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I intentionally designed SecretSplitter to be fully compatible with existing
tools since they’ve been around for many years. In addition, this helps assure
people that I’m not doing anything special.
Although ssss-split, ssss-combine, and GPG are available on Windows, I tested
everything here using Ubuntu 11.10 to ensure broad compatibility. You're
welcome to verify my results by first getting ssss which is available via:
sudo apt-get install ssss
NOTE: I do everything manually here for demonstration purposes. You're
encouraged to create and share shell scripts to help others who might do this
from the command line.
========================= Working with Messages ===============================
In my blog post, you can see the following split message pieces ("shares"):
3c1-1-ed6c3642885d0fb57a4bb078513f8cca4306f00c7eba
061-2-e6d823681303ef4bd49cccfe39623aa788a1d67b1d4f
151-3-1fb42f8e65c9b0e1b12e1883e156a88331c334563be5
To verify compatibility, I ran these commands:
jeff@ubuntu:~$ ssss-combine -t 2
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Enter 2 shares separated by newlines:
Share [1/2]: 3c1-1-ed6c3642885d0fb57a4bb078513f8cca4306f00c7eba
Share [2/2]: 061-2-e6d823681303ef4bd49cccfe39623aa788a1d67b1d4f
Resulting secret: 1.big.BOOM@thunder.mil
and verified the 3rd share as:
jeff@ubuntu:~$ ssss-combine -t 2
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Enter 2 shares separated by newlines:
Share [1/2]: 061-2-e6d823681303ef4bd49cccfe39623aa788a1d67b1d4f
Share [2/2]: 151-3-1fb42f8e65c9b0e1b12e1883e156a88331c334563be5
Resulting secret: 1.big.BOOM@thunder.mil
(NOTE: you can avoid the ENOMEM warning by using "sudo ssss-combine -t 2"
instead.)
I also verified that you can create compatible messages:
jeff@ubuntu:~$ ssss-split -t 2 -n 3
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Enter the secret, at most 128 ASCII characters: 1.big.BOOM@thunder.mil
Using a 176 bit security level.
1-9d97f21a25671d5bdd77008bb4e3cdb1b9738df5cab0
2-072fabd94977ca969ae5ad19f2dab8507c4b2d88755b
3-8eb86367928787d2586bc997cf326b0f3f5cb25ce7fb
I verified that any 2 of these 3 messages work in SecretSplitter as-is.
However, we can also create fully-compatible checksums too. First, we
prefix every share with "1-" to denote that it's a message. Then, we
get the SHA-1 hash of each of these shares:
jeff@ubuntu:~$ echo -n '1-1-9d97f21a25671d5bdd77008bb4e3cdb1b9738df5cab0' | sha1sum
65a7751182da8eb474d34367d070c986fe0aaaee -
jeff@ubuntu:~$ echo -n '1-2-072fabd94977ca969ae5ad19f2dab8507c4b2d88755b' | sha1sum
a40fbadc80dfbe354f360cd31e28880468ead79b -
jeff@ubuntu:~$ echo -n '1-3-8eb86367928787d2586bc997cf326b0f3f5cb25ce7fb' | sha1sum
fb47cd67facd56dbb788d7edc6324369bc8a17d2 -
Now, just append the first byte (i.e. the first two characters/nibbles) of each SHA-1
hash above to get:
651-1-9d97f21a25671d5bdd77008bb4e3cdb1b9738df5cab0
a41-2-072fabd94977ca969ae5ad19f2dab8507c4b2d88755b
fb1-3-8eb86367928787d2586bc997cf326b0f3f5cb25ce7fb
You can use any of these two in SecretSplitter to recover the message without
errors.
========================= Working with Files ==================================
You can also open files created in SecretSplitter on Linux. First, we'll need
to recover the secret passphrase from the shares:
jeff@ubuntu:~$ ssss-combine -t 2 -x
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Enter 2 shares separated by newlines:
Share [1/2]: 632-1-207c695c143a22eb32e76e8f4c675cbd
Share [2/2]: a22-2-29e3156730e49746bcc4f9ff201a922c
Resulting secret: c6b9e1dbf5f6c09a62b75693f517768d
Alternatively, we could use the bottom 2 shares:
jeff@ubuntu:~$ ssss-combine -t 2 -x
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Enter 2 shares separated by newlines:
Share [1/2]: a22-2-29e3156730e49746bcc4f9ff201a922c
Share [2/2]: 952-3-d169c171d351042239258b2f0431d7dc
Resulting secret: c6b9e1dbf5f6c09a62b75693f517768d
As you can see, the recovered passphrase is the same.
NOTE: It's critical to note the "-x" flag that specifies that heXadecimal
output is assumed.
We can now use this recovered key directly with GPG:
jeff@ubuntu:~$ gpg "If Something Happens to Jeff.splitsecret"
gpg: AES256 encrypted data
(passphrase dialog appears where we type "c6b9e1dbf5f6c09a62b75693f517768d")
gpg: encrypted with 1 passphrase
gpg: If Something Happens to Jeff.splitsecret: unknown suffix
Enter new filename [If Something Happens to Jeff.zip]:
At this point, I verified the recovered file contents.
We can also create files on Linux and have them work with SecretSplitter.
First, we create a random 128 bit key in hexadecimal notation (32 hex characters):
jeff@ubuntu:~$ cat /dev/urandom | tr -dc ‘0-9a-f’ | fold -w 32 | head -n 1
a95970240705fc04d3ca67c6bf7ceeed
We can then split this random key:
jeff@ubuntu:~$ ssss-split -t 2 -n 3 -x
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
Generating shares using a (2,3) scheme with dynamic security level.
Enter the secret, as most 256 hex digits: a95970240705fc04d3ca67c6bf7ceeed
Using a 128 bit security level.
1-368a7486c6b01e7922a55889dc6316d9
2-d87036d1c5171259b4d0f029dbb5c651
3-822608e33b8a1646390397b626f8762b
Like before, we add a prefix to indicate each share's type (it's a file = 2)
and then get the SHA-1 hash:
jeff@ubuntu:~$ echo -n '2-1-368a7486c6b01e7922a55889dc6316d9' | sha1sum
83937c41d8ee0faf766b35ba9e6fc8f676f414c7 -
jeff@ubuntu:~$ echo -n '2-2-d87036d1c5171259b4d0f029dbb5c651' | sha1sum
2e8ef2956183885e1422fe76f3be37b4f6046527 -
jeff@ubuntu:~$ echo -n '2-3-822608e33b8a1646390397b626f8762b' | sha1sum
e7a88b43de1b91bd4230181617e8ce0a4912a8f9 -
Adding the first byte of the hash gives us these shares:
832-1-368a7486c6b01e7922a55889dc6316d9
2e2-2-d87036d1c5171259b4d0f029dbb5c651
e72-3-822608e33b8a1646390397b626f8762b
We can now create the encrypted file using GPG in a way that's compatible with
SecretSplitter:
jeff@ubuntu:~$ echo -n "Hello from Ubuntu!" > hello.txt
jeff@ubuntu:~$ gpg --s2k-digest-algo SHA256 --s2k-cipher-algo AES256 -c hello.txt
(prompted for passphrase, entered in "a95970240705fc04d3ca67c6bf7ceeed" and
then hello.txt.gpg was generated)
You can then use any 2 of the above 3 shares and the generated GPG file in
SecretSplitter to decrypt it.
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