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seen Oct 30 at 13:04

Oct
30
comment Public key encryption without ciphertext expansion
It is strictly for use in a deterministic sense. By specifying VARCHAR(255), I assume that it is a deterministic permutation between 0 .. 2^(8*255).
Oct
30
comment Public key encryption without ciphertext expansion
@DrLecter Several reasons I would need it. The app is running on cloud and stores the data on cloud. The app only writes the data but does not need to read it. Then I would like to use public key encryption to protect it from the cloud provider.
Jan
10
comment How secure is the knapsack?
I am using the special properties of the knapsack (the sum). It is actually meant to be used in another protocol. In my case $X$ (the target sum) is defined by the user. We are free to choose $W$. However, as a first solution, I will be happy even if both $(W, X)$ are freely chosen, as this might be extended even when $X$ is fixed.
Jan
10
comment How secure is the knapsack?
@Ilmari Karonen: Not really, but good point. In my use-case, we don't need the solution, just the problem to be hard. I have updated the question with this information.
Oct
3
comment Reduction from signatures to encryption?
I guess someone would have written a paper on it. If not, it is a good topic for one.
Sep
30
comment How did the Koblitz/Menezes papers affect the cryptography community?
I found several things in the paper interesting and useful. So it has certainly affected my way of thinking. I think we will only see long-term effects. One thing I can foresee is the rebirth of random-oracle model.
Sep
27
comment Need an introduction to SPKI (or “SPKI for dummies”)
1. Is there anything specific to S-expressions? (i.e., do they have any particular property that enable them to be used here? 2. Is there any globally unique way to write all authorizations?
Jul
18
comment Reduction from signatures to encryption?
@Zooko, Paolo: yes, the last para does elude to "designated verifier signatures" (DVS), which might work. The only issue is that DVS require the knowledge of verifiers or share a secret with them.
Jul
18
comment Reduction from signatures to encryption?
It seems one of the motivation for DSA was to make it hard to use for encryption (as export restrictions on signature schemes are not so strict).
Jul
17
comment Reduction from signatures to encryption?
(1) Keeping the signing key public may enable computation of verification key directly (at least it cannot be proved that it would not). Let (G, S, V) be a signature scheme, with usual meanings, now consider the modified scheme (G', S', V') as: G' = G, S' = (S, V), V' = V. Then the above idea does not work. (2) Alice does not send the forgery to Bob . Rather she uses the forgery (forged signature) as a secret key and only sends the message on which the forged signature was created. Using this message, Bob could compute the same forged signature, which can now act as a symmetric encryption key.
Jul
17
comment Reduction from signatures to encryption?
It would be great if there is a proof of this.
Jul
17
comment Reduction from signatures to encryption?
@Paulo: hmm yes Designated verifier signatures are a different beast. They might work. Though the question was motivated from DSA.
Jul
17
comment Reduction from signatures to encryption?
This won't work. The public verification key is public, so I am talking specifically about signatures, not MACs. But thanks for the answer :)
Jul
16
comment How can SSL secure a two-way communication with only one key-pair?
I am assuming you meant that the "third value that the eavesdropper cannot discern" is a nonce. At least thats what it seems from the text.
Jul
16
comment How can SSL secure a two-way communication with only one key-pair?
And of course, the client needs a certificate too, to support the client authentication.
Jul
16
comment How can SSL secure a two-way communication with only one key-pair?
Note: I think you refer to authentication via a certificate. You didn't mention it.
Jul
16
comment How can SSL secure a two-way communication with only one key-pair?
nonces are used to avoid replay attacks, and not for "protecting" the secret value from eveasdroppers. And, TLS does not require the server to have an encryption key. A DSA key will also work. The two parties will use DH key exchange in this case.
Jul
16
comment How can SSL secure a two-way communication with only one key-pair?
and don't believe everything that wikipedia says.
Jul
12
comment What is the general justification for the hardness of finding preimages for cryptographic hash functions?
The difference is more on the underlying primitives you call as "mathematical". A discrete log problem is as mathematical (IMO) as the "fuzzy" problems involved in hash functions. The reason (as you probably know) for using such fuzzy security is efficiency. It is much faster to use a SHA256 than to use a DL based hash.