Tarsnap - Online backups for the truly paranoid

Tarsnap is a secure, efficient online backup service:

Encryption: your data can only be accessed with your personal keys.
We can't access your data even if we wanted to!
Source code: the client code is available.
You don't need to trust us; you can check the encryption yourself!
Deduplication: only the unique data between your current files and encrypted archives is uploaded.
This reduces the bandwidth and storage required, saving you money!

Tarsnap runs on UNIX-like operating systems (BSD, Linux, macOS, Cygwin, etc).

Tarsnap uses a prepaid model based on actual usage:

Storage:	250 picodollars / byte-month of encoded data ($0.25 / GB-month)
Bandwidth:	250 picodollars / byte of encoded data ($0.25 / GB)

There are no other fees — Tarsnap has no fixed costs or minimum monthly fees.

Consider a typical backup scenario:

Alice begins a backup, which takes a complete snapshot of her files.
She does not need to decide whether to do a "full backup" or "incremental backup". [Why?]
Tarsnap automatically finds the unique data within her files.
Only this data is uploaded and stored. [How?]
Alice pays less than $5/month.
Even though she has thousands of daily backups, adding up to several terabytes of non-unique data. [Why?]
Alice's data is secure.
Even if an attacker (Mallory) breaks into Tarsnap's storage, he lacks her private keys and thus cannot read or modify her data. [Why?]

Changes in this version compared to 1.0.39:

tarsnap now accepts a --resume-extract option to skip extracting files whose filesize and mtime match existing files on disk.
tarsnap now accepts --progress-bytes SIZE, which prints a progress message after each SIZE bytes are processed, up to once per file. This can be disabled with --no-progress-bytes.
tarsnap now accepts a --passphrase method:arg option which accepts:
- --passphrase dev:tty-stdin
- --passphrase dev:stdin-once
- --passphrase dev:tty-once
- --passphrase env:VARNAME
- --passphrase file:FILENAME
tarsnap now accepts a --dump-config option to print the command-line and all non-blank lines read from config files.
tarsnap now exits with an error if there are unused command-line arguments. (i.e. "tarsnap -d -f a1 a2", where "a2" is unused.)
Improved performance on some x86, amd64, and arm64 systems by using cryptographic instruction set extensions.
When sent SIGINFO or SIGUSR1, tarsnap now prints the number of files and the number of uncompressed bytes processed, in addition to the previous output.
A zsh completion file can be installed with configure --with-zsh-completion=DIR.

As usual, there are also lots of minor build fixes, harmless bug fixes, and code cleanups.

You can see all of the changes between 1.0.39 and this version in our tarsnap git repository.