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1d
comment Diffie-Hellman and man-in-the-middle attacks
@GuutBoy: $g^a$ and $g^b$ are 'public keys' in the sense that they allow you to compute some of the operations on the key, but not all. It's clearer when you consider long term DH. As for the corresponding private key, that's $a$ and $b$
2d
comment Diffie-Hellman and man-in-the-middle attacks
@GuutBoy: actually, while we don't typically call the values $g^a$ and $g^b$ exchanged in the DH key exchange "public keys", it doesn't do violence to the language to call them that, and in fact they are on occasion referred to as public keys. They do share the attributes that we normally expect from "public keys".
2d
comment Is it possible (how difficult) to find MORE than one valid RSA signature?
@CodesInChaos: actually, if $\operatorname{GCD}(e, \phi(n)) > 1$, then it's more likely that no such signature exists. However, if one does exist, it is likely that many others do as well (if $e$ is prime, both $e$ and $e^2$ total are possible).
2d
comment Is it possible (how difficult) to find MORE than one valid RSA signature?
Depends entirely on the padding method. With any nondetermanistic padding method (e.g. PSS), it's easy. With, say, PKCS#1.5, well, I suppose you could generate distinct signatures by using different hash functions (say, SHA-256 and SHA-512)
Sep
18
comment GCM: Math behind update of AAD after ciphertext has been processed
@owlstead: that'd work too... That's more work to handle the A||C||A case, however if you're optimizing for the A||C case (and just want to handle the A||C||A case correctly, and not dreadfully slowly), that's a reasonable solution.
Sep
18
answered Is there any definition for “generic attack” in context of cryptography or more specific “hash functions”?
Sep
18
reviewed Leave Closed Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
Sep
18
reviewed No Action Needed How do institutions like banks do RSA with big primes?
Sep
18
reviewed No Action Needed VKO GOST R 34.10-2001 (described in RFC4357), Key Agreement Algorithm. Looking for its implementation/detailed description/examples
Sep
18
comment GCM: Math behind update of AAD after ciphertext has been processed
@owlstead: I don't believe that quite works (unless you know the length of the AAD beforehand). The problem is that if you've already computed $\operatorname{GHASH}_H(A_{0..x}||C)$, there's no easy way to insert $A_{(x+1)...z}$ into the middle. If that's a requirement, I would suggest you keep running $\operatorname{GHASH}_H(A_{0..x})$ and $\operatorname{GHASH}_H(C_{0..y})$, and glue them together only when you've seen the entire $A$
Sep
17
reviewed No Action Needed Finding algorithm: desire RSA's uniqueness and ECDSA's space efficiency
Sep
17
comment Encryption with data loss protection
If you want to ensure authentication, adding a hash is the wrong answer (anyone could modify your book and update the hash). Instead, I suggest you start looking at signatures; in short, you'd sign your book with your private key; someone (who gets a verified copy of your public key; the "verified" is the tricky part) can verify that the book is precisely as you signed it.
Sep
17
reviewed Close Are there cryptographic hash functions with homomorphic properties?
Sep
17
reviewed Close Ciphertext-only cyptanalytic attack agianst the affine cipher?
Sep
17
reviewed Close Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
Sep
17
reviewed No Action Needed Understanding Pseudo Random Generators
Sep
17
comment Encryption with data loss protection
The obvious way to do this is encrypt your data normally, and then apply an unkeyed redundancy transform (such as what's in QR); that'd meet the requirements, and we don't have to worry about the redundancy aspects from causing security problems.
Sep
17
revised GCM: Math behind update of AAD after ciphertext has been processed
added 53 characters in body
Sep
17
revised GCM: Math behind update of AAD after ciphertext has been processed
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Sep
17
answered GCM: Math behind update of AAD after ciphertext has been processed