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.\" ========================================================================
.\"
.IX Title "ecdsa 3"
.TH ecdsa 3 "2007-10-24" "0.9.8g" "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 \- 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 \fB\s-1ECDSA_SIG\s0\fR structure consists of two BIGNUMs for the
r and s value of a \s-1ECDSA\s0 signature (see X9.62 or \s-1FIPS\s0 186\-2).
.PP
.Vb 5
\& struct
\&        {
\&        BIGNUM *r;
\&        BIGNUM *s;
\& } ECDSA_SIG;
.Ve
.PP
\&\fIECDSA_SIG_new()\fR allocates a new \fB\s-1ECDSA_SIG\s0\fR structure (note: this
function also allocates the BIGNUMs) and initialize it.
.PP
\&\fIECDSA_SIG_free()\fR frees the \fB\s-1ECDSA_SIG\s0\fR structure \fBsig\fR.
.PP
\&\fIi2d_ECDSA_SIG()\fR creates the \s-1DER\s0 encoding of the \s-1ECDSA\s0 signature
\&\fBsig\fR and writes the encoded signature to \fB*pp\fR (note: if \fBpp\fR
is \s-1NULL\s0 \fBi2d_ECDSA_SIG\fR returns the expected length in bytes of 
the \s-1DER\s0 encoded signature). \fBi2d_ECDSA_SIG\fR returns the length
of the \s-1DER\s0 encoded signature (or 0 on error).
.PP
\&\fId2i_ECDSA_SIG()\fR decodes a \s-1DER\s0 encoded \s-1ECDSA\s0 signature and returns
the decoded signature in a newly allocated \fB\s-1ECDSA_SIG\s0\fR structure.
\&\fB*sig\fR points to the buffer containing the \s-1DER\s0 encoded signature
of size \fBlen\fR.
.PP
\&\fIECDSA_size()\fR returns the maximum length of a \s-1DER\s0 encoded
\&\s-1ECDSA\s0 signature created with the private \s-1EC\s0 key \fBeckey\fR.
.PP
\&\fIECDSA_sign_setup()\fR may be used to precompute parts of the
signing operation. \fBeckey\fR is the private \s-1EC\s0 key and \fBctx\fR
is a pointer to \fB\s-1BN_CTX\s0\fR structure (or \s-1NULL\s0). 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
\&\fIECDSA_sign()\fR is wrapper function for ECDSA_sign_ex with \fBkinv\fR
and \fBrp\fR set to \s-1NULL\s0.
.PP
\&\fIECDSA_sign_ex()\fR computes a digital signature of the \fBdgstlen\fR bytes
hash value \fBdgst\fR using the private \s-1EC\s0 key \fBeckey\fR and the optional
pre-computed values \fBkinv\fR and \fBrp\fR. The \s-1DER\s0 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
\&\fIECDSA_verify()\fR verifies that the signature in \fBsig\fR of size
\&\fBsiglen\fR is a valid \s-1ECDSA\s0 signature of the hash value
value \fBdgst\fR of size \fBdgstlen\fR using the public key \fBeckey\fR.
The parameter \fBtype\fR is ignored.
.PP
\&\fIECDSA_do_sign()\fR is wrapper function for ECDSA_do_sign_ex with \fBkinv\fR
and \fBrp\fR set to \s-1NULL\s0.
.PP
\&\fIECDSA_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 \fB\s-1ECDSA_SIG\s0\fR structure (or \s-1NULL\s0 on error).
.PP
\&\fIECDSA_do_verify()\fR verifies that the signature \fBsig\fR is a valid
\&\s-1ECDSA\s0 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"
\&\fIECDSA_size()\fR returns the maximum length signature or 0 on error.
.PP
\&\fIECDSA_sign_setup()\fR and \fIECDSA_sign()\fR return 1 if successful or \-1
on error.
.PP
\&\fIECDSA_verify()\fR and \fIECDSA_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 \fIERR_get_error\fR\|(3).
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Creating a \s-1ECDSA\s0 signature of given \s-1SHA\-1\s0 hash value using the
named curve secp192k1.
.PP
First step: create a \s-1EC_KEY\s0 object (note: this part is \fBnot\fR \s-1ECDSA\s0
specific)
.PP
.Vb 10
\& int        ret;
\& ECDSA_SIG *sig;
\& EC_KEY    *eckey = EC_KEY_new();
\& if (eckey == NULL)
\&        {
\&        /* error */
\&        }
\& key\->group = EC_GROUP_new_by_nid(NID_secp192k1);
\& if (key\->group == NULL)
\&        {
\&        /* error */
\&        }
\& if (!EC_KEY_generate_key(eckey))
\&        {
\&        /* error */
\&        }
.Ve
.PP
Second step: compute the \s-1ECDSA\s0 signature of a \s-1SHA\-1\s0 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 \s-1ECDSA\s0 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"
\&\s-1ANSI\s0 X9.62, \s-1US\s0 Federal Information Processing Standard \s-1FIPS\s0 186\-2
(Digital Signature Standard, \s-1DSS\s0)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIdsa\fR\|(3), \fIrsa\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).