Ok I have taken comment so far and this is my plan - if I am way off please let me know
create a public salt (anyone can see this and will) of X length (128bits) take sha512 hash of file to be encryted (and keep it) supply a password to the pbkdf2 - to create a 256bit key for my AES256 CFB encryption use the hash with same salt in pbkdf2 and create a 128 bit iv Encrypt the file and leave it anywhere in public for me to get later (even in an untrusted place). Would this work and where are the weaknesses in the plan? many thanks for your , hopefully, continued patience with me. David
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