Problem - Kevin Tafuro

siglen
The number of bytes written into the signature buffer will placed in the integer
pointed to by this argument. The number of bytes will always be the same size as
the prime parameter q, which can be determined by calling DSA_size( ) with the
DSA object that will be used to generate the signature.
dsa
DSA object to be used to generate the signature. The DSA object must contain the
parameters and the private key for signing.
Here’s a slightly higher-level function that wraps the DSA_sign( ) function, signing an
arbitrary message:
#include
#include
#include
int spc_DSA_sign(unsigned char *msg, int msglen, unsigned char *sig, DSA *dsa) {
unsigned int ignored;
unsigned char hash[20];
if (!SHA1(msg, msglen, hash)) return 0;
return DSA_sign(NID_sha1, hash, 20, sig, &ignored, dsa);
}
Verification of a signature is done with the function DSA_verify( ):
int DSA_verify(int type, unsigned char *md, int mdlen, unsigned char *sig,
int siglen, DSA *dsa);
The arguments for DSA_verify( ) are essentially the same as the arguments for DSA_
sign( ). The DSA object must contain the public key of the signer, and the fourth
argument, sig, must contain the signature that is to be verified. Unlike with DSA_
sign( ), it actually makes sense to pass in the length of the signature because it saves
the caller from having to check to see if the signature is of the proper length. Nonetheless,
DSA_verify( ) could do without the first argument, and it could hash the
message for you. Here’s our wrapper for it:
#include
#include
#include
int spc_DSA_verify(unsigned char *msg, int msglen, unsigned char *sig, int siglen,
DSA *dsa) {
unsigned char hash[20];
if (!SHA1(msg, msglen, hash)) return 0;
return DSA_verify(NID_sha1, hash, 20, sig, siglen, dsa);
}
Using the Digital Signature Algorithm (DSA) | 351
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