Problem - Kevin Tafuro

cb_arg
If a callback function is specified to obtain the password or passphrase for key
derivation, this application-specific value is passed directly to the callback function.
If encryption is desired, OpenSSLwill use PKCS #5 Version 1.5 to derive an encryption
key from a password. This is an earlier version of the algorithm described in
Recipe 4.10.
This function will return 1 if the encoding is successful, 0 otherwise (for example, if
the underlying file is not open for writing).
The type pem_password_cb is defined as follows:
typedef int (*pem_password_cb)(char *buf, int len, int rwflag, void *cb_arg);
It has the following arguments:
buf
Buffer into which the password or passphrase is to be written.
len
Length in bytes of the password or passphrase buffer.
rwflag
Indicates whether the password is to be used for encryption or decryption. For
encryption (when writing out data in PEM format), the argument will be 1; otherwise,
it will be 0.
cb_arg
This application-specific value is passed in from the final argument to the PEM
encoding or decoding function that caused this callback to be made.
Make sure that you do not overflow buf when writing data into it!
Your callback function is expected to return 1 if it successfully reads a password;
otherwise, it should return 0.
The function for writing an RSA private key to a BIO object has the following signature,
which is essentially the same as the function for writing an RSA private key to a
FILE object. The only difference is that the first argument is the BIO object to write to
instead of a FILE object.
int PEM_write_bio_RSAPrivateKey(BIO *bio, RSA *obj, EVP_CIPHER *enc,
unsigned char *kstr, int klen,
pem_password_cb callback, void *cbarg);
360 | Chapter 7: Public Key Cryptography
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