OpenSSL verify RSA signature, read RSA public key from X509 PEM certificate

openssl-verify-rsa-signature.c

#include <stdio.h>

#include <openssl/pem.h>
#include <openssl/rsa.h>

void verifyRSASignature(unsigned char *originalMessage, unsigned int om_length,
                        unsigned char *signature, unsigned siglen)
{
    int result;
    FILE *file;
    X509 *x509;
    EVP_PKEY *evp_pubkey;
    RSA *rsa_pubkey;

    file        = fopen("developer_signer.pem", "r");
    x509        = PEM_read_X509(file, NULL, NULL, NULL);
    evp_pubkey  = X509_get_pubkey(x509);
    rsa_pubkey  = EVP_PKEY_get1_RSA(evp_pubkey);

    result      = RSA_verify(NID_md5, originalMessage, om_length,
                             signature, siglen, rsa_pubkey);

    printf("Signature is %s\n", result == 1 ? "valid" : "invalid");

    RSA_free(rsa_pubkey);
    EVP_PKEY_free(evp_pubkey);
    X509_free(x509);
    fclose(file);
}

This function is wrong. originalMessage has to be the message digest. Check out the manpage: https://www.openssl.org/docs/man1.1.1/man3/RSA_verify.html

Yep, you're right.

…

On Tue, Aug 20, 2019 at 1:18 AM paxter ***@***.***> wrote: This function is wrong. originalMessage has to be the message digest. Check out the manpage: https://www.openssl.org/docs/man1.1.1/man3/RSA_verify.html — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/396f289682089e1d767e?email_source=notifications&email_token=ABFWDOFRAW7COXTNSGL7CQ3QFLIWRA5CNFSM4IND6EL2YY3PNVWWK3TUL52HS4DFVNDWS43UINXW23LFNZ2KUY3PNVWWK3TUL5UWJTQAFXIBS#gistcomment-3002393>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABFWDOH7624N67ZGKN5CYJ3QFLIWRANCNFSM4IND6ELQ> .

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