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  • 13 votes cast
Aug
27
comment Inverse public-key encryption
The "inverse" of encryption that you are wondering about is a digital signature - like poncho mentioned. The server alone knows the signing key and all clients get the verification key - even with the verification key, one cannot sign a server response, only the server with the signing key can do that. It's the same system that's used on playstation games, for example - every PS has a copy of the verification and will only run games that have been signed by Sony.
Aug
27
reviewed No Action Needed Can iterated hashing be used to mitigate collision and preimage weaknesses?
Aug
20
awarded  Critic
Aug
20
revised Combining several symmetric ciphers using XOR
added 288 characters in body
Aug
20
comment Is entropy being lost when the hash of a secret has a specific format?
No obvious examples come to mind - perhaps the entropy of credit card numbers, bearing in mind the checksum? There's point compression on Elliptic Curves, it doesn't lose entropy since it's only getting rid of redundancy but it does demonstrate that you can send only "part of the point" and have someone else recompute the rest.
Aug
20
answered Is entropy being lost when the hash of a secret has a specific format?
Aug
20
revised variant of Diffie–Hellman key exchange protocol
added 1069 characters in body
Aug
20
comment variant of Diffie–Hellman key exchange protocol
To avoid this becoming an extended chat discussion - can you edit your original question and post the multi-A case on the end? Then I'll edit my reply as I think I have the answer.
Aug
20
comment variant of Diffie–Hellman key exchange protocol
Is the adversary still passive, or are some of the $A_i$ dishonest too?
Aug
20
comment Combining several symmetric ciphers using XOR
It was just an intuitive example. If AES is real-or-random secure, then you should not be able to tell AES(m) from a random string r of the same length. It follows by reduction that you also cannot tell (AES(m) XOR Twofish(m)) from (r XOR Twofish(m)) - as long as you use different keys for the two ciphers. But (r XOR Twofish(m)) is a one-time pad, hence it gives you no information on m, even if Twofish is broken.
Aug
20
answered Combining several symmetric ciphers using XOR
Aug
20
comment Cryptography and FPGA
Correct - perhaps "embedded devices" would have been a better description. Though, looking at the "security" of some of today's IoT devices and protocols, you wish they did spend the money for a decent crypto chip ...
Aug
20
answered variant of Diffie–Hellman key exchange protocol
Aug
19
answered Let $G$ be a PRG. Are the following $G'$ constructions based on $G$ necessarily PRGs?
Aug
19
answered How ECDH algorithm selects modulus value?
Aug
19
comment variant of Diffie–Hellman key exchange protocol
By "security", I presume that you mean the real key is indistinguishable from a random one to a passive attacker - I don't think this protocol is actively/MITM secure, for example. Your first reduction actually looks ok to me, I don't understand what the problem is?
Aug
19
awarded  Scholar
Aug
19
accepted Point addition in NaCl/libsodium (Curve25519)
Aug
19
awarded  Custodian
Aug
19
reviewed Close keytool -genseckey -alias TDES -keyalg DESede -keysize 128 works within jre/bin folder but not when the keytool.exe is on another location