EVP_PKEY_sign.pod revision 273399 
1=pod
2
3=head1 NAME
4
5EVP_PKEY_sign_init, EVP_PKEY_sign - sign using a public key algorithm
6
7=head1 SYNOPSIS
8
9 #include <openssl/evp.h>
10
11 int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
12 int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
13			unsigned char *sig, size_t *siglen,
14			const unsigned char *tbs, size_t tbslen);
15
16=head1 DESCRIPTION
17
18The EVP_PKEY_sign_init() function initializes a public key algorithm
19context using key B<pkey> for a signing operation.
20
21The EVP_PKEY_sign() function performs a public key signing operation
22using B<ctx>. The data to be signed is specified using the B<tbs> and
23B<tbslen> parameters. If B<sig> is B<NULL> then the maximum size of the output
24buffer is written to the B<siglen> parameter. If B<sig> is not B<NULL> then
25before the call the B<siglen> parameter should contain the length of the
26B<sig> buffer, if the call is successful the signature is written to
27B<sig> and the amount of data written to B<siglen>.
28
29=head1 NOTES
30
31EVP_PKEY_sign() does not hash the data to be signed, and therefore is
32normally used to sign digests. For signing arbitrary messages, see the
33L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)> and
34L<EVP_SignInit(3)|EVP_SignInit(3)> signing interfaces instead.
35
36After the call to EVP_PKEY_sign_init() algorithm specific control
37operations can be performed to set any appropriate parameters for the
38operation (see L<EVP_PKEY_CTX_ctrl(3)|EVP_PKEY_CTX_ctrl(3)>).
39
40The function EVP_PKEY_sign() can be called more than once on the same
41context if several operations are performed using the same parameters.
42
43=head1 RETURN VALUES
44
45EVP_PKEY_sign_init() and EVP_PKEY_sign() return 1 for success and 0
46or a negative value for failure. In particular a return value of -2
47indicates the operation is not supported by the public key algorithm.
48
49=head1 EXAMPLE
50
51Sign data using RSA with PKCS#1 padding and SHA256 digest:
52
53 #include <openssl/evp.h>
54 #include <openssl/rsa.h>
55
56 EVP_PKEY_CTX *ctx;
57 /* md is a SHA-256 digest in this example. */
58 unsigned char *md, *sig;
59 size_t mdlen = 32, siglen;
60 EVP_PKEY *signing_key;
61
62 /*
63  * NB: assumes signing_key and md are set up before the next
64  * step. signing_key must be an RSA private key and md must
65  * point to the SHA-256 digest to be signed.
66  */
67 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
68 if (!ctx)
69	/* Error occurred */
70 if (EVP_PKEY_sign_init(ctx) <= 0)
71	/* Error */
72 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
73	/* Error */
74 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
75	/* Error */
76
77 /* Determine buffer length */
78 if (EVP_PKEY_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
79	/* Error */
80
81 sig = OPENSSL_malloc(siglen);
82
83 if (!sig)
84	/* malloc failure */
85 
86 if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
87	/* Error */
88
89 /* Signature is siglen bytes written to buffer sig */
90
91
92=head1 SEE ALSO
93
94L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
95L<EVP_PKEY_CTX_ctrl(3)|EVP_PKEY_CTX_ctrl(3)>,
96L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,
97L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>,
98L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
99L<EVP_PKEY_verify_recover(3)|EVP_PKEY_verify_recover(3)>,
100L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> 
101
102=head1 HISTORY
103
104These functions were first added to OpenSSL 1.0.0.
105
106=cut
107