Re: [libmicrohttpd] Some questions about the example "digest_auth_example.c"

[silvioprog]

Very good explanations. I'll comment some of them and make a new question at the bottom.

On Thu, Mar 3, 2016 at 5:06 AM, Christian Grothoff <address@hidden> wrote:

No, see:

http://security.stackexchange.com/questions/24425/what-is-the-opaque-field-in-http-digest-access-authentication-used-for

If I understood, I just need to do something like "opaqueStr = generate_md5(generate_uuid())" generating a unique opaque for each request and use it instead of the static MY_OPAQUE_STR.

MHD_OPTION_NONCE_NC_SIZE is optional, the value will default to 4 if you
specify none. Note that 4 may be a bit small for real uses. 

You can technically also leave out MHD_OPTION_DIGEST_AUTH_RANDOM, but
then you're reducing the security of your authentication as you are no
longer using salted hashes.

I'll use that. If I understood, I can use these two flags in Digest and X.509 auths. Does the timeout passed to MHD_digest_auth_check() need to be the same passed in the MHD_OPTION_NONCE_NC_SIZE?

Provide a cryptographic salt, and the size of a buffer to manage nonces. 

The size of "rnd" on memory or the length of characteres in the "rnd"?

> The example uses the "/dev/urandom" feature, but I need to make a
> cross-platform solution, so can I use a hash like a UUID (I can generate
> it using a own function) instead of using urandom?

For the opaque, sure.  For the salt, you may want to make it vary each
time the program runs.

Just to check if I understood:

- instead of using the static MY_OPAQUE_STR, I need to generate a hash for each request, something like a md5 from a UUID;

- the timeout of the MY_OPAQUE_STR need be same of the MHD_OPTION_NONCE_NC_SIZE;

- MHD_OPTION_DIGEST_AUTH_RANDOM needs a hash for each server startup, something like a md5 of the server startup time;

- MHD_OPTION_NONCE_NC_SIZE specify the timeout for the nonce (salt) specified in the MHD_OPTION_DIGEST_AUTH_RANDOM;

And now the new question: is this example validating the user name? I just put any username and it allows the login, checking only the password.

--

Silvio Clécio