if you first bundle them into a tar, then only one salt, but yes, new salt for every one, as the RNG seeds off the salt and if you don't use a different salt for each encryption the very same sequence of scramble bits are used each time
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also, it is exactly the same as the nonce, i've always hated that ambiguity. salt=nonce
you can use different encryption schemes, CBC, CTR, etc, but they all use a cleartext nonce in front, and the olden days they called that a "salt" - it's like a HD derivation path, same prinicple, ensures the hash you generate is different, no matter which way it's sliced by the encryption algo