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ristsender includes an “authorized listener” mechanism. Highly secure user/password hashes are stored in an external file. ristsender then listens upon a particular IP address or port (or several, if the server is so provisioned). Receivers can contact the sender, present their authorization credentials, and if duly authorized, the input(s) are then sent using the main or advanced protocol to the receiver. In practice, this means that libRIST can function as a quasi-media server.
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This section first describes the security protocol for the secure exchange of credentials, then, use of the utility for creation of the credentials repository, and finally provides example command lines.
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**Authorization Protocol Overview**
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The diagram below provides an overview of the process. The authenticator is the server. The authenticatee is the client.
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![Authentication_Overview](uploads/b80ffb1a4c659fcf0a54726b1a22e6dc/Authentication_Overview.jpg)
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As you can see, it's a multi-step process, using SRP and EAP as "inspiration." It adapts those protocol's step-by-step challenge-response methods to take into account possible packet loss when using the udp protocol.
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At the point illustrated above, both sides have already connected with each other. It doesn't matter which side initiates the connection. What is important is that the server, which has the password file, is the one who initiates the authentication. Needless to say, the client doesn't get a stream until they're authenticated.
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In the first step, the server sends an identity request.
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The client responds with an identity response. That includes a value that the then server looks up in its srp password file.
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If the server finds the client's ID in that database, it generates a response. This is based upon the value from the client's first message.
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Once the client has the response, it generates an ephemeral public key. It does this using the value in the server's response, and its own private key. It sends that to the server. In the illustration above, you'll see a red key, labeled public key A.
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Once the server/authenticator receives that, it mathematically cross checks it and validates it. It then generates another ephemeral public key, and sends that to the client. In the illustration, this is the blue key, and it's labeled public Key B.
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This is only the first exchange. The client must still send a validating value, called M1. In the illustration, it is illustrated by a small curve, in red.
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The server validates M1. Once validated, the server then generates M2, and sends that to the client.
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The client then validates M2, and sends an acknowledgment to the server.
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The server acknowledges the acknowledgement, and the authorization process is complete.
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**ristsrppasswd**
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libRIST now includes a utility called ristsrppasswd. If you're familiar with Apache's htpasswd utility, it's something along those lines. It will generate a SHA256 password hash.
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Usage is simply:
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ristsrppasswd [username] [password]
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An example script specifying "user##" as user and "user##" as password, which you can then adapt and run at your own command line, is as follows:
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| bash script: generate_password_file.sh |
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| ------ |
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| #!/bin/sh |
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| ristsrppasswd user01 user01 > /tmp/srp_pass.txt |
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| ristsrppasswd user02 user02 >> /tmp/srp_pass.txt |
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| ristsrppasswd user03 user03 >> /tmp/srp_pass.txt |
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| ristsrppasswd user04 user04 >> /tmp/srp_pass.txt |
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| ristsrppasswd user05 user05 >> /tmp/srp_pass.txt |
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| # ... and so forth |
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If we run the script, the output of the "user01" will be the following:
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| Output of "user01" |
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| ------ |
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| user01:GATh2Brq81MG15B2Si/wSrbnM4a7dIvZ7kz7ohSfyiWCidb9Y5NyNRrpBlYvFGyzvWY2E67o27U3/a3/D3aLDkxR8UauHTZ2wHe8QI+MAbk7fChqGzpzjZCZ1Q+VLbU8FFxvb0U5ApbXBp19/1VCUfDcBD8KtKKmMBkmuonQnLF8+lgvqVttnfh9Mdsl/7gdRgfHMMa/Aou66KTUWv82L5WwK9JruVi4c2Xo2ba/5PENq51QpHEZCjn6b7ZQy5fQcRPcFM+dMlZ2w8Su5zo3NKWgH6nd6W5/G2oeUkjBMVp/tx2UDsFfovXYEiEg87JMxpQcrFxgzgQkOHYx1rTFaA:nX3DaJ2YxbswTkqlrTPIABP6xLPw5dFgI7lLQLZ6seU:3 |
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*Note that in addition to the SHA256 password hash storage, librist includes an https client dynamic authorization mechanism. This will be documented elsewhere. It allows you to create a query to your own billing or other system. The librist server sends a query to the server, and the server responds with an HTTP 200 response for "yes" or any other response for "no."*
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**Usage of the srppassword File**
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| Sender Sample Usage |
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| ------ |
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| ristsender -i 'udp://127.0.0.1:8292?stream-id=1000' -o 'rist://@123.123.123.123:8192?cname=MYSERVER&bandwidth=10000&buffer-min=1000&buffer-max=1000&rtt-min=25&rtt-max=105&reorder-buffer=25&virt-dst-port=1968&weight=0&congestion-control=1&aes-type=128&secret=MyPassPhrase' -p 1 -v 6 --srpfile /tmp/srp_pass.txt |
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In the command line above, the sender pulls a udp input stream from 127.0.0.1:8292. The output URL is where the authorization takes place. It listens (notice the "@" sign) on its publically accessible IP (123.123.123.123:8192). Various parameters such as its canonical name, buffer and delay, congestion control and AES 128 encryption are set. Then the srp file (/tmp/srp_pass.txt) is specified at end.
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At the rist receiver, the command line could then be specified as follows:
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| Receiver Sample Usage |
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| ------ |
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| ristreceiver -i 'rist://123.123.123.123:8192?cname=MYRECEIVER&bandwidth=10000&buffer-min=1000&buffer-max=1000&rtt-min=25&rtt-max=105&reorder-buffer=25&virt-dst-port=1968&weight=0&congestion-control=1&aes-type=128&secret=MyPassPhrase&username=user01&password=user01' -o 'udp://192.168.1.11:8300' -p 1 -v 6 |
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The command line above mostly "mirrors" the parameters of the server. The credentials are given for a single use only, because the receiver (presumably) does not know any credentials but their own. These are appended at the end of the rist:// URL. |
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\ No newline at end of file |