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25 votes
Accepted

Is the Caesar cipher really a cipher?

He is talking about the original version of the Caesar Cipher where the substitution was just a +3: ...
Biv's user avatar
  • 10k
21 votes
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Make a Strong, Easy-to-Remember Password Using Classical Cryptography?

I fail to see why one would want to use classical or pencil and paper tools for derivation. For anyone attacking your technique it will make no difference. An attacker with a modern computer will only ...
Meir Maor's user avatar
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18 votes
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How were one-time pads and keys historically generated?

Your interesting questions deserve to be answered more thoroughly, but here goes: According to a highly classified document written in 1947 and finally declassified in 2013, the Germans started using ...
Patriot's user avatar
  • 3,142
15 votes

Creating your own encryption and decryption algorithm

Edit: I think the edit to the question makes it as vigenere cipher; which invalidates my answer below. @galvatron answer gives the suitable answer why vigenere is not secure. The old answer below ( ...
NuminousName's user avatar
15 votes
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Common Classical Ciphers

Cryptography as we know it today dates from the Renaissance, in a certain sense, in a mathematical sense. --Whitfield Diffie If you look at introductory cryptography texts, you will usually see some ...
Patriot's user avatar
  • 3,142
12 votes

Which is the simplest cryptographic algorithm which is close to commercial-level security?

I would say MiMC is the simplest block cipher with plausible security. The idea is to cube the state, add a random constant, and repeat. This is typically done in a large prime field, but it is ...
Daniel Lubarov's user avatar
11 votes

Creating your own encryption and decryption algorithm

Encryption is naïvely viewed as a way to send messages from A to B that cannot be deciphered (at least in practice) by an adversary. Sure, encryption does do that, but modern ciphers do so much more......
Dennis's user avatar
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11 votes
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Which is the simplest cryptographic algorithm which is close to commercial-level security?

I will throw tiny encryption algorithm into the mix: https://en.m.wikipedia.org/wiki/Tiny_Encryption_Algorithm It's a very respectable block cipher. It really works as a block cipher with convenient ...
Meir Maor's user avatar
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9 votes
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Was the Enigma's double stepping mechanism intentional?

I suspect it was a semi-deliberate feature. That is, while it probably wasn't a design goal in and of itself, it neatly solved a mechanical issue that would otherwise have required a more complicated ...
Ilmari Karonen's user avatar
9 votes

Which is the simplest cryptographic algorithm which is close to commercial-level security?

The one time pad technically meets all your criteria and I think it's the simplest. It gets used all the time within encryption schemes where it's usually called blinding. Otherwise I would look into ...
user82867's user avatar
  • 366
8 votes
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In English, are there any words which encrypt to other words under the Caesar Cipher?

Actually, we have a four-way (that is, four words that will can be converted into any of the others with the right shift). These words are: ax, by, he, if Other ...
poncho's user avatar
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8 votes

Which is the simplest cryptographic algorithm which is close to commercial-level security?

I think the most simple ciphers that are available are stream ciphers. Of course there are secure and non-secure stream ciphers. But e.g. LFSR's based ciphers are pretty easy to understand, and ...
Maarten Bodewes's user avatar
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8 votes

Make a Strong, Easy-to-Remember Password Using Classical Cryptography?

If there is no upper bound on the length of the password to be used, the most common suggestion I know to create strong, easily-memorable (for some definition of "easy") password is diceware....
Mark Schultz-Wu's user avatar
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7 votes

How to find the keyword of the Playfair cipher, given the plaintext and the ciphertext?

First of all, you cannot uniquely determine the keyword of a Playfair cipher, or even the key table constructed from it, simply because there are multiple equivalent key tables that will produce the ...
Ilmari Karonen's user avatar
7 votes

Is there any quantum resistant pen-and-paper or mind cipher?

You are not likely to find such a construction. One problem you will run in to is that of size: In order to be secure against brute force search with Grover's algorithm, you will need to use at least ...
Ella Rose's user avatar
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7 votes

How were one-time pads and keys historically generated?

If you consider that the quality of randomness can only be assessed in proportion to the size of the data sample, you'll realise that it's not really that hard to make random numbers. Depending of ...
Paul Uszak's user avatar
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6 votes
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Does Kasisky test for Vigenère cyphers assumption always hold?

There is imprecision in what is stated in your notes. The Kasisky test only works if the corresponding letters in the two segments are separated by a distance that is a multiple of the key length (in ...
puzzlepalace's user avatar
  • 4,062
6 votes

Is a book cipher provably secure?

NO, that book cipher is not provably secure. Much to the contrary, it miserably fails a basic security criteria in modern cryptography: ciphertext indistinguishability under chosen plaintext. Assume ...
fgrieu's user avatar
  • 143k
6 votes

Most secure but feasible encryption running on WWII technology

It depends on what you mean by widespread (military) use. The Russian VIC cipher, which used a lagged Fibonacci generator, classified as a "straddling bipartite monoalphabetic substitution ...
Patriot's user avatar
  • 3,142
6 votes
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How can frequency analysis be applied to modern ciphers?

Classical ciphers operate on letters. If we consider the frequency attack on classical ciphers it considers the frequency of the letters. Modern ciphers, if we consider only block ciphers, operates on ...
kelalaka's user avatar
  • 49.1k
6 votes

How were codes in WW1 reciphered (to enhance security levels) without them turning meaningless?

The concept is called superencipherment or multiple encryption, and works as follows: The original message M is enciphered using the code book, resulting in an enciphered message C1. C1 is then ...
Eugene Styer's user avatar
  • 1,676
6 votes
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How to determine which type of transposition cipher I have?

However how do I determine which transposition cipher I would need to use? Am I right to assume this is definitely a transposition cipher also? As you found out that the ciphertext has a similar ...
kelalaka's user avatar
  • 49.1k
5 votes
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Has the Linear Congruent Generator ever been used in any of the early crypto algorithms?

It is indeed the case that the linear congruential generator was used—or at the very least suggested—for cryptographic purposes early on. Below are three examples, but it is likely that there are many ...
Samuel Neves's user avatar
  • 12.7k
5 votes
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Vigenère cipher - sorted order

ADLY is the order those letters appear in the alphabet, so A=1, D=2, L=3, Y=4. But I've never seen such a substitution in a Vigenere cipher, and it's dumb, since it makes a weak algorithm even weaker....
CodesInChaos's user avatar
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5 votes

An unbreakable book cipher?

Book ciphers are well understood and this seems like a fairly minor variation. Following Kerchoff's Principle we separate the key being the book and the arithmetic operator and numbers and the rest. ...
Meir Maor's user avatar
  • 11.8k
5 votes
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Does the Richard Sorge cipher still provide good security?

Short Answer: No But it depends on what you mean by good. If pretty lousy by modern standards is your idea of good enough, and you want to use it on your little brother, then this cipher may exceed ...
Patriot's user avatar
  • 3,142
5 votes

How were codes in WW1 reciphered (to enhance security levels) without them turning meaningless?

Anyone could be confused by this, especially by the part about the Zimmermann telegram. Codebooks come in three flavors: one-part, two-part, and hybrid. You described a one-part codebook. These are ...
Patriot's user avatar
  • 3,142
5 votes

Common Classical Ciphers

It's disputable that historic ciphers are necessary knowledge to understand how modern cryptography works. Towards this, the historic Kerckhoffs's principles (especially the second: the key shall be ...
fgrieu's user avatar
  • 143k

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