I started developing this library when I was trying to use MongoDB with the cl-mongo driver, and it became apparent that the driver had not been updated to use mongo's modern SCRAM-SHA1 authentication method.
Given the choices of relying on an antiquated MD5-based login method or writing a shiny new library, I chose the latter. The purpose of
cl-scram is to allow for everything the client needs to do SCRAM login with the SHA1 hash algorithm.
The library is dependent on
ironclad for all cryptographic functions. It does not rely on any DIY crypto.
The project is licensed under the Revised BSD License.
Copyright (c) 2015, Matt Prelude All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of Matt Prelude nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATT PRELUDE BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Use ASDF to install
cl-scram as it has a number of dependencies. I will be looking to include
cl-scram in Quicklisp later on.
* (asdf:load-system :cl-scram)
All of the functions are in the
TODO: Add regression tests.
Generating a client nonce
The first step in a SCRAM request is to generate a nonce for the request. This can be done as follows:
* (gen-client-nonce) "x6uHptrIM6PAFMtmbGCN8uuy0LSnZCww"
This is fully supported by
cl-scrams message-generating functions, which accept a
Generating first client message
Next, we need to generate the first client message. To generate an un-encoded message, you can call the
gen-client-initial-message function with the username & nonce:
* (gen-client-initial-message :username "username" :nonce "x6uHptrIM6PAFMtmbGCN8uuy0LSnZCww") "n,,n=username,r=x6uHptrIM6PAFMtmbGCN8uuy0LSnZCww"
You'll need to pass this to the server.
Generating final client message
The server should respond with a base64-encoded string, which when decoded looks something like this:
In order to generate the final response, we'll need to create a new request (this is based on the exchange from the RFC document, in order to show that it creates the same final message):
* (gen-client-final-message :password "pencil" :client-nonce "fyko+d2lbbFgONRv9qkxdawL" :client-initial-message "n,,n=user,r=fyko+d2lbbFgONRv9qkxdawL" :server-response "r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,s=QSXCR+Q6sek8bf92,i=4096") ((CL-SCRAM::SERVER-SIGNATURE . #(174 97 125 166 165 124 75 187 46 2 134 86 141 174 29 37 25 5 176 164)) (CL-SCRAM::FINAL-MESSAGE . "c=biws,r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,p=v0X8v3Bz2T0CJGbJQyF0X+HI4Ts="))
Your application will want to send the
final-message back to the server, and store the
server-signature for validating the server's final response.
Dealing with final server message
The server will respond with a base64-encoded string. If this is the same as the
server-signature from the last step, then authentication was successful.
If this library has been helpful to you, I don't seek any donations, but please feel free to donate to Quicklisp, one of the most important projects in the CL ecosystem.
Understanding the first server response
The server should respond with a base64-encoded string, when decoded, this will have three parameters:
- The value of
ris the nonce.
- The value of
sis the salt (base64-encoded).
- The value of
iis the number of iterations.
cl-scram provides three convenience methods to access & validate the data.
To get the nonce (and confirm that it correctly starts with the client nonce), call
parse-server-nonce passing the decoded message response & the client nonce:
* (parse-server-nonce :nonce "6d44" :response "r=6d442b5d9e51a740f369e3dcecf3178ec12b3985bbd4a8e6f814b422ab766573,s=Vdptv0j/N6fs2qtVADc1Xg==,i=8192") "6d442b5d9e51a740f369e3dcecf3178ec12b3985bbd4a8e6f814b422ab766573"
And to get the salt (base64-decoded), call
* (parse-server-salt :response "r=6d442b5d9e51a740f369e3dcecf3178ec12b3985bbd4a8e6f814b422ab766573,s=Vdptv0j/N6fs2qtVADc1Xg==,i=8192") "U?m?H?7????U75^"
And finally, to get the number of iterations, you can call
* (parse-server-iterations :response "r=6d442b5d9e51a740f369e3dcecf3178ec12b3985bbd4a8e6f814b422ab766573,s=Vdptv0j/N6fs2qtVADc1Xg==,i=8192") "8192"
- Implement SASLprep algorithm to support the full gamut of passwords. For now, using the library with passwords containing unsupported characters is considered unsupported behavior.
- Add regression tests.
- Support algorithms other than SHA-1.
- Matt Prelude <email@example.com>
- Revised BSD License (see LICENSE)