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Is it considered bad practice to use the same N and q parameters for all users in an SRP-6A based authentication system?

I know that q MUST be a Sophie Germain prime and N a safe prime, but can they be generated ahead of time and be somewhat fixed / hardcoded in the client and server? Or should I generate a fresh pair for each new user registration?

I imagine, it's better to have a different one for each account, but if it's not affecting the security of the system in any way...

cryptonerd
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  • what is q? the parameters are usually defined as N a safe prime and g its generator which you can create from OpenSSL with openssl dhparam -text <bit-length> – simbo1905 Oct 10 '15 at 22:29

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You can pre-compute and hardcode N and g into your client and server. There's no harm in doing this. I do not believe that using per-user N will provide any additional security.

It is common practice to define SRP parameters for a particular application or (larger) protocol, see e.g. RFC 5054.

Community
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Andrey
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