NAME
SSL_CTX_set_default_passwd_cb,
SSL_CTX_set_default_passwd_cb_userdata —
set passwd callback for encrypted PEM
file handling
SYNOPSIS
#include
<openssl/ssl.h>
void
SSL_CTX_set_default_passwd_cb(SSL_CTX
*ctx, pem_password_cb
*cb);
void
SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX
*ctx, void *u);
int
pem_passwd_cb(char
*buf, int size,
int rwflag,
void *userdata);
DESCRIPTION
SSL_CTX_set_default_passwd_cb()
sets the default password callback called when loading/storing a PEM
certificate with encryption.
SSL_CTX_set_default_passwd_cb_userdata()
sets a pointer to userdata u which will be provided to
the password callback on invocation.
The
pem_passwd_cb(),
which must be provided by the application, hands back the password to be
used during decryption. On invocation a pointer to
userdata is provided. The pem_passwd_cb must write the
password into the provided buffer buf which is of size
size. The actual length of the password must be
returned to the calling function. rwflag indicates
whether the callback is used for reading/decryption
(rwflag = 0) or
writing/encryption (rwflag =
1).
NOTES
When loading or storing private keys, a password might be supplied
to protect the private key. The way this password can be supplied may depend
on the application. If only one private key is handled, it can be practical
to have pem_passwd_cb() handle the password dialog
interactively. If several keys have to be handled, it can be practical to
ask for the password once, then keep it in memory and use it several times.
In the last case, the password could be stored into the
userdata storage and the
pem_passwd_cb() only returns the password already
stored.
When asking for the password interactively,
pem_passwd_cb()
can use rwflag to check whether an item shall be
encrypted (rwflag = 1). In
this case the password dialog may ask for the same password twice for
comparison in order to catch typos which would make decryption
impossible.
Other items in PEM formatting (certificates) can also be encrypted; it is however atypical, as certificate information is considered public.
RETURN VALUES
SSL_CTX_set_default_passwd_cb() and
SSL_CTX_set_default_passwd_cb_userdata() do not
provide diagnostic information.
EXAMPLES
The following example returns the password provided as userdata to the calling function. The password is considered to be a ‘\0’ terminated string. If the password does not fit into the buffer, the password is truncated.
int pem_passwd_cb(char *buf, int size, int rwflag, void *password)
{
strncpy(buf, (char *)password, size);
buf[size - 1] = '\0';
return strlen(buf);
}