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Jan
13
answered Implementing a web app where the server cannot decrypt its own data?
Jan
13
comment Key derivation of public key without knowledge of private key?
Yep. ten letters
Jan
12
comment Key derivation of public key without knowledge of private key?
The Elgamal signature scheme is quite different from the Elgamal encryption scheme. This idea won't work for Elgamal signatures, indeed, it can't work for any signature scheme.
Jan
12
comment Key derivation of public key without knowledge of private key?
Any encryption of $1$ can be used as a public key. The extra per-key information is not needed, as the same decryption key can be used for all the public keys made in this way.
Jan
11
awarded  Custodian
Jan
11
reviewed Close private keys for multiple devices
Jan
11
answered Key derivation of public key without knowledge of private key?
Jan
11
comment How much (home PC) CPU time is required to generate a prime number of a given size?
Would you do AKS for every candidate? Why not eliminate candidates with simpler tests first, then do AKS (or ECPP) once you know you have a prime?
Jan
11
comment Strength of RSA with OAEP
You could also mention that RSA-KEM is often a better alternative than RSA-OAEP (simpler, better security guarantee).
Jan
8
comment Variant of the Decisional Bilinear Diffie Hellman problem
I've looked at it for a few minutes, and I wouldn't expect them to be equivalent. The information about $y$ in your problem lies only in the field. To get a DBDH relation related to $y$ seems to require some kind of pairing inversion, which is very hard to do.
Jan
6
awarded  Nice Answer
Jan
6
revised Why is the private key generated first in public key crypto?
added 10 characters in body
Jan
6
revised Why is the private key generated first in public key crypto?
deleted 1 character in body
Jan
5
reviewed Approve Why is the private key generated first in public key crypto?
Jan
5
answered Why is the private key generated first in public key crypto?
Dec
29
comment Formal proof of theorem concerning the Random Oracle Model
It's obvious. Recall that choosing a random function is equivalent to choosing the function values independently, one at a time.
Dec
23
comment Which multiplicatively homomorphic encryption scheme supports encryption of 0?
If you can live with $\{0,1\}$ as the message space, use any additively homomorphic scheme with a large message space and interpret encryptions of zero as $1$, and encryptions of anything else as $0$. Note that if you combine a ciphertext with itself a random number of times, this does not change the interpreted value of the ciphertext. To "multiply" two ciphertexts, randomize them (as above) and combine them.
Dec
22
comment Protecting a short password
Clarify your question, then add a n choose k. By the way, if you replace bytes in the Base64 expansion, you should use 6 above, not 8.
Dec
21
answered Protecting a short password
Dec
21
answered Which multiplicatively homomorphic encryption scheme supports encryption of 0?