File: //usr/local/openssl/man/man3/ECDSA_sign_setup.3
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.\" ========================================================================
.\"
.IX Title "ecdsa 3"
.TH ecdsa 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
ECDSA_SIG_new, ECDSA_SIG_free, i2d_ECDSA_SIG, d2i_ECDSA_SIG, ECDSA_size, ECDSA_sign_setup, ECDSA_sign, ECDSA_sign_ex, ECDSA_verify, ECDSA_do_sign, ECDSA_do_sign_ex, ECDSA_do_verify \- Elliptic Curve Digital Signature Algorithm
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ecdsa.h>
\&
\& ECDSA_SIG* ECDSA_SIG_new(void);
\& void ECDSA_SIG_free(ECDSA_SIG *sig);
\& int i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
\& ECDSA_SIG* d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp,
\& long len);
\&
\& ECDSA_SIG* ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
\& EC_KEY *eckey);
\& ECDSA_SIG* ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
\& const BIGNUM *kinv, const BIGNUM *rp,
\& EC_KEY *eckey);
\& int ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
\& const ECDSA_SIG *sig, EC_KEY* eckey);
\& int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx,
\& BIGNUM **kinv, BIGNUM **rp);
\& int ECDSA_sign(int type, const unsigned char *dgst,
\& int dgstlen, unsigned char *sig,
\& unsigned int *siglen, EC_KEY *eckey);
\& int ECDSA_sign_ex(int type, const unsigned char *dgst,
\& int dgstlen, unsigned char *sig,
\& unsigned int *siglen, const BIGNUM *kinv,
\& const BIGNUM *rp, EC_KEY *eckey);
\& int ECDSA_verify(int type, const unsigned char *dgst,
\& int dgstlen, const unsigned char *sig,
\& int siglen, EC_KEY *eckey);
\& int ECDSA_size(const EC_KEY *eckey);
\&
\& const ECDSA_METHOD* ECDSA_OpenSSL(void);
\& void ECDSA_set_default_method(const ECDSA_METHOD *meth);
\& const ECDSA_METHOD* ECDSA_get_default_method(void);
\& int ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth);
\&
\& int ECDSA_get_ex_new_index(long argl, void *argp,
\& CRYPTO_EX_new *new_func,
\& CRYPTO_EX_dup *dup_func,
\& CRYPTO_EX_free *free_func);
\& int ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg);
\& void* ECDSA_get_ex_data(EC_KEY *d, int idx);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
The \fBECDSA_SIG\fR structure consists of two BIGNUMs for the
r and s value of a ECDSA signature (see X9.62 or FIPS 186\-2).
.PP
.Vb 5
\& struct
\& {
\& BIGNUM *r;
\& BIGNUM *s;
\& } ECDSA_SIG;
.Ve
.PP
\&\fBECDSA_SIG_new()\fR allocates a new \fBECDSA_SIG\fR structure (note: this
function also allocates the BIGNUMs) and initialize it.
.PP
\&\fBECDSA_SIG_free()\fR frees the \fBECDSA_SIG\fR structure \fBsig\fR.
.PP
\&\fBi2d_ECDSA_SIG()\fR creates the DER encoding of the ECDSA signature
\&\fBsig\fR and writes the encoded signature to \fB*pp\fR (note: if \fBpp\fR
is NULL \fBi2d_ECDSA_SIG\fR returns the expected length in bytes of
the DER encoded signature). \fBi2d_ECDSA_SIG\fR returns the length
of the DER encoded signature (or 0 on error).
.PP
\&\fBd2i_ECDSA_SIG()\fR decodes a DER encoded ECDSA signature and returns
the decoded signature in a newly allocated \fBECDSA_SIG\fR structure.
\&\fB*sig\fR points to the buffer containing the DER encoded signature
of size \fBlen\fR.
.PP
\&\fBECDSA_size()\fR returns the maximum length of a DER encoded
ECDSA signature created with the private EC key \fBeckey\fR.
.PP
\&\fBECDSA_sign_setup()\fR may be used to precompute parts of the
signing operation. \fBeckey\fR is the private EC key and \fBctx\fR
is a pointer to \fBBN_CTX\fR structure (or NULL). The precomputed
values or returned in \fBkinv\fR and \fBrp\fR and can be used in a
later call to \fBECDSA_sign_ex\fR or \fBECDSA_do_sign_ex\fR.
.PP
\&\fBECDSA_sign()\fR is wrapper function for ECDSA_sign_ex with \fBkinv\fR
and \fBrp\fR set to NULL.
.PP
\&\fBECDSA_sign_ex()\fR computes a digital signature of the \fBdgstlen\fR bytes
hash value \fBdgst\fR using the private EC key \fBeckey\fR and the optional
pre-computed values \fBkinv\fR and \fBrp\fR. The DER encoded signatures is
stored in \fBsig\fR and it's length is returned in \fBsig_len\fR. Note: \fBsig\fR
must point to \fBECDSA_size\fR bytes of memory. The parameter \fBtype\fR
is ignored.
.PP
\&\fBECDSA_verify()\fR verifies that the signature in \fBsig\fR of size
\&\fBsiglen\fR is a valid ECDSA signature of the hash value
\&\fBdgst\fR of size \fBdgstlen\fR using the public key \fBeckey\fR.
The parameter \fBtype\fR is ignored.
.PP
\&\fBECDSA_do_sign()\fR is wrapper function for ECDSA_do_sign_ex with \fBkinv\fR
and \fBrp\fR set to NULL.
.PP
\&\fBECDSA_do_sign_ex()\fR computes a digital signature of the \fBdgst_len\fR
bytes hash value \fBdgst\fR using the private key \fBeckey\fR and the
optional pre-computed values \fBkinv\fR and \fBrp\fR. The signature is
returned in a newly allocated \fBECDSA_SIG\fR structure (or NULL on error).
.PP
\&\fBECDSA_do_verify()\fR verifies that the signature \fBsig\fR is a valid
ECDSA signature of the hash value \fBdgst\fR of size \fBdgst_len\fR
using the public key \fBeckey\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBECDSA_SIG_new()\fR returns NULL if the allocation fails.
.PP
\&\fBECDSA_size()\fR returns the maximum length signature or 0 on error.
.PP
\&\fBECDSA_sign_setup()\fR and \fBECDSA_sign()\fR return 1 if successful or 0
on error.
.PP
\&\fBECDSA_verify()\fR and \fBECDSA_do_verify()\fR return 1 for a valid
signature, 0 for an invalid signature and \-1 on error.
The error codes can be obtained by \fBERR_get_error\fR\|(3).
.SH EXAMPLES
.IX Header "EXAMPLES"
Creating a ECDSA signature of given SHA\-1 hash value using the
named curve secp192k1.
.PP
First step: create a EC_KEY object (note: this part is \fBnot\fR ECDSA
specific)
.PP
.Vb 12
\& int ret;
\& ECDSA_SIG *sig;
\& EC_KEY *eckey;
\& eckey = EC_KEY_new_by_curve_name(NID_secp192k1);
\& if (eckey == NULL)
\& {
\& /* error */
\& }
\& if (!EC_KEY_generate_key(eckey))
\& {
\& /* error */
\& }
.Ve
.PP
Second step: compute the ECDSA signature of a SHA\-1 hash value
using \fBECDSA_do_sign\fR
.PP
.Vb 5
\& sig = ECDSA_do_sign(digest, 20, eckey);
\& if (sig == NULL)
\& {
\& /* error */
\& }
.Ve
.PP
or using \fBECDSA_sign\fR
.PP
.Vb 9
\& unsigned char *buffer, *pp;
\& int buf_len;
\& buf_len = ECDSA_size(eckey);
\& buffer = OPENSSL_malloc(buf_len);
\& pp = buffer;
\& if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey);
\& {
\& /* error */
\& }
.Ve
.PP
Third step: verify the created ECDSA signature using \fBECDSA_do_verify\fR
.PP
.Vb 1
\& ret = ECDSA_do_verify(digest, 20, sig, eckey);
.Ve
.PP
or using \fBECDSA_verify\fR
.PP
.Vb 1
\& ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
.Ve
.PP
and finally evaluate the return value:
.PP
.Vb 12
\& if (ret == \-1)
\& {
\& /* error */
\& }
\& else if (ret == 0)
\& {
\& /* incorrect signature */
\& }
\& else /* ret == 1 */
\& {
\& /* signature ok */
\& }
.Ve
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
ANSI X9.62, US Federal Information Processing Standard FIPS 186\-2
(Digital Signature Standard, DSS)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBdsa\fR\|(3), \fBrsa\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
The ecdsa implementation was first introduced in OpenSSL 0.9.8
.SH AUTHOR
.IX Header "AUTHOR"
Nils Larsch for the OpenSSL project (http://www.openssl.org).