sts's Introduction

STS - Simple Text Signing library

STS started as a fork of slm4j. It is now rewritten in Scala, has a new API and the "license" part has been removed: the intended purpose of STS is simply to sign text and verify a signed text, regardless of what the text is.

The signing uses the DSA algorithm.

Building

Build the library using SBT:

$ sbt compile
$ sbt package

Command line tool

First, create the wrapper script bin/sts.sh with SBT by issuing command sbt mksh.

Get usage help with option --help:

$ bin/sts.sh --help

To create a private/public key pair in files test1 and test1.pub, respectively:

$ bin/sts.sh genkeys --base-name test1

To sign file unsigned.txt using private key test1 and write the result to signed.txt.

$ bin/sts.sh sign --private-key test1 --input unsigned.txt --output signed.txt

To verify that signed file signed.txt is valid (i.e., has not been tampered with):

$ bin/sts.sh verify --public-key test1.pub --input signed.txt
Signed text is valid.
$ echo $?
0

Let's check what happens if we modify a signed file:

$ cp signed.txt tamperedWith.txt
$ vim tamperedWith.txt
$ bin/sts.sh verify --public-key test1.pub --input tamperedWith.txt
Signed text is NOT valid.
$ echo $?
2

Example signed file

As an example, here's a file that was signed by STS:

----- BEGIN TEXT -----
RegistredTo=John Smith
ExpirationDate=20090630
Version=Full
----- END TEXT -----
----- BEGIN SIGNATURE -----
MCwCFCKRoTnYFdE7JJzH
W2XQddSq9wqCR43hRQ+J
BZV5FS+ZU5j90JAZFUA2
WQ==
----- END SIGNATURE -----

Note that STS imposes no restrictions on the text except that it must not contain any line starting with the delimiter marker -----.

Any changes to the text (or the signature) and the validator will consider the file invalid.

STS on GitHub.

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