Problem - Kevin Tafuro

This function has the following arguments:
md_type
OpenSSL-specific identifier for the hash function. Possible values are NID_sha1,
NID_ripemd, orNID_md5. A fourth value, NID_md5_sha1, can be used to combine
MD5 and SHA1 by hashing with both hash functions and concatenating the
results. These four constants are defined in the header file openssl/objects.h.
dgst
Buffer containing the digest of the data whose signature is to be verified. The
digest should have been generated by the algorithm specified by the md_type
argument.
dlen
Length in bytes of the digest buffer. For MD5, the digest buffer should always be
16 bytes. For SHA1 and RIPEMD, it should always be 20 bytes. For the MD5
and SHA1 combination, it should always be 36 bytes.
sig
Buffer containing the signature that is to be verified.
siglen
Number of bytes contained in the signature buffer. The number of bytes should
always be the same size as the public modulus, which can be determined by calling
RSA_size( ) with the RSA object that will be used to verify the signature.
r
RSA object to be used to verify the signature. The RSA object must contain the
signer’s public key for verification to be successful.
As we discussed in Recipe 7.12, OpenSSLRSA signatures only support PKCS #1 v1.5
and do not support RSASSA-PSS.
Here’s code that implements verification on an arbitrary message, given a signature
and the public RSA key of the signer:
#include
#include
#include
#include
int spc_verify(unsigned char *msg, unsigned int mlen, unsigned char *sig,
unsigned int siglen, RSA *r) {
unsigned char hash[20];
BN_CTX *c;
int ret;
if (!(c = BN_CTX_new( ))) return 0;
if (!SHA1(msg, mlen, hash) || !RSA_blinding_on(r, c)) {
BN_CTX_free(c);
return 0;
}
342 | Chapter 7: Public Key Cryptography
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