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Editing: ECDSA_sign.3
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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 \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 186\-2\s0). .PP .Vb 5 \& struct \& { \& BIGNUM *r; \& BIGNUM *s; \& } ECDSA_SIG; .Ve .PP \&\fBECDSA_SIG_new()\fR allocates a new \fB\s-1ECDSA_SIG\s0\fR structure (note: this function also allocates the BIGNUMs) and initialize it. .PP \&\fBECDSA_SIG_free()\fR frees the \fB\s-1ECDSA_SIG\s0\fR structure \fBsig\fR. .PP \&\fBi2d_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 \&\fBd2i_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 \&\fBECDSA_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 \&\fBECDSA_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 \&\fBECDSA_sign()\fR is wrapper function for ECDSA_sign_ex with \fBkinv\fR and \fBrp\fR set to \s-1NULL.\s0 .PP \&\fBECDSA_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 \&\fBECDSA_verify()\fR verifies that the signature in \fBsig\fR of size \&\fBsiglen\fR is a valid \s-1ECDSA\s0 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 \s-1NULL.\s0 .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 \fB\s-1ECDSA_SIG\s0\fR structure (or \s-1NULL\s0 on error). .PP \&\fBECDSA_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" \&\fBECDSA_SIG_new()\fR returns \s-1NULL\s0 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 \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 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 \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 X9.62, US\s0 Federal Information Processing Standard \s-1FIPS 186\-2\s0 (Digital Signature Standard, \s-1DSS\s0) .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).
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