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comment RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?
In PKCS#1 (the RSA standard), the term "encoding" clearly indicates all the various steps (including padding) that turn the message into an integer suitable for the RSA algorithm. I would not say that the terminology is irrelevant, at least if we give a value to the ability to be understood by the rest of the world...
comment Which MACs can be converted into a secure unkeyed hash function?
An attack on the hash does not automatically apply to the HMAC construction (used as an unkeyed hash). To say, the hash could be broken in that you can construct collisions for messages that follow a certain structure. If you cannot efficiently force the hash to produce digests according to said structure, the attack won't apply to the HMAC construction. So, IMO iterating the hash function twice might foil certain attacks the original hash function is subject to.
comment Which MACs can be converted into a secure unkeyed hash function?
@MartinSuecia You are totally right. I edited the question. However, I believe an HMAC (used really as a MAC) can be more secure than the underlying hash. It really depends on how broken the hash is. To say, MD5 is broken, but HMAC-MD5 is not currently deemed to be so (although it is not a brilliant idea to use it for new designs). RFC6151 explains it better than I can.
comment Is it secure to use the hash of key as the IV in AES encryption?
@Lacek Reusing an IV in CBC and CFB is not as bad, but it is still insecure. ECB should simply not be used. An example of mode which is in most cases still secure enough even if the IV is wrong or abused, is SIV.
comment How to collect, process, and transmit data securely?
I mostly disagree. Examples exist of protections based on obfuscation that practically withstood RE for years. Skype's protocol is one example: it was released 10 years ago and although some clever people published some partial analysis, and some others claimed to have partially reversed it, it is still considered unbroken in practice. Anyway, I don't believe obfuscation is cryptographically secure (so it's off topic here). I would rather say it could be made economically secure, if done properly.
comment Blind signature with openssl
It's not true that RSA padding makes blinding impossible. You simply blind/unblind the encoded message, as opposed to the original message.
comment Combating traffic analysis over request-response protocols
From the question I took that the confirmation message is irrelevant security wise.