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3

Stream cipher and CSPRNG aren't the same thing. CSPRNGs must handle initial seeding, post-compromise reseeding, back-tracing resistance among other things; stream ciphers only need to be able to output something indistinguishable from random. So can we turn a CSPRNG into a stream cipher? Possibly, if we make every generate requests to the CSPRNG idempotent, ...


4

Not much; signing the GCM tag using RSA is inadequate. For a start, knowing the AES secret key, it's easy to make a message with any desired content (except in the very end), and an AES-GCM cryptogram that checks, and has any desired tag. Thus any holder of the AES secret key can forge a message that pass verification under the RSA public key of another ...


3

Generally the RSA key is used to sign the key agreement. The key agreement is used to establish the key used within GCM. Generally the secret key isn't distributed using some kind of out-of-band procedure after all. After that the GCM authentication tag should provide enough security for message integrity and authenticity. Another issue is that a signature ...


3

I have a solution that may satisfy you Splitting the file into parts and chaining is a solution for you. To prevent the truncation we will use the associated data, that same for the first and last. Assume that you divide the file into $n$ parts each around 16KB ( need adjustments). Encrypt each of them with $\operatorname{AES-GCM}$ with the following ...


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