Amazon S3 Encrypted File Backup System

Question

I am designing my backup system to Amazon S3 (probably Singapore) and I would like to have all my files strongly encrypted on the server. I use ArchLinux x64. My system will append only once an encrypted folder is upload nothing inside this folder will change. eg. I have documents and each month I will upload a folder for that month.

please note I do not want to use Amazon SSE something about them having the keys to my data feels like a waste of time to me (I may use this in addition to what I describe below).

I wish to do the following (to encrypt the folder foo):

1. sha512 every file in foo and place the list of hashes in foo/hashes.sha512
2. dd if=/dev/urandom | tr -dc '[:print:]' | fold -w 256 | head -n 1 > foo.key
3. tar -cvjO "foo" | openssl aes-256-cbc -salt -kfile foo.key | dd of="foo.enc"
4. sha512sum foo.enc >> foo.key (openssl only reads the first line for the key)
5. sha512sum foo/hashes.sha512 >> foo.key
6. openssl aes-256-cbc -salt -in foo.key -out foo.key.enc
7. Manually specify password
8. Upload foo.enc to S3
9. Keep foo.key.enc safe!

I have a few key questions:

• Is this a proper use of each of these tools?
• Is using /dev/urandom a good method of generating a password?
• Is my method of storing locally the file encrypted with the weaker key (the one I remember) and only uploading the files that are encrypted with the larger unique keys as strong as it seems?
• What is the largest value I can put in as the key value for openssl?
• Any obvious serious issues?

Answer 1

+1 for Yoav Aner's comment.

I don't have any particular experience with the questions you asked, but it seems like designing such a system from scratch without any prior knowledge and experience will only lead to trouble.

Is there are particular reason you do not want to use premade tools?