OpenSSL sha256 signing and verifying with CPP - c++

Question

My code should read a PKCS12 to get the private key to sign some files and check its signature.
Reading and parse the PKCS12 seems to work fine. the problem happend specially at verifying. Here follows the signing and verifying.
int sign (EVP_PKEY *pkey, char* msg,unsigned char** sig, size_t* slen){
EVP_MD_CTX *mdctx = NULL;
int ret = 0;
size_t req = 0;
*sig = NULL;
/* Create the Message Digest Context */
if(!(mdctx = EVP_MD_CTX_create())) {
qDebug()<<"0";
return 0;
}
/* Initialise the DigestSign operation - SHA-256 has been selected as the message digest function in this example */
if(1 != EVP_DigestSignInit(mdctx, NULL, EVP_sha256(), NULL,pkey)) {
qDebug()<<"A";
return 0;
}
/* Call update with the message */
if(1 != EVP_DigestSignUpdate(mdctx, msg, strlen(msg))) {
qDebug()<<"B";
return 0;
}
/* Finalise the DigestSign operation */
/* First call EVP_DigestSignFinal with a NULL sig parameter to obtain the length of the
* signature. Length is returned in slen */
if(1 != EVP_DigestSignFinal(mdctx, NULL, slen)) {
qDebug()<<"C";
return 0;
}
/* Allocate memory for the signature based on size in slen */
if(!(*sig =(unsigned char *) OPENSSL_malloc(sizeof(unsigned char) * (*slen)))){
qDebug()<<"D";
return 0;
}
/* Obtain the signature */
if(1 != EVP_DigestSignFinal(mdctx, *sig, slen)){
qDebug()<<"E";
return 0;
}
//qDebug()<<(char*)sig;
/* Success */
ret = 1;
/* Clean up */
if(*sig && !ret) OPENSSL_free(*sig);
if(mdctx) EVP_MD_CTX_destroy(mdctx);
qDebug()<<"SIGNED";
return 1;
}
/*------------------------------*/
int verify(EVP_PKEY *pubkey, const char* msg,unsigned char* sig, size_t slen){
EVP_MD_CTX *mdctx;
ERR_get_error();
if(!(mdctx = EVP_MD_CTX_create())) {
qDebug()<<"DEU RUIM";
}
EVP_MD_CTX_init(mdctx);
if(1 != EVP_DigestVerifyInit(mdctx, NULL, EVP_sha256(), NULL, pubkey)){
qDebug()<<"Err1";
return 0;
}
if(1 != EVP_DigestVerifyUpdate(mdctx, msg, strlen(msg))){
qDebug()<<"Err2";
return 0;
}
ERR_print_errors_fp(stderr);
if(1 == EVP_DigestVerifyFinal(mdctx, sig, slen)) {
qDebug()<<"THE FILE IS ORIGINAL";
return 1;
} else{
qDebug()<<"THE FILE IS NOT ORIGINAL";
return 0;
}
}
The idea is to write the certificate to a file and read it from the file when I want to verify. The problem is the it only verifies correctly(prints 'THE FILE IS ORIGINAL') when I call the verify() after sign() passing the 'sig' and 'slen' parameters altered in the sign() to the verify(), otherwise I just receive 'THE FILE IS NOT ORIGINAL' without any error.
Printed out the parameters used in verify() when it works and when it doesn't, but they look exactly the same the same.
Here is how I call the functions
/*---(START)IF COMMENT THIS PART, VERIFIES WRONGLY---*/
sign(prkey, msg, &sig, &len);
/*write file certificate*/
ofstream outfile("outCert",ios::out | ios::binary);
outfile.write((reinterpret_cast<const char*>(sig)),len);
/*---(END)---*/
//set public key
EVP_PKEY* pubkey=X509_get_pubkey(cert);
FILE* file2;
unsigned char *msg2;
size_t sz;
file2=fopen ("outCert","rb");
if(file2!=NULL){
fseek(file2, 0L, SEEK_END);
sz = ftell(file2);
fseek(file2, 0, SEEK_SET);
msg2 = new unsigned char [sz];
fread(msg2,1,sz,file2);
fclose(file2);
}else cout << "Unable to open file";
//change 'msg2' and 'sz' for 'sig' and 'len' to work respectively
verify(pubkey,msg,msg2,sz);
One problem is that it can't read from the file right after writing in it. So I have to run once to write, comment the writing part and run to read. << SOLVED this part. Just added outfile.close() after writing
I don't know if OpenSSL functions are affected by time, but tried put some delay between the functions and got same result.
Any help is welcome!