Problem - Kevin Tafuro

h_ret
Optional argument that, if not specified as NULL, will have the number of iterations
the function went through to find a suitable generator stored in it.
callback
Pointer to a function that will be called by BN_generate_prime( ) to report status
when generating the primes p and q. It may be specified as NULL, in which case
no progress will be reported. See Recipe 7.4 for a discussion of BN_generate_
prime( ).
cb_arg
Application-specific value that will be passed directly to the callback function for
progress reporting if one is specified.
Note that DSA_generate_parameters( ) does not generate an actual key pair. Parameter
sets can be reused across multiple users; key pairs cannot. An OpenSSL DSA object
with the parameters set properly can be used to generate a key pair with the function
DSA_generate_key( ), which will allocate and load BIGNUM objects for the pub_key and
priv_key fields. It returns 1 on success.
int DSA_generate_key(DSA *ctx);
With OpenSSL, there is an optional precomputation step to DSA signing. Basically,
for each message you sign, DSA requires you to select a random value and perform
some expensive math operations on that value. You can do this precomputation
before there’s actually data to sign, or you can wait until you have data to sign,
which will slow down the signature process.
To maintain security, the results of precomputation can only be used
for a single signature. You can precompute again before the next signature,
though.
DSA signature precomputation is a two-step process. First, you use DSA_sign_setup( ),
which will actually perform the precomputation of two values, kinv and r:
int DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp, BIGNUM **rp);
This function has the following arguments:
dsa
ctx
Context object containing the parameters and the private key that will be used
for signing.
Optional BN_CTX object that will be used for scratch space (see Recipe 7.4). If it is
specified as NULL, DSA_sign_setup( ) will internally create its own BN_CTX object
and free it before returning.
Using the Digital Signature Algorithm (DSA) | 349
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