# Questions tagged [key-size]

Key size is the size measured in bits of the key used in a cryptographic algorithm.

10 questions
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### Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
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### Post-quantum candidates for asymmetric cryptography with small key sizes

One of the things that I have come to like about elliptic curve cryptography is that the key only needs to be twice as long as the desired security level. That's a very small expansion (I also like it ...
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### Computing cost for a trillionaire to compute GNFS in RFC 3766

RFC 3766, Section 4.1 discusses picking $n$ to achieve some target cost for employing the GNFS, i.e., $T$ is known and $N$ is unknown in the below equation: T = \kappa \cdot \exp{\left(c \cdot (\ln{...
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### Safely using ciphers that take small key sizes

Is it feasible to use triple encryption for block ciphers with the maximum keysize being the only significant security issue? I mean $C = E_{k_1}(E_{k_2}(E_{k_3}(P)))$ and \$P = D_{k_1}(D_{k_2}(D_{k_3}(...
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### Security strength of JPBC Type A curve compared to SecP curve

I recently encountered some problems when learning about the JPBC library. Does the curve generated by (J)PBC using the method typeAcurvegenerator(160,512) and the ...
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### Does the length of the keyword used for keytable for Playfair matter?

So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'. Does the ...
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### Maximum security strength in bits of ISAAC cipher?

Wikipedia claims key length can be very big in this cipher, so I assume it can offer a million bits of security provided entropy of key is the same? Of course I can SHA-256 hash the key to allow any ...
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### How many possible keys are in a columnar transposition cipher?

In a book I am reading it says that the message "Common sense is not so common." (which has 30 characters, space and punctuation included) has a range of possible keys of 2 to 15, half the message ...