SSL_CTX_set_default_passwd_cb, SSL_CTX_set_default_passwd_cb_userdata — set passwd callback for encrypted PEM file handling
SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, pem_password_cb *cb);
SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx, void *u);
pem_passwd_cb(char *buf, int size, int rwflag, void *userdata);
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 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).
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, that would make decryption
Other items in PEM formatting (certificates) can also be encrypted,
it is however not usual, as certificate information is considered
SSL_CTX_set_default_passwd_cb() and SSL_CTX_set_default_passwd_cb_userdata()
do not provide diagnostic information.
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';