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127 .TH ecdsa 3 "2012-04-26" "1.0.1b" "OpenSSL"
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129 .\" way too many mistakes in technical documents.
133 ecdsa \- Elliptic Curve Digital Signature Algorithm
135 .IX Header "SYNOPSIS"
137 \& #include <openssl/ecdsa.h>
139 \& ECDSA_SIG* ECDSA_SIG_new(void);
140 \& void ECDSA_SIG_free(ECDSA_SIG *sig);
141 \& int i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
142 \& ECDSA_SIG* d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp,
145 \& ECDSA_SIG* ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
147 \& ECDSA_SIG* ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
148 \& const BIGNUM *kinv, const BIGNUM *rp,
150 \& int ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
151 \& const ECDSA_SIG *sig, EC_KEY* eckey);
152 \& int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx,
153 \& BIGNUM **kinv, BIGNUM **rp);
154 \& int ECDSA_sign(int type, const unsigned char *dgst,
155 \& int dgstlen, unsigned char *sig,
156 \& unsigned int *siglen, EC_KEY *eckey);
157 \& int ECDSA_sign_ex(int type, const unsigned char *dgst,
158 \& int dgstlen, unsigned char *sig,
159 \& unsigned int *siglen, const BIGNUM *kinv,
160 \& const BIGNUM *rp, EC_KEY *eckey);
161 \& int ECDSA_verify(int type, const unsigned char *dgst,
162 \& int dgstlen, const unsigned char *sig,
163 \& int siglen, EC_KEY *eckey);
164 \& int ECDSA_size(const EC_KEY *eckey);
166 \& const ECDSA_METHOD* ECDSA_OpenSSL(void);
167 \& void ECDSA_set_default_method(const ECDSA_METHOD *meth);
168 \& const ECDSA_METHOD* ECDSA_get_default_method(void);
169 \& int ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth);
171 \& int ECDSA_get_ex_new_index(long argl, void *argp,
172 \& CRYPTO_EX_new *new_func,
173 \& CRYPTO_EX_dup *dup_func,
174 \& CRYPTO_EX_free *free_func);
175 \& int ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg);
176 \& void* ECDSA_get_ex_data(EC_KEY *d, int idx);
179 .IX Header "DESCRIPTION"
180 The \fB\s-1ECDSA_SIG\s0\fR structure consists of two BIGNUMs for the
181 r and s value of a \s-1ECDSA\s0 signature (see X9.62 or \s-1FIPS\s0 186\-2).
191 \&\fIECDSA_SIG_new()\fR allocates a new \fB\s-1ECDSA_SIG\s0\fR structure (note: this
192 function also allocates the BIGNUMs) and initialize it.
194 \&\fIECDSA_SIG_free()\fR frees the \fB\s-1ECDSA_SIG\s0\fR structure \fBsig\fR.
196 \&\fIi2d_ECDSA_SIG()\fR creates the \s-1DER\s0 encoding of the \s-1ECDSA\s0 signature
197 \&\fBsig\fR and writes the encoded signature to \fB*pp\fR (note: if \fBpp\fR
198 is \s-1NULL\s0 \fBi2d_ECDSA_SIG\fR returns the expected length in bytes of
199 the \s-1DER\s0 encoded signature). \fBi2d_ECDSA_SIG\fR returns the length
200 of the \s-1DER\s0 encoded signature (or 0 on error).
202 \&\fId2i_ECDSA_SIG()\fR decodes a \s-1DER\s0 encoded \s-1ECDSA\s0 signature and returns
203 the decoded signature in a newly allocated \fB\s-1ECDSA_SIG\s0\fR structure.
204 \&\fB*sig\fR points to the buffer containing the \s-1DER\s0 encoded signature
207 \&\fIECDSA_size()\fR returns the maximum length of a \s-1DER\s0 encoded
208 \&\s-1ECDSA\s0 signature created with the private \s-1EC\s0 key \fBeckey\fR.
210 \&\fIECDSA_sign_setup()\fR may be used to precompute parts of the
211 signing operation. \fBeckey\fR is the private \s-1EC\s0 key and \fBctx\fR
212 is a pointer to \fB\s-1BN_CTX\s0\fR structure (or \s-1NULL\s0). The precomputed
213 values or returned in \fBkinv\fR and \fBrp\fR and can be used in a
214 later call to \fBECDSA_sign_ex\fR or \fBECDSA_do_sign_ex\fR.
216 \&\fIECDSA_sign()\fR is wrapper function for ECDSA_sign_ex with \fBkinv\fR
217 and \fBrp\fR set to \s-1NULL\s0.
219 \&\fIECDSA_sign_ex()\fR computes a digital signature of the \fBdgstlen\fR bytes
220 hash value \fBdgst\fR using the private \s-1EC\s0 key \fBeckey\fR and the optional
221 pre-computed values \fBkinv\fR and \fBrp\fR. The \s-1DER\s0 encoded signatures is
222 stored in \fBsig\fR and it's length is returned in \fBsig_len\fR. Note: \fBsig\fR
223 must point to \fBECDSA_size\fR bytes of memory. The parameter \fBtype\fR
226 \&\fIECDSA_verify()\fR verifies that the signature in \fBsig\fR of size
227 \&\fBsiglen\fR is a valid \s-1ECDSA\s0 signature of the hash value
228 value \fBdgst\fR of size \fBdgstlen\fR using the public key \fBeckey\fR.
229 The parameter \fBtype\fR is ignored.
231 \&\fIECDSA_do_sign()\fR is wrapper function for ECDSA_do_sign_ex with \fBkinv\fR
232 and \fBrp\fR set to \s-1NULL\s0.
234 \&\fIECDSA_do_sign_ex()\fR computes a digital signature of the \fBdgst_len\fR
235 bytes hash value \fBdgst\fR using the private key \fBeckey\fR and the
236 optional pre-computed values \fBkinv\fR and \fBrp\fR. The signature is
237 returned in a newly allocated \fB\s-1ECDSA_SIG\s0\fR structure (or \s-1NULL\s0 on error).
239 \&\fIECDSA_do_verify()\fR verifies that the signature \fBsig\fR is a valid
240 \&\s-1ECDSA\s0 signature of the hash value \fBdgst\fR of size \fBdgst_len\fR
241 using the public key \fBeckey\fR.
243 .IX Header "RETURN VALUES"
244 \&\fIECDSA_size()\fR returns the maximum length signature or 0 on error.
246 \&\fIECDSA_sign_setup()\fR and \fIECDSA_sign()\fR return 1 if successful or 0
249 \&\fIECDSA_verify()\fR and \fIECDSA_do_verify()\fR return 1 for a valid
250 signature, 0 for an invalid signature and \-1 on error.
251 The error codes can be obtained by \fIERR_get_error\fR\|(3).
253 .IX Header "EXAMPLES"
254 Creating a \s-1ECDSA\s0 signature of given \s-1SHA\-1\s0 hash value using the
255 named curve secp192k1.
257 First step: create a \s-1EC_KEY\s0 object (note: this part is \fBnot\fR \s-1ECDSA\s0
263 \& EC_KEY *eckey = EC_KEY_new();
264 \& if (eckey == NULL)
268 \& key\->group = EC_GROUP_new_by_nid(NID_secp192k1);
269 \& if (key\->group == NULL)
273 \& if (!EC_KEY_generate_key(eckey))
279 Second step: compute the \s-1ECDSA\s0 signature of a \s-1SHA\-1\s0 hash value
280 using \fBECDSA_do_sign\fR
283 \& sig = ECDSA_do_sign(digest, 20, eckey);
290 or using \fBECDSA_sign\fR
293 \& unsigned char *buffer, *pp;
295 \& buf_len = ECDSA_size(eckey);
296 \& buffer = OPENSSL_malloc(buf_len);
298 \& if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey);
304 Third step: verify the created \s-1ECDSA\s0 signature using \fBECDSA_do_verify\fR
307 \& ret = ECDSA_do_verify(digest, 20, sig, eckey);
310 or using \fBECDSA_verify\fR
313 \& ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
316 and finally evaluate the return value:
323 \& else if (ret == 0)
325 \& /* incorrect signature */
327 \& else /* ret == 1 */
329 \& /* signature ok */
333 .IX Header "CONFORMING TO"
334 \&\s-1ANSI\s0 X9.62, \s-1US\s0 Federal Information Processing Standard \s-1FIPS\s0 186\-2
335 (Digital Signature Standard, \s-1DSS\s0)
337 .IX Header "SEE ALSO"
338 \&\fIdsa\fR\|(3), \fIrsa\fR\|(3)
341 The ecdsa implementation was first introduced in OpenSSL 0.9.8
344 Nils Larsch for the OpenSSL project (http://www.openssl.org).