Newest 'pen-and-paper' Questions

1

vote

0answers

26 views

What cipher requires the full message to solve

I am working on a scavenger hunt and wanted to encode a clue in a cipher that requires the full message to decipher. My goal in this is to prevent players from predicting the result before obtaining ...

decryption pen-and-paper

asked Nov 12 '20 at 22:41

Jackson Medina

111 bronze badge

0

votes

1answer

34 views

Where can I find information on the speed of basic hand-operated ciphers?

I have a science fair project coming along, and I'd like to focus on a basic cipher (something simple, like a substitution cipher) and how I could make a similar system that would be about equally ...

pen-and-paper

asked Nov 6 '20 at 12:57

T-bone

12 bronze badges

1

vote

1answer

149 views

The most secure hand cipher in 2020

I found this thread from 2011: Is there a secure cryptosystem that can be performed mentally? Are there new secure hand or pen-and-paper ciphers in 2020? (I know, that hand ciphers are not as secured ...

encryption pen-and-paper

asked Nov 1 '20 at 12:14

TheDummy

412 bronze badges

0

votes

2answers

75 views

Text cipher option that can decrypt the same ciphertext to two DIFFERENT and DESIRED outputs given DIFFERENT keys (and/or alphabet)

I have a pen pal that I discuss with. In our latest discussion it was proposed to write a short message that is ciphered and have the other one find what it is, given some clues. I would like to ask ...

encryption stream-cipher pen-and-paper affine-cipher

asked Oct 18 '20 at 22:29

Lucian Viorel

11 bronze badge

1

vote

0answers

48 views

Is there a name for strong human-computable encryption schemes? Are there definitions for “human-computable”?

Background: There is some interest in encryption schemes meant for humans to perform without computational aid. (Relevant questions here, here, and here.) People often cite the VIC pen-and-paper ...

encryption classical-cipher pen-and-paper

asked Jul 11 '20 at 16:46

lynn

1234 bronze badges

0

votes

0answers

44 views

Easiest Simple-Key Hand Cipher

I need a little help choosing the right cipher. I'm looking for a simple pen-and-paper cipher that is easy enough for kids to quickly decode by hand, preferably using an alphanumeric decoding table ...

pen-and-paper

asked May 9 '20 at 1:11

harvest316

101

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0answers

58 views

What is the strength of this machine? [closed]

This machine has the stator, with one half of the alphabet, and three rotors with replications of the other half in different order and repeated twice. There can have two rotors in use or the full ...

encryption classical-cipher pen-and-paper

asked Sep 30 '19 at 15:49

Neo1009

2401 silver badge8 bronze badges

0

votes

2answers

77 views

Is there a way to easily encode a message without a computer on either end?

I enjoy making notes and passing them to my friends, and I also like making them encrypted for no reason. My friends enjoy it too, but it's a bit annoying to use the Caesar cipher for everything ...

algorithm-design classical-cipher pen-and-paper

asked Sep 23 '19 at 3:51

Just-her-4-fud

33 bronze badges

7

votes

1answer

196 views

Pen and Paper Authentication

What is the best way to prove that you wrote the encrypted message on a piece of paper? As most of us know, many conspirators have died because of false message implants, Mary Queen of Scots, for ...

authentication classical-cipher pen-and-paper

asked Jun 27 '19 at 21:18

Neo1009

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1

vote

0answers

48 views

Strong and Practical Hand Ciphers [duplicate]

I know monoalphabetic ciphers are weak, but my message recipient doesn't like taking the time for the decryption process. I've tried Vigenere, Gronsfeld, Beaufort and Digraphic Ciphers, but he doesn't ...

classical-cipher pen-and-paper

asked May 30 '19 at 0:04

Neo1009

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1

vote

0answers

38 views

Using Alberti Disks to Create a Strong Cipher

Could one use three different disks set at different positions and encrypt a strong message? For example: Wheel 1: A = J Wheel 2: A = E Wheel 3: A = B First letter is encrypted using 1 and then ...

encryption pen-and-paper

asked May 28 '19 at 23:54

Neo1009

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3

votes

2answers

492 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 ...

aes pen-and-paper

asked Feb 27 '19 at 4:15

user3656142

1433 bronze badges

2

votes

3answers

353 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 ...

key-size pen-and-paper

asked Dec 9 '18 at 11:14

daniel

8725 silver badges13 bronze badges

4

votes

1answer

617 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 ...

pen-and-paper

asked Oct 19 '18 at 13:05

user62738

571 bronze badge

2

votes

3answers

496 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, ...

symmetric pen-and-paper

asked Dec 29 '17 at 22:35

bash.d

1214 bronze badges

3

votes

2answers

210 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 ...

authentication pen-and-paper

asked Dec 13 '17 at 0:46

fstanis

1311 bronze badge

11

votes

0answers

246 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 ...

public-key key-exchange pen-and-paper

asked Nov 18 '17 at 4:43

e-sushi

16.9k9 gold badges69 silver badges204 bronze badges

1

vote

1answer

59 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 ...

cryptanalysis known-plaintext-attack pen-and-paper

asked Oct 19 '17 at 6:18

oen

195 bronze badges

7

votes

2answers

485 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\...

asked Oct 16 '17 at 13:54

fgrieu♦

109k9 gold badges229 silver badges461 bronze badges

1

vote

0answers

96 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 ...

asked Oct 13 '17 at 15:26

Himmators

1192 bronze badges

0

votes

1answer

194 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 ...

encryption symmetric known-plaintext-attack pen-and-paper

asked Oct 5 '17 at 16:22

the8thbit

112 bronze badges

7

votes

2answers

556 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?

encryption stream-cipher classical-cipher pen-and-paper post-quantum-cryptography

asked Jul 16 '17 at 6:04

vasili111

1994 bronze badges

2

votes

0answers

206 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 ...

zero-knowledge-proofs pen-and-paper

asked Jun 22 '17 at 8:53

Meir Maor

8,4441 gold badge15 silver badges38 bronze badges

2

votes

2answers

941 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 ...

encryption permutation pen-and-paper

asked Feb 9 '17 at 1:55

Bob

2911 silver badge4 bronze badges

-2

votes

1answer

651 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. ...

stream-cipher pen-and-paper affine-cipher

asked Sep 20 '16 at 20:02

MooCow

991 bronze badge

2

votes

1answer

273 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 ...

pseudo-random-generator proof-of-work pen-and-paper password-hashing

asked Mar 13 '16 at 2:06

PyRulez

7994 silver badges17 bronze badges

9

votes

1answer

2k 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 ...

public-key elliptic-curves dsa cryptocurrency pen-and-paper

asked Oct 22 '15 at 21:22

Bob van Luijt

2071 silver badge6 bronze badges

9

votes

1answer

3k 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?

encryption pen-and-paper

asked Aug 15 '15 at 7:15

John Doe

931 silver badge3 bronze badges

1

vote

0answers

162 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",...

algorithm-design encryption pen-and-paper

asked Jun 30 '15 at 16:02

lg22woo

212 bronze badges

4

votes

1answer

218 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 ...

hash classical-cipher pen-and-paper

asked May 18 '15 at 19:17

SEJPM♦

41.7k6 gold badges79 silver badges173 bronze badges

1

vote

1answer

82 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 ...

signature pen-and-paper

asked May 18 '15 at 18:24

Erik Engheim

1951 silver badge8 bronze badges

0

votes

1answer

230 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 ...

classical-cipher vigenere pen-and-paper enigma

asked Mar 21 '15 at 16:03

Muis

1,0191 gold badge10 silver badges14 bronze badges

6

votes

3answers

1k 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, ...

classical-cipher pen-and-paper education

asked Aug 25 '14 at 7:16

Angela

3531 silver badge10 bronze badges

0

votes

3answers

450 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 ...

hash protocol-design pen-and-paper

asked Dec 17 '13 at 4:06

Slackware

1173 bronze badges

-1

votes

1answer

120 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 ...

rsa pen-and-paper

asked Dec 8 '13 at 16:42

d33tah

3431 silver badge12 bronze badges

5

votes

1answer

611 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 ...

hash one-way-function pen-and-paper

asked Nov 12 '13 at 18:22

David Cary

4,9082 gold badges17 silver badges33 bronze badges

10

votes

1answer

307 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 ...

mac classical-cipher pen-and-paper education

asked Nov 1 '13 at 4:05

e-sushi

16.9k9 gold badges69 silver badges204 bronze badges

8

votes

4answers

1k 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 ...

rsa pen-and-paper

asked Oct 1 '13 at 17:04

d33tah

3431 silver badge12 bronze badges

4

votes

1answer

861 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 ...

encryption substitution-cipher pen-and-paper

asked Sep 19 '13 at 11:37

Jenny

432 bronze badges

20

votes

5answers

4k 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 ...

hash one-way-function pen-and-paper white-box

asked Aug 17 '13 at 2:55

Vincent Yu

3634 silver badges9 bronze badges

5

votes

1answer

855 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 ...

pen-and-paper

asked Jul 23 '13 at 2:37

AndresQ

2351 silver badge5 bronze badges

8

votes

3answers

510 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 ...

complexity one-way-function pen-and-paper

asked May 29 '13 at 22:06

BeingQuisitive

833 bronze badges

13

votes

2answers

5k 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 ...

pen-and-paper

asked May 4 '13 at 21:44

Smit Johnth

1,4214 gold badges12 silver badges26 bronze badges

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 ...

hash collision-resistance pen-and-paper

asked Apr 29 '13 at 13:37

AndresQ

2351 silver badge5 bronze badges

1

vote

0answers

357 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 ...

ntru arithmetic pen-and-paper

asked Mar 11 '13 at 6:55

Sunia Raharja

494 bronze badges

2

votes

1answer

687 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. ...

encryption rc4 reference-request pen-and-paper

asked Mar 6 '13 at 10:42

cobus

212 bronze badges

-3

votes

1answer

271 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: ...

cryptanalysis substitution-cipher pen-and-paper

asked Nov 29 '12 at 9:32

illsecure

1277 bronze badges

44

votes

5answers

9k 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 ...

encryption passwords pen-and-paper

asked Sep 28 '11 at 18:07

John Gietzen

1,3951 gold badge13 silver badges16 bronze badges

47

votes

8answers

28k 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 ...

hash pen-and-paper

asked Sep 23 '11 at 21:22

FUZxxl

5731 gold badge4 silver badges10 bronze badges

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