.\" $OpenBSD: ECDSA_SIG_new.3,v 1.20 2023/08/29 10:07:42 tb Exp $
.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100
.\" selective merge up to: OpenSSL da4ea0cf Aug 5 16:13:24 2019 +0100
.\"
.\" This file was written by Nils Larsch <nils@openssl.org>.
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.Dd $Mdocdate: August 29 2023 $
.Dt ECDSA_SIG_NEW 3
.Os
.Sh NAME
.Nm ECDSA_SIG_new ,
.Nm ECDSA_SIG_free ,
.Nm ECDSA_SIG_get0 ,
.Nm ECDSA_SIG_get0_r ,
.Nm ECDSA_SIG_get0_s ,
.Nm ECDSA_SIG_set0 ,
.Nm i2d_ECDSA_SIG ,
.Nm d2i_ECDSA_SIG ,
.Nm ECDSA_size ,
.Nm ECDSA_sign ,
.Nm ECDSA_verify ,
.Nm ECDSA_do_sign ,
.Nm ECDSA_do_verify
.Nd Elliptic Curve Digital Signature Algorithm
.Sh SYNOPSIS
.In openssl/ec.h
.Ft ECDSA_SIG*
.Fo ECDSA_SIG_new
.Fa void
.Fc
.Ft void
.Fo ECDSA_SIG_free
.Fa "ECDSA_SIG *sig"
.Fc
.Ft void
.Fo ECDSA_SIG_get0
.Fa "const ECDSA_SIG *sig"
.Fa "const BIGNUM **r"
.Fa "const BIGNUM **s"
.Fc
.Ft "const BIGNUM *"
.Fo ECDSA_SIG_get0_r
.Fa "const ECDSA_SIG *sig"
.Fc
.Ft "const BIGNUM *"
.Fo ECDSA_SIG_get0_s
.Fa "const ECDSA_SIG *sig"
.Fc
.Ft int
.Fo ECDSA_SIG_set0
.Fa "ECDSA_SIG *sig"
.Fa "BIGNUM *r"
.Fa "BIGNUM *s"
.Fc
.Ft int
.Fo i2d_ECDSA_SIG
.Fa "const ECDSA_SIG *sig_in"
.Fa "unsigned char **der_out"
.Fc
.Ft ECDSA_SIG*
.Fo d2i_ECDSA_SIG
.Fa "ECDSA_SIG **sig_out"
.Fa "const unsigned char **der_in"
.Fa "long len"
.Fc
.Ft int
.Fo ECDSA_size
.Fa "const EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_sign
.Fa "int type"
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "unsigned char *sig"
.Fa "unsigned int *siglen"
.Fa "EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_verify
.Fa "int type"
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "const unsigned char *sig"
.Fa "int siglen"
.Fa "EC_KEY *eckey"
.Fc
.Ft ECDSA_SIG*
.Fo ECDSA_do_sign
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_do_verify
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "const ECDSA_SIG *sig"
.Fa "EC_KEY* eckey"
.Fc
.Sh DESCRIPTION
These functions provide a low level interface to ECDSA.
Most applications should use the higher level EVP interface such as
.Xr EVP_DigestSignInit 3
or
.Xr EVP_DigestVerifyInit 3
instead.
Creation of the required
.Vt EC_KEY
objects is described in
.Xr EC_KEY_new 3 .
.Pp
The
.Vt ECDSA_SIG
structure consists of two
.Vt BIGNUM Ns s
for the
.Fa r
and
.Fa s
value of an ECDSA signature (see X9.62 or FIPS 186-2).
.Bd -literal -offset indent
struct {
	BIGNUM *r;
	BIGNUM *s;
} ECDSA_SIG;
.Ed
.Pp
.Fn ECDSA_SIG_new
allocates a new
.Vt ECDSA_SIG
structure (note: this function also allocates the
.Vt BIGNUM Ns s )
and initializes it.
.Pp
.Fn ECDSA_SIG_free
frees the
.Vt ECDSA_SIG
structure
.Fa sig .
.Pp
.Fn ECDSA_SIG_get0
retrieves internal pointers the
.Fa r
and
.Fa s
values contained in
.Fa sig .
The values
.Fa r
and
.Fa s
can also be retrieved separately by the corresponding function
.Fn ECDSA_SIG_get0_r
and
.Fn ECDSA_SIG_get0_s ,
respectively.
.Pp
.Fn ECDSA_SIG_set0
sets the
.Fa r
and
.Fa s
values in
.Fa sig .
Calling this function transfers the memory management of the values to
.Fa sig .
Therefore, the values that have been passed in
should not be freed by the caller.
.Pp
.Fn i2d_ECDSA_SIG
creates the DER encoding of the ECDSA signature
.Fa sig_in
and writes the encoded signature to
.Pf * Fa der_out .
.Fn d2i_ECDSA_SIG
decodes the DER-encoded signature stored in the buffer
.Pf * Fa der_in
which is
.Fa len
bytes long into
.Pf * Fa sig_out .
For details about the semantics, examples, caveats, and bugs, see
.Xr ASN1_item_d2i 3 .
.Pp
.Fn ECDSA_size
returns the maximum length of a DER-encoded ECDSA signature created with
the private EC key
.Fa eckey .
.Pp
.Fn ECDSA_sign
computes a digital signature of the
.Fa dgstlen
bytes hash value
.Fa dgst
using the private EC key
.Fa eckey .
The DER-encoded signature is stored in
.Fa sig
and its length is returned in
.Fa siglen .
Note:
.Fa sig
must point to
.Fn ECDSA_size
bytes of memory.
The parameter
.Fa type
is ignored.
.Pp
.Fn ECDSA_verify
verifies that the signature in
.Fa sig
of size
.Fa siglen
is a valid ECDSA signature of the hash value
.Fa dgst
of size
.Fa dgstlen
using the public key
.Fa eckey .
The parameter
.Fa type
is ignored.
.Pp
.Fn ECDSA_do_sign
computes a digital signature of the
.Fa dgst_len
bytes hash value
.Fa dgst
using the private key
.Fa eckey .
The signature is returned in a newly allocated
.Vt ECDSA_SIG
structure (or
.Dv NULL
on error).
.Pp
.Fn ECDSA_do_verify
verifies that the signature
.Fa sig
is a valid ECDSA signature of the hash value
.Fa dgst
of size
.Fa dgst_len
using the public key
.Fa eckey .
.Sh RETURN VALUES
.Fn ECDSA_SIG_new
returns the new
.Vt ECDSA_SIG
object or
.Dv NULL
if an error occurs.
.Pp
.Fn i2d_ECDSA_SIG
returns the number of bytes successfully encoded
or a negative value if an error occurs.
.Pp
.Fn d2i_ECDSA_SIG
returns a pointer to the decoded
.Vt ECDSA_SIG
structure or
.Dv NULL
if an error occurs.
.Pp
.Fn ECDSA_size
returns the maximum length signature or 0 on error.
.Pp
.Fn ECDSA_SIG_get0_r
and
.Fn ECDSA_SIG_get0_s
return a pointer owned by the
.Vt ECDSA_SIG
object if it has been set or
.Dv NULL
otherwise.
.Pp
.Fn ECDSA_SIG_set0
and
.Fn ECDSA_sign
return 1 if successful or 0 on error.
.Pp
.Fn ECDSA_do_sign
returns a pointer to an allocated
.Vt ECDSA_SIG
structure or
.Dv NULL
on error.
.Pp
.Fn ECDSA_verify
and
.Fn ECDSA_do_verify
return 1 for a valid signature, 0 for an invalid signature and -1 on
error.
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh EXAMPLES
Creating an ECDSA signature of given SHA-1 hash value using the named
curve secp192k1.
.Pp
First step: create an
.Vt EC_KEY
object.
This part is
.Em not
ECDSA specific.
.Bd -literal -offset indent
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 */
}
.Ed
.Pp
Second step: compute the ECDSA signature of a SHA-1 hash value using
.Fn ECDSA_do_sign
.Bd -literal -offset indent
sig = ECDSA_do_sign(digest, 20, eckey);
if (sig == NULL) {
	/* error */
}
.Ed
.Pp
or using
.Fn ECDSA_sign
.Bd -literal -offset indent
unsigned char *buffer, *pp;
int buf_len;

buf_len = ECDSA_size(eckey);
buffer  = malloc(buf_len);
pp = buffer;
if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) {
	/* error */
}
.Ed
.Pp
Third step: verify the created ECDSA signature using
.Fn ECDSA_do_verify
.Pp
.Dl ret = ECDSA_do_verify(digest, 20, sig, eckey);
.Pp
or using
.Fn ECDSA_verify
.Pp
.Dl ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
.Pp
and finally evaluate the return value:
.Bd -literal -offset indent
if (ret == -1) {
	/* error */
} else if (ret == 0) {
	/* incorrect signature */
} else {
	/* ret == 1 */
	/* signature ok */
}
.Ed
.Sh SEE ALSO
.Xr crypto 3 ,
.Xr d2i_ECPKParameters 3 ,
.Xr DSA_new 3 ,
.Xr EC_GROUP_new 3 ,
.Xr EC_KEY_METHOD_new 3 ,
.Xr EC_KEY_new 3 ,
.Xr EC_KEY_set_ex_data 3 ,
.Xr EVP_DigestSignInit 3 ,
.Xr EVP_DigestVerifyInit 3 ,
.Xr RSA_new 3
.Sh STANDARDS
ANSI X9.62, US Federal Information Processing Standard FIPS 186-5
(Digital Signature Standard, DSS)
.Sh HISTORY
.Fn ECDSA_SIG_new ,
.Fn ECDSA_SIG_free ,
.Fn i2d_ECDSA_SIG ,
.Fn d2i_ECDSA_SIG ,
.Fn ECDSA_size ,
.Fn ECDSA_sign ,
.Fn ECDSA_verify ,
.Fn ECDSA_do_sign ,
and
.Fn ECDSA_do_verify
first appeared in OpenSSL 0.9.8 and have been available since
.Ox 4.5 .
.Pp
.Fn ECDSA_SIG_get0
and
.Fn ECDSA_SIG_set0
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 6.3 .
.Fn ECDSA_SIG_get0_r
and
.Fn ECDSA_SIG_get0_s
first appeared in OpenSSL 1.1.1 and have been available since
.Ox 7.1 .
.Sh AUTHORS
.An Nils Larsch
for the OpenSSL project.