Problem - Kevin Tafuro

salt_len
Length of the salt that will be used. The salt value is not actually entirely random.
Three bytes of the salt are used to encode the iteration count and the public
key size. The rest of it is random. We recommend that, if the salt is public,
you use 16-byte salts. If the salt is kept private, you will not want to make them
too large, because you will have to convert them into a printable format that the
user has to carry around and enter. The minimum size AX allows is 11 bytes,
which base64-encodes to 15 characters.
out
Pointer to a container into which credentials will be placed. You are expected to
allocate this object.
AX provides an API for serializing and deserializing credential objects:
char *AX_CRED_serialize(AX_CRED *c, size_t *outlen);
AX_CRED *AX_CRED_deserialize(char *buf, size_t buflen);
These two functions each allocate their result with malloc( ) and return 0 on error.
In addition, if the salt value is to stay private, you will need to retrieve it so that you
can encode it and show it to the user. AX provides the following function for doing
that:
char *AX_get_salt(AX_CRED *creds, size_t *saltlen);
The result is allocated by malloc( ). The size of the salt is placed into the memory
pointed to by the second argument.
Now that we can set up account information and store credentials in a database, we
can look at how to actually set up a server to handle connections. The high-level AX
API does most of the work for you. There’s an actual server abstraction, which is of
type AX_SRV.
You do need to define at least one callback, two if you want to log errors. In the first
callback, you must return a credential object for the associated user. The callback
should be a pointer to a function with the following signature:
AX_CRED *AX_get_credentials_callback(AX_SRV *s, char *user, size_t ulen,
char *extra, size_t elen);
This function has the following arguments:
s
Pointer to the server object. If you have multiple servers in a single program, you
can use this pointer to determine which server produced the request.
user
Username given to the server.
ulen
Length of the username.
424 | Chapter 8: Authentication and Key Exchange
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