Hello,
I found your example of ECDSA_do_sign/verify very uselful.
Now I'm trying to modify the code and I would like to use an SHA-256's
message digest in your sign function. Something like:
unsigned char obuf[32];
SHA-256(data, len, obuf);
// now, in obuf there's the message digest (calculated using the SHA-256
function).
but I have an error in the ECDSA_do_sign function when I pass the message
digest in this way:
sig = ECDSA_do_sign(obuf, 32, pkey);
what's wrong?
Problably I'm missing the conversion between data types: I mean, something
used to convert the output of the SHA to an integer. In this case: which
function should I use and how?
Thanks in advance,
Kirk
Oezguer Kesim wrote:
>
> Hello,
>
> attached you can find some test code of mine utilizing ECDSA_do_sign and
> ECDSA_do_verify. It simply signs "fnord" and verifys the signature.
>
> The strange thing is: sig->r and sig->s are different from call to
> call of the program. i2d_ECDSA_SIG also returns different length of the
> DER encoded version of the signature at each call of the program, for
> that matter.
>
> Am I missing something or is this a bug in ecdsa?
>
> regards,
>
> Özgür Kesim
>
> #include <openssl/objects.h>
> #include <openssl/ecdsa.h>
> #include <openssl/evp.h>
> #include <openssl/ec.h>
> #include <openssl/pem.h>
> #include <stdio.h>
> #include <assert.h>
>
> ECDSA_SIG* sig;
> ECDSA_SIG* sig2;
>
> /* Keys generated with:
> *
> * ecdsa.key:
> * openssl ecparam -genkey -name wap-wsg-idm-ecid-wtls8 \
> * -conv_form compressed > ecdsa.key
> * ecdsa.pub:
> * openssl ec -in ecdsa.key -pubout -out ecdsa.pub
> */
>
> char privkey[]=
> "-----BEGIN EC PARAMETERS-----\n"
> "BgVnKw0ECA==\n"
> "-----END EC PARAMETERS-----\n"
> "-----BEGIN EC PRIVATE KEY-----\n"
> "MD4CAQEEDthN31VEyito/izDlzDPoAcGBWcrDQQIoSADHgAE8qeUbBtKNIUgmHIl\n"
> "goPQpt7McJZvBbz0/NF88Q==\n"
> "-----END EC PRIVATE KEY-----\n";
>
> char pubkey[]=
> "-----BEGIN PUBLIC KEY-----\n"
> "MDIwEAYHKoZIzj0CAQYFZysNBAgDHgAE8qeUbBtKNIUgmHIlgoPQpt7McJZvBbz0\n"
> "/NF88Q==\n"
> "-----END PUBLIC KEY-----\n";
>
> int sign(const char* data,unsigned int len) {
> BIO* in;
> EC_KEY* pkey;
>
> in=BIO_new_mem_buf(privkey,sizeof(privkey));
> if (!in) return -1;
>
> /* load private key */
> pkey=PEM_read_bio_ECPrivateKey(in, NULL, NULL, NULL /* passphrase */);
> if (!pkey) return -1;
>
> /* sign data */
> sig = ECDSA_do_sign(data, len, pkey);
> if (!sig) return -1;
> return 1;
> }
>
> int verify(const char* data,unsigned int len) {
> int r;
> BIO* in;
> EC_KEY *pub_key;
>
> in=BIO_new_mem_buf(pubkey,sizeof(pubkey));
> if (!in) return -1;
>
> /* load public key */
> pub_key = PEM_read_bio_EC_PUBKEY(in, NULL, NULL, NULL);
> if (!pub_key) return -1;
>
> r = ECDSA_do_verify(data, len, sig2, pub_key);
> if (r < 0) return -1;
> else if (r == 0) return 0;
> else return 1;
> }
>
> int main() {
> unsigned char buf[1024];
> unsigned char* x;
> int r;
> r=sign("fnord",5);
> printf("sign returned %d\n",r);
> x=buf;
> printf("(sig->r, sig->s): (%s,%s)\n", BN_bn2hex(sig->r),
> BN_bn2hex(sig->s));
> r=i2d_ECDSA_SIG(sig,&x);
> printf("i2d_ECDSA_SIG returned %p, length %d\n",sig, r);
> *x=0; x=buf;
> sig2=d2i_ECDSA_SIG(&sig2,(const unsigned char**)&x,r);
> printf("d2i_ECDSA_SIG returned %p\n",sig2);
> r=verify("fnord",5);
> printf("verify returned %d\n",r);
> }
>
>
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