How Can One Use Hashes to Ensure that Two Dropbox Folders are Synced?

garchws · 2015-11-11 22:07:31

**Problem:** Right now I have two computers (both running Arch on xfce4) connected to Dropbox. Superficially, Dropbox places an icon in the taskbar which tells you if it is adequately synced to the cloud; however, I've recently come into issues in the past when taking this indicator at face value. So I've been trying to brainstorm a way to *ensure* that my Dropbox folders are actually synced up.

**Proposed Solution:** My best guess is to use hashes. This is similar to the strategy employed by Git to ensure that repositories are the same: here, you can just compare repository commit hashes and, if they are the same, be more than 99.9% certain that your repositories are identical.

**Questions:**

1. Can one use hashes to ensure that two Dropbox folders are synced?

2. Are there any obvious pitfalls to this method that I'm missing?

3. Using this strategy, would it be possible to know ahead of time -- while both of my computers are syncing -- that they are NOT in sync (i.e., could I somehow access the Dropbox hashes ahead of time even before the Dropbox folders are fully synced)?

ewaller · 2015-11-11 23:08:25

1. Hashes are an excellent way to determine that two files are identical. Not that it matters for what you are doing, use a strong hash such as a 256 bit SHA-2. Not that anyone would, but MD5 and SHA-1 can be spoofed.
2. How do you plan to exchange hashes? That is the critical piece.
3. Yes.

BTW, for a 1Meg file, that probability for SHA-256 is about 99.9999999999999999999999999999999%
(1 - 1.4 x 10^-33)
http://crypto.stackexchange.com/questio … hed-values

Last edited by ewaller (2015-11-11 23:09:14)

Awebb · 2015-11-11 23:20:19

This is something the client should do for you. If the client claims to be connected and synced (green check), then it is either saying the truth or it is lying about its connection status (blue arrow circle). Long story short, if either of these happen problems happen regularly enough to make you think about a hackish solution, then I'd say this service is not fit to hold your data.

ewaller · 2015-11-11 23:26:16

Awebb wrote:

This is something the client should do for you. If the client claims to be connected and synced (green check), then it is either saying the truth or it is lying about its connection status (blue arrow circle). Long story short, if either of these happen problems happen regularly enough to make you think about a hackish solution, then I'd say this service is not fit to hold your data.

*Cough*https://wiki.archlinux.org/index.php/Syncthing*Cough*

Arch Linux

#1 2015-11-11 22:07:31

How Can One Use Hashes to Ensure that Two Dropbox Folders are Synced?

#2 2015-11-11 23:08:25

Re: How Can One Use Hashes to Ensure that Two Dropbox Folders are Synced?

#3 2015-11-11 23:20:19

Re: How Can One Use Hashes to Ensure that Two Dropbox Folders are Synced?

#4 2015-11-11 23:26:16

Re: How Can One Use Hashes to Ensure that Two Dropbox Folders are Synced?

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