Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [classical-cipher]

Ciphers invented before the era of computers and modern cryptographic theory. Classical ciphers typically operate on letters instead of bits and are usually designed to be implemented by hand or using simple mechanical devices.

239 questions
23
votes
6 answers

What is the most secure hand cipher?

By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient user. Additional simple tools, e.g. a deck of cards…
Jordan
  • 575
  • 1
  • 4
  • 9
5
votes
1 answer

What are Alternatives to basic ROT-n Ciphers which Don't Lose 'Context'?

I've got this neural network running like a champ on my machine. The data is concatenated works of shakespeare in a plaintext file. RNN trains on the data, then gives you a 'sample', aka it tries to freestyle its own shakespeare based on what it…
Bango
  • 153
  • 3
5
votes
6 answers

Why does ROT13 provide no cryptographic security?

I can understand that ROT13 is not secure for obvious reasons, but I'm looking for the theoretical answer. Wikipedia says "The algorithm provides no cryptographic security.." What does it mean to provide cryptographic security? Why does it provide…
Explosion Pills
  • 161
  • 1
  • 5
5
votes
1 answer

Is there a general method to crack this type of fractionating cipher?

I've seen a few puzzles based on a type of cipher in which letters in the plaintext are substituted with groups of characters in the ciphertext. The ciphertext only uses a handful of unique characters. For example: a -> 154 b -> 53 c -> 12 d ->…
PhiNotPi
  • 159
  • 2
4
votes
2 answers

security of Felix cipher

I just find this pencil and paper cipher 'Felix' and I want to know how secure it is? EDIT From http://web.archive.org/web/20110825142054/http://topcat.hypermart.net/papers/felix.txt Felix a pencil-and-paper cipher I. Synopsis Felix is a…
illsecure
  • 147
  • 7
4
votes
1 answer

Is frequency analysis a useful tool against encryption by multiplication?

If I transform natural plaintext by: making each letter two decimal digits, considering the whole as a decimal number; multiplying by the key (some integer constant), giving the ciphertext; would frequency analysis still work? Exemple: Plaintext: …
illsecure
  • 147
  • 7
4
votes
3 answers

How to attack a general polyalphabetic cipher?

I am able to decrypt Vigenere ciphertext using the index of coincidence and chi-squared test. However, out of interest, how do you go about attacking ciphertext that was encrypted using a mixed alphabet shifted 26 times? Also, what about a…
Lunar
  • 215
  • 3
  • 5
3
votes
1 answer

Does the Richard Sorge cipher still provide good security?

Is the cipher used by soviet spy Richard Sorge still sufficiently secure nowadays?
user65597
  • 107
  • 6
2
votes
1 answer

Shuffling alphabet cipher

Disclaimer: this is actually a coding challenge therefore I am expressly not looking for complete solutions. The way the cipher works is as follows: Start with ABCDEFGHIJKLMNOPQRSTUVWXYZ and a keyword KEYWORD. We construct our first alphabet by…
S. L.
  • 421
  • 3
  • 14
2
votes
1 answer

Why don't homophones hide multiple-letter patterns?

I am reading about mono-alphabetic ciphers, which are prone to letter frequency analysis. To counter this, we can provide multiple substitutions, known has homophones for a single letter e.g. e could be assigned 17, 74, 35, 21. Each homophone could…
ishaq
  • 143
  • 5
2
votes
1 answer

Monoalphabetic cipher key

I'm new to cryptography and have just completed homework on Monoalphabetic cipher. I managed to decrypt the cipher text successfully but I cannot identify the key from my plaintext to ciphertext mapping table which is shown below (top is ciphertext…
user23
  • 75
  • 3
  • 8
2
votes
0 answers

For fun puzzle has me stumped on a book cipher

So originally a puzzle was given out to a community i'm a part of and what was given was this. . .. . ... . . . . . . . ... . .. . . . . . .. . ... . . . . . .... . .. . . . . . .. .. .. . . . . . .. . . . . .. ..... . . . . . .. .. ..... . . . . .…
Halfuhmeatball
  • 21
  • 1
2
votes
1 answer

Interesting and fun facts about cryptology

We are planning to organize a workshop with the participation of academicians, engineers and graduate students working in the field of cryptology. On the first day, we are planning a fun competition for the participants as an ice-breaking event. Our…
NB_1907
  • 630
  • 4
  • 14
1
vote
2 answers

Does anyone have any hard ciphers to be cracked for fun?

The title says it all. Do you have any ciphers or encoded messages that you could post as a brainteaser? Thanks!
Cole Henrich
  • 113
  • 3
1
vote
0 answers

Classic cipher method

I am struggling with these two cipher texts, I cannot identify which king of cipher was used. First: otnpeetrnneepeufofutisrtrllohcdmetoeheeatyngonrmrm And second: mvevgpwosytaeeisvcgofotbisfnoamtersmeslykuoakaypep
Bálint Ružinský
  • 11
  • 1
1
2