CODEWITHSUNDEEP
encryptionrandomnumbers
EthernetCable
EthernetCable

Reputation: 1327

Cryptographically-secure pseudorandom number generator seed

Do we need to seed a CSPRNG with a truly random number? Examples and documentation use truly random numbers, but no justification is given (that I can find).

If we were to seed one with a pseudorandom number, I don't see what the difference would be compared to with a truly random seed. If someone finds either of the seeds, then the encryption fails anyway.

Upvotes: 2

Views: 499

Answers (2)

Slartibartfast
Slartibartfast

Reputation: 1700

Essentially, determining the seed is sufficient to determine the entire output of a pseudorandom generator.

As a result, you want a seed that isn't predictable or determinable.

Pseudorandom output is (under some circumstances as described two paragraphs ago) determinable or predictable.

Beyond that, it is a trade-off. You've already decided to use pseudorandom numbers instead of real randomness, so it is probably an acceptable trade-off in your mind.

Upvotes: 0

David Titarenco
David Titarenco

Reputation: 33406

You are correct, but the idea is that it's easier to find a successive pseudorandom seed than it is to find a truly random seed. This is especially true if a lot of numbers are generated in succession really quickly (and if the seed ever changes, which it usually does).

Upvotes: 0

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