5 EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions
9 #include <openssl/evp.h>
11 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
12 void 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 int EVP_PKEY_size(EVP_PKEY *pkey);
19 The EVP signature routines are a high level interface to digital
22 EVP_SignInit() initialises a signing context B<ctx> to using digest
23 B<type>: this will typically be supplied by a function such as
26 EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the
27 signature context B<ctx>. This funtion can be called several times on the
28 same B<ctx> to include additional data.
30 EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey>
31 and places the signature in B<sig>. If the B<s> parameter is not NULL
32 then the number of bytes of data written (i.e. the length of the signature)
33 will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes
34 will be written. After calling EVP_SignFinal() no additional calls to
35 EVP_SignUpdate() can be made, but EVP_SignInit() can be called to initialiase
36 a new signature operation.
38 EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
39 signature returned by EVP_SignFinal() may be smaller.
43 EVP_SignInit() and EVP_SignUpdate() do not return values.
45 EVP_SignFinal() returns 1 for success and 0 for failure.
47 EVP_PKEY_size() returns the maximum size of a signature in bytes.
49 The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
53 The B<EVP> interface to digital signatures should almost always be used in
54 preference to the low level interfaces. This is because the code then becomes
55 transparent to the algorithm used and much more flexible.
57 Due to the link between message digests and public key algorithms the correct
58 digest algorithm must be used with the correct public key type. A list of
59 algorithms and associated public key algorithms appears in
60 L<EVP_DigestInit(3)|EVP_DigestInit(3)>.
62 When signing with DSA private keys the random number generator must be seeded
63 or the operation will fail. The random number generator does not need to be
64 seeded for RSA signatures.
68 Several of the functions do not return values: maybe they should. Although the
69 internal digest operations will never fail some future hardware based operations
74 L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
75 L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
76 L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
77 L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
78 L<sha(3)|sha(3)>, L<digest(1)|digest(1)>
82 EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
83 available in all versions of SSLeay and OpenSSL.