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.\" ========================================================================
.\"
.IX Title "ECDSA_SIGN 3ossl"
.TH ECDSA_SIGN 3ossl "2026-01-16" "3.5.1" "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_size, ECDSA_sign, ECDSA_do_sign,
ECDSA_verify, ECDSA_do_verify, ECDSA_sign_setup, ECDSA_sign_ex,
ECDSA_do_sign_ex \- deprecated low\-level elliptic curve digital signature algorithm
(ECDSA) functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ecdsa.h>
.Ve
.PP
The following functions have been deprecated since OpenSSL 3.0, and can be
hidden entirely by defining \fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value,
see \fBopenssl_user_macros\fR\|(7):
.PP
.Vb 1
\& int ECDSA_size(const EC_KEY *eckey);
\&
\& int ECDSA_sign(int type, const unsigned char *dgst, int dgstlen,
\&                unsigned char *sig, unsigned int *siglen, EC_KEY *eckey);
\& ECDSA_SIG *ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
\&                          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_do_verify(const unsigned char *dgst, int dgst_len,
\&                     const ECDSA_SIG *sig, 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_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);
\& 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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
See \fBECDSA_SIG_new\fR\|(3) for a description of the \fB\s-1ECDSA_SIG\s0\fR object.
.PP
See \fBi2d_ECDSA_SIG\fR\|(3) and \fBd2i_ECDSA_SIG\fR\|(3) for information about encoding
and decoding \s-1ECDSA\s0 signatures to/from \s-1DER.\s0
.PP
All of the functions described below are deprecated. Applications should
use the higher level \fB\s-1EVP\s0\fR interface such as \fBEVP_DigestSignInit\fR\|(3)
or \fBEVP_DigestVerifyInit\fR\|(3) instead.
.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 \fIeckey\fR. To obtain the actual signature
size use \fBEVP_PKEY_sign\fR\|(3) with a \s-1NULL\s0 \fIsig\fR parameter.
.PP
\&\fBECDSA_sign()\fR computes a digital signature of the \fIdgstlen\fR bytes hash value
\&\fIdgst\fR using the private \s-1EC\s0 key \fIeckey\fR. The \s-1DER\s0 encoded signatures is
stored in \fIsig\fR and its length is returned in \fIsiglen\fR. Note: \fIsig\fR must
point to ECDSA_size(eckey) bytes of memory. The parameter \fItype\fR is currently
ignored. \fBECDSA_sign()\fR is wrapper function for \fBECDSA_sign_ex()\fR with \fIkinv\fR
and \fIrp\fR set to \s-1NULL.\s0
.PP
\&\fBECDSA_do_sign()\fR is similar to \fBECDSA_sign()\fR except the signature is returned
as a newly allocated \fB\s-1ECDSA_SIG\s0\fR structure (or \s-1NULL\s0 on error). \fBECDSA_do_sign()\fR
is a wrapper function for \fBECDSA_do_sign_ex()\fR with \fIkinv\fR and \fIrp\fR set to
\&\s-1NULL.\s0
.PP
\&\fBECDSA_verify()\fR verifies that the signature in \fIsig\fR of size \fIsiglen\fR is a
valid \s-1ECDSA\s0 signature of the hash value \fIdgst\fR of size \fIdgstlen\fR using the
public key \fIeckey\fR.  The parameter \fItype\fR is ignored.
.PP
\&\fBECDSA_do_verify()\fR is similar to \fBECDSA_verify()\fR except the signature is
presented in the form of a pointer to an \fB\s-1ECDSA_SIG\s0\fR structure.
.PP
The remaining functions utilise the internal \fIkinv\fR and \fIr\fR values used
during signature computation. Most applications will never need to call these
and some external \s-1ECDSA ENGINE\s0 implementations may not support them at all if
either \fIkinv\fR or \fIr\fR is not \s-1NULL.\s0
.PP
\&\fBECDSA_sign_setup()\fR may be used to precompute parts of the signing operation.
\&\fIeckey\fR is the private \s-1EC\s0 key and \fIctx\fR is a pointer to \fB\s-1BN_CTX\s0\fR structure
(or \s-1NULL\s0). The precomputed values or returned in \fIkinv\fR and \fIrp\fR and can be
used in a later call to \fBECDSA_sign_ex()\fR or \fBECDSA_do_sign_ex()\fR.
.PP
\&\fBECDSA_sign_ex()\fR computes a digital signature of the \fIdgstlen\fR bytes hash value
\&\fIdgst\fR using the private \s-1EC\s0 key \fIeckey\fR and the optional pre-computed values
\&\fIkinv\fR and \fIrp\fR. The \s-1DER\s0 encoded signature is stored in \fIsig\fR and its
length is returned in \fIsiglen\fR. Note: \fIsig\fR must point to ECDSA_size(eckey)
bytes of memory. The parameter \fItype\fR is ignored.
.PP
\&\fBECDSA_do_sign_ex()\fR is similar to \fBECDSA_sign_ex()\fR except the signature is
returned as a newly allocated \fB\s-1ECDSA_SIG\s0\fR structure (or \s-1NULL\s0 on error).
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBECDSA_size()\fR returns the maximum length signature or 0 on error.
.PP
\&\fBECDSA_sign()\fR, \fBECDSA_sign_ex()\fR and \fBECDSA_sign_setup()\fR return 1 if successful
or 0 on error.
.PP
\&\fBECDSA_do_sign()\fR and \fBECDSA_do_sign_ex()\fR return a pointer to an allocated
\&\fB\s-1ECDSA_SIG\s0\fR structure or \s-1NULL\s0 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 an \s-1ECDSA\s0 signature of a given \s-1SHA\-256\s0 hash value using the
named curve prime256v1 (aka P\-256).
This example uses deprecated functionality. See \*(L"\s-1DESCRIPTION\*(R"\s0.
.PP
First step: create an \s-1EC_KEY\s0 object (note: this part is \fBnot\fR \s-1ECDSA\s0
specific)
.PP
.Vb 3
\& int ret;
\& ECDSA_SIG *sig;
\& EC_KEY *eckey;
\&
\& eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
\& if (eckey == NULL)
\&     /* error */
\& if (EC_KEY_generate_key(eckey) == 0)
\&     /* error */
.Ve
.PP
Second step: compute the \s-1ECDSA\s0 signature of a \s-1SHA\-256\s0 hash value
using \fBECDSA_do_sign()\fR:
.PP
.Vb 3
\& sig = ECDSA_do_sign(digest, 32, eckey);
\& if (sig == NULL)
\&     /* error */
.Ve
.PP
or using \fBECDSA_sign()\fR:
.PP
.Vb 2
\& 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) == 0)
\&     /* 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, 32, sig, eckey);
.Ve
.PP
or using \fBECDSA_verify()\fR:
.PP
.Vb 1
\& ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);
.Ve
.PP
and finally evaluate the return value:
.PP
.Vb 6
\& if (ret == 1)
\&     /* signature ok */
\& else if (ret == 0)
\&     /* incorrect signature */
\& else
\&     /* error */
.Ve
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1ANSI X9.62, US\s0 Federal Information Processing Standard \s-1FIPS186\-2\s0
(Digital Signature Standard, \s-1DSS\s0)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEC_KEY_new\fR\|(3),
\&\fBEVP_DigestSignInit\fR\|(3),
\&\fBEVP_DigestVerifyInit\fR\|(3),
\&\fBEVP_PKEY_sign\fR\|(3)
\&\fBi2d_ECDSA_SIG\fR\|(3),
\&\fBd2i_ECDSA_SIG\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
All functionality described here was deprecated in OpenSSL 3.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2004\-2022 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
