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Date: Mon, 30 Sep 1996 12:43:15 +1000 (EST)
From: Eric Young <eay@mincom.com>
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To: Sampo Kellomaki <sampo@neuronio.pt>
Cc: ssl-users@mincom.com, sampo@brutus.neuronio.pt
Subject: Re: Signing with envelope routines
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On Mon, 30 Sep 1996, Sampo Kellomaki wrote:
> I have been trying to figure out how to produce signatures with EVP_
> routines. I seem to be able to read in private key and sign some
> data ok, but I can't figure out how I am supposed to read in
> public key so that I could verify my signature. I use self signed
> certificate.
hmm... a rather poorly documented are of the library at this point in time.
> I figured I should use
> EVP_PKEY* pkey = PEM_ASN1_read(d2i_PrivateKey, PEM_STRING_EVP_PKEY,
> fp, NULL, NULL);
> to read in private key and this seems to work Ok.
>
> However when I try analogous
> EVP_PKEY* pkey = PEM_ASN1_read(d2i_PublicKey, PEM_STRING_X509,
> fp, NULL, NULL);
What you should do is
X509 *x509=PEM_read_X509(fp,NULL,NULL);
/* which is the same as PEM_ASN1_read(d2i_X509,PEM_STRING_X509,fp,
* NULL,NULL); */
Then
EVP_PKEY *pkey=X509_extract_key(x509);
There is also a X509_REQ_extract_key(req);
which gets the public key from a certificate request.
I re-worked quite a bit of this when I cleaned up the dependancy on
RSA as the private key.
> I figured that the second argument to PEM_ASN1_read should match the
> name in my PEM encoded object, hence PEM_STRING_X509.
> PEM_STRING_EVP_PKEY seems to be somehow magical
> because it matches whatever private key there happens to be. I could
> not find a similar constant to use with getting the certificate, however.
:-), PEM_STRING_EVP_PKEY is 'magical' :-). In theory I should be using a
standard such as PKCS#8 to store the private key so that the type is
encoded in the asn.1 encoding of the object.
> Is my approach of using PEM_ASN1_read correct? What should I pass in
> as name? Can I use normal (or even self signed) X509 certificate for
> verifying the signature?
The actual public key is kept in the certificate, so basically you have
to load the certificate and then 'unpack' the public key from the
certificate.
> When will SSLeay documentation be written ;-)? If I would contribute
> comments to the code, would Eric take time to review them and include
> them in distribution?
:-) After SSLv3 and PKCS#7 :-). I actually started doing a function list
but what I really need to do is do quite a few 'this is how you do xyz'
type documents. I suppose the current method is to post to ssl-users and
I'll respond :-).
I'll add a 'demo' directory for the next release, I've appended a
modified version of your program that works, you were very close :-).
eric
/* sign-it.cpp - Simple test app using SSLeay envelopes to sign data
29.9.1996, Sampo Kellomaki <sampo@iki.fi> */
/* converted to C - eay :-) */
#include <stdio.h>
#include "rsa.h"
#include "evp.h"
#include "objects.h"
#include "x509.h"
#include "err.h"
#include "pem.h"
#include "ssl.h"
void main ()
{
int err;
int sig_len;
unsigned char sig_buf [4096];
static char certfile[] = "plain-cert.pem";
static char keyfile[] = "plain-key.pem";
static char data[] = "I owe you...";
EVP_MD_CTX md_ctx;
EVP_PKEY * pkey;
FILE * fp;
X509 * x509;
/* Just load the crypto library error strings,
* SSL_load_error_strings() loads the crypto AND the SSL ones */
/* SSL_load_error_strings();*/
ERR_load_crypto_strings();
/* Read private key */
fp = fopen (keyfile, "r"); if (fp == NULL) exit (1);
pkey = (EVP_PKEY*)PEM_ASN1_read ((char *(*)())d2i_PrivateKey,
PEM_STRING_EVP_PKEY,
fp,
NULL, NULL);
if (pkey == NULL) { ERR_print_errors_fp (stderr); exit (1); }
fclose (fp);
/* Do the signature */
EVP_SignInit (&md_ctx, EVP_md5());
EVP_SignUpdate (&md_ctx, data, strlen(data));
sig_len = sizeof(sig_buf);
err = EVP_SignFinal (&md_ctx,
sig_buf,
&sig_len,
pkey);
if (err != 1) { ERR_print_errors_fp (stderr); exit (1); }
EVP_PKEY_free (pkey);
/* Read public key */
fp = fopen (certfile, "r"); if (fp == NULL) exit (1);
x509 = (X509 *)PEM_ASN1_read ((char *(*)())d2i_X509,
PEM_STRING_X509,
fp, NULL, NULL);
if (x509 == NULL) { ERR_print_errors_fp (stderr); exit (1); }
fclose (fp);
/* Get public key - eay */
pkey=X509_extract_key(x509);
if (pkey == NULL) { ERR_print_errors_fp (stderr); exit (1); }
/* Verify the signature */
EVP_VerifyInit (&md_ctx, EVP_md5());
EVP_VerifyUpdate (&md_ctx, data, strlen((char*)data));
err = EVP_VerifyFinal (&md_ctx,
sig_buf,
sig_len,
pkey);
if (err != 1) { ERR_print_errors_fp (stderr); exit (1); }
EVP_PKEY_free (pkey);
printf ("Signature Verified Ok.\n");
}