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What would be the best Cryptography method without the use of a computer?

This could be a list of the current options available, that could be used without the use of a computer system/electronic device. Moreover, would like to identify what types of Cryptography techniques could be used to encrypt a small a amount of hand written, "plain text" without numbers or symbols just (characters). that being hard to implement or easy to implement.

Would like A brief description of:

  • E.g. types of cipher's
  • Different types of algorithm.
  • The range in security, low to high etc.
Mattlinux1
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    There is the classic solitare, done with a deck of cards. Although the original formulation was found to be flawed there are modified versions out there. http://en.wikipedia.org/wiki/Solitaire_%28cipher%29

    It is also possible to do a base-10 LFSR in your head, Although a single LFSR is not secure, using two and clocking one with the other is generally believed to be secure but has not had as much scrutiny as other systems.

     – John Meacham Dec 15 '14 at 02:53
  • I must say, that is a very interesting and innovative way to implement encryption. I like the way of using an item that would also seem so unsuspecting, to the average person. – Mattlinux1 Dec 15 '14 at 03:08
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    Playfair tableaux have the advantage of being compact. You could also use a few of them to transcribe successive pairs or overlapping pairs. – Mok-Kong Shen Dec 15 '14 at 10:57
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    See Is there any strong enough pen-and-paper or mind cipher? – CodesInChaos Dec 18 '14 at 12:54

2 Answers2

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For confidentiality purposes?

  • one time pad (when possible)
  • rc4 (because you can by hand)
Thomas M. DuBuisson
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  • Confidentiality would be one of the main aspects. – Mattlinux1 Dec 14 '14 at 11:05
  • Some great examples though. – Mattlinux1 Dec 15 '14 at 02:31
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    OTP is quite terrible from a usage point of view. Because instead of storing the key, you can just store the plaintext (key has the same length as the plaintext). And it is crucial for OTP that keys are not used more than once. Shorter keys or repeating keys are not OTP - and you can not apply OTPs security definition. – tylo Dec 15 '14 at 12:24
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    @tylo I don't know any secure hand cipher that's less terrible than the OTP from a usage point of view. RC4, solitaire etc. have the same key reuse problems. – CodesInChaos Dec 16 '14 at 11:38
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    The OTP is AT LEAST the length of the plaintext, by definition. There are OTP-like ciphers (using a book as a key) that are more usable, but they lack enough entropy (because they would at least have no more entropy than the language they were written in). – outis nihil Dec 17 '14 at 17:15
  • Let me rephrase: People call all sorts of things "OTP", which aren't OTP but streamciphers. And if you use OTP, you can just store the plaintext instead of the key, because OTP does not consider key storage. Simply put: Using OTP is almost always entirely pointless. It cant be much terrible than that, because with RC4 you have weak security, but at least you could just store the short key for a longer message. Same goes for sending messages: If you can somehow transmit a key of equal length securely, then you could just send the real message securely instead. – tylo Dec 18 '14 at 17:44
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I suggest Vigenère cipher, it is fun on paper and also you can be creative in using key. you can use your phone number as key or your entire family phone number in age order. 

Key:        ABCDABCDABCDABCDABCDABCDABCD
Plaintext:  CRYPTOISSHORTFORCRYPTOGRAPHY
Ciphertext: CSASTPKVSIQUTGQUCSASTPIUAQJB

http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher

Nima
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  • I have used this at university, in one of my Cisco CCNA security labs. But good point, almost forgot about this. The only problem being the security, isn't up to today's standards. – Mattlinux1 Dec 15 '14 at 02:25
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    It is unrealistic to expect today's standards to be met while not using a computer. – tylo Dec 15 '14 at 12:28
  • Fair point, I could of rewritten what I have wrote above, to say something near/like or even close. todays. I also understand, that it would be very hard to implement what a computer could do. E.g. Calculations per minute. Encryption and decryption times. Etc. – Mattlinux1 Dec 15 '14 at 14:08