Questions tagged [pen-and-paper]
The term "pen and paper" can practically be interpreted as "using no tools like electronic devices", since it targets cryptographic functions, schemes, and procedures which can be handled by humans who have nothing more available than the option to use manual writing. So, "pen and paper" can also mean "pencil and post-it", "chalkboard and chalk", "wall and spraycan", etc.
3
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2answers
130 views
Efficient pen-and-paper calculation of the Galois Field multiplication?
I have been reading on multiplication over GF for the Inverse Matrix Step in AES, and I feel like converting the hex numbers to binary, multiplying them and then doing the modifications required for ...
2
votes
3answers
185 views
What is the largest key size that could be carried by a shuffled deck of playing cards?
If you are carrying a standard 52 card pack of cards (no jokers) what is the largest key size, or the amount of data the cards can hold?
Without the cards being marked or distinguishable from an ...
4
votes
1answer
196 views
Are there any strong manual ciphers? [duplicate]
Are there any strong manual (i.e. performed only by pen and paper) ciphers for practical use?
It should be:
no less strong than modern cryptography algorithms used in computers,
at least relatively ...
2
votes
3answers
205 views
Encrypt password for oneself on paper
Assume the following:
You have to encrypt a file (ZIP-file) containing import information. This file should be password-protected and you want to leave yourself the password encrypted (on paper, ...
1
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0answers
57 views
Authentication over the phone?
Are there any known good methods of performing authentication over the phone in a way that's not susceptible to replay attacks?
The specific scenario that comes to mind is having an automated call ...
10
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0answers
209 views
Is there a pen-and-paper way to securely share a secret via public key encryption? [duplicate]
We have several questions tagged pen-and-paper talking about encryption, hashing, signing, etc. but no question asks about exchanging a secret via public key encryption in a secure way.
Does any ...
1
vote
1answer
56 views
While encrypting what can happen between words
From some time I am working with "pen and paper" encrypted text.
Keys are not known, algorithm is not known.
I managed to find simple algorithm and key that seems to be nearly perfect.
Nearly perfect ...
7
votes
2answers
370 views
Manual secret sharing?
What are feasible options for an equivalent of Shamir Secret Sharing using small tables, preferably usable with pen-and-paper? We want to share a secret $K$ into $n\ge2$ shares, so that $m$ shares ($2\...
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0answers
74 views
What is a simple way to “2 out of 3”-secure a mnemonic phrase without computers? [closed]
I'm working on a safe way to store a mnemonic key.
It's 24 words long.
Each word is 11 bits of entropy
I want to store it in 3 locations
One plate should not allow you to unlock the code
Two plates ...
0
votes
1answer
120 views
Whats the most secure way to encrypt a string without the use of a computer? [duplicate]
I want to decrease attack surface by preventing the plaintext string or encryption key from ever being typed or otherwise entered into a computer. Ideally the decryption key would be something that ...
7
votes
2answers
450 views
Is there any quantum resistant pen-and-paper or mind cipher?
I know about VIC and Solitare but as I understand they are not quantum resistant ciphers. Is there any quantum resistant pen-and-paper or mind cipher?
2
votes
0answers
140 views
Pencil & paper spyfall [closed]
As a followup to previously asked question: What's a good strategy for the game "spyfall"?
I was wondering if we could build a pencil & paper solution for the problem resistant ...
2
votes
2answers
477 views
Apply a permutation cipher by hand
I did the following problem from the book "Cryptography Theory and Practice" as
I am doing some self-study.
Problem:
a) Suppose that $\pi$ is the following permutations of the set $\lbrace 1,\dots,8 ...
-2
votes
1answer
471 views
Given alphabetic key and cipher text decrypt the cipher text [closed]
I've been at this for a while. I've been given two things
Ciphertext = bsaspp kkuosp
Key = rsidpy dkawoa
Now seeing the domain that the characters are in. ...
0
votes
1answer
225 views
Is there a password hash function with a human component?
Sort of Related: Is there a cryptographic hash function that can be performed with pencil and paper?
One problem with hashing passwords is that the attacker has more of everything it seems. More ...
9
votes
1answer
1k views
Simple digital signature example that one could compute without a computer?
I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms.
There is a great question ...
9
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1answer
2k views
How hard is the Solitaire cipher to crack?
Assuming your deck is completely random and that it is not retrivable, how hard would it be for a casual person to decrypt a message encrypted with the Solitaire cipher?
1
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0answers
88 views
Fast mental encryption algorithm? [duplicate]
Are there any algorithms that exist to encode messages written with pen and paper such that the messages can be encrypted/decrypted mentally? For example, Bob thinks of the text "This is my plaintext",...
3
votes
1answer
187 views
Do hand-based hash functions / MACs exist?
Is there research on a hash function or a MAC that can be executed without computers?
I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using ...
1
vote
1answer
78 views
Are digital signatures using preprocessed paper pads possible?
My idea was, given that a computer could produce some sort of lookup tables on paper, could then a human use those lookup tables to create a system for digital signatures?
This was really an idea for ...
0
votes
1answer
206 views
Which algorithm can be performed by humans?
Suppose I want my grandmother to perform encryption without any help from a computer, and she must encrypt the word 'HELLO' for me.
I could ask her to instead of typing the real keys, that she always ...
6
votes
3answers
929 views
Good challenges for a crypto competition for teenagers
I'm holding a cryptography workshop for teenagers (around 16 years old) at our university. As part of the workshop, I'm planning to run a crypto competition with prizes: there will be different tasks, ...
0
votes
3answers
440 views
Would it be possible to create a game where one would need to decrypt a simple encryption?
This might sound pretty weird, but I was thinking of a game a person could play alone with a pen and paper.
I got this idea where the person would write a random four letter string on a paper, and ...
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votes
1answer
115 views
Assuming that we had a way of finding primes, could RSA be used without computers?
I once asked a question "Would RSA make sense if we used no computers?". The answer was negative, because finding primes that would make secure keys would prove too hard. Assuming that we had found ...
5
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1answer
566 views
Is there a cryptographic hash function that can be performed with pencil and paper?
Imagine I'm signing up for the 99th new web site this month.
I somehow take my secret key (which I have written down on a card in my wallet) and the domain name of the site and feed them both into ...
9
votes
1answer
271 views
How would you encrypt-then-MAC when using pen-and-paper and a Caesar cipher?
I'll probably get shot for asking this, but I've got some kids (aged 8-10) in my neighbourhood that I've been showing/teaching the simple pen-and-paper Caesar cipher and they're successfully playing ...
8
votes
2answers
919 views
Would RSA make sense if we used no computers?
I was recently wondering - would RSA be useful if we brought it to, say, medieval times? Could you choose the keys so that you could encrypt/decrypt messages quite easily, but factoring the private ...
4
votes
1answer
774 views
How would I make a secret notation alphabet more secure?
Disclaimer: I was looking for a place to ask this question on SE and this site seems to be the most fitting. If this question doesn't belong here, feel free to redirect me.
Just out of boredom and ...
19
votes
5answers
3k views
Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?
I am looking for a cryptographic hash function that can be computed by a human using only paper and pen without ever leaking any information about the plaintext on the paper.
The cryptographic hash ...
5
votes
1answer
686 views
Toy encryption system that provides “hints”
I'm looking for a toy encryption system that has a specific property that when decrypting it with a key that is close enough to the key used in the encryption, it will produce some of the original ...
8
votes
3answers
456 views
Pen-and-paper one-way function for externally-anonymous survey
When conducting surveys, an Administrator might send an Enumerator to survey a Respondent. For "sensitive" questions (e.g. about embarrassing behavior), the Respondent may be fine with the truth being ...
13
votes
2answers
4k views
Is there any strong enough pen-and-paper or mind cipher?
Some ciphers are talked about at “Is there a secure cryptosystem that can be performed mentally?”, but (at the time of writing) I don't see an answer.
Are they strong enough, or are non-computer ...
8
votes
2answers
1k views
Toy hash algorithm that can be broken
I'm looking for a toy hash function, where the idea is to have high school students break (i.e. find a collision) a hash function by hand, in order to teach them how one way functions and hashing ...
1
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0answers
307 views
computing inverses in truncated polynomial rings manually for NTRU encryption [duplicate]
Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)?
As an example from the tutorial:
Example. Take $N=7$, $q=11$, $a=3+2X^2-3X^4+X^6$. The ...
2
votes
1answer
640 views
Can you help me understand how RC4-52 is done using pen-and-paper?
I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher. However, RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand.
...
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votes
1answer
264 views
Can someone tell if my Hand Cipher is secure? [closed]
In easy steps, this is how it works:
Convert txt to numbers. mod 1-26.
Generate random numbers (by my other cipher) equal to plain txt.
Write random numbers under txt numbers.
Like this:
...
41
votes
5answers
8k views
Is there a secure cryptosystem that can be performed mentally?
I, myself, do not plan on getting into a situation where I would be unable to use a computer in order to communicate securely. However, I can think of many practical situations in which mental ...
42
votes
7answers
22k views
Is there a simple hash function that one can compute without a computer?
I am looking for a hash function that is computable by hand (in reasonable time). The function should be at least a little bit secure: There should be no trivial way to find a collision (by hand). For ...
