xref: /freebsd/crypto/openssl/doc/man3/ECDSA_SIG_new.pod (revision dbfb4063ae95b956a2b0021c37c9a8be4c2e4393) 
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, i2d_ECDSA_SIG, d2i_ECDSA_SIG, ECDSA_size,
7ECDSA_sign, ECDSA_do_sign, ECDSA_verify, ECDSA_do_verify, ECDSA_sign_setup,
8ECDSA_sign_ex, ECDSA_do_sign_ex - low level elliptic curve digital signature
9algorithm (ECDSA) functions
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 int i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
22 ECDSA_SIG *d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, long len);
23 int ECDSA_size(const EC_KEY *eckey);
24
25 int ECDSA_sign(int type, const unsigned char *dgst, int dgstlen,
26                unsigned char *sig, unsigned int *siglen, EC_KEY *eckey);
27 ECDSA_SIG *ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
28                          EC_KEY *eckey);
29
30 int ECDSA_verify(int type, const unsigned char *dgst, int dgstlen,
31                  const unsigned char *sig, int siglen, EC_KEY *eckey);
32 int ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
33                     const ECDSA_SIG *sig, EC_KEY* eckey);
34
35 ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
36                             const BIGNUM *kinv, const BIGNUM *rp,
37                             EC_KEY *eckey);
38 int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);
39 int ECDSA_sign_ex(int type, const unsigned char *dgst, int dgstlen,
40                   unsigned char *sig, unsigned int *siglen,
41                   const BIGNUM *kinv, const BIGNUM *rp, EC_KEY *eckey);
42
43=head1 DESCRIPTION
44
45Note: these functions provide a low level interface to ECDSA. Most
46applications should use the higher level B<EVP> interface such as
47L<EVP_DigestSignInit(3)> or L<EVP_DigestVerifyInit(3)> instead.
48
49B<ECDSA_SIG> is an opaque structure consisting of two BIGNUMs for the
50B<r> and B<s> value of an ECDSA signature (see X9.62 or FIPS 186-2).
51
52ECDSA_SIG_new() allocates an empty B<ECDSA_SIG> structure. Note: before
53OpenSSL 1.1.0 the: the B<r> and B<s> components were initialised.
54
55ECDSA_SIG_free() frees the B<ECDSA_SIG> structure B<sig>.
56
57ECDSA_SIG_get0() returns internal pointers the B<r> and B<s> values contained
58in B<sig> and stores them in B<*pr> and B<*ps>, respectively.
59The pointer B<pr> or B<ps> can be NULL, in which case the corresponding value
60is not returned.
61
62The values B<r>, B<s> can also be retrieved separately by the corresponding
63function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.
64
65The B<r> and B<s> values can be set by calling ECDSA_SIG_set0() and passing the
66new values for B<r> and B<s> as parameters to the function. Calling this
67function transfers the memory management of the values to the ECDSA_SIG object,
68and therefore the values that have been passed in should not be freed directly
69after this function has been called.
70
71i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature B<sig> and
72writes the encoded signature to B<*pp> (note: if B<pp> is NULL i2d_ECDSA_SIG()
73returns the expected length in bytes of the DER encoded signature).
74i2d_ECDSA_SIG() returns the length of the DER encoded signature (or 0 on
75error).
76
77d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns the decoded
78signature in a newly allocated B<ECDSA_SIG> structure. B<*sig> points to the
79buffer containing the DER encoded signature of size B<len>.
80
81ECDSA_size() returns the maximum length of a DER encoded ECDSA signature
82created with the private EC key B<eckey>.
83
84ECDSA_sign() computes a digital signature of the B<dgstlen> bytes hash value
85B<dgst> using the private EC key B<eckey>. The DER encoded signatures is
86stored in B<sig> and its length is returned in B<sig_len>. Note: B<sig> must
87point to ECDSA_size(eckey) bytes of memory. The parameter B<type> is currently
88ignored. ECDSA_sign() is wrapper function for ECDSA_sign_ex() with B<kinv>
89and B<rp> set to NULL.
90
91ECDSA_do_sign() is similar to ECDSA_sign() except the signature is returned
92as a newly allocated B<ECDSA_SIG> structure (or NULL on error). ECDSA_do_sign()
93is a wrapper function for ECDSA_do_sign_ex() with B<kinv> and B<rp> set to
94NULL.
95
96ECDSA_verify() verifies that the signature in B<sig> of size B<siglen> is a
97valid ECDSA signature of the hash value B<dgst> of size B<dgstlen> using the
98public key B<eckey>.  The parameter B<type> is ignored.
99
100ECDSA_do_verify() is similar to ECDSA_verify() except the signature is
101presented in the form of a pointer to an B<ECDSA_SIG> structure.
102
103The remaining functions utilise the internal B<kinv> and B<r> values used
104during signature computation. Most applications will never need to call these
105and some external ECDSA ENGINE implementations may not support them at all if
106either B<kinv> or B<r> is not B<NULL>.
107
108ECDSA_sign_setup() may be used to precompute parts of the signing operation.
109B<eckey> is the private EC key and B<ctx> is a pointer to B<BN_CTX> structure
110(or NULL). The precomputed values or returned in B<kinv> and B<rp> and can be
111used in a later call to ECDSA_sign_ex() or ECDSA_do_sign_ex().
112
113ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes hash value
114B<dgst> using the private EC key B<eckey> and the optional pre-computed values
115B<kinv> and B<rp>. The DER encoded signature is stored in B<sig> and its
116length is returned in B<sig_len>. Note: B<sig> must point to ECDSA_size(eckey)
117bytes of memory. The parameter B<type> is ignored.
118
119ECDSA_do_sign_ex() is similar to ECDSA_sign_ex() except the signature is
120returned as a newly allocated B<ECDSA_SIG> structure (or NULL on error).
121
122=head1 RETURN VALUES
123
124ECDSA_SIG_new() returns NULL if the allocation fails.
125
126ECDSA_SIG_set0() returns 1 on success or 0 on failure.
127
128ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value,
129or NULL if it is unset.
130
131ECDSA_size() returns the maximum length signature or 0 on error.
132
133ECDSA_sign(), ECDSA_sign_ex() and ECDSA_sign_setup() return 1 if successful
134or 0 on error.
135
136ECDSA_do_sign() and ECDSA_do_sign_ex() return a pointer to an allocated
137B<ECDSA_SIG> structure or NULL on error.
138
139ECDSA_verify() and ECDSA_do_verify() return 1 for a valid
140signature, 0 for an invalid signature and -1 on error.
141The error codes can be obtained by L<ERR_get_error(3)>.
142
143=head1 EXAMPLES
144
145Creating an ECDSA signature of a given SHA-256 hash value using the
146named curve prime256v1 (aka P-256).
147
148First step: create an EC_KEY object (note: this part is B<not> ECDSA
149specific)
150
151 int ret;
152 ECDSA_SIG *sig;
153 EC_KEY *eckey;
154
155 eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
156 if (eckey == NULL)
157     /* error */
158 if (EC_KEY_generate_key(eckey) == 0)
159     /* error */
160
161Second step: compute the ECDSA signature of a SHA-256 hash value
162using ECDSA_do_sign():
163
164 sig = ECDSA_do_sign(digest, 32, eckey);
165 if (sig == NULL)
166     /* error */
167
168or using ECDSA_sign():
169
170 unsigned char *buffer, *pp;
171 int buf_len;
172
173 buf_len = ECDSA_size(eckey);
174 buffer = OPENSSL_malloc(buf_len);
175 pp = buffer;
176 if (ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) == 0)
177     /* error */
178
179Third step: verify the created ECDSA signature using ECDSA_do_verify():
180
181 ret = ECDSA_do_verify(digest, 32, sig, eckey);
182
183or using ECDSA_verify():
184
185 ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);
186
187and finally evaluate the return value:
188
189 if (ret == 1)
190     /* signature ok */
191 else if (ret == 0)
192     /* incorrect signature */
193 else
194     /* error */
195
196=head1 CONFORMING TO
197
198ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
199(Digital Signature Standard, DSS)
200
201=head1 SEE ALSO
202
203L<DSA_new(3)>,
204L<EVP_DigestSignInit(3)>,
205L<EVP_DigestVerifyInit(3)>
206
207=head1 COPYRIGHT
208
209Copyright 2004-2018 The OpenSSL Project Authors. All Rights Reserved.
210
211Licensed under the OpenSSL license (the "License").  You may not use
212this file except in compliance with the License.  You can obtain a copy
213in the file LICENSE in the source distribution or at
214L<https://www.openssl.org/source/license.html>.
215
216=cut
217