HP Open Source Security for OpenVMS Volume 2: HP SSL for OpenVMS > SSL Application Programming Interface (API)
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 impossible.
Other items in PEM formatting (certificates) can also be encrypted, it is however not usual, as certificate information is considered public.
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.