5 EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions
9 #include <openssl/evp.h>
11 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
12 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
13 int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
15 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
17 int EVP_PKEY_size(EVP_PKEY *pkey);
21 The EVP signature routines are a high level interface to digital
24 EVP_SignInit_ex() sets up signing context B<ctx> to use digest
25 B<type> from ENGINE B<impl>. B<ctx> must be initialized with
26 EVP_MD_CTX_init() before calling this function.
28 EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the
29 signature context B<ctx>. This function can be called several times on the
30 same B<ctx> to include additional data.
32 EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey>
33 and places the signature in B<sig>. If the B<s> parameter is not NULL
34 then the number of bytes of data written (i.e. the length of the signature)
35 will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes
38 EVP_SignInit() initializes a signing context B<ctx> to use the default
39 implementation of digest B<type>.
41 EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
42 signature returned by EVP_SignFinal() may be smaller.
46 EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
47 for success and 0 for failure.
49 EVP_PKEY_size() returns the maximum size of a signature in bytes.
51 The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
55 The B<EVP> interface to digital signatures should almost always be used in
56 preference to the low level interfaces. This is because the code then becomes
57 transparent to the algorithm used and much more flexible.
59 Due to the link between message digests and public key algorithms the correct
60 digest algorithm must be used with the correct public key type. A list of
61 algorithms and associated public key algorithms appears in
62 L<EVP_DigestInit(3)|EVP_DigestInit(3)>.
64 When signing with DSA private keys the random number generator must be seeded
65 or the operation will fail. The random number generator does not need to be
66 seeded for RSA signatures.
68 The call to EVP_SignFinal() internally finalizes a copy of the digest context.
69 This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
70 later to digest and sign additional data.
72 Since only a copy of the digest context is ever finalized the context must
73 be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak
78 Older versions of this documentation wrongly stated that calls to
79 EVP_SignUpdate() could not be made after calling EVP_SignFinal().
83 L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
84 L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
85 L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
86 L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
87 L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
91 EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
92 available in all versions of SSLeay and OpenSSL.
94 EVP_SignInit_ex() was added in OpenSSL 0.9.7.