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secretbox

Encrypt / decrypt files using Shamir secret sharing.

Encrypt

$ echo "hello world" >foo.txt
$ secretbox encrypt -p 4 -t 2 -i foo.txt -o foo.crypted -e base64

Generated secret key in 4 parts with thresdhold 2:

 [1] GfrtqFq8sYWCWggF5cO8EVjFAzpIA18p7CeqC9IyovCgp+yBW1v61ikQMGpyuwhVZTKVdNlEgsAB
 [2] uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC
 [3] Li9jwAunsExtEJtCnYB/VxbdPjGiKPmYEVziW89r5F1kINtQWYZr6HX/mlxvzEMazNGkWeRMRYQD
 [4] 4aytTF0KPuW96/ElKenNvuP56qTyzVuF/mEeg2shDWpRfBTdXhkGtb8vKh3L4zZh9RNitTBQ+WoE

Encrypting to 'foo.crypted'

Success!

Decrypt

$ secretbox decrypt -i foo.crypted -o foo.decrypted -e base64

Interactively enter the Shamir secrets and decrypt the file:

This interactive shell will allow you to enter the key parts.

Commands:

 add <part>    - adds a key part
 list          - view the parts that have been entered
 del <num>     - deletes the part by #
 done          - indicate you have entered parts and are ready to decrypt

 exit          - exit immediately without decrypting
 help          - display this message

>>

Add at least threshold parts:

>> add uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC
add: uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC

>> add 4aytTF0KPuW96/ElKenNvuP56qTyzVuF/mEeg2shDWpRfBTdXhkGtb8vKh3L4zZh9RNitTBQ+WoE
add: 4aytTF0KPuW96/ElKenNvuP56qTyzVuF/mEeg2shDWpRfBTdXhkGtb8vKh3L4zZh9RNitTBQ+WoE

Use up-arrow / del to edit / re-enter a part:

>> list
 [1] uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC
 [2] 4aytTF0KPuW96/ElKenNvuP56qTyzVuF/mEeg2shDWpRfBTdXhkGtb8vKh3L4zZh9RNitTBQ+WoE

>> del 2
deleting key at index 2

>> list
 [1] uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC

>> add Li9jwAunsExtEJtCnYB/VxbdPjGiKPmYEVziW89r5F1kINtQWYZr6HX/mlxvzEMazNGkWeRMRYQD
add: Li9jwAunsExtEJtCnYB/VxbdPjGiKPmYEVziW89r5F1kINtQWYZr6HX/mlxvzEMazNGkWeRMRYQD

>> list
 [1] uMgk9K4nPaWXNV/soSyTdDHRrbnXsKpN4uzGc0zKx4YG7k21WGWu91sFz0fseuuwFS0xwndIq6YC
 [2] Li9jwAunsExtEJtCnYB/VxbdPjGiKPmYEVziW89r5F1kINtQWYZr6HX/mlxvzEMazNGkWeRMRYQD

When ready, type done to decrypt:

>> done
2 keys entered. validating.

Success!

$ cat foo.decrypted
hello world

Encrypting secrets using a PGP keyring

Create an ASCII-armored keyring containing the PGP keys for the recipients of the secrets. If you have the public keys but don't have them on a keyring, you can create a temporary keyring:

$ gpg --no-default-keyring --keyring ./recipients.gpg --import bob-pub.asc alice-pub.asc bill-pub.asc

Then export the list of recipients you want to receive the secrets:

$ gpg --no-default-keyring --keyring ./recipients.gpg --export -a \
	bob@example.com alice@example.com bill@example.com >keyring.asc

Finally, use secretbox to encrypt a file, and then encrypt the secrets for the recipients.

Note: The number of secret parts must equal the number of keys in the keyring. In this case we're splitting the secret into 3 parts and have 3 recipients.

$ secretbox encrypt -p 3 -t 2 -i foo.txt -o foo.crypted -k keyring.asc >secrets.txt
$ cat secrets.txt

Encrypting to 'foo.crypted'
Encrypted using secret key in 3 parts with threshold 2:

Encrypting secret 1 for recipient:
 --> Bob Jones <bob@example.com>

-----BEGIN PGP MESSAGE-----
...
-----END PGP MESSAGE-----

Encrypting secret 2 for recipient:
 --> Alice Smith <alice@example.com>

-----BEGIN PGP MESSAGE-----
...
-----END PGP MESSAGE-----

Encrypting secret 3 for recipient:
 --> Bill Davis <bill@example.com>

-----BEGIN PGP MESSAGE-----
...
-----END PGP MESSAGE-----

Now you can snip out each encrypted message and send it to the recipients.

Acknowledgements

Derived from levigross/keylesscrypto