keys ($k_{A_1}, k_{A_2}$) for a first encryption so, that you can calculate another pair of keys (\$k_{B_1},...
220 views

### Non malleable Encryption scheme

I know that one time pad is malleable. Can you give me an example of an encryption scheme which is non-malleable?