xref: /openssl/doc/man3/ECDSA_SIG_new.pod (revision 0b3d2594)
1=pod
2
3=head1 NAME
4
5ECDSA_SIG_get0, ECDSA_SIG_get0_r, ECDSA_SIG_get0_s, ECDSA_SIG_set0,
6ECDSA_SIG_new, ECDSA_SIG_free, ECDSA_size, ECDSA_sign, ECDSA_do_sign,
7ECDSA_verify, ECDSA_do_verify, ECDSA_sign_setup, ECDSA_sign_ex,
8ECDSA_do_sign_ex - low-level elliptic curve digital signature algorithm (ECDSA)
9functions
10
11=head1 SYNOPSIS
12
13 #include <openssl/ecdsa.h>
14
15 ECDSA_SIG *ECDSA_SIG_new(void);
16 void ECDSA_SIG_free(ECDSA_SIG *sig);
17 void ECDSA_SIG_get0(const ECDSA_SIG *sig, const BIGNUM **pr, const BIGNUM **ps);
18 const BIGNUM *ECDSA_SIG_get0_r(const ECDSA_SIG *sig);
19 const BIGNUM *ECDSA_SIG_get0_s(const ECDSA_SIG *sig);
20 int ECDSA_SIG_set0(ECDSA_SIG *sig, BIGNUM *r, BIGNUM *s);
21
22The following functions have been deprecated since OpenSSL 3.0, and can be
23hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
24see L<openssl_user_macros(7)>:
25
26 int ECDSA_size(const EC_KEY *eckey);
27
28 int ECDSA_sign(int type, const unsigned char *dgst, int dgstlen,
29                unsigned char *sig, unsigned int *siglen, EC_KEY *eckey);
30 ECDSA_SIG *ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
31                          EC_KEY *eckey);
32
33 int ECDSA_verify(int type, const unsigned char *dgst, int dgstlen,
34                  const unsigned char *sig, int siglen, EC_KEY *eckey);
35 int ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
36                     const ECDSA_SIG *sig, EC_KEY* eckey);
37
38 ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
39                             const BIGNUM *kinv, const BIGNUM *rp,
40                             EC_KEY *eckey);
41 int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);
42 int ECDSA_sign_ex(int type, const unsigned char *dgst, int dgstlen,
43                   unsigned char *sig, unsigned int *siglen,
44                   const BIGNUM *kinv, const BIGNUM *rp, EC_KEY *eckey);
45
46=head1 DESCRIPTION
47
48B<ECDSA_SIG> is an opaque structure consisting of two BIGNUMs for the
49I<r> and I<s> value of an ECDSA signature (see X9.62 or FIPS186-2).
50
51ECDSA_SIG_new() allocates an empty B<ECDSA_SIG> structure. Note: before
52OpenSSL 1.1.0 the: the I<r> and I<s> components were initialised.
53
54ECDSA_SIG_free() frees the B<ECDSA_SIG> structure I<sig>.
55
56ECDSA_SIG_get0() returns internal pointers the I<r> and I<s> values contained
57in I<sig> and stores them in I<*pr> and I<*ps>, respectively.
58The pointer I<pr> or I<ps> can be NULL, in which case the corresponding value
59is not returned.
60
61The values I<r>, I<s> can also be retrieved separately by the corresponding
62function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.
63
64Non-NULL I<r> and I<s> values can be set on the I<sig> by calling
65ECDSA_SIG_set0(). Calling this function transfers the memory management of the
66values to the B<ECDSA_SIG> object, and therefore the values that have been
67passed in should not be freed by the caller.
68
69See L<i2d_ECDSA_SIG(3)> and L<d2i_ECDSA_SIG(3)> for information about encoding
70and decoding ECDSA signatures to/from DER.
71
72All of the functions described below are deprecated. Applications should
73use the higher level B<EVP> interface such as L<EVP_DigestSignInit(3)>
74or L<EVP_DigestVerifyInit(3)> instead.
75
76ECDSA_size() returns the maximum length of a DER encoded ECDSA signature
77created with the private EC key I<eckey>. To obtain the actual signature
78size use L<EVP_PKEY_sign(3)> with a NULL I<sig> parameter.
79
80ECDSA_sign() computes a digital signature of the I<dgstlen> bytes hash value
81I<dgst> using the private EC key I<eckey>. The DER encoded signatures is
82stored in I<sig> and its length is returned in I<sig_len>. Note: I<sig> must
83point to ECDSA_size(eckey) bytes of memory. The parameter I<type> is currently
84ignored. ECDSA_sign() is wrapper function for ECDSA_sign_ex() with I<kinv>
85and I<rp> set to NULL.
86
87ECDSA_do_sign() is similar to ECDSA_sign() except the signature is returned
88as a newly allocated B<ECDSA_SIG> structure (or NULL on error). ECDSA_do_sign()
89is a wrapper function for ECDSA_do_sign_ex() with I<kinv> and I<rp> set to
90NULL.
91
92ECDSA_verify() verifies that the signature in I<sig> of size I<siglen> is a
93valid ECDSA signature of the hash value I<dgst> of size I<dgstlen> using the
94public key I<eckey>.  The parameter I<type> is ignored.
95
96ECDSA_do_verify() is similar to ECDSA_verify() except the signature is
97presented in the form of a pointer to an B<ECDSA_SIG> structure.
98
99The remaining functions utilise the internal I<kinv> and I<r> values used
100during signature computation. Most applications will never need to call these
101and some external ECDSA ENGINE implementations may not support them at all if
102either I<kinv> or I<r> is not NULL.
103
104ECDSA_sign_setup() may be used to precompute parts of the signing operation.
105I<eckey> is the private EC key and I<ctx> is a pointer to B<BN_CTX> structure
106(or NULL). The precomputed values or returned in I<kinv> and I<rp> and can be
107used in a later call to ECDSA_sign_ex() or ECDSA_do_sign_ex().
108
109ECDSA_sign_ex() computes a digital signature of the I<dgstlen> bytes hash value
110I<dgst> using the private EC key I<eckey> and the optional pre-computed values
111I<kinv> and I<rp>. The DER encoded signature is stored in I<sig> and its
112length is returned in I<sig_len>. Note: I<sig> must point to ECDSA_size(eckey)
113bytes of memory. The parameter I<type> is ignored.
114
115ECDSA_do_sign_ex() is similar to ECDSA_sign_ex() except the signature is
116returned as a newly allocated B<ECDSA_SIG> structure (or NULL on error).
117
118=head1 RETURN VALUES
119
120ECDSA_SIG_new() returns NULL if the allocation fails.
121
122ECDSA_SIG_set0() returns 1 on success or 0 on failure.
123
124ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value,
125or NULL if it is unset.
126
127ECDSA_size() returns the maximum length signature or 0 on error.
128
129ECDSA_sign(), ECDSA_sign_ex() and ECDSA_sign_setup() return 1 if successful
130or 0 on error.
131
132ECDSA_do_sign() and ECDSA_do_sign_ex() return a pointer to an allocated
133B<ECDSA_SIG> structure or NULL on error.
134
135ECDSA_verify() and ECDSA_do_verify() return 1 for a valid
136signature, 0 for an invalid signature and -1 on error.
137The error codes can be obtained by L<ERR_get_error(3)>.
138
139=head1 EXAMPLES
140
141Creating an ECDSA signature of a given SHA-256 hash value using the
142named curve prime256v1 (aka P-256).
143
144First step: create an EC_KEY object (note: this part is B<not> ECDSA
145specific)
146
147 int ret;
148 ECDSA_SIG *sig;
149 EC_KEY *eckey;
150
151 eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
152 if (eckey == NULL)
153     /* error */
154 if (EC_KEY_generate_key(eckey) == 0)
155     /* error */
156
157Second step: compute the ECDSA signature of a SHA-256 hash value
158using ECDSA_do_sign():
159
160 sig = ECDSA_do_sign(digest, 32, eckey);
161 if (sig == NULL)
162     /* error */
163
164or using ECDSA_sign():
165
166 unsigned char *buffer, *pp;
167 int buf_len;
168
169 buf_len = ECDSA_size(eckey);
170 buffer = OPENSSL_malloc(buf_len);
171 pp = buffer;
172 if (ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) == 0)
173     /* error */
174
175Third step: verify the created ECDSA signature using ECDSA_do_verify():
176
177 ret = ECDSA_do_verify(digest, 32, sig, eckey);
178
179or using ECDSA_verify():
180
181 ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);
182
183and finally evaluate the return value:
184
185 if (ret == 1)
186     /* signature ok */
187 else if (ret == 0)
188     /* incorrect signature */
189 else
190     /* error */
191
192=head1 CONFORMING TO
193
194ANSI X9.62, US Federal Information Processing Standard FIPS186-2
195(Digital Signature Standard, DSS)
196
197=head1 SEE ALSO
198
199L<EC_KEY_new(3)>,
200L<EVP_DigestSignInit(3)>,
201L<EVP_DigestVerifyInit(3)>,
202L<EVP_PKEY_sign(3)>
203L<i2d_ECDSA_SIG(3)>,
204L<d2i_ECDSA_SIG(3)>
205
206=head1 HISTORY
207
208The ECDSA_size(), ECDSA_sign(), ECDSA_do_sign(), ECDSA_verify(),
209ECDSA_do_verify(), ECDSA_sign_setup(), ECDSA_sign_ex() and ECDSA_do_sign_ex()
210functions were deprecated in OpenSSL 3.0.
211
212=head1 COPYRIGHT
213
214Copyright 2004-2021 The OpenSSL Project Authors. All Rights Reserved.
215
216Licensed under the Apache License 2.0 (the "License").  You may not use
217this file except in compliance with the License.  You can obtain a copy
218in the file LICENSE in the source distribution or at
219L<https://www.openssl.org/source/license.html>.
220
221=cut
222