=pod

=head1 NAME

SRP_VBASE_new,
SRP_VBASE_free,
SRP_VBASE_init,
SRP_VBASE_add0_user,
SRP_VBASE_get1_by_user,
SRP_VBASE_get_by_user
- Functions to create and manage a stack of SRP user verifier information

=head1 SYNOPSIS

 #include <openssl/srp.h>

 SRP_VBASE *SRP_VBASE_new(char *seed_key);
 void SRP_VBASE_free(SRP_VBASE *vb);

 int SRP_VBASE_init(SRP_VBASE *vb, char *verifier_file);

 int SRP_VBASE_add0_user(SRP_VBASE *vb, SRP_user_pwd *user_pwd);
 SRP_user_pwd *SRP_VBASE_get1_by_user(SRP_VBASE *vb, char *username);
 SRP_user_pwd *SRP_VBASE_get_by_user(SRP_VBASE *vb, char *username);

=head1 DESCRIPTION

The SRP_VBASE_new() function allocates a structure to store server side SRP
verifier information.
If B<seed_key> is not NULL a copy is stored and used to generate dummy parameters
for users that are not found by SRP_VBASE_get1_by_user(). This allows the server
to hide the fact that it doesn't have a verifier for a particular username,
as described in section 2.5.1.3 'Unknown SRP' of RFC 5054.
The seed string should contain random NUL terminated binary data (therefore
the random data should not contain NUL bytes!).

The SRP_VBASE_free() function frees up the B<vb> structure.
If B<vb> is NULL, nothing is done.

The SRP_VBASE_init() function parses the information in a verifier file and
populates the B<vb> structure.
The verifier file is a text file containing multiple entries, whose format is:
flag base64(verifier) base64(salt) username gNid userinfo(optional)
where the flag can be 'V' (valid) or 'R' (revoked).
Note that the base64 encoding used here is non-standard so it is recommended
to use L<srp(1)> to generate this file.

The SRP_VBASE_add0_user() function adds the B<user_pwd> verifier information
to the B<vb> structure. See L<SRP_user_pwd_new(3)> to create and populate this
record.
The library takes ownership of B<user_pwd>, it should not be freed by the caller.

The SRP_VBASE_get1_by_user() function returns the password info for the user
whose username matches B<username>. It replaces the deprecated
SRP_VBASE_get_by_user().
If no matching user is found but a seed_key and default gN parameters have been
set, dummy authentication information is generated from the seed_key, allowing
the server to hide the fact that it doesn't have a verifier for a particular
username. When using SRP as a TLS authentication mechanism, this will cause
the handshake to proceed normally but the first client will be rejected with
a "bad_record_mac" alert, as if the password was incorrect.
If no matching user is found and the seed_key is not set, NULL is returned.
Ownership of the returned pointer is released to the caller, it must be freed
with SRP_user_pwd_free().

=head1 RETURN VALUES

SRP_VBASE_init() returns B<SRP_NO_ERROR> (0) on success and a positive value
on failure.
The error codes are B<SRP_ERR_OPEN_FILE> if the file could not be opened,
B<SRP_ERR_VBASE_INCOMPLETE_FILE> if the file could not be parsed,
B<SRP_ERR_MEMORY> on memory allocation failure and B<SRP_ERR_VBASE_BN_LIB>
for invalid decoded parameter values.

SRP_VBASE_add0_user() returns 1 on success and 0 on failure.

=head1 SEE ALSO

L<srp(1)>,
L<SRP_create_verifier(3)>,
L<SRP_user_pwd_new(3)>,
L<SSL_CTX_set_srp_password(3)>

=head1 HISTORY

The SRP_VBASE_add0_user() function was added in OpenSSL 3.0.0.

All other functions were added in OpenSSL 1.0.1.

=head1 COPYRIGHT

Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
