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Apr
9
comment Security of this deterministic encryption scheme
The one flaw I see is the one the author pointed out; it uses "the same key for confidentiality and integrity." $\;$
Apr
9
comment How to know private key is computed from specific partial private key?
Are you asking about some specific proposed CT-less scheme? $\:$ Even schemes in which the Key Generation Center can know that don't necessarily let it achieve such knowledge in the same way. $\hspace{.55 in}$
Apr
9
comment Zero-knowledge proof for committing a choice?
Note that the signature proposal would not necessarily hide what the choice is before the string gets published, and publishing the string would not necessarily prove that the person "had decided on that choice by the time" the person "published the signature". $\;$
Apr
8
comment Is it possible to deduce the IV from CBC ciphered data, without knowing the key?
Creating "an IV by, for example, filename⊕Key," would result in applying $\hspace{1.9 in}$ the block cipher to key-dependent data. $\:$
Apr
8
revised Is it safe to derive ephmeral keys by hashing a curve25519 key and a sequential number?
fixed typo ad capitalized first letter
Apr
8
comment Is there a malleable pubkey digital signature scheme?
sort-of. $\:$ Generate s1 at random and then let s2 be the ordered pair whose left entry is s1 and whose right entry is a (standard) signature on the ordered pair (m,s1). $\;\;\;\;$
Apr
8
comment Is there a malleable pubkey digital signature scheme?
Just let s1 always be the bit zero. $\:$ I can't think of any role s1 might play that would make the resulting definition achievable but non-trivial. $\:$ You might be interested in ring signatures. $\;\;\;\;$
Apr
8
comment Is there a malleable pubkey digital signature scheme?
I think something like this could at most give implausible deniability, since unforgeability implies that the probability of another party getting the same signature is negligible. $\;$
Apr
8
comment Is there a malleable pubkey digital signature scheme?
What you're trying to build may be related to multi-signatures‌​. $\;$
Apr
7
comment How could Fully Homomorphic Encryption support power operations?
"XOR and AND" do not "form universal gates", since they can never map an all-false input to true. $\hspace{.4 in}$
Apr
7
comment RSA: Letting $p$ and $q$ have different bit-size
Fail-Stop Signatures dispense much more quickly with the argument mentioned in the last paragraph. $\;\;\;\;\;\;$
Apr
7
comment For a one-time pad, which MAC method is information-theoretically secure?
If one "can't do the same, but use a one-time HMAC instead" then that's because HMAC's statistical properties differ significantly from those of a random oracle. $\;$
Apr
4
comment Is timestamping possible without publishing?
eprint.iacr.org/2011/553.pdf $\;$
Apr
4
answered Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
Apr
4
comment For a one-time pad, which MAC method is information-theoretically secure?
"using HMAC and encrypting the MAC tag with OTP" is a possibility, it's just $\hspace{1.73 in}$ far from known to be unconditionally secure. $\:$
Apr
4
comment What is the difference between authenticate a document and sign a document?
One could authenticate with a MAC or an interactive protocol. $\;$
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
I'm typing up a short version of what I discussed in the comments. $\;$
Apr
4
comment For a one-time pad, which MAC method is information-theoretically secure?
@hakoja : $\:$ These approaches could make sense if lightspeeder wants $\hspace{1.98 in}$ Long-Term security with minimum key size. $\;\;\;\;$
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
Do you know if BitTorrent file blocks are hashed directly or via a Merkle tree? $\;$
Apr
4
comment Is it possible to create a “proof-of-upload” system for BitTorrent ratio tracking?
@JoeZ. : $\;\;\;$ The fact that "people participating in the torrent were required to register an account with the tracker" is part of the solution anyway. $\:$ I suppose if the use case you're thinking of has some way to sufficiently discourage the same person from holding multiple accounts, then that would simplify things. $\;\;\;\;\;\;$