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Oct
7
comment Why do we require a CSPRNG's output to be indistinguishable from true random?
I said nothing even remotely resembling that.
Oct
7
comment Is there a correct way to generate a symmetric key?
TL;DR, symmetric keys for modern ciphers are nothing more than cryptographically random blobs of the appropriate length.
Oct
6
comment Is my protocol that uses hybrid cryptography and AES-GCM secure?
Also, it should be said that if you're implementing this as a toy project for the sake of learning, great! If you intend to ever use this in a real-world system, just use GPG.
Oct
6
comment Is my protocol that uses hybrid cryptography and AES-GCM secure?
In fact, typically the point of the AAD is to be provided implicitly as context rather than being something entirely attacker-controlled. Also, the filename being used as the nonce is extremely bad — nonces must never repeat, and if you ever reuse a filename or send the same file with a few modifications, the entire security of the system collapses.
Oct
6
comment Is it safe to initialize secret keys by just reading /dev/random on Linux?
The early boot entropy problem is entirely a non-issue outside of very special-case software. By the time your userspace service has started, there is already plenty of entropy in the kernel. And I'm rather swayed by the argument that userspace CSPRNGs have been a frequently-recurring source of failures in the real world: for example, Debian OpenSSH keys and repeated ECDSA keys in Android bitcoin wallets.
Oct
6
comment Why do we require a CSPRNG's output to be indistinguishable from true random?
A block cipher and random number generator have distinct and independent security requirements.
Oct
6
comment Is it safe to initialize secret keys by just reading /dev/random on Linux?
Additionally, it's worth mentioning that getrandom(2) is a better option, if available on the platform.
Oct
6
comment Is it safe to initialize secret keys by just reading /dev/random on Linux?
Why bother with a userspace CSPRNG and not simply read from /dev/urandom directly? One in userspace should be totally unnecessary.
Oct
6
comment Is it safe to initialize secret keys by just reading /dev/random on Linux?
It should give a \0 on average once every 256 bytes.
Oct
5
comment Why do we require a CSPRNG's output to be indistinguishable from true random?
Now you need to demonstrate that a) this is the only thing the attacker can possibly learn, and b) that this can't possibly lead to an exploitable weakness. See points 4 and 2, respectively, in CodesInChaos' answer.
Oct
5
comment Why do we require a CSPRNG's output to be indistinguishable from true random?
#2 is just as important, to me. Known shortcomings are obvious areas for analysts to attack, which they frequently do, and to devastating effect.
Oct
5
comment Why do we require a CSPRNG's output to be indistinguishable from true random?
"The only information the attacker can get from this is the cipher's block size, and this doesn't weaken the security one bit." [citation needed]
Oct
4
awarded  Yearling
Sep
21
comment If I know the hash function that produced a hash key, how easily can I generate an input to hash to the same key?
Also, your clarification about the difference between "any" and "particular" only confuses the issue more. You say by "any" you don't care what the string is, and then you say by "particular" that there may be several, but you don't care what the string is — both of those seem to be the exact same thing. Additionally, it's unclear what you mean by the word "convey".
Sep
21
comment If I know the hash function that produced a hash key, how easily can I generate an input to hash to the same key?
Keep in mind that if you know $k$ where $k = H(p)$ and $p$ is low entropy (for instance, the string hello), it is not considered difficult to find $p$.
Aug
28
comment Are there ANY text strings that will generate the same SHA-512 Hash output?
Good point. I've edited the answer to reflect that.
Aug
28
revised Are there ANY text strings that will generate the same SHA-512 Hash output?
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Aug
28
awarded  Nice Answer
Aug
28
revised Are there ANY text strings that will generate the same SHA-512 Hash output?
added 289 characters in body
Aug
28
answered Are there ANY text strings that will generate the same SHA-512 Hash output?