ecdsa.pod revision 337982 
1=pod
2
3=head1 NAME
4
5ECDSA_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
6
7=head1 SYNOPSIS
8
9 #include <openssl/ecdsa.h>
10
11 ECDSA_SIG*	ECDSA_SIG_new(void);
12 void		ECDSA_SIG_free(ECDSA_SIG *sig);
13 int		i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
14 ECDSA_SIG*	d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, 
15		long len);
16
17 ECDSA_SIG*	ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
18			EC_KEY *eckey);
19 ECDSA_SIG*	ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen, 
20			const BIGNUM *kinv, const BIGNUM *rp,
21			EC_KEY *eckey);
22 int		ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
23			const ECDSA_SIG *sig, EC_KEY* eckey);
24 int		ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx,
25			BIGNUM **kinv, BIGNUM **rp);
26 int		ECDSA_sign(int type, const unsigned char *dgst,
27			int dgstlen, unsigned char *sig,
28			unsigned int *siglen, EC_KEY *eckey);
29 int		ECDSA_sign_ex(int type, const unsigned char *dgst,
30			int dgstlen, unsigned char *sig,
31			unsigned int *siglen, const BIGNUM *kinv, 
32			const BIGNUM *rp, EC_KEY *eckey);
33 int		ECDSA_verify(int type, const unsigned char *dgst,
34			int dgstlen, const unsigned char *sig,
35			int siglen, EC_KEY *eckey);
36 int		ECDSA_size(const EC_KEY *eckey);
37
38 const ECDSA_METHOD*	ECDSA_OpenSSL(void);
39 void		ECDSA_set_default_method(const ECDSA_METHOD *meth);
40 const ECDSA_METHOD*	ECDSA_get_default_method(void);
41 int		ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth);
42
43 int		ECDSA_get_ex_new_index(long argl, void *argp,
44			CRYPTO_EX_new *new_func,
45			CRYPTO_EX_dup *dup_func,
46			CRYPTO_EX_free *free_func);
47 int		ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg);
48 void*		ECDSA_get_ex_data(EC_KEY *d, int idx);
49
50=head1 DESCRIPTION
51
52The B<ECDSA_SIG> structure consists of two BIGNUMs for the
53r and s value of a ECDSA signature (see X9.62 or FIPS 186-2).
54
55 struct
56	{
57	BIGNUM *r;
58	BIGNUM *s;
59 } ECDSA_SIG;
60
61ECDSA_SIG_new() allocates a new B<ECDSA_SIG> structure (note: this
62function also allocates the BIGNUMs) and initialize it.
63
64ECDSA_SIG_free() frees the B<ECDSA_SIG> structure B<sig>.
65
66i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature
67B<sig> and writes the encoded signature to B<*pp> (note: if B<pp>
68is NULL B<i2d_ECDSA_SIG> returns the expected length in bytes of 
69the DER encoded signature). B<i2d_ECDSA_SIG> returns the length
70of the DER encoded signature (or 0 on error).
71
72d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns
73the decoded signature in a newly allocated B<ECDSA_SIG> structure.
74B<*sig> points to the buffer containing the DER encoded signature
75of size B<len>.
76
77ECDSA_size() returns the maximum length of a DER encoded
78ECDSA signature created with the private EC key B<eckey>.
79
80ECDSA_sign_setup() may be used to precompute parts of the
81signing operation. B<eckey> is the private EC key and B<ctx>
82is a pointer to B<BN_CTX> structure (or NULL). The precomputed
83values or returned in B<kinv> and B<rp> and can be used in a
84later call to B<ECDSA_sign_ex> or B<ECDSA_do_sign_ex>.
85
86ECDSA_sign() is wrapper function for ECDSA_sign_ex with B<kinv>
87and B<rp> set to NULL.
88
89ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes
90hash value B<dgst> using the private EC key B<eckey> and the optional
91pre-computed values B<kinv> and B<rp>. The DER encoded signatures is
92stored in B<sig> and it's length is returned in B<sig_len>. Note: B<sig>
93must point to B<ECDSA_size> bytes of memory. The parameter B<type>
94is ignored.
95
96ECDSA_verify() verifies that the signature in B<sig> of size
97B<siglen> is a valid ECDSA signature of the hash value
98B<dgst> of size B<dgstlen> using the public key B<eckey>.
99The parameter B<type> is ignored.
100
101ECDSA_do_sign() is wrapper function for ECDSA_do_sign_ex with B<kinv>
102and B<rp> set to NULL.
103
104ECDSA_do_sign_ex() computes a digital signature of the B<dgst_len>
105bytes hash value B<dgst> using the private key B<eckey> and the
106optional pre-computed values B<kinv> and B<rp>. The signature is
107returned in a newly allocated B<ECDSA_SIG> structure (or NULL on error).
108
109ECDSA_do_verify() verifies that the signature B<sig> is a valid
110ECDSA signature of the hash value B<dgst> of size B<dgst_len>
111using the public key B<eckey>.
112
113=head1 RETURN VALUES
114
115ECDSA_SIG_new() returns NULL if the allocation fails.
116
117ECDSA_size() returns the maximum length signature or 0 on error.
118
119ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or 0
120on error.
121
122ECDSA_verify() and ECDSA_do_verify() return 1 for a valid
123signature, 0 for an invalid signature and -1 on error.
124The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
125
126=head1 EXAMPLES
127
128Creating a ECDSA signature of given SHA-1 hash value using the
129named curve secp192k1.
130
131First step: create a EC_KEY object (note: this part is B<not> ECDSA
132specific)
133
134 int        ret;
135 ECDSA_SIG *sig;
136 EC_KEY    *eckey;
137 eckey = EC_KEY_new_by_curve_name(NID_secp192k1);
138 if (eckey == NULL)
139	{
140	/* error */
141	}
142 if (!EC_KEY_generate_key(eckey))
143	{
144	/* error */
145	}
146
147Second step: compute the ECDSA signature of a SHA-1 hash value 
148using B<ECDSA_do_sign> 
149
150 sig = ECDSA_do_sign(digest, 20, eckey);
151 if (sig == NULL)
152	{
153	/* error */
154	}
155
156or using B<ECDSA_sign>
157
158 unsigned char *buffer, *pp;
159 int            buf_len;
160 buf_len = ECDSA_size(eckey);
161 buffer  = OPENSSL_malloc(buf_len);
162 pp = buffer;
163 if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey);
164	{
165	/* error */
166	}
167
168Third step: verify the created ECDSA signature using B<ECDSA_do_verify>
169
170 ret = ECDSA_do_verify(digest, 20, sig, eckey);
171
172or using B<ECDSA_verify>
173
174 ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
175
176and finally evaluate the return value:
177
178 if (ret == -1)
179	{
180	/* error */
181	}
182 else if (ret == 0)
183	{
184	/* incorrect signature */
185	}
186 else	/* ret == 1 */
187	{
188	/* signature ok */
189	}
190
191=head1 CONFORMING TO
192
193ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
194(Digital Signature Standard, DSS)
195
196=head1 SEE ALSO
197
198L<dsa(3)|dsa(3)>, L<rsa(3)|rsa(3)>
199
200=head1 HISTORY
201
202The ecdsa implementation was first introduced in OpenSSL 0.9.8
203
204=head1 AUTHOR
205
206Nils Larsch for the OpenSSL project (http://www.openssl.org).
207
208=cut
209